Four-dimensional multi-level stimulated rotational Raman scattering dynamics in air

Abstract

Stimulated rotational Raman scattering in air is a powerful parasitic process that degrades high intensity pulses propagated over significant distances. Through this inelastic scattering process, laser photons are converted to higher (Anti-Stokes) or lower (Stokes) energies, according to rotational mode transitions in the nitrogen and oxygen molecules. The full wave-mixing problem involves numerous frequencies including both Stokes and Anti-Stokes processes, multiple rotational line transitions, and multi-harmonic generation, with each generated field acting as a seed for subsequent scattering processes. Multiple numerical models of these processes were integrated into Lawrence Livermore National Laboratory's in-house nonlinear optical chain propagation software, Virtual Beamline++. The complex spatio-temporal dynamics of single, and multi-frequency stimulated rotational Raman scattering are highlighted and discussed. General limitations of steady-state, dynamic two-level, multi-harmonic, and multi-rotational models are demonstrated and compared.