Reflecting light from a mirror moving close to the speed of light has been envisioned as a route towards producing bright X-ray pulses since Einstein’s seminal work on special relativity. For an ideal relativistic mirror, the peak power of the reflected radiation can substantially exceed that of the incident radiation due to the increase in photon energy and accompanying temporal compression. Here we demonstrate for the first time that dense relativistic electron mirrors can be created from the interaction of a high-intensity laser pulse with a freestanding, nanometre-scale thin foil. The mirror structures are shown to shift the frequency of a counter-propagating laser pulse coherently from the infrared to the extreme ultraviolet with an efficiency >104 times higher than in the case of incoherent scattering. Our results elucidate the reflection process of laser-generated electron mirrors and give clear guidance for future developments of a relativistic mirror structure.

A class of spectroscopic line ratios has been adapted as a diagnostic of electron temperature from (100 eV to &1 keV. The diagnostic makes use of the ratio of line intensities from isoelectronic states of diA'erent elements in specially prepared targets. The diagnostic is simple to interpret, shows weak dependence on plasma density, requires only low to moderate spectral resolution, uses a single charge state, and can be adapted to minimize line reabsorption and wavelength coincidences with other spectral lines. We present theoretical and experimental results.

International audienceThe effects of small amounts of energy delivered at times before the peak intensity of ultrahigh-intensity ultrafast-laser pulses have been a major obstacle to the goal of studying the interaction of ultraintense light with solids for more than two decades now. We describe implementation of a practical double-plasma-mirror pulse cleaner, built into a f = 10 m null telescope and added as a standard beamline feature of a 100 TW laser system for ultraintense laser-matter interaction. Our measurements allow us to infer a pulse-height contrast of 5×10^11—the highest contrast generated to date—while preserving ∼ 50% of the laser intensity and maintaining excellent focusability of the delivered beam. We present a complete optical characterization, comparing empirical results and numerical modeling of a double-plasma-mirror system

The development of bright free-electron lasers (FEL) has revolutionized our ability to create and study matter in the high-energy-density (HED) regime. Current diagnostic techniques have been successful in yielding information on fundamental thermodynamic plasma properties, but provide only limited or indirect information on the detailed quantum structure of these systems, and on how it is affected by ionization dynamics. Here we show how the valence electronic structure of solid-density nickel, heated to temperatures of around 10 of eVon femtosecond timescales, can be probed by single-shot resonant inelastic x-ray scattering (RIXS) at the Linac Coherent Light Source FEL. The RIXS spectrum provides a wealth of information on the HED system that goes well beyond what can be extracted from x-ray absorption or emission spectroscopy alone, and is particularly well suited to time-resolved studies of electronicstructure dynamics.