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Ultrafast laser systems based on Cr-doped ZnSe/S gain media can provide powerful, flexible laser light in the mid-infrared. Beyond their mid-infrared output, Cr:ZnSe/S lasers often possess a second-harmonic output. Second harmonic is naturally generated via random quasi-phasematching (RQPM) in polycrystalline ZnSe/S when driven by infrared light. In Cr:ZnSe/S lasers, this second-harmonic generation (SHG) can often reach powers comparable to the output powers of conventional pulsed laser systems, on the order of hundreds of milliwatts. Although interesting, there has been limited experimental investigation into this naturally generated SHG. In this thesis, we tackle the problem of measuring these SHG pulses. The measurement of these ultrafast pulses requires an understanding of nonlinear optical interactions as well as the development of both precision electronics and optics. In this thesis, background is provided on the nonlinear interactions that lead to SHG as well as the techniques and instrumentation necessary to measure ultrafast pulses. Additionally, the development of high-gain, low-noise transimpedance amplifiers for pulse measurement is described. Furthermore, a precision optical system for the measurement of SHG pulses from a Cr:ZnSe/S laser is presented and initial measurement results are discussed.

Ultrashort pulses are important for resolving electron motion in semiconductors to measure electronic transport properties. Electron wave packet motion is on the order of attoseconds, requiring temporal resolution on this time scale. However, a major constraint on femtosecond (1 fs = 10−15 s) and attosecond (1 as = 10−18 s) science is how well we can control and compress the excitation and measurement pulses in pump-probe experiments. Such ultrashort pulses require a broad spectrum with careful phase control across its bandwidth to minimize the duration. We discuss a new optical measurement technique that can directly measure the electric field that constitutes the laser pulse. We find that compared to other techniques for electric field measurements, our method is relatively inexpensive and robust in characterizing pulses around 100 fs regime and below. This method requires only a commercially available CCD camera as opposed to spectrometers or other expensive instruments and provides the ability to reconstruct the electromagnetic field without ambiguities. The measurements from our technique only require a small fraction of the incoming beam to give accurate results. In this way, we can directly measure the temporal evolution of the field amplitude and phase. We developed the technique in single shot, providing a real-time access to measurements, hence can be used to optimize pulse compression experiments in real-time. We characterized pulses from 115 fs down to 30 fs using this technique, bench-marked against other well-established pulse characterization methods.

Orientador: Rene Alfonso Nome Silva Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química Resumo: Polímeros de PEG-PEO tem sido muito utilizado em diversas áreas, incluindo novas energias, como o aumento da condução de prótons em células a combustível e condução de íons em eletrólitos poliméricos de baterias. Previamente, estudos de partição de polímero PEO em sistemas bifásicos aquoso/orgânico em função do peso molecular do polímero e também de sua concentração foram reportados. Este trabalho também reportou a conexão entre os resultados termodinâmicos e os mecanismos a nível microscópico, incluindo a extensão da hidratação em cada uma das duas fases. Em nosso grupo, previamente nós reportamos medidas de espectroscopia de femtossegundos em soluções de eletrólitos simples integradas em células eletroquímicas para estudar os efeitos do potencial eletroquímico aplicado sobre a dinâmica molecular. No presente trabalho, nós realizamos medidas de espectroscopia de femtossegundos no mesmo sistema, em função da concentração, incluindo as fases aquosa e orgânica do sistema bifásico, bem como os experimentos-controle com solventes puros e as misturas binárias monofásicas correspondentes em cada uma das concentrações. Os resultados experimentais são usados para caracterizar as escalas de tempo fundamentais nas escalas de femtossegundos e picossegundos para cada fase, além de obter as densidades espectrais Raman de baixa-frequência. Os resultados são consistentes com estudos de partição descritos previamente. No domínio da frequência, os resultados são usados para discutir como a aditividade das densidades espectrais depende das interações entre o sistema e o banho para cada amostra estudada. Em termos mais gerais, nós discutimos como a técnica de espectroscopia ultrarrápida utilizada neste trabalho se conecta com experimentos de partição e calorimétricos, e também em como a dinâmica ultrarrápida do sistema se correlaciona com o mecanismo macroscópico de partição inferido a partir de medidas termodinâmicas Abstract: PEG-PEO polymers have been widely used in several areas, including new energies, such as increasing proton conduction in fuel cells and ion conduction in polymeric battery electrolytes. Previously, studies of PEO polymer partitioning in two-phase aqueous/organic systems as a function of the molecular weight of the polymer and also of its concentration were reported. This work also reported the connection between thermodynamic results and mechanisms at the microscopic level, including the extent of hydration in each of the two phases. In our group, we previously reported femtosecond spectroscopy measurements on simple electrolyte solutions integrated into electrochemical cells to study the effects of applied electrochemical potential on molecular dynamics. In the present work, we performed femtosecond spectroscopy measurements in the same system, as a function of concentration, including the aqueous and organic phases of the two-phase system, as well as control experiments with pure solvents and the corresponding single-phase binary mixtures at each of the concentrations. The experimental results are used to characterize the fundamental time scales in the femtosecond and picosecond scales for each phase, in addition to obtaining the low-frequency Raman spectral densities. In general, we observed ultra-fast dynamics with shorter time scales in the two-phase mixtures, compared to the corresponding binary mixtures. The results are consistent with previously described partition studies. In the frequency domain, the results are used to discuss how the additivity of spectral densities depends on the interactions between the system and the bath for each sample studied. In more general terms, we discuss how the ultrafast spectroscopy technique used in this work connects with partitioning and calorimetric experiments, and also how the ultrafast dynamics of the system correlates with the macroscopic partitioning mechanism inferred from thermodynamic measurements Mestrado Físico-Química Mestra em Química CAPES 001

