Search results for "Ash"
showing 10 items of 1718 documents
On the possibility of observing bound soliton pairs in a "wave-breaking-free" mode-locked fiber laser
2007
To generate ultrashort pulses with higher energy in passively mode-locked fiber lasers, several groups have recently focused on the development of laser cavities operating in normal path-averaged dispersion, with a view to achieve wave-breaking-free operation. The mode-locking mechanism in fiber laser play a key role in providing scalability limitation: for instance, nonlinear polarization evolution can be overdriven. Furthermore, the differential gain of the doped fiber decreases along with the traveled distance. From all of these limitations, it follows that power scalability is always bounded for virtually any mode-locked laser cavity design. In general, the consequence is the emergence …
Alignement moléculaire par impulsions laser ultrabrèves : Mesures & Applications
2009
The interaction of an intense ultrashort laser pulse with a molecular sample leads, after the end of the pulse, to molecular alignment at specific time under field-free conditions. This thesis is dedicated to the measurements and applications of this effect. The degree of alignment is determined through the variation of the refractive index induced by the rearrangement of the molecular dipoles. A two-dimensional technique allowing to measure molecular alignment on a single-shot basis is reported in this document. The alignment is then exploited in order to determine physical quantities which are usually difficult to estimate through others methods. The "cross-defocusing technique" has been …
Self-Optimising Breather Ultrafast Fibre Laser
2021
We demonstrate the self-optimisation of the breather regime in an ultrafast fibre laser through an evolutionary algorithm. Depending on the specified merit function, single breathers with controllable breathing ratio and period, and breather molecular complexes with a controllable number of constituents can be obtained.
Optical Cavity-Less 40-GHz Picosecond Pulse Generator in the Visible Wavelength Range
2019
International audience; High-repetition-rate optical frequency-comb sources emitting picosecond pulses play important roles in variousscientific researches and industrial applications. Such ultrafast pulse sources are mostly generated in opticalcavities or microresonators. By means of the wavelength-conversion techniques, it is possible to transfer thecavity-based near-IR robust and compact sources to the mid-IR or to the visible wavelength regions [1-2], forwhich there is an increasing demand, for biophotonics and other applications. Here we demonstrate the generationof high-repetition-rate picosecond pulses in the visible wavelength range by using a fully optical cavity-lessconfiguration.…
All-optical fiber-based devices for ultrafast amplitude jitter magnification
2012
International audience; We propose two fiber-based architectures that enable the all-optical magnification of ultrafast amplitude fluctuations of picosecond or femtosecond pulse trains. An increase of the fluctuations by more than one order of magnitude is experimentally achieved.
Deviation from threshold model in ultrafast laser ablation of graphene at sub-micron scale
2015
International audience; We investigate a method to measure ultrafast laser ablation threshold with respect to spot size. We use structured complex beams to generate a pattern of craters in CVD graphene with a single laser pulse. A direct comparison between beam profile and SEM characterization allows us to determine the dependence of ablation probability on spot-size, for crater diameters ranging between 700 nm and 2.5 μm. We report a drastic decrease of ablation probability when the crater diameter is below 1 μm which we interpret in terms of free-carrier diffusion.
Wavelength conversion and temporal compression of a pulse train using a dispersion oscillating fiber
2014
International audience; We demonstrate the generation of a picosecond pulse train taking advantage of the cross gain occurring in a dispersion oscillating fibre. The resulting frequency-converted signal is detuned by more than 20 nm from the pump and can be temporally compressed by a factor 2 compared to the input sinusoidal pump wave.
High speed cleaving of crystals with ultrafast Bessel beams
2017
International audience; We develop a novel concept for ultra-high speed cleaving of crystalline materials with femtosecond lasers. Using Bessel beams in single shot, fracture planes can be induced nearly all along the Bessel zone in sapphire. For the first time, we show that only for a pulse duration below 650 fs, a single fracture can be induced in sapphire, while above this duration, cracks appear in all crystallographic orientations. We determine the influential parameters which are polarization direction, crystallographic axes and scanning direction. This is applied to cleave sapphire with a spacing as high as 25 μm between laser impacts.
Micron-precision in cleaving glass using ultrafast bessel beams with engineered transverse beam shapes
2017
International audience; Ultrafast lasers in association to beam shaping have shown to be excellent candidates for transparent material processing. Non-diffractive solutions such as Bessel beams allows for precise energy deposition since they are robust to undesired non-linear effects and as they do not distort along the propagation. This offers important opportunities in laser-assisted cleaving, i.e. mechanical medium separation after single-pass laser illumination. Here we break the Bessel beam cylindrical symmetry using a novel anisotropic and non-diffractive solutions to investigate both lateral intensity contributions on material response and induced processing effect for non-cylindrica…
Porous architecture and thermal properties of thermal barrier coatings deposited by suspension plasma spray
2020
Abstract Besides the intrinsic low heat transfer capability of material, the thermal insulation property of thermal barrier coatings (TBCs) also relies on their microstructures. For better understanding the relationship between process parameters, porous architecture, and thermal properties of coatings, YSZ coatings were firstly manufactured by suspension plasma spray (SPS). Afterwards their total porosities were characterized by using the technique of X-ray transmission, the nano/submicro pores in those coatings were detected with Ultra-Small Angle X-ray Scattering (USAXS), and the thermal properties of coatings were measured using the laser flash method. The results indicated that: i) the…