Self-aligning concave relativistic plasma mirror with adjustable focus

TL;DR

This study demonstrates that relativistic plasma mirrors can be highly reflective and focus reflected light to intensities ten times the incident, with adjustable focus and reflectivity controlled by pre-plasma conditions, combining experimental and computational insights.

Contribution

It introduces a method to control the focusing and reflectivity of relativistic plasma mirrors through pre-plasma management, supported by experimental and particle-in-cell simulation data.

Findings

Relativistic plasma mirrors achieve 0.6 to 0.8 reflectivity.

Reflected light can be focused to 10 times the incident intensity at 25 microns.

Reflectivity and focus are adjustable via pre-plasma length control.

Abstract

We report an experimental-computational study of the optical properties of plasma mirrors (PMs) at the incident laser frequency when irradiated directly at relativistic intensity (1e18 < I_0 < 1e19 W/cm^2) by near-normally incident (4 degree), high-contrast, 30 fs, 800 nm laser pulses. We find that such relativistic PMs are highly reflective (0.6 to 0.8), and focus a significant fraction of reflected light to intensity as large as 10I_0 at distance f as small 25 microns from the PM, provided that pre-pulses do not exceed 1e14 W/cm^2 prior to 20 ps before arrival of the main pulse peak. Particle-in-cell simulations show that focusing results from denting of the reflecting surface by light pressure combined with relativistic transparency, and that reflectivity and f can be adjusted by controlling pre-plasma length L over the range 0.5 < L < 3 microns. Pump-probe reflectivity measurements show the PM's focusing properties evolve on a ps time scale.