Orientador: René Alfonso Nome Silva Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química Resumo: Nos últimos anos, várias descobertas vêm sendo realizada sobre como características intrínsecas de um dado sistema podem afetar a transferência eletrônica de energia. Um dos objetivos desta pesquisa é estudar experimentalmente como a estrutura vibrônica pode afetar a transferência eletrônica de energia em moléculas orgânicas segundo o modelo de Förster. Utilizando um sistema molecular com sobreposição espectral sobre bandas vibrônicas bem definidas, podemos verificar experimentalmente que o abaixamento da intensidade de emissão do doador unicamente nos comprimentos de onda de absorção do receptor caracteriza transferência de energia pelo modelo emissivo. Abaixamento da intensidade integrada de emissão caracteriza transferência de energia pelo mecanismo de Förster. A taxa de transferência de energia pelo mecanismo de Förster foi mais significativa quando a sobreposição espectral ocorre nas bandas vibrônica 0-1,0-2 ao invés da banda 0-0. Na segunda parte do trabalho realizado, aplicamos a técnica de absorção transiente para o estudo de nano prismas de ouro depositados sobre dois substratos diferentes. Neste trabalho, nós descrevemos a preparação e caracterização de matrizes isoladas de nanoprismas triangulares de ouro sobre o vidro contendo uma camada de ITO por litografia de nanoesferas. O espectro de absorção linear de Au / vidro e Au / ITO / vidro exibe ressonância de plásmon de superfície em 800 nm e 870 nm, com um deslocamento para o vermelho de 70 nm associado ao índice de refração de ITO. Foram realizadas medidas de espectroscopia de uma única cor de bombeio e prova com resolução temporal de 100 fs em comprimentos de onda inferiores a ressonância, em ressonância, e acima da ressonância de plásmon de superfície para cada um destes dois sistemas. A dinâmica ultra-rápida em ambos os sistemas pode ser bem descrita com um modelo que contabiliza o espalhamento elétron-elétron, o acoplamento elétron-fônon, e oscilações acústicas no término do resfriamento da estrutura de ouro. Os resultados para as nanopartículas de ouro, para cada um dos comprimentos de onda são bem descritos como tendo índice de refração complexo com dependência do comprimento de onda, que modula os sinais de bombeio e prova medidos Abstract: Structure-property relationships for electronic energy transfer have been investigated in recent years. One of the goals of the present research is to perform an experimental study vibronic structure effects in electronic energy transfer between small organic molecules according to Forster¿s model. We have chosen organic molecules with well-defined spectral overlap between vibronic bands, which enabled us to experimentally characterize a decrease in donor emission intensity at the acceptor absorption wavelengths thereby indicating radiative energy transfer. A decrease in the emission integrated intensity characterizes energy transfer by the Forster mechanism. Forster energy transfer rates were higher when the spectral overlap involved 0-1 and 0-2 vibronic bands rather than 0-0 band. In the second part of this work, we have employed ultrafast transient absorption spectroscopy to investigated gold nano prisms deposited over two different substrates: Au over glass (Au/glass) and Au over ITO deposited on glass (Au/ITO/glass). In the present work, we describe the preparation and characterization of these two samples employing the nanosphere lithography technique. The linear absorption spectra of Au/glass and Au/ITO/glass respectively show surface plasmon resonances at 800 nm and 870 nm, with a 70nm redshift attributed to the ITO refractive index. We have performed femtosecond one-color pump-probe measurements with 100 fs time resolution below the surface plasmon resonance, at resonance, and above the surface plasmon resonance for each of these two systems. For both systems, the ultrafast dynamics can be well described with a model that takes into account electron-electron scattering, electron-phonon coupling, phonon-phonon coupling and acoustic damping. The wavelength-dependence observed can be explained in terms of the sample frequency-dependent complex refractive index which modulates the measured pump-probe signals Mestrado Físico-Química Mestre em Química

