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Fordyce, Jordan. "Single-mode interband cascade lasers for petrochemical process monitoring." Electronic Thesis or Diss., Université de Montpellier (2022-....), 2023. http://www.theses.fr/2023UMONS070.
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Les lasers à cascade interbandes (ICL) fournissent des sources pour la gamme spectrale du moyen infrarouge compris entre 3 et 6 µm particulièrement efficaces en termes de consommation d’énergie. Cette gamme spectrale est particulièrement intéressante pour la détection des gaz impliqués dans l’industrie pétrochimique, car des gaz tels que le méthane, l'éthane et le dioxyde de carbone présentent une forte absorption dans cette gamme de longueur d’onde. L'identification correcte d'un gaz présent dans un échantillon nécessite des lasers avec une émission monomode et une certaine accordabilité en longueur d’onde. L'amélioration de cette plage de réglage possible avec une source laser offre de nouvelles opportunités dans des applications liées à la spectroscopie. Une alternative à ce qui est actuellement disponible dans le commerce peut être réalisée grâce à l'utilisation de guides d'ondes à fente, qui peuvent être fabriqués en utilisant de la photolithographie conventionnelle, réduisant ainsi le coût de fabrication.Deux nouveaux types d'ICL ont été conçus, fabriqués, et étudiés dans le cadre de cette thèse : un ICL à fentes à section unique et un ICL à fentes multiples accordé par Vernier (SVT). Une étude approfondie des étapes de fabrication et en particulier de la gravure sèche a été réalisée pour obtenir une gravure verticale des matériaux constituants les ICLs. Les premiers ICLs à fentes ont été fabriqués démontrant un e une émission monomode en régime continu à température ambiante avec une émission proche de 3.4 µm. Sur cette base, l'ICL SVT a été fabriqué pour étendre la plage d'accord et démontrer que l'accord par effet Vernier pouvait être mis en œuvre sur ce système de matériauxInterband cascade lasers (ICLs) provide sources for the mid-infrared spectral range between 3 – 6 µm with low power consumption and efficient performance. This spectral range is of particular interest to the detection of gases involved with petrochemical processing, such as methane, ethane, and carbon dioxide due to their strong absorption in this range. Correct identification of a gas present in a sample requires single-mode emission and some tuning to match the absorption line, depending on the environmental conditions. Increasing the tuning range possible with one laser source opens up new possibilities in spectroscopic applications. An economical design alternative to what is currently commercially available can be realized through the use of slotted waveguides, which can be fabricated using photolithography, reducing the cost of fabrication.Two new types of ICLs have been designed, fabricated, and studied in this thesis: a single-section slotted ICL and a multi-section slotted Vernier tuned (SVT) ICL. An extensive study of the fabrication step and in particular dry etching was carried out to achieve vertical etching of the materials constituting the ICLs. First, the slotted ICLs were fabricated demonstrating single-mode emission in continuous wave operation at room temperature with emission close to 3.4 µm. Building from this foundation, the SVT ICL was fabricated to extend the tuning range and demonstrate that Vernier tuning could be implemented on this material system
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O'Hagan, Seamus. "Multi-mode absorption spectroscopy for multi-species and multi-parameter sensing." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:6f422683-7c50-47dd-8824-56b4b4ea941d.
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The extension of Multi-mode Absorption Spectroscopy (MUMAS) to the infra-red spectral region for multi-species gas sensing is reported. A computationally efficient, theoretical model for analysis of MUMAS spectra is presented that avoids approximations used in previous work and treats arbitrary and time-dependent spectral intensity envelopes, thus facilitating the use of commercially available Interband Cascade Lasers (ICLs) and Quantum Cascade Lasers (QCLs). The first use of an ICL for MUMAS is reported using a multi-mode device operating at 3.7 μm to detect CH4 transitions over a range of 30 nm. Mode-linewidths are measured using the pressure-dependent widths of an isolated absorption feature in HCl. Multi- species sensing is demonstrated by measurement of partial pressures of CH4, C2H2 and H2CO in a low-pressure mixture with uncertainties of around 10%. Detection of CH4 in N2 at 1 bar is demonstrated using a shorter-cavity ICL to resolve spectral features in pressure-broadened and congested spectra. The first use of a QCL for MUMAS is reported using a commercially available device operating at 5.3 μm to detect multiple absorption transitions of NO at a partial pressure of 2.79 μbar in N2 buffer gas. The revised model is shown to enable good fits to MUMAS data by accounting for the time-variation of the spectral intensity profile during frequency scanning. Individual mode-linewidths are derived from fits to pressure- dependent MUMAS spectra and features from background interferences due to H2O in laboratory air are distinguished from those of the target species, NO. Data obtained at scan rates up to 10 kHz demonstrate the potential for achieving short measurement times. The development of a balanced ratiometric detection scheme for MUMAS with commercially available multi-mode lasers operating at 1.5 μm is reported for simultaneous detection of CO and CO2 showing improved SNR performance over previous direct transmission methods and suitability for a compact field-employable instrument. In addition, MUMAS spectra of CO2 are used to derive gas temperatures with an uncertainty of 3.2% in the range 300 - 700 K.
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Ikyo, Achakpa Barnabas. "Physical properties of interband and interband cascade edge- and surface-emitting mid-infrared lasers." Thesis, University of Surrey, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549457.
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Herdt, Andreas Verfasser], Wolfgang [Akademischer Betreuer] Elsäßer, and Thomas [Akademischer Betreuer] [Walther. "The laser-as-detector approach exploiting mid-infrared emitting interband cascade lasers: A potential for spectroscopy and communication applications / Andreas Herdt ; Wolfgang Elsäßer, Thomas Walther." Darmstadt : Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1224048725/34.
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Herdt, Andreas [Verfasser], Wolfgang [Akademischer Betreuer] Elsäßer, and Thomas [Akademischer Betreuer] Walther. "The laser-as-detector approach exploiting mid-infrared emitting interband cascade lasers: A potential for spectroscopy and communication applications / Andreas Herdt ; Wolfgang Elsäßer, Thomas Walther." Darmstadt : Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1224048725/34.
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Patterson, Steven Gregory. "Bipolar cascade lasers." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8805.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references.
This thesis addresses issues of the design and modeling of the Bipolar Cascade Laser (BCL), a new type of quantum well laser. BCLs consist of multiple single stage lasers electrically coupled via tunnel junctions. The BCL ideally operates by having each injected electron participate in a recombination event in the topmost active region, then tunnel from the valence band of the first active region into the conduction band of the next active region, participate in another recombination event, and so on through each stage of the cascade. As each electron may produce more than one photon the quantum efficiency of the device can, in theory, exceed 100%. This work resulted in the first room temperature, continuous-wave operation of a BCL, with a record 99.3% differential slope efficiency. The device was fully characterized and modeled to include light output and voltage versus current bias, modulation response and thermal properties. A new singlemode bipolar cascade laser, the bipolar cascade antiresonant reflecting optical waveguide laser, was proposed and modeled.
by Steven G. Patterson.
Ph.D.
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Williams, Benjamin S. (Benjamin Stanford) 1974. "Terahertz quantum cascade lasers." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17012.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 297-310).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
The development of the terahertz frequency range has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) that operate in the terahertz with photon energies below the semiconductor Reststrahlen band. Photons are emitted via electronic intersubband transitions that take place entirely within the conduction band, where the wavelength is chosen by engineering the well and barrier widths in multiple-quantum-well heterostructures. Fabrication of such long wavelength lasers has traditionally been challenging, since it is difficult to obtain a population inversion between such closely spaced energy levels, and because traditional dielectric waveguides become extremely lossy due to free carrier absorption. This thesis reports the development of terahertz QCLs in which the lower radiative state is depopulated via resonant longitudinal-optical phonon scattering. This mechanism is efficient and temperature insensitive, and provides protection from thermal backfilling due to the large energy separation between the lower radiative state and the injector. Both properties are important in allowing higher temperature operation at longer wavelengths. Lasers using a surface plasmon based waveguide grown on a semi-insulating (SI) GaAs substrate were demonstrated at 3.4 THz in pulsed mode up to 87 K, with peak collected powers of 14 mW at 5 K, and 4 mW at 77 K.
Additionally, the first terahertz QCLs have been demonstrated that use metalmetal waveguides, where the mode is confined between metal layers placed immediately above and below the active region. These devices have confinement factors close to unity, and are expected to be advantageous over SI-surface-plasmon waveguides, especially at long wavelengths. Such a waveguide was used to obtain lasing at 3.8 THz in pulsed mode up to a record high temperature of 137 K, whereas similar devices fabricated in SI-surface-plasmon waveguides had lower maximum lasing temperatures due to the higher losses and lower confinement factors. This thesis describes the theory, design, fabrication, and testing of terahertz quantum cascade laser devices. A summary of theory relevant to design is presented, including intersubband radiative transitions and gain, intersubband scattering, and coherent resonant tunneling transport using a tight-binding density matrix model. Analysis of the effects of the complex heterostructure phonon spectra on terahertz QCL design are considered. Calculations of the properties of various terahertz waveguides are presented and compared with experimental results. Various fabrication methods have been developed, including a robust metallic wafer bonding technique used to fabricate metal-metal waveguides. A wide variety of quantum cascade structures, both lasing and non-lasing, have been experimentally characterized, which yield valuable information about the transport and optical properties of terahertz devices. Finally, prospects for higher temperature operation of terahertz QCLs are considered.
by Benjamin S. Williams.
Ph.D.
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Rochat, Michel. "Far-infrared quantum cascade lasers." Online version, 2002. http://bibpurl.oclc.org/web/24095.
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Dhirhe, Devnath. "Monolithic tuneable quantum cascade lasers." Thesis, University of Glasgow, 2013. http://theses.gla.ac.uk/4604/.
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This thesis is concerned with the design, fabrication and characterisation of monolithic tuneable quantum cascade lasers (QCLs), which are suitable for tuneable diode laser based absorption spectroscopy and polarisation dependent spectroscopy in the mid-infrared wavelength range. All investigations and device development work were carried out using the QCL structure based on strain-compensated Ga0.331In0.669As/Al0.659In0.341As grown on an InP substrate that emits light around 4500 nm wavelength. To make the QCLs electrically tuned, two laser designs were investigated: the double ring quantum cascade laser based on the Vernier-tuning effect, and the integrated tuneable birefringent waveguide utilising current controlled birefringence in quantum-wells. The key advantage of the Vernier tuning effect based the double ring laser design is that it can facilitate both a single mode and wide-tuning range operation. The Vernier tuning enhancement factor associated with the coupled waveguide is responsible for a wide-tuning range observed in double ring configuration. However, the tuning range is limited by the available gain bandwidth (i.e. FWHM of spontaneous spectra) in the material and the maximum obtainable index change of the tuner ring. Theoretically, the tuning range of 155 nm was estimated for the double ring quantum cascade laser (DRQCL) design employed in this thesis. However, experimentally, a single mode (~19 dB single sideband suppression ratio) and tuning range of 59 nm which covers almost half the bandwidth were observed. For the first time in the history of the QCL, a research into the design, fabrication and characterisation of integrated polarisation mode convertors (PMCs) has been carried out. The PMC design is based upon etching trenches, using the RIE lag effect, of sub-wavelength dimensions into one side of a waveguide in order to achieve an asymmetric cross-sectional profile, resulting in a waveplating effect. This thesis presents such PMCs integrated with QCLs that emit 69% TE light with the polarisation angle of 65 degree from one facet and a pure TM light emitted from the other facet using a 256 μm long PMC design (design D2). An integrated tunable birefringent waveguide (ITBW) consisting of two PMCs with a differential phase shift (DPS) section between them. To probe the birefringence operation, a sub-threshold electroluminescence was employed to investigate the single pass operation of the ITBW. A theory based on the electro-optic properties of birefringence in QCL waveguides was used combined with a Jones-matrix based description to gain an understanding of the electroluminescence results. With the QCL operating above threshold, polarisation and wavelength tuning of the signal output was demonstrated. By comparing the sub-threshold electroluminescence and active polarisation angle measurement result with the Jones matrix model, the material birefringence (no DPS current), 4n, was estimated to be around 0.005 for the QCL employed in this work. However, single mode emission was not observed and 24 nm discontinuous tuning was recorded. Despite this, using a QCL incorporating an ITBW device, active polarisation control over 45 degree was demonstrated, and currently, to the best of the authors knowledge there has been no other QCL device that is capable of electronically controlling the output polarisation.
