58 research outputs found
Controllable Spatial Array of Bessel-like Beams with Independent Axial Intensity Distributions for Laser Microprocessing
Bessel beams generated via axicons are widely used for various applications
like optical tweezers or laser microfabrication of transparent materials. The
specific intensity profile having high aspect ratio of beam width and length in
turn generates high aspect ratio void that resembles a needle. In contrast to
commonly generated Bessel beam that has a fixed axial intensity distribution.
We present a novel method to engineer an optical needle that can have an
arbitrary axial intensity distribution via superposition of different cone
angle Bessel beams. We analytically describe spatial spectra of an optical
needle having arbitrary axial intensity distribution. We also demonstrate a
superposition of independent optical needles and analyze the physical
limitations to observe well separated optical needles as they are influence by
mutual interference of the individual beams. In order to verify our theoretical
and numerical results we generate controllable spatial arrays of individual
beams with various numbers and spatial separations by altering a spectrum of
incoming laser beam via spatial light modulator. Lastly, we numerically examine
distortions caused by propagation through planar air-dielectric interface and
show compensation method by appropriately modifying spectral masks
Laser beam self-symmetrization in air in the multifilamentation regime
We show experimental and numerical evidence of spontaneous
self-symmetrization of focused laser beams experiencing multi-filamentation in
air. The symmetrization effect is observed as the multiple filaments generated
prior to focus approach the focal volume. This phenomenon is attributed to the
nonlinear interactions amongst the different parts of the beam mediated by the
optical Kerr effect, which leads to a symmetric redistribution of the wave
vectors even when the beam consists of a bundle of many filaments.Comment: 9 pages, 7 figure
Superfilamentation in air
The interaction between a large number of laser filaments brought together
using weak external focusing leads to the emergence of few filamentary
structures reminiscent of standard filaments, but carrying a higher intensity.
The resulting plasma is measured to be one order of magnitude denser than for
short-scale filaments. This new propagation regime is dubbed
superfilamentation. Numerical simulations of a nonlinear envelope equation
provide good agreement with experiments.Comment: 5 pages, 4 figure
Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses
Acoustic signals generated by filamentation of ultrashort TW laser pulses in
water are characterized experimentally. Measurements reveal a strong influence
of input pulse duration on the shape and intensity of the acoustic wave.
Numerical simulations of the laser pulse nonlinear propagation and the
subsequent water hydrodynamics and acoustic wave generation show that the
strong acoustic emission is related to the mechanism of superfilamention in
water. The elongated shape of the plasma volume where energy is deposited
drives the far-field profile of the acoustic signal, which takes the form of a
radially directed pressure wave with a single oscillation and a very broad
spectrum.Comment: 9 pages, 12 figure
Study of filamentation with a high power high repetition rate ps laser at 1.03 µm
International audienceWe study the propagation of intense, high repetition rate laser pulses of picosecond duration at 1.03 µm central wavelength through air. Evidence of filamentation is obtained from measurements of the beam profile as a function of distance, from photoemission imaging and from spatially resolved sonometric recordings. Good agreement is found with numerical simulations. Simulations reveal an important self shortening of the pulse duration, suggesting that laser pulses with few optical cycles could be obtained via double filamentation. An important lowering of the voltage required to induce guided electric discharges between charged electrodes is measured at high laser pulse repetition rate.-repetition-rate picosecond pump laser based on a Yb:YAG disk amplifier for optical parametric amplification
Kūginių bangų nenuostovūs erdvėlaikiniai reiškiniai netiesinėse Kerro terpėse
Thesis consists of introduction, followed by five main chapters and conclusions. Introduction is devoted to the explanation of filamentation process. The mechanisms responsible for filament generation and evolution are explained first and various models of the filamentation are presented as well. The second chapter is devoted to the study on supercontinuum spectrum dependence on the initial pulse diameter. The chapter 4 is devoted to the study of the filamentation in scattering medium, and covers the performed experiment, explanation of new developed numerical scheme, and finally comparison of the numerical and experimental results. The chapter 5 describes the multifilamentation with elliptical beam. The role of the four wave mixing to the filaments periodicity is briefly explained. The periodicity dependence on the wave of intensity as well the evolution of multifilamentation is shown. Three dimensional study of the modulation instability during multifilamentation process is also presented in chapter 5. The last chapter 6 is devoted to the origin of the rogue wave statistics in supercontinuum generation, and comparison of the numeric results with experimental. At the end (chapter 7) the main conclusions of the current work are presented
