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Heilmann, Anke. "Highly scalable femtosecond coherent beam combining system of high power fiber amplifiers." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX112/document.
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Allier de fortes puissances moyennes et crêtes donne accès à un champ applicatif très large pour un système laser ultrarapide. Une technique qui s’est avérée capable de satisfaire ces exigences est la combinaison cohérente de faisceaux (CBC). Elle permet de séparer spatialement les faisceaux avant l’amplification pour les recombiner ensuite d’une manière cohérente en un unique faisceau. Afin d’obtenir une recombinaison efficace, les propriétés spatiales et spectrales de tous les faisceaux doivent être parfaitement en accord.Pour des applications comme l’accélération de particules, le recours à plusieurs milliers de fibres doit être envisagé. Il est donc nécessaire d’étudier des architectures CBC fortement évolutives en termes de canaux amplificateurs.Le projet XCAN vise à une première démonstration d’un tel système en réalisant la combinaison cohérente de 61 fibres amplificatrices. Afin d’étudier les défis scientifiques et techniques d’une telle architecture, une version de taille réduite comprenant sept fibres a été mise en place.La conception et la réalisation de ce prototype sont le sujet de cette thèse.Dans un premier temps, des simulations ont été effectués afin d’estimer les désaccords tolérables entre les propriétés spatiales et spectrales des différents faisceaux.Basé sur ce travail de modélisation, un système laser de combinaison cohérente de sept fibres a été ensuite assemblé et caractérisé. Les résultats obtenus sont très prometteurs et montrent que notre architecture est bien adaptée pour accueillir les 61 fibres du démonstrateur final XCANFuture applications of high power ultrafast laser systems require simultaneously high average and peak powers. A technique which has proved to be capable of meeting these demands is coherent beam combining (CBC).In this technique, the beam is spatially split prior to amplification, and coherently recombined in one single beam afterwards. In order to achieve an efficient recombination, the spatial and spectral properties of all beams need to be perfectly matched.For applications such as particle acceleration, the coherent combining of several thousands of fibers needs to be considered. It is thus necessary to investigate highly scalable CBC architectures.The XCAN project aims at a first demonstration of such a scalable setup by coherently combining 61 fiber amplifiers. In order to study the scientific and technical challenges of such a system, a downscaled version consisting of seven fibers has been implemented.The design and characterization of this prototype is the subject of this thesis.As a starting point, numerical simulations have been performed in order to estimate the maximum tolerable mismatches between the spatial and spectral properties of the beams.Based on this modeling work, a seven fiber CBC system has been assembled and characterized. The obtained results are very promising and imply that our setup is well suited for the accommodation of all 61 fibers of the final XCAN demonstrator
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Fragoso, Joshua. "Setup of a laser system for structuring organic solar cells and ablation of the silver electrode." Thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-129760.
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Lombaard, Martin. "An investigation into the activation of methane using a tuneable femtosecond laser system / Martin Lombaard." Thesis, North-West University, 2008. http://hdl.handle.net/10394/3840.
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Using a tuneable femtosecond- and nanosecond laser system at room temperature,
it was observed that by photo-irradiation in the infrared region, methane can be
photo-excited to undergo the coupling reaction in which ethane and hydrogen is
formed. In similar conditions, the addition of carbon dioxide results in the
formation of carbon monoxide through the photoreduction of carbon dioxide by
methane.
Molecular modelling calculations were used to determine the photoabsorption
wavelength needed for C-H bond activation of methane. Calculations showed that
the 2v3 overtone at 1.67 pxn was ideal for excitation. Fourier transform infrared
spectroscopy was used to analyze the samples after excitation. These results
suggested that partial dehydrogenation of ethane to ethylene also occurred during
the coupling reaction of methane while traces of methanol were found in the
CH4/CO2 mixture after excitation.
Although pleasing results were obtained with the nanosecond laser system, the
femtosecond laser system proved more reliable and efficient.Thesis (M.Sc. (Chemistry)--North-West University, Potchefstroom Campus, 2009.
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Tompkins, Richard John. "The design and construction of a solid state femtosecond laser system and its application to chemistry." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367892.
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Harten, Paul Alexander. "Ultrafast phenomena in gallium arsenide/aluminum gallium arsenide multiple quantum well waveguide structures using a near infrared femtosecond laser system." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185954.
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A near infrared hybridly mode-locked dye laser system consisting of a femtosecond oscillator and a high repetition rate dye amplifier was designed and built. This system was then applied to the study of room temperature below-bandgap femtosecond switching and coherent pulse propagation in GaAs/GaAlAs multiple quantum well waveguides. The noise properties of the oscillator output were studied using radio frequency spectrum analysis techniques. Two distinct modes of operation were identified: The first is characterized by the shortest pulse duration and its real-time autocorrelation signal appears more strongly modulated. The second mode of operation, which exhibits a slightly longer pulse duration and a smoother real-time autocorrelation signal, is obtained for a relative cavity length detuning of ΔL = -0.7 μm. Unexpectedly, the second mode features larger pulse duration fluctuations than the first mode and self-pulsing, while the pulse repetition timing and pulse energy fluctuations were found to be similar in both cases, making the first mode preferable for use in time-resolved experiments. Femtosecond all-optical switching under off-resonance room temperature excitation was demonstrated in a passive GaAs/AlGaAs multiple quantum well directional coupler for the first time. The required phase mismatch originates from an ultrafast refractive index change caused by the optical Stark effect. The main obstacle regarding practical device applications is its low transmission (less than 10%). The use of electrically pumped semiconductor waveguides that provide gain promises to remove this disadvantage. Below-resonance, coherent pulse breakup in a room temperature semiconductor waveguide was observed for the first time. Numerical simulations of the coupled semiconductor Maxwell-Bloch equations show that the light-matter interaction can induce enough chirp through self-phase modulation during propagation in order to violate the initial adiabatic following regime and cause pulse breakup. This coherent effect is distinctly different from self-induced transparency, because it does not involve Rabi-oscillations at the start of propagation, from temporal solitons, because it does not require group velocity dispersion, and from self-steepening. However, it should be ubiquitous under off-resonance pulse propagation with a pulse duration less than the polarization dephasing time.
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Archer, Jieutonne Jansen. "AN INVESTIGATION INTO THE VERSATILITY OF A TITANIUM:SAPPHIRE REGENERATIVE AMPLIFIER LASER SYSTEM FOR AMBIENT MASS SPECTROMETRY." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/595840.
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ChemistryPh.D.
