Dissertations / Theses on the topic 'Ultrafast Pulse'
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Chauhan, Vikrant Chauhan Kumar. "Pulse compression and dispersion control in ultrafast optics." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/37153.
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Pulse Compression and Dispersion Control in Ultrafast Optics
Vikrant K. Chauhan
116 Pages
Directed by Dr. Rick P. Trebino
In this thesis, we introduced novel pulse compressors that are easy to align and which also compensate for higher order dispersion terms. They use a single dispersive element or a combination of dispersive elements in single-element-geometry. They solve the problem of extra-cavity pulse compression by providing control of the pulse width in almost all of the experiments performed using ultrashort pulses, and they even compensate for higher order dispersion. We performed full spatiotemporal characterization of these compressors and demonstrated their performance. We also developed a theoretical simulation of pulse compressors which is based on a matrix based formalism. It models the full spatiotemporal characteristics of any dispersion control system. We also introduced a simple equation, in its most general form, to relate the total dispersion and magnification introduced by an arbitrary sequence of dispersive devices. Pulse compressor characterization was done using interferometric measurements in the experiments presented in this work, but we also developed a method to measure pulses that uses polarization gating FROG for measuring two unknown pulses. In the last part, we briefly discuss the designing of a high energy chirped pulse amplification system.
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Liu, Xuan. "Numerical Simulations of Ultrafast Pulse Measurements." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16175.
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This thesis contains two major components of research: numerical simulation of optical-parametric amplification cross correlation of Frequency-Resolved Optical Gating (OPA-XFROG) and numerical simulation of GRENOUILLE and its related issues.
Recently, an extremely sensitive technique--OPA-XFROG has been developed. A short pump pulse serves as the gate by parametrically amplifying a short segment of the signal pulse in a nonlinear crystal. High optical parametric gain makes possible the complete measurement of ultraweak, ultrashort light pulses. Unlike
interferometric methods, it does not carry prohibitively restrictive requirements, such as perfect mode-matching, perfect spatial coherence, highly stable absolute phase, and a same-spectrum
reference pulse. We simulate the OPA-XFROG technique and show that by a proper choice of the nonlinear crystal and the noncollinear mixing geometry it is possible to match the group velocities of the pump, signal, and idler pulses, which permits the use of relatively thick crystals to achieve high gain without measurement distortion. Gain bandwidths of ~100 nm are possible, limited by group velocity dispersion.
In the second part of the thesis, we numerically simulate the performance of the ultrasimple ultrashort laser pulse measurement device- GRENOUILLE. While simple in practice, GRENOUILLE has many theoretical subtleties because it involves the second-harmonic generation of relatively tightly focused and broadband pulses. In addition, these processes occur in a thick crystal, in which the phase-matching bandwidth is deliberately made narrow compared to the pulse bandwidth. We developed a model that include all
sum-frequency-generation processes, both collinear and noncollinear. We also include dispersion using the Sellmeier equation for the crystal BBO. Working in the frequency domain, we compute the
GRENOUILLE trace for practical-and impractical-examples and show that accurate measurements are easily obtained for properly designed devices.
For pulses far outside a GRENOUILLE's operating range (on the long side), we numerically deconvolve the GRENOUILLE trace with the
response function of GRENOUILLE to improve its spectral resolution.
In the last part of the thesis, we simulate the second harmonic generation with tightly focused beams by use of lens. Thus, we are able to explain the `weird' focusing effect that has been a
`puzzles' for us in the GRENOUILLE measurement.
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Wang, Feihu. "Ultrafast terahertz pulse generation from quantum cascade lasers." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066752.
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Lasers à cascades quantiques (LCQs) THz sont des dispositifs à semi-conducteurs fondamentaux pour l'action du laser dans la gamme THz. Des évolutions considérables ont été réalisées dans la dernière décennie en termes de fonctionnement de la température et de la puissance de sortie. LCQs THz peuvent posséder de bandes spectrales très larges, les rendant approprié pour la génération d'impulsions THz ultracourtes par blocage de mode. Cependant, à ce jour, la génération d'impulsions THz de LCQ a été limitée à 10 - 20 ps, en dépit de plusieurs années d'efforts de recherche. Dans cette thèse, ce goulot d'étranglement dans la technologie QCL est étudié et surmontée. Plusieurs étapes qui ont permis la réalisation de génération d'impulsions ultracourtes de LCQ ont été réalisées. Performances de "state-of-the-art" actuelles sont représentés, à l'aide de LCQ avec une bande passante étroite dans des guides d'ondes "single-plasmon" et des impulsions THz de 20 ps sont générés à basse température (10K). Ceci est suivi par, pour la première fois, le verrouillage de modes des LCQs des bandes spectrales larges dans les guides d'onde métal-métal à des températures élevées (77k). Même avec de bandes spectrales larges, les impulsions obtenus étaient seulement 11 ps et nous montrent que la dispersion de l'indice et la modulation électrique sont les facteurs critiques. Enfin, ces effets sont compensés par un interféromètre de Gires-Tournois et un modulation de perte. Cette approche permet de générer des impulsions aussi courtes que 4 ps, avec la possibilité d'aller beaucoup plus loin dans la sous-picosecondeTHz quantum cascade lasers (QCLs) are foundational semiconductor devices for laser action in the THz range. Considerable developments have been made in the last decade in terms of temperature operation and high output power. THz QCLs can also possess extremely large spectral bandwidths, rendering them suitable for ultrashort THz pulse generation through modelocking, with pulse widths of a few picoseconds theoretically obtainable. However, to date, the generation of THz pulses from QCLs has been limited to 10 - 20 ps, despite several years of research effort. In this thesis, this bottleneck in QCL technology is investigated and overcome. Several milestones have been achieved that permitted the realization of ultrashort pulse generation from QCLs. Current state-of-the-art performances are shown, using narrow spectral bandwidth QCLs in single-plasmon waveguides, and where modelocking results in 20 ps long THz pulses at low temperatures (10K). This is followed by, for the first time, mode-locking of broad spectral bandwidth QCLs in sub-wavelength metal-metal waveguides at ‘high’ temperatures (77K). Even with large spectral bandwidths, the shortest pulses achieved were only 11 ps and we show that the index dispersion and the electrical modulation are the critical factors. Finally, these effects are compensated through a Gires-Tournois interferometer and an extra loss mechanism, respectively, integrated monolithically onto a QCL. This approach permits to generate pulses as short as 4 ps, with the potential to go considerably further to the sub-picosecond or single cycle regime
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Lee, Dongjoo. "Ultra-broadband phase-matching ultrashort-laser-pulse measurement techniques." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-07032007-113912/.
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Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2008.First, Phillip, Committee Member ; Adibi, Ali, Committee Member ; Raman, Chandra, Committee Member ; Buck, John, Committee Member ; Trebino, Rick, Committee Chair.
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Ma, Jun. "Ultrafast Electron Transfer in Solutions Studied by Picosecond Pulse Radiolysis." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS023/document.
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L'interaction de particules énergétiques avec les résultats de l'eau dans l'excitation et l'ionisation des molécules d'eau. Le processus d'ionisation se rapporte à la génération de l'excès d'électrons détachés de leurs molécules parentes et laissant derrière le trou positive (notée H₂O•⁺). Cela se produit sur le calendrier d'une transition électronique ~ 10⁻¹⁵s. Les processus chimiques plus anciens de H₂O•⁺ et l'excès d'électrons vers autre question suivie de l'eau en vrac ionisants restent encore peu par rapport connu et constitue un sujet difficile dans la chimie de rayonnement. Dans ma thèse, les techniques de radiolyse d'impulsions picoseconde ont été utilisés pour observer la cinétique de la SO₄•⁻, H₂PO₄• dans de l'acide sulfurique très concentré et solutions d'acide phosphorique sur une large gamme de concentrations (de 1 mol L⁻¹ à l'acide pur). Les résultats expérimentaux montrent clairement que le radical secondaire de sulfurique (SO₄•⁻) et de l'acide phosphorique (H₂PO₄•) peuvent être formés par l'intermédiaire de deux mécanismes : détachement d'électrons direct par l'impulsion d'électrons (7 ps) et le transfert d'électrons ultra-rapide des solutés au radical cation de l'eau H₂O•⁺. La réactivité des espèces oxydantes fortes, H₂O•⁺ vers les solutés dans des solutions aqueuses très concentrées est quantitativement démontréThe interaction of energetic particles with water results in the excitation and ionization of water molecules. The ionization process refers to the generation of the excess electrons detached from their parent molecules and leaving behind the positive hole (denoted as H₂O•⁺). This occurs on the timescale of an electronic transition ~10⁻¹⁵ s. The earliest chemical processes of H₂O•⁺ and excess electron towards other matter followed water ionizing in bulk still remain relative little known and constitute a challenging subject in radiation chemistry. In my thesis, picosecond pulse radiolysis techniques were used to observe the kinetics of the SO₄•⁻, H₂PO₄• in highly concentrated sulfuric acid and phosphoric acid solutions over a large range of concentrations (from 1 mol L⁻¹ to neat acid). The experimental results showed clearly that the secondary radical of sulfuric (SO₄•⁻) and phosphoric acid (H₂PO₄•) can be formed via two mechanisms: direct electron detachment by the electron pulse (7 ps) and ultrafast electron transfer from the solutes to the radical cation of water H₂O•⁺. The reactivity of the strongest oxidizing species, H₂O•⁺ towards the solutes in highly concentrated aqueous solutions is quantitatively demonstrated
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Lamour, Tobias Paul. "High pulse energy near-infrared ultrafast optical parametric oscillators." Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2509.