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bin, Hashim Hasnul Hidayat. "Travelling-wave series cascade lasers." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493548.
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A travelling-wave microwave fibre-optic hnk (TWMFL) is proposed consisting of two transmission line structures that are periodically loaded with laser diodes and photodiodes, connected to one another by a fibre array.
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Commin, James Paul. "Short wavelength quantum cascade lasers." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.575411.
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Quantum Cascade Lasers (QCLs) are unipolar lasers based on intersubband transitions that have emission wavelengths in the mid- to far-infrared. Mid-infrared QCLs have recently reached a high level of technological maturity with watt level continuous wave output powers being demonstrated at room temperature. However, the performance of these conventional QCLs falls away very rapidly below -4 urn where a number of important applications exist. This thesis details the design, fabrication and characterisation of high performance 'short wavelength' QCLs that operate in the 3-4 urn region. The high conduction band offset of the InGaAs/ AIAsSb material system and its compatibility with InP based waveguides and fabrication technology has made it the most attractive solution to achieving high performance QCLs in the 3-4 urn region. This thesis covers the development of InGaAs/AIAsSb based QCLs and covers the demonstration of a number of record high output powers and maximum operating temperatures. Watt level peak powers at room temperature and operation up to at least 400 K have been achieved across the -3.3-3.7 urn range. These high performance InGaAs/ AIAsSb lasers are well suited for the realization of single-mode devices that can be used to create compact, ultra-sensitive trace-gas sensors based on absorption spectroscopy. To this effect, single-mode distributed feedback (DFB) QCLs where developed at -3.35-3.45 urn with side mode suppression ratios of up to 30 dB. The lasers employed buried third order DFB gratings and operated at room temperature. Finally, the development of strain compensated InGaAs/AlInAs QCLs grown by metal- organic vapour phase epitaxy (MOVPE) is detailed. This growth technique presents significant advantages for commercial device production when compared to the more typically employed molecular beam epitaxy growth technique. MOVPE grown InGaAs/ AlInAs QCLs with 70% indium composition in the wells operating at -4 urn are reported.
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Freeman, J. R. "Heterogeneous terahertz quantum cascade lasers." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599209.
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Although terahertz quantum cascade lasers (QCLs) are promising devices for cheap, compact and coherent sources of terahertz radiation, the full potential of these lasers has not been realised. In this work we shall examine the active region design of THz QCLs and study the behaviour of heterogeneous active regions, where there are several quantum cascade designs combined in the same active region. We will present a study of the systematic design of THz QCLs and show that it is possible to systematically tune the frequency of these devices by simple modifications to the active region design. We then present some active region designs, together with results for some high-performance designs, operating around 2 THz. Two of these designs have shown high efficiency and high temperature performance at this frequency range. From this we move on to the subject of heterogeneous active regions, and present electrically switchable emission from heterogeneous THz QCLs; devices which emit at different, widely separated frequencies depending on the electrical conditions. This is the first reported electrically switchable emission from THz QCL devices without a magnetic field.
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Kischkat, Jan-Ferenc. "External Cavity Quantum Cascade Lasers." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17303.
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Diese Arbeit untersucht den Einfluss verschiedener physikalischer Parameter auf das Verhalten von Frequenz-abstimmbaren External-Cavity Quantenkaskadenlasern (EC-QCLs) theoretisch und experimentell. Diese beinhalten unter anderen die Antireflexschicht, die Art der Optiken, die geometrischen und die mechanisch/strukturellen Eigenschaften. Dies wurde erreicht durch Aufbau dreier sehr unterschiedlicher EC-Konfigurationen, der Diskussion und dem Vergleich ihrer Leistungsmerkmale und ihrer Vor- und Nachteile für verschiedene Anwendungen unter hauptsächlicher Verwendung von QCLs desselben Wafers der Vergleichbarkeit wegen. Für den letzten Teil dieser Arbeit wurde ein neuer Typus EC-QCL mit vielversprechenden Eigenschaften entwickelt, sodass wir glauben er hat das Potential das Littrow Design langfristig abzulösen. Dieses selbststabilisierende Design verwendet einen Retroreflektor als externen Reflektor. Für die Demonstration dieses Konzepts war die Entwicklung eines Tuning-Elements in Form eines Winkel-verstimmbaren Mittinfrarot-Bandpass-Interferenzfilters mit sehr hohem Gütefaktor vonnöten. Für das Design des Filters wurden Materialien mit sehr strengen Toleranzen bezüglich ihrer physikalischen und optischen Eigenschaften auf Basis von theoretischen Überlegungen ausgewählt und eine Fabrikationsmethode mit hochoptimierten Prozessparametern entwickelt. Die ersten Filter auf Basis von Yttriumfluorid/Yttriumoxid/Germanium/Silizium haben eine Transmissionsbandbreite von 0.14% der Zentralwellenlänge und eine maximale Transmission von etwa 60%. Die EC Konfiguration resultierte in verminderter Empfindlichkeit gegenüber Mechanischen Störungen des Reflektors um zwei Größenordnungen. Das Design behebt die grundsätzliche Limitierung des Littrow Designs bezüglich Miniaturisierung, da kein großer Strahldurchmesser vonnöten ist um kleine Bandbreiten des Littrowgitters zu erreichen.This thesis thoroughly investigates theoretically and experimentally the effects many physical parameters have on the performance of Tunable External-Cavity Quantum-Cascade Lasers (EC-QCLs). These include, among others, the anti-reflection coating, the type of optics, and the geometrical as well as mechanical and structural properties of the EC setup. This was done by assembling three very different EC setups and comparing and discussing their performance, as well as advantages and disadvantages for different purposes using mainly QCLs from the same original wafer for better comparability. For the last part of this thesis, a new type of EC-QCL configuration was developed with properties so promising that we believe it has the potential to replace the Littrow Cavity in the long term. This is an alignment-stabilized and interference filter-tuned design using a retroreflector as the external reflector. For the demonstration of this concept, development of the tuning element in the form of an angle-tunable high-Q mid-infrared bandpass filter was necessary. For the design of the filter, materials with very strict tolerances on the physical and optical properties were selected from theoretical considerations and a fabrication method with highly optimized process parameters was developed. The first filters on the basis of yttrium fluoride/yttrium oxide/germanium/silicon have a transmission bandwidth of 0.14% of the central wavelength and a peak transmission of approximately 60%. The EC configuration resulted in a sensitivity reduction to mechanical perturbations of the reflector by two orders of magnitude, with a calculated potential for three orders of magnitude using optimized optics. This design lifts the fundamental constraint on miniaturization imposed on the Littrow design that requires large beam diameters to ensure a small bandwidth of the Littrow grating.
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Flores, Yuri Victorovich. "Mid-infrared quantum cascade lasers." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17224.
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Quantenkaskadenlaser (QCLs) wurden vor gerade zwanzig Jahren erfunden und haben seitdem stetig im weltweiten Markt der optoelektronischen Bauelemente für den Infrarot an Bedeutung gewonnen. Anwendungsbeispiele für aktuelle und potenzielle Einsatzgebiete von QCLs sind photoakustische Spektroskopie, Umweltüberwachung, Simulation von heißen Körpern, und optische Freiraumdatenübertragung. Rekord optische Leistungen von 14 W und Leistungseffizienzen zwischen 15-35 % wurden bei mittelinfraroten QCLs für Betriebstemperaturen zwischen 80-300 K erreicht. Die weitere Verbesserung dieser Eigenschaften hängt nicht nur von Aspekten wie Wärmemanagement und Chip-Packaging ab, sondern auch von Verbesserungen im Laserdesign zwecks der Reduzierung des Ladungsträgerleckstroms. Dennoch sind die verschiedenen Mechanismen und Komponenten des Leckstroms in Quantenkaskadenlasern leider noch nicht gründlich untersucht worden. Die vorliegende Arbeit liefert a realistische Beschreibung der Ladungsträgertransports in QCLs. Wir beschreiben u.a. Leckströme vom Quantentopf- in höhere Zustände und diskutieren elastische und inelastische Streumechanismen von Ladungsträgern bei mittelinfraroten Quantenkaskadenlasern. Wir illustrieren außerdem die Notwendigkeit zur Berücksichtigung der Elektronentemperatur für eine vollständigere Analyse der Ladungsträgertransporteigenschaften von Quantenkaskadenlasern. Methoden zur experimentellen Ermittlung des temperaturabhängigen Leckstroms in Quantenkaskadenlasern werden präsentiert. Unser Ansatz liefert eine Methode zur effektiven Analyse von der QCL-Leistung und Vereinfacht die Optimierung von QCL aktive Regionen.Two decades after their invention in 1994, quantum-cascade lasers (QCLs) become increasingly important in the global infrared optoelectronics market. Photoacoustic spectroscopy, environment monitoring, hot object simulation, and free-space communication systems are selected examples of the current and potential applications of QCLs. Record optical powers as large as 14 W and power-conversion efficiencies ranging between 15-35 % have been reported for MIR QCLs for temperatures 80-300 K. Further improvement of these characteristics depends not only of aspects as heat management and chip-packaging, but also on improving the active-region design to reduce several leakage channels of charge carriers. However, mechanisms through which leakage of charge carriers affects QCLs performance have not been thoroughly researched. A better understanding of the several (non-radiative) scattering mechanisms involved in carrier transport in QCLs is needed to design new structures and optimize their performance. This work provides a realistic description of charge carriers transport in QCLs. We discuss in particular carrier leakage from QCL quantum-well confined states into higher and lower states. The two main mechanisms for non-radiative intersubband scattering in MIR QCLs are electron-longitudinal-optical-phonon scattering and interface roughness-induced scattering. We present methods for the experimental determination of the leakage current in QCLs at and above laser threshold, which allowed us to estimate the sheet distributions of conduction band states and better understand the impact of temperature activated leakage on QCLs characteristics. We found that even at temperatures low enough to neglect ELO scattering, carriers leakage due to IFR becomes significant for devices operating at high electron temperatures. Altogether, this approach offers a straightforward method to analyze and troubleshoot new QCL active region designs and optimize their performance.
