High-repetition-rate hard X-ray generation with sub-millijoule femtosecond laser pulses

Hard X-ray radiation is generated at 1-kHz repetition rate on metal targets using 30-fs sub-millijoule laser pulses. Spinning-disc targets of medium-Z (Ti, Ci, Fe, Ni, Cu, Zn and Mo) and high-Z (Ta) metals are investigated. For medium-Z targets, characteristic K-shell emission (K-alpha and K-beta) is observed in the 4-20 keV energy range in addition to a broadband bremsstrahlung background. Whereas in former studies similar results have been obtained by applying laser pulses in the tens-to-hundreds-of-millijoules range, we observe characteristic X-ray generation even at applied pulse energies as low as 100 muJ. The well-defined emission wavelength, the high intensity and the high brightness of this radiation makes this source a promising tool for time-resolved experiments with high-repetition-rate (greater than or equal to 10 kHz) small-scale table-top laser systems.