This thesis was aimed to develop, investigate and optimize high power Nd:YAG laser system for OPCPA (Optical Parametric Chirped Pulse Amplifiers) pump. The particular attention is paid for the temporal characteristics of the Nd:YAG amplifies output pulse. Employment of Fabry-Perоt etalons in the cavities of two-stage Nd:YAG regenerative amplifier enables for amplified pulse stretching from 60 fs to ~ 100 ps pulse widths. The modulation of amplified pulse envelope is minimal when ration of thickness of the etalons is around 2. Envelope modulation can be controlled by changing the reflectivity of etalons. In order to improve amplified pulse contrast, we for the first time to our knowledge implemented second order intensity dependent filter, based on the effect of fundamental pulse polarization rotation in unbalanced second harmonic generators. By using this method, the contrast of the output pulses was improved by >102 times. We also demonstrated that Gaussian pulses from the output of Nd: YAG amplifiers can be transformed into flat–top pulses by using cascade second harmonic generation processes. The developed high output energy Nd:YAG amplifiers system for OPCPA pumping is optically synchronized with pulses of Yb:KGW oscillator and features two 532 nm outputs with pulse parameters: a) Gaussian pulse profile, ~ 300 mJ energy, 75 ps pulsewidth; b) hiper- Gaussian pulse profile, ~100 mJ energy, pulse width 100-150 ps. / Disertacija yra skirta sukurti, ištirti ir optimizuoti didelės galios Nd: YAG lazerių sistemą efektyviam moduliuotos fazės signalų optinių parametrinių stiprintuvų kaupinimui. Ypatingas dėmesys yra skiriamas Nd:YAG stiprintuvų išvadinių impulsų laikinių parametrų formavimui. Pademonstravome, kad Fabry-Pero interferometrų panaudojimas Nd:YAG dvipakopio regeneracinio stiprintuvo rezonatoriuose leidžia stiprinamų impulsų trukmę padidinti nuo ~ 60 fs iki 100 ps. Tuo tarpu išvadinių impulsų laikinės plėtros mastas bei gaubtinės moduliacijos gylis gali būti valdomas keičiant etalonų atspindžio koeficientą, o jų gaubtinės moduliacijos vertė mažiausia, kai etalonų storio santykis artimas 2. Sustiprintų impulsų kontrasto gerinimui pirmą kartą pritaikėme netiesinį antros eilės filtrą, veikiantį fundamentinės spinduliuotės poliarizacijos sukimo, išderintame antros harmonikos generatoriuje, efekto pagrindu. Tokiu būdu Nd:YAG stiprintuvuose sustiprintų impulsų kontrasto vertė pagerinta apie 102 kartų. Taip pat pademonstruota, kad Nd: YAG stiprinimo sistemos išėjime naudojant pakopinius antros harmonikos generacijos procesus, Gauso formos impulsus galima transformuoti į hipergauso impulsus. Sukurta didelės išvadinės energijos pikosekundinė Nd:YAG stiprintuvų sistema yra optiškai sinchronizuota su užduodančio femtosekundinio Yb:KGW osciliatoriaus impulsais ir turi ~ 300 mJ , 75 ps trukmės Gauso impulsų bei 100 mJ, > 100 ps trukmės hipergauso laikinės formos impulsų išvadus.

A method to implement high-speed pulse shaping filters has been discussed. This technique uses a unique look up table based architecture implemented in 90nm CMOS using a standard cell based ASIC flow. This method enables the implementation of pulse shaping filters for multi-giga bit per second data transmission. In this work a raised cosine FIR filter operating at 4 GHz has been designed. Various Implementation issues and solutions encountered during the synthesis and layout stages have been discussed. In the second portion of this work, the design of a unique address based serial peripheral interface (SPI) for initializing, calibrating and controlling various blocks in a large system has been discussed. Some modifications have been made to the standard four-wire SPI protocol to enable high control speeds with lesser number of top-level pads. This interface has been designed to function in the duplex mode to do both read and write operations.