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Hay, Kenneth Gillespie. "Gas sensing using quantum cascade lasers." Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=12766.
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Houghton, M. "Gain in terahertz quantum cascade lasers." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604257.
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This thesis focuses on experiments involving coupled cavity THz QCLs. These take the form of either monolithic devices with etched gaps to form two cavities on the same device, or separate devices aligned under vacuum and at cryogenic temperatures using a specially built piezo-electric micropositioner system. After an introductory chapter briefly reviewing the current state of QCL research, processing techniques and other standard experimental techniques, the thesis begins with the presentation of some experiments dealing with the effects of optical feedback between the two cavities. This leads on to a theoretical chapter in which a mathematical model of a double section QCL is presented, along with some explanation of some unexpected results seen experimentally. The final chapter returns to experimental work. Findings from the previous chapters are used to attempt to develop methods for the measurement of gain and loss in QCLs using coupled cavities, something for which there is currently no reliable method at THz frequencies and which involves considerable experimental difficulties. The thesis concludes with a discussion of possible future work including an extension of the mathematical model, and other possibilities to improve the gain measurement method.
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Kumar, Sushil Ph D. Massachusetts Institute of Technology. "Development of terahertz quantum-cascade lasers." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40501.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 321-340).
The terahertz or the far-infrared frequency range of the electromagnetic spectrum ( ... ) has historically been technologically underdeveloped despite having many potential applications, primarily due to lack of suitable sources of coherent radiation. Following on the remarkable development of mid-infrared ( ... ) quantum-cascade lasers (QCLs) in the past decade, this thesis describes the development of electrically-pumped terahertz quantum-cascade lasers in GaAs/AlsGal_.As heterostructures that span a spectral range of 1.59 - 5.0 THz ( ... ). A quantum-cascade laser (QCL) emits photons due to electronic intersubband transitions in the quantum-wells of a semiconductor heterostructure. The operation of terahertz QCLs at frequencies below the Reststrahlen band in the semiconductor ( ... ), is significantly more challenging as compared to that of the mid-infrared QCLs. Firstly, due to small energy separation between the laser levels various intersubband scattering mechanisms are activated, which make it difficult to selectively depopulate the lower laser level. Additionally, as electrons gain enough kinetic energy in the upper laser level thermally activated longitudinal-optical (LO) phonon scattering reduces the level lifetime and makes it difficult to sustain population inversion at higher temperatures.
(cont.) Secondly, waveguide design for terahertz mode confinement is also more challenging due to higher free-carrier losses in the semiconducting doped regions at the terahertz frequencies. For successful designs reported in this work, the lower radiative state depopulation is achieved by a combination of resonant-tunneling and fast LO phonon scattering, which allow robust operation even at relatively high temperatures. An equally important enabling mechanism for these lasers is the development of metal-metal waveguides, which provide low waveguides losses, and strong mode confinement due to subwavelength mode localization in the vertical dimension. With these techniques some record performances for terahertz QCLs are demonstrated including the highest pulsed operating temperature of 169 K, the highest continuous-wave (cw) operating temperature of 117 K, and the highest optical power output (248 mW in pulsed and 138 mW in cw at 5 K) for any terahertz QCL. Towards the bigger goal of realizing a 1-THz solid-state laser to ultimately bridge the gap between electronic and optical sources of electromagnetic radiation, QCLs with a unique one-well injection scheme, which minimizes intersubband absorption losses that occur at longer wavelengths, are developed.
(cont.) Based on this scheme a QCL operating at 1.59 THz (A - 189 ym) is realized, which is amongst the lowest frequency solid-state lasers that operate without the assistance of a magnetic field. This thesis also reports on the development of distributed-feedback lasers in metal-metal waveguides to obtain single-mode operation, with greater output power and better beam quality. The subwavelength vertical dimension in these waveguides leads to a strongly coupled DFB action and a large reflection from the end-facets, and thus conventional coupled-mode theory is not directly applicable to the DFB design. A design technique with precise control of phase of reflection at the end-facets is developed with the aid of finite-element analysis, and with some additional unique design and fabrication methods, robust DFB operation has been obtained. Single-mode surface-emitting terahertz QCLs operating up to - 150 K are demonstrated, with different grating devices spanning a range of approximately 0.35 THz around v - 3 THz using the same gain medium. A single-lobed far-field radiation pattern, higher output power due to surface-emission, and a relatively small degradation in temperature performance compared to the Fabry-Perot ridge lasers makes these DFB lasers well suited for practical applications that are being targeted by the terahertz quantum-cascade lasers.
by Sushil Kumar.
Ph.D.
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Han, Ningren. "Electrically tunable terahertz quantum cascade lasers." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84723.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 113-118).
In this thesis, microelectromechanical systems (MEMS) assisted electrically tunable terahertz quantum cascade lasers (THz QCLs) are designed and demonstrated. Two MEMS tuner devices are proposed to achieve electrically tunable THz QCLs. One is the electrostatic comb drive actuated tuner design and the other one is a two-stage flexure design that is actuated by an external piezo nano-positioning actuator. The MEMS tuner devices are all fabricated using standard foundry process SOIMUMPs from MEMSCAP Inc. with some additional in-house post-processings. First order distributed-feedback (DFB) THz wire QCLs with robust mode selectors are designed and fabricated at the MIT Microsystems Technology Laboratories (MTL) using processes developed at our group. By integrating the MEMS tuner chips with the THz QCL chips, broadband electrically tunable THz QCLs are successfully demonstrated. This thesis work provides an important step towards realizing turn-key tunable THz coherent sources for a variety of applications such as THz spectroscopy and THz coherent tomography.
by Ningren Han.
S.M.
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Worrall, Christopher Henry. "Long wavelength Terahertz quantum cascade lasers." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612926.
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Gambari, Johannes. "Nonlinear effects in quantum cascade lasers." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7824.
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Kundu, Iman. "Frequency tunable terahertz quantum cascade lasers." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7890/.
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Terahertz (THz) quantum cascade lasers (QCLs) are compact solid–state sources of coheren radiation operating in the far–infrared (FIR) range of the electromagnetic spectrum. THz QCL ridge waveguides are typically Fabry–Pérot (FP) cavities and exhibit characteristic multiple–mode emission. However, widely tunable single–mode (SM) THz QCLs are ideally suited to many THz-sensing applications, such as trace gas detection, atmospheric observations and security screening. Tunable THz QCLs are also highly desirable for techniques like heterodyne mixing and self–mixing interferometry. SM emission from THz QCLs has been demonstrated using distributed feedback (DFB) cavities, photonic lattices (PLs) and photonic crystals (PhCs). Tunable THz QCLs have also been demonstrated using various techniques, such as external coupled mirrors, variation of growth parameters, deposition of nitrogen gas and dielectric materials, and aperiodic PLs. In this study, SM emission from THz QCLs is obtained from PLs patterned with electron beam lithography (EBL). This lithography based processing has the advantage of integrated device processing. Spectral performance of the PLs was simulated using finite element modelling (FEM) and coupled mode theory. A frequency stopband centred at the characteristic Bragg frequency was computed with emission predicted outside this stopband. Spectral emission of experimentally fabricated devices was observed outside the stopband, as was predicted from simulations. The design of the THz QCLs with PL was modified to investigate frequency tenability by depleting carriers under the PL metallised sections using a three–section device. A bulk Drude model was used to simulate the variation of refractive index as a function of carrier concentration. The PLs were deposited such that they form a Schottky junction and a thin depletion layer at the active material interface. The PLs were driven with an independent external electrical connection. An electrical model was designed, which explained the experimentally observed behaviour. This electrical model was used to calculate the depletion layer and the redistribution of carriers under the PL. The resulting variation in the refractive index was computed using FEM. A 15–20 GHz shift in the Bragg frequency was predicted using the Drude model. The frequency stopband was also predicted to reduce from ~90 GHz to ~77 GHz with carrier depletion and a ~5–6 GHz shift in the stopband band edge was predicted. In an exemplar device, a tuning of 15 GHz was observed. A change in spectral power density (SPD) amongst modes was observed in all other devices. A different approach towards the realisation of a frequency tunable THz QCLs was adopted based on two–coupled cavities. This design was based on a Vernier selection rule and promised a wide band tuning from a small refractive index perturbation. One of the two cavities formed the lasing section, while the other formed a tuning section. A thermal tuning mechanism based on a localised Joule heating was used to tune frequency of the coupled–cavity. THz QCLs with coupled–cavities were modelled using transfer matrices and a bulk thermal model. Two devices were designed to exhibit a blue shift in frequency when the shorter of the coupled–cavities acted as a tuning element. The frequency spacing of the devices were ~15 and ~25 GHz respectively. The devices were also optimised such that a reversal in tuning direction is observed by swapping the functions of the lasing and tuning cavities. A monotonic discrete frequency hopping with a blue shift of ~50 and ~85 GHz was observed from the two devices. A red shift in frequency was also observed as the lasing and tuning cavities were swapped. Additionally, since the tuning element is isolated from the lasing section, the power emission of the lasing section was unaffected by the tuning current. The coupled cavity designs were further optimised to disrupt the monotonic frequency hopping to obtain a quasi–continuous frequency tuning. Unlike, the discrete tuning design, this detuned design required variation of current at the lasing and tuning cavities simultaneously, along with a variation in heat sink temperature. Spectral behaviour was modelled using the same transfer matrices, bulk thermal mode and coupled mode theory. Closely spaced discrete tuning over a range of ~67 and 100 GHz was observed from two devices, with continuous tuning of ~5 GHz observed at certain dominant modes. Continuous tuning was also investigated using coupled–cavities with an integrated PL. A continuous tuning of ~3 GHz was observed from experimental devices. Unlike the detuned coupled cavity devices, the power emission from these devices were unaffected by the tuning current. However, these devices are limited by a low tuning range.
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Fujita, Kazuue. "Mid-infrared InGaAs/InAlAs Quantum Cascade Lasers." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/192129.
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Devenson, Jan. "InAs/AlSb short wavelength quantum cascade lasers." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20101102_153710-37964.
