Effect of the Laser Wave Front in a Laser-Plasma Accelerator

Abstract

International audienceA high-repetition rate electron source is generated by tightly focusing kHz, few-mJ laser pulses into an underdense plasma. This high-intensity laser-plasma interaction leads to stable electron beams over several hours but with strikingly complex transverse distributions even for good quality laser focal spots. We find that the electron beam distribution is sensitive to the laser wave front via the laser midfield distribution rather than the laser focal spot itself. We are able to measure the laser wave front around the focus and include it in realistic particle-in-cell simulations demonstrating the role of the laser wave front on the acceleration of electrons. Distortions of the laser wave front cause spatial inhomogeneities in the midfield laser intensity and, consequently, the laser pulse drives an inhomogeneous transverse wakefield whose focusing and defocusing properties affect the electron distribution. These findings explain the experimental results and suggest the possibility of controlling the electron spatial distribution in laser-plasma accelerators by tailoring the laser wave front

Effect of experimental laser imperfections on laser wakefield acceleration and betatron source

“…This algorithm has already been used to reconstruct the phase in LWFA with mJ laser27. In our case, the validity of the algorithm was checked on a gaussian beam with satisfactory results: if two intensity profiles in two different planes are given as an input, the algorithm can reconstruct the intensity and phase profiles in any plane with a good agreement with the theoretical gaussian beam profiles.…”

Pulse front tilt steering in laser plasma accelerators

“…Improving electron beam quality and understanding beam degradation is an active field of research. Defects and spatiotemporal coupling in the laser pulse were shown to modify the electron beam dynamics [4]. One particular form of spatiotemporal coupling, pulse front tilt (PFT), was observed to affect the electron trajectories in particle-in-cell (PIC) simulations and in experiments [5,6], resulting in deflection of the accelerated electrons with respect to the laser axis.…”

Measurements of self-guiding of ultrashort laser pulses over long distances

“…In fact, the location of the filament was found to be very stable for multiple shots taken at conditions similar to that in Panel (f) in Figure 2. This asymmetry can be explained by considering the often imperfect quasi-nearfield of the laser near the focus [33]. In the full nearfield the spatial profile of the laser exhibits a top hat nature, where in the Fraunhofer limit in the far field a confined focal spot is observed.…”