Orientador: Pablo Sebastián Fernández Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química Resumo: A eletroquímica é uma área de extremo impacto que atinge diversos segmentos da economia, ciência e tecnologia. A eletrocatálise é particularmente relevante devido à sua presença em diversas aplicações industriais e ambientais, além de grande relevância no armazenamento e produção de energia. Neste contexto, compreender o eletrodo e a interface eletrodo/solução é, sem dúvida, necessário para que possamos melhorar as reações eletrocatalíticas existentes. Assim, o desenvolvimento de novas técnicas para examinar esses sistemas é essencial para obtermos novas informações sobre eles, a fim de proporcionar melhorias futuras na área. Neste trabalho apresentamos o desenvolvimento de instrumentação para realizar medidas eletroquímicas acopladas a espectroscopia de femtossegundos e imageamento por difração coerente de Bragg. A dinâmica do eletrólito no lado da solução da interface eletroquímica é estudada usando espectroscopia de femtossegundos, mais especificamente a espectroscopia de efeito Kerr óptico. Além disso, mostramos como as medidas de BCDI permitem obter imagens de alterações na morfologia das nanopartículas e observar sua deformação (em 3D), um parâmetro que pode influenciar fortemente o comportamento eletrocatalítico de materiais nanocristalinos. Vale ressaltar que essas técnicas espectroscópicas, e a instrumentação específica a ser desenvolvida, estarão disponíveis tanto em nosso grupo para futuras colaborações quanto na linha de luz Carnaúba do SIRIUS para serem aplicadas em qualquer estudo na área de eletroquímica por futuros usuários externos Abstract: Electrochemistry is an extremely impactful field, which affects several segments in economy, science, and technology. Electrocatalysis is particularly relevant due to its presence in several industrial and environmental applications, and extreme relevance in energy storage and production. In this context, understanding the electrode and electrode-solution interface is undoubtedly necessary to improve the existing electrocatalytic reactions. Thus, the development of new techniques to probe these systems is essential in order to get new information about them for further improvements in the field. Herein, we show the development of instrumentation to perform electrochemical measurements coupled to both femtosecond spectroscopy and Bragg coherent diffraction imaging. The electrolyte dynamics at the solution side of the electrochemical interface is probed using femtosecond spectroscopy, more specifically optical Kerr effect spectroscopy. In addition, we show how BCDI can be used to image changes in the nanoparticle morphology and to observe its strain (in 3D), a parameter that can strongly influence the electrocatalytic behavior of nanocrystalline materials. It is worth noting that these techniques, and the specific instrumentation being developed, will be available both in our group for future collaborations and in the Carnaúba beamline at SIRIUS to be applied in any study in the field of electrochemistry for future external users Mestrado Físico-Química Mestre em Química CNPQ 136436/2019-6 FAPESP 2019/13888-6

