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1
David, Romain. "Study and design of integrated laser diode driver for 3D-depth sensing applications." Thesis, Lyon, 2021. http://www.theses.fr/2021LYSE1033.
Full textAbstract:
Les nouveaux capteurs d’image 3D sont des éléments clés pour exploiter pleinement les applications émergentes dans les domaines de l'imagerie 3D et de la vision par ordinateur telles que la reconnaissance faciale, la capture de mouvement, la détection de présence ou encore la réalité augmentée. Ces capteurs reposent essentiellement sur une technique de mesure de distance. Parmi celles-ci, la mesure indirecte du temps de vol des photons présente l’avantage d’une mise en œuvre simple, fiable et économique appropriée aux applications mobiles grâce au fonctionnement conjugué d’un capteur d’image et d’une diode laser. Le principe consiste à calculer une distance en mesurant le déphasage entre un signal laser infrarouge modulé et le signal optique renvoyé après réflexion sur un objet de la scène. Des impulsions laser avec un rapport cyclique proche de 50\% sont généralement utilisées comme signal laser en modulant le courant à travers une diode laser. Le travail de thèse se focalise sur l'étude et la conception d'un circuit intégré de pilotage de diode laser qui soit à la fois compact, efficace et peu cher, pour des applications d'imagerie 3D utilisées dans les téléphones portables. La nouveauté ici concerne l'intégration du pilote entier (hormis la diode laser et quelques composants passifs) sur une seule puce tout en respectant les contraintes des applications mobiles (faibles tensions d'alimentation, forte intégration). Un autre défi important concerne les pics de tension se produisant pendant les transitoires rapides dus aux inductances parasites. Enfin, un fort rendement électrique s’avère indispensable dans le but de prolonger l’autonomie de la batterie et minimiser l’auto-échauffement. A des fins de comparaison, deux topologies de pilotage différentes, mettant en oeuvre un convertisseur DC/DC associé à un élément de commutation connecté soit en série soit en parallèle de la diode laser, ont été retenues comme base pour concevoir le pilote de diode laser. Deux prototypes ont été réalisés en utilisant une technologie CMOS 130nm de STMicroelectronics, qui sont capables de fournir des impulsions de courant jusqu'à 3A avec une largeur d'impulsion de 2,5ns à une fréquence maximale de 200MHz sous une tension d'alimentation de 3,6V. Dans ces conditions, ils délivrent une puissance électrique de sortie moyenne de 4,5W à la diode laser avec un rendement électrique d'environ 60%Three-dimensional (3D) image sensors are key enablers for unlocking emerging applications in consumer electronics such as facial recognition, presence detection, gesture control or Augmented Reality (AR). These sensors mostly rely on range measuring techniques such as structured-light or Time-of-Flight (ToF) principles. The indirect Time-of-Flight (iToF) principle offers the advantage of a simple, reliable and low cost solution for mobile applications by using a laser transmitter and an image sensor. Its operating principle is to calculate a distance by measuring the phase shift between a modulated infrared laser signal and the optical signal received by the sensor after reflection on an object from the scene. Laser pulses with a duty cycle close to 50\% are usually sent through the scene by modulating the current through a semiconductor laser diode. The thesis is focused on the study and design of a compact, cost-effective and efficient integrated Laser Diode Driver (LDD) for 3D-depth sensing applications used in mobile phones. The novelty here concerns the integration of the whole driver (except laser diode and some passive components) on a single chip while accommodating mobile phone constraints (low supply voltages, high integration). Another important requirement concerns the high voltage spikes occurring during fast transients due to stray inductance. Finally, a high efficiency and low losses in the chip are critical for saving the battery lifetime and minimizing the self-heating. For comparison purposes, two different driving topologies, implementing a DC/DC converter connecting a switching element either in series or in parallel with a laser diode, have been retained as basis for designing the laser diode driver. Two IC prototypes have been realized using a 130nm CMOS technology from STMicroelectronics. Both drivers are able to generate current pulses up to 3A with a 2.5ns pulse width at a maximum 200MHz frequency under a 3.6V supply voltage. Under theses conditions, they provide an average output electrical power of 4.5W to the laser diode with an electrical efficiency of around 60%
2
Deeny, J. A. "Tunable diode laser spectroscopy." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253325.
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3
Lee, Junho. "Semiconductor diode laser with saturable absorber (S-laser)." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0004277.
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4
Smith, David Murray. "Diode laser spectroscopy of silane plasmas." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259622.
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5
Nisar, Salman. "Diode laser cutting of float glass." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508981.
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6
Maker, Gareth Thomas. "Diode laser pumped solid state lasers." Thesis, University of Southampton, 1990. https://eprints.soton.ac.uk/397281/.
Full textAbstract:
This thesis deals with the development of diode laser pumped solid state lasers. The earliest work presented enabled 125W peak power, single frequency Q-switched pulses to be obtained from a 100mW diode laser pumped Nd:YAG laser. Using a 500mW diode laser as a pump source for C.W. Nd:YAG and Nd:YLF oscillators an Yb:Er fibre laser was pumped, producing 0.75mW C.W. power at a wavelength of 1.56µm. Acousto-optic mode-locking techniques were used to provide C.W. mode-locked pulse durations in Nd:YAG and Nd:YLF of 55ps and 18ps respectively, at repetition rates of 240MHz. Frequency modulation mode-locking was shown to be a superior technique, giving pulse durations of 11.5ps and 10ps in diode laser pumped Nd:YAG and Nd:YLF oscillators respectively. FM operation of diode laser pumped Nd:YAG lasers was investigated, yielding a maximum FM bandwidth of 70GHz. Spatial hole burning was considered to be an important factor in this result. Using a 1W diode laser to pump a mode-locked and Q-switched Nd:YLF oscillator peak power levels of 70kW were obtained at a wavelength of 1.047µm. Frequency doubling this output in MgO:LiNbO3 with an energy conversion efficiency of 47% enabled other tunable lasers to be pumped using the second harmonic. Firstly, a synchronously pumped rhodamine 6G dye laser is described which is capable of producing 3.2ps mode-locked pulses in a Q-switched envelope with peak powers of around 10kW. Secondly, a synchronously pumped doubly resonant optical parametric oscillator tunable between 983nm and 1119nm is described. Lastly, a Ti:Sapphire laser producing 400ns pulses with peak powers of 3W at a wavelength of 755nm is demonstrated. This oscillator could be wavelength tuned between 746nm and 838nm. A highly efficient method of frequency doubling C.W. mode-locked lasers was developed. Using an external resonant cavity a frequency doubling energy conversion efficiency of 61% to 532nm was achieved, giving 87mW average power in 8.5ps pulses.
7
Feldon, Paul. "Diode laser debonding of ceramic brackets." Thesis, NSUWorks, 2008. https://nsuworks.nova.edu/hpd_cdm_stuetd/39.
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8
Loeser, Markus. "Diode-Pumped High-Energy Laser Amplifiers for Ultrashort Laser Pulses." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-232571.
Full textAbstract:
The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime.
This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown.
Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control
filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results.
The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range.
The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach.
Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.
9
Smith, Edward J. "The diode array velocimeter." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09122009-040337/.
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10
Ehlers, Bodo. "Development of high power diode laser systems /." Aachen : Shaker, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014901694&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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11
Gibb, Jennifer Susanne. "Diode laser studies of atmospherically important species." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403975.
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12
Barry, Hugh R. "Diode laser studies of atmospherically important species." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400551.
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13
Hunt, N. T. "Infrared diode laser spectroscopy of transient species." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604796.
