Nonlinear scattering processes in aerosol optics

The physical basis of four basic nonlinear stimulated scattering processes in transparent droplets (SRS, SBS, lasing, scattering on droplet surface vibrations) caused by intensive pumping radiation is considered. The vector Maxwell equations, where the nonlinear polarization is the source for nonlinear harmonics origin, are used as a starting point for theoretical analysis of stimulated processes in a droplet. The solution of this system of equations is written in the form of series through droplet resonance eigenmodes. The main attraction is devoted to the energetic thresholds and angular characteristics of nonlinear scattering processes to be considered. The threshold values of the stimulated scattering in droplets are evaluated depending on the droplets radius. The paper presents the results of theoretical investigations of the task on droplet surface deformations and vibrations under the pressure of the ponderomotive forces caused by intensive laser field also. It is pointed out that for small particles (less or compared to laser radiation wavelength) the surface deformations are initated in perpendicular direction to laser beam axis, while large droplets begin to vibrate along the laser beam. This fact is the consequence of the inhomogenouty of internal electromagnetic field distribution in large droplets, that can lead to strong local surface deformations and even droplet destruction. The induced surface deformations cause the intensive nonlinear scattering of pumping electromagnetic field at the Raman frequency. The angular characteristics of this scattering are considered.