Studies of spatial self-phase modulation of the laser beam passing through the liquids

Theoretical studies of the formation and temporal evolution of the far-field diffraction patterns of the Gaussian laser beam passing through a self-defocusing liquid media are given in this paper. The behavior of the diffraction ring patterns are interpreted theoretically based on the Fresnel–Krichhoff integral and the analytical solution of the heat transfer equation. Laser heating is caused by coupled conductive and convective transport of thermal energy. The analysis of the local temperature changes of the heated liquid leads to calculate the refractive index changes of the sample. The simulation results of the diffraction patterns are evaluated with the conductive and convective heating effects. When the conductive effects predominate, and convective effects are negligible, the far-field intensity distribution patterns can be observed as circularly-symmetric diffraction rings. Circularly asymmetric diffraction ring patterns can be observed when the convective effects become relevant. The numerical results suggest the importance of the thermal convection effect in the thermo-optical responds of the liquids when the laser beam passing through the sample.