Comparison of transverse (blue) and axially recorded (red) Kr(L) spectra

<p><strong>Figure 6.</strong> Comparison of transverse (blue) and axially recorded (red) Kr(L) spectra. These data correspond to file 677/18 May 2012. (a) The transverse spectrum corresponding to <em>Z</em> = −0.9 mm illustrated in figure <a href="http://iopscience.iop.org/0953-4075/46/15/155601/article#jpb468344f5" target="_blank">5</a>(a) is directly compared to the axial spectrum associated with the focal plane of the axial spectrometer located at Z = 0.3 mm. The Kr<sup>26+</sup> transition at λ 7.504 Å in the axial spectrum is sharply enhanced and significantly narrowed (FWHM) with respect to the transverse spectrum. The other Kr<sup>26+</sup> and Kr<sup>25+</sup> lines are neither enhanced nor spectrally narrowed. (b) Plasma channel morphology showing the spatial location of focal plane of the spectrometer associated with the axial Kr(L) spectrum (red) presented in panel (a) with a spatial resolution estimated to be ~50 µm. The shaded zone centred at <em>Z</em> = 0.3 mm represents the depth-of-field of the axial von Hámos spectrometer.</p> <p><strong>Abstract</strong></p> <p>Experimental evidence demonstrating amplification on the Kr<sup>26+</sup> 3s→2p transition at λ 7.5 Å (~1652 eV) generated from a (Kr)<em><sub>n</sub></em> 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.</p>