ANISOTROPIC EFFECTS IN THE 3RD-HARMONIC-GENERATION PROCESS IN CUBIC-CRYSTALS

The third-harmonic-generation process is governed by the fourth-rank t ensor chi(3), which reflects the crystal symmetry. We use the fundamen tal output of a Nd:YAG laser as excitation energy to show the anisotro pic character of the nonlinear response of a cubic crystal for differe nt samples. A clear dependence of the third-harmonic-generation effici ency on the crystal orientation has been observed in NaF, LiF, Ge, Si, and gadolinium gallium garnet crystals, the last of which has the low est value of anisotropy