Spatial coherence of transient stimulated Raman scattering

Numerical model describing transient stimulated Raman scattering and taking into account diffraction was developed and Stokes wave evolution in compressed hydrogen was simulated to study space-time dynamics of amplitude-phase SRS characteristics. Space-time intensity and phase dependencies as well as spectrum and spatial coherence function of pump and Stokes waves were obtained. Considerable difference in mentioned characteristics was found out for transient and quasi-stationary stimulated Raman scattering modes. More complicated space-time dependencies are typical for transient mode in comparison with quasi-stationary mode. However, under quasi-stationary conditions Stokes wave phase varies in wider limits, which results in spatial coherency lowering. Module of spatial coherency function value lowers to threshold and then becomes stable as conversion coefficient increases. Presence of Stokes beam focusing is shown at stimulated Raman scattering, which can be explained by competition of strong Raman amplification and diffraction. Results of simulations are in good agreement with experimental data.