Supersonic radiative heat waves in low-density high- Z material

The propagation of a radiation heat wave through lead-doped foam with a density of 80 mg/cm[sup 3] was experimentally investigated. The wave is driven by 100--150 eV [ital Hohlraum] radiation generated in 1--3 mm diam gold cavities heated by a 2.5 kJ, 0.8 ns laser pulse (wavelength 0.35 [mu]m). The propagation velocity was obtained from the delayed onset of intense thermal emission from the rear side of the foam sample. The results agree with theoretical predictions for a nonablative heat wave and with numerical simulations, and indicate that the radiation heat wave propagates with a velocity that is larger than the sound velocity in the heated foam.