Areal-density measurement of laser targets using absorption lines

Absorption lines due to 1s-2p transitions in titanium ions are predicted to be observed in the implosion of titanium-doped shells. The measured absorption of these lines can be used to determine the peak areal density, rho Delta r, of the doped layer and hence of the total compressed shell. The absorption lines are studied by solving the radiation transport equation using opacity tables and hydrodynamic simulations. The absorption is a function not only of rho Delta r but also of the density and temperature of the absorbing layer. However, it is shown that the areal density can be estimated with reasonable accuracy by using the measured intensity of absorption and its distribution over the various absorption lines. The considerations affecting the choice of doping parameters are discussed, as well as the effect of integrating the measured spectrum over time and target volume. Published by Elsevier Science Ltd.