Opacity Measurements of a Hot Iron Plasma Using an X-Ray Laser

Abstract

The temporal evolution of the opacity of an iron plasma at high temperature (30-350 eV) and high density (0.001-0.2 g cm-3) has been measured using a nickel-like silver x-ray laser at 13.9 nm. The hot dense iron plasma was created in a thin (50 nm) iron layer buried 80 nm below the surface in a plastic target that was heated using a separate 80 ps pulse of 6-9 J, focused to a 100 microm diameter spot. The experimental opacities are compared with opacities evaluated from plasma conditions predicted using a fluid and atomic physics code.

Applications of laser wakefield accelerator-based light sources

“…Although experiments can now recreate conditions that are similar in density and temperature to the conditions in the Sun's interior, they usually do not directly measure opacity over a broad X-ray energy range. They either measure the emission properties of the heated plasma and assume that emissivity and opacity are in equilibrium [281], or use non-tunable X-ray lasers [282]. Recent seminal experiments at Sandia's Z machine [238] measured the iron opacity at solar interior conditions higher than predicted at energies around 1 keV, which could explain discrepancies between solar models and helioseismic observations.…”

Producing ultrashort, ultraintense plasma-based soft-x-ray laser pulses by high-harmonic seeding

“…It is expected that the uniformity of the gain region could be increased significantly by tamping the Se target on both sides (by CH, for instance) [29]. With a seed pulse of 0.1I s intensity under the revised conditions, sub-100-fs pulses (∼80 fs) of slightly higher intensity (∼2 × 10 11 W cm −2 for the unfocussed beam) are predicted.…”

Extreme ultraviolet interferometry of laser plasma material between the critical and ablation surfaces

“…with h > 1) can exist in plasmas dominated by strong absorption features [13]. Previously transmission measurements of plasma-based EUV lasers have provided information on plasma opacity [14] and the rate of ablation of solid targets irradiated by optical lasers [15]. In an experiment by Edwards et al [15], the rate of laser ablation was measured from the transmission of the EUV laser through the ablated target using the observation that ablated plasma material becomes transparent, so that the target transmission is dominated only by absorption in the remaining solid target.…”