This dissertation details an investigation into the use of laser pulses from a titanium:sapphire regenerative amplifier laser system to vaporize analytes in ambient air for mass spectral analysis. The laser system was modified to operate in one of two distinct modes. In femtosecond (fs) mode the laser produced 2.5 mJ, ~60 fs laser pulses centered at 800 nm. In nanosecond (ns) mode the laser produced 2.4 mJ, ~10 ns laser pulses centered at 800 nm. Using appropriate optical components the laser pulse energy was attenuated to achieve pulses varying from 0.15 mJ to 2.0 mJ. Laser pulses were used to vaporize liquid and solid samples on different substrates. The laser vaporized material was captured and ionized by an electrospray source and then detected via a mass spectrometer instrument. It was discovered that samples on glass substrate could be vaporized by fs laser pulses, but not by ns laser pulses. Samples on metal substrate were successfully vaporized by both fs and ns laser pulses. Low energy ns laser pulses were less efficient than fs laser pulses of the same energy for vaporizing off metal substrate. A comparison of vaporization from aluminum, copper and stainless steel substrates revealed limited vaporization from copper by ns laser pulses. The electrospray ionization (ESI) mass spectral response of wet and dry proteins on stainless steel was similar for both fs and ns laser pulses. Experiments to test the capabilities of ns laser electrospray mass spectrometry (ns-LEMS) revealed that sample vaporization was limited to analysis on metal surfaces. This dissertation details methods for femtosecond laser electrospray ionization (fs-LEMS) to be used to quantify non-covalent protein-ligand interactions. Hen egg white lysozyme (HEWL) and N,N’,N”-triacetylchitotriose (NAG3) interactions were quantified via dissociation constant (Kd) measurements. The Kd for HEWL and N,N’,N”,N”’-tetraacetylchitotetraose (NAG4) were also measured. This dissertation also reports a miniaturized flowing atmospheric pressure afterglow (micro-FAPA) for use as an alternative ionization source of fs-laser vaporized analytes. Loratadine pills were vaporized and reacted with the gas stream from the micro-FAPA source to generate ions which were then detected by a mass analyzer. The ions detected varied in distribution as a response to the distance the sample was vaporized from the ion source. Complexed samples were tested and molecular assignments were difficult due to the numerous pathways for ion formation. The use of an ion filter to decrease the energy imparted on sample molecules during the ionization process of the micro-FAPA is also reported.
Temple University--Theses
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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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Vidal, José Tort. "Desenvolvimento de um sistema opto-mecânico para micro usinagem com laser de femtosegundos." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-10082011-150643/.
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A usinagem de estruturas micrométricas pode ser feita com pulsos laser de nano, pico ou fentossegundos. Destes, porém, somente os mais curtos podem resultar em uma interação não térmica com a matéria, o que evita a fusão, formação de rebarba e zona afetada pelo calor. Devido à sua baixa potência média, contudo, a sua utilização na produção em massa somente pode ser considerada em casos muito especiais, isto é, quando o processamento não-térmico é essencial. Este é o caso da usinagem de semicondutores, aços elétricos, produção de MEMS (sistemas micro eletro-mecânicos), de micro canais e diversos dispositivos médicos e biológicos. Assim, visando a produção destes tipos de estruturas, uma estação de trabalho foi construída com capacidade de controlar os principais parâmetros de processo necessários para uma usinagem micrométrica com laser de pulsos ultracurtos. Os principais problemas deste tipo de estação são o controle da fluência e do posicionamento do ponto focal. Assim, o controle do diâmetro do feixe (no foco) e da energia devem ser feitos com grande precisão. Além disso, o posicionamento do ponto focal com precisão micrométrica nos três eixos, também é de fundamental importância. O sistema construído neste trabalho apresenta soluções para estes problemas, utilizando diversos sensores e posicionadores controlados simultaneamente por um único programa. A estação de trabalho recebe um feixe vindo de um laser de pulsos ultracurtos localizado em outro laboratório, e manipula este feixe de maneira a focalizá-lo com precisão na superfície da amostra a ser usinada. Os principais parâmetros controlados dinamicamente são a energia, o número de pulsos e o posicionamento individual de cada um deles. A distribuição espacial da intensidade, a polarização e as vibrações também foram medidas e otimizadas. O sistema foi testado e aferido com medidas de limiar de ablação do silício, que é um material bastante estudado neste regime de operação laser. Os resultados, quando confrontados com a literatura, mostram a confiabilidade e a precisão do sistema. A automatização, além de aumentar esta precisão, também aumentou a rapidez na obtenção dos resultados. Medidas de limiar de ablação também foram realizadas para o metal molibdênio, levando a resultados ainda não vistos na literatura. Assim, de acordo com o objetivo inicial, o sistema foi desenvolvido e está pronto para utilização em estudos que levem à produção de estruturas micrométricas.Machining of very small structures has been made with nano, pico and femtosecond pulsed lasers. Among then, only femtosecond lasers may result in nonthermal interaction with matter, avoiding melting, formation of slag and heat affected zone. Mass production with such lasers yet can only be considered in cases where nonthermal effects are of prime importance. This is the case in machining of semiconductors and electric steels, the production of MEMS, microchannels, and many medical and biological devices. Hence, a workstation for production of such kind of microstructures was built with the capability of controlling the main parameters necessary for the machining process. Control of the laser fluence and focus positioning are the main concern in this kind of processing. So, the control of the laser beam diameter (in the focus) and of the pulse energy must be very precise. Positioning of focal point with micrometric precision in the three axes is also fundamental. The system built in this work provides solutions for these problems incorporating several sensors and positioning stages simultaneously controlled by a single software. The workstation receives a laser beam coming from another laboratory and delivers it to the surface of the sample managing with precision the main process parameters. The system can dynamically control the energy, number of pulses and positioning for each individual laser spot. Besides, the spatial distribution of the laser intensity, polarization and vibrations were also measured and optimized. The system was tested and calibrated with threshold ablation measurement for silicon, which is well studied in this regime of laser operation. The results where compared with data found in the literature and attested the reliability and precision of the system. Besides the increase in precision, the automation also turned much faster the data acquisition. Threshold ablation for metallic molybdenum was also obtained and resulted in data not found in the literature yet. Concluding the initial goal, the workstation was developed and is ready to be used in studies that can lead to production of micrometric structures.
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French, Paul Michael William. "New femtosecond dye laser systems." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38321.
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MENIS, THIERRY. "Reponse d'un systeme atomique simple a une impulsion laser femtoseconde." Paris 6, 1993. http://www.theses.fr/1993PA066176.
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La these porte sur la reponse d'un systeme atomique simple soumis a une impulsion laser tres breve "femtoseconde" et tres intense. Des effets nouveaux et inattendus ont ete recemment observes dans ce contexte. La these aborde l'etude theorique de deux de ces effets : la generation d'harmoniques d'ordres tres eleves et la possible stabilisation d'atomes vis a vis de l'ionisation dans un champ ultra-intense. Sont abordes successivement dans ce contexte : la theorie des perturbations exponentielles qui utilise le developpement de magnus de l'operateur d'evolution. Une application specifique est traitee, qui montre les avantages et les limitations de la methode. La reponse de systemes classiques et quantique unidimensionnels (oscillateurs anharmoniques monomiaux, potentiels modeles,. . . ) et tridimensionnels (systeme de kepler) a ete modelisee. Les spectres d'harmoniques et le phenomene de stabilisation sont etudies en detail. Le caractere universel de la reponse de ces systemes est bien mise en evidence.
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Efimov, Anatoly. "Adaptive control of lasers and their interactions with matter using femtosecond pulse shaping." [Florida] : State University System of Florida, 2000. http://etd.fcla.edu/etd/uf/2000/ane5949/thesis.pdf.
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Thesis (Ph. D.)--University of Florida, 2000.Title from first page of PDF file. Document formatted into pages; contains v, 181 p.; also contains graphics. Vita. Includes bibliographical references (p. 165-180).
