Thermal transport measurements in six-beam, ultraviolet irradiation of spherical targets

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Abstract
Thermal transport, mass ablation rates, and preheat have been studied in spherical irradiation at λ=351 nm, using six of the 24 beams of the OMEGA spherical irradiation laser system at the Laboratory for Laser Energetics. Mass ablation rates are higher at 351-nm than at 1054-nm irradiation, even when compared at the same absorbed irradiance. Similar to the case of 1054-nm irradiation, very deep burnthrough was found at 351 nm. However, the shallow-gradient temperature profile at the heat front, characteristic of the experiments at 1054 nm, was not observed here, nor was the large difference between uniform and tight focus irradiation of spherical targets. Ablation pressures derived from charge-collector data rise from 10 to 100 Mbar for absorbed irradiance in the range of 4×1013 to 9×1014 W/cm2.