Generation of incoherent picosecond x-ray pulses: Resonant production and advantage of using thin films

The feasibility of using thin, freely suspended films as a target in femtosecond laser-produced plasma (FLP) experiments is discussed. The conditions for producing a significant increase in the FLP temperature (as much as a few kilo-electron-volts) are determined by use of a simple numerical code. An increase in temperature leads to an increase in x-ray yield as well as to a shift of the x-ray spectrum toward shorter wavelengths. The experimental results on soft-x-ray generation from FLP on resonance lines of highly stripped hydrogenlike and heliumlike boron ions are supported by results obtained with this code. FLP is also analyzed as a source of soft x-rays, particularly in the 2-4-nm region (the so-called water window). (C) 1996 Optical Society of America