Experimental data of several forms have been obtained which constitute interlocking concordant evidence of amplification in self-trapped plasma channels on several transitions of the Xe(L) hollow atom spectrum at wavelengths in the range λ ~ 2.71−2.93 Å. Specifically, they are (α) strongly enhanced spectra arising from Xe31+, Xe32+, Xe34+, Xe35+, Xe36+, and Xe37+ ions recorded from the channel in the forward (axial) direction, (β) the measurement of a corresponding spectral narrowing on the directionally enhanced lines emitted from the channel, (γ) evidence for saturation of three of these transition arrays (Xe34+, Xe35+, Xe36+) given by the simultaneous quenching (spectral hole-burning) of the corresponding spontaneous emission from them in transversely recorded spectra only when amplifying channels are, observations that correlate fully with the measured spectral narrowing, and (δ) small-scale structural damage to both (i) the 12.7 µm thick Ti foil located at a separation of ~2.5 cm from the source at the entrance to the axially located von Hámos spectrograph used for spectral measurements and, with the von Hámos spectrograph removed, (ii) similar Ti foils protecting film packs axially positioned at a distance of 12.5 cm from the xenon cluster target. In the case involving the Ti foil shielding the spectrograph, we have recorded a canonical spatial mode pattern consisting of a regular circular array of holes pierced in the foil having an individual feature size of ~1 µm and an overall diameter of ~5 µm. This observation (a) indicates a divergence of δθx ≅ 0.2 mr, a value approximately twice that expected from a coherent aperture formed by a channel with a diameter of 2−3 µm that radiates at a wavelength ~2.9 Å, and (b) demonstrates the spatial coherence of the amplified x-rays. The detection of the amplified beam with the film packs at a distance of ~12.5 cm from the source confirms the divergence of δθx ≅ 0.2 mr. In this case, since the damage to the Ti foil is not fully penetrating, the morphology of the physical damage produced on the Ti surface is matched by the shape of the exposure of the transmitted x-rays on the film located directly behind it. Further, the observed damage to the Ti foils is consistent with the estimated saturation flux of ~10 J/cm2 for the Xe(L) transitions and, consequently, with the observation of the spectral hole-burning. The spectral width of a single enhanced feature attributed to Xe32+ at 2.71 Å shown in Fig. (1) is δ32 ~4 eV, the experimental resolution limit; the corresponding width of the full Xe(L) hollow atom spectral profile is δσ ~200 eV. These results give a peak brightness of ~ 1031−1032 photons ⋅ s−1 ⋅ mm−2 ⋅ mr−2 (0.1% Bandwidth)−1.
© 2003 Optical Society of AmericaPDF Article