Recent developments in X-ray laser research at LLE

Recent experiments using multiple-foil target designs for a collisional-excitation X-ray laser in Ne-like nickel and germanium are reported. These targets, which are designed to yield higher gains than single-exploding-foil targets, are irradiated by 600-ps pulses of 351-nm light in a single 18-mm line. The lasing lines at approximately 230 AA are observed with a 1-m grazing incidence grating spectrometer. The relative merits of different pump-laser wavelengths have been studied, and experimental results have been obtained for three wavelengths: 1.06 mu m, 527 nm, and 351 nm. For recombination X-ray laser studies, 1000-2000-AA foils have been irradiated with 100-ps pulses of 351-nm light. The spatially resolved X-ray spectra show the extent to which the hydrogenic and heliumlike species expand and recombine. Plans have been developed for the conversion of the laser to a approximately 100-J-10-ps laser (10 TW), which will be used for producing a recombinationally pumped laser in Al that is predicted to emit at 39 AA.<>