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A source-demand in the near- and mid-IR wavelength spectrum exists for various applications such as waveguide inscription, multiphoton imaging, and nonlinear spectroscopy. All of the applications seek for higher repetitions rates for faster processing speed, better signal to noise ratios or to improve the results for applications like laser waveguide inscription. This is in contrast to the high pulse energies, required to drive the nonlinear processes involved with these applications. Available systems are either based on low-energy, high-repetition-rate optical parametric oscillators or high-energy, low-repetition-rate optical parametric amplifiers. In this thesis a sources was developed that can bridge the wide gap between these two extremes, providing sufficient energy to drive nonlinear processes, with repetition rates in the MHz domain. This was achieved by introducing three techniques previously employed for energy scaling in laser cavities. Firstly an exchange from the conventionally used Ti:sapphire pump to a commercial high power Yb:fibre laser system readily scaled the usable pump energy. This was combined with a technique known as cavity-length extension, which allows a lowering of the cavity roundtrip time offering the build-up of pulses with increased energy. In a final stage, cavity-dumping on basis of an acousto-optic modulator was introduced into the a redesigned cavity. The combination of these three techniques, novel to synchronously pumped optical parametric oscillators, enabled the extraction of record-high pulse energies and peak powers
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Shimotsuma, Yasuhiko. "Nano-modification of transparent materials using ultrafast pulse laser." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144535.
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Benane, Mehdi Yanis. "Ultrafast, broadband and multi-pulse transmissions for ultrasonic imaging." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1268/document.
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L'échographie est un outil de diagnostic largement utilisé grâce à des vertus telles que l'acquisition / traitement de données en temps réel, la facilité d'utilisation et la sécurité pour le patient / praticien pendant l'examen. Cependant, comparée à d'autres méthodes d'imagerie telles que la tomographie à rayons X et l'imagerie par résonance magnétique, l'échographie présente l'inconvénient de fournir une qualité d'image relativement basse. Dans cette thèse, nous étudions une méthode capable d'augmenter la qualité d'image, permettant ainsi de meilleurs diagnostics échographiques. Afin d'augmenter le rapport signal / bruit des signaux reçus, nous proposons d'utiliser des signaux modulés en fréquence (chirps). Pour éviter l'effet négatif de la bande passante limitée de la sonde, nous modulons en amplitude les signaux d'excitations afin d'augmenter l'énergie du signal dans les bandes de fréquences où la sonde est moins efficace. Pour compresser l'énergie des échos, nous utilisons des filtres de Wiener afin d'obtenir un bon compromis résolution spatiale / stabilité du bruit. Nous combinons cette méthode appelée REC (Resolution Enhancement Technique) avec l’imagerie ultrarapide. Nous montrons des résultats simulés et expérimentaux (in-vitro, ex-vivo et in-vivo) prometteurs. De plus, nous adaptons REC afin de compenser l'effet d'atténuation tissulaire. Cette amélioration est validée expérimentalement sur des phantoms. Nous adaptons également REC à la propagation non linéaire des ondes ultrasonores, en proposant une technique d'inversion d'impulsions qui utilise REC pour fournir une meilleure résolution et un meilleur rapport contraste / bruit. Ensuite, nous appliquons REC à différents schémas d’acquisition tels que les ondes divergentes et la transmission multi-lignes (MLT). Nous montrons également que la qualité d’image peut être augmentée davantage en tenant compte de la réponse impulsionnelle spatiale de la sonde lorsque REC et MLT sont combinésUltrasound imaging is a diagnostic tool widely used thanks to such virtues as real-time data acquisition / processing, ease of use and safety for the patient / practitioner during examination. However, when compared to other imaging methods such as X-ray tomography and Magnetic Resonance Imaging, the echography has the disadvantage to provide relatively low image quality. In this thesis, we study a method that is able to increase the ultrasound image quality, thus paving the way towards improved diagnostics based on echography and novel ultrasound applications. In order to increase the echo signal to noise ratio of the received signals, we propose to use linear frequency modulated signals, also called chirps. To avoid the negative effect of the bandlimited acquisition probe, we apply a pre-enhancement step on the probe excitation signals in order to boost the signal energy in the frequency bands where the probe is less efficient. To compress the echo energy in reception, we use Wiener filters that allow obtaining a good trade-off between the spatial resolution and noise stability. We apply the previously detailed pipeline, also called REC (Resolution Enhancement Technique) on ultrafast imaging schemes. We show promising results in simulation and in-vitro, ex-vivo, in-vivo acquisitions. Furthermore, we adapt REC in such way that the frequency dependent tissue attenuation effect is compensated for. This improvement is validated in simulation and phantom experiments. We also adapt REC to the nonlinear propagation of ultrasound waves, by proposing a pulse inversion technique that uses REC to provide a better image resolution and contrast to noise ratio. Then, we demonstrate the generality of the REC method by applying it to different acquisition schemes such as diverging wave compounding and Multi Line Transmit (MLT). We also show that the image quality can be increased more by taking into account the spatial impulse response of the ultrasound probe when REC and MLT are combined
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Akturk, Selcuk. "Extending ultrashort-laser-pulse measurement techniques to new dimensions, time scales, and frequencies." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6892.
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In the last decade, there has been tremendous progress in the field of ultrashort-pulse measurement. However, this effort has focused mostly on the temporal behavior of 100-fs, 800-nm ultrashort pulse, ignoring other pulse lengths, wavelengths, and the very common space-time couplings or so called spatio-temporal distortions. In this thesis work, I do an extensive study of spatio-temporal distortions and their measurement using Frequency Resolved Optical Gating (FROG) and its relatives. I clarify some ambiguities in the descriptions of these effects in the existing theory and establish a more general description of such distortions in ultrashort pulses. I also extend these measurement techniques to different wavelengths and pulse lengths. Specifically, I develop measurement devices for few-cycle NIR pulses, weak and narrowband fiber laser pulses, long (several-ps) NIR pulses, and visible pulses from NOPAs.
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Timilsina, Pratap. "Development of an electron time of flight spectrometer for ultrafast pulse characterization and ultrafast dynamics studies." Kansas State University, 2016. http://hdl.handle.net/2097/32598.
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Master of ScienceDepartment of Physics
Carlos Trallero
This report presents the details of an electron time-of-flight (ETOF) spectrometer to be used for characterizing ultrafast electric field pulses. The pulses will range in pulse-duration from femtosecond to attoseconds and in wavelength from the far infrared (FIR) to the extreme ultra violet (XUV). By measuring the photoelectrons in the presence of two electric fields and their quantum interference we will be able to extract the amplitude and phase of the electric field. For XUV pulses this is the well-known streaking and Reconstruction of Attosecond Beating by Interference of Two-Photon Transition (RABITT) method. The ETOF is based on a set of tunable electrostatic lenses capable of detecting 0-150 eV electrons. In addition, we can selectively increase the photoelectron yield of the spectrum. The precise tuning of the electrostatic lens system is done with a Genetic Algorithm (GA) with an intensity fluctuation discriminator in the fitness.
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Kassier, Gunther Horst. "Ultrafast electron diffraction : source development, diffractometer design and pulse characterisation." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5359.
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Thesis (PhD (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Ultrafast Electron Diffraction (UED) is a rapidly maturing field which allows investigation of the evolution of atomic arrangement in solids on timescales comparable to the vibrational period of their constituent atoms (~10-13 s). The technique is an amalgamation of conventional high energy electron diffraction methods and pump-probe spectroscopy with femtosecond (1 fs = 10-15 s) laser pulses. Ultrafast pulsed electron sources generally suffer from limitations on the attainable electron number per pulse (brightness) due to Coulomb repulsion among the electrons. In this dissertation, the design and construction of a compact UED source capable of delivering sub-300 fs electron pulses suitable for diffraction experiments and containing about 5000 electrons per shot is described. The setup has been characterised by measurement of the transverse beam size and angular spread, and through recording and analyzing an electron diffraction pattern from a titanium foil. Measurement of the temporal duration of fs electron pulses is not trivial, and a specialised compact streak camera operating in accumulation mode has been developed as part of this study. A sub-200 fs temporal resolution has been achieved, and the dependence of temporal duration on electron number per pulse was investigated for the current UED source. The observed trends correlate well with detailed electron bunch simulations. In order to investigate ultrafast processes on samples that cannot be probed repeatedly, it becomes necessary to significantly increase the brightness of current state of the art compact sources such as the one constructed in the present study. UED sources employing electron pulse compression techniques offer this possibility. Traditional pulse compression schemes based on RF cavities, while simple in principle, pose significant technical challenges in their realisation. The current thesis describes two novel UED pulse compression methods developed by the author: achromatic reflectron compression and pulsed cavity compression. Both concepts are expected to be easier to realise than conventional RF compression. Detailed simulations predict that such sources can attain a brightness improvement of more than one order of magnitude over compact sources that do not employ compression techniques. In addition, such sources show much promise for the attainment of pulse durations in the sub-100 fs range.
