The effect of prepulse on X-ray laser development using a powerful subpicosecond KrF laser

A high power UV laser has been developed as a pump source for short wavelength (down to 1 nm) X-ray lasers. Various schemes are considered and theoretical analysis is discussed. Spectroscopic studies of laser-target interaction have been performed and, in particular, the effect of a prepulse on plasma generation has been investigated. Analysis of the observed spectra indicates that reduction of the prepulse energy results in a higher temperature plasma. Investigation of the interaction using thin layered targets is also presented. These data provide evidence for initially hot plasma conditions generated from target layers ≦150 A. Discussions of proposed laser schemes at 1–5 nm are presented.