Comparative Kr(L) spectra obtained under three different modalities of excitation are shown
Figure 12. Comparative Kr(L) spectra obtained under three different modalities of excitation are shown. (a) Axially recorded Kr(L) spectrum produced with self-trapped 248 nm channel (this work, file 677/18 May 2012). The principal feature is the 1P1 → 1S0 Kr26+ 3s → 2p transition at λ 7.504 Å. (b) Kr(L) emission spectrum recorded with 248 nm excitation without channelled propagation. The emission profile is dominated by a broad feature involving several transitions in the 6.8–7.2 Å range. For details, see . (c) Kr(L) spectrum obtained with excitation at ~1 µm without channelled propagation. See  for additional details.
Experimental evidence demonstrating amplification on the Kr26+ 3s→2p transition at λ 7.5 Å (~1652 eV) generated from a (Kr)n cluster medium in a self-trapped plasma channel produced with 248 nm femtosecond pulses is presented. The x-ray beam produced had a spectral width of ~3 eV and a corresponding beam diameter of ~150 µm, properties that were simultaneously determined by a two-dimensional x-ray spectral image formed with an axially placed von Hámos spectrometer and a matching Thomson image of the spatial electron density generated by the x-ray propagation.