AFRIKAANSE OPSOMMING: Ultra vinnige elektron diffraksie is ‘n meettegniek wat tans in die proses is om vinnige ontwikkeling te ondergaan. Die tegniek het ten doel om strukturele omsettingsprosesse op ‘n lengteskaal van atoombindings en ‘n tydskaal van die vibrasie periode van atome in materie, ongeveer 10-13 s, te ondersoek. Dit word bewerkstellig deur die spasieresolusievermoë van gewone hoë energie elektron diffraksie met die tydresolusievermoë van femtosekonde (1 fs = 10-15 s) laserspektroskopie te kombineer. Die aantal elektrone per puls (intensiteit) van ultravinnige gepulsde elektronbronne word beperk deur die Coulomb afstootingskragte tussen die elektrone. Hierdie dissertasie beskryf die ontwerp en konstruksie van ‘n kompakte ultravinnige elektron bron. Die elektronpulse wat geproduseer word bevat tot 5000 elektrone per puls met ‘n tyd durasie van minder as 300 fs, en is geskik vir diffraksie eksperimente. Die aparaat is gekarakteriseer deur die volgende metings: elektronpulsdiameter, straaldivergensie, en ‘n titaan foelie se statiese diffraksie patroon. Dit is nie triviaal om die durasie van femtosekonde elektronpulse te meet nie, en n spesiale kompakte akkumulerende “streak camera” is vir die doeleindes van hierdie projek onwikkel. Die tydresolusie van hierdie “streak camera” is beter as 200 fs, en die afhanklikheid van die pulsdurasie wat deur die ultravinnige elektron bron geproduseer word as n funksie van die elektrongetal per puls is met behulp van hierdie toestel bepaal. Die resultate klop redelik goed met gedetaileerde simulasies van die elektron puls dinamika. Die karakterisasie van monsters wat nie herhaaldelik gemeet kan word nie vereis verkieslik ‘n nog hoër pulsintensiteit as wat met huidige bronne bereik kan word. ‘N verdere doelstelling is dus om ultravinnige elektron bronne te ontwikkel wat pulse met meer elektrone per puls kan genereer. Dit kan bewerkstellig word deur bronne wat van elektron puls kompressie tegnieke gebruik maak. Die tradisionele manier waarop dít gedoen word is deur middel van n kontinu gedrewe radio frekwensie holte. Hierdie metode gaan egter gepaard met aanmerklik hoë tegniese uitdagings. Om hierdie rede het die outeur twee alternatiewe puls kompressie konsepte ontwikkel: akromatiese reflektron kompressie and gepulsde holte kompressie. Albei konsepte sal waarskeinlik makliker wees om te realiseer as die tradisionele radio frekwensie kompressie, en is deur middel van gedetaileerde simulasies geverifiseer. Hierdie simulasies voorspel dat die intensiteit van genoemde bronne met ten minste n grooteorde meer kan wees as wat tans met kompakte ultravinnige elektron bronne moontlik is. Verder blyk dit dat sulke bronne n pulsdurasie van minder as 100 fs kan bereik.
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Miura, Kiyotaka. "Studies on Modification of Glass Structure Using Ultrafast Pulse Laser." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/77753.
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Savage, Shelby Jay 1978. "All-optical pulse regeneration in a Faraday stabilized ultrafast nonlinear interferometer." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86730.
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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (leaves 105-110).
by Shelby Jay Savage.
M.Eng.
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Friedman, Melissa E. "Pulse shaping for broadband photoassociation of cold molecules." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:18d49cc2-9146-4ff8-b3b3-9e045bff039c.
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The development of the field of the science of ultra-cold matter has opened some exciting possibilities in exploring the quantum-mechanical processes which dominate matter interactions at the sub-microscopic scale. Although methods of cooling atoms are well established, molecular cooling is made difficult by molecules’ additional vibrational and rotational degrees of freedom. It was the goal of the research in this work to approach molecular cooling indirectly, by using broadband shaped-pulse photoassociation for the generation of tightly bound ultracold Rb2 molecules. The experiments towards this goal conducted by our group included a pumpdecay experiment to observe the generation of ground state singlet or triplet molecules. However, attempts to observe an increase in ground state population have been unsuccessful. A pump-probe study of wavepacket dynamics in the 5s+5p electronic state was conducted in order to determine the appropriate timing for the application of an additional pulse to dump population into the ground state. Although the attempt to observe wavepacket oscillations has been unsuccessful, pump-probe studies have yielded the observation of loosely bound excited state molecules as a result of the photoassociation pulse. These results are promising as a first stage in a fully coherent pump-dump approach to stabilisation into the lowest vibrational ground state. This thesis will provide an introduction and overview to the concerns involved in addressing the problem of molecular cooling and generation. Experimental techniques will be discussed including pulsed laser systems, optical parametric amplifi- cation, and the presentation of an original design for pulse shaping with an acoustooptic modulator. The emphasis of these discussions will be on the principles and operating procedures required for the use of these devices as home-built systems. The thesis will conclude with the results of pump-probe experiments utilising the pulse shaper as a spectral cutting device.
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Nguyen, Dat. "Dynamic feedback pulse shaping for high power chirped pulse amplification system." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5826.
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The topic of this proposal is the development of high peak power laser sources with a focus on linearly chirped pulse laser sources. In the past decade chirped optical pulses have found a plethora of applications such as photonic analog-to-digital conversion, optical coherence tomography, laser ranging, etc. This dissertation analyzes the aforementioned applications of linearly chirped pulses and their technical requirements, as well as the performance of previously demonstrated parabolic pulse shaping approaches. The experimental research addresses the topic of parabolic pulse generation in two distinct ways. First, pulse shaping technique involving a time domain approach is presented, that results in stretched pulses with parabolic profiles with temporal duration of 15 ns. After pulse is shaped into a parabolic intensity profile, the pulse is compressed with DCF fiber spool by 100 times to 80 ps duration at FWHM. A different approach of pulse shaping in frequency domain is performed, in which a spectral processor based on Liquid Crystal on Silicon technology is used. The pulse is stretched to 1.5 ns before intensity mask is applied, resulting in a parabolic intensity profile. Due to frequency to time mapping, its temporal profile is also parabolic. After pulse shaping, the pulse is compressed with a bulk compressor, and subsequently analyzed with a Frequency Resolved Optical Gating (FROG). The spectral content of the compressed pulse is feedback to the spectral processor and used to adjust the spectral phase mask applied on the pulse. The resultant pulse after pulse shaping with feedback mechanism is a Fourier transform, sub-picosecond ultrashort pulse with 5 times increase in peak power. The appendices in this dissertation provide additional material used for the realization of the main research focus of the dissertation. Specification and characterization of major components of equipment and devices used in the experiment are present. The description of Matlab algorithms that was used to calculate required signals for pulse shaping are shown. A brief description of the Labview code used to control the spectral processor will also be illustrated.Ph.D.
Doctorate
Physics
Sciences
Physics
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Kim, Daekeun Ph D. Massachusetts Institute of Technology. "Ultrafast optical pulse manipulation in three dimensional-resolved microscope imaging and microfabrication." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49759.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references.
The availability of lasers with femtosecond, ultrafast light pulses provides new opportunities and challenges in instrument design. This thesis addresses three aspects of utilizing ultrafast light pulses in two-photon excitation microscopy. First, optical fibers are routinely used in many optical instruments but their use in two-photon microscopy is very limited. As ultrafast light pulses propagate through conventional fiber optics, light pulses are dispersed and broadened, as a result of nonlinear interactions between light and material. Two-photon excitation efficiency is reduced with pulse broadening. The recent development of photonic crystal fibers allows unprecedented control of light properties through them. This thesis provides a thorough quantitative characterization of different conventional optical fibers and photonic crystal fibers enabling better utilization of these fibers for two-photon microscopic imaging. Second, two-photon microscopic imaging is relatively slow due to the sequential nature of raster scanning. Several groups have recently sought to overcome this limitation by developing a 3D-resolved wide-field two-photon microscope using the concept of temporal focusing that is based on manipulating the dispersion of ultrafast light pulses spatially. However, the existing temporal focusing systems have poor optical sectioning capability and, due to a shortage of illumination power, low actual frame rate. In this thesis, a comprehensive mathematical model is derived for temporal focusing two-photon microscope taking key instrument design parameters into account.
(cont.) By optimizing instrument design and the use of high two-photon cross section quantum dots, we demonstrate single quantum dot imaging at micron level resolution at video rate. Lastly, we realize that the temporal focus concept may also be used for microfabrication. A prototype three-dimensional lithographic microfabrication system is developed and micro patterning capability based on photobleaching process is demonstrated.
by Daekeun Kim.
Ph.D.
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Stoian, Razvan. "Adaptive techniques for ultrafast laser material processing." Habilitation à diriger des recherches, Université Jean Monnet - Saint-Etienne, 2008. http://tel.archives-ouvertes.fr/tel-00352662.
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Le besoin d'une très grande précision lors du traitement des matériaux par laser a fortement encouragé le développement des études de l'effet des impulsions ultra brèves pour la structuration des matériaux à une échelle micro et nano métrique. Une diffusion d'énergie minimale et une forte non linéarité de l'interaction permet un important confinement énergétique à des échelles les plus petites possibles. La possibilité d'introduire des changements de phases rapides et même de créer de nouveaux états de matière ayant des propriétés optimisées et des fonctions améliorées donne aux impulsions ultra brèves de sérieux arguments pour être utilisées dans des dispositifs très précis de transformation et de structuration des matériaux. L'étude de ces mécanismes de structuration et, en particulier, de leurs caractéristiques dynamiques, est une clé pour l'optimisation de l'interaction laser-matière suivant de nombreux critères utiles pour les procédés laser : efficacité, précision, qualité. Ce mémoire synthétise les travaux de l'auteur sur l'étude statique et dynamique du dépôt d'énergie ultra rapide, avec application aux procédés laser. La connaissance de la réponse dynamique des matériaux après irradiation laser ultra brève montre que les temps de relaxation pilotent l'interaction lumière-matière. Il est alors possible d'adapter l'énergie déposée à la réponse du matériau en utilisant les toutes récentes techniques de mise en forme spatio temporelle de faisceaux. Un couplage optimal de l'énergie donne la possibilité d'orienter la réponse du matériau vers un résultat recherché, offrant une grande flexibilité de contrôle des procédés et, sans doute, la première étape du développement de procédés « intelligents ».
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Galbraith, Martin Christopher Edward [Verfasser]. "Time-resolved spectroscopy with attosecond pulses and pulse trains: ultrafast relaxation in benzene cations / Martin Christopher Edward Galbraith." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1124465170/34.
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Vaughan, Joshua Charles. "Two-dimensional ultrafast pulse shaping and its application to coherent control and spectroscopy." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32492.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Vita.
