Modeling, measurements, and analysis of x-ray emission from 0.26-μm-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-μm wavelength, using 0.5–1.5-kJ, 1-ns full width at half maximum Gaussian pulses at intensities of 1×${10}^{14}$–2×${10}^{15}$ W/${\mathrm{cm}}^2$. 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 (${<10\mathrm{}}^{\mathrm{-}3}$ $E_{\mathrm{inc}}$). We infer increased conversion of incident light to soft x rays (72%±15% at 1×${10}^{14}$ and 38%±12% at 2×${10}^{15}$), 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.