Spatial coherence of transient stimulated Raman scattering

Abstract

The Stokes wave evolution at transient stimulated Raman Scattering (SRS) in compressed hydrogen was simulated taking into account diffraction effects. A corresponding numerical model was developed to study different amplitude-phase SRS characteristics, such as space–time and phase dependencies, spectrum and spatial coherence function of pump and Stokes waves. Simulation results showed significant differences in these characteristics between transient and quasi-stationary cases. The strong oscillatory process of energy exchange between pump and Stokes waves in the transient case results in complicated intensity and phase space–time dependencies. However, under quasi-stationary conditions the Stokes wave phase varies in wider limits, which leads to spatial coherency lowering. The module value of the spatial coherency function lowers to a threshold and then becomes stable as the conversion coefficient increases for both the transient and quasi-stationary cases. Stokes beam focusing is shown for SRS, which arises from competition between diffraction and non-uniform in a cross-section strong Raman amplification. Results of simulations are in good agreement with experimental data.