Diagnosis of laser-compressed shells based on absorption of core radiation

A diagnostic method for laser-imploded targets, particularly plastic shells, is described. It is based on the observation of a peak in the continuum x-ray spectrum emitted from the target. The peak is the result of the high absorption of low-energy x rays from the implosion core by the cooler, compressed shell surrounding the core. In glass targets, where the shell absorption is typically dominated by bound-free transitions (photoionization), the position of this peak in the spectrum depends on the shell {ρ} {Δ}r. In plastic targets, where the shell absorption is due mainly to free-free transitions (inverse bremsstrahlung), the position of the peak depends on the ρ² {Δ}r/T1/2 for the shell. We study the relationship between the position of the peak and these two quantities, both analytically as well as with a simulation code.