DAMAGES TO B4C W MULTILAYER MIRRORS BY INTENSE SOFT-X-RAY BURSTS/

B4C/W an x-ray beamline at the MEGAJOULE facility are susceptible to x -ray damage. The OCTAL laser was implemented to generate a gold plasma with a continuous x-ray spectrum (0.1 to 1.5 keV) used to irradiate t he mirror. The fluence on the sample is 0.05 J/cm(2) per shot. The pul se duration is about 1 ns. The temporally integrated spectrum reflecte d by the mirror is analyzed by a bent crystal spectrometer and recorde d on photographic film. The spectral analysis suggests that an increas e of the mean period of the multilayer happens during the second shot. This expansion is estimated to be 5% with respect to the unexposed mi rror. After the second shot, destruction of the multilayer coating in the central part of the sample and irreversible damages in the other p art characterized by a decrease of Bragg reflectivity have been observ ed. (C) 1996 American Institute of Physics.