Non-Maxwellian electron distributions resulting from direct laser acceleration in near-critical plasmas

The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and lower than critical densities with plasmas extending over few micrometers,i.e.multiple wavelengths.The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam.Experiments at the Glass Hybrid OPCPA Scaled Test-bed(GHOST)laser system at University of Texas,Austin using such targets measured non-Maxwellian,peaked electron distribution with large bunch charge and high electron density in the laser propagation direction.These results are reproduced in 2D PIC simulations using the EPOCH code,identifying direct laser acceleration(DLA)[1]as the responsible mechanism.This is the first time that DLA has been observed to produce peaked spectra as opposed to broad,Maxwellian spectra observed in earlier experiments[2].This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.

A tabletop, ultrashort pulse photoneutron source driven by electrons from laser wakefield acceleration

Relativistic electron beams driven by laser wakefield acceleration were utilized to produce ultrashort neutron sources.The experiment was carried out on the 38 fs,~0.5 J,800 nm Ti:Sapphire laser in the 10 TW UT 3 laser lab at University of Texas at Austin.The target gas was a high density pulsed gas jet composed of 90%He and 10%N 2.The laser pulse with a peak intensity of 1.5×10^(18) W/cm^(2) interacted with the target to create a cylindrical plasma channel of 60 mm radius(FWHM)and 1.5 mm length(FWHM).Electron beams of~80 pC with the Gaussian energy distribution centered at 37 MeV and a width of 30 MeV(FWHM)were produced via laser wakefield acceleration.Neutron fluences of~2.4×10^(6) per shot with hundreds of ps temporal length were generated through bremsstrahlung and subsequent photoneutron reactions in a 26.6 mm thick tungsten converter.Results were compared with those of simulations using EPOCH and GEANT4,showing agreement in electron spectrum,neutron fluence,neutron angular distribution and conversion rate.

ARCTURUS laser: a versatile high-contrast,high-power multi-beam laser system

With the latest configuration,the Ti:Sa laser system ARCTURUS(Düsseldorf University,Germany)operates with a double-chirped pulse amplification(CPA)architecture delivering pulses with an energy of 7 J before compression in each of the two high-power beams.By the implementation of a plasma mirror system,the intrinsic laser contrast is enhanced up to 10^-12 on a time scale of hundreds of picoseconds,before the main peak.The laser system has been used in various configurations for advanced experiments and different studies have been carried out employing the high-power laser beams as a single,high-intensity interaction beam(I≈1020 W/cm^2),in dual-and multi-beam configurations or in a pump–probe arrangement.

ReLaX:the Helmholtz International Beamline for Extreme Fields high-intensity short-pulse laser driver for relativistic laser-matter interaction and strong-field science using the high energy density instrument at the European X-ray free electron laser fac

High-energy and high-intensity lasers are essential for pushing the boundaries of science.Their development has allowed leaps forward in basic research areas,including laser±plasma interaction,high-energy density science,metrology,biology and medical technology.The Helmholtz International Beamline for Extreme Fields user consortium contributes and operates two high-peak-power optical lasers using the high energy density instrument at the European X-ray free electron laser(EuXFEL)facility.These lasers will be used to generate transient extreme states of density and temperature to be probed by the X-ray beam.This paper introduces the ReLaX laser,a short-pulse high-intensity Ti:Sa laser system,and discusses its characteristics as available for user experiments.It will also present the first experimental commissioning results validating its successful integration into the EuXFEL infrastructure and viability as a relativisticintensity laser driver.