ABSTRACT
In Chapter 4, the most typical situations in the atmosphere, where nonlinear optical effects during laser radiation propagation that should be taken into account, are described. The stimulated Raman scattering (SRS) effect in airborne liquid droplets is considered, which is connected with excitation and amplification of Stokes waves in the whispering gallery zones in cavity droplets. Equations for the SRS excitation threshold in microparticles are given. Much attention is paid to the pump depletion case. The threshold conditions are found for the incident light intensity resulting in steady-state generation of Stokes radiation of a preset strength. The computational framework of light field intensity for thermal nonlinear effects, where the medium is heated due to light energy dissipation or kinetically cooled, is presented. The corresponding calculations are carried out on the basis of original algorithms based on the radiation transfer equation. The results presented in the chapter, which are based on this equation, allow to calculate the wide-aperture laser beams, which can be strongly distorted in the region of geometric shadow of a beam.
The calculations of high-power laser radiation propagation along a long stratospheric path under the SRS effect are also described in this chapter. Additionally, the diffraction effect on the nonlinear distortions of wide-aperture laser beams is discussed. Special attention is paid to the pump depletion effect under light field transformation into the Stokes components.
