The absorption of laser radiation by a laser produced plasma.
Kunihiro, Dean Masao.
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Intense, Q-switched, neodynium laser pulses (1 -9 joules), were focused into a vacuum chamber containing 5 mil and .5 mil Mylar targets to investigate the absorption of laser radiation by the subsequent plasma produced. Absolute measurements of the incident and transmitted laser energies were obtained for various background pressures and incident beam intensities. The data show that the absorbed energy for both the 5 and .5 mil targets is linearly dependent on the input energy. At the same time, however, the percentage of energy absorbed is greater in the 5 mil target (78-90%) than in the .5 mil target (44-73%). Increased plasma temperatures both at higher input energies, and from the .5 mil targets may partially account for these observed results. Time resolved measurements of the incident and transmitted laser power pulses were also taken in order to determine the time dependent behavior of the absorption process. The results of these measurements substantiated that greater percentages of energy were absorbed by the 5 mil target. In addition, the measurements revealed a decrease, followed by an unexpected increase, in the transmitted power which would indicate that optimum absorption conditions exist relatively early during the expansion of the plasma.
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