Soft x-ray emission from double-pulse laser-produced plasma

A frequency-doubled 2-GW Nd:glass laser with a small satellite pulse (1% of the main pulse) was used for investigations of the soft x-ray conversion efficiency in double-pulse irradiation of planar Cu targets. The separation of the two pulses was varied between ±1.3 ns, and the pulse duration between 45 and 800 ps. For the case of a prepulse, an enhancement of the soft x-ray emission by a factor of 2–3 was observed at pulse durations between 45 and 200 ps. A smaller increase was achieved for positive delays (‘‘post-pulse’’), and no improvement for 800-ps pulses.