Full textAbstract:
The introduction discusses the advantages of using lasers as opposed to conventional light sources for spectroscopic applications. Lasers output light of a monochromatic nature, enabling extremely high-resolution measurements to be made, whilst their high power engenders excellent sensitivity. These properties are essential for the application of the ion specific velocity modulation technique employed extensively in this work. The development of tuneable infrared sources, especially the semiconductor diode laser, is also described. Also discussed are experimental methods for generating transient species in the laboratory. A review of previous spectroscopic measurements of transient species is then presented with particular attention being paid to ionic and boron-containing species, which form the main focus of the experimental work presented here. A diode laser velocity modulation spectrometer equipped with an ac electric discharge has been used to study such short-lived species in the experiments reported in this thesis, and is described in chapter 2. Chapter 2 presents the infrared spectrum of the transient molecule BBr. Over 150 lines consisting of both fundamental and hot bands up to v"=5 have been fitted to Watson's isotopically invariant coefficients (Ukl). In Chapter 4 the infrared spectrum of HBC1+ and HBBr+ is presented. Both ions have been observed in the infrared for the first time and spectroscopic constants are obtained for ground and first excited vibrational states of some of the more naturally abundant isotopomers. Ab initio calculations have been performed for HBBr+ based upon the experimental data obtained for HBC1+. Chapter 5 presents the observation of the v1 fundamental band of C1BO recorded on a different spectrometer incorporating a multi-pass White Cell and microwave discharge while Chapter 6 discusses the origin of some apparently unassignable lines observed in discharges containing argon, hydrogen and helium.
14
Taylor, Sarah R. "Diode laser based studies of transient species." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510245.
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15
Claps, Ricardo Javier. "Novel developments in laser diode raman spectroscopy /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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16
Hu, Youfang. "Ultrashort pulse generation from diode laser devices." Thesis, Aston University, 2005. http://publications.aston.ac.uk/8009/.
Full textAbstract:
High power pulses generation is one of the major topics discussed in the thesis. Although gain switching is the simplest way for ultrashort pulse generation, it proves to be quite effective to deliver high energy pulses on condition that the pumping pulses with extremely fast rising time and high enough amplitude are applied on specially designed pulse generators. In the experiment on a grating-coupled surface emitting laser (GCSEL), peak power as high as 1W was achieved even when its spectral bandwidth was controlled within 0.2nm. Another experiment shows violet picosecond pulses with peak power as high as 7W was achieved when the intensive electrical pulses were applied on optimised DC bias to pump on InGaN violet diode laser. The physical mechanism of this phenomenon, as we considered, may attributed to the self-organised quantum dots structure in the laser. Control of pulse quality, including spectral quality and temporal profile, is an important issue for high power pulse generation. The ways to control pulse quality described in the thesis are also based on simple and effective techniques. For instance, GCSEL used in our experiment has a specially designed air-grating structure for out-coupling of optical signals; hence, a tiny flat aluminium mirror was placed closed to the grating section and resulted in a wavelength tuning range over 100nm and the best side band suppression ratio of 40dB. Self-seeding, as an effective technique for spectral control of pulsed lasers, was demonstrated for the first time in a violet diode laser. In addition, control of temporal profile of the pulse is demonstrated in an overdriven DFB laser. Wavelength tuneable fibre Bragg gratings were used to tailor the huge energy tail of the high power pulse. The whole system was compact and robust. The ultimate purpose of our study is to design a new family of compact ultrafast diode lasers. Some practical ideas of laser design based on gain-switched and Q-switched devices are also provided in the end.
17
MacCormack, Stuart. "Photorefractive techniques for diode laser brightness enhancement." Thesis, University of Southampton, 1991. https://eprints.soton.ac.uk/403318/.
Full textAbstract:
The experimental investigation of a number of techniques using photorefractive materials to increase the spectral and spatial brightness of the output from high power semiconductor laser arrays are discussed. The topics of semiconductor lasers and photorefractive materials are reviewed briefly, and the experimental and theoretical background of array transverse modes and laser array injection locking are discussed fully. Single longitudinal mode operation of a 100mW array coupled to a simple, hemispherical external cavity is reported. A side mode suppression ratio of 14dB was achieved. A spatial brightness enhancement by a factor of 10 is reported for a 1W laser array coupled to a phase conjugate external cavity. A number of techniques for the combination of multiple array outputs into a single beam were investigated. A power of 108mW (220mW, Fresnel corrected) was obtained in a diffraction limited, single mode laser beam using photorefractive two-beam coupling with an injection locked 1W laser array pump. Results on the operation of a reflection geometry phase conjugate master-oscillator, power-amplifier using a 500mW diode laser array are presented. The observation of coherent energy transfer between the outputs from the separate stripes of a laser array is discussed, and an external photorefractive beam combining element is proposed. Phase conjugate fidelity results are presented for a double pass, phase conjugate, multimode fibre amplifier geometry. The experiments suggest that phase conjugate modal unscrambling will still take place in the presence of ~6dB gain. A scheme for a high efficiency, high power multimode fibre amplifier is proposed.
18
Hultgren, Charles T. (Charles Timothy). "Femtosecond nonlinearities in AlGaAs diode laser amplifers." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32621.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (leaves 141-148).
by Charles Timothy Hultgren.
Ph.D.
19
Weidmann, Damien. "Radiométrie hétérodyne infrarouge par diode laser accordable." Reims, 2002. http://www.theses.fr/2002REIMS005.
Full textAbstract:
Ce travail présente l'étude, la réalisation complète et la caractérisation d'un radiomètre hétérodyne infrarouge. Un tel radiomètre allie sensibilité et sélectivité spectrale. Ce dernier, pour être accordable continûment en fréquence, utilise comme oscillateur local des diodes lasers à hétérostructure de sels de plomb. Un tel système s'applique notamment à la télédétection passive de signatures moléculaires ; ici il s'agit de démontrer l'efficacité de l'instrument à détecter des espèces moléculaires provenant d'une réaction de combustion. Les lasers à semi-conducteurs bipolaires émettant dans le moyen infrarouge restent très éloignés du laser idéal. Pour cette raison, nous avons abordé l'ensemble des propriétés de ce type de laser, celles ci gouvernant principalement les performances de l'instrument. Nous avons insisté sur les mécanismes physiques d'accord continu en fréquence, puisque ceux ci sont l'avantage inégalable que procure une diode laser. L'instrument a été validé sur une source de combustion que nous avons conçue. Il a permis l'enregistrement de spectres d'émission de molécules présentes dans une chambre de combustion méthane/air, à savoir la vapeur d'eau et le dioxyde de soufre, polluant de combustion notoire. Ces mesures montrent qu'en dépit de l'utilisation d'un oscillateur local imparfait car peu puissant, un radiomètre hétérodyne accordable est un outil puissant pour les diagnostics de combustion, notamment pour la détection à longue portée de combustions polluantes. L'intérêt de ce type d'instrument est relancé par l'avènement de nouvelles sources laser infrarouges accordables émettant dans le moyen infrarouge telles que les lasers à cascade quantique.
20
Bopegedera, A. M. Ranjika Priyadarshi. "Dye laser and diode laser spectroscopy of gas phase free radicals." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184695.
