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, l5532 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 l53.37 nm line emission is more than 3310 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. © 1996 American Institute of Physics. @S0003-6951~96!03938-1#