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Nishizawa, Norihiko, and Toshio Goto. "Compact system of wavelength-tunable femtosecond soliton pulse generation using optical fibers." IEEE, 1999. http://hdl.handle.net/2237/6767.
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Herrera, Cristhiano da Costa. "Desenvolvimento e controle de circuitos microfluídicos." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-29012019-084425/.
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A primeira etapa do projeto foi realizar testes para usinagem controlada e otimizada de vidro ótico de borosilicato (BK7) por laser de femtossegundos. Parâmetros como energia, pulsos sobrepostos e a variação da posição focal foram investigados para controle da taxa de remoção do material e extensão da cratera ablacionada. Especial atenção foi dada à condição física e topográfica da superfície resultante da usinagem para torná-la menos rugosa e evitar a retenção de reagentes que possam contaminar e alterar as reações pretendidas. Microcanais, microválvulas, microbombas, misturadores, microrreatores, aquecedores e outros componentes foram desenvolvidos para compor sistemas microfluídicos. Os microcanais construídos sobre a superfície de vidro BK7 vedados por uma lâmina de polidimetilsiloxano (PDMS) são a base dos sistemas microfluídicos. O controle de fluxo de reagentes é feito por miniválvulas pneumáticas controladas por um microcontrolador Arduino através de uma plataforma Labview. Este trabalho mostra os componentes desenvolvidos e dois sistemas microfluídicos criados. O primeiro contém um circuito capaz de replicar ensaios imunoenzimáticos (ELISA) com um custo muito menor de insumos. O segundo é um sistema para a produção de nanocristais fluorescentes de NaYF4 especialmente utilizados como marcadores em imagens de sistemas biológicos.The first stage of the project was to perform tests for controlled and optimized machining of borosilicate optical glass (BK7) by femtosecond laser. Parameters such as energy, number of overlapped pulses, and the focal position variation were investigated for a better extraction of material. Microchannels, microvalves, micropumps, mixers, reactors, heaters and other components were developed to compose applied microfluidic systems. Microchannels built on the surface of BK7 glass sealed by a polydimethylsiloxane (PDMS) sheet form the basis of the microfluidic circuits. The reagents flow control is done by pneumatic mini-valves controlled by an Arduino microcontroller through a Labview platform. This work shows the components developed and two microfluidic systems created. The first contains a microfluidic circuit capable of replicating enzyme-linked immunosorbent assays (ELISA) with a much lower cost of materials. The second has a microfluidic circuit for the production of NaYF4 fluorescent nanocrystals specially used as markers in images of biologic systems.
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Chakravarty, Prerona. "Photoacoustic drug delivery using carbon nanoparticles activated by femtosecond and nanosecond laser pulses." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33842.
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Cellular internalization of large therapeutic agents such as proteins or nucleic acids is a challenging task because of the presence of the plasma membrane. One strategy to facilitate intracellular drug uptake is to induce transient pores in the cell membrane through physical delivery strategies. Physical approaches are attractive as they offer more generic applicability compared with viral or biochemical counterparts. Pulsed laser light can induce the endothermic carbon-steam reaction in carbon-nanoparticle suspensions to produce explosive photoacoustic effects in the surrounding medium. In this study, for the first time, these photoacoustic forces were used to transiently permeabilize the cell membrane to deliver macromolecules into cells. Intracellular delivery using this method was demonstrated in multiple cell types for uptake of small molecules, proteins and DNA. At optimized conditions, uptake was seen in up to 50% of cells with nearly 100% viability and in 90% of cells with ≥90% viability, which compared favorably with other physical methods of drug delivery. Cellular bioeffects were shown to be a consequence of laser-carbon interaction and correlated with properties of the carbon and laser, such as carbon concentration and size, laser pulse duration, wavelength, intensity and exposure time. Similar results were observed using two different lasers, a femtosecond Ti: Sapphire laser and a nanosecond Nd: YAG laser. Uptake was also shown in murine skeletal muscles in vivo with up to 40% efficiency compared to non-irradiated controls. This synergistic use of nanotechnology with advanced laser technology could provide an alternative to viral and chemical-based drug and gene delivery.
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Bičiūnas, Andrius. "Semiconductor materials for components of optoelectronic terahertz systems activated by femtosecond 1 µm wavelength laser pulses." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121107_091148-13422.
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The aim of dissertation was to develop and explore the semiconductor material terahertz (THz) pulse emitters, for Terahertz time–domain spectroscopy (THz–TDS) systems using a 1 μm wavelength femtosecond laser radiation. THz pulse generation and detection using optoelectronic semiconductor components in THz–TDS excited by femtosecond laser pulses become these days a powerful experimental technique. Traditionally, mode-locked Ti:sapphire lasers emitting at the wavelengths ~800 nm are used. However Ti:sapphire lasers require many-stage optical pumping arrangement, the system is quite bulky and complicated. The solution could be the lasers emitting in 1 – 1.55 µm, which can be directly pumped by diode laser bars. Recently, several compact, efficient and cost-effective solid-state and fiber laser systems that generate femtosecond pulses at near-infrared wavelengths have been developed and employed for activating THz–TDS systems. The main obstacle of these systems is the lack of material with appropriate bandgap, high dark resistivity and short (~ ps) carrier lifetimes.Disertacijos darbo tikslas buvo sukurti ir ištirti puslaidininkinius terahercinių (THz) impulsų emiterius ir detektorius, skirtus sistemoms, naudojančioms 1 μm bangos ilgio femtosekundinę lazerinę spinduliuotę. THz impulsų generavimo ir detektavimo sistema, kurios optoelektroninius puslaidininkinius komponentus aktyvuoja femtosekundiniai lazerio impulsai, yra plačiai taikoma terahercinėje laikinės srities spektroskopijoje. Tradiciškai tokiose sistemose naudojami Ti:safyre femtosekundiniai lazeriai, kurių spinduliuotės bangos ilgis yra ~800 nm. Šios sistemos nėra patogios dėl jų matmenų, nes lazeriai turi sudėtingą kelių pakopų kaupinimo sistemą. Pastaruoju metu THz impulsų generavimui vis dažniau naudojami femtosekundiniai kietakūniai ir šviesolaidiniai lazeriai, kurių spinduliuotės bangos ilgis patenka į artimosios IR spinduliuotės sritį. Tačiau šios sistemos vis dar neturi tinkamos medžiagos fotolaidiems elementams gaminti, kurie būtų žadinami 1 – 1,55 µm bangos ilgio lazeriais. Tokios medžiagos, visų pirmą, turi būti jautrios optinei spinduliuotei, o jų draustinės energijos tarpas turi atitikti žadinamos spinduliuotės fotonų energiją, be to sluoksniai turi pasižymėti didele tamsine varža bei labai trumpomis krūvininkų gyvavimo trukmėmis (~ 1 ps). Šioje disertacijoje yra pateikiami THz impulsų generavimo panaudojus puslaidininkių paviršius ir fotolaidžias antenas rezultatai, žadinant 1 µm bangos ilgio femtosekundiniais lazerio impulsais.