This dissertation is intended for parametric light oscillators synchronously pumped by femtosecond pulses of Yb:KGW laser (SPOPO), which generate tunable radiation in the near infrared spectral range. Such devices generate pulses at a high repetition rate (>50 MHz) and have recently become increasingly used in nonlinear microscopy and spectroscopy. Various periodically polished nonlinear crystals (PPLN, MgO: PPLN, PPKTP) were tested and the peculiarities of the radiation generated by such SPOPO were investigated. In the case of PPKTP SPOPO, the 40 % conversion efficiency from pump power into signal power in the range of ∼1500 nm was demonstrated. It was shown that an increasing of a transmittance of the output mirror of the SPOPO, which cavity is characterized by total negative group delay dispersion, results in a shortening of the generated signal pulses. In this work, the resistance of nonlinear crystals used in SPOPO devices to high-repetition laser radiation was investigated and a nonlinear absorption measurement method was demonstrated, which allows to estimate the limits of such resistance without damaging these crystals. Also, the investigation of dependency of continuum generation in the optical fiber on a pump wavelength in the region of zero dispersion wavelength using PPKTP SPOPO pulses, tunable in the 1,45-1,8 µm spectral range, was demonstrrated.

Agradecimentos: The authors would like to thank the LNLS staff for technical support. This work received financial support from FAPESP (the Sao Paulo Research Foundation, Process number 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil's National Oil, Natural Gas and Biofuels Agency) through the R\&D levy regulation, National Council for Scientific and Technological Development, CNPq (401581/2016-0), the Swedish-Brazilian collaboration STINT-CAPES (9805/2014-01) and the Swedish Research Council VR (Grant 2017-04162). We acknowledge SNIC for allocated computing time on NSC and Uppmax. CC acknowledges the Helmholtz Association through the CFEL at DESY, the Swedish Research Council (VR Grant No. 2018-05973) Abstract: We present a combined experimental and theoretical study of the fragmentation of molecular CS2 after sulfur 1s Auger cascade decay, consisting of electron-multi-ion coincidence spectra of charged fragments and theoretical simulations combining density functional theory and molecular dynamics. On the experimental side, a procedure for a complete determination of all sets of ions formed is described. For many of the fragmentation channels, we observed a higher charge in one of the sulfur atoms than the other atoms. Based on these observations and the theoretical simulations where the time scale of the nuclear motion and decay is taken into account, we propose that KLL Auger decay after the 1s core hole creation, via 2p double hole states, results in highly charged and strongly repulsive states with one localized core hole. These localized core holes are sufficiently long-lived that some will decay after fragmentation of the molecular ion, thereby efficiently impeding charge exchange between the fragments FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

We generated 106-fs, 4.1-nJ pulses at 778 nm from a single green diode-pumped multipass-cavity Kerr-lens mode-locked Ti3+:sapphire laser. To our knowledge, these represent the highest pulse energies generated directly with a diode-pumped Ti3+:sapphire laser., NA

Date of Conference: 31 July-4 August 2017 Conference Name: 12th Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2017 We report a single-mode, 42 MHz, 3.5-W average power chirped pulse amplification fiber laser system operating at 1560 nm. The laser system comprises a dispersion-managed mode-locked oscillator and twoamplifier stages. The output pulses are compressed to 180 fs by using two diffraction gratings.

Femtosecond X-ray scattering offers the opportunity to investigate reversible lattice dynamics with unprecedented accuracy. We show in a prototype experiment how strain propagation modifies the functionality of a ferroelectric system on its intrinsic time scale.

Femtosecond written fiber Bragg gratings, have shown great potential for sensing in extreme environments. This paper discusses the fabrication and deployment of several fs-IR written FBG arrays, for monitoring main-spool skin temperatures of an entrained-flow gasifier, as well as the internal temperature gradient of a fluidized bed combustor., 24th International Conference on Optical Fibre Sensors, OFS 2015, September 28- October 2, 2015, Series: Proceedings of SPIE; no. 9634

