Search results for "Ultrashort pulse"
showing 10 items of 153 documents
High-quality optical pulse train generator based on solitons on finite background
2013
International audience; We report a simple method to exploit the typical properties of solitons on finite background in order to generate high repetition rate and high quality optical pulse trains. We take advantage of the nonlinear evolution of a modulated continuous wave towards localized structures upon a nonzero background wave in anomalous dispersive fiber. After a stage of nonlinear compression, a delay-line interferometer enables the annihilation of the finite background and simultaneously allows the repetition rate doubling of the pulse train.
Effects of fourth-order fiber dispersion on ultrashort parabolic optical pulses in the normal dispersion regime
2011
International audience; We propose a new method for the generation of both triangular-shaped optical pulses and flat-top, coherent supercontinuum spectra using the effect of fourth-order dispersion on parabolic pulses in a passive, normally dispersive highly nonlinear fiber. The pulse re-shaping process is described qualitatively and is compared to numerical simulations.
Characterization of Locally Excited and Charge-Transfer States of the Anticancer Drug Lapatinib by Ultrafast Spectroscopy and Computational Studies
2020
[EN] Lapatinib (LAP) is an anticancer drug, which is metabolized to theN- and O-dealkylated products (N-LAP andO-LAP, respectively). In view of the photosensitizing potential of related drugs, a complete experimental and theoretical study has been performed on LAP,N-LAP andO-LAP, both in solution and upon complexation with human serum albumin (HSA). In organic solvents, coplanar locally excited (LE) emissive states are generated; they rapidly evolve towards twisted intramolecular charge-transfer (ICT) states. By contrast, within HSA only LE states are detected. Accordingly, femtosecond transient absorption reveals a very fast switching (ca. 2 ps) from LE (lambda(max)=550 nm) to ICT states (…
Strong-field molecular ionization: determination of ionization probabilities calibrated with field-free alignment
2006
International audience; We report an original optical method providing the probability of molecular ionization induced by femtosecond laser pulses. The approach consists of exploiting molecular alignment in order to extract reliable information about ionization. The cross defocusing technique implemented for this purpose reveals a sensitivity with respect to post-pulse alignment, as well as to free electron density induced by the ultra-short laser pulse. The analysis of the resulting signal gives thus access to absolute single-ionization probabilities calibrated through the degree of alignment provided that free electrons are mainly produced from single-ionization. The relevance of the meth…
In situ synchrotron radiation monitoring of phase transitions during microwave heating of Al–Cu–Fe alloys
2008
The effect of rapid microwave heating has so far been evaluated mainly by comparing the state of materials before and after microwave exposure. Yet, further progress critically depends on the ability to follow the evolution of materials during ultrafast heating in real time. We describe the first in situ time-resolved monitoring of solid-state phase transitions during microwave heating of metallic powders using wide-angle synchrotron radiation diffraction. Single-phase Al–Cu–Fe quasicrystal powders were obtained by microwave heating of nanocrystalline alloy precursors at 650 °C in <20 s.
Measurement of laser-induced alignment of molecules by cross defocusing
2005
0146-9592; The field-free alignment of CO2 produced in response to the excitation of a molecule by a high-intensity femtosecond pump pulse is measured with a simple coronography-like technique. The technique is based on the defocusing of a time-delayed probe pulse produced by the spatial distribution of aligned molecules. In the intensity regime explored here, the technique is shown to give valuable information about dynamic alignment. With the help of simulations, the degree of alignment is extracted from the data. (C) 2005 Optical Society of America.
Reexamining Different Factors of the Resonance-Enhanced High-Order Harmonic Generation in Atomic and Nanoparticle Laser-Induced Tin Plasmas
2021
We reexamine the resonance enhancement of a single harmonic emission during the propagation of ultrafast pulses through atomic and nanoparticle tin-containing laser-induced plasma (LIP). We compare the single atomic Sn and Sn nanoparticle plasmas to demonstrate a distinction in the enhancement factor of the single harmonic in the case of fixed and tunable near-infrared pulses. The analysis of the dynamics of Sn LIP shows the range of optimal delays between heating and driving pulses (130–180 ns), at which the maximal harmonic yield can be achieved. The enhancements of the 17th and 18th harmonics of 806 nm pulses were analyzed in the case of single-color and two-color pumps of LIP, showing u…
Broadband tuning of a long-cavity all-fiber mode locked Thulium-doped fiber laser using an acousto-optic bandpass filter
2019
A long-cavity passively mode-locked thulium-doped all-fiber laser is reported incorporating a tapered acousto-optic tunable bandpass filter (AOTBF). The operation of the AOTBF relies on the intermodal coupling between core and cladding modes when a flexural acoustic wave propagates along an 80-microm tapered fiber. The filter works in transmission and exhibits a 3-dB bandwidth of 9.02 nm with an insertion loss of 3.4 dB. The laser supports ultrashort pulse generation at a low repetition rate of 784.93 kHz. Optical pulses with 2.43 nm of optical bandwidth and 2.1 ps pulse duration were obtained in a broad tuning range from 1824.77 to 1905.16 nm.
Mechanism for ultrafast electric-field driven skyrmion nucleation
2021
We show how a Dzyaloshinskii-Moriya interaction can be generated in an ultrathin metal film from a femtosecond pulse in electric field. This interaction does not require structural inversion-symmetry breaking, and its amplitude can be tuned depending on the amplitude of the field. We perform first-principles calculations to estimate the strength of the field-induced magnetoelectric coupling for ferromagnetic Fe, Co, and Ni, and antiferromagnetic Mn, as well as FePt and MnPt alloys. Last, using atomistic simulations, we demonstrate how an isolated antiferromagnetic skyrmion can be coherently nucleated from the collinear background by an ultrashort pulse in electric field on a hundred-femtose…
Optical Diagnostics with Ultrafast and Strong Field Raman Techniques
2014
In this chapter, we will discuss some coherent techniques, namely Raman Induced Polarization Spectroscopy (RIPS) and femtosecond Coherent Raman Anti-Stokes Spectroscopy (fs-CARS). We will demonstrate their ability to be used as non-invasive optical diagnostic tools for temperature, density, or concentration measurements, as well as a means of testing collision induced energy transfer models (in a low field regime), and studying the so-called inhomogeneous lineshape effects that are particularly enhanced in the case of hydrogen. We will also show how molecular alignment achieved in a strong field regime can provide additional information about collisional relaxation processes. In all cases, …