Includes bibliographical references (p. 167-182).
This thesis develops powerful new methods for shaping femtosecond laser pulses in two dimensions and explores their application to coherent control of propagating lattice excitations and degenerate four-wave mixing spectroscopy. Pulse shaping in two dimensions is achieved by manipulating the spectral components of ultrashort laser pulses within many horizontal slices of the pulse. Each horizontal slice is independently shaped by means of a two-dimensional liquid crystal spatial light modulator, and taken together the shaped regions form sophisticated optical waveforms with time-dependent spatial profiles. Automated optical control over coherent lattice responses that are both time- and position-dependent across macroscopic length scales is demonstrated. Two- dimensional (2D) femtosecond pulse shaping was used to generate excitation light fields that were directed toward distinct regions of crystalline samples, producing terahertz-frequency lattice vibrational waves that emanated outward from their multiple origins at lightlike speeds. Interferences among the waves resulted in fully specified far-field responses, including tilted, focusing, or amplified wavefronts. Generation and coherent amplification of terahertz travelling waves and terahertz phased-array generation are also demonstrated. A novel approach to coherent nonlinear optical spectroscopy based on 2D femtosecond pulse shaping is introduced. Multiple phase-stable output beams are created and overlapped at the sample in a phase-matched boxcars geometry via 2D femtosecond pulse shaping.
(cont.) The pulse timing, shape, phase, and spectral content within all beams may be specified, yielding an unprecedented level of control over the interacting fields in nonlinear spectroscopic experiments. Heterodyne detection and phase cycling of the nonlinear signal is easily implemented due to the excellent phase stability between each output beam. This approach combines the waveform generation capabilities of magnetic resonance spectroscopy with the wavevector specification and phase-matching of nonlinear optical spectroscopy, yielding the signal selectivity and control capabilities of both. Results on three prototype systems will be used to illustrate the exciting possibilities with this method.
by Joshua Charles Vaughan.
Ph.D.
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Harper, Matthew R. "Control and measurement of ultrafast pulses for pump/probe-based metrology." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/430.
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Balasubramanian, Haribhaskar. "Two photon luminescence from quantum dots using broad and narrowband ultrafast laser pulses." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2020.
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Ganz, Thomas. "Supercontinuum generation by chirped pulse compression for ultrafast spectroscopy and broadband near-field microscopy." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-148551.
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Khanolkar, Ankita Nayankumar. "Effect of Spectral Filtering on Pulse Dynamics of Ultrafast Fiber Oscillators at Normal Dispersion." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1628171764933755.
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Ghimire, Shambhu. "Study on generation of attosecond pulse with polarization gating." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/283.
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Wu, Yi. "High flux isolated attosecond pulse generation." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6038.
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This thesis outlines the high intensity tabletop attosecond extreme ultraviolet laser source at the Institute for the Frontier of Attosecond Science and Technology Laboratory.
First, a unique Ti:Sapphire chirped pulse amplifier laser system that delivers 14 fs pulses with 300 mJ energy at a 10 Hz repetition rate was designed and built. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two stage Ti:Sapphire chirped pulse power amplifier with mJ-level white light pulses from a gas filled hollow core fiber. It is the highest energy level ever achieved by a broadband pulse in a chirped pulse amplifier up to the current date.
Second, using this laser as a driving laser source, the generalized double optical gating method is employed to generate isolated attosecond pulses. Detailed gate width analysis of the ellipticity dependent pulse were performed. Calculation of electron light interaction dynamics on the atomic level was carried out to demonstrate the mechanism of isolated pulse generation.
Third, a complete diagnostic apparatus was built to extract and analyze the generated attosecond pulse in spectral domain. The result confirms that an extreme ultraviolet super continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The extreme ultraviolet pulse energy was ~100 nJ at the exit of the argon gas target.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
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Yang, Chang. "Ultra-Compact Grating-Based Monolithic Optical Pulse Compressor for Laser Amplifier Systems." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/731.
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Ultra-short and high-peak-power laser pulses have important industrial and scientific applications. While direct laser amplification can lead to peak powers of several million watts, higher values than these cannot be achieved without causing damage to the amplifier material. Chirped pulse amplification technique is thus invented to break this barrier. By temporally stretching pulses before entering amplifier, the pulse peak power is significantly reduced and thus becomes safe to be passed through the amplifier. After amplification, a compressor is used to recover the pulse width, and high-power ultra-short laser pulses are produced. Chirped pulse amplification technology increases the pulse energy by transferring the damaging effects of high-peak power laser pulses from the vulnerable amplifier to a relatively robust compressor system. The compressor is therefore a crucial device for producing high peak powers. However, there are some major drawbacks associated with it. First, compressors in high-energy laser system are usually over 1 cubic meter in size. For many applications, this large and cumbersome size is a limiting factor. Second, compressors are sensitive to outside disturbances; a little misalignment can lead to failure of pulse compression process. Third, gratings with large uniformly ruled area are difficult to fabricate, which impose a limit on achievable peak powers and pulse durations of laser pulses through the use of conventional compressors. In this project, we present a grating-based monolithic optical compressor that offers a way around some of the major problems of existing compressors. By integrating the key optical components, one can make a robust and monolithic compressor that requires no alignment. In the new scheme, folding the optical path with reflective coatings allows one to design a compressor of significantly reduced size by minimizing both the longitudinal and transverse dimensions of the device. The configuration and operation mechanism of this novel compressor are described. A method for calculating the volume of the compressor is investigated. This is validated by computing the size of a specific monolithic compressor. Simulation results obtained through finite-difference time-domain method are presented, proving that the new compressor provides a compact, portable, and robust means for temporally compressing long duration pulses.
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Ciesielski, Richard [Verfasser], and Achim [Akademischer Betreuer] Hartschuh. "Ultrafast dynamics in single nanostructures investigated by pulse shaping microscopy / Richard Ciesielski. Betreuer: Achim Hartschuh." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1111505330/34.
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Patel, Aabid. "Phenomena of ultrafast laser material modification with respect to spatio-temporal couplings of the laser pulse." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/415994/.
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The nano-structuring of transparent media with subpicosecond laser pulses has attracted significant interest due to its unique applications. In contrast to nanosecond pulses where the energy introduced to the lattice is absorbed, leading to melting/boiling of the material around the focal volume, femtosecond lasers can alter material properties of the glass at high pressures without excessive production of heat, modifying the structures with sub-micron resolution. Permanent modifications can then be induced without strong collateral damage. Although femtosecond pulses are beneficial for material processing, short pulse durations and broad spectral bandwidths require a novel approach to femtosecond pulse control. It is well known that laser induced modification depends on fluence, wavelength and polarization. Another dependence of material modification is the spatio-temporal properties of the ultrashort pulse. These spatio-temporal couplings give rise to intrinsic nonlinear optical phenomena, which are well known in experiment but otherwise lack a clear explanation. While the formation mechanisms with respect to the nano-structuring of transparent media is still under debate, a better understanding of the nonlinear optical phenomena that affects the formation would provide insight into the physics of ultrafast light-matter interaction. In this thesis, the origin and thorough investigation of spatio-temporal induced phenomena are reported. By controlling the spatio-temporal couplings separately, I demonstrate complete control of all of the dependencies with the use of prism compressors and grating compressors and discuss the intricacies behind the control of the spatio-temporal couplings with complete characterization of the pulse. By investigating two of the main phenomena associated with spatio-temporal couplings, which give rise to a directional dependence when writing in the bulk (“quill-writing effect”) and a photosensitive anisotropy (“blade effect”), a more thorough understanding of the light-matter interaction is demonstrated and reported. I demonstrate that spatio-temporal couplings are inherent for all ultrafast laser systems with chirped-pulse amplification and result in a strongly anisotropic light-matter interaction. I identify angular dispersion in the focus as the main cause for the anisotropic photosensitivity coming from the spatially chirped pulse, which shows to yield a 200% increase in modification strength. With tighter focusing (NA ≥ ~0.4), this non-paraxial effect leads to a more apparent manifestation of spatio-temporal couplings in photo-induced modification. I control the anisotropy and exploited it as a new degree of freedom in tailoring laser induced modification in transparent material. A non-paraxial field structure analysis near the focus is conducted, with an elliptical optical beam, to provide insight on the origin of the photosensitive anisotropy. After a complete identification of the spatio-temporal properties of the electric field, the quill-effect was confirmed to be due to pulse front tilt in the focus with a direct comparison with other major spatio-temporal couplings including wavefront rotation. I reveal that the non-reciprocity during femtosecond laser writing in transparent media induces either an isotropic damage-like structure or a self-assembled nanostructure depending on the movement direction of the beam - known as the “quill-writing effect.” I also identify the switching of the modification regime from the formation of isotropic damage-like to anisotropic grating-like structures observed when the translation of the beam is in the direction of the tilt and is qualitatively described in terms of the first-order phase transition in the irradiated volume of a transparent dielectric. The structural evolution from void modification to self-assembled nanogratings in fused silica for moderate (NA > 0.4) focusing conditions is also discussed in this thesis. Void formation appears before the geometrical focus after the initial few pulses with nanogratings gradually occurring at the top of the induced structures after subsequent irradiation. Nonlinear Schrödinger equation-based simulations are conducted to simulate the laser fluence, intensity and electron concentration in the regions of modification. Comparing the experiment with simulations, the voids form due to cavitation in the regions where electron concentration exceeds 1020 cm-3 but remains below critical. In this scenario, the energy absorption is insufficient to reach the critical electron concentration that was once assumed to occur in the regime of void formation and nanogratings, shedding light on the potential formation mechanism of nanogratings. In-situ observations of harmonic generation during the ultrafast laser writing is presented to better understand the underlying physics that occur during the process of nanograting formation. Second and third harmonic generation is observed, with third harmonic distributed as two lobes following the polarization orientation of the electric field, identified as Cherenkov Third Harmonic. These harmonics are observed and correlated with the different regimes of material modification to understand whether they are part of the nanograting formation or corollary to give insight on the formation mechanisms of the self-assembled nanostructures. Finally, I discuss the work on the concept of an on-axial simultaneous spatio-temporal focusing with the use of a simple polarization dependent circular grating for the purpose of material modification using the expertise of the group on polarization gratings. The design and theoretical validation of the technique is reported in this thesis with the potential of further work in perfecting it for material modification and chirped-pulse amplification applications.
