Detailed space-resolved characterization of a laser-plasma soft-x-ray source at 13.5-nm wavelength with tin and its oxides

Space-resolved soft-x-ray spectra of laser-produced plasmas of pure-Sn metal and its oxides were measured in the spectral range 7-23 nm. We established a comprehensive spectroscopic database of the emission characteristics of the transition array of highly ionized Sn near 13.5-nm wavelength by varying the incident laser energy and the angle between the observation axis and the target normal. We examined the narrow spectral bandwidth of the transition array obtained by use of a gas-mixed fine-particle (SnO2 powder) target proposed by Matsui et al. [Proc. SPIE 3886, 610 (2000)]. We selected pure-Sn metal, SnO and SnO2 powder, and SnO2 thin-film targets with which to clarify the roles of additional constituent ions, such as O and Ar, in plasmas of the gas-mixed fine-particle targets. The space-resolved spectra show that the bandwidth of the transition ar Pay broadens dramatically and that the wavelength at peak intensity shifts slightly toward longer wavelengths with increasing distance from the original target surface or with decreasing incident laser energy. The origins of the broadening and the wavelength shift can be explained in terms of an increase in the range of ion stages that contribute to the transition array and in terms of transfer of the dominant ion stages to lower stages. The narrow bandwidth of the gas-mixed line-particle target is probably due to the presence of a narrow range of moderate ion stages. (C) 2000 Optical Society of America [S0740-3224(00)01609-X].