Characterization of hard X-ray sources produced via the interaction of relativistic femtosecond laser pulses with metallic targets
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X-ray emission resulting from interactions of intense laser pulses with solid metal targets (Ni, Cu, Mo, Ag, and Sn) at 0.5 kHz repetition rate is measured using pulse energies of up to 12 mJ. A comparison of the conversion of laser pulse energy to total X-ray emission energy is made with respect to the previous measurements at lower energy (< 3 mJ). In the present experiments, the total bremsstrahlung conversion efficiency is found to increase by an order of magnitude for all targets as the energy in increased. The Kα line emission conversion efficiency also increases with incident pulse energy for all targets. In addition, the ratio between line and bremsstrahlung emission in the X-ray spectral region was significantly reduced at higher energies because of the large increase in bremsstrahlung. In general, the X-ray source size increases as the laser energy increased and the ellipticity of the X-ray source also increased in the laser polarization direction, with the effect becoming very pronounced at higher energies. Phase-contrast imaging of a nanospray emitter and a 3D printed plastic target was also performed using Cu and Mo targets.
This work is supported by the Defense Advanced Research Projects Agency under contract number N66001-11-1-4208 and by the Air Force Office of Scientific Research under award number FA9550-16-1-0121. The author wishes to acknowledge the Lurie Nanofabrication Facility for their support in coating the targets.
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