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Macpherson, James. "Characterisation and Optimization of Ultrashort Laser Pulses." Thesis, University of Waterloo, 2003. http://hdl.handle.net/10012/1237.
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The ultrafast optical regime is defined, as it applies to laser pulses, along with a brief introduction to pulse generation and characterisation technologies. A more extensive description of our particular amplified pulse generation and SPIDER characterisation systems follows. Data verifying the correct operation of the characterisation system is presented and interpreted. Our laser system is then characterised in two different configurations. In each case, the data describing the system is presented and analyzed. Conclusions are made regarding the performance of both the characterisation and laser systems, along with suggested improvements for each.
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Zang, Yimin. "Simulation of the Optical Loop Mirror in Ultrafast Fiber Lasers." University of Dayton / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1523377900786586.
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Rützel, Stefan [Verfasser], Tobias [Gutachter] Brixner, and Bernd [Gutachter] Engels. "Pulse-Sequence Approaches for Multidimensional Electronic Spectroscopy of Ultrafast Photochemistry / Stefan Rützel. Gutachter: Tobias Brixner ; Bernd Engels." Würzburg : Universität Würzburg, 2014. http://d-nb.info/1102826197/34.
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Fischer, Jonathan [Verfasser]. "Ultrafast Yb:YAG thin-disk amplifier with multi-millijoule pulse energy for high-power frequency conversion / Jonathan Fischer." Konstanz : Bibliothek der Universität Konstanz, 2016. http://d-nb.info/1114894672/34.
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Hyyti, Janne Juhani. "Ultrafast Nonlinear Nano-Optics via Collinear Characterization of Few-Cycle Pulses." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19410.
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Die Methode „interferometric frequency-resolved optical gating“ (iFROG) zur Charakterisierung ultrakurzer Laserimpulse wurde erweitert. Als optische Nichtlinearität werden sowohl die Erzeugung der 2. als auch der 3. Harmonischen (THG) separat verwendet. Eine iFROG-Messung stellt ein inverses Problem dar, bei dem die Amplitude und Phase des elektrischen Feldes des Laserimpulses nur durch einen iterativen Algorithmus rekonstruiert werden kann. In dieser Arbeit wird ein mathematischer Formalismus entwickelt und mit einem evolutionären Optimierungsalgorithmus kombiniert, um einen neuartigen Impuls-Rekonstruktions-Algorithmus für iFROG zu erschaffen.
Während iFROG ursprünglich ausschließlich zur Charakterisierung von Laserimpulsen konzipiert wurde, kann die Technik gleichermaßen für spektroskopische Zwecke eingesetzt werden. Wird das nichtlineare Medium in iFROG durch ein Untersuchungsobjekt ersetzt und ein bekannter Laserimpuls erneut charakterisiert, so kann die Antwortfunktion des Untersuchungsobjekts mit einer sub-Femtosekunden-Auflösung entschlüsselt werden. Da für die THG-Variante bisher keine Lösung bekannt ist, ermöglicht der vorgestellte Rekonstruktion-Algorithmus die erstmalige Nutzung von iFROG zur Untersuchung ultraschneller nichtlinearer Effekte dritter Ordnung.
Die spektroskopische Fähigkeit von iFROG wird durch das Studium von drei unterschiedlichen physikalischen Systemen (Nanostrukturen) geprüft. In ZnO-Nanostäben wird die Leistungsabhängigkeit der durch Multiphotonenabsorption induzierten Lumineszenz gemessen, wobei nachgewiesen werden konnte, dass diese mit einer Lokalisierung des optischen Nahfelds verknüpft ist. Eine Dreiphotonenresonanz in einem dünnen Titandioxid Film und eine Oberflächenplasmonenresonanz in Au-Nanoantennen führen beide zu einer endlichen Lebensdauer der induzierten Materialpolarisation. Die iFROG-Methode wird verwendet, um die ultraschnelle zeitliche Dynamik dieser Systeme auf der Nanometer- und wenige Femtosekunden-Skala zu messen.The ultrashort laser pulse characterization method “interferometric frequency-resolved optical gating” (iFROG) is extended. Both second- and third harmonic generation (SHG and THG) are separately employed as the optical nonlinearity. An iFROG measurement represents an inverse problem, where the electric field amplitude and phase of the underlying laser pulse can only be reconstructed by an iterative algorithm. In this work, a mathematical formalism for both the SHG and THG variants of iFROG is developed and combined with an evolutionary optimization algorithm to create a novel pulse retrieval algorithm for iFROG. While iFROG was originally conceived solely for pulse characterization, the technique can equally well be applied for spectroscopic purposes. By replacing the nonlinear medium in iFROG with an object of study, say a nanostructure, and characterizing a known pulse again such that the sample affects the harmonic generation process, the response of the object can be deciphered with sub-femtosecond precision. As no previous solution for the THG variant exists, the presented retrieval algorithm allows iFROG to be exploited in the study of ultrafast third-order nonlinear effects for the first time. The spectroscopic capability of iFROG is put to test by studying three differing physical systems, each consisting of nanostructures resting on dielectric substrates. Subjecting these specimen to few-cycle near-infrared pulses, a rich variety of nonlinear optical phenomena is observed. In ZnO nanorods, the power dependence of multiphoton-absorption induced luminescence is measured and found to be connected to a localization of the optical near-field. A three-photon resonance in a thin film of titania and a localized surface plasmon resonance in Au nanoantennas both lead to a finite lifetime of the induced material polarization. The THG-iFROG method is harnessed to measure the ultrafast temporal dynamics of these systems at the nanometer and few-femtosecond scales.
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Bubelnik, Matthew. "THE EFFECTS OF ELECTRODE GEOMETRY ON CURRENT PULSE CAUSED BY ELECTRICAL DISCHARGE OVER AN ULTRA-FAST LASER FILAMENT." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3695.
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The time-resolved electrical conductivity of a short-pulse generated plasma filament in air was studied. Close-coupled metal electrodes were used to discharge the stored energy of a high-voltage capacitor and the resulting microsecond-scale electrical discharge was measured using fast current sensors. Significant differences in the time dependence of the current were seen with the two electrode geometries used. Using sharp-tipped electrodes additional peaks in the time-resolved conductivity were seen, relative to the single peak seen with spherical electrodes. We attribute these additional features to secondary electron collisional ionization brought about by field enhancement at the tips. Additional discrepancies in the currents measured leaving the high-voltage electrode and that returning to ground were also observed. Implications for potential laser-induced discharge applications will be discussed.M.S.
Other
Optics and Photonics
Optics
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Resan, Bojan. "DISPERSION-MANAGED BREATHING-MODE SEMICONDUCTOR MODE-LOCKED RING LASER." Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2907.
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A novel dispersion-managed breathing-mode semiconductor mode-locked ring laser is developed. The "breathing-mode" designation derives from the fact that intracavity pulses are alternately stretched and compressed as they circulate around the ring resonator. The pulses are stretched before entering the semiconductor gain medium to minimize the detrimental strong integrating self-phase modulation and to enable efficient pulse amplification. Subsequently compressed pulses facilitate bleaching the semiconductor saturable absorber. The intracavity pulse compression ratio is higher than 50. Down chirping when compared to up chirping allows broader mode-locked spectra and shorter pulse generation owing to temporal and spectral semiconductor gain dynamics. Pulses as short as 185 fs, with a peak power of ~230 w, and a focused intensity of ~4.6 gw/cm2 are generated by linear down chirp compensation and characterized by shg-frog method. To our knowledge, this is the highest peak power and the shortest pulse generation from an electrically pumped all-semiconductor system. The very good agreement between the simulated and the measured results verifies our understanding and ability to control the physical mechanisms involved in the pulse shaping within the ring cavity. Application trends such as continuum generation via a photonic crystal fiber, two-photon fluorescence imaging, and ultrafast pulse source for pump-probe experiments are demonstrated.Ph.D.
Other
Optics and Photonics
Optics
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Bücker, Kerstin. "Characterization of pico- and nanosecond electron pulses in ultrafast transmission electron microscopy." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE014/document.