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Takayanagi, Jun, Norihiko Nishizawa, Hiroyuki Nagai, Makoto Yoshida, and Toshio Goto. "Generation of high-power femtosecond pulse and octave-spanning ultrabroad supercontinuum using all-fiber system." IEEE, 2005. http://hdl.handle.net/2237/6770.
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Mortag, Dirk [Verfasser]. "Investigation of femtosecond fiber laser systems with respect to low repetition rates, pulse energy scaling, and all-fiber-integrability / Dirk Mortag." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1025794168/34.
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Steinmann, Lena [Verfasser]. "Lithium isotope fractionation in magmatic systems: Constraints from in situ δ7Li determinations on magmatic minerals by femtosecond-laser ablation-MC-ICP-MS / Lena Steinmann." Hannover : Gottfried Wilhelm Leibniz Universität, 2020. http://d-nb.info/1213445914/34.
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Sharma, Nipun. "Self-organization of silver nanoparticles with femtosecond laser in TiO2 matrix : Applications to plasmonic colours, multiple hidden images and Colour Image-Multiplexing." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSES032.
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L'auto-organisation de nanoparticules métalliques dans un support est un moyen efficace et peu coûteux de produire des systèmes plasmoniques pouvant être utilisés pour des applications d'affichage couleur actif, de codage d'image et de sécurité. De tels systèmes nanocomposites doivent être synthétisés sous forme de films stables qui pourraient être enduits sur tout type de surface pour un traitement laser. Cette thèse de doctorat porte sur l 'auto - organisation induite par laser de couches minces nanocomposites d' argent et d 'oxyde de titane mésoporeux.Dans ce travail, nous étudions d'abord la synthèse de couches minces mésoporeuses de TiO2 à l'aide d'un processus hydrolytique, facile à mettre en œuvre, pour fournir des films cristallisés à partir de 100 ° C. sont rapportés dans ce travail. En outre, les mécanismes de croissance des nanocristaux dans les films mésoporeux de TiO2 sont étudiés sous la forme de mesures ellipsométriques mettant en évidence son effet sur la porosité et la cristallinité du film avec la température de recuit.La deuxième étude démontre la fabrication de différentes structures nanocomposites à l'aide de la technique de balayage laser femtoseconde, déclenchant la croissance et l'auto-organisation de nanoparticules d'argent à l'intérieur d'une matrice de titane amorphe poreuse donnant lieu à des couleurs dichroïques plasmoniques. Une recherche plus approfondie sur l'étude paramétrique de ces nanocomposites donne lieu à différentes nanostructures à deux régimes de vitesse de balayage différents, qui se forment à la surface et sont noyées en dessous en raison de l'excitation de la surface et des modes guidés. La flexibilité de cette technologie de marquage laser permet également de fabriquer des nanostructures hybrides composées de différents types de nanostructures adjacentes, entrelacées pour couvrir de grandes surfaces. Une extension de cette étude est conclue sur des substrats plastiques / flexibles pour encoder des images imprimées diffractives. Ici, les nanostructures de surface (LIPSS) sont formées en utilisant le contrôle de la polarisation du laser et donc de l'orientation du réseau, qui est utilisé pour coder des images de niveau de gris qui peuvent être observées dans les modes de diffraction.De plus, cette étude se conclut en produisant trois multiplexages d'images qui peuvent être observés dans trois modes sélectionnés d'observation sous lumière blanche en réflexion avec lumière non polarisée et transmission entre polariseurs pour deux angles de polarisation différents. Cela est dû au fait que la biréfringence et le dichroïsme du film peuvent être contrôlés pour produire des gammes de couleurs sans précédent pour le multiplexage. Un tel traitement laser intelligent sur des films minces nanocomposites donne lieu à des applications artistiques et de sécurité en codant différentes images jusqu'à trois sous la même zoneSelf-organization of metallic nanoparticles in a medium is an efficient and a low-cost way to produce plasmonic systems that can be used for applications to active colour display, image encoding, and security. Such nanocomposite systems must be synthesized in form of stable films which could be coated on any kind of surface for laser processing. This doctoral thesis focuses on laser‐induced self‐organization of nanocomposite thin films of silver and mesoporous titania.In this work, we first investigate synthesizing mesoporous TiO2 thin films using hydrolytic process, which is easy to implement, to provide crystallized films starting at 100°C. First activation energies in mesoporous TiO2 films using Raman spectroscopy in combination with the phonon quantum confinement model are reported in this work. Further, growth mechanisms of nanocrystals in mesoporous TiO2 films are investigated in form of ellipsometric measurements highlighting its effect on film porosity and crystallinity with annealing temperature.The second study demonstrates fabrication of different nanocomposite structures using femtosecond laser scanning technique, triggering growth and self-organization of silver nanoparticles inside porous amorphous titania matrix giving rise to plasmonic dichroic colours. Further investigation on the parametric study of such nanocomposites gives rise to different nanostructures at two different scan speed regimes, which are formed at the surface and are embedded below due to excitation of surface and the guided modes. The flexibility of this laser-based marking technology also allows to fabricate hybrid nanostructures composed of different adjacent nanostructure types, interlaced to cover large areas. An extension of this study is concluded on plastic/flexible substrates to encode diffractive printed images. Here surface nanostructures (LIPSS) are formed by using the control of laser polarization and thus grating orientation, which is used to encode grey-level images that can be observed in diffraction modes.Further, this study is concluded by producing three image multiplexing which can be observed in three selected modes of observation under white light in reflection with non-polarized light and transmission between polarizers for two different polarization angles. This is due to the fact that the film birefringence and dichroism can be controlled to produce unprecedented colour gamuts for multiplexing. Such smart laser processing on nanocomposite thin films gives rise to artistic and security applications by encoding different images up to three under same area
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Moretto, Simone Gonçalves. "Estudo longitudinal da resistência e qualidade de união de diferentes sistemas adesivos à dentina irradiada com laser de femtossegundos." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/23/23134/tde-13042013-123740/.