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Application of InAs/AlSb materials system for development of short-wavelength quantum cascade lasers is explored. Molecular beam epitaxy (MBE) technology allowing to grow multiperiodical unstrained InAs/AlSb heterostructures with roughness of 1-2 monolayers is developed. It is demonstrated that InAs/AlSb materials system is well-suitable for development of short-wavelength quantum cascade lasers operating below 4 µm wavelength. Lasers containing plasmon-enhanced waveguides as well as the short period InAs/AlSb superlattices as waveguides were designed, MBE-grown and studied. The effect of waveguide properties on the device parameters is revealed. Usage of these waveguides and innovations in laser active region introducing “funnel” injector allowed one to reach operation temperature 420 K at the emission wavelength of 3.3 µm. The obtained optical peak power exceeded 1 W per facet. The room temperature operation has been obtained at wavelength below 3 µm. As for wavelength range, applying the new active region design strategy and the short period InAs/AlSb superlattice spacers InAs based quantum cascade lasers emitting at the wavelengths as short as 2.63 µm were developed, which is today the shortest emission wavelength of the operation of semiconductor lasers based on the intersubband transitions.Disertaciniame darbe nagrinėjamas InAs/AlSb medžiagų sistemos panaudojimas trumpabangių tarppajuostinių lazerių kūrimui. Buvo išplėtota molekulinių pluoštelių epitaksijos technologija, leidžianti auginti daugiaperiodines neįtemptas InAs/AlSb heterosandūras su mažu 1-2 atominių sluoksnių šiurkštumu. Buvo parodyta, jog InAs/AlSb medžiagų sistema yra tinkama kurti trumpabangiams kvantiniams kaskadiniams lazeriams, veikiantiems žemiau 4 µm bangos ilgio ribos. Buvo ištirtas kvantinių kaskadinių lazerių, turinčių tiek plazmoninius bangolaidžius su stipriai legiruotais InAs apdariniais sluoksniais, tiek ir mažo periodo InAs/AlSb supergardelių bangolaidžius, veikimas bei jų įtaka prietaiso parametrams. Šie sprendimai dėl bangolaidžių bei tolimesni aktyviosios terpės patobulinimai, naudojant piltuvėlio formos injektorių, leido sukurti didelio našumo prietaisus, galinčius veikti iki 420 K temperatūros, esant 3,3 µm bangos ilgio emisijai, ir pasiekti maksimalią optinę galią siekiančią 1 W kambario temperatūroje. Šios inovacijos leido sukurti ir InAs/AlSb kvantinį kaskadinį lazerį, emituojantį ~2,6 µm bangos ilgio spinduliuotę šiai dienai tai yra trumpiausią bangos ilgį spinduliuojantis tokio tipo prietaisas pasaulyje.
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Zervos, Charalampos. "Non-linear optics in quantum cascade lasers." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429194.
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Mc, Tavish James Peter. "Band Structure Effects in Quantum cascade Lasers." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503285.
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Bloom, Guillaume. "Combinaison cohérente de lasers à cascade quantique." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00678958.
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Des applications comme les contre-mesures optiques nécessitent des sources puissantes et avec une bonne qualité de faisceau dans le moyen infrarouge. Le laser à cascade quantique (LCQ) est une solution prometteuse mais la puissance fournie par ces lasers n'est pas suffisante. La combinaison cohérente de plusieurs de ces sources devrait permettre de sommer leurs puissances tout en conservant la qualité de faisceau d'un émetteur unique et constitue donc une solution intéressante pour contourner l'actuelle limitation en puissance des LCQ.Nous présentons une étude théorique et expérimentale de la combinaison de faisceaux cohérente de LCQ dans une cavité externe commune utilisant un coupleur de faisceaux. La mise en phase est ici totalement passive puisque fondée sur la minimisation des pertes dans la cavité globale : on parle d'auto-organisation. Un modèle général permettant de quantifier l'efficacité de combinaison et la stabilité de telles cavités est développé. Dans un premier temps, on montre expérimentalement que la combinaison cohérente de deux LCQ dans une cavité Michelson est une solution efficace et stable. Pour combiner plus d'émetteurs il est nécessaire de concevoir des coupleurs de faisceaux dans le moyen infrarouge efficaces. Pour cela, nous avons étudié deux types de réseaux : les réseaux de phase binaire (réseaux de Dammann) et des structures à gradient d'indice composées de motifs sub-longueur d'onde. Le dessin et l'optimisation de telles structures fait appel à la théorie des milieux artificiels et nécessite l'utilisation d'un code de résolution rigoureuse des équations de Maxwell (RCWA). Enfin, la combinaison cohérente de cinq LCQ en cavité externe avec un coupleur de faisceaux est démontrée expérimentalement et la combinaison d'un plus grand nombre de LCQ est discutée. En conclusion, nous présentons une solution originale pour réaliser la combinaison cohérente passive de LCQ et ainsi apporter une solution à l'augmentation de puissance dans le moyen infrarouge.
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Carder, Damian Andrew. "Studies of GaAs based quantum cascade lasers." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275215.
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Burghoff, David Patrick. "Characterization of mid-infrared quantum cascade lasers." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55343.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 97-99).
Quantum cascade lasers provide some of the highest output powers available for light in the mid-infrared range (from 3 to 8 m). As many of their applications require portability, designs that have a high wall-plug efficiency are essential, and were designed and grown by others to achieve this goal. However, because a large fraction of these devices did not operate at all, very few of the standard laser measurements could be performed to determine their properties. Therefore, measurements needed to be performed that could non-destructively probe the behavior of QCLs while still providing useful information. This thesis explores these types of measurements, all of which fall into the category of device spectroscopy. Through polarization-dependent transmission and photovoltaic spectroscopy, a large portion of the quantum mechanical bandstructure could be determined, along with many of the parameters characterizing crystal growth quality. In addition, high-resolution transmission spectroscopy was used to find the properties of the QCL waveguide. In order to find the correspondence between theory and experiment, bandstructure simulations were performed using a three-band p model, and two-dimensional electromagnetic simulations were performed to describe the laser's optical properties. These simulations were found to be in relatively good agreement with the device measurements, and any discrepancies were found to be consistent with problems in the growth and fabrication.
by David Patrick Burghoff.
S.M.
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Alton, Jesse. "Bound-to-continuum THz quantum cascade lasers." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615160.
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Wilson, David. "Trace gas spectrometry using quantum cascade lasers." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18580.
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This project was initially the continuation of a previous PhD students work. This changed slightly to incorporate the initial steps of development of a new system. However the main underlying focus was the absorption of infrared light by molecular gases using a still relatively new light source. This thesis will present the results of experimental work carried out during studies on the detection of gases and the nonlinear optical effects that arise from the absorption of light from a rapid frequency swept laser. A bench mounted two channel quantum cascade laser absorption spectrometer was used during experiments to observe and reduce nonlinear effects that arise from tuning the lasers during the absorption of light by several atmospherically important gases. These gases include the oxides of nitrogen (nitrous oxide, nitrogen dioxide and nitric oxide), methane and ammonia. The pulsed laser systems used as part of the spectrometer have also been put to use performing measurements on gaseous hydrocarbon combustion (methane and ethylene flames), to determine the feasibility of making measurements within the combustion zone of a jet engine and in conjunction with a continuous wave device during pump-probe experiments at the Chemistry Department of Oxford University. A portable four channel spectrometer was used at the beginning of the project to make measurements of the exhaust fumes of diesel powered vehicles. It will also cover the initial steps and tests performed in the early stages of development of a continuous wave quantum cascade laser based spectrometer for high speed detection of trace gases.
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Matsuoka, Yohei. "Broadly Tunable External Cavity Quantum Cascade Lasers." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21073.
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Mitt-Infrarot-Technologie (mid-IR) ist ein äußerst leistungsfähiges Werkzeug für die Anwendung in der Molekülspektroskopie, da die Schwingungsmoden vieler Moleküle in diesem Wellenlängenbereich liegen. Der Quantenkaskadenlaser mit externem Resonator (EC-QCL) kann alle Bereiche dieses Spektrums abdecken. Das Hauptanliegen dieser Arbeit ist die Verbesserung der Leistung des EC-QCL im Hinblick auf die Breite des Wellenlängen-Durchstimmbereichs und die Laserleistung. Theoretische Untersuchungen bestätigen zunächst, dass der QCL die Schlüsselrolle bei EC-Systemen einnimmt: Die Effizienz des EC wird bestimmt durch die Effizienz des QCL und die Güte der Antireflex-Schicht (ARC) der Laserfacette. Die Breite des Durchstimmbereichs wird bestimmt durch das Gain-Spektrum des QCL. Im Rahmen dieser Arbeit wurden die QCL in unserer Gruppe hergestellt und vom QCL-Wachstum selbst bis hin zur Facettenbeschichtung optimiert. Eine der größten Herausforderungen in der Herstellung des EC-Systems ist die Reduktion des Reflexionsvermögens innerhalb der Facetten des Laserchips. Dafür haben wir ein neues ARC-Konzept entwickelt und auf dem beschichteten Substrat demonstriert, dass innerhalb des gesamten, sehr breiten Wellenlängenbereichs von 7–12 μm die Reflexion auf unter 1% reduziert wird. Das Beschichtungsmodell wurde außerdem auf „broad-gain“-QCL-Facetten angewendet, wodurch die Reflexion auf 0,75% über den gesamten Emissions-Wellenlängenbereich reduziert werden konnte. Ein weiterer Schwerpunkt dieser Arbeit ist die Entwicklung und Konstruktion von EC-Lasersystemen. Es wurden zwei kompakte Laser vom Littrow-Typ entwickelt, die von 920 cm-1 bis 1190 cm-1 durchstimmbar sind und die eine Pulsleitung von 0.45 W erreichen. Außerdem wurde eine neue optische Konfiguration des EC-Systems vorgeschlagen um eine höhere Ausgangsleistung zu erzielen. Dieser „Intra-cavity Out-coupling Laser“ erreicht eine Pulsleistung von 1 W und den gleichen Emissionbereich wie die beiden Littrow-Laser.Mid-infrared (mid-IR) technology is a very powerful tool for molecular spectroscopy since vibration modes of many molecules lie in this wavelength range. The External-Cavity Quantum Cascade Laser (EC-QCL) can cover any part of this spectral range. The main goal of this study is to improve EC-QCL performance in terms of wavelength tunability and laser power. The theoretical study about Quantum Cascade Laser (QCL) and EC systems has confirmed that the QCL plays the core role of EC-QCL systems; the power efficiency of an EC system is determined by the combination of the power efficiency of QCL and AR-coating of the laser facet. The width of the tuning range is determined by the gain spectrum of QCL. During this work, QCLs have been fabricated in our group and the optimization of these factors were carried out with various approaches, from QCL growth to facet coatings. One of the major challenges in making EC systems is to reduce the intra-facet reflectivity of the laser chip, and we first proposed a new anti-reflection (AR) coating concept and demonstrated its performance for the first time to the community, achieving good reduction of reflection of the AR-coated substrate over 7-12 μm range, keeping below R < 1% reflection over the entire spectrum. The coating model was applied on broad-gain QCL facets, and the reflection was reduced to 0.75% over the entire emission wavelength range. Furthermore, this work focused on the development and engineering of laser systems, and two compact Littrow-type lasers and an EC system with a new optical configuration have been developed, achieving good performances; tunable from 920 cm-1 to 1190 cm-1 and 0.45 W pulse power. The new type of laser, an Intra-cavity out-coupling EC laser, was also proposed to enhance the power output and achieved over 1 W pulse power with keeping the same tuning range as the Littrow-type.