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Cette thèse présente une étude des impulsions électroniques ultra-brèves en utilisant le nouveau microscope électronique en transmission ultrarapide (UTEM) à Strasbourg. La première partie porte sur le mode d’opération stroboscopique, basé sur l’utilisation d’un train d’impulsions d’électrons de l’ordre de la picoseconde pour l’étude des phénomènes réversibles ultrarapides. L’étude paramétrique effectuée a permis de révéler les dynamiques fondamentales des impulsions électroniques. Des mécanismes inconnus jusqu’alors et décisifs dans les caractéristiques des impulsions ont été dévoilés. Il s’agit des effets de trajectoire, qui limitent la résolution temporelle, et du filtrage chromatique, qui impacte la distribution en énergie et l’intensité du signal. Ces connaissances permettent aujourd’hui un paramétrage affiné de l’UTEM de manière à satisfaire les divers besoins expérimentaux. La deuxième partie concerne l’installation du mode d’opération complémentaire : le mode « singel-shot ». Ce mode fait appel à une impulsion unique d’intensité élevé et d’une durée de l’ordre de la nanoseconde pour l’étude des phénomènes irréversibles. L’UTEM de Strasbourg étant le premier instrument single-shot équipé d’un spectromètre de perte d’énergie des électrons (EELS), l’influence de l’aberration chromatique a pu été étudiée en détail. Elle s’est dévoilée être une limitation majeure pour la résolution en imagerie, nécessitant d’ajuster le bon compromis avec l’aberration sphérique d’une part et l’intensité du signal d’autre part. Enfin, la faisabilité de mener des études en EELS ultrarapide avec une seule impulsion nanoseconde a pu être démontrée, ceci constituant une première mondiale. Ce résultat très prometteur ouvre un tout nouveau domaine d’expériences résolu en tempsThis thesis presents a study of ultrashort electron pulses by using the new ultrafast transmission electron microscope (UTEM) in Strasbourg. The first part focuses on the stroboscopic operation mode which works with trains of picosecond multi-electron pulses in order to study ultrafast, reversible processes. A detailed parametric study was carried out, revealing fundamental principles of electron pulse dynamics. New mechanisms were unveiled which define the pulse characteristics. These are trajectory effects, limiting the temporal resolution, and chromatic filtering, which acts on the energy distribution and signal intensity. Guidelines can be given for optimum operation conditions adapted to different experimental requirements. The second part starts with the setup of the single-shot operation mode, based on intense nanosecond electron pulses for the investigation of irreversible processes. Having the first ns-UTEM equipped with an electron energy loss spectrometer, the influence of chromatic aberration was studied and found to be a major limitation in imaging. It has to be traded off with spherical aberration and signal intensity. For the first time, the feasibility of core-loss EELS with one unique ns-electron pulse is demonstrated. This opens a new field of time-resolved experiments
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Bodnar, Nathan. "Phase-locking Stability of a Quasi-single-cycle Pulse." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5606.
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There is increasing interest in the generation of very short laser pulses, even down to attosecond (10-18 s) durations. Laser systems with femtosecond pulse durations are needed for these applications. For many of these applications, positioning of the maximum electric field within the pulse envelope can affect the outcome. The peak of the electric field relative to the peak of the pulse is called the Carrier Envelope Phase (CEP). Controlling the position of the electric field becomes more important when pulse duration approaches single-cycle. This thesis focuses on the stabilization of a quasi-single-cycle laser facility. Improvements to this already-established laser facility, HERACLES (High Energy, Repetition rate Adjustable, Carrier-Locked-to-Envelope System) described in this thesis include a stabilized pump line and the improvement in CEP stabilization electronics. HERACLES is built upon an Optical Parametric Chirped Pulse Amplification (OPCPA) architecture. This architecture uses Optical Parametric Amplification (OPA) as the gain material to increase the output energy of the system. OPA relies on a nonlinear process to generate high gain (106) with ultra-wide bandwidth. Instabilities in the OPA driving pump energy can create dynamically fluctuations in the final OPCPA output energy. To reduce these fluctuations two key upgrades were implemented on the pump beam. Both were major improvements in the stability. Firstly, an improved regenerative amplifier design reduced beam pointing fluctuations. Secondly, the addition of a pump monitoring system with feedback-control eliminated long-term power drifts. Both enhanced the OPA pulse-to-pulse and long-term stability. To improve the stability in measuring CEP drifts, modification of the feedback electronics was needed. The modification consisted of integrating noise reduction electronics. This novel noise reducer uses a similar process to a super-heterodyne receiver. The noise reducer resulted in 60 dB reduction of out-of-band noise. This led to increased signal quality with cleaner amplification of weaker signals. The enhanced signal quality led to more reliable long-term locking. The synthetically increased signal-to-noise ratio allows locking of the CEP frequency below the typically requirements. This integration allows relaxed constraints on the laser systems. The optics and electronics of a high-power, quasi-single cycle laser facility were improved. This thesis included the stabilization of the pump line and the stabilization of the CEP. This work allows for new long-duration experiments.M.S.
Masters
Optics and Photonics
Optics and Photonics
Optics; International
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Ganz, Thomas [Verfasser], and Ferenc [Akademischer Betreuer] Krausz. "Supercontinuum generation by chirped pulse compression for ultrafast spectroscopy and broadband near-field microscopy / Thomas Ganz. Betreuer: Ferenc Krausz." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2011. http://d-nb.info/102665355X/34.
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Abend, Stefan. "Ultrafast dynamics of chlorins and porphyrins in proteins and solution investigated by time resolved three pulse photon echo spectroscopy." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249371.
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Bowlan, Pamela. "Measuring the spatiotemporal electric." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28188.
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Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009.Committee Chair: Rick Trebino; Committee Member: Jennifer Curtis; Committee Member: John Buck; Committee Member: Mike Chapman; Committee Member: Stephen Ralph.
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Wang, Bingxia. "Second harmonic generation in disordered nonlinear crystals : application to ultra-short laser pulse characterization." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461570.
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The PhD project, entitled "Second harmonic generation in disordered nonlinear crystals: application to ultra-short laser pulse characterization", is devoted to the study of second harmonic generation in nonlinear ferroelectric crystals formed by a random distribution of domains with inverted quadratic nonlinear susceptibility (such as the Strontium Barium Niobate and Calcium Barium Niobate crystals) and its application to the single-shot characterization of ultrashort laser pulses. The basic principle of operation is related to the unique type of emission associated to those kinds of crystals where the second harmonic signal is emitted transversally to the beam propagation direction. Using the transverse second harmonic generation from these crystals we measure the pulse duration, the chirp parameter and the temporal profile in a single-shot configuration. This method has been implemented both in transverse auto-correlation and transverse cross-correlation schemes for the measurement of pulses with durations in the range from several tens up to several hundreds of femtoseconds. The main advantages gained with the developed techniques against other traditional methods include the removal of the requirement of thin nonlinear crystals for harmonic generation, the possibility to get automatic phase matching without angular alignment or temperature control over a very wide spectrum and a simplified operation process. Different types of pulses have been measured in different conditions and the limits of validity of the technique have been explored.
Since this work relies strongly upon the characteristics of emission of the second harmonic signal by these random crystals, an important part of this work has been focused on the characterization of the distribution of domains of the random nonlinear ferroelectric crystals and its relation with the angular emission of the second harmonic signal. The domain distribution of the nonlinear polarization implies an associated distribution of reciprocal lattice vectors, which can compensate the phase mismatch in the nonlinear interaction. Any change in the domain distribution would have a direct impact in the second harmonic generated and in its intensity angular distribution. Based on these fundamental concepts we demonstrate an indirect non-destructive optical method for the characterization of nonlinear domain statistics based on the analysis of the second harmonic generation intensity angular distribution. This method has been implemented experimentally and tested in crystals with different types of distributions. To gain a deeper insight on these processes, numerical simulations have been performed using a split-step fast-Fourier transform beam propagation method. It has been demonstrated that the analysis of the dependence of the second harmonic generation angular emission with the fundamental beam wavelength can be used to obtain relevant information about complicated domain structures. This method could be used for real time monitoring of the unknown domain distribution during the poling or crystal growing processEsta tesis doctoral es un estudio de la generación de segundo armónico en cristales no lineales compuestos por dominios ferroeléctricos que alternan el signo de la non linealidad de segundo orden y distribuidos de una forma aleatoria (como por ejemplo niobato de estroncio y bario o niobato de calcio y bario). Como primera aplicación proponemos una técnica de caracterización de pulsos laser ultracortos, cuyo principio de operación está relacionado con la manera singular en la que este tipo de cristal emite la señal de segundo armónico en una dirección transversal a la dirección de propagación del pulso a medir. Utilizando esta señal no lineal podemos determinar la duración del pulso, el parámetro de chirp y el perfil temporal en una configuración de single-shot. Hemos implementado este método en dos configuraciones distintas -auto correlación y correlación cruzada- para la medida de pulsos con duraciones entre 10 fs y 1 ps. Este método, en comparación con otros métodos tradicionales para la caracterización de pulsos ultracortos, permite obtener el ajuste de fase (phase matching) de forma automática sobre un rango espectral muy amplio, sin necesidad de aliñamiento crítico ni ajuste de temperatura, elimina el requisito de utilizar cristales delgados y tiene un proceso de operación más sencillo. Se han medido diferentes tipos de pulsos y se han explorado las limitaciones de la técnica. Como este trabajo se basa en las propiedades específicas de la emisión de segundo armónico en los cristales no lineales con distribución aleatoria de dominios, un objetivo importante ha sido la caracterización del tamaño y la distribución de los dominios ferroelectricos y su relación con la distribución angular específica del segundo armónico generado. La distribución espacial de los dominios implica una distribución correspondiente de vectores en la red recíproca que puede compensar el ajuste de fase en la interacción no lineal. Cualquier cambio en la distribución de dominios tendrá pues un impacto directo en la intensidad y distribución angular de la señal de segundo armónico generado. Basándolos en estos conceptos, demostramos un método óptico non destructivo indirecto para la caracterización estadística de los dominios no lineales basado en el análisis de la intensidad y la distribución angular del segundo armónico generado. Implementamos este método experimental en la caracterización de cristales con diferentes tipos de dominios. Para un estudio más detallado hemos desarrollado un modelo numérico basado en el método de "split-step fast-Fourier transform beam propagation" que simula el proceso no lineal observado experimentalmente. Demostramos que el análisis de la dependencia angular del segundo armónico puede aportar información relevante sobre estructuras con distribuciones complejas de dominios. Este método se puede utilizar para la monitorización en tiempo real de distribuciones desconocidas en el mismo proceso de crecimiento o del poling del cristal ferroelectrico.
