Efficient laser-induced 6-8 keV x-ray production from iron oxide aerogel and foil-lined cavity targets

The performance of new iron-based laser-driven x-ray sources has been tested at the OMEGA laser facility for production of x rays in the 6.5-8.5 keV range. Two types of targets were experimentally investigated: low-density iron oxide aerogels (density 6 - 16 mg / cm³) and stainless steel foil-lined cavity targets (steel thickness 1 - 5 μ m). The targets were irradiated by 40 beams of the OMEGA laser (500 J/beam, 1 ns pulse, wavelength 351 nm). All targets showed good coupling with the laser, with 5 of the incident laser light backscattered by the resulting plasma in all cases (typically 2.5 ). The aerogel targets produced T e 2 to 3 keV, n e 0.12 - 0.2 critical density plasmas yielding a 40-60 laser-to-x-ray total conversion efficiency (CE) (1.2-3 in the Fe K-shell range). The foil cavity targets produced T e ∼ 2 keV, n e ∼ 0.15 critical density plasmas yielding a 60-75 conversion efficiency (1.6-2.2 in the Fe K-shell range). Time-resolved images illustrate that the volumetric heating of low-density aerogels allow them to emit a higher K-shell x-ray yield even though they contain fewer Fe atoms. However, their challenging fabrication process leads to a larger shot-to-shot variation than cavity targets.