X-RAY-EMISSION FROM PLASMAS CREATED BY SMOOTHED KRF LASER IRRADIATION

The x-ray emission from plasmas created by the Naval Research Laborato ry Nike KrF laser [Phys. Plasmas 3, 2098 (1996)] was characterized usi ng imaging and spectroscopic instruments. The laser wavelength was 1/4 mu m, and the beams were smoothed by induced spatial incoherence (ISI ). The targets were thin foils of CH, aluminum, titanium, and cobalt a nd were irradiated by laser energies in the range 100-1500 J. A multil ayer mirror microscope operating at an energy of 95 eV recorded images of the plasma with a spatial resolution of 2 mu m. The variation of t he 95 eV emission across the 800 mu m focal spot was 1.3% rms. Using a curved crystal imager operating in the 1-2 keV x-ray region, the dens ity, temperature, and opacity of aluminum plasmas were determined with a spatial resolution of 10 mu m perpendicular to the target surface. The spectral Line ratios indicated that the aluminum plasmas were rela tively dense, cool, and optically thick near the target surface. The a bsolute radiation flux was determined at 95 eV and in x-ray bandpasses covering the 1-8 keV region. The electron temperature inferred from t he slope of the x-ray flux versus energy data in the 5-8 keV region wa s 900 eV for an incident laser energy of 200 J and an intensity of app roximate to 10(13) W/cm(2).