Beam Pointing of Relativistic High-order Harmonics Genrated on a Nonuniform Pre-plasma

TL;DR

This paper investigates how non-uniform pre-plasma density affects the direction of high-order harmonic beams generated by relativistic laser interactions, revealing the roles of plasma dynamics and optical effects.

Contribution

It provides new insights into the influence of electron density shape and plasma dynamics on harmonic beam pointing in high-order harmonic generation.

Findings

Beam pointing deviation is caused by plasma hydrodynamics.

Geometrical optical effects contribute to beam deviation.

Simulation results match experimental observations.

Abstract

The use of tunable pre-pulse is a common technique to enhance the high-order harmonic generation from surface plasma. The shape and dynamic of the electron density, the degree of ionization and its rate, and the plasma heating are influenced by the pre-pulse properties. Non-uniform pre-pulse could cause a spatially varying density map to the pre-plasma region, which serves as the spectrally up-conversion and reflection surface. The corresponding geometrical feature and plasma nature under laser field will affect the harmonic emission properties. In this study, the variation in harmonic beam pointing due to the electron density shape was investigated. Particle-in-cell simulations demonstrated that both plasma hydrodynamics and geometrical optical effect induce the deviation of harmonic beam from specular reflection. This research contributes to the understanding of the surface plasma dynamics during high harmonic generation process.