Neste trabalho é feito um estudo da formatação de pulsos ultracurtos de laser de Ti:Safira para a geração de segundo harmônico em cristal de KDP. Para a formatação dos pulsos, é utilizado um aparato que inclui um modulador espacial de luz de cristal líquido (LC SLM), que altera unicamente a fase espectral dos pulsos. Este aparelho tem a vantagem de não introduzir perdas durante a propagação da luz, além de sua ação ser controlada via computador, através de um software em LabVIEW. Utilizando uma função senoidal, é feito um estudo das limitações do controle da geração do segundo harmônico provindas da pixelação do LC SLM, isto é, do fato de que os elementos moduladores possuem tamanhos finitos e produzem uma modulação discreta ao longo das componentes espectrais do pulso. É apresentada a geração de luz sintonizável em torno de 400 nm por duplicação de frequências de pulsos cuja fase espectral é modulada por uma soma de funções senoidais de frequências diferentes. A largura de banda do ultravioleta produzido é da ordem de 1 nm, em contraste com a largura de linha de cerca de 12 nm do segundo harmônico gerado na ausência de modulação do pulso fundamental. A sintonização é feita basicamente através de uma varredura na fase das funções moduladoras do pulso fundamental. Esse tipo de sintonização nessa região do espectro possui algumas aplicações, tais como a microscopia seletiva por dois fótons ou mesmo a espectroscopia de um fóton. Para comprovar a utilidade da geração de segundo harmônico sintonizável, é apresentada uma medida espectroscópica da transmissão em uma amostra de cloreto de európio, sendo que os resultados obtidos concordaram com as medidas da mesma amostra realizadas em um espectrofotômetro, com o mínimo de transmissão em cerca de 394 nm. / This work presents a study on the shaping of ultrashort pulses of a Ti:Sapphire laser for second harmonic generation in KDP crystals. To achieve the pulse shaping, a setup based on a phase-only crystal-based spatial light modulator (LC SLM) is used. This device has the advantage of low loss, and can be computer controlled, by means of a LabVIEW software. The use of a sinusoidal function, allows to study the limitations of the second harmonic generation due to the pixelation of the LC SLM, i. e., due to the fact that the modulating elements have finite sizes and produce a stepwise modulation along the spectral components of the pulse. The generation of tunable light around 400 nm by frequency doubling of laser pulses is presented for the case where the spectral phase is modulated by a sum of sinusoidal functions with different frequencies. The linewidth of the ultraviolet band produced is narrower than 1 nm, in contrast to the 12 nm linewidth of the non-modulated incident spectrum. The tuning is done primarily through a sweep in the phase of the modulating functions of the fundamental pulse. The possibility of tuning in this region of the spectrum has a few applications, such as in selective two-photon microscopy or even in one photon spectroscopy. To demonstrate the usefulness of tunable second harmonic generation, a spectroscopic measurement of the transmission in a sample of europium chloride is presented, and the results agreed with the measures of those performed in a spectrophotometer, with the minimal transmission occurring around 394 nm.

Constantly increasing demand for wireless communications in various applications has always led to new ways of modulating the radio frequency (RF) carrier signal by advancing waveform structure throughout generations. Although communication data rates are limited by the theoretical capacity, specific signaling designs for the signal that experiences natural and artificial effects in the transmission medium such as multipath fading channel, hardware impairments and multiuser environment promised better solutions in providing improved wireless access to various type of users and networks. Besides communication capacity, broadcasting nature of radio signals poses the information security as another main concern in wireless communications. In this dissertation, new advanced methods for improving signal statistics in multiple domains are studied. Instead of focusing on a single aspect, the waveform design approaches studied in this dissertation tackle with improving the orthogonal frequency-division multiplexing (OFDM)-based signaling in multiple perspectives such as out-of-band (OOB) emission reduction, peak-to-average-power ratio (PAPR) reduction, and secure transmission with minimum or no eect at the receiver side. Various concepts are coherently exploited while achieving aforementioned goals with minimal cost such as unexplored spaces in the signal space like (CP), guard band, multipath fading; multivariate nature of the multicarrier signals; time spreading and location uniqueness of the wireless channels. The proposed techniques are analyzed theoretically and performance results are presented including related previous works in the literature. It is worth noting that the methods presented in the dissertation can be easily applicable to conventional OFDM systems thanks to having no or minimal change in the receiver structure.

