Time-Resolved X-Ray Brightness Measurements from Short-Pulse, Laser-Irradiated Thin Foils

The production of soft x rays ($\sim $keV) from high-intensity, short-pulse laser plasmas is important for future applications such as backlighting cryogenic targets on OMEGA. The physics of short-pulse laser--plasma interactions and the coupling of laser energy into both the thermal plasma and fast electrons were studied to optimize x-ray production from mass-limited aluminum foil targets. Foil targets of various sizes from 50 to 500 \textit{$\mu $}m were irradiated with picosecond pulse duration laser pulses at intensities similar to OMEGA area backlighter schemes (10$^{18}$ to $>$10$^{19}$ W/cm$^{2})$. The time-resolved x-ray emission was measured with a conically curved crystal coupled with an ultrafast x-ray streak camera. The He$_{\alpha }$ and the Ly$_{\alpha }$ line emission from aluminum foils was spectrally measured and temporally resolved. In addition, the x-ray source was characterized with a calibrated time-integrated spectrograph and spatially resolved images were taken with a spherically curved Bragg crystal. The combination of these measurements allows the brilliance of the x-ray line source to be inferred. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.