Convective motion generated by Gaussian laser beam impinging normally on the sample was theoretically discussed in this study for both isotropic liquids and liquid crystals. Heat transfer, Navier-Stokes and director equations were solved numerically and corresponding distributions of heat, velocity and director were obtained. Rayleigh-Benard and Benard-Marangoni convections in liquid crystals were also discussed. It was shown that theoretical calculations are in a strong agreement with experiments done previously.