Full textAbstract:
The gaseous free radicals, alkaline-earth metal monoalkylamides, monoacetylides, monoformamidates and monopyrrolidates, consisting of a metal atom (Ca or Sr) bonded to a single ligand, were synthesized in a Broida oven. The electronic and vibrational structures of these molecules were studied by low-resolution laser spectroscopy techniques. These inorganic molecules are ionic, well represented by the structure M⁺L⁻ (M = Ca, Sr: L = ligand). Three electronic transitions were identified for the metal monoalkylamides and the metal monoformamidates. The formamidate anion bonds to the metal in a bidentate fashion through the oxygen and nitrogen atoms. Two electronic transitions were observed for the metal monopyrrolidates. The pyrrolide anion ring bonds to the metal to provide these "open-faced sandwich" type molecules with pseudo-C₅ᵥ symmetry. For the metal monoacetylide molecules, only one electronic transition (Ā²Π-Ẋ²Σ⁺) was observed. Several vibrational frequencies were determined for these inorganic molecules from the low-resolution spectra. The Ā²Π-Ẋ²Σ⁺ transition of the calcium monoacetylide molecule was rotationally analyzed at high-resolution using the filtered laser excitation spectoscopy technique. The rotational line positions were fitted to a ²Π-²Σ⁺ Hamiltonian to obtain several rotational constants. The calcium-carbon bond length in CaCCH was calculated for the ground (2.248 Å) and excited (2.200 Å) electronic states. The vibration-rotation spectra of the gaseous bismuth hydride and bismuth deuteride molecules were recorded, using a diode laser system. The 1-0 fundamental band and several hot bands with Δv-1 were rotationally analyzed. The rotational line positions were fitted first, to a Dunham energy expression and then to a ³Σ⁻ Hamiltonian, to obtain ground state rotational constants. The bismuth-hydrogen (deuterium) bond distance was calculated to be 1.809 Å (1.807 Å).
21
Löser, Markus. "Diode-Pumped High-Energy Laser Amplifiers for Ultrashort Laser Pulses The PENELOPE Laser System." Helmholtz-Zentrum Dresden - Rossendorf, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-232322.
Full textAbstract:
The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime.
This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown.
Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control
filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results.
The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range.
The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach.
Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.
22
Löser, Markus. "Diode-Pumped High-Energy Laser Amplifiers for Ultrashort Laser Pulses The PENELOPE Laser System." Doctoral thesis, Helmholtz-Zentrum Dresden - Rossendorf, 2017. https://tud.qucosa.de/id/qucosa%3A30755.
Full textAbstract:
The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime.
This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown.
Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control
filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results.
The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range.
The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach.
Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.
23
Valle, Dornelles Rodrigo de Faria, Lima e. Silva Adriano De, Juarez Missel, and Patricio Centurión. "Laser lipolysis with a 980-nm diode laser: experience with 400 cases." Sociedade Brasileira de Cirurgia Plástica, 2014. http://hdl.handle.net/10757/320972.
Full textAbstract:
Introduction: Liposuction has undergone several improvements since its first description,
including changes in the cannulas, variation in the concentration of the infiltrating
solution, and the use of different devices and technologies. The use of laser technology
devices for lipolysis and stimulation of skin retraction has contributed to the procedure.
This article presents the authors’ experience with laser lipolysis in 400 patients, within
a 5-year period, and discusses the principles of the technology and its effect on tissues.
Methods: This is a study performed between July 2007 and July 2012 and included
400
patients who underwent laser lipolysis. All procedures were performed following the original
protocol – infiltration of cold saline, passage of the cannula with an optic fiber for
conducting the energy needed for laser lipolysis, skin retraction, and finally, conventional
liposuction. Results: Hospitalization type ranged from outpatient to overnight surgery.
Approximately 45% (180 of 400) of patients had minimal bruising, with involvement of
2% or more of the affected body surface. Hematoma, seroma, and dehiscence occurred
in a total of 9% (36 of 400) of patients. We did not find any case of thermal burn of the
skin. Conclusions: Laser lipolysis performed according to the described
technique was
safe and reproducible.
24
Zhang, Jun. "Nonlinear frequency conversion of a continuous-wave, laser diode-pumped Nd:YLF laser." Thesis, University of St Andrews, 1996. http://hdl.handle.net/10023/13718.
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A continuous-wave, frequency-doubled, diode-pumped Nd:YLF laser, capable of generating 1-W of single-frequency radiation at 523.5 nm, with a linewidth of 10 kHz and frequency tunability of 9 GHz has been developed. By using the tunable green laser as pump source, 4.5 GHz continuous smooth tuning in the range of 1020 - 1070 nm has been demonstrated in a low threshold doubly-resonant optical parametric oscillator. The investigation of thermal effect in the end-pump Nd:YLF laser crystal and the consideration of diode array end-pump geometry have led to an optimum folded-cavity design. Such an optical resonator can eliminate the astigmatism in the laser output, which is induced by the cavity folding on a curved mirror and the anisotropic thermal effect in Nd:YLF, resulting in a circular fundamental laser mode. In addition, a tightly focused beam waist is produced inside the cavity so that efficient intracavity SHG can be achieved. Over 30% optical conversion efficiency from diode to TEM00 1047 nm laser output and 10% conversion efficiency from diode to single-frequency SHG green radiation has been demonstrated. A novel intracavity birefringent filter frequency selection technique has been applied in the standing-wave laser resonator to achieve the single-frequency operation. The performances of the laser in the fundamental wave and in second harmonic generation are investigated in detail in this thesis. The tuning behaviour and stability requirements of type-I and type-II CW doubly-resonant OPO have been compared by using the above green laser as the pump source and LBO, KTP as nonlinear crystals. Through utilisation of a simple cavity length servo, type-II phase matching allows single signal-idler mode-pair operation. By means of pump frequency tuning, and cavity length servo control, the output of signal and idler frequency can be tuned continuously over the KTP crystal phase-matching range. Theoretical analyses on diode-end-pumped Nd:YLF lasers, intracavity frequency doubling, the novel intracavity birefringent filter, and the timing behaviour and stability requirements of single cavity DRO are also presented in this work.
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Rahlff, Christian. "Diode-laser pumped, high-repetition-rate, Nd:YLF laser and its frequency conversion." Thesis, University of St Andrews, 1996. http://hdl.handle.net/10023/13763.
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This thesis describes the development of a continuous-wave (cw), diode pumped, repetitively Q-switched Nd:YLF laser, and its application as a pump source for non-linear optical frequency converters and optical parametric oscillators (OPO's), with typical pulse widths of several tens of nanoseconds and repetition rates in the kHz region. At the core of this thesis is the proposal and realisation of a novel rhombic Nd:YLF slab geometry, which is pumped by two 20W cw AlGaAs diode arrays, each focused by means of 3 lenses into a folded resonator path. The novelty of this adaptation is that it uses Yttrium Lithium Fluoride (YLF), known for its comparatively low tensile strength, as the Neodymium host crystal, by addressing and solving the thermal stress fracture problem in YLF for pump powers up to 20W per surface in an end-pumped configuration. With the excellent beam quality, high average output power and short pulses achieved, Nd:YLF has been established as an excellent material for high density, diode pumped, Q-switched lasers at 1047nm. With identical slabs coated for 1321nm operation also available, the performance and laser parameters such as crossection, linewidth and thermal lensing for these two transitions were compared. The pronounced change in the thermal lensing of the 1321nm transition led to an investigation of excited state upconversion (ESA) in Nd:YLF at 1047 and 1321nm under cw and Q-switched operation. The excellent access to the pumped volume made not only a time dependent spectral analysis of the visible and near UV fluorescence bands possible, but also permitted a spatial analysis of the different up-conversion areas. This pump density and laser transition dependent loss mechanism has implications on the end-effect governed lensing, upper state lifetime and Q-switched pulse form. The low threshold, high repetition rate conversion schemes realised during this thesis expanded the spectral cover of the 1mum pump laser from the near UV (349nm) at one end of the spectrum over the green (523.5nm) and 1.5mum region up to the near infrared at 3.445mum. The progress in this area lies not in the well known phase match configuration of the materials used such as KTP, KTA and LBO, but in the adaptation of these nonlinear converters and non-critically phase matched (NCPM) OPO's to achieve high conversion efficiencies at low pulse energies (typically less than 1mJ, 40kW). With average output powers in the green of 3W (~60% conversion from the IR at 6kHz repetition rate), 750mW in the UV, IW at 1.54mum and 280mW at 3.44mum it has been demonstrated that the high average output power of the repetitively Q-switched system can be preserved in the up- and down-converted radiation.
