X-ray generation in a cavity heated by 1.3- or 0.44-μm laser light. II. Time-resolved measurements

Abstract

Results are presented from experiments aiming at the study of the process of thermalization and confinement of the laser energy in closed geometry targets. The interior of spherical gold cavities (0.3–1.0 mm in diameter) has been irradiated with 300-ps pulses at average laser fluxes between 2×${10}^{12}$ and 5×${10}^{13}$ W/${\mathrm{cm}}^2$. A systematic study has been performed at 1.3- and 0.44-μm laser wavelength. The time-resolved x-ray spectrum of the radiation emitted by the cavities shows a double pulse structure. Furthermore, for λ=1.3 μm and during the second emission burst, M-band emission is observed. Analysis supports the hypothesis that, while the first burst emanates from the indirectly heated wall element, the second burst is due to expanding coronal plasma. Measurements showed that more favorable conditions can be achieved for λ=0.44 μm and deleterious effects like plasma filling and entrance hole closure can be avoided.