EXPERIMENTAL AND THEORETICAL INVESTIGATION OF NEON-LIKE SELENIUM X-RAY LASER SPECTRAL LINEWIDTHS AND THEIR VARIATION WITH AMPLIFICATION

This paper describes our recent x-ray laser spectral linewidth measure ments and discusses the consequences of these measurements. The experi ments observed the 206.38- and 182.45-angstrom laser transitions in ne onlike selenium using an extremely high-resolution soft-x-ray spectrom eter, and measured the spectral linewidths and relative spectral inten sities of the laser lines from amplifiers of varying lengths. The data allow the intrinsic (unamplified) linewidths of the 206- and 182-angs trom lasers to be extrapolated as 50 and 35 mangstrom, respectively. T he intrinsic spectral width of the 206-angstrom laser is somewhat grea ter than the predicted 43-mangstrom Voigt-profile width based on calcu lated transition rates and on the expected ion temperature in the plas ma, and while the number of data points obtained with the 182-angstrom laser is small and a conclusive comparison with calculations is not p ossible, the extrapolated intrinsic linewidth of this laser is clearly consistent with the predicted 37-mangstrom Voigt-profile width and is not significantly broader or narrower than expected. The data also sh ow significant gain narrowing of both lines with increasing amplifier length and show no significant rebroadening of the 206-angstrom laser in long, saturated amplifiers. We discuss line broadening and line tra nsfer calculations we have performed which show that the saturated 206 -angstrom laser line transfer behavior can be treated homogeneously du e to non-negligible homogeneous lifetime broadening contributions, whi ch significantly reduce inhomogeneous Doppler saturation rebroadening, and due to collisional redistribution rates which are large enough in any case to homogenize the otherwise inhomogeneous Doppler contributi ons. We also discuss the implications of these results with regard to earlier suggestions that Dicke narrowing effects could play a signific ant role in determining the intrinsic line profiles of these laser tra nsitions, and we conclude that Dicke narrowing effects are not likely to be significant for either laser.