arXiv subjects

Dominique Descamps

Publications and source records attributed to Dominique Descamps.

25 records · Page 2Linked to original sources

arXiv2019

High-harmonics of harmonics of a fiber laser: a milliwatt XUV ultrashort source

Recent progresses in femtosecond ytterbium-doped fiber laser technology areopening new perspectives in strong field physics and attosecond science. Highorder harmonic generation from these systems is particularly interesting because it provides high flux beams of ultrashort extreme ultraviolet radiation. A lot of efforts have been devoted to optimize the macroscopic generation parameters. Here we investigate the possibility of enhancing the single-atom response by producing high-harmonics from the second, third and fourth harmonics of a turnkey Yb-fiber laser at 1030 nm. We show that the harmonic efficiency is optimal when the process is driven by the third harmonic, producing 4.4 1014 photon/s at 18 eV, which corresponds to 1.3 mW average power.

physics.optics↗

arXiv2018

Multiphoton Photoelectron Circular Dichroism of Limonene with Independent Polarization State Control of the Bound-Bound and Bound-Continuum Transitions

Photoionization of randomly oriented chiral molecules with circularly polarized light leads to a strong forward/backward asymmetry in the photoelectron angular distribution. This chiroptical effect, referred to as Photoelectron Circular Dichroism (PECD), was shown to take place in all ionization regimes, from single photon to tunnel ionization. In the Resonance Enhanced Multiphoton Ionisation (REMPI) regime, where most of the table-top PECD experiments have been performed, understanding the role of the intermediate resonances is currently the subject of experimental and theoretical investigations. In an attempt to decouple the role of bound-bound and bound-continuum transitions in REMPI-PECD, we photoionized the (+)-limonene enantiomer using two-color laser fields in [1+1'] and [2+2'] ionization schemes, where the polarization state of each color can be controlled independently. We demonstrate that the main effect of the bound-bound transition is to break the sample isotropy by orientation-dependent photoexcitation, in agreement with recent theoretical pre- dictions. We show that the angular distribution of PECD strongly depends on the anisotropy of photoexcitation to the intermediate state, which is different for circularly and linearly polarized laser pulses. On the contrary, the helicity of the pulse that drives the bound-bound transition is shown to have a negligible effect on the PECD.

physics.chem-ph↗

arXiv2017

Phase-Resolved Two-Dimensional Spectroscopy of Electronic Wavepackets by Laser-Induced XUV Free Induction Decay

We present a novel time- and phase-resolved, background-free scheme to study the extreme ultraviolet dipole emission of a bound electronic wavepacket, without the use of any extreme ultraviolet exciting pulse. Using multiphoton transitions, we populate a superposition of quantum states which coherently emit extreme ultraviolet radiation through free induction decay. This emission is probed and controlled, both in amplitude and phase, by a time-delayed infrared femtosecond pulse. We directly measure the laser-induced dephasing of the emission by using a simple heterodyne detection scheme based on two-source interferometry. This technique provides rich information about the interplay between the laser field and the Coulombic potential on the excited electron dynamics. Its background-free nature enables us to use a large range of gas pressures and to reveal the influence of collisions in the relaxation process.

physics.atom-ph↗

arXiv2016

Relaxation Dynamics in Photoexcited Chiral Molecules Studied by Time-Resolved Photoelectron Circular Dichroism: Toward Chiral Femtochemistry

Unravelling the main initial dynamics responsible for chiral recognition is a key stepin the understanding of many biological processes. However this challenging task requires a sensitive enantiospecic probe to investigate molecular dynamics on their natural femtosecond timescale. Here we show that, in the gas phase, the ultrafast relaxationdynamics of photoexcited chiral molecules can be tracked by recording Time-ResolvedPhotoElectron Circular Dichroism (TR-PECD) resulting from the photoionisation bya circularly polarized probe pulse. A large forward/backward asymmetry along theprobe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump-probe delay reveals ultrafast dynamics that are inaccessible in theangle-integrated photoelectron spectrum nor via the usual electron emission anisotropyparameter ($β$). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamicsin chiral systems.

physics.chem-ph↗

arXiv2016

Role of Excited States In High-order Harmonic Generation

We investigate the role of excited states in High-order Harmonic Generation by studying the spectral, spatial and temporal characteristics of the radiation produced near the ionization threshold of argon by few-cycle laser pulses. We show that the population of excited states can lead either to direct XUV emission through Free Induction Decay or to the generation of high-order harmonics through ionization from these states and recombination to the ground state. By using the attosecond lighthouse technique, we demonstrate that the high-harmonic emission from excited states is temporally delayed by a few femtoseconds compared to the usual harmonics, leading to a strong nonadiabatic spectral redshift.

physics.atom-ph↗

arXiv2015

Post-compression of high energy terawatt-level femtosecond pulses and application to high order harmonic generation

We perform a post-compression of high energy pulses by using optical-field ionization of low pressure helium gas in a guided geometry. We apply this approach to a TW chirped-pulse-amplification based Ti:Sapphire laser chain and show that spectral broadening can be controlled both with the input pulse energy and gas pressure. Under optimized conditions, we generate 10 fs pulses at TW level directly under vacuum and demonstrate a high stability of the post compressed pulse duration. These high energy post-compressed pulses are thereafter used to perform high harmonic generation in a loose focusing geometry. The XUV beam is characterized both spatially and spectrally on a single shot basis and structured continuous XUV spectra are observed.

physics.optics↗

arXiv2014

Transient grating spectroscopy of SF6 molecular vibrations

Strong field transient grating spectroscopy has shown to be a very versatile tool in time-resolved molecular spectroscopy. Here we use this technique to investigate the high-order harmonic generation from SF6 molecules vibrationally excited by impulsive stimulated Raman scattering. Transient grating spectroscopy enables us to reveal clear modulations of the harmonic emission. This heterodyne detection shows that the harmonic emission generated between 14 to 26 eV is mainly sensitive to two among the three active Raman modes in SF6, i.e. the strongest and fully symmetric nu 1-A1g mode (774 cm-1, 43 fs) and the slowest mode nu5-T2g (524 cm-1, 63 fs). A time-frequency analysis of the harmonic emission reveals additional dynamics: the strength and central frequency of the nu 1 mode oscillate with a frequency of 52 cm-1 (640 fs). This could be a signature of the vibration of dimers in the generating medium. Harmonic 11 shows a remarkable behavior, oscillating in opposite phase, both on the fast (774 cm-1) and slow (52 cm-1) timescales, which indicates a strong modulation of the recombination matrix element as a function of the nuclear geometry. These results demonstrate that the high sensitivity of high-order harmonic generation to molecularvibrations, associated to the high sensitivity of transient grating spectroscopy, make their combination a unique tool to probe vibrational dynamics.

physics.chem-ph↗