Absorption of laser radiation by a target in the case of a ponderomotive force and a finite thermal conductivity

The absorption of laser radiation by a spherical microtarget is analyzed with the ponderomotive force included explicitly in the gasdynamic equations. The analysis is carried out for the experimental conditions at the ISKRA-4 apparatus, in which the wavelength of the heating pulse is 1.315 μm, and the pulse duration is 0.3 ns (the intensity of the radiation at the surface of the target is 10¹⁴–10¹⁵ W/cm²). The calculations predict a pulsation in the reflection coefficient of the plasma for the laser radiation with a characteristic period of 8 ns. The results obtained on the absorption of laser radiation are in fairly good agreement with calculations based on the SNDP method, in which the distortion of the density profile under the action of the ponderomotive force is included in the model. This agreement validates the absorption model used in the SNDP program. Inclusion of a finite electron thermal conductivity in the equations along with the ponderomotive force sharply decreases the absorption coefficient. When a limitation factor of ~ 0.03 is used, the limitation on the thermal conductivity is found to have a decisive effect on the laser energy absorbed by the target.