中赤外分光の技術は非常に有用である。これはとりわけ多くの分子振動モードがこの波長帯域に存在しているためである。可変長レーザーである外部共振器量子カスケードレーザー(External cavity quantum cascade laser, EC-QCL)は、これらスペクトル領域を網羅することが可能で、したがって、EC-QCLは産業スケールを含めた、標準的な光源として非常に潜在的である。商品化のフェーズをさらに推し進めるため、このレーザー性能におけるボトムアップの技術が求められてる。 多くの中赤外光のアプリケーションには広帯域の光源が求められている。この研究はおもにそうした性能を最大化することを背景としている。具体的な目的としては、波長の変調性および光源の強度の向上である。これらの目的に取り組むため、我々はいくつかの段階にステージ化して研究を進めてきた。まず初めに、QCLおよびEC-QCLの基本的な特性の追求から始めた。QCLおよびEC-QCLの物理機構の理論的な考察を行い、これらからEC-QCL形態における要素の最適条件もしくは要請を求めた。QCL素子が、その主要な部位であり、EC系におけるほとんどの性能特性である量子効率、変調領域幅、増幅器の光学損失を決定する。 さまざまなアプローチによりこれら緒特性の最適化が行われた。 この研究のなかで、我々グループ内でシステムの心臓となるQCL素子の全製造プロセス(結晶成長から素子コーティングに至るまで)をおこなった。これら製造手順および性能特性の詳細もまた本論文に記す。 ECレーザーにおける要請特性の中で特に困難な課題として、レーザー素子の内部断面(intra-facet)の反射率の低減があげられる。これに応じるものとして、我々は新たな反射防止膜のコンセプトで、特に中赤外光領域に有益なものを提案した。この実現のために、様々な誘電体物質の光学特性を調べ、中赤外光の応用に最適なものを選択し、実際のコーティングに応用した。ここで提案されたモデル``quasi-Lockhart'' (疑ロックハート)のコーティングは、実験によりその高い性能が実証された。波長7–12 μmの領域をカバーし、かつその全領域内で反射率を1%以下に抑えることができた。またこのコーティングは広帯域ゲインのチップにも施され、その反射率を全体域をカバーしながら、0.75%まで低減させた。この成果はEC-QCLだけでなく、一般の中赤外光の光学コーティングにおいても大いに有用であろう。 さらに、我々は本研究の中でレーザーシステムの構築にも取り組んだ。この研究のなかで、二台のLittrow型レーザーと、新たな光学系をもつECレーザーを構築し、その高性能性を実証した。Littrow型では920 cm-1-1190 cm-1の帯域とパルス強0.45 Wを達成。新たなレーザーシステムであるIntra-cavity out-coupling系は従来の系にくらべ高出力することを目的とされ、その帯域を維持しながら、パルス強1~Wの出力を達成した。またこれら新たなシステムを用いて、またプロジェクトバートナーとの食道癌の細胞イメージングも試験、およびグループにおいてアンモニアの吸光度測定を実施した。
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Kirkbride, James M. R. "Coherent transient spectroscopy with quantum cascade lasers." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c7b897e5-052f-4c15-a3c9-f95ca3b56d70.
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This thesis is concerned with coherent effects in high resolution mid-infrared gas phase spectroscopy using quantum cascade lasers (QCLs). An introductory chapter explains the importance of QCLs as radiation sources in the mid-infrared region of the spectrum and goes on to detail their development and structure. A discussion of coherent effects in spectroscopy follows, leading into the second chapter which discusses the theories relevant to the experimental sections of the thesis. In chapter 2 the theory underpinning direct and velocity selective, Doppler-free spectroscopy is discussed and a density matrix formalism is followed to derive the equations of motion that govern coherent excitation effects in two-level systems. In the final part of the chapter this treatment is extended to three-level systems. The equations derived in this chapter form the basis of quantitative interpretations of the phenomena observed in experimental data and presented in the remainder of the thesis. In chapter 3 the characterisation of a high power, narrow linewidth QCL is carried out. This laser is then used to perform direct and sub-Doppler resolution spectroscopy on NO, demonstrating non-linear absorption at high laser intensities and providing a measurement of the laser linewidth in the limit of slow frequency tuning. As the slow tuning rate increases, evidence of coherent transient effects is presented and density matrix theory used to model this behaviour. The data presented include the first observations of asymmetric Lamb dips and the onset of rapid passage oscillations from a Lamb dip. Pump-probe experiments on NO, utilising two cw QCLs are presented in chapter 4. The high level of velocity selection afforded by QCL excitation leads to coherent transient signals at far lower probe scan rates than previously reported. The effect of altering both the scan rate and the gas pressure and the importance of hyperfine structure are presented. A radio frequency noise source applied to one of the lasers is shown to broaden the laser linewidth, leading to rapid dephasing. A two-colour polarisation spectroscopy experiment is also presented which allows the measurement of both the absorption and the Doppler-free dispersion signals and the three-level density matrix formalism presented at the end of chapter 2 used to model the non-linear response of the system. The final chapter details the use of an acousto-optic modulator to create a pulse of mid-IR light using a cw QCL and the application of this to time resolved pump-probe spectroscopy. This capability suggests the prospect of achieving coherent population transfer by stimulated Raman adiabatic passage (STIRAP) using two such pulses. Simulations based on a simple three-level model and including Zeeman coherences are presented, which take the measured properties of the lasers used in this thesis as inputs to predict the potential population transfer achievable in NO as well as providing useful information about the angular momentum polarisation of the excited molecules. An experimental realisation of STIRAP would require the lasers to be stabilised, and so the final part of the chapter details experimental attempts to achieve stabilisation of an external cavity QCL, and suggests future avenues for improved implementation.
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Keeley, James Thomas. "Self-mixing in terahertz quantum cascade lasers." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/12509/.
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Terahertz (THz) quantum cascade lasers (QCL) have stimulated significant interest in THz laser imaging systems due to their compact size, broad spectral coverage (~1.2-5.2 THz) and high output power ( > 1 W). Due to their continuous wave (CW) narrowband emission and quantum noise limited linewidths, THz QCLs are particularly suited to coherent detection, but the majority of previously reported imaging systems have employed incoherent detection. Furthermore THz detectors typically fall into one of two categories (thermal or electrical), both of which have downsides (slow response rate or limited frequency range respectively). Self-mixing (SM) can be seen as a solution to these problems while also gaining the advantages of a reduced experimental set-up and cost, and increased sensitivity. SM occurs when radiation emitted from a laser is re-injected into the laser cavity by reflection from a remote target. The re-injected field interferes with the intracavity field, resulting in perturbations to both the measured output power and laser terminal voltage that depend on both the amplitude and phase of the reflected field. In this work, new SM imaging and modulation techniques were developed for both two- (2D) and three-dimensional (3D) imaging systems, including improvements leading to improved acquisition speed and depth resolution. Other techniques were developed to identify parameters of the QCL spectral emission and tunability, and SM was also exploited for extraction of optical parameters of explosive materials; a precursor to identification of such materials, something that is very important to national security and public safety. Further work was also developed in the areas of phase-nulling for the purpose of vibromacy measurements and extraction of laser parameters, and near-field (NF) spectroscopy, which has led to a massively improved lateral imaging resolution (~1 um).
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Friart, Gaetan. "Semiconductor laser dynamics: two polarization feedback, quantum cascade lasers, and ring lasers." Doctoral thesis, Universite Libre de Bruxelles, 2017. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/248835.
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Semiconductor lasers (Sls) are very sensitive to external perturbations which may destabilize their steady output. This is particularly striking when the SL is subject to optical feedback, i.e. when part of the light coming out of the laser is reinjected in the cavity after reflection from a distant mirror. For some applications, this is a nuisance that we wish to avoid. But optical feedback may also drive the laser into dynamical regimes which are useful for new applications. In this thesis, we study different problems where an SL is subject to a delayed feedback or to an injected signal. These problems are motivated by recent experiments, technological issues, or particular dynamical phenomena. Specifically, we combine analytical techniques, numerical simulations, and experiments to investigate the bifurcation mechanisms leading to a large variety of oscillatory outputs. The systems that we discuss are an edge-emitting laser with polarization-rotated optical feedback, a two-mode laser with optical injection, a quantum cascade laser with optical feedback, and a semiconductor ring laser with optical feedback. We show that the bifurcations from the steady-states are of primary importance. They not only delimit the stability boundaries of the laser output but they also form the backbone structure of many pulsating waveforms. We investigate these bifurcations in detail in order to find the best operating conditions to observe specific dynamical regimes. Our results highlight laser key parameters that allow their efficient control.Les lasers à semi-conducteur sont sensibles aux perturbations externes et celles-ci peuvent déstabiliser leur faisceau de sortie d’intensité constante. Ceci est particulièrement marquant quand le laser à semi-conducteur est sujet à un feedback optique, c’est-à-dire quand une partie de la lumière sortant du laser est réinjectée dans sa cavité après réflexion par un miroir distant. Pour certaines applications, cela représente une nuisance que l’on souhaite éviter. Mais le feedback optique peut aussi engendrer des régimes dynamiques utiles pour de nouvelles applications. Dans cette thèse, nous étudions différents problèmes où un laser à semi-conducteur est soumis à un feedback retardé ou à un signal injecté. Nos travaux sont motivés par de récentes expériences, des questions technologiques ou des phénomènes dynamiques particuliers. Nous combinons des techniques analytiques, des simulations numériques ainsi que des expériences afin d’analyser les mécanismes de bifurcation menant à une large variété de régimes oscillants.Nous étudions en premier lieu la dynamique d’un laser à semi-conducteur soumis à un feedback avec rotation de la polarisation. Nous examinons, à la fois théoriquement et expérimentalement, la séquence de bifurcations menant à des oscillations sous forme d’ondes carrées. Nous mettons en évidence une multistabilité entre différentes ondes carrées de périodes spécifiques. Nous introduisons alors un mécanisme de contrôle qui nous permet de sélectionner l’onde carrée désirée. Nous analysons ensuite les frontières de stabilité d’un laser à semi-conducteur à deux polarisations soumis à une injection optique. Nous montrons que si les gains des deux modes de polarisation sont suffisamment proches, un état stationnaire mixte stable peut exister. Nous explorons également les conditions permettant une bistabilité entre un état stationnaire pur et un état stationnaire mixte. Les lasers à cascade quantique sont de nouveaux lasers à semi-conducteur prometteurs qui possèdent une forte tolérance au feedback optique. Nous examinons de façon systématique leur stabilité dans la limite des grands retards. Nous montrons que des instabilités oscillantes sont cependant possibles pour de faibles valeurs du courant de pompe. Le dernier dispositif que nous étudions dans cette thèse est le laser à semi-conducteur en anneau soumis à un feedback optique. Nous identifions le mécanisme de bifurcation, appelé pont de bifurcation, responsable des instabilités oscillantes dans le faisceau de sortie du laser. Ces oscillations sont indésirables pour la plupart des applications impliquant de tels lasers. Nous montrons qu’elles peuvent être évitées en contrôlant la phase du feedback.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Wang, Cheng. "Modulation dynamics of InP-based quantum dot lasers and quantum cascade lasers." Thesis, Rennes, INSA, 2015. http://www.theses.fr/2015ISAR0009/document.