Full textAbstract:
Recentemente, os lasers de pulsos ultracurtos têm sido avaliados para o preparo dos tecidos duros dentais devido à sua habilidade de reduzir os efeitos térmicos resultantes da irradiação. O objetivo deste estudo foi avaliar a efetividade de união de 3 sistemas adesivos à dentina preparada com o laser de femtossegundos (10-15 s). Para isso, 60 terceiros molares foram preparados com o laser de femtossegundos (1.450 nm; 0,3W; 100.000Hz) ou ponta diamantada, divididos em 3 subgrupos (n=10) restaurados utilizando o adesivo condicione e lave de 3 passos Optibond FL (OFL; Kerr), o autocondicionante de 2 passos Clearfil SE (CSE; Kuraray) ou o autocondicionante de 1 passo G-aenial Bond (GAB; GC). Após 1 semana de armazenamento em água, os dentes foram seccionados (1,0x1,0 mm) e testados imediatamente e após 6 meses de armazenamento. Vinte e quatro amostras adicionais foram preparadas com o laser ou ponta diamantanda conforme descrito acima. Seis amostras foram seccionadas em espécimes menores e aleatoriamente preparados para observação das características morfológicas da superfície (n=3) e subsuperfície (n=3) em Microscópio Eletrônico de Varredura (MEV) (n=3) e Microscopia Eletrônica de Transmissão (MET) (n=3). As outras 18 amostras foram restauradas com os sistemas adesivos supramencionados, seccionados em espécimes menores e distribuídos para avaliação da interface adesiva em MEV (n=3) e padrão de nanoinfiltração após 1 semana (n=2) e 6 meses (n=2) em MET. O modelo linear de efeitos mistos (=0,05) revelou um efeito significante dos fatores adesivo, armazenagem e a interação preparo x armazenagem na resistência de união. Todos os adesivos apresentaram uma redução significante da resistência de união após 6 meses de armazenamento (p<0,0001) para ambos os tipos de preparo. Com relação ao sistema adesivo, a única diferença verificada foi o maior valor de resistência de união do GAB quando aplicado sobre as superfícies irradiadas (56,71±10,72 MPa) quando comparadas com as preparadas com ponta diamantada (43,14±14,93 MPa) após 1 semana de armazenamento. A análise de fratura revelou fraturas mistas, adesivas e coesivas em dentina para ambos os métodos de preparo com um discreto aumento do número de fraturas mistas após 6 meses de armazenamento exceto para o GAB, que apresentou principalmente fraturas adesivas e mistas. A análise em MEV revelou uma fina camada de debris sobre a superfície da dentina irradiada e a hibridização com todos os sistemas adesivos resultou num íntimo contado da interface adesiva com o substrato. A análise em MET da subsuperfície irradiada revelou fibrilas colágenas preservadas. A análise da interface adesiva revelou um aumento dos depósitos de prata na camada híbrida para todos os adesivos, após 6 meses de armazenamento, independentemente do tipo de preparo. Apenas o GAB apresentou maiores depósitos de prata após 1 semana de armazenamento para as superfícies preparadas com ponta diamantada. A irradiação com o laser de femtossegundos não reduziu a receptividade da dentina aos sistemas adesivos, resultando em valores de resistência de união similares aos obtidos com a ponta diamantada; além de uma ótima interação do substrato com os sistemas adesivos e deposições de prata similares àquelas obtidas com a ponta diamantada.Recently, the applicability of ultrashort pulsed lasers has been studied for dental hard-tissue irradiation because of its reduced residual thermal damage. The aim of this study was to determine the bonding effectiveness of 3 contemporary adhesive systems to dentin prepared by femtosecond (10-15 sec) laser-irradiation. For this, 60 third molars were prepared either by the femtosecond laser (1450 nm; 0.3W; 100,000Hz) or by bur, randomly divided into 3 subgroups (n=10) and restored with a composite using either the 3-step etch-and-rinse adhesive Optibond FL (OFL; Kerr), the 2-step self-etch adhesive Clearfil SE (CSE; Kuraray) or the 1-step self-etch adhesive G-aenial Bond (GAB; GC). After 1-week water storage, the teeth were sectioned (1.0x1.0 mm) and half of the specimens were tested until failure using a micro-tensile bond-strength (TBS) approach. The other half was stored in water and tested after 6 months. Twenty-four additional dentin samples were exposed to the diamond bur and the laser, following the same abovementioned parameters. Three samples of each treatment were sectioned in smaller specimens in order to be characterized for surface (n=3) and cross-sectional morphological analysis using Scanning Electron Microscopy (SEM) (n=3) and Transmission Electron Microscopy (TEM) (n=3). The other eighteen samples were hybridized with the abovementioned adhesive systems, sectioned in smaller samples and distributed for evaluation of the interface under SEM (n=3) and nanoleakage distribution for 1 week (n=2) and 6 months (n=2) under TEM. Linear mixed effect model (=0.05) revealed a significant effect of the factors adhesive, storage and the interaction of preparation x storage on the TBS. All adhesives presented a significant reduction of the bond strength after 6-month storage (p<0.0001) for both preparation methods. Regarding the adhesive system, the only difference found was a significantly higher TBS of GAB to laser-irradiated (56.71±10.72 MPa) than to bur-cut dentin (43.14±14.93 MPa) after 1-week water storage. Fracture analysis showed mixed, adhesive and cohesive failures in dentin similarly for both preparation methods with a slightly increase of the mixed failures after 6-months water storage for OFL and CSE, but not for GAB that presented mainly adhesive and mixed failures. SEM disclosed a thin layer of debris on the laser-irradiated dentin surface and the hybridization with all adhesive systems resulted in a very tight interface. TEM analysis of the irradiated subsurface revealed collagen fibrils preserved and for the nanoleakage evaluation an increase of silver deposits at hybrid layer for all adhesives testes after 6-months water storage, irrespective of the preparation methods. Only the GAB presented great silver deposits even after 1-week water storage for the bur-cut preparation method. Femtosecond laser irradiation did not reduce the bonding receptiveness of dentin resulting in similar values obtained with the preparation by bur. Additionally it led to a great interaction with different adhesive systems and silver deposits comparable to those obtained with the bur-cut preparation method.
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Djekounyom, Eric. "Etude d'une structure métamatériau HIW coplanaire à substrat de ferrite : application à un isolateur hyperfréquence." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSES030.
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Les enjeux majeurs des dispositifs hyperfréquences utilisés dans les systèmes de télécommunication modernes sont la montée en fréquence de fonctionnement, la miniaturisation des circuits et l’intégrabilité des composants.Grâce à l’émergence des métamatériaux et à la maîtrise des propriétés des ferrites, il est possible de développer nouveaux dispositifs répondant à ces nouvelles exigences de l’électronique embarquée.Cette thèse développe, à partir d’une ligne métamatériau HIW coplanaire basée sur un substrat de ferrite, un nouveau dispositif hyperfréquence non réciproque de faible encombrement, opérant à des fréquences situées entre 13 et 15 GHz.Les prototypes fabriqués et caractérisés sous de faibles valeurs de champ magnétique, présentent les performances caractéristiques d’un isolateur bande étroite: isolation supérieure à 30 dB, pertes d’insertion inférieures à 1 dBThe main challenges of microwave devices used in modern telecommunication systems are the increase of the operating frequency, the circuit’s miniaturization and the integration of components.Thanks to the emergence of metamaterials and the control of the properties of ferrites, it is possible to develop new circuits that meet these new requirements for embedded electronics.This thesis investigates, from a coplanar HIW metamaterial line based on a ferrite substrate, a new non-reciprocal microwave device, operating in frequency range between 13 and 15 GHz.Prototypes were fabricated and characterized under low magnetic field. They achieved the characteristic performances of a narrow band isolator: isolation over 30 dB and insertion losses of less than 1 dB
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Wan, CHIA-YU, and 王嘉右. "Design of System Control Module for Femtosecond Laser." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/v9m2gn.
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碩士國立高雄應用科技大學
電子工程系
105
Recently laser industry grown up rapidly, according to market condition and the requirement of industry ,laser industry is heading to high power cutting and precision machining, such as precision machining is combined with biomedical, therefore the need of surgeon leads to the development femtosecond laser. In this thesis, we work on the femtosecond laser, which we focused on electronic control of the femtosecond laser system, through distinctive design of circuit dividers to control seed laser’s repetition frequency. According to the requirement of optics and operating on different optical devices which making us to choose different IC and control it by adaptive firmware and then integrated optics and electronics will be our final goal. In order to overcome high frequency signal processing, to choose and detect different MCU is an important issue, through controlling MCU and integrating IC’s function, using RS232 to connect user interface for completing the ability of communication. Finally , we combine electronics and optics ,and the femtosecond laser system at last will be establish.