Ce projet de thèse de doctorat est intitulé « Génération du second harmonique dans des cristaux non-linéaires désordonnés: application pour la caractérisation d'impulsions laser ultra-courtes ». Il est consacré à l'étude de la génération de deuxième harmonique dans des cristaux ferroélectriques non linéaires formés par une distribution aléatoire de domaines. Ceci conduit à une distribution aléatoire de la susceptibilité non linéaire quadratique (Tels que le nitrate de baryum de strontium –SBN- et les cristaux de nitrate de calcium et de calcium) et son application à la caractérisation unique des impulsions laser ultra-courtes. Le principe de base de l'opération est lié au type unique d'émission associé à ces types de cristaux où le second signal harmonique est émis transversalement à la direction de propagation du faisceau. En utilisant la génération transversale de deuxième harmonique à partir de ces cristaux, nous mesurons la durée de l'impulsion, le paramètre chirp et le profil temporel dans une configuration à un seul pulse laser. Cette méthode a été mise en oeuvre à la fois dans l'autocorrélation transversale et les schémas transversaux de corrélation croisée pour la mesure des impulsions avec des durées allant de plusieurs dizaines à plusieurs centaines de femtosecondes. Les principaux avantages obtenus avec les techniques développées par rapport à d'autres méthodes traditionnelles comprennent l'élimination de l'exigence de cristaux minces non linéaires pour la génération harmonique, la possibilité d'obtenir une correspondance automatique de phase sans alignement angulaire ou contrôle de la température sur un spectre très large et un processus d'opération simplifié. Différents types d'impulsions ont été mesurés dans différentes conditions et les limites de validité de la technique ont été explorées. Étant donné que ce travail repose fortement sur les caractéristiques de l'émission du second signal harmonique par ces cristaux ferroélectriques à distribution aléatoire des domaines, une partie importante de ce travail a été axée sur la caractérisation de la distribution des domaines des cristaux ferroélectriques non linéaires aléatoires et sa relation avec l'émission angulaire du signal de la deuxième harmonique. La distribution de la polarisation non linéaire implique une distribution associée de vecteurs de réseau réciproque, ce qui peut compenser le décalage de phase dans l'interaction non linéaire. Toute modification de la répartition des domaines aurait un impact direct dans la distribution angulaire de la deuxième harmonique et de sa distribution angulaire d'intensité. Sur la base de ces concepts fondamentaux, nous démontrons une méthode optique non destructive indirecte pour la caractérisation de statistiques des domaines non linéaire basées sur l'analyse de la distribution angulaire d'intensité de génération de la deuxième harmonique. Cette méthode a été mise en oeuvre expérimentalement et testée dans des cristaux avec différents types de distributions. Pour obtenir une meilleure compréhension de ces processus, des simulations numériques ont été effectuées en utilisant une méthode de propagation de faisceau adaptée aux matériaux non linéaires. Il a été démontré que l'analyse de la dépendance de l'émission angulaire de la deuxième génération harmonique avec la longueur d'onde fondamentale du faisceau peut être utilisée pour obtenir des informations pertinentes sur les structures de domaines compliquées. Cette méthode pourrait être utilisée pour la surveillance en temps réel de la distribution de domaines inconnue pendant le processus de polling ou de croissance des cristaux.
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Walker, Stephen. "Development and Characterization of a Regeneratively Amplified Ultrafast Laser System with an All-Glass Stretcher and Compressor." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2981.
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High-peak power laser systems are defined along with a brief introduction of the technology used in their development and application to the project. A review of concepts surrounding optical pulses, focusing on the particular phenomena involved with the ultrafast, follows. Numerical models involving optical pulses are introduced and verified. An extensive description of the laser system is presented, including models used in its design. Data verifying the correct operation of the laser system is presented and interpreted. A dispersion compensation system, including a function model, is introduced, and its application to the laser system is analyzed. An introduction to pulse characterization techniques is presented followed by the design and verification of two different characterization devices. Experiments utlizing the dispersion compensation system and pulse characterization devices are presented and the results are interpreted. Conclusions are made regarding the performance of the laser system models and pulse characterization devices, along with suggested improvements for each. The results of the experiments are discussed including suggestions for future work.
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Hilbert, Vinzenz [Verfasser], Eckart Gutachter] Förster, Georg [Gutachter] [Pretzler, and Thomas [Gutachter] Wilhein. "XUV diagnostics tailored to resolve short-pulse-laserdriven ultrafast plasma dynamics / Vinzenz Johannes Hilbert ; Gutachter: Eckart Förster, Georg Pretzler, Thomas Wilhein." Jena : Friedrich-Schiller-Universität Jena, 2017. http://d-nb.info/1177600129/34.
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Schönenberger, Norbert [Verfasser], Peter [Akademischer Betreuer] Hommelhoff, and Philip [Gutachter] Russell. "Control of free electrons with ultrafast laser pulses:Generation of attosecond electron pulse trains / Norbert Schönenberger ; Gutachter: Philip Russell ; Betreuer: Peter Hommelhoff." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2021. http://d-nb.info/1239898436/34.
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Stibenz, Gero. "Neue Methoden der Charakterisierung und Kompression intensiver ultrakurzer optischer Impulse." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15995.
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Die Erzeugung immer kürzerer und energiereicherer Laserimpulse ist eine der wichtigsten Aufgaben der Laserphysik, um physikalische Phänomene in bisher unerreichten elektrischen Feldstärkebereichen zugängig zu machen und Beobachtungen auf kleinster Zeitskala zu ermöglichen. Mit Hilfe der Nachkompression verstärkter, in edelgasgefüllten Hohlfasern selbstphasenmodulierter Ti:Saphir-Laserimpulse werden die momentan kürzesten Impulse des sichtbaren Spektralbereiches erzeugt, die nur noch wenige Schwingungszyklen des elektrischen Feldes umfassen. Ebenso notwendig wie ein solcher Schritt der Impulskompression ist der verlässliche Nachweis seines Ergebnisses. Allerdings wächst auch die physikalische und technische Herausforderung einer präzisen und vollständigen Messung des ultrakurzen Laserimpulses mit zunehmender Komplexität und Breite des Impulsspektrums. Die vorliegende Arbeit stellt sowohl auf dem Gebiet der Kompression von Sub-10-fs Impulsen als auch auf dem der vollständigen Charakterisierung solcher Impulse optimierte aber auch neue Verfahrenstechniken vor. In Experimenten an einem zweistufigen Hohlfaserkompressor wird die Erzeugung der momentan kürzesten, nicht adaptiv komprimierten Impulse mit einer Dauer von lediglich 3,8 fs demonstriert. Eine elegante Alternative zu bisherigen Kompressionsmethoden zeigt der Nachweis effektiver Selbstkompression von mJ-Impulsen auf unter 8 fs in einem selbstführenden Edelgasfilament auf. Zur Kontrolle erfolgreicher Impulskompression und für eine phasenempfindliche Untersuchung des Prozesses der Dispersionskompensation über spektrale Bandbreiten von bis zu einer Oktave mussten etablierte Impulsmesstechniken wie das SPIDER- (Spectral Phase Interferometry for Direct Electric-field Reconstruction) und das FROG- (Frequency-Resolved Optical Gating) Verfahren weiterentwickelt werden. So wird mit der Realisierung und vollständigen Analyse interferometrischer FROG-Messungen ein neues phasenempfindliches Impulsmessverfahren vorgestellt.One challenge of today’s laser physics is the stable compression of more and more intense laser pulses to the shortest possible pulse duration to enable new high-field laser experiments and to investigate fast atomic or molecular dynamics. At present, the shortest laser pulses of the visible spectral region envelop only a few cycles of the electric field. The state of the art method to generate such short pulses behind a Ti:sapphire amplifier laser system is by means of successive steps of spectral broadening inside a gas-filled hollow fibre and dispersion compensation. However, a reliable pulse characterization is as important as the pulse compression. The more spectral bandwidth the pulse covers the more technically challenging is the measurement of the pulse’s electric field structure. In this work, new concepts of compression and characterization of pulses down to durations below 10 fs are demonstrated as well as further optimization of established techniques. Due to modern, chirped-mirror based dispersion compensation pulses as short as 3.8 fs were generated with a two-stage hollow fibre compressor. At present, these are the shortest pulses of the visible spectral region, compressed without adaptive means for dispersion compensation. For the first time the effect of self-compression of mJ-pulses to below 8 fs in a self-guiding noble gas filament is demonstrated experimentally and determined by numerical simulations. Advanced pulse characterization schemes were needed for a phase-sensitive investigation of dispersion compensation and pulse compression of white light pulses. An optimized design of the SPIDER (Spectral Phase Interferometry for Direct Electric-field Reconstruction) technique is demonstrated that facilitates the measurement of the pulse’s spectral phase in case of broadband structured spectra. With the implementation of an interferometric FROG (Frequency-Resolved Optical Gating) a new phase-sensitive pulse characterization method is introduced.
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Budkina, Darya S. "Ultrafast photophysical and photochemical dynamics of polyhalogenated alkanes, cycloalkanes, and transition metal complexes." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1553686775405944.
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Kim, Kyungbum. "ALL-SEMICONDUCTOR HIGH POWER MODE-LOCKED LASER SYSTEM." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2482.
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The objective of this dissertation is to generate high power ultrashort optical pulses from an all-semiconductor mode-locked laser system. The limitations of semiconductor optical amplifier in high energy, ultrashort pulse amplification are reviewed. A method to overcome the fundamental limit of small stored energy inside semiconductor optical amplifier called "eXtreme Chirped Pulse Amplification (X-CPA)" is proposed and studied theoretically and experimentally. The key benefits of the concept of X-CPA are addressed. Based on theoretical and experimental study, an all-semiconductor mode-locked X-CPA system consisting of a mode-locked master oscillator, an optical pulse pre-stretcher, a semiconductor optical amplifier (SOA) pulse picker, an extreme pulse stretcher/compressor, cascaded optical amplifiers, and a bulk grating compressor is successfully demonstrated and generates >kW record peak power. A potential candidate for generating high average power from an X-CPA system, novel grating coupled surface emitting semiconductor laser (GCSEL) devices, are studied experimentally. The first demonstration of mode-locking with GCSELs and associated amplification characteristics of grating coupled surface emitting SOAs will be presented. In an effort to go beyond the record setting results of the X-CPA system, a passive optical cavity amplification technique in conjunction with the X-CPA system is constructed, and studied experimentally and theoretically.Ph.D.