Full textAbstract:
Le besoin incessant de débits toujours plus élevés dans les systèmes de télécommunications a un impact sur tous les éléments composant la chaine de transmission. Ainsi, pour faire face à l’augmentation croissante du volume de données échangées à travers le monde, le développement de nouvelles sources optiques semi-conductrices est absolument nécessaire. La modulation directe de lasers nanostructurés constitue une alternative bas coût et à faible consommation énergétique qui permettra de remplacer progressivement les diodes lasers à puits quantiques actuelles. De nombreux efforts en recherche ont été consacrés au cours des dernières années en vue d’améliorer les performances dynamiques des lasers nanostructurés notamment en terme de bande passante, de facteur de couplage phase-amplitude (facteur α) et de dérive de fréquence (chirp). Pour les applications aux très grands réseaux et systèmes de communication, la croissance d’îlots ou de fils quantiques déposés sur substrat InP permet de réaliser des dispositifs nanostructurés émettant dans le proche infra-rouge autours de 1550 nm. Dans ce mémoire, la dynamique de modulation des lasers nanostructuré est étudiée en régime de modulation directe. Les caractéristiques analysées comprennent: la modulation en amplitude (AM) et en fréquence (FM), le chirp, et les réponses en régime grandsignal. Grâce à une approche semi-analytique, il est démontré que la bande passante et l’amortissement sont fortement limités par les phénomènes de capture et de relaxation des porteurs de charge dans les nanostructures. Afin d’étudier les propriétés du facteur α et du chirp, un nouveau modèle dynamique a été proposé, prenant en compte la contribution à l’indice optique des porteurs de charge dans des états hors résonance. Il est ainsi montré que, contrairement au cas des lasers à puits quantiques, le facteur α dépend fortement du courant de pompe et de la fréquence de modulation. Le facteur α reste constant à basses fréquences (<0,1 GHz) et supérieur aux valeurs obtenues à hautes fréquences (au-delà de quelques GHz) à partir de la technique FM/AM. Ces caractéristiques sont essentiellement attribuées aux contributions des porteurs dans les états hors résonance. Les simulations montrent que le facteur α peut être réduit en augmentant la séparation énergétique entre l’état fondamental résonant (GS) et les états hors résonance. En particulier, un effet laser sur 1’état excité des nanostructures (ES) constitue une solution prometteuse pour améliorer les performances dynamiques, en accroissant notamment la bande passante de modulation et en réduisant le facteur α d’environ 40%. Les techniques d’injection optique sont également intéressantes pour régénérer les performances dynamiques des lasers. Le couplage phase-amplitude et le gain optique y sont substantiellement modifiés via le contrôle de l’amplitude et du désaccord en fréquence du faisceau injecté. Dans ce cadre, ce travail propose une nouvelle technique dérivée de la méthode Hakki-Paoli, permettant de mesurer, sous injection optique, le facteur α à la fois en dessous et au-dessus du seuil. Les lasers à cascade quantique (QCL) sont basés sur des transitions électroniques inter-sous-bandes dans des hétérostructures à puits quantiques. Ces lasers présentent une bande passante (AM) relativement de quelques dizaines de GHz et sans résonance ce qui est prometteur pour les transmissions en espace libre. De manière surprenante, les calculs montrent que les QCL présentent une largeur de bande FM extrêmement large de l’ordre quelques dizaines de THz, environ trois ordres de grandeur supérieure à la largeur de bande AM. L’injection optique dans ces lasers présente les mêmes avantages que ceux procurés dans les lasers à transitions interbandes. Des désaccords positifs ou négatifs en fréquence augmentent notamment la largeur de la bande passanteHigh performance semiconductor lasers are strongly demanded in the rapidly increasing optical communication networks. Low dimensional nanostructure lasers are expected to be substitutes of their quantum well (Qwell) counterparts in the next-generation of energy-saving and high-bandwidth telecommunication optical links. Many efforts have been devoted during the past years to achieve nanostructure lasers with broad modulation bandwidth, low frequency chirp, and reduced linewidth enhancement factor. Particularly, 1.55-μm InP-based quantum dash (Qdash)/dot (Qdot) lasers are preferable for long-haul transmissions in contrast to the 1.3-μm laser sources. In this dissertation, we investigate the dynamic characteristics of InPbased nanostructure semiconductor lasers operating under direct current modulation, including the amplitude (AM) and frequency (FM) modulation responses, the linewidth enhancement factor (also known as α-factor), as well as large-signal modulation responses. Using a semi-analytical analysis of the rate equation model, it is found that the modulation bandwidth of the quantum dot laser is strongly limited by the finite carrier capture and relaxation rates. In order to study the α- factor and chirp properties of the quantum dot laser, we develop an improved rate equation model, which takes into account the contribution of carrier populations in off-resonant states to the refractive index change. It is demonstrated that the α-factor of quantum dot lasers is strongly dependent on the pump current as well as the modulation frequency, in comparison to the case of Qwell lasers. The α-factor remains constant at low modulation frequencies (<0.1 GHz) and higher than the value derived at high modulation frequencies (beyond several GHz) from the FM/AM technique. These unique features are mostly attributed to the carrier populations in off-resonant states. Further simulations show that the α-factor can be reduced by enlarging the energy separation between the resonant ground state (GS) and off-resonant states. Lasing from the excited state (ES) can be a promising alternative to enhance the laser’s dynamic performance. The laser exhibits a broader modulation response and the α-factor can be reduced by as much as 40%. The optical injection technique is attractive to improve the laser’s dynamical performance, including bandwidth enhancement and chirp reduction. These are demonstrated both theoretically and experimentally. The phase-amplitude coupling property is altered as well in comparison with the free-running laser and the optical gain depends on the injection strength and the frequency detuning. This work proposes a new method derived from the Hakki-Paoli method, enabling to measure the α-factor of semiconductor lasers under optical injection both below and above threshold. In addition, it is demonstrated theoretically that the α-factor in nanostructure lasers exhibits a threshold discontinuity, which is mainly attributed to the unclamped carrier populations in the off-resonant states. It is a fundamental limitation, preventing the reduction of the α-factor towards zero. Quantum cascade (QC) lasers rely on intersubband electronic transitions in multi-quantum well heterostructures. QC lasers show flat broadband AM response (tens of GHz) without resonance, which constitutes promising features for free-space communications. Surprisingly, calculations show that the QC laser exhibits an ultrabroad FM bandwidth on the order of tens of THz, about three orders of magnitude larger than the AM bandwidth. Optically injection-locked QC lasers also exhibit specific characteristics by comparison to interband semiconductor lasers. Both positive and negative frequency detunings enhance the modulation bandwidth
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Chassagneux, Yannick. "Photonique pour les lasers à cascade quantique térahertz." Phd thesis, Université Paris Sud - Paris XI, 2009. http://tel.archives-ouvertes.fr/tel-00740111.
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Situées entre l'infrarouge et les micro-ondes, les ondes dites "terahertz" (THz) ont les propriétés de passer aussi bien à travers la peau et les vêtements que les papiers, le bois, le carton ou encore le plastique. Autant d'atouts qui permettent d'envisager de multiples applications dans les secteurs de l'imagerie médicale, de la spectroscopie, de la sécurité et de l'environnement. D'où l'intérêt que suscitent les lasers à cascade quantique terahertz, une récente famille de lasers semi-conducteurs qui émettent à des fréquences de l'ordre du terahertz. Pourtant, s'ils sont aujourd'hui les seules sources compactes fonctionnant dans cette gamme de fréquences, ils présentent deux inconvénients : Premièrement, ils ne fonctionnent qu'à des températures cryogéniques. En vue d'une augmentation future de la température maximale de fonctionnement (Tmax), nous avons développé une étude comparative en fonction de la fré- quence d'émission, ce qui a permis de déterminer les mécanismes principaux limitant la Tmax (courant parasite ainsi que l'émission de phonons optiques lon- gitudinaux activés thermiquement). Deuxièmement, afin d'obtenir les meilleures Tmax, l'utilisation d'un guide métal- métal est nécessaire. Néanmoins, dans un tel guide, l'émission obtenue est fortement divergente, ce qui s'avère rédhibitoire pour une utilisation généralisée. Pour résoudre ce point, nous avons intégrés des cristaux photoniques bidimensionnels définis uniquement par la géométrie du métal supérieur, ce qui a permis l'obtention d'une émission directive par la surface, spectralement mono-mode, tout en maintenant des températures de fonctionnement assez élevées.
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Charlton, Christy. "Quantum Cascade Lasers for Mid-Infrared Chemical Sensing." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/13953.
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The mid-infrared (MIR) spectral range (2-20 m) is particularly useful for chemical sensing due to the excitation of fundamental rotational and vibrational modes. In the fingerprint region (10-20 m), most organic analytes have unique absorption patterns; absorption measurements in this region provide molecule-specific information with high sensitivity.
Quantum cascade lasers (QCLs) present an ideal light source for (MIR) chemical sensing due to their narrow linewidth, high spectral density, compact size, and ease of fabrication of nearly any MIR wavelength. As the emission wavelength is dependent on layer size within the heterostructure rather than material composition, various wavelengths in the MIR can be achieved through bandstructure engineering.
High sensitivity measurements have been achieved in both gas and liquid phase by developing integrated sensing systems. The laser emission frequency is selected to match a strong absorption feature for the analyte of interest where no other interfering bands are located. A waveguide is then developed to fit the application and wavelength used.
Gas sensing applications incorporate silica hollow waveguides (HWG) and an OmniGuide fiber (or photonic bandgap HWG). Analyte gas is injected into the hollow core allowing the HWG or OmniGuide to serve simultaneously as a waveguide and miniaturized gas cell. Sensitivities of parts per billion are achieved with a response time of 8 s and a sample volume of approximately 1 mL.
Liquid sensing is achieved via evanescent wave measurements with planar waveguides of silver halide (AgX) and gallium arsenide (GaAs). GaAs waveguides developed in this work have a thickness on the order of the wavelength of light achieving single-mode waveguides, providing a significant improvement in evanescent field strength over conventional multimode fibers. Liquid samples of L volume at the waveguide surfaces are detected.
QCLs have begun to be utilized as a light source in the MIR regime over the last decade. The next step in this field is the development of compact and highly integrated device platforms which take full advantage of this technology. The sensing demonstrations in this work advance the field towards finding key applications in medical, biological, environmental, and atmospheric measurements.
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Bai, Jing. "Optimization of Optical Nonlinearities in Quantum Cascade Lasers." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19797.
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Nonlinearities in quantum cascade lasers (QCL¡¯s) have wide applications in wavelength tunability and ultra-short pulse generation. In this thesis, optical nonlinearities in InGaAs/AlInAs-based mid-infrared (MIR) QCL¡¯s with quadruple resonant levels are investigated. Design optimization for the second-harmonic generation (SHG) of the device is presented. Performance characteristics associated with the third-order nonlinearities are also analyzed.
The design optimization for SHG efficiency is obtained utilizing techniques from supersymmetric quantum mechanics (SUSYQM) with both material-dependent effective mass and band nonparabolicity. Current flow and power output of the structure are analyzed by self-consistently solving rate equations for the carriers and photons. Nonunity pumping efficiency from one period of the QCL to the next is taken into account by including all relevant electron-electron (e-e) and longitudinal (LO) phonon scattering mechanisms between the injector/collector and active regions. Two-photon absorption processes are analyzed for the resonant cascading triple levels designed for enhancing SHG. Both sequential and simultaneous two-photon absorption processes are included in the rate-equation model. The current output characteristics for both the original and optimized structures are analyzed and compared. Stronger resonant tunneling in the optimized structure is manifested by enhanced negative differential resistance. Current-dependent linear optical output power is derived based on the steady-state photon populations in the active region. The second-harmonic (SH) power is derived from the Maxwell equations with the phase mismatch included. Due to stronger coupling between lasing levels, the optimized structure has both higher linear and nonlinear output powers. Phase mismatch effects are significant for both structures leading to a substantial reduction of the linear-to-nonlinear conversion efficiency. The optimized structure can be fabricated through digitally grading the submonolayer alloys by molecular beam epitaxy (MBE).
