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 (1018<I0<1019 W/cm2) by near-normally incident (4°), high-contrast, 30 fs, 800 nm laser pulses. We find that such relativistic PMs are highly reflective (0.6–0.8) and focus a significant fraction of reflected light to intensity as large as ∼10I0 at distance f as small as ∼25 μm from the PM, provided that pre-pulses do not exceed 1014 W/cm2 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 μm. Pump-probe reflectivity measurements show that the PM's focusing properties evolve on a ps time scale.
Highlights
Plasma mirrors (PMs) have become standard tools for improving temporal contrast1–5 and spatial profile6 of intense, ultrashort laser pulses
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 (1018 < I0 < 1019 W=cm2) by near-normally incident (4), high-contrast, 30 fs, 800 nm laser pulses
A pulse cleaned by reflection from one or more primary PMs can subsequently be focused to relativistic intensity (I տ 1018 W/cm2 for visible or near infrared wavelengths), where its interaction with a secondary PM can be studied without severely pre-expanding its surface
Summary
Plasma mirrors (PMs) have become standard tools for improving temporal contrast and spatial profile of intense, ultrashort laser pulses. A pulse cleaned by reflection from one or more primary PMs can subsequently be focused to relativistic intensity (I տ 1018 W/cm for visible or near infrared wavelengths), where its interaction with a secondary PM can be studied without severely pre-expanding its surface.. A pulse cleaned by reflection from one or more primary PMs can subsequently be focused to relativistic intensity (I տ 1018 W/cm for visible or near infrared wavelengths), where its interaction with a secondary PM can be studied without severely pre-expanding its surface.7,8 Such relativistic PMs generate high-order harmonics in the form of attosecond bursts, and even focus those harmonics when the light pressure of the incident pulse dents the PM’s reflecting critical surface. These include self-aligned retroreflection of the transmitted drive pulse of a laser-plasma accelerator (LPA) onto trailing electrons to produce bright Compton backscatter x-rays and coupling such a drive pulse over a short distance into the second or subsequent stage of a multi-stage LPA. In addition, even for studies primarily devoted to highly nonlinear laser-PM processes such as high-order harmonic generation, vacuum heating, a)Present address: Center for High Energy Density Science, The University of Texas at Austin, Austin, TX 78712, USA
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