Optics and Photonics
Optics
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Fang, Li. "Development of ultrafast saturable absorber mirrors for applications to ultrahigh speed optical signal processing and to ultrashort laser pulse generation at 1.55 µm." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112313/document.
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Dans cette thèse, nous avons développé et étudié des miroirs absorbants saturables ultra-rapides, pour des applications au traitement de signaux optiques à très haut débit et la génération d’impulsions laser ultra-courtes à 1.55 µm. Dans une première partie, nous avons développé un miroir absorbant saturable ultra-rapide basé sur le semi-conducteur In₀.₅₃Ga₀.₄₇As soumis à une implantation ionique à température élevée de 300 °C. Des ions Fe ont été utilisés car il a été démontré que les niveaux Fe²⁺/Fe³⁺ peuvent agir comme des centres de recombinaison efficaces pour les électrons et les trous dans In₀.₅₃Ga₀.₄₇As. Nous avons étudié la durée de vie des porteurs en fonction de la dose ionique, la température et le temps de recuit. A part la durée de vie rapide, les caractéristiques de réflectivité non-linéaire, telles que l’absorption linéaire, la profondeur de modulation, les pertes non saturables ont été étudiées dans différentes conditions de recuit. Après un recuit à 600 °C pendant 15 s, un échantillon présentant une grande amplitude de modulation de 53,9 % et une durée de vie de porteurs de 2 ps a été obtenu. Dans une seconde partie, la gravure par faisceau d’ions focalisés (FIB) a été utilisée pour fabriquer une structure en biseau ultrafin sur de l’InP cristallin, pour réaliser un dispositif photonique multi-longueur d’onde à cavité verticale. Les procédures de balayage FIB et les paramètres appropriés ont été utilisés pour contrôler le re-dépôt du matériau cible et pour minimiser la rugosité de surface de la zone gravée. Le rendement de pulvérisation de la cible en InP cristallin a été déterminé en étudiant la relation entre la profondeur de gravure et la dose ionique. En appliquant les conditions de rendement optimales, nous avons obtenu une structure en biseau ultrafin dont la profondeur de gravure est précisément ajustée de 25 nm à 55 nm, avec une pente horizontale de 1:13000. La caractérisation optique de ce dispositif en biseau a confirmé le comportement multi-longueur d’onde de notre dispositif et montré que les pertes optiques induites par le procédé de gravure FIB sont négligeables. Dans une troisième partie, nous avons démontré que la réponse optique non-linéaire du graphène est augmentée de manière résonnante quand une monocouche de graphène est incluse dans une microcavité verticale comportant un miroir supérieur. Une couche mince de Si₃N₄ a été déposée selon un procédé de dépôt par PECVD spécialement développé pour agir comme couche de protection préalable avant le dépôt du miroir supérieur proprement dit, permettant ainsi de préserver les propriétés optiques du graphène. En incluant une monocouche de graphène dans une microcavité appropriée, une profondeur de modulation de 14,9 % a été obtenue pour une fluence incidente de 108 µJ/cm². Cette profondeur de modulation est beaucoup plus élevée que la valeur maximale de 2 % obtenue dans les travaux antérieurs. De plus un temps de recouvrement aussi bref que 0,7 ps a été obtenuIn this thesis, we focus on the development of ultrafast saturable absorber mirrors for applications to ultra-high speed optical signal processing and ultrashort laser pulse generation at 1.55 μm. In the first part, we have developed an ultrafast In₀.₅₃Ga₀.₄₇As -based semiconductor saturable absorber mirror by heavy ion implantation at the elevated temperature of 300 ºC. Fe ion has been employed as the implant since it has been shown that Fe²⁺/Fe³⁺ level can act as efficient recombination centers for electrons and holes in In₀.₅₃Ga₀.₄₇As. We studied the carrier lifetime of Fe-implanted sample as a function of ion dose, temperature and annealing time. Apart from the fast carrier lifetime, the characteristics of nonlinear reflectivity for the Fe-implanted sample, such as linear absorption, modulation depth, nonsaturable loss, have are also been investigated under different annealing temperature. Under annealing at 600 ºC for 15 s, the Fe-implanted sample with a big modulation depth of 53.9 % and a fast carrier lifetime of 2 ps has been achieved. In the second part, focused ion beam milling has been applied to fabricate an ultra-thin taper structure on crystalline indium phosphide to realize a multi-wavelength vertical cavity photonic device. The appropriate FIB scanning procedures and operating parameters were used to control the target material re-deposition and to minimize the surface roughness of the milled area. The sputtering yield of crystalline indium phosphide target was determined by investigating the relationship between milling depth and ion dose. By applying the optimal experimentally obtained yield and related dose range, we have fabricated an ultra-thin taper structure whose etch depths are precisely and progressively tapered from 25 nm to 55 nm, with a horizontal slope of about 1:13000. The optical characterization of this tapered device confirms the expected multi-wavelength behavior of our device and shows that the optical losses induced by the FIB milling process are negligible. In the third part, we demonstrate that the nonlinear optical response of graphene is resonantly enhanced by incorporating monolayer graphene into a vertical microcavity with a top mirror. A thin Si₃N₄ layer was deposited by a developed PECVD process to act as a protective layer before subsequent top mirror deposition, which allowed preserving the optical properties of graphene. Combining monolayer graphene with a microcavity, a modulation depth of 14.9 % was achieved at an input energy fluence of 108 µJ/cm². This modulation depth is much higher than the value of about 2 % in other works. At the same time, an ultrafast recovery time of 0.7 ps is retained
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Smit, Albert Bart. "A new femtosecond electron diffractometer for structural dynamics experiments at cryogenic temperatures." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96015.
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Thesis (MSc)--Stellenbosch University, 2014.ENGLISH ABSTRACT: In this thesis, a femtosecond electron diffraction (FED) set-up that is capable of investigating the photo-induced switching of Cu(DCNQI)2 from being an insulator to being a conductor is presented. Movies of atomic structural changes with temporal resolution within the typical photo-switching transition timescales (sub-picoseconds) are obtainable with this set-up by employing a femtosecond laser. The experimental technique and the design of a crucial instrument of the machine, the electron gun, are extensively described and characterised both numerically and experimentally. The interest in observing atomic structural changes of Cu(DCNQI)2 in real time is because of the rich variety of the radical salts available that show alloy-specific Charge Density Wave (CDW) transitions. Valuable insights about the driving mechanisms behind these structural changes that are responsible for a change in conductivity are obtainable, as well as the relation between crystal alloys and their transition characteristics. Electron diffraction patterns of crystals in their metallic phase (room temperature) are shown in this thesis, but diffraction patterns of cryo-cooled Cu(DCNQI)2 in its insulating phase are still to be acquired. The temporal resolution of the atomic movie can be improved by recompression of electron pulses that are debunched due to Coulomb repulsion and electron energy spread within a pulse. Numerical and preliminary experimental results presented in this work expose the potential of a simple compression technique. In this way, more electrons in a single electron pulse can be afforded which allows to perform experiments at shorter integration time or lower repetition rate.
AFRIKAANSE OPSOMMING: In hierdie tesis word ’n femtosekonde elektron diffraksie opstelling aangebied wat daartoe in staat is om die foto-geïnduseerde omskakeling in Cu(DCNQI)2 van nie-geleier tot geleier te ondersoek. Deur gebruik te maak van ’n femtosekonde laser in hierdie opstelling, is ’rolprente’ van strukturele veranderinge op atoomskaal met ’n tyd resolusie beter as die tipiese foto-omskakelings tydskaal (sub-pikosekonde) verkrygbaar. Die eksperimentele tegniek en die ontwerp van ’n noodsaaklike instrument van die masjien, die elektron geweer, word breedvoerig beskryf en numeries en eksperimenteel gekenmerk. Die belangstelling om strukturele veranderinge in Cu(DCNQI)2 op atoom skaal in reële tyd waar te kan neem is as gevolg van die ryke verskeidenheid van radikale soute, wat allooispesifieke ladings digtheid golf (CDW) oorgange toon, wat beskikbaar is. Waardevolle insigte oor die meganismes wat hierdie strukturele veranderinge wat ’n verandering in geleiding veroorsaak dryf is verkrygbaar, sowel as die verwantskap tussen die kristal allooi en die oorgang kenmerke. Diffraksie patrone van kristalle in die metaalagtige fase (kamer temperatuur) word in hierdie tesis getoon, maar diffraksie patrone van cryo-verkoelde Cu(DCNQI)2 in die niegeleier fase moet nog verkry word. Die tyd resolusie van die atomiese rolprent kan verbeter word deur die elektron puls — wat deur Coulomb afstoting en elektron energie spreiding versprei is — weer saam te pers. Numeriese en voorlopige eksperimentele resultate toon die potensiaal van ’n eenvoudige kompressie tegniek. Hierdeur kan meer elektrone in ’n elektron puls gegun word en so die integrasie tyd of die herhalingstempo van die eksperimente verkort kan word.
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Eickemeyer, Felix. "Ultrafast dynamics of coherent intersubband polarizations in quantum wells and quantum cascade laser structures." Doctoral thesis, [S.l.] : [s.n.], 2002. http://dochost.rz.hu-berlin.de/dissertationen/eickemeyer-felix-2002-07-03.
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