Modeling, measurements, and analysis of x-ray emission from 0.26- microm-laser-irradiated gold disks.

We present modeling, measurements and analysis that extend our understanding of laser-plasma coupling and x-ray conversion processes to shorter laser wavelengths at kilojoule energies. We have studied the x-ray emission from gold-disk targets irradiated at 0.26-..mu..m wavelength, using 0.5--1.5-kJ, 1-ns full width at half maximum Gaussian pulses at intensities of 1 x 10/sup 14/--2 x 10/sup 15/ W/cm/sup 2/. We interpret measurements of the absolute broadband x-ray spectrum, the time history of sub-keV x-ray emission flux, and the broadband hard-x-ray spectrum. We find negligible hot-electron levels (<10/sup -3/E/sub inc/). We infer increased conversion of incident light to soft x rays (72% +- 15% at 1 x 10/sup 14/ and 38% +- 12% at 2 x 10/sup 15/), compared with longer wavelengths, as predicted. We find good overall agreement between the modeling and the data, but identify some areas that need to be better understood, including certain aspects of the x-ray emission spectrum and the decay rate of the emission pulse.