# Physics of the laser-plasma interface in the relativistic regime of interaction

## TL;DR

This paper investigates the microscopic physics of the laser-plasma interface in relativistic interactions, revealing how layer parameters influence the generation of intense, short XUV bursts and harmonic spectra.

## Contribution

It provides a detailed analysis of the microscopic physics governing the plasma layer, linking its properties to the characteristics of emitted XUV radiation.

## Key findings

- Layer thickness and internal structure critically affect XUV burst intensity and duration.
- Microscopic parameters of the plasma layer determine the high-energy harmonic spectrum.
- Conditions for producing singularly intense XUV bursts are identified.

## Abstract

The reflection of intense laser radiation from solids appears as a result of relativistic dynamics of the electrons driven by both incoming and self-generated electromagnetic fields at the periphery of the emerging dense plasma. In the case of highly-relativistic motion, electrons tend to form a thin oscillating layer, which makes it possible to model the interaction and obtain the temporal structure of the reflected radiation. The modelling reveals the possibility and conditions for producing singularly intense and short XUV bursts of radiation, which are interesting for many applications. However, the intensity and duration of the XUV bursts, as well as the high-energy end of the harmonic spectrum, depends on the thickness of the layer and its internal structure which are not assessed by such macroscopic modelling. Here we analyse the microscopic physics of this layer and clarify how its parameters are bound and how this controls outlined properties of XUV bursts.