The study of the dynamical evolution of a system, e.g. a chemical reaction or a phase transition, has become nowadays a subject of growing scientific interest. The direct observation of the steps and the structural changes through which chemical reactions and phase transitions occur requires the study of out-of-equilibrium intermediate states, with a typical time scale of femtoseconds (10─15s) and with high spatial resolution (10─10m), for molecules as well as for complex biological samples and for condensed matter systems. In this frame, Ultrafast Electron Diffraction (UED) allows for the observation of changes in the response function of different systems through phase transitions and chemical reactions, with atomic resolution, at the femtosecond (fs) time scale. In this thesis the implementation of a flexible UED set-up capable of working in both transmission and RHEED geometries with 30 keV electrons is described; the experiment is characterized by 300 fs time-resolution for bunches containing up to 105 electrons at 20 kHz, and constitutes the first demonstration of far-field and small-angle diffraction (from few Å to a few tens of nm spatial resolution) with electrons in a single diffractometer. The transverse coherence of the probing electrons can be tuned at the cost of brightness, enabling the observation of the speckle pattern originating from the constructive and destructive interference of the scattered waves from a sample. Diffractive Imaging is carried out to study complex ordering/disordering phenomena in structure, charge and spin textures, with time resolution. The investigation of the dynamics of a supracrystal of alkanethiol-coated gold nanoparticles is reported, and its photo-induced thermal disorder is reconstructed in a real-space movie alongside with an ordering transition of the organic ligands in the picosecond (ps) time scale, by means of UED. The same principles developed for the analysis of the gold nanoparticles diffraction patterns, based on Angular Cross-Correlation and Angular Normalized Intensity Analysis, are applied to the speckle pattern from spin textures detected in Lorentz microscopy. With this aim, magnetic field-dependent diffractive imaging of spin textures in the Dzyaloshinkii-Moriya chiral insulator Cu2OSeO3 is carried out with cryo- Lorentz TEM. Following a similar approach, ultrafast diffractive imaging on the charge density modulation in the Charge Density Waves system 1T-TaS2 is demonstrated. Finally, the main conclusions are summarized and the potential for extending the applicability of the UED system to the regime of ultrafast coherent diffractive imaging and inline holography using 30 keV electrons on a table-top is described.

We report the first demonstration of femtosecond pulse generation from a Cr:LiSAF laser mode-locked with a monolayer graphene saturable absorber. Nearly transform-limited 72-fs pulses were generated at 850 nm with only two 135-mW pump diodes.

[EN] We demonstrated a simple diffractive method to map the self-similar structure shown in squared radial coordinate of any set of circularly symmetric fractal plates into self-similar light pulses in the corresponding temporal domain. The space-to-time mapping of the plates was carried out by means of a kinoform diffractive lens under femtosecond illumination. The spatio-temporal characteristics of the fractal pulses obtained in this way were measured by means of a spectral interferometry technique assisted by a fiber optics coupler (STARFISH). Our proposal allows synthesizing suited sequences of focused fractal femtosecond pulses potentially useful for several current applications, such as femtosecond material processing, atomic, and molecular control of chemical processes or generation of nonlinear effects. © 2012 Optical Society of America., This research was funded by the Spanish Ministerio de Ciencia e Innovación (MICINN) and FEDER, through the projects FIS2010-15746, DPI2008-02953, and SAUUL (CSD2007-00013) and the Fundació Caixa Castelló (P1-1B2010-26).

We propose a new approach to split up the velocities of atoms of flexible molecules into translational, rotational, and vibrational components. As a result, the kinetic energy of the system can easily be expressed in terms of only three parts related to the above components. This is distinct from the standard Eckart method, where the cumbersome Coriolis contribution to the kinetic energy appears additionally. The absence of such a contribution within the proposed approach allows us to readily extend the microcanonical multiple-time-step dynamics of flexible molecules to the canonical-isokinetic Nos\'e-Hoover chain ensemble by explicitly integrating the translational, orientational, and vibrational motion. The previous extensions dealt exclusively with translational degrees of freedom of separate atoms, leading to a limitation on the size of the outer time step of 100 femtoseconds. We show on molecular dynamics simulations of the flexible TIP3P water model that the new canonical-isokinetic formulation gives a possibility to significantly overcome this limitation. In particular, huge outer time steps of order from a few hundred femtoseconds up to several picoseconds can now be employed to study conformational properties without loss of accuracy.

