Anomalous Relativistic Emission from Self-Modulated Plasma Mirrors

TL;DR

This paper uncovers a novel regime of highly-efficient, directionally anomalous coherent XUV radiation from plasma mirrors, caused by laser-driven electron nanobunch oscillations and surface instabilities.

Contribution

It reveals a new emission regime with anomalous propagation and high efficiency, supported by analytical and simulation evidence.

Findings

Loss of coherence leads to a new XUV generation regime.

Radiation propagates parallel to the mirror surface.

Emission driven by relativistic electron nanobunch oscillations.

Abstract

The interaction of intense laser pulses with plasma mirrors has demonstrated the ability to generate high-order harmonics, producing a bright source of extreme ultraviolet (XUV) radiation and attosecond pulses. Here, we report an unexpected transition in this process. We show that the loss of spatio-temporal coherence in the reflected high-harmonics can lead to a new regime of highly-efficient coherent XUV generation, with an extraordinary property where the radiation is directionally anomalous, propagating parallel to the mirror surface. With analytical calculations and numerical particle-in-cell simulations, we discover that the radiation emission is due to laser-driven oscillations of relativistic electron nanobunches which originate from a plasma surface instability induced by collisionless absorption of the laser.