Highly stable plasma source produced on the liquid-gallium surface by a femtosecond laser pulse

Experimental results are presented which demonstrate that a plasma produced on the melted-gallium surface by a femtosecond laser pulse of intensity above 10¹⁶ W cm^-2 is an efficient and stable source of incoherent hard X-rays with a pulse repetition rate of 10 Hz. For gallium heated up to 270°C, the X-ray yield decreased by ~25% [from (2.2 ± 0.4) × 10^-4 % to (1.7 ± 0.4) × 10^-4 %] after 50000 laser shots, while the average energy of hot electrons decreased from 9.3 ± 0.9 to 9.0 ± 1.1 keV.