Details of Thomson images shown in panels (a) and (b) of figure 9

<p><strong>Figure 10.</strong> Details of Thomson images shown in panels (a) and (b) of figure <a href="" target="_blank">9</a>. These data correspond to file 520/14 June 2012. (a) Isometric view of Thomson image showing extension into the dark x-ray zone <em>Z</em> ≥ 0.5 mm illustrated in figure <a href="" target="_blank">9</a>(c). The arrow at <em>Z</em> = <em>Z</em><sub>1</sub>  1.8 mm specifies the location of the endpoint of the visible Thomson signal that indicates the presence of ionized material. (b) Axial line-out of the Thomson data pictured in panel (a). A discernable extension of the ionization is visible out to <em>Z</em> = <em>Z</em><sub>1</sub>  1.8 mm, a distance that represents a penetration of ~1.3 mm into the x-ray dark region shown in figure <a href="" target="_blank">9</a>(c) and is estimated to be comparable to the linear absorption length of the Kr cluster medium. This observation agrees with an earlier estimate [<a href="" target="_blank">13</a>] of the ability to reach saturation of the absorption in Kr by Kr(L) emission; the clear conclusion was that, with a saturation parameter <em>ħ</em>ω/σ 400 J cm<sup>−2</sup>, linear absorption would necessarily govern.</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>