Search results for "Femtosecond pulse"
showing 10 items of 41 documents
Parallel laser micromachining based on diffractive optical elements with dispersion compensated femtosecond pulses
2013
We experimentally demonstrate multi-beam high spatial resolution laser micromachining with femtosecond pulses. The effects of chromatic aberrations as well as pulse stretching on the material processed due to diffraction were significantly mitigated by using a suited dispersion compensated module (DCM). This permits to increase the area of processing in a factor 3 in comparison with a conventional setup. Specifically, 52 blind holes have been drilled simultaneously onto a stainless steel sample with a 30 fs laser pulse in a parallel processing configuration.
Dynamique induite par champ laser femtoseconde intense : alignement moléculaire en milieu gazeux dense et effet Kerr
2011
This thesis is devoted to the study of dynamics induced by intense femtoseconds lasers pulses. The first studied dynamics deals with molecular alignment of CO2-X mixtures (X=CO2, Ar, N2), in dense gases (up to 20 bar). Up to now, this regime has never been studied experimentally. In the field-free regime (after laser/matter interaction), molecular alignment exhibits two components : a permanent alignment and a transient one. The influence of collisions appears through population transfers between rotational states, which leads to a decrease of these two contributions. Permanent alignment relaxation time is only tied to inelastics collisions whereas transient alignment relaxation time is tie…
High spatiotemporal resolution in multifocal processing with femtosecond laser pulses.
2006
We report spatial and temporal dispersion compensation for fan-out of femtosecond pulses with a low-frequency diffraction grating by means of a hybrid diffractive-refractive lens triplet. In this way, we achieve a multifocal light structure with nearly diffraction-limited light spots even for 20 fs pulse duration. The spatial chromatic compensation, which drastically reduces the lateral walk-off of the various spectral components, also allows us to improve the available bandwidth at the dispersion-compensated diffraction orders. In fact, the temporal width of the output pulse is essentially limited by the group-delay dispersion term, which is shown to be small. The high spatiotemporal resol…
All-fibered high-quality 1.5–2 THz femtosecond pulse sources
2009
Generation of high-quality ultra-high repetition rate optical pulse trains around 1.55µm has become increasingly interesting for many scientific applications such as optical sampling, ultra-high capacity transmission systems, component testing or nonlinear phenomena studies. Unfortunately, the current bandwidth limitations of optoelectronic devices do not enable the direct generation of pulses with repetition rate higher than 80GHz and a temporal width below a few ps.
Diffractive optics for quasi-direct space-to-time pulse shaping.
2008
The strong chromatic behavior associated with a conventional diffractive lens is fully exploited to propose a novel optical device for pulse shaping in the femtosecond regime. This device consists of two optical elements: a spatially patterned circularly symmetric mask and a kinoform diffractive lens, which are facing each other. The system performs a mapping between the spatial position of the masking function expressed in the squared radial coordinate and the temporal position in the output waveform. This space-to-time conversion occurs at the chromatic focus of the diffractive lens, and makes it possible to tailor the output central wavelength along the axial location of the output point…
Fiber-based device for the detection of low-intensity fluctuations of ultrashort pulses
2012
International audience; We describe a fiber-based device that can significantly enhance the low intensity fluctuations of an ultrashort pulse train to detect them more easily than with usual direct detection systems. Taking advantage of the Raman intrapulse effect that progressively shifts the central frequency of a femtosecond pulse propagating in an anomalous dispersion fiber, a subsequent spectral filtering can efficiently increase the level of fluctuations by more than one order of magnitude. We show that attention has to be paid to maintain the shape of the statistical distribution unaffected by the nonlinear process.
Femtosecond pulse compression in a hollow-core photonic bandgap fiber by tuning its cross section
2012
Abstract We present a numerical study of soliton pulse compression in a seven-cell hollow-core photonic bandgap fiber. We analyze the enhancement of both the compression factor and the pulse shape quality of 360 nJ femtosecond pulses at the wavelength of 800 nm by tuning the cross section size of the fiber. We use the generalized non-linear Schrodinger equation in order to modeled the propagation of light pulses along the fiber. Our numerical results show that output compressed pulses can be obtained, in a propagation length of 31 cm, with a compression factor of 5.7 and pulse shape quality of 77% for a reduction of 4.5% of the cross section size of the fiber. The predicted compression fact…
Pulse trains produced by phase-modulation of ultrashort optical pulses: tailoring and characterization
2009
1094-4087; In this paper, creation of pulse doublets and pulse trains by spectral phase modulation of ultrashort optical pulses is investigated. Pulse doublets with specific features are generated through step-like and triangular spectral phase modulation, whereas sequences of pulses with controllable delay and amplitude are produced via sinusoidal phase modulations. A temporal analysis of this type of tailored pulses is exposed and a complete characterization with the SPIDER technique (Spectral Phase Interferometry for Direct Electric-field Reconstruction) is presented. (C) 2004 Optical Society of America.
Formation of ultrashort triangular pulses in optical fibers
2014
Specialty shape ultrashort optical pulses, and triangular pulses in particular, are of great interest in optical signal processing. Compact fiber-based techniques for producing the special pulse waveforms from Gaussian or secant pulses delivered by modern ultrafast lasers are in demand in telecommunications. Using the nonlinear Schr¨odinger equation in an extended form the transformation of ultrashort pulses in a fiber towards triangular shape is characterized by the misfit parameter under variety of incident pulse shapes, energies, and chirps. It is shown that short (1-2 m) conventional single mode fiber can be used for triangular pulse formation in the steady-state regime without any pre-…
Coherent control in single plasmonic nanostructures
2015
Coherent control in plasmonic nanostructures is a door to space-time confinement of optical excitation and femtosecond super-resolution spectroscopy. Towards this goal, here we demonstrate femtosecond pulse-shaping of single gold nanostructure and local phase compensation.