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Chin-HungWang and 王智弘. "Development of Sub-Femtosecond Pulsed Laser Processing System." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/48743112266253578179.
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碩士國立成功大學
工程科學系碩博士班
101
In this thesis, we want to develop a sub-femtosecond pulsed laser machining system integrated with prism pair and acousto-optic modulator (AOM) for 3D imaging and processing of bio-tissue. Because of conventional laser machining systems (even at nanosecond pulse) have very serious thermal effect. There are many disadvantages such as melting residues, micro-cracks, and poor fineness etc. They can be significantly improved via using femtosecond laser, but generally speaking, the pulse width of femtosecond laser is about 100 fs, there is still has thermal effect in such pulse width level. Dispersion effect will be very severe issue when machining pulse width is below 100 fs. The SF-11 prism pair was utilized to compensate overall optical system’s second order dispersion. The major compensation components are AOM and objective. After compensating, the system pulse width is 45 fs, and the AOM was utilized to become laser switch and laser pulse selector for precision control the dose of laser intensity. We get the two-photon image from different sizes of fluorescent beads and second harmonic generation image from chicken tendon. Finally, we also use different pulse width on bio-tissue processing. Improving the image spatial resolution, processing efficiency, and reducing thermal effect have been successfully accomplished.
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Ngoi, Kok Ann Bryan, K. Venkatakrishnan, P. Stanley, and L. E. N. Lim. "Femtosecond Pulsed Laser Direct Writing System for Photomask Fabrication." 2002. http://hdl.handle.net/1721.1/4029.
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Photomasks are the backbone of microfabrication industries. Currently they are fabricated by lithographic process, which is very expensive and time consuming since it is a several step process. These issues can be addressed by fabricating photomask by direct femtosecond laser writing, which is a single step process and comparatively cheaper and faster than lithography. In this paper we discuss about our investigations on the effect of two types of laser writing techniques, namely, front and rear side laser writing with regard to the feature size and the edge quality of the feature. It is proved conclusively that for the patterning of mask, front side laser writing is a better technique than rear side laser writing with regard to smaller feature size and better edge quality. Moreover the energy required for front side laser writing is considerably lower than that for rear side laser writing.Singapore-MIT Alliance (SMA)
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Huang, Huai-Tzun, and 黃懷諄. "Design of Beam Stabilization System for Femtosecond Laser Micromachining." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/67520790336476566489.
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碩士國立臺灣大學
機械工程學研究所
99
Recently the invention of the ultrafast laser makes the field of laser processing to a new legend. Femtosecond laser can machine the opaque material and also can machine the transparent material through the multi-photon absorption. This advantage could make the femtosecond laser process many materials. Femtosecond laser is the most perspective laser on research. Compared with the conventional nanosecond laser, femtosecond laser could result in the smaller heat affected zone, the burr is less and the accuracy is better. There are many factors that influence the laser processing in reality, for example, the temperature variation, vibration of the air conditioner and the air flow in the environment. All these factors would makes the laser beam unstable and affect the machining accuracy down. The research is to design and set an active stabilization system for correcting the unstable laser beam and eliminate the disturbance in the environment. The research uses two fast steering mirrors and two dimensional photodiode detectors to install stabilization system. The research use two detectors to test the ability of stabilization system to demonstrate that the system exactly can correct the disturbance in the environment and can stabilize the laser beam. Finally use the system in the silicon ablation, setting different energy of pulse and different pulses of ablation to discuss the result of the material processing.
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Keng-ChiCho and 卓粳佶. "Novel Three-dimensional Micro/nano-processing via Multifunction Femtosecond Laser System." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/43540478551845157370.
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Huang, Shih-Che, and 黃士哲. "Analysis of Application in Micro-Machining with Femtosecond Laser Beam Stabilization System." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/99229146349616109907.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
100
The development of ultra-fast technology has given a brand new approach in laser fabricating applications. With this technology featuring with the principles of single photon absorption and multi-photon absorption, machining any kind of transparent or opaque materials is now available and has superior advantages of small thermal effected zone and high machining precision. In real world, however, there are kinds of factors that may be able to degrade the laser pointing stability, such as mechanical vibration, air flow disturbance, variation in ambient temperature and humidity, etc. Those factors may degrade the precision in ultra-fast laser fabrication. The main purpose in this thesis is to observe the correlation of laser pointing stability and laser fabrication result and make an assessment of influence of laser instability in ultra-fast laser fabrication regime. Moreover, with the adjusted laser pointing stabilization system in this work, finding the relationship of laser pointing instability with machining result by making worse laser pointing condition with the fast steering mirror in the system is the second objective in this thesis. With the relation of laser pointing and laser machining result, it may provide a new reference to those want to build up a laser pointing stabilization system in ultra-fast laser fabricating regime.
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Li, Yue-Ying, and 李岳穎. "High-power Femtosecond Pulse Generation in a Chirped-Pulse Amplified Ytterbium-Doped Fiber Laser System." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/61637106219008095724.
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碩士國立清華大學
光電工程研究所
102
In this thesis, we demonstrated the chirped pulse amplification (CPA) of a high-power ytterbium-doped fiber amplifier at wavelength of 1064 nm without a stretcher. The all-normal dispersion (ANDi) passively mode-locked fiber laser is used to generate highly chirped seed pulse. Therefore, the pulse stretcher could be optional. The spectrum bandwidth of our ANDi fiber laser is 9 nm which can support 185-fs-width pulses. The actual output pulses width is 11.7 ps. In this case, it is equivalent to -60 times stretching of the seed pulses to reduce the peak power. After amplification, the output signal power can achieve ~1 W with pulse width of 20 picosecond (repetition rate ~ 15 MHz). The output power is basically limited by stimulated Raman scattering (SRS), which reduces the gain of the signal power. After compression by the gratings pair, the output peak power was shown to be 25 kW with a compression ratio ~ 25 (~900 fs). In the meantime, the power loss of the compressor is around 50%. Further, the compressed-pulse was frequency doubled by a type-I critically phase-matched (CPM) Lithium Triborate (LBO) crystal with optimal focal parameter of ξ~ 1.5. With 370 mW of fundamental light, we can generate 88 mW of green output (λ= 532 nm) with conversion efficiency of 23% which is much higher than that achieved with our picosecond laser system (10%). Power scaling is possible but requires introducing second amplification stage with larger mode-field-diameter active fiber or increasing the stretching ratio before the amplification.
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She, Nian-Zu, and 佘念祖. "A study of nonvacuum CIGS thin film solar cells annealed by femtosecond laser scanning system." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/88631219811141209786.
