Surface modulation and back reflection from foil targets irradiated by a Petawatt femtosecond laser pulse at oblique incidence.

S Ter-Avetisyan,K Platonov,J Y Yoo,H W Lee,C Scullion,A Andreev,H Ahmed,P Hadjisolomou,K F Kakolee,M Borghesi,S K Lee,J H Sung,T W Jeong,P K Singh

doi:10.1364/oe.24.028104

Abstract

A significant level of back reflected laser energy was measured during the interaction of ultra-short, high contrast PW laser pulses with solid targets at 30° incidence. 2D PIC simulations carried out for the experimental conditions show that at the laser-target interface a dynamic regular structure is generated during the interaction, which acts as a grating (quasi-grating) and reflects back a significant amount of incident laser energy. With increasing laser intensity above 1018 W/cm2 the back reflected fraction increases due to the growth of the surface modulation to larger amplitudes. Above 1020 W/cm2 this increase results in the partial destruction of the quasi-grating structure and, hence, in the saturation of the back reflection efficiency. The PIC simulation results are in good agreement with the experimental findings, and, additionally, demonstrate that in presence of a small amount of pre-plasma this regular structure will be smeared out and the back reflection reduced.

Highlights

The interaction of high intensity, ultrashort laser pulses with solid targets has been studied extensively over the last decade [1]
A significant level of back reflected laser energy was measured during the interaction of ultra-short, high contrast PW laser pulses with solid targets at 30° incidence. 2D PIC simulations carried out for the experimental conditions show that at the laser-target interface a dynamic regular structure is generated during the interaction, which acts as a grating and reflects back a significant amount of incident laser energy
1020 W/cm2 this increase results in the partial destruction of the quasi-grating structure and, in the saturation of the back reflection efficiency

Summary

Introduction

The interaction of high intensity, ultrashort laser pulses with solid targets has been studied extensively over the last decade [1]. During the interaction of high contrast, ultrashort and intense laser pulses (above 1018 W/cm2) with steep plasma of solid density, laser energy is transferred to the electrons mainly via the ponderomotive mechanism [2], leading to the penetration of large electron currents into the bulk of the target. For short laser pulses (100 fs) the back reflection was studied in [5], at relatively low laser intensities (~1016 W/cm2) and pulse contrast In this case the backscattering process was attributed to scattering from a plasma wave generated within the preplasma present in front of the target surface. To make sure that the measured back reflected light comes from the laser beam itself, rather than from plasma emission, the spectrum of the back reflected light was calibrated by comparing the spectrum to reflected laser radiation reflected from Al mirrors placed before the off-axis parabola [Fig. 2]. The energy and the spectrum of back reflected radiation were monitored throughout the whole experiment

Experimental and theoretical results

Conclusion