Stable Power Compression with Efficient Relativistic UV Channel Formation in Cluster Targets

Abstract

Comparative single-pulse studies of self-trapped plasma channel formation in Xe and Kr cluster targets produced with 1–2 TW femtosecond 248 nm pulses reveal energy-efficient (>90 %) power compression with formation of relativistic ultraviolet (248 nm) self-trapped plasma channels. A key observation is the highly robust stability of the channeled propagation characteristic of both materials. Images of the channel morphology produced by Thomson scattering from the electron density correlated with the direct visualization of the Xe(M) and Kr(L) X-ray emission from radiating ions illustrate (1) the channel formation, (2) the narrow region of confined trapped propagation, (3) the abrupt termination of the channel that occurs at the point the power falls below the critical power P_cr, and, in the case of Xe channels, (4) the presence of saturated absorption of Xe(M) radiation that generates an extended peripheral zone of ionization. These observations provide new quantitative information on the channeling mechanism and its ability to produce very high power densities under stable conditions. The measured rates for energy deposition per unit length are ∼1.46 J/cm and ∼0.82 J/cm for Xe and Kr targets, respectively, and the single-pulse Xe(M) energy yield is estimated to be >50 mJ, a value indicating an efficiency >20 % for ∼1 keV X-ray production from the incident 248 nm pulse. An efficiency of this magnitude heralds the future production of kiloelectronvolt X-ray pulses with energies of ∼1 J.