Reflectivity Evolution and Preplasma Expansion in Front of Periodic and Flat Tilted Targets Under Laser Prepulse Influence

In this article, we compare laser prepulse interactions with flat and periodic 1D grating aluminum targets. We describe the cases of normal and oblique radiation incidence. The choice of an appropriate radiation incidence angle and target geometry reduces back-reflection and increases the performance of laser-driven experiments due to more uniform target heating. We studied preplasma generation in front of the targets and described its temporal evolution for different angles of radiation incidence. The electron density has a symmetric periodic distribution in front of grating targets and an irregular distribution in front of flat targets. It varies from 0.3×1022cm−3 to 3.5×1022cm−3 for grating targets, and from 1×1022cm−3 to 2.5×1022cm−3 for flat targets. The generation of overcritical density regions occurs before the end of the prepulse stage. We developed a semi-analytical model based on the effective refractive index and Bloch wave approximation to describe changes in reflectivity during the simulations. During the preplasma expansion, the reflectivity varies from 0.1 to 0.8. The numerical simulation results align well with the analytically predicted behavior of the preplasma–target ensemble. Grating targets are more suitable for experiments compared with flat ones. The most convenient angle of radiation incidence is about 15°.