Stress-induced second harmonic generation(SHG) has been phenomenologically investigated by introducing the nonlinear photoelastic tensor. The relations between the stress and the nonlinear optical susceptiblity for the 4mm and 3m crystals has been described by applying the symmetric conditions of the nonlinear photoelastic tensor. From these relations, we can determine the stress components by measuring the nonlinear photoelastic tensor. This method for measuring the stress is surface sensitive because the second harmonic signal can be generated only at the surface in centrosymmetric media.
We need the unstressed second harmonic signal as well as stressed one for the stress measurement. However, if we know the cystal class of the media, we can get some stress components without the unstressed second harmonic signal. This is possible beacause the nonlinear optical susceptibility reflects the symmetries of the crystal. The angular variation of SHG shows these symmetry properties of the crystal. Thus, we can determine the stress components which cause any symmetry change of the crystal from the angular variation of SHG.
