Plasma dynamics of a confined extreme ultraviolet light source

Abstract

Laser plasmas were generated by ablation of aluminum targets via a Nd:YAG glass laser, of pulse energy 0.8 J, and duration 15 ns (full width at half maximum) at the fundamental wavelength (1.064 μm). Emission lines in the wavelength range of 27–32 nm (45–37.8 eV) were mapped over a spatial range extending out 1.8 mm from the target surface and for a temporal range of 42 ns after the termination of the laser pulse. Two targets were utilized: a planar surface and a rectangular cavity. The latter was composed of a rectangular shaped cavity of depth 3 mm and height 1.2 mm, cut into an aluminum massive. An irradiance of Ip∼1011 W/cm2 was delivered to both targets and the confining influence of the rectangular cavity upon plasma formation and expansion was studied. Diagnostics of the emitted spectra reveal the unique dynamics of restricted plasma plume expansion, which results in plasma-surface collisions and subsequent plasma rebound within the cavity. These effects give rise to strong enhancement of both continuum and line emission in the contained plasma plume. These enhancements are especially evident for the more highly charged ions. Superior emission from plasma-surface collisions are associated with “forced recombination” during early time scales, while enhanced emission at later stages are associated with plasma plume component rebound and collision.