The influence of spatio-temporal couplings on laser-plasma interactions

Laser–plasma interactions are determined both by plasma dynamics and by the properties of the driving laser pulse. While stimulated Raman scattering has been extensively studied, the influence of spatio-temporal couplings on such instabilities remains largely unexplored. This thesis investigates the impact of pulse-front tilt, one of the most common spatio-temporal couplings, on stimulated Raman side-scattering. Experiments were performed at the JETi-200 laser facility (Helmholtz Institute Jena/Institute of Optics and Quantum Electronics Jena) and directly observed using few-cycle microscopy. The measurements revealed asymmetric Raman scattering, propagation-dependent behavior, and larger scattering angles than predicted by conventional Raman theory, indicating a strong influence of pulse-front tilt. To explain these observations, the theory of Gaussian beam propagation with spatio-temporal couplings was extended to converging and diverging beams. Based on this, an analytical model combining conventional Raman scattering theory with pulse-front tilt was developed and successfully reproduced the experimental dependence on tilt, propagation distance, and electron density. Complementary two-dimensional particle-in-cell simulations provided insight into the microscopic dynamics of the instability and showed quantitative agreement with both experiment and theory. The results demonstrate that the observed scattering behavior is governed by the interplay of pulse-front tilt, laser propagation dynamics, and resonance conditions determined by the plasma electron density.