Amplification at λ ∼ 2.8 Å on double-vacancy states produced by 248 nm excitation of Xe clusters in plasma channels

Abstract

double-vacancy states undergo strong amplification in relativistic self-trapped plasma channels on 3d → 2p transitions in the λ = 2.78–2.81 Å region. The 2P3/2 → 2S1/2 component at λ ≅ 2.786 Å exhibits saturated amplification demonstrated by both (1) the observation of spectral hole-burning in the spontaneous emission profile and (2) the correlated enhancement of 3p → 2s cascade transitions (2S1/2 → 2Pj; j = 1/2, 3/2) at λ = 2.558 Å and λ = 2.600 Å. The condition of saturation places a lower limit of ∼1017 W cm−2 on the intensity of the x-ray beam produced by the amplification in the channel. The anomalous strength of the amplification signalled by the saturation mirrors the equivalently anomalous behaviour observed for all 3d → 2p transitions corresponding to single-vacancy Xeq+ arrays (q = 31, 32, 34, 35, 36) that exhibit gain. The conspicuous absence of amplification involving states with double-vacancy configurations suggests the operation of a selective interaction that enhances the production of states. Overall, the generation of double-vacancy states of this genre demonstrates that an excitation rate approaching ∼1 W/atom for ionic species is achievable in self-trapped plasma channels.