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Hong, Junhua. "Diode laser pumped Nd:YAG laser for 946-nm and its frequency doubling." Thesis, University of St Andrews, 1992. http://hdl.handle.net/10023/13715.
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The development of a pulsed all-solid-state blue laser system is described in this thesis. The laser system was constructed on the basis of the latest diode laser pumping technology and the availability of the nonlinear material, potassium niobate, in single crystals of high optical quality. With the advantages of diode laser pumping, the 946-nm line in Nd:YAG was successfully made to lase at room temperature, both in cw and Q-switched operation. By frequency doubling the Q-switched 946-nm pulses in a KNbO3 nonlinear crystal, pulses of coherent blue light at a wavelength of 473 nm were obtained with high conversion efficiency. The 946 nm laser line differs from the more usual transitions used in the Nd:YAG laser in having a lower laser level in the ground state manifold. As a result it experiences significant reabsorption loss due to the (thermally excited) lower level population. Because of this reabsorption loss, the length of the crystal is an important parameter, and as a result of a trade-off between the pumping efficiency and the reabsorption loss, there is an optimum crystal length for every pump power level. A theoretical model was developed to describe this system, and with output coupler transmission, pump beam size and cavity mode size as parameters, optimum conditions for laser oscillation were obtained numerically. The theoretical model was tested with both a diode laser and a Ti:Sapphire laser as a pump source for the 946-nm laser. The theory was found to be in excellent agreement with the results. When pumping with the Ti:Sapphire laser, a slope efficiency of 58 % was obtained with a 2-mm long Nd:YAG crystal, but this dropped to about 11 % with diode laser pumping, which shows the advantage of pumping with a beam of high optical quality. The Q-switched version of the 946-nm Nd:YAG laser was also studied theoretically, and a modified four level model was developed to describe the dynamic behaviour of the laser in the presence of lower state reabsorption. The relation of this quasi-three level model to the ideal four level model used in the absence of such absorption was explored. The experiments on Q-switching described here were the first to be reported on the application of this technique to a diode laser pumped 946-nm Nd:YAG laser. Q-switching was achieved by a Brewster-angled acoustic-optic Q-switch, which also acted as a linear polariser. When the laser was pumped by a 0.5 W diode-laser array, pulses with an energy of 4.9 muJ and pulse duration of 68.5 ns were observed at room temperature. Cooling the Nd:YAG crystal to 5 °C improved the laser performance to give pulses of 5.6 muJ pulse energy and 62 ns pulse duration, corresponding to peak powers of 76 W. The pulse repetition rate was kept at 1.5 kHz throughout. Blue light was generated by passing the 946-nm laser pulses along the a-axis of a 5.1-mm long potassium niobate nonlinear crystal, which was kept at 185 °C to obtain noncritical phase matching. The nonlinear coefficient used in this case was d32 (~19.5 pm/V 946 nm). Problems connected with crystal depoling were successfully solved both by the use of a uniform and well controlled temperature environment for the crystal and by providing a poling electric field during heating/cooling. Pulses of coherent blue light at 473 nm with 42 ns duration and 22 W peak power were generated from the output of the 946 nm laser described above, corresponding to an internal peak-power conversion efficiency of 40%, which was in excellent agreement with the second-harmonic-generation theory.
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La, Rosa Giuseppe. "Spectroscopy of Tm3+ : YLF as a laser material for diode laser pumping." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14385.
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Boudreau, Marcel Gerard. "Optical coatings for improved semiconductor diode laser performance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30075.pdf.
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Beaudoin, Gerald R. "Fiber optic based tunable diode laser gas detector." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0013/MQ60101.pdf.
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Boudreau, Marcel G. "Optical coatings for improved semiconductor diode laser performance /." *McMaster only, 1997.
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Roth, Peter. "Directly diode-laser-pumped titanium-doped sapphire lasers." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18125.
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Titanium-doped sapphire is one of the most versatile laser gain materials. Tunable between 0.7 m and 1.1 m and capable of generating femtosecond pulses, the Ti:sapphire laser has become an important tool for many applications. Its ubiquitous use across many scientific disciplines is increasingly complemented by commercial applications including imaging, spectroscopy, micro-processing of materials and the generation of terahertz radiation. However, today's Ti:sapphire lasers are complex, bulky and expensive, leaving many applications unaddressed, particularly where lower costs and smaller footprints are vital. The biggest hurdle to smaller and cheaper Ti:sapphire lasers is the pump light source - typically a frequency-doubled, multi-watt neodymium or optically pumped semiconductor laser. Ideally, such intricate and expensive pump lasers would be replaced by compact, robust and cheap diode lasers. Two factors have prevented this: first, Ti:sapphire has a broad but relati vely weak absorption in the blue-green region of the spectrum where high-power diode lasers are not currently available; and second, the very short upper laser level lifetime of Ti:sapphire and relatively large parasitic losses result in a high intrinsic laser threshold. Combined, these factors strongly favour high-brightness pump sources. The recent progress in diode lasers based on gallium nitride materials now opens the way to challenge the perceived wisdom that Ti:sapphire cannot be diode-pumped. In this work diode-laser pumping of Ti:sapphire lasers has been shown to be possible. The world's first diode-laser-pumped Ti:sapphire laser has been developed, enabling drastic reductions in cost and size over current systems. Using innovative approaches to exploit gallium nitride diode lasers as the pump source, both continuous-wave operation and generation of femtosecond pulses have been demonstrated. As a result, some of the unrivalled performance of today's high-cost, lab- bound Ti: lasers may soon be available at a fraction of the current cost and footprint.
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Thornton, Lee James. "Diode laser absorption studies of gas phase species." Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:5119b209-f6ee-4525-8d01-36276eaa30a5.