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碩士國立交通大學
電子物理系所
105
In this thesis, we have successfully demonstrated that femtoscond laser annealing nonvacuum nanoparticle synthesized CIGS thin films without melt effect. The laser fluence was optimized by XRD measurement, and the quality of crystallinity in (112)-preferred orientation and the signal of A1 mode in chalcopyrite structure were significantly enhanced after fs-LA. These phenomenon can be attributed {112} is polar surface, so that the structural changes can be driven whereas electronic excitation from intensive electric field of fs laser pulses. Furthermore, the laser scanning rate was also optimized by carrier lifetimes acquired pump-probe spectroscopy. The better stoichiometry in CIGS thin films was achieved with optimized laser scanning rate owing to that the excess indium were reacting with other ions insides. It is beneficial to decrease the defect states of InSe, VSe, and InCu, which has been elaborately verified by PL spectra. These abovementioned advantages of fs-LA had greatly decreased shut leakage current and recombination centers in CIGS TFPV, resulting the significant enhancement in conversion efficiency. These results has indicated that fs-LA is a promising approach to boosting high-efficiency flexible nonvacuum CIGS TFPV.
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Liu, Pei-Chia, and 劉佩佳. "Developing a Femtosecond Laser Microsurgery System to Dissect Caenorhabditis Elegans Touch Neuron for Studying Neural Regeneration." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/73853639162919486699.
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碩士國立臺灣大學
物理研究所
100
After years of development, laser has been applied in numerous medical treatment procedures. Surgeries such as correcting near and far sightedness, dissection on soft tissue and even cancer-relate therapies are gradually being implemented. Choosing different power, repetition, wavelength of the laser, we can create multifarious chemical or physical reactions with different bio-materials. In our experiment, we use 780nm, femtosecond laser to dissect neuron cell (PC12) and the touch neuron of Caenorhabditis elegans, in order to observe the following behaviors after excising distinct cellular componentss. Femtosecond pulse laser embraces plenty of advantages in surgical purposes. The repetition rate of our laser pulse is 80-MHz, and the maximum cutting power is 20mW. Since Ti-sapphire laser provides high energy in each laser pulse, we can cut neurons by tuning pulse energy around 0.25nJ, without extensive tissue damage. In addition, we use near infrared light as source (780nm wavelength), pushing the focus deeper into biological specimens. Therefore, we can successfully execute precise surgery on the micron-sized sample such as collagen, cells or even the specific parts of neuron. Combining two optical systems, we confirm the position of C.elegans neuron by GFP, and meanwhile, use Ti-Sapphire laser to dissect the targeted neuron section . After witnessing the damage on neuron, we use a picker to motivate the exercise of C.elegans and to study its post-surgery behaviors.
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Sheng, Shi-yun, and 盛世雲. "An external electro-optic sampling system for microwave standing wave measurement using femtosecond Ti:sapphire laser as the light source." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/16538000892683356524.
Full textAbstract:
碩士國立交通大學
電子物理系
88
The applications of the Ti:Sapphire Laser and E-O Sampling system which use the photoconductive switch as a opto-electronic harmonic mixer have been studied. Free running microwave signals up to 12GHz have been phase tracked and electro-optic sampled (EOS) by the aforementioned system, respectively. Using the system, an impedence-mismatched coplannar waveguide has been characterized in traveling wave regime. The amplitude and phase of RF traveling wave and standing wave patterns in the coplannar waveguide have been measured up to 2GHz. The effective dielectric constants of the coplannar waveguide we measured at 1GHz and 2GHz are 5.46 and 5.30, respectively. This is close to the theoretical value.
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Sayrac, Muhammed. "Generation of High Harmonics in Argon, Hydrogen and Their Mixture with Neon." Thesis, 2013. http://hdl.handle.net/1969.1/150970.
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Femtosecond time scale allows us to follow and control atomic and molecular motion. The atomic vibrations happen in the range of femtosecond scale. Thus, femtosecond technology effectively measures the atomic vibration. However, to determine electron motion, one needs to reach sub-femtosecond time scale that is in attosecond time scale.
High Harmonic Generation (HHG) is a non-linear process that converts infrared light to shortest wavelength, such as in the XUV regime. HHG allows to explore electronic motion and to control electron dynamics. HHG easily reaches to XUV region and is enabling attosecond pulse generation.
In this thesis we focused to generate attosecond pulses by using noble gases and their mixtures. We used only argon gas, only hydrogen molecule and their mixture with neon gas. We wanted to improve the conversion efficiency (10^-6) of the fundamental light into high harmonics. We use Ne and H2 gas mixture to look enhancement of the HHs.
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Kayal, Surajit. "Understanding Ultrafast Molecular Structural Dynamics in Liquids : Ultrafast Raman Loss and Transient Absorption Study." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4210.
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The present thesis deals with the detailed ultrafast experimental studies on the ex-cited state vibrational dynamics of model chemical systems in condensed phase. The molecular systems are studied by means of Ultrafast Raman Loss Spectroscopy (URLS) and femtosecond transient absorption (TA) spectroscopy. The primary objective of the current thesis is to look at structural dynamics immediately after Franck-Condon excitation, influenced by surrounding solvent molecules.
The thesis is divided into six chapters and a brief summary of each chapter is given below.
In Chapter 1, I have included the concept of femtosecond time-resolved spectroscopy and nuclear dynamics. Some important aspects of spontaneous and stimulated Raman scattering are discussed. Subsequently, I have described the theoretical framework and methodologies that are important to understand non-linear spectroscopy. Important aspects of time-resolved stimulated Raman pro-cess are described here. A brief outline of the current thesis is also presented at the end of this chapter.
In Chapter 2, I have described in detail the instrumentation and data process-ing methods. A detailed explanation of spectroscopic techniques like transient ab-sorption and femtosecond stimulated Raman spectroscopy and their experimen-tal aspects are discussed. The optimization of the setup, detailed data analysis processes are described. Finally, I have described step-by-step data processing method using DaFitUma software which is developed in our lab.
In Chapter 3, I have studied the excited state isomerization dynamics of tetrap-henylethylene in various solvents using femtosecond TA and URLS spectroscopy. Tetraphenylethylene, a model molecular motor, known to exhibit low-frequency torsional dynamics. TA measurements in the S1 state reveal a step-wise struc-tural rearrangement from Franck-Condon (FC) state ! relaxed state ! twisted state on photoexcitation. Furthermore, oscillation in TA kinetics was observed with-in 1 ps. Fourier transformation of this oscillation leads to a 130 cm 1 low-frequency mode which is responsible for the excited state wavepacket dynamics during the course of FC state ! relaxed state structural rearrangement. Two vi-brational marker band Cet=Cet stretching ( 1512 cm 1) and Cph=Cph stretching ( 1584 cm 1) modes appear immediately after photoexcitation in URLS spectra. From the peak frequency shift, we confirm that the initial structural relaxation is dominated by phenyl torsion rather than central Cet=Cet twist.
In Chapter 4, the structural dynamics and solvent induced internal conversion of 2-(20-Hydroxyphenyl)benzothiazole (HBT), an extensively studied excited state intramolecular proton transfer (ESIPT) system, are investigated. We have obtained snapshots of vibrational spectra of the photoexcited HBT, by URLS, providing de-tailed structural change at an early time. From the URLS peak amplitude analysis we have observed 400 fs amplitude decay in acetonitrile. This is assigned to a rapid structural change induced by polar acetonitrile due to the torsional mo-tion. The ultrafast amplitude decay is associated with coherent excitation of tor-sional mode ( 40 cm 1). Oscillatory peak position in the high-frequency Raman modes indicates a coupling between low-frequency torsional and high-frequency vibrations. Activation of torsional motion in polar solvents provides an additional route for non-radiative decay, responsible for a short lifetime ( 12 ps) and low fluorescence quantum yield. For hexane, the URLS spectral evolution is assigned to vibrational cooling (2-4 ps) followed by population relaxation (115 ps).