Conical wave triggered transient spatio-temporal effects in Kerr media
Thesis consists of introduction, followed by five main chapters and conclusions. Introduction is devoted to the explanation of filamentation process. The mechanisms responsible for filament generation and evolution are explained first and various models of the filamentation are presented as well. The second chapter is devoted to the study on supercontinuum spectrum dependence on the initial pulse diameter. The chapter 4 is devoted to the study of the filamentation in scattering medium, and covers the performed experiment, explanation of new developed numerical scheme, and finally comparison of the numerical and experimental results. The chapter 5 describes the multifilamentation with elliptical beam. The role of the four wave mixing to the filaments periodicity is briefly explained. The periodicity dependence on the wave of intensity as well the evolution of multifilamentation is shown. Three dimensional study of the modulation instability during multifilamentation process is also presented in chapter 5. The last chapter 6 is devoted to the origin of the rogue wave statistics in supercontinuum generation, and comparison of the numeric results with experimental. At the end (chapter 7) the main conclusions of the current work are presented
Thermodynamical analysis of the formation of α-Si ring structures on silicon surface
Superficial modifications on silicon wafers produced by single-shot focused femtosecond laser irradiation having a 1030 nm wavelength and 300 fs pulse duration were experimentally and theoretically analyzed. The laser fluence window when the amorphous silicon phase develops, resulting in a ring-like modification shape, was experimentally estimated to be between 0.26 J/cm2 and 0.40 J/cm2 and was independent of the silicon dopant type and laser focusing conditions; however, the window was narrower when compared to results reported for shorter pulse durations. In addition, we present a simplified numerical model that can explain and predict the formation of these patterns based on the caloric coefficients of silicon and the energy distribution of the deposited material
Ultra-short laser induced electron excitation/relaxation kinetics
Laser-induced electronic excitation, absorption and relaxation are the key issues in ultra-short laser interactions with dielectric materials. To numerically analyze these processes, several approaches are typically used. First, several detailed non-equilibrium models are based on a system of the detailed kinetic Boltzmann equations. Then, Fokker-Planck equations are also used. Finally, much more simplified rate equations are typically used in engineering modelling [1,2]. These models require additional sub-models to account for photo-ionization, electron-impact ionization, defect formation, recombination and other relaxation processes. In these sub-models, many parameters are rather unknown and are calculated based on additional considerations. One of such parameters is electron collision frequency [1-3], which was found to be crucial in determination of laser absorption and hence of laser damage.Boltzmann-based calculations are performed including all possible collisional processes. As a result, electron energy distributions are obtained allowing a better analysis of ultra-short laser interactions. The results reveal an effect of the laser-field on collision frequencies resulting in smaller free-carriers absorption than the one predicted by commonly used rate-equation models. Both electron-electron and electron-phonon relaxation are then examined, and the mean energy density of the electron sub-system is investigated as a function of laser fluence and pulse duration. Because efficient bond breaking requires energy, these calculations provide the required thresholds [4]. The dependency of the calculated damage threshold on laser pulse duration is compared with the available experimental data. The developed model is useful for many laser applications including high precision in laser treatment, laser-assisted atomic probe analysis, and for the development of new powerful laser systems.References[1] B. Chimier, O. Utéza, N. Sanner, M. Sentis, T. Itina, P. Lassonde, F. Légaré, F. Vidal, and J. C. Kieffer. "Damage and ablation thresholds of fused-silica in femtosecond regime." Physical Review B 84 (9), 094104, (2011).[2]T.E. Itina, N.S. Shcheblanov, N. Electronic excitation in femtosecond laser interactions with wide-band-gap materials. Applied Physics A, 98(4), 769-775 (2010).[3] C. Xie, V. Jukna, C. Milián, R. Giust, I. Ouadghiri-Idrissi, T. Itina, J. M. Dudley, A. Couairon, F. Courvoisier. "Tubular filamentation for laser material processing. Scientific reports, 5 (2015).[4] N. S. Shcheblanov, T. E. Itina, Appl. Phys. Femtosecond laser interactions with dielectric materials: insights of a detailed modeling of electronic excitation and relaxation processes, Appl. Phys. A, 110(3), 579-583 (2013).Surface & Interface Science & Engineerin
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