X-ray brilliance measurements of a subpicosecond laser plasma using an elliptical off-axis reflection zone plate

Abstract

An absolutely calibrated spectrograph based on a new single x-ray optical element, namely, an elliptical off-axis reflection zone plate, has been used for brilliance measurements of a laser-produced plasma of solid carbon and boron nitride. The spectral range investigated, λ≈2.1–4.3 nm, covers the emission from excited H- and He-like carbon states to the ground state. The plasma was generated by a subpicosecond high-intensity KrF*-laser pulse at an intensity of 2×1016 W/cm2. Under these conditions more than 1011 photons/sr per pulse were emitted in the strongest lines, demonstrating that this plasma can serve as an intense x-ray source. The measured spectra were in good agreement with a simulation that used the radiation program ration for an electron density of ne=4×1022 cm3 and an electron temperature of Te=90 eV. Measurements of spectral changes at different angles of incidence of the laser beam confirmed theoretical predictions for line intensities.