Cataloged from PDF version of article. We report on the development of a ultrafast fiber laser-microscope system for femtosecond photodisruption of biological targets. A mode-locked Yb-fiber laser oscillator generates few-nJ pulses at 32.7 MHz repetition rate, amplified up to similar to 125 nJ at 1030 nm. Following dechirping in a grating compressor, similar to 240 fs-long pulses are delivered to the sample through a diffraction-limited microscope, which allows real-time imaging and control. The laser can generate arbitrary pulse patterns, formed by two acousto-optic modulators (AOM) controlled by a custom-developed field-programmable gate array (FPGA) controller. This capability opens the route to fine optimization of the ablation processes and management of thermal effects. Sample position, exposure time and imaging are all computerized. The capability of the system to perform femtosecond photodisruption is demonstrated through experiments on tissue and individual cells. (c) 2012 Optical Society of America

We used the world's first hard x-ray FEL to investigate the response of molecular systems to the ultra-intense, femtosecond x-ray radiation. We report sequential multiphoton ionization, frustrated absorption and double core hole production mechanisms.

The majority of the applications of ultrashort laser pulses require a control of its spectral bandwidth. In this paper we show the capability of volume phase holographic gratings recorded in photopolymerizable glasses for spectral pulse reshaping of ultrashort laser pulses originated in an Amplified Ti: Sapphire laser system and its second harmonic. Gratings with high laser induce damage threshold (LIDT) allowing wide spectral bandwidth operability satisfy these demands. We have performed LIDT testing in the photopolymerizable glass showing that the sample remains unaltered after more than 10 million pulses with 0,75 TW/cm2 at 1 KHz repetition rate. Furthermore, it has been developed a theoretical model, as an extension of the Kogelnik's theory, providing key gratings design for bandwidth operability. The main features of the diffracted beams are in agreement with the model, showing that non-linear effects are negligible in this material up to the fluence threshold for laser induced damage. The high versatility of the grating design along with the excellent LIDT indicates that this material is a promising candidate for ultrashort laser pulses manipulations. © 2010 Optical Society of America.

Ultrashort-pulse lasers operating around the 2-μm spectral region are of great interest for applications in time-resolved spectroscopy, nonlinear frequency up-conversion to the mid/far-infrared spectral regions, mid-IR supercontinuum generation, optical communications and photomedicine. Tm 3+ doped crystalline gain media represent an attractive option for development of high-power, broadly tunable diode-pumped lasers around 2 μm that can be readily configured for ultrashort pulse generation through appropriate mode locking schemes. The best results in terms of pulse duration have to date been obtained with a Tm:KLu(WO 4) 2 laser [1] that produced 10-ps pulses at 1944 nm and a Tm:GdLiF 4 laser that generated ∼17-44 ps pulses tuned from 1868 nm to 1926 nm. [2] Here we report, for the first time to our knowledge, a femtosecond Tm 3+:KY(WO 4) 2 (Tm:KYW) laser that operates in the 1985-2065 nm spectral range by incorporating a semiconductor saturable absorber mirror (SESAM) © 2011 IEEE., 2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011, 22 May 2011 through 26 May 2011, Munich

Cataloged from PDF version of article. We propose and demonstrate the use of short pulsed fiber lasers in surface texturing using MHz-repetition-rate, microjoule- and sub-microjoule-energy pulses. Texturing of titanium-based (Ti6Al4V) dental implant surfaces is achieved using femtosecond, picosecond and (for comparison) nanosecond pulses with the aim of controlling attachment of human cells onto the surface. Femtosecond and picosecond pulses yield similar results in the creation of micron-scale textures with greatly reduced or no thermal heat effects, whereas nanosecond pulses result in strong thermal effects. Various surface textures are created with excellent uniformity and repeatability on a desired portion of the surface. The effects of the surface texturing on the attachment and proliferation of cells are characterized under cell culture conditions. Our data indicate that picosecond-pulsed laser modification can be utilized effectively in low-cost laser surface engineering of medical implants, where different areas on the surface can be made cell-attachment friendly or hostile through the use of different patterns. (C) 2011 Optical Society of America

We report on the generation of high-average-power and high-peak-power ultrashort pulses from a mode-locked fiber laser operating in the all-normal-dispersion regime. As gain medium, a large-mode-area ytterbium-doped large-pitch photonic-crystal fiber is used. The self-starting fiber laser delivers 27 W of average power at 50:57 MHz repetition rate, resulting in 534 nJ of pulse energy. The laser produces positively chirped 2 ps output pulses, which are compressed down to sub-100 fs, leading to pulse peak powers as high as 3:2 MW. © 2011 Optical Society of America.

