We used the method of nets to calculate the thermoelastic stresses on the GaAs surface caused by a non-destructive nanosecond pulse laser irradiation (λ = 0.532 µm) with diffraction spatial intensity modulation from a shield with rectangular cut. The structure of irradiated subsurface layers of samples was studied by the AFM method. A periodic islet structure formed in the process of diffusive redistribution of defects was revealed by the level-by-level chemical etching.