In addition to the second-order nonlinearity, performance characteristics brought by the third-order nonlinearities are also discussed, which include third-harmonic generation (THG) and intensity dependent (Kerr) refractive index. Linear to third-harmonic (TH) conversion efficiency is evaluated based on the phase-mismatched condition. The enhanced self-mode-locking (SML) effect over a typical three-level laser is predicted, which will stimulate further investigations of pulse duration shortening by structures with multiple harmonic levels.
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Soulby, Michael Richard. "Mid-infrared spectroscopic studies of quantum cascade lasers." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527223.
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Qin, Qi Ph D. Massachusetts Institute of Technology. "Development of tunable terahertz quantum cascade wire lasers." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78548.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 179-188).
For a long time, terahertz (THz) radiation has been of great interest to scientific community because of its spectroscopic and imaging applications based on its unique properties, such as the capabilities to penetrate many materials which are opaque in other frequency range (e.g. packaging, plastics, paints and semiconductors), and spectroscopic signatures of many important materials. In this thesis, a continuously tunable THz wire QC laser, which comprises a QC laser with deep sub-wavelength transverse dimensions, and a movable side object, termed as "plunger", is demonstrated. This deep sub-wavelength cross-section results in a large fraction of mode propagating outside of the laser core (GaAs/A1₀.₁₅Ga₀.₈₅As material system). The frequency tuning is achieved by changing the transverse wave vector, using a plunger made by metal (metal plunger) or silicon (dielectric plunger). When nudged close to the wire laser core, the metal plunger can push modes to the opposite side of the waveguide. Confined by a metal-metal waveguide, the mode is squeezed and the transverse wave vector is increased, resulting in a blue-shifted frequency. In contrast, a silicon plunger can suck the mode out due to its similar refractive index to GaAs/Al₀.₁₅Ga₀.₈₅As material system of laser core. Thus a decreased transverse wave vector results in a redshifted frequency. Although a tuning record of 138GHz (3.6%) was achieved, a discontinuous tuning resulted from a jittering movement of the plungers due to its friction with the guiding system. To solve this problem, an improved plunger based on micro-mechanical system (MEMS) was implemented. This MEMS plunger uses a two-stage folded-beam flexure to isolate the misaligned external actuation. The plunger is attached with the flexure which suspends above a silicon substrate to eliminate friction. Eventually, this MEMS flexure was actuated by a mechanical system which comprised a lever to de-amplify the displacement of a linear mechanical feedthrough. This MEMS plunger enabled a restorable and frictionless movement which led to a continuous tuning range of 330GHz (8.6%) centered at ~3.85 THz. The challenges posted by the weak mode discrimination led to the development of comb-shape connectors which electrically connect the top metal of wire lasers and the side bonding pad. This design can significantly increase the mode discrimination by selectively guiding undesired mode into the lossy bonding pad. This robust design of single mode operation enables the initial lasing at a frequency far below the gain peak, which can potentially increase the tuning range significantly.
by Qi Qin.
Ph.D.
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Atkins, Chris. "New developments in GaAs-based quantum cascade lasers." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/5105/.
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This thesis presents a study of the design and optimisation of gallium-arsenide-based quantum cascade lasers (QCLs). Traditionally, the optical and electrical performance of these devices has been inferior in comparison to QCLs that are based on the InP material system, due mainly to the limitations imposed on performance by the intrinsic material properties of GaAs. In an attempt to improve the performance of GaAs QCLs, indium-gallium-phosphide and indium-aluminium-phosphide have been used as the waveguide cladding layers in several new QCL designs. These two materials combine low waveguide losses with a high confinement of the laser optical mode, and are easily integrated into typical GaAs QCL structures. Devices containing a double-phonon relaxation active region design have been combined with an InAlP waveguide, with the result being that the lowest threshold currents yet observed for a GaAs-based QCL have been observed - 2.1kA/cm2 and 4.0kA/cm2 at 240K and 300K respectively. Accompanying these low threshold currents however, were large operating voltages approaching 30V at room-temperature and 60V at 80K. These voltages were responsible for a high rate of device failure due to overheating. In an attempt to address this situation, two transitional layer (TL) designs were applied at the QCL GaAs/InAlP interfaces in order to aid electron flow at these points. The addition of the TLs resulted in a lowering of operating voltage by ~12V and 30V at 300K and 240K respectively, however threshold current density increased to 5.1kA/cm2 and 2.7kA/cm2 at the same temperatures. By utilising a high-reflectivity coating and epi-layer down bonding process, a QCL comprising an InGaP waveguide and double-phonon active region was observed to operate in continuous-wave mode up to a temperature of 80K, with an optical output power of 26mW.
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Vaitiekus, Deivis. "Development of quantum cascade lasers for gas sensing applications." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/13916/.
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Quantum cascade lasers (QCLs) are capable of high power, tunable wavelength and single mode emission at room temperature in the mid-infrared wavelength region. These capabilities make them perfect light sources for laser based gas spectroscopy. The work described in this thesis focuses on development of QCLs suitable for selective gas sensing applications. The thesis starts with the description of different changes to the QCL active region design. These changes were studied in order to improve laser performance while keeping the emission wavelength fixed. The proposed modifications were performed on short mid-infrared wavelength (lambda=3-4um) quantum cascade lasers based on InGaAs/AlAsSb and InAs/AlSb material systems. The focus of this work is then moved to the description of a single mode quantum cascade laser with a third order unilateral grating. The previously unreported grating architecture that was used to achieve distributed feedback (DFB) in a QCL, as well as grating design and laser characterization are detailed in Chapter \ref{chap:uni}. The reported laser generates single mode emission with 30 dB side mode suppression ratio and a linewidth of 0.4cm^(-1). The simplified fabrication process for a third order DFB grating is developed for lambda=3.3-3.6um emission wavelength. A different approach to achieve single mode emission in a QCL is described in Chapter 6. An external cavity QCL setup combined with the Fabry-Perot (FP) reflector is reported for the first time. The FP reflector is used to provide selective feedback that is controlled by the separation distance between two FP reflector mirrors. This external cavity arrangement allows generation of a wide spectral range and the rapid wavelength tuning capability. Finally, the thesis is concluded with sensitive gas detection experiments. The direct absorption technique is utilized to demonstrate the 160ppmv detection of methane with the ro-vibrational absorption line located at lambda=3.3um and 1ppmv detection of nitric oxide with the absorption line located at lambda=5.3um. The experiments were performed using single mode lasers that were designed and fabricated in Sheffield.
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Mohd, Ibrahim Mohamed Shahrizan bin. "Segmented and patterned single-metal terahertz quantum cascade lasers." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545707.
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Laffaille, Pierre. "Lasers à cascade quantique moyen infrarouge à base d'InAs." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2013. http://tel.archives-ouvertes.fr/tel-01021281.
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Les lasers à cascade quantique sont des sources lasers à semiconducteur compactes et capables de délivrer une forte puissance optique sur une large gamme de longueur d'onde dans l'infrarouge. Les QCLs de la filière InP sont les plus établis. Le système de matériaux InAs/AlSb est une solution alternative encore peu développée mais qui, en vertu de ses propriétés, présente des atouts incontestables pour la réalisation de lasers à cascade quantique. Le travail de cette thèse a apporté une meilleure connaissance du système InAs/AlSb et de ses possibilités pour les QCLs, à la fois sur un plan théorique, expérimental et technologique.Nous avons œuvré à l'amélioration des performances des lasers à cascade quantique sur ce système de matériaux, notamment en cherchant à augmenter la température maximum de fonctionnement dans les courtes longueurs d'onde et le lointain infrarouge. Un modèle de transport électronique a été développé. Ce modèle permet de reproduire de manière relativement précise les résultats expérimentaux. Il est un outil utile pour l'amélioration des designs de zone active et, en conséquence, des performances des lasers.La finalité de ces lasers est leur utilisation pour des applications telles que la spectroscopie moléculaire par absorption. Nous avons donc travaillé à les rendre plus adaptés aux besoins de celles-ci, à savoir que leur émission soit monomode, ce que nous avons rendu possible grâce au développement d'une technologie DFB à haut rendement et très reproductible, et qu'ils puissent fonctionner en régime continu, ce qui a été accompli, autour de 9 µm de longueur d'onde d'émission, jusqu'à une température de 255 K en s'appuyant sur un modèle prédictif basé sur une approche analytique.Afin d'atteindre le fonctionnement en régime continu en dessous de 4 µm de longueur d'onde, nous nous sommes penchés sur l'utilisation d'un substrat alternatif en GaSb, qui nous permet de réaliser des claddings conciliant un faible indice de réfaction et de faibles pertes optiques. Nous avons à cette occasion fait la démonstration du premier QCL fonctionnant sur ce substrat, et ce jusqu'à température ambiante à 3,3 µm de longueur d'onde.
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Spitz, Olivier. "Mid-infrared quantum cascade lasers for chaos secure communications." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLT054.
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Les lasers à cascades quantiques (LCQs) sont des lasers semiconducteurs émettant dans le moyen-infrarouge. Ce domaine optique est bien connu pour ses propriétés d'absorption pour de nombreuses molécules et les lasers à cascades quantiques ont déjà fait leurs preuves en spectroscopie. Des expériences de communication en espace libre ont également vu le jour à ces longueurs d'onde et l'objectif de cette thèse était d'explorer plus en détail ce champ d'applications en réalisant une communication sécurisée reposant sur le chaos optique. La thèse avait pour but de préciser de manière expérimentale les conditions optimales (température, courant de pompe, longueur de cavité externe...) pour obtenir du chaos optique afin de l'utiliser dans des applications futures. Durant cette thèse, une transmission sécurisée a été réalisée avec deux LCQs grâce au principe de synchronisation du chaos, ce qui est une première. Cela permet d'entrevoir tout le potentiel offert par ces lasers en terme de communication au moyen-infrarouge, où la transparence de l'atmosphère donne un net avantage aux LCQs comparés aux diodes laser conventionnelles émettant dans le proche infrarouge. En parallèle de ces expériences sur les communications sécurisées, d'autres phénomènes non-linéaires ont également été observés en fonction des conditions d'opération. Ainsi, le phénomène d'entrainement, connu pour les diodes laser, a pu être démontré expérimentalement. Lors d'une réinjection avec rotation de polarisation, il a été possible de voir que le LCQ était capable d'émettre une onde carrée dont la période et le rapport cyclique pouvaient être modifiés en fonction des paramètres du montage. Enfin, la présence d'événements extrêmes, commune à d'autres systèmes optiques et même d'autres systèmes physiques, a également pu être observée, ce qui pourrait être un frein à un système de communication utilisant des LCQs car les événements extrêmes ont tendance à perturber le signal du laser et ainsi à brouiller le message envoyé. L'ensemble de ces résultats expérimentaux a permis une meilleure compréhension des dynamiques non-linéaires présentes dans un LCQ et contribueront à étendre les champs d'application pour ce type de laser moyen-infrarouge qui reste pour le moment restreint à la spectroscopie et aux contre-mesures optiques mais dont le potentiel est très élevéThe mid-infrared domain is a promising optical domain because it holds two transparency atmospheric windows, as well as the fingerprint of many chemical compounds. Quantum cascade lasers (QCLs) are one of the available sources in this domain and have already been proven useful for spectroscopic applications and free-space communications. The purpose of that dissertation is to go one step further by implementing a secure free-space communication relying on optical chaos and consequently, to give an accurate cartography of non-linear phenomena in quantum cascade lasers. Initial efforts about free-space secure chaotic transmission have been carried out during this Ph.D. thesis with two chaos-synchronized QCLs, which is a pioneer result paving the way for mid-infrared private communications. In order to have a global picture about the non-linear dynamics in QCLs under external optical feedback, we tuned many experimental parameters and this allowed us studying new phenomena in QCLs. We thus found similarities between QCLs and laser diodes when the chaotic dropouts are synchronized with an external modulation, known as the entrainment phenomenon. A cross-polarization reinjection technique led to square-wave emission in the output of the QCL. Eventually, we studied the triggering of rogue waves in QCLs. Rogue waves are a quite common phenomenon in optics (among other domains in science) but they have never been triggered on-demand in semiconductor lasers under external optical feedback before. Further studies will try to avoid such phenomenon in the output of a QCL under external optical feedback since it can disturb the message to be transmitted in a secure communication. All these experimental results allowed a better understanding of the non-linear dynamics of QCLs and will extend the potential applications of this kind of semiconductor lasers, which have currently been restricted to molecular spectroscopy and optical countermeasure systems
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Leuliet, Aude. "Simulation du transport dans les lasers à cascade quantique." Paris 7, 2010. http://www.theses.fr/2010PA077070.
