Transverse Thomson and x-ray images of the plasma channel
Figure 9. Transverse Thomson and x-ray images of the plasma channel. Data represent file 520/14 June 2012. The physical parameters are the following: 248 nm pulse energy 200 mJ, Kr plenum temperature T = 295 K, and Kr plenum pressure 185 psi. The centre of the nozzle is located at position Z = 0 mm. The arrows located at position Z = 1.25 mm in all panels indicate the position of the focal plane of the axial von Hámos spectrometer. (a) Thomson image of the electron density. A lateral extension is visible at Z 0 mm along with a narrow axial elongation well into the zone Z ≥ 0.5 mm. This axial extension is illustrated further in figure 10. (b) Panel (a) represented as an isometric view. (c) The x-ray morphology of the plasma channel viewed transversely with the pinhole camera corresponding to the Thomson image shown in panel (a). The spatial region defined by Z ≥ 0.5 mm is completely dark. The shaded zone centred on Z = 1.25 mm indicates the depth-of-field of the axial von Hámos spectrometer.
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.