Ultraviolet prepulse for enhanced x-ray emission and brightness from droplet-target laser plasmas

We show that an ultraviolet prepulse significantly enhances the water-window x-ray emission and brightness for a droplet-target laser plasma. By combining a 65 mJ, 120 ps, lambda = 532 nm main pulse with an up to 3 mJ prepulse, the emitted x-ray photon flux may be increased more than eight times. The resulting C VI lambda = 3.37 nm line emission is more than 3 x 10(12) photons/sr . pulse, corresponding to a conversion efficiency above 3%/line. The integrated spectral brightness is increased two times and is found to reach its maximum for different prepulse parameters than those resulting in maximum photon flux. (C) 1996 American Institute of Physics.