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Sensitive and selective absorption spectroscopy techniques are applied to the detection of the excited species present in a range of low pressure inductively coupled plasmas (ICPs). The state densities and temperatures of various species are investigated across the parameter space accessible (plasma power and pressure) to aid in the understanding of the kinetic processes occurring. The experimental methods are based upon various forms of absorption spectroscopy, incorporating wavelength modulation and/or an optical enhancement cavity. The probing radiation is generated either directly using a CW diode laser or indirectly through the use of frequency conversion techniques. The absolute number densities of all four levels (1s2, 1s3, 1s4 and 1s5) present in the first excited manifold of atomic argon and neon are determined as a function of plasma operating conditions. A kinetic model is constructed to simulate these populations using cross-sections taken from the literature together with further measurements on the electron density and temperature obtained with a Langmuir probe. The model elucidates the importance of populational redistribution within the 1s manifold via excitation to the 2pn levels, and highlights the mechanism of radiative decay (with radiative trapping taken into account) as the ultimate loss route for the 1s manifold. Measurements are made using cavity enhanced absorption spectroscopy (CEAS) on the 2p5 and 2p6 state densities in argon in order to draw additional conclusions about the nature of the discharge and to verify the kinetic model. The populations of the 1s3 and 1s4 states are probed in a neon plasma with helium, argon and nitrogen as a dopant gas, with the aim of manipulating the EEDFs. The addition of N2 and Ar to the neon discharge resulted in a reduction in the 1s3 and 1s4 populations, while the addition of He resulted in an increase. These observations are consistent with a decrease and an increase, respectively, in the electron temperatures. The populations of the vibrational levels v = 0, 1, 3, and 6 of the A(3Σu+) state of molecular nitrogen are determined as a function of plasma operating conditions in a N2 discharge using CEAS. A selection of vibrational bands within the B(3Πg)←A(3Σu+) system are probed, with calibration achieved using cavity ring-down spectroscopy. At 25 mTorr and 200 W power the populations of the v = 0, 1,3, and 6 levels are (1.31 ± 0.16) × 1011 cm-3, (8.44 ± 1.01) × 1010 cm-3, (2.83 ± 0.34) × 1010 cm-3 and (5.27 ± 0.63) × 109 cm-3, respectively, corresponding to a vibrational temperature of 3600 ± 150 K. In addition, the observation of the N2+(X2Σg+) molecular ion in v = 0 using both CEAS and CEAS in combination with wavelength modulation spectroscopy is presented (which is found to improve the sensitivity for this measurement by approximately an order of magnitude). At 10 mTorr and 400 W the total population in N2+(X2Σg+, v = 0) is (1.26 ± 0.15) × 109 molecules cm-3, consistent with data obtained using a Langmuir probe. The density of oxygen atoms present in their ground state (3P2) is investigated using the technique of CEAS, and at 500 W and 100 mTorr the concentration is estimated to be (2.2 ± 0.3) × 1014 cm-3. This corresponds to a dissociation efficiency, δ, of O2 of 0.06. Furthermore, a difference frequency generation (DFG) system is constructed to generate radiation at 1.9 μm in order to probe the (0,0) band of the O2(b1Σg+←a1Δg) quadrupolar system. A minimum detectable absorbance of 1.3 × 10-5 over a 10 cm cell is determined by calibrating the system on an ammonia absorption, placing a limit of 1.8 × 1016 cm-3 on the total v = 0 population of O2(a1Δg) in a microwave discharge operating with 5 Torr pure O2.
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Modi, Nihar Triplett Gregory Edward. "Thermal management in GaAs/AlGaAs laser diode structures." Diss., Columbia, Mo. : University of Missouri--Columbia, 2007. http://hdl.handle.net/10355/6262.
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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 16, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis supervisor: Dr. Gregory Triplett. Includes bibliographical references.
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Crow, Martin Brian. "High resolution diode laser spectroscopy of transient species." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:64bd9688-fdb3-4d05-ac2b-2a9bb621bb7c.
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This thesis presents applications of near infrared diode lasers to high resolution spectroscopy of transient radical species. Firstly, time resolved near infrared laser gain versus absorption is utilised in Chapter 2 to determine the I∗ quantum yield following ultraviolet photolysis of iodobenzene and its fluorinated analogues. The experimental method is first confirmed by comparison with literature values of the quantum yield for iodomethane photolysis, returning a quantum yield of Φ(I∗) = 0.71 ± 0.04 in good agreement with the literature, before being applied to determine the I∗ quantum yield following 248 nm and 266 nm photolysis of iodobenzene (Φ(I∗) = 0.28 ± 0.04) and pentafluoroiodobenzene (Φ(I∗) = 0.32 ± 0.05). The I∗ quantum yields for 4-fluoroiodobenzene, 2,4-difluoroiodobenzene and 3,5-difluoroiodobenzene are also reported in order to determine the effect of selective fluorination on the dynamics of the photodissociation process. This work complements velocity-map ion imaging studies and spin-orbit resolved ab initio calculations of the ultraviolet photolysis of these compounds. Chapter 3 details the development of a narrow-bandwidth tunable continuous wave ultraviolet radiation source, through sum frequency mixing of tunable near infrared diode lasers with a fixed frequency, high powered, solid state laser. The application of the UV radiation source to spectroscopy of the A 1A2 − X 1A1 electronic band of formaldehyde is explored, where absolute absorption cross sections are determined for rotational transitions within the 220410 and 220430 vibronic bands. The sub-Doppler resolution has allowed refinement of the rotational constants for the slowly predissociating excited state of the 220430 vibronic band. The lifetimes of several rotational levels is determined to be in the range 0.74 ns to 1.46 ns. In Chapter 4 the UV radiation source developed in Chapter 3 is applied to the A 2Σ+ − X 2Π electronic band of the OH radical. Firstly, this source is utilised to probe a continuous supply of hydroxyl radicals using cavity-enhanced absorption spectroscopy and wavelength modulation spectroscopy. Pressure induced broadening parameters for the Q1(2) rotational transition for He, Ne, Ar and N2 buffer gases are also measured. Following the successful application of this source to probe a continuous OH source at atmospheric pressure, the UV spectrometer is used to probe OH radicals from nitric acid photolysis at 193 nm, where the nascent speed distribution and Doppler lineshape is shown to be in excellent agreement with the literature. Time resolved absorption spectroscopy of the nascent OH fragment also returns a translational relaxation constant of ktrans = (3.85±1.06)×10−10cm3molecule−1s−1, which is in good agreement with literature values. These preliminary results indicate the potential of this narrow-bandwidth tunable UV source as an absorption-spectroscopy-based probe of nascent Doppler profiles. Chapter 5 presents the application of frequency-modulated radiation from a near infrared diode laser as a probe of the angular momentum polarisation of the nascent CN fragments, produced by 266 nm photolysis of ICN. These CN fragments are probed in the high rotational states of both the ground and first excited vibrational level on the A 2Π − X 2Σ+ electronic transition; in particular these constitute the first measurements of alignment and orientation in the first excited vibrational level at this photolysis wavelength. The alignment parameters reported for both vibrational levels are comparable, indicating that the incoherent dynamics contributing to their formation are the same. In contrast, the orientation of the v = 1 CN fragment is shown to be of opposite sign to that of v = 0 at this photolysis wavelength, although the absolute differences in their orientation parameters are similar to that observed for photolysis at 248 nm. This observation is consistent with coherent orientation arising from phase differences between wavepackets propagating on multiple excited potential energy surfaces.
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Renaud, Cyril C. "High-power diode-pumped ytterbium-doped fibre-laser." Thesis, University of Southampton, 2001. https://eprints.soton.ac.uk/38210/.
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This thesis details the work I have done on double cladding ytterbium-doped fibre lasers. The two main subjects developed were the study of an efficient compact-launching system, and the operation of the double cladding compact fibre as a continuous-wave laser and a Q-switched laser.During this work, highly efficient side launching systems were developed. These allowed coupling of more than 70% of the pump light into the doped fibre and gave as good lasing efficiency as end-pumping system. The pump and the signal were also well separated in two different guides at the ends of the device. Efficient lasing at 976 nm (85% slope efficiency) was demonstrated too, by using small inner cladding area and double passed pump. Finally, pulse-energy as high as 7.7 mJ was achieved with a large core cladding pumped ytterbium doped Q-switched fibre laser.
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Gallaher, Nigel R. "Narrow linewidth, diode laser pumped, solid state lasers." Thesis, University of St Andrews, 1994. http://hdl.handle.net/10023/13717.
