Short pulse laser-produced plasma x-ray sources

Abstract

The interaction of intense laser radiation (l > 1013 W/cm2) with plasmas has been extensively studied for the past decade. Since the primary motivations for these studies have been laser-driven inertial confinement fusion and XUV laser research, pulse lengths have ranged from 20 ps to > 1 ns with the majority of experiments being conducted with pulses longer than 100 ps. The physics characterizing the laser–plasma coupling in such experiments is qualitatively well known with the intense laser pulse interacting by a variety of processes with a low density (ne ≲ n c ≃ 1021 λ−2 μm, λ is the laser wavelength) rapidly expanding (v > 107 cm/s) plasma that forms early in the pulse. The interaction of intense ultrashort pulses (τ ≲ 1 ps) with plasmas, however, has not been extensively studied. The physics are of fundamental interest in the study of the early formation of laser plasmas, energy transport, and of the generation of ultrashort x-ray bursts. Such x-ray flashes, if sufficiently short, would be useful as a probe for exciting and studying relaxation processes in solids, in high resolution x-ray imaging, and in characterizing the impulse response of a wide number of x-ray detectors. In this presentation, we describe the results of a series of experiments characterizing the x-ray emission of a high density plasma irradiated with a 1-ps, 1–2-mJ dye laser focused to peak intensities of 1013 to 2 × 1014 W/cm2. Measurements of the total yield of XUV and x-ray energy (50 eV to 3 keV) spectra, and spatial and temporal characteristics of the emission are reported.