High repetition rate plasma mirror device for attosecond science.

This report describes an active solid target positioning device for driving plasma mirrors with high repetition rate ultra-high intensity lasers. The position of the solid target surface with respect to the laser focus is optically monitored and mechanically controlled on the nm scale to ensure reproducible interaction conditions for each shot at arbitrary repetition rate. We demonstrate the target capabilities by driving high-order harmonic generation from plasma mirrors produced on glass targets with a near-relativistic intensity few-cycle pulse laser system operating at 1 kHz.

Electron vacuum acceleration in a regime beyond Brunel absorption.

We describe a new regime of electron acceleration in laser plasmas driven by ultrafast pulses of relativistic intensity, in which space-charge separation leads to strongly enhanced laser absorption and the production of 20 MeV (p/m0c approximately = 40) electrons driven outward in vacuum. 1D PIC simulations show that intense attosecond pulses generated around critical density can sweep electrons outward over many wavelengths in distance. With increasing interaction scale length, absorption generalizes from the Brunel regime to one in which absorption is primarily into electrons of energy >>5 MeV.

Phase properties of laser high-order harmonics generated on plasma mirrors.

As a high-intensity laser-pulse reflects on a plasma mirror, high-order harmonics of the incident frequency can be generated in the reflected beam. We present a numerical study of the phase properties of these individual harmonics, and demonstrate experimentally that they can be coherently controlled through the phase of the driving laser field. The harmonic intrinsic phase, resulting from the generation process, is directly related to the coherent sub-laser-cycle dynamics of plasma electrons, and thus constitutes a new experimental probe of these dynamics.