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The design, construction, evaluation and development of an all solid state, narrow linewidth laser source is presented. The narrow linewidth laser system was based on a miniature standing wave Nd:YAG laser cavity, end-pumped with 100mW of 809nm light from a fibre coupled GaAlAs diode laser array. This basic CW laser generated up to 30mW at 1064nm in a single, diffraction limited transverse mode (TEM00) but multi-longitudinal mode output beam. The laser had a pump power threshold of 24mW and an optical to optical slope efficiency of 39%. A simple rate equation based numerical model of this laser was developed to allow various design parameters such as length of Nd:YAG gain medium and amount of output coupling to be optimised. Excellent agreement between the numerical model predictions of the output power as a function of input pump power and experimental data from the optimised multi-longitudinal mode laser was obtained. To restrict this laser to operate on a single longitudinal mode, twisted cavity mode and intracavity etalon, mode selecting techniques were investigated. Both methods were found to produce reliable single mode laser operation and resulted in output powers at the 10mW level. The relative free running frequency stability between a pair of single longitudinal mode diode laser pumped Nd:YAG lasers was investigated. By isolating these lasers from environmental noise using a small, custom built anechoic chamber the linewidth of the optical heterodyne signal between the two free running lasers was reduced from tens of megahertz to around 10kHz measured on a millisecond time scale. Further improvement in linewidth was achieved by actively locking the laser frequency to a novel ultra high finesse (F~12,500, free spectral range ~500MHz) spherical mirror Fabry-Perot reference interferometer using the technique of Pound-Drever locking. The locked laser displayed a maximum frequency deviation of only 1kHz from the centre of the reference cavity transmission and a frequency noise spectral density of ~20Hz/ √Hz at 1kHz. In one of the first reported demonstrations of an all solid state injection seeded laser system, this single frequency laser was used to injection seed a diode laser array, transversely pumped, Q-switched Nd:YAG laser to produce 0.25mJ, 35ns pulses in a single longitudinal, single transverse mode beam. Preliminary results on injection locking between two single frequency diode laser pumped Nd:YAG laser are also reported. A novel frequency stabilisation scheme based on resonant optical feedback locking iproposed and some preliminary experimental work on this technique is presented.
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Humphries, Gordon S. "Novel diode laser absorption techniques for combustion diagnostics." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28843.
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In-situ optical techniques offer one of the most attractive options for measuring species concentration and spatial distribution profiles in reacting environments, such as flames. The generally non-intrusive nature and spatial resolution of these techniques are now preferred over on extractive sampling, followed by analysis using techniques such as gas chromatography. In this thesis two laser absorption measurement techniques are applied to measure the soot distribution, and acetylene concentration profiles in a flat-flame burner. The in-situ measurement of the distribution of particulate matter in flames is a key step in understanding the mechanism of its formation. Most in-situ measurement systems for this purpose are based on laser induced incandescence where particles are heated using high power laser sources and the increased incandescence emission of the soot particles is detected. However as the soot cools by heat transfer to the surrounding gas, following laser heating, the pressure of the gas is increased creating an acoustic effect. Photoacoustic detection has been applied to quantify low concentrations of particulate matter in ambient air but there have been few applications of photoacoustic detection to the in-situ measurement of particulate matter formation in combustion processes. A novel simple approach using a modulated continuous wave diode laser is presented in this thesis. The measurements taken using this new technique are compared to measurements of the visible emission from the flame, and previous soot distribution measurements using laser induced incandescence. Absorption spectroscopy using near-infrared tunable diode lasers has been applied to measure species in several harsh environments such as aero-engine exhaust plumes, flames, and other industrial processes. Simple single pass absorption techniques are not always suitable for this purpose due to the low absorption of the target species, either due to low concentration or weak absorption line-strength at high temperatures. One method to increase the sensitivity of such techniques is by using cavity enhanced methods which increase the effective path length of the laser through the absorbing medium. One such cavity enhanced method is Cavity Ring-Down Spectroscopy (CRDS). CRDS uses a cavity constructed of highly reflecting mirrors, laser light is then coupled into this cavity and absorption measurements can be evaluated from the decay rate of light from the cavity. The design and, novel application of continuous wave CRDS to measure the concentration profile of acetylene in the flat-flame burner is presented. Difficulties in deriving an absolute acetylene concentration from the measured ringdown times were encountered due to the large number of interfering features. Serveral fitting and extraction techniques are applied and compared to attempt to overcome these difficulties.
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VILAIN, CHARLES-HENRI. "Laser cr : lisaf monomode accordable pompe par diode." Paris 11, 1996. http://www.theses.fr/1996PA112449.
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Le cr:lisaf (cr#3#+:lisralf#6) est le premier materiau laser permettant de realiser directement une source tout solide accordable de 820 a 960nm dans le proche infrarouge. Sa plage d'absorption dans le rouge permet egalement son pompage longitudinal par des diodes lasers algainp emettant a 670nm. Nous avons etudie le pompage longitudinal en tenant compte de la mauvaise conductivite thermique de ce materiau qui entraine une elevation locale de la temperature et a pour consequence une reduction de la duree de vie de l'etat excite, donc de la puissance de sortie du laser. De meme, le phenomene non lineaire d'up-conversion, resultant du couplage de deux ions cr#3#+ excites, reduit la population de l'etat excite, participe a cette elevation de temperature et diminue egalement l'efficacite du laser. Apres avoir cherche a realiser le laser cr:lisaf, pompe par diode, le plus efficace possible en optimisant le profil du faisceau de pompe et la geometrie de la cavite laser, nous avons evalue deux methodes permettant de realiser un laser monomode et accordable. La premiere consiste a adjoindre a la cavite hemispherique de notre laser une cavite couplee dans laquelle est placee un element spectralement selectif. Nous avons modelise et realise experimentalement deux types de cavites couplees: l'une avec un filtre de lyot et l'autre avec un reseau de diffraction dans la configuration de littman qui seule a permis d'obtenir un fonctionnement monomode, limite aux faibles puissances de pompe et instable. La seconde methode, c'est a dire l'utilisation d'une cavite depliee dans laquelle est place directement le filtre de lyot, nous a permis d'obtenir un fonctionnement monomode dynamique plus stable et une accordabilite de 140nm pour une puissance maximale de sortie de 15mw pour 450mw de puissance de pompe dans le cristal
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Druon, Frédéric. "Nouvelles sources laser d'impulsions breves pompees par diode." Paris 11, 2000. http://www.theses.fr/2000PA112184.
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Les travaux exposes dans ce memoire de these ont ete consacres a l'etude et a la realisation d'oscillateurs et d'amplificateurs laser a impulsions courtes pompes par diodes laser de puissance. Une premiere partie est consacree a la modelisation du gain et de l'amplification en pompage par diode. Une deuxieme partie porte sur le developpement d'une source compacte uv a base de microlasers amplifies. Cette etude a consiste tout d'abord a modeliser les regimes de fonctionnement pour les microlasers a declenchement passif par un absorbant saturable. Un regime haute cadence en pompage par diodes brillantes a alors ete mis en evidence. Un amplificateur entierement passif, simple et efficace a base de cristaux composites a ensuite ete developpe. Finalement, une conversion en frequence a permis l'obtention d'uv a 355 nm. Des impulsions sub nanosecondes (<<<>500 ps) ont ete obtenues a des cadences de l'ordre de 50 khz avec une puissance moyenne dans l'uv de 100 mw. Nous montrons enfin le transfert de technologie realise avec la pme nanolase qui a permis de rendre cette source commercialisable. Une troisieme partie porte sur l'etude et le developpement de sources a impulsions femtosecondes a base de gdcob dope a l'ytterbium. L'etude de ce cristal pompe par diode, pour la premiere fois a 976 nm, a montre une large accordabilite et une bonne efficacite en fonctionnement continu. Un oscillateur femtoseconde a base de ce cristal fut ensuite realise. Des impulsions de 90 fs ont ete obtenues avec un miroir a absorbant saturable pour verrouiller les modes en phase ; ces impulsions sont les plus courtes jamais obtenues avec un cristal dope avec des ions ytterbium. On a ensuite developpe un amplificateur regeneratif dans un systeme d'amplification a derive de frequence. Une amplification d'un facteur 2. 10 9 avec une energie par impulsion de 21 mj a ete obtenue conduisant a des impulsions recomprimees de 350 fs avec une energie de 12 mj.
