Kα x-ray imaging of laser-irradiated, limited-mass zirconium foils

Abstract

X-ray fluorescence measurements to determine the effect of target heating on imaging efficiency, at a photon energy of 15.7 keV corresponding to the Kα line of zirconium, have been carried out using limited-mass foils irradiated by the Texas Petawatt Laser. Zirconium foils that ranged in volume from 3000 × 3000 × 21 μm3 to 150 × 150 × 6 μm3 were irradiated with 100 J, 8 ps-long pulses and a mean intensity of 4 × 1019 W/cm2. The Kα emission was measured simultaneously using a highly ordered pyrolytic graphite crystal spectrometer and a curved quartz imaging crystal. The measured ratio of the integrated image signal to the integrated spectral signal was, within the experimental error, constant, indicating that the imaging efficiency's dependence on temperature is weak throughout the probed range. Based on our experience of target heating under similar conditions, we estimate a temperature of ∼200 eV for the smallest targets. The successful imaging of Kα emission for temperatures this high represents an important proof of concept for Zr Kα imaging. At these temperatures, the imaging of Kα emission from lower-Z materials (such as Cu) is limited by temperature-dependent shifts in the Kα emission energy.