Prospect of multiphoton induced inner shell excitations for X-ray laser pumping

Summary Form only given, as follows. The possibility that modest-energy, high-brightness table-top lasers could be used to pump a medium in an X-ray laser geometry is being studied. The ultrahigh irradiance produced in the focal volumes of such lasers generate multiphoton-induced nonlinear effects in target materials. Focusing 20-mJ, 0.7-ps pulses to a peak irradiance of approximately 3*10/sup 17/ W/cm/sup 2/ at a repetition rate of 3 Hz, the authors have searched for prompt fluorescence photons from inner shell excitations in Xe gas atoms at a density of approximately 5*10/sup 15/ cm/sup -3/. In more than 100000 laser shots they observed only delayed photons (distributed from 3 to 200 ns after the laser pulse), presumably due to recombination processes, but not a single prompt photon of energy >or approximately=50 eV. This sets an approximate upper limit for the production of prompt photons per Xe atom at P>