Brigitte Mercier

Generation of quasi-monoenergetic electron beams using ultrashort and ultraintense laser pulses

Plasma-based accelerators have been proposed for the next generation of compact accelerators because of the huge electric fields they can support. However, it has been difficult to use them efficiently for applications because they produce poor quality particle beams with large energy spreads. Here, we demonstrate a dramatic enhancement in the quality of electron beams produced in laser-plasma interaction: an ultrashort laser pulse drives a plasma bubble which traps and accelerates plasma electrons to a single energy. This produces an extremely collimated and quasi-monoenergetic electron beam with a high charge of 0.5 nanocoulomb at energy 170 ± 20 MeV.

Passive coherent combining of CEP-stable few-cycle pulses from a temporally divided hollow fiber compressor

We demonstrate a robust passive coherent combining technique for post-compression of mJ energy CEP-stable laser pulses down to few-cycle duration in a gas-filled hollow-fiber. High combining efficiency is achieved using carefully oriented calcite plates.

Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system

We present the first carrier-envelope-phase stable chirped-pulse amplifier (CPA) featuring high temporal contrast for relativistic intensity laser-plasma interactions at 1 kHz repetition rate. The laser is based on a double-CPA architecture including cross-polarized wave (XPW) filtering technique and a high-energy grism-based compressor. The 8 mJ, 22 fs pulses feature 10⁻¹¹ temporal contrast at -20  ps and a carrier-envelope-phase drift of 240 mrad root mean square.

Temporal pulse division in hollow fiber compressors

We propose a detailed analysis of a temporal multiplexing technique suited to the post-compression of energetic femtosecond laser pulses in gas-filled hollow-core fibers down to the few-cycle regime. Twofold temporal division and combination are achieved using two birefringent plates with specific crystallographic orientation. We demonstrate a simple interferometric method for measuring the relative spectral phase between two replicas, which gives a measure of the phase mismatch in the combining plate, as well as that induced by eventual cross-phase modulation or ionization during propagation in the fiber. We present the experimental conditions required for producing few-cycle pulses with high fidelity. This passive combination technique will aid the energy scaling of hollow fiber compressors to the multi-millijoule level.

Imaging electron trajectories in laser wakefield cavity using betatron x-ray radiation

We demonstrate that betatron x-ray radiation provides a direct imaging of electrons trajectories accelerated in laser wakefields. Electron excursions down to 0.7 ¿m ± 0.2 ¿tm have been measured in our parameter regime.

Passive coherent combining of CEP-stable few-cycles pulses from a temporally divided hollow fiber compressor

We demonstrate a robust passive coherent combining technique for post-compression of mJ energy CEP-stable laser pulses down to few-cycle duration in a gas-filled hollow-fiber. High combining efficiency is achieved using carefully oriented calcite plates.

High-efficiency single-crystal XPW temporal filter for contrast enhancement and pulse shortening

We propose an efficient scheme for femtosecond contrast filtering based on cross-polarized wave generation with a super-Gaussian-shaped beam. We reach 50% intensity transmission with a 2.2 time pulse shortening.

Single-shot SPectral interferometry resolved in time

Shearing interferometry applied to the spectral domain is used for femtoseconde pulse single-shot measurement. An innovating configuration delivering a bidimensional experimental direct representation of the spectral phase of the pulse is also presented.

All optical ultrafast synchrotron hard x‐ray source

Collimated beams of radiation can now be generated in the X‐ray spectral range using laser systems. These new tools may provide efficient probing radiation for the analysis of dense plasmas and ultrafast atomic dynamics phenomena in the matter. Using relativistic laser‐matter interaction, we have shown that X‐ray radiation can be emitted within a collimated 20 mrad cone, in the spectral range of few keV, and with the additional unique properties to be ultrafast (100 fs timescale) and perfectly synchronized with the driving laser system.

Optimization of high harmonic generation by genetic algorithm

In order to develop an intense Extreme Ultra-Violet source based on High Harmonics Generation (HHG) for many applications, we have performed HHG signal optimization experiments. It has been shown that HHG is very sensitive to temporal fundamental pulse shape. For these experiments, we have used an acousto-optical programmable dispersive filter (Dazzler) in order to modify the spectral phase of the fundamental laser. We have optimized harmonic signals generated in argon gas cell with the help of an genetic algorithm up to a factor 6. We stress on the influence of macroscopic parameters on the optimization process. For the first time, we show and explain the algorithm sensitivity to phase-matching conditions.