Enhancement of hard x-ray emission from a copper target by multiple shots of femtosecond laser pulses

The x-ray generation from a copper disk target by irradiation of femtosecond laser pulses (42 fs, 4T W in maximum) has been investigated. The intensity of the x rays is enhanced about 100 times by the multiple laser shots on the target. A temporal profile of the x rays consists of two components: a short pulse with a time duration of 6 ps and a pulse with exponential decay. The enhancement of the x rays corresponds to the increase of the short-pulse component. A relationship between the intensity enhancement and morphology of the irradiated target is discussed.