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Alimohammadian, Ehsan. "Modeling of Performance of Diode-Pumped Nd:YVO4 Laser Systems." SPIE, 2014. http://hdl.handle.net/1993/24074.
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This thesis focuses on numerical study of a longitudinally pumped continuous wave (CW) Nd:YVO4 laser by high power VCSEL modules. Two VCSEL pump modules (6 W and 15 W) were compared. The performance of Nd:YVO4 crystal was found to be better than that of Nd:YAG crystal. Our numerical results indicate that VCSELs can serve as efficient pump sources for the end-pumped CW Nd:YVO4 lasers.
Internal cavity loss (Li) is an important parameter in the modeling and optimization of laser’s performance. A new method for the calculation of the Li for longitudinally pumped lasers was introduced. This method can be conducted without making any changes to the CW laser cavity and it also can be performed faster compared to the widely used method called Findlay-Clay analysis. A successful experiment was conducted to find the Li based on both methods with good agreement between the two.
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Ferrari, Marco Antonio. "Laser de Nd:YLF para aplicações em LIDAR." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-02092009-150039/.
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A utilização de lasers de estado sólido bombeados por diodos laser tem atraído interesse crescente devido a sua alta eficiência, seu tamanho compacto e com a possibilidade da operação com altas potências-pico. O objetivo deste trabalho foi estudar configurações de cavidades ressonantes laser, que possibilitem a obtenção de pulsos chaveados Q e futura dobra de freqüência, para aplicações em LIDAR (Light Detection and Ranging), utilizando como meio ativo cristais de Nd:YLF crescidos pelo método de Czochralski no Centro de Lasers e Aplicações IPEN USP, com bombeio lateral por diodo laser, com uma, duas, quatro e nove reflexões internas totais do feixe laser na superfície do cristal. Das seis cavidades construídas, três cavidades foram desenvolvidas para operarem com baixo ganho, grande armazenamento de energia e com grande aproveitamento de inversão de população, bombeadas com diodo laser em 806 nm e outras três cavidades foram desenvolvidas para operarem com alta absorção de bombeio e alto ganho, bombeadas com diodo laser emitindo em 797 nm. Das seis cavidades desenvolvidas, as que apresentaram melhor eficiência de conversão óptica, foram as cavidades operando com alto ganho e alta absorção (cavidade quatro a seis), com 29,5% e 20,7% de eficiência de conversão óptica, propiciando a obtenção de pulsos chaveados de 20 ns com potência-pico de 160kW.The use of diode pumped, solid state lasers has caused increasing interest due its high efficiency, compactness and possibility of operation in high peak powers. The goal of this work was the study of configurations of laser resonators that allow to obtain Q-switched pulses and a future frequency doubling, for LIDAR (Light Detection and Ranging) applications. Using as active medium Nd:YLF crystals grown by the Czochralski method at the Centro de Lasers e Aplicações IPEN USP, side pumping by laser diodes, with one, two, four and nine total internal reflexions of the laser beam at the surface of the crystals was employed. From the six resonators built, three of them were designed to work with low gain, pumped by a laser diode emitting at 806 nm. Another three laser resonators were designed to work with high pump absorption and high gain, pumped by a laser diode emitting at 797 nm. From the six developed resonators, the ones which showed the best optical conversion efficiency, were the resonators designed to work with high gain and high absorption (resonator four to six), showing 29,5% and 20,7% optical conversion efficiency, and enabling obtaining Q-switched pulses of 20 ns, with 160 kW peak power.
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Palaghita, Tudor I. "Combustor Exhaust Temperature Nonuniformity Sensing Using Diode Laser Absorption." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14574.
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This thesis describes the development of a sensing technique for temperature nonuniformity along the line of sight through combustion exhaust, geared for gas turbine applications. Tunable diode laser absorption spectroscopy is used to measure three absorption lines and compute a variable to characterize the level of temperature nonuniformity along the laser path.
Nonuniformity information is obtained from one line of sight sensor because the absorption has a nonlinear dependence on temperature. This dependence is analyzed to determine the behaviour, shape, and response of absorption lines measured through mediums with nonuniform temperature profiles. Based on this analysis a new line selection process for nonuniformity sensing is developed.
A sensor for temperature nonuniformity is proposed and demonstrated through computer simulations and experiments in the exhaust of a laboratory-scale combustor. The nonuniformity variable, U, is shown to monotonically track the level of temperature nonuniformity along the laser path. The capabilities of this sensing technique are determined based on a comprehensive analysis of errors and their effect on sensor performance. Methods to mitigate these errors are described, and the overall sensor capability is determined based on the characteristics of state of the art diode laser and absorption sensor technology. Such a sensor is capable of measuring minimum temperature deviations of 17% or more, which is well within the needed capabilities for industrial applications. Furthermore, the results and knowledge presented in this thesis apply to other absorption based sensing techniques.
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Masiyano, Dackson. "Use of diffuse reflections in tunable diode laser spectroscopy." Thesis, Cranfield University, 2009. http://hdl.handle.net/1826/4425.
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Tunable diode laser absorption spectroscopy (TDLAS) is an optical gas sensing technique in which the emission frequency of a laser diode is tuned over a gas absorption line of interest. A fraction of the radiation is absorbed by the sample gas and this can be determined from measurements of initial intensity and the intensity transmitted through the sample. The amount of light absorbed is related to the gas concentration. Additional modulation techniques combined with phase sensitive detection allow detection of very low gas concentrations (several parts per million).
The advantages of using TDLAS for trace gas sensing include; fast response times, high sensitivity and high target gas selectivity. However, the sensitivity of many practical TDLAS systems is limited by the formation of unintentional Fabry-Perot interference fringes in the optical path between the source and detector. The spacing between the maxima of these fringes, in particular those generated in gas cells, can be in the same wavelength range as Doppler and pressure-broadened molecular line widths. This can lead to (1) interference fringe signals being mistaken for gas absorption lines leading to false concentration measurements or (2) distortion or complete obscuring of the shape and strength of the absorption line, such that the sensitivity of the instrument is ultimately limited by the fringes.
The interference fringe signals are sensitive to thermal and mechanical instabilities and therefore can not be removed by simple subtraction techniques. Methods that have been proposed by previous workers to reduce the effects of interference fringes include careful alignment of optical components and/or mechanically jittering the offending components.
In general the alignment of the optical components is critical. This often leads to complex and fragile designs with tight tolerances on optical component alignment, and can therefore be difficult and expensive to maintain in field instruments.
