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Measurements of Kα line and bremsstrahlung continuous x-ray emission from high-intensity laser-irradiated thin targets are presented. The experiments were performed at the SG-II UP Petawatt laser. Self-standing Sn foils varying thicknesses and Sn foils backed by the thick substrate were irradiated by the laser pulses up to 300 J of energy with peak intensity higher than 1018 W/cm2. A transmission curved crystal spectrometer and a filter-stack spectrometer were used to measure the Kα line and bremsstrahlung x-ray spectral distribution, respectively. Both Kα and 70–200 keV x-ray yields decrease 3- to 5-fold for target backed by the substrate. 2- to 4-fold reduction of Kα and 70–200 keV x-ray yields for the 8.5 μm targets relative to 50 μm targets was observed. Moreover, a significant background x-ray emission generated from the target holder reduces the ratio of signal to noise. Adopting a low-Z material holder can mitigate the x-ray background noises. This study is instructive to optimize target design for the high-intensity laser-driven Kα or continuous x-ray sources.
Li et al. (Sat,) studied this question.