Key diagnostic components showing the triple pinhole x-ray camera, the Thomson imaging system with the objective lens and periscope to direct the signal to the camera equipped with a 248 nm interference filter and functioning with a spatial resolution of ~22 µm, and the transverse von Hámos spectrometer enabling the recording of a spatially resolved Kr(L) spectrum along the axis of the channel with a spectral resolution of ~3 eV and a spatial resolution of ~50 µm

<p><strong>Figure 1.</strong> Key diagnostic components showing the triple pinhole x-ray camera, the Thomson imaging system with the objective lens and periscope to direct the signal to the camera equipped with a 248 nm interference filter and functioning with a spatial resolution of ~22 µm, and the transverse von Hámos spectrometer enabling the recording of a spatially resolved Kr(L) spectrum along the axis of the channel with a spectral resolution of ~3 eV and a spatial resolution of ~50 µm. The axial von Hámos spectrometer is located on the channel <em>Z</em>-axis. The incident 248 nm beam with a pulse rate of ~0.1 Hz and diameter of ~10 cm enters from the right and is focused by the off-axis parabolic mirror to the position of the Kr cluster target. The orifice of the 2.65 mm diameter sonic nozzle that furnishes the (Kr)<em><sub>n</sub></em> target with upward vertically directed flow is indicated. The single-pulse data from all four cameras are collected under computer control along with the 248 nm pulse energy, nozzle plenum pressure, and Kr gas temperature.</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>