This thesis presents an alternative approach based on the deliberate use of diffusely scattering surfaces in gas cells as a means of eliminating spurious signals due to Fabry-Perot etalons. However, their use introduced laser speckle that contributed an intensity uncertainty to gas detection measurements. A methodology for investigating the laser speckle related intensity uncertainty has been developed and confirmed. The intensity uncertainty has been quantified for the different gas cell geometries employing diffusely scattering surfaces including integrating spheres. Methods for reducing the speckle related intensity uncertainty were also investigated and are presented.
It has been shown that under the right circumstances robust gas cell designs that do not suffer from Fabry-Perot etalon effects and are relatively easy to align can be realised. The performance was found to be comparable to a conventional cell design (e.g. 3ppm detection limit for a 10cm standard cell and 11ppm for a 10cm diffusive cell). The technique could potentially simplify instrument design, thereby aiding the transfer of technology to industry.
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Hutchinson, Andrew. "Diode laser studies of trace species and their reactions." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437045.
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Ahmed, H. H. I. S. "Frequency selection and stabilization of semiconductor laser diode systems." Thesis, Swansea University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635861.
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Different types of semiconductor diode laser sources were tested in a range of spectroscopic and metrological applications to demonstrate the versatility of our laser set-up implementations. Two main topics were pursued in this study: (a) experiments on absorption spectroscopy were carried out using external cavity laser diode modules in the wavelength range (410 – 1550 nm) while vertical cavity surface emitting lasers (VCSELs) were used in the experiments involving opto-galvanic spectroscopy and laser frequency stabilization at 800.6 nm. Absorption experiments were performed for the quantitative detection of (atmospheric) trace gases such as H2O, CO, and CO2. The Tuneable Diode Laser Absorption Spectroscopy (TDLAS) was realised without the need for sophisticated detection electronics (e.g. lock-in amplifiers, etc.). A notebook-data acquisition system in conjunction with dedicated software developed during this study was fully adequate and allowed us to generate “any” desired shape of the modulation signal; and – after the data had been acquired – post-collection processing could be carried out (like averaging, noise removal, signal normalization, trend plots, etc.). In order to implement the opto-galvanic (OG) spectroscopy experiment, the opto-galvanic driver, control and detection unit was designed and built in-house. This electronic device was one of the centrepieces of the set-up for locking the laser diode frequency to an atomic transition in a hollow cathode discharge lamp. An integrated device such as the one required in this study is not available commercially. The observed OG signal revealed a series of sub-structures in the form of doublets (0.0074 nm or 4 GHz apart). The doublet frequency splitting results from the fact that VCSEL light is composed of two clearly-resolved spectral components, both linearly polarized, associated with transverse mode oscillation. Locking the laser frequency in the OG signal of the Argon transition at 800.6 nm was achieved using modulation of the injection current of the laser diode. This was done by feeding the OG signal into the data acquisition and control card to generate the suitable error signal (in magnitude and sign) to the laser current driver. This process was entirely controlled by a software program written during the course of this work. Incomplete attempts were made to couple the Fabry-Perout (FP) laser radiation to a fibre Bragg grating (FBG) due to some technical problems. Specifically, the fabricated FB didn’t match fully to any diodes available to us during the time of the experiments. Thus, only very weak feedback on FBG side-bands was observed which was insufficient to push the laser into single-wavelength oscillation.
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Ehlers, Bodo [Verfasser]. "Development of High Power Diode Laser Systems / Bodo Ehlers." Aachen : Shaker, 2005. http://d-nb.info/1186589256/34.
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Yao, I.-Chen, and 姚懿珍. "Laser Diode Driver." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/07856479799443606255.
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碩士國立中央大學
電機工程研究所
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Two laser diode drivers, of which one is operated at 1.25 Gbps while the other at 2.5 Gbps, are presented in this thesis. Both of them contain a driver, a reference voltage generator, and an automatic power control circuit. In addition, digital control blocks of bias current and modulation current are included in the 2.5 Gbps laser diode driver. TSMC 0.35um 1P4M digital process is used to fabricate these chips. The experimental results demonstrate that the 1.25 Gbps version can work at 1.2Gbps and APC works well, too.
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Unfried, Kenneth Gary. "Diode laser kinetic spectroscopy." Thesis, 1991. http://hdl.handle.net/1911/16490.
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High resolution infrared diode laser kinetic spectroscopy has been used to study reaction kinetics and spectroscopy of short-lived species. These unstable molecules were produced in a flowing system by excimer laser photolysis of suitable precursors. Their concentrations were monitored using an infrared diode laser with fast InSb detectors. Time resolution of better than 1$\mu$s was achieved.
HNO production is predicted by the reaction sequence NH$\sb2$ + NO $\to$ HN$\sb2$ + OH, HN$\sb2$ + NO $\to$ HNO + N$\sb2$ in the Miller mechanism for the thermal deNOx process. A search was made for the HNO molecule in the reaction system NH$\sb2$ + NO at room temperature using diode laser infrared kinetic spectroscopy to search for NH stretch absorptions of HNO. No HNO attributable to the deNOx process was observed. Sensitivity calibration measurements using known amounts of HNO produced from the reaction of HCO with NO were used to set an upper bound of 1% for the conversion of NH$\sb2$ into HNO.
The high resolution infrared spectrum of the heavy atom antisymmetric stretch of the ketenyl radical (HCCO) was observed by means of infrared kinetic spectroscopy. Ketenyl was produced by 193 nm photolysis of ketene. The resulting transient absorption was probed with an infrared diode laser. Individual rovibrational transitions have been identified and molecular parameters have been determined from a least-squares fit of the data. The band origin is located near 2023 cm$\sp{-1}$.
Acquisition of ketenyl infrared spectra allowed for determination of reaction rate constants by directly observing ketenyl decay. Kinetic studies of the ketenyl radical's reaction with nitric oxide, oxygen, acetylene and ethylene were conducted. A second order rate constant of 4.4(10) $\times$ 10$\sp{-11}$ cm$\sp3$molecule$\sp{-1}$s$\sp{-1}$ was obtained for the reaction with NO and a second order constant of 6.5 $\times$ 10$\sp{-13}$ cm$\sp3$molecule$\sp{-1}$s$\sp{-1}$ was obtained for the reaction with O$\sb2$. Acetylene appeared not to react with the ketenyl radical. An upper limit of 3.8 $\times$ 10$\sp{-13}$ cm$\sp3$molecule$\sp{-1}$s$\sp{-1}$ for the rate constant was determined by measuring the ketenyl decay in the presence of acetylene. The addition of ethylene appeared to slow the ketenyl decay. This behavior was attributed to the reaction of ethylene with a chemical species (probably H atoms) responsible for depletion of ketenyl.
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Dias, Francisco João Cunha. "Laser Diode Pulse Driver." Master's thesis, 2019. https://hdl.handle.net/10216/118960.
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A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.
It can have many applications in different fields like communications systems, sensorization equipment, marking and cutting of materials, 3D printing, and many others.
The Laser converts electrical power into optical power, and it is the aim of this project to study pulse modulation techniques, test existing pulse drivers and propose and design electronics for a pulse driver. It's important to understand how Lasers work, their characteristics and limitations, as well as different technics and different concepts of drivers.
Another challenge proposed by the company was to use free software for the design and simulation of circuits as well as for the design of the PCB, being the gEDA tools for the schematic and the PCB and Ngspice for the simulation.
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YI, XU-ZHONG, and 易序忠. "Fabrication and study of surface emitting laser diode & high power laser diode." Thesis, 1990. http://ndltd.ncl.edu.tw/handle/57x83t.
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