Thermal x-ray confinement in a laser-heated gold cavity was investigated. Intense blue laser light (wavelength 351 nm, energy 5 kJ, duration 0.9 ns) irradiated the inner surface of (1–3)-mm-diam gold shells at average intensities up to 2×${10}^{14}$ W/${\mathrm{cm}}^2$ to generate the source x ray for the confinement. A maximum brightness temperature of 240 eV and a quality factor of confinement of N=5.3 (corresponding to a reemission coefficient of r=0.84) have been achieved. Experimental results are in satisfactory agreement with theoretical predictions based on the self-similar ablative heat wave driven by radiation and with numerical simulations.

• Received 1 April 1991

DOI:https://doi.org/10.1103/PhysRevA.44.8323