Full textAbstract:
Les lasers à cascade quantique (LCQs) sont des dispositifs semiconducteurs unipolaires dont le principe de fonctionnement est basé sur des transitions électroniques dans la bande de conduction d'un système de puits quantiques et sur l'effet tunnel résonant. Ce sont les seules sources semiconductrices cohérentes de lumière de grande efficacité pour le moyen infrarouge fonctionnant l température ambiante. Leur longueur d'onde étant indépendante de l'énergie du gap du matériau utilisé, leur gamme spectrale s'étend dans l'infrarouge de 3|im à 24 \im. La thèse -dont le but est le calcul du transport dans la région active- après une introduction sur les lasers à cascade quantique se divise en 3 parties. La première s'intéresse aux diffusions ayant lieu dans la région active et permet de déterminer quels sont les processus les plus importants. La seconde partie est une étude du comportement des LCQs sous champ magnétique, permettant d'affiner la détermination des diffusions. Enfin la dernière contient le calcul du transport, basé sur les diffusions déterminées dans les premiers chapitresQuantum cascade lasers (QCLs) are unipolar semiconductor devices based on the electronic transitions in the conduction band of a multiple quantum wells Systems and on resonant tunnelling. They are the only coherent semiconducting sources in the mid infrared to allow ambient temperature operation. The thesis aims at calculating the current in QCLs. After a short introduction on QCLs, the thesis is divided into 3 parts. The first part details the different diffusion processes taking place in the active region and determines which are the most important processes. The second part contains a study of QCLs under strong magnetic fields (up to 45 Teslas). This allow a more precise determination of processes taking place in the active region. The last part describes the calculation of the current in the QCL, based on the diffusion determined in the first chapters
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Storck, Joakim. "A Measurement Platform for Characterization of Quantum Cascade Lasers." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-191097.
Full textAbstract:
A measurement platform has been built to characterize quantum cascade lasers regrown at KTH by measuring their spectral and electrical properties at room temperature. Since the current source used in this work had a compliance voltage which was too low to get above threshold, an adapter was made to put an external voltage source in series with it, raising the voltage over the laser. The adapter was first simulated using OrCAD PSPICE and then soldered together and put inside a plastic box with connections for the voltage source, current source and laser mount. A software was made using LabView to automate the electrical characterization. It ramps the current over a specified range, records current, voltage and output power of the laser and saves the data in a file. The platform was tested using a QCL sample borrowed from III-V Lab, France. The L-I-V curve and the spectrum of the sample was measured at different optical output power levels and temperatures. From the L-I-V curves the slope efficiency, , and the threshold current, Ith were extracted and in turn used to calculate the characteristic temperatures T0 = 40K and T1 = 10K. This led to the conclusion that either the sample had degraded or the thermal dissipation was not efficient enough, since typical values for these temperatures lie around 200K. From the spectral measurement results, a qualitative analysis was made that indicated a slight increase of mode wavelength with rising temperature as well as mode jumps to longer wavelength modes. It could also be seen that the laser showed single-mode behaviour that became more unstable as temperature or current or both were increased. Unstable multi-mode behaviour was seen at an optical output power of 60mW at 20oC. After tests and analysis, suggestions on possible future improvements of the platform were made.En mätplattform har konstruerats för att karaktärisera kvantkaskadlasrar som återodlats på KTH genom att mäta deras spektrala och elektriska egenskaper vid rumstemperatur. Strömkällan som användes i detta arbete hade en spänningsgräns som var för låg för att kunna driva en kvantkaskadlaser över tröskeln. Därför byggdes en adapter för att sätta en extern spänningskälla i serie med denna och därmed höja spänningen över lasern. Adaptern simulerades först i OrCAD PSPICE och löddes sedan ihop och monterades i en plastlåda med kontakter för ström- och spänningskälla samt laserfästet. Automationsmjukvara gjordes i LabView för att automatisera den elektriska karaktäriseringen. Den ökar gradvis strömmen över ett definierat intervall och mäter ström och spänning över lasern samt dess optiska uteffekt och sparar alla data i en fil. Plattformen testades på ett en laserchip lånat från III-V Lab i Frankrike. Laserns L-I-V-kurva och spektrum mättes vid olika uteffekter och temperaturnivåer. Från L-I-V-kurvorna kunde verkningsgraden η och strömmens tröskelvärde Ith bestämmas och användas för att räkna ut de karakteristiska temperaturerna T0 = 40K och T1 = 10K. Detta resultat ledde till slutsatsen att antingen var lasern skadad eller så fungerade värmeledningen bort från lasern dåligt. Typiska värden på dessa temperaturer är i storleksordningen 200K. En kvalitativ analys gjordes av de spektrala mätresulteten, vilken indikerade en liten ökning av modernas våglängder och även modhopp till moder med längre våglängd vid ökning av temperaturen. Lasern var enkelmod men blev instabilare ju mer effekten eller temperaturen eller båda två ökade. Instabilt multimodbeteende sågs vid en uteffekt på 60mW vid 20oC. Efter mätningar och analyser framlades förslag på möjliga framtida förbättringar av plattformen.
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Alhathlool, Raed Hussain S. "The development and applications of terahertz quantum cascade lasers." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/6421/.
Full textAbstract:
Terahertz frequency quantum cascade lasers (THz QCLs) are compact, semiconductor sources of coherent THz radiation, and have numerous potential applications in chemical sensing and industrial inspection, as well as security and biomedical imaging. In this thesis, the development of QCLs as sources of THz radiation is explored, together with their application in self-mixing (SM) imaging systems. The effect of reducing the etch depth of the THz QCL active region was explored, and its influence on QCL performance evaluated. This was aimed of improving the thermal management in QCLs, as well as optimizing the structures for integration with electrical photonic components. The reliance of THz QCLs on slow and incoherent thermal detectors has limited their practical use in THz systems. This was addressed by using a THz QCL as both the radiation source and an interferometric detector. THz sensing and imaging through SM interferometry in a QCL was demonstrated, in which radiation is reflected from an object back into the QCL cavity, causing changes in the laser properties, depending on the amplitude and phase of the reflection. This allows simple, ‘detector-free’, sensing of displacement and reflectivity, with high-sensitivity owing to the coherent nature of the detection. The equivalence between SM-perturbations to the THz power and the laser voltage was shown. Owing to the high SM sensitivity, high-resolution stand-off imaging at round-trip distances of up to 21 m through air was demonstrated - the longest range interferometric sensing with a THz QCL to date. Coherent three-dimensional (3D) terahertz imaging through SM in a THz QCL was also performed, in which the surface height was extracted from the phase of the SM signal. To achieve tunable single mode THz QCL emission, which is highly beneficial for imaging and sensing applications, surface acoustic waves (SAWs) propagation across the sloped etched facets of a QCL mesa was demonstrated. The work also investigated the effect on device performance of SAW propagation over the QCL active region. This demonstration could pave the way for monolithic integration of QCLs into terahertz circuits.
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Evans, Craig A. "The optical and thermal properties of quantum cascade lasers." Thesis, University of Leeds, 2008. http://etheses.whiterose.ac.uk/5079/.
Full textAbstract:
The optical and thermal properties of quantum cascade lasers (QCLs) are investigated through the development of comprehensive theoretical models. The optical properties of various multilayer quantum cascade laser waveguides are investigated by solving Maxwell’s equations using a transfer-matrix method. The complex material refractive indices are calculated using a Drude-Lorentz model which takes into account both phonon and plasma contributions to the material properties. A Caughey-Thomas-like mobility model is used to estimate the temperature dependence of the electron mobility which is found to have a significant effect on the optical waveguide properties. The incorporation of this effect leads to better agreement with experimentally measured threshold current densities. In order to investigate the thermal properties of QCLs, a multi-dimensional anisotropic heat diffusion model is developed which includes temperature-dependent material parameters. The model is developed using finite-difference methods in such a way that is can be solved in both the time-domain and in the steady-state. Various heat management techniques were compared in the time-domain in order to extract the heat dissipation time constants. In the steady-state, the model is used to extract the temperature dependence of the cross-plane thermal conductivity of a GaAs-based THz QCL and compare the thermal properties of THz and InP-based mid-infrared QCL optical waveguides. In addition, fully self-consistent scattering rate equation modelling of carrier transport in short-wavelength QCLs is carried out in order to understand the internal carrier dynamics. This knowledge is then used to optimise the device design and the model predicts significant improvements in the performance of the optimised device.
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Valavanis, Alexander. "n-type silicon-germanium based terahertz quantum cascade lasers." Thesis, University of Leeds, 2009. http://etheses.whiterose.ac.uk/1262/.
Full textAbstract:
Terahertz quantum cascade lasers (THz QCLs) have many potential applications, including detection of skin tumours, and of illicit drugs and explosives. To date, all THz QCLs use III–V compound semiconductors, but silicon (Si)-based devices could offer significant benefits. The high thermal conductivity of Si may allow higher operating temperatures, removing the need for large and costly cryogenic coolers, and the non-polar nature of Si may allow a wider range of emission frequencies. The mature Si processing technology may reduce fabrication costs and ultimately allow integration of THz QCLs with mainstream semiconductor electronics. This work investigates the suitability of a range of Si-based material configurations for THz QCL design. An effective mass/envelope function model of the electronic bandstructure is developed, taking into account the effects of strain and crystal orientation. Scattering models for Coulombic interactions, structural imperfections and interactions with phonons (lattice vibrations) are developed and used to predict the electron distribution, current density and gain in a range of device designs. The effect of nonabrupt interface geometries is investigated and the effect of intervalley mixing upon the emission spectrum is considered. It is shown that germanium/germanium–silicon heterostructures offer much better prospects for THz QCL development than silicon/silicon–germanium systems and can yield sufficient optical gain to overcome the threshold for copper–copper waveguides.