Chapter 5, deals with the ultrafast intersystem crossing (ISC) dynamics of thioxanthone (TX) in various solvents. It has striking solvent dependent photo-physical properties. For example, the fluorescence quantum yield ( f ) and life-time ( f ) of the primarily populated singlet (1 *) state strongly depends on the solvent properties. We have studied TX in three different solvents: acetonitrile (ACN; aprotic), methanol (MeOH; polar protic) and in cyclohexane (CX; nonpo-lar). Following electronic excitation to the S1 (1 ) state, the molecule relaxes to the lowest T1 (3 ) state in 50 ps, 4 ps in ACN and in CX respectively. In the case of TX in methanol, two stages of ISC with time constants of 4 ps and > 2ns were obtained. These two stages are assigned to direct ( 4 ps) ISC to the T2 state (1 ! 3n ) followed by slow internal conversion ( 2 ns) to the T1 state (3 ). Analysis of peak position dynamics further allows us to obtain vibrational relaxation times during ISC process. The present study sheds light on a complete understanding of the structural changes accompanying the ISC process.
Finally, in Chapter 6, we have briefly summarized the main results of the the-sis. This chapter also includes our comments on some of the future extensions of the present work.
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Maia, João Miguel Mendes da Silva. "Fabrication of Optofluidic Systems by Femtosecond Laser Micromachining." Doctoral thesis, 2021. https://hdl.handle.net/10216/136195.
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Kung-Hsuan, Lin. "Femtosecond-Laser-Based Nano-Acoustic Systems: Principles and Applications." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1907200612272900.
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Lin, Kung-Hsuan, and 林宮玄. "Femtosecond-Laser-Based Nano-Acoustic Systems: Principles and Applications." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/10831498862659909902.
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博士國立臺灣大學
光電工程學研究所
94
Piezoelectric semiconductor nanostructures can be treated as optical piezoelectric transducers to generate and detect acoustic nanowaves through the piezoelectric effects by femtoseocond pump-probe techniques. With the optical piezoelectric transducer, several physical issues and applications in nano-ultrasonics can be investigated. In this thesis, the theories of generation and detection of acoustic nanowaves in the optical piezoelectric transducers have been presented, and verified by experiments. With the theories and optical techniques, the design principles and characterization methods of the optical piezoelectric transducers have been illustrated from the viewpoint of acoustic engineering. We have discussed several topics such as acoustic sensors, narrowband and broadband acoustic wave generator, and frequency-tunable acoustic transducers. Based on the nano-acoustic system, several novel applications have been demonstrated in this thesis. Firstly, we have found that the energy distributions of electrons and holes can follow the band modulation due to the acoustic nanowaves in THz regime. These investigations imply the feasibility to utilize acoustic nanowaves for controlling electronic devices. Secondly, we have demonstrated that acoustic nanowaves can be utilized for ultrasonic imaging. The accuracy of one-dimensional ultrasonic scan measurement is less than one nanometer. For resolving a two-dimensional subsurface structure, the axial resolution is less than 20 nm while the transverse resolution can be less than 100 nm if the images are post-processed. We have demonstrated that the novel nano-ultrasonic technology has the advantages of non-destructive measurement, three-dimensional imaging capability, and nanometer resolutions, of which another state-of-the-art imaging technology does not possess all. Thirdly, to directly obtain a three-dimensional ultrasonic image with nanometer resolutions, the technique of generating acoustic nanospots has been demonstrated. With beam shaped optical pulses for exciting saturation carriers, the acoustic spot size can be smaller than the optical spot size, which is on the micron scale due to the diffraction limit. On the other hand, we have also used the nano-acoustic system to characterize nanowave devices. By using a single-quantum-well structure optical piezoelectric transducer, the waveforms of sub-THz or THz acoustic nanowaves can be directly measured in the time domain. We have used this method to experimentally obtain the reflection transfer function of a phononic bandgap nano-crystal, which can be served as a mirror for acoustic nanowaves. Moreover, we have investigated the energy propagation of bandgap waves in the phononic bandgap nano-crystal. Besides the piezoelectric semiconductor heterostructures, we have also demonstrated that acoustic nano-pulses can be generated in the depletion region of a p-n junction through the piezoelectric effects. The shape and width of the acoustic nano-pulses are determined by the depletion region, which can be controlled by an external bias. This interesting demonstration has shown the possibility to integrate electronic technologies for controlling acoustic nanopulses. In this study, the high optoacoustic conversion efficiency of the piezoelectric effects has also been experimentally confirmed in piezoelectric semiconductors.
37
Malabi, Rudzani. "Laser-based technologies for targeted drug delivery and label-free diagnostics in HIV-1." Thesis, 2019. http://hdl.handle.net/10500/27259.
Full textAbstract:
Human immunodeficiency virus type 1 (HIV-1) still causes a chronic infection that affects millions of individuals worldwide. The infection remains incurable and presents a huge challenge for treatment, as it tends to disable a patient’s immune system. Although the current HIV-1 treatment regime possesses the ability to reduce the viral load to undetectable limits, complete eradication of the virus cannot be achieved while latent HIV-1 reservoirs go unchallenged. These viral reservoirs are established early on during HIV-1 infection and are a major hurdle since they remain unaffected by antiretroviral drugs and have the ability to replenish systemic infections once treatment is interrupted. Further ailments with the highly active antiretroviral therapy (HAART) include issues such as the cumbersome lifelong treatment, development of drug resistant strains of HIV-1 and adverse side effects. Contrarily, early diagnosis of the HIV-1 infection and HIV-1 treatment is a major challenge in resource-limited countries. The current available diagnostic tools for HIV-1 infection have shown to be highly accurate in monitoring CD4+ T lymphocyte count and viral load measurements. However, these tests such as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) which are highly efficient, are usually very expensive with complex operation, time consuming, require skilled personnel and training that makes them incompatible for the application in resource-limited areas. Therefore, this raises the urgent need for developing an HIV point of care (POC) diagnostic tool that is label-free, highly specific and sensitive as well as therapeutic modalities, which can be used to address the previously mentioned challenges. Much research has been conducted to resolve these problems but to date, there has not been application of laser and/or photonics in HIV research. Therefore, in this thesis a femtosecond laser was used in HIV infected cells for targeted antiretroviral drug delivery while preserving their viability. For the first time according to our knowledge, antiretrovirals (ARVs) that target all the life stages of the HIV-1 life cycle were utilized and they proved to be significant in reducing HIV-1 infection. Furthermore, through the employment of a continuous wave laser at 640 nm, for the first time, surface plasmon resonance was conducted to facilitate label-free detection of HIV-1. Success of these laser based technologies will open doors for incorporation in POC HIV diagnostic tools for the detection and treatment monitoring of HIV in resource-limited settings.College of Engineering, Science and Technology
Ph. D. (Physics)