Using the tools of femtosecond X-ray diffraction [1], electron diffraction [2] and laser-induced recollision [3], scientists are developing new methods to image chemical reactions as they occur. However, all of these methods face a common problem - only a small fraction of the molecules can be excited with an ultrashort pulse. When this problem was confronted in femtochemistry, a careful selection of the probe wavelength provided a way to discriminate excited molecules from unexcited molecules. Spectral selection is not available for any of these new methods. © 2011 IEEE., 2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011, 22 May 2011 through 26 May 2011, Munich

Conference name: Advanced Solid-State Photonics 2011 We report the generation of 830 nJ energy from a mode-locked all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. After external compression, 550 fs pulses with 1.2 MW peak power are demonstrated. © 2011 OSA.

Efficient mode-locking in a Tm:KY(WO4)(2) laser is demonstrated by using InGaAsSb quantum-well SESAMs. Self-starting ultrashort pulse generation was realized in the 1979-2074 nm spectral region. Maximum average output power up to 411 mW was produced around 1986 nm with the corresponding pulse duration and repetition rate of 549 fs and 105 MHz respectively. Optimised pulse durations of 386 fs were produced with an average power of 235 mW at 2029 nm. (C) 2011 Optical Society of America Publisher PDF

The broadband parametric upconverted conical emission (CE) has been investigated in a ?-barium borate crystal with phase matching angles away from second harmonic generation. A broad range of CE from 340 to 800 nm has been observed by varying the crystal thickness and the incident energy of the pump beam. It has been found that the tunability range can be increased with the thickness of the medium. The CE spectra and their angular positions have been measured and found to match with those calculated from recent theoretical models. � 2010 Optical Society of America.

We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15:5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1:9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber. © 2010 Optical Society of America.

Agradecimentos: The authors acknowledge financial support from the State of São Paulo Research Agency FAPESP under Grant Nos. 05/56324 and 06/56456. One of the authors (A.R.B.C) benefited from many discussions with Thomas Möller and his group (TU Berlin), which motivated this study, and gratefully acknowledges the kind hospitality received during several visits to TU Berlin Abstract: We present an analysis of the time evolution of a highly excited silicon substrate after partial absorption of a femtosecond soft x-ray pulse. The detailed time-dependent thermoelastic behavior of the substrate in terms of the displacements u(r,t) is derived for time delays for which the usual local thermodynamic variables, temperature T(r,t) and density n(r,t), become well-defined, namely, a few hundred femtoseconds after x-ray pulse absorption. For practical optical components under present conditions of operation with trains of pulses, we find that in a worst case scenario, already the second pulse in the train could be adversely affected by dynamic thermal distortion induced by the preceding pulse FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Ultrashort intensity optical pulses are often used in science, physic or med. Therefore I will be make work, which examine these pulses. In this work I measuring width of ultrashort laser pulses. Load of this work is a make experimental measuring system, which can measure these pulses. The light is propagating as electromagnetic waves. This waves contains electric and magnetic particles. I using light characterized by electric particle. In this case, light is propagating as femtosecond laser pulse. This laser pulses are generating in modelocking lasers, they are based on phase synchronization of longitudinal modes. If pulses are propagating through anisotropic medium (nonlinear crystal), can arrive phenomenon called frequency doubling (second harmonic generating). Further in this work I explore expansion of pulse, propagating through the medium. This phenomenon called group velocity dispersion. I´m measuring the pulse width by two methods. Both of these methods are compare. Addition measure is pulse spectrum measure. From these results are calculated quality of laser source INTEGRA-i. From theoretical formulas are calculated possibility values. Theoretical and practical results are compare on end of this work.

We report large-aperture volume holographic chirped Bragg reflector recorded in a photopolymer material. It permits to realize compact optical pulse stretchers (230-ps) for femtoseconds lasers.