Dans le cadre de cette thèse, nous avons construit et caractérisé un soustracteur de photons uniques pour l'ingénierie d'états quantiques de la lumière. Le but étant de réaliser une soustraction de photon pure et spectralement sélective sur une ressource multimode dans le domaine spectral. Ce soustracteur repose sur une interaction paramétrique de somme de fréquence entre un faisceau signal et un faisceau de contrôle au sein d'un milieu non-linéaire. Le spectre du faisceau de contrôle est mis en forme à l'aide d'un procédé de mise en forme d'impulsion. Le photon convertit est filtré et détecté grâce à détecteur de photon unique. Le soustracteur est donc la combinaison de tous ces éléments successifs. Nous avons développé un cadre théorique décrivant la soustraction multimode de photons uniques et montré qu'elle peut être décrite, peu importe l'implémentation, par une matrice de soustraction dans une base de modes. Grâce à ce formalisme, nous avons montré que le processus pouvait être caractérisé sans mesurer le signal transformé mais simplement en lui substituant un faisceau sonde dont les impulsions sont aussi mises en forme. Nous avons réalisé une tomographie du processus au niveau du photon unique pour une large gamme de faisceaux de contrôle différents. Nos résultats sont correctement décrits par la théorie développée et démontre la pureté du processus ainsi que l'agilité de la technique employée. / During this thesis, we have built and characterized a single-photon subtractor to engineer the quantum states of light. The aim is to perform a pure and spectrally selective photon subtraction on a multimode resource in the spectral domain. This subtractor consists in a parametric sum-frequency interaction between a signal beam and a control beam within a non-linear medium. The optical spectrum of the control beam is shaped using ultrafast pulse shaping. The up-converted photon is filtered and detected by a single-photon detector. The subtractor is therefore the combination of all these successive elements. We have developed a theoretical framework to describe the multimode subtraction of a single photon and showed that it can be summed up by a subtraction matrix in a modal basis independently of the physical implementation. Thanks to this formalism, we have shown that the process can be characterized without measuring the transformed signal beam but simply by using a probe beam whose pulses are also shaped. We carried out a process tomography at the single-photon level for a wide range of different control beams. Our results are correctly described by the theory we developed and demonstrates the purity of the process as well as the agility of the technique we used.

Processing of Si in the semiconductor and solar cell industry has been dominated by the Diode Pumped Solid State (DPSS) Ultraviolet (UV) laser. Recent advances in laser source technology have produced fibre lasers with Master Oscillator Power Amplifier (MOPA) architectures that offer high repetition rates, high operational efficiencies, and pulse modulation controls exceeding those of typical Q-switched DPSS lasers. The aim of this research is to investigate 1 μm fibre laser machining of Si with a view to identifying the influential laser parameters for optimum processing of high quality, high efficiency micro drilling and surface texturing applications. A secondary aim is to develop a greater understanding of the laser material interactions and material removal mechanism when using fast rise-time nanosecond laser pulse envelopes. The IR fibre laser was able to perform percussion drilling and single pulse machining on the polished Si over a range of intensities up to 1.22 GW/cm2. With the optimum parameters, the micro-sized holes generated by the IR laser have a well defined edge, no heavy recast and no cracks. With a pulse shape of fast rise time (<7.5 ns for a 10-90% rise in signal), a high front peak power zone (approaching 14 kW) and an energetic long tail (40-180 ns), the absorption coefficient of Si at IR wavelength increased dramatically with time and temperature due to the fact that the liquid Si has a metal like absorption behavior. As a result, Si was quickly melted and the rest of pulse energy was able to remove the liquid Si effectively. The machining process left a limited amount of resolidified melt droplets and vapor condensates, which could be washed off ultrasonically. The drilling process was energy efficient when melt expulsion dominated the machining mechanism (0.08-0.2 mJ pulse energy depending on the pulse durations). The low energy pulse (~0.2 mJ) can achieve similar depth as the high energy pulse (~0.7 mJ), so high repetition rates of 100 kHz can be used to instead of 25 kHz, resulted in high processing speed. In addition, by comparing the single pulse machining with the state of the art UV laser, the IR fibre laser machined deeper features and better surface finish in the pulse energy region of >0.07 mJ. With the pulse shaping capability, the material properties can be varied and the wavelength factor can be minimized. The results suggest that applications like microvia drilling can now be carried out with the more flexible and low cost IR fibre laser. The increased repetition rates of fibre laser can increase production speed to satisfy the needs of drilling ~10 thousands holes per second, required by the modern semiconductor and solar cell production. The shortened optical penetration length of 1 μm wavelength laser on Si with increasing temperature and sufficient thermal diffusion length resulted from the asymmetrical fibre laser pulse and the dynamic properties of Si produced a thick liquid layer. A one-dimensional heat conduction model based on the surface heating source predicted that this superheated liquid layer was able to stay above 4706 K (0.905 times the thermal critical temperature 5200 K of Si) for longer than 70 ns to induce explosive boiling. This proposed material removal mechanism was also confirmed by the shadowgraph images, showing particulates ejection lasting up to ten microseconds after the laser pulse. The estimated hole depth based on the explosive boiling alone were different from the measured ones at varying peak power densities (<1.22 GW/cm2) but fixed pulse duration (200 ns), since Si was removed by a mixture of mechanisms. With varying pulse durations (40-200 ns) but fixed peak power density (~0.63 GW/cm2), the estimated depth based on the explosive boiling was in close agreement with the measured ones (6% difference on average). The SEM images at this power density showed a micron- /submicron-sized debris field, which was also observed with the explosive boiling in the past. Although the improved quality of Si machining was demonstrated with the 1 μm MOPA based fibre laser, the setup of this system was only applicable to surface texturing, blind holes and through holes of less than 100 μm in depth. Further research is required to demonstrate the capability of more energetic pulse with higher peak power and large pulse duration range to explore more machining options.

No description available.

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 iv 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 equipments 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.

No description available.

La surface d’un matériau exposé à une irradiation laser à une fluence proche de son seuil d'ablation laisse apparaître des structures périodiques LIPSS (Laser Induced Periodic Surface Structure) d’orientation dépendant de la polarisation de faisceau incident et dont la période est de l'ordre de la longueur d'onde. Les causes de ce phénomène qui suscite l'attention des chercheurs depuis plus d’une trentaine d’années sont maintenant bien connues. Cependant, son étude dans le cadre de l'utilisation récente de lasers à impulsions ultra-brèves fait surgir de nouvelles interrogations et relance l'intérêt pour le sujet. Ce travail est consacré à l’étude dynamique de la formation des nanostructures sur une surface métallique suite à une interaction laser femtoseconde. Nous nous intéressons aux mécanismes responsables de la formation de ces structures et nous proposons des explications permettant de comprendre leur origine. Dans le premier chapitre on présente une étude de l’état de l’art sur la formation des LIPSS, on y aborde les paramètres influant sur la formation de ces structures ainsi que les différents modèles explicatifs élaborés par les chercheurs. Ce chapitre traite également de l’interaction laser matière et de ses différents processus. Le deuxième chapitre met l’accent sur les dispositifs expérimentaux réalisés dans ce cadre. Le troisième chapitre présente, quant à lui une étude expérimentale permettant de rendre compte du rôle de l’excitation du plasmon de surface dans la formation de LIPSS. Dans le quatrième chapitre on analyse les résultats relatifs à l’influence du couplage électron phonon sur la formation des LIPSS. Enfin, le cinquième et dernier chapitre met en évidence le rôle de la relaxation électron-phonon sur la formation des LIPSS à l’aide d’une expérience pompe-sonde / When a material is irradiated with laser fluency close to its ablation threshold, periodic surface structures LIPSS (Laser Induced Periodic Surface Structure) appears on its surface. These structures are dependent of the polarization vector of incident electric field and their periods are close to the laser wavelength. They have been extensively studied for more than thirty years, and their origins are quite well understood. However, the recent use of ultra-short laser sources has renewed the subject. Present work is dedicated to the dynamics study of the nanostructures formation on a metal surface by femtosecond laser irradiation. We are interested in mechanisms responsible for the formation of these structures and we propose an explanation of their origin. The first chapter presents a literature review on the formation of LIPSS. Here, the parameters affecting the formation of these structures as well as a different models developed by researchers will be discussed. This chapter also addresses the laser material interaction and its processes. The second chapter focuses on the experimental devices used in this context. The third chapter deals with the experimental study concerning the role of excitation of surface plasmon in the formation of LIPSS. In the fourth chapter, the results on the influence of electron phonon coupling on the formation of LIPSS are analyzed. Finally, the last chapter highlights the role of electron-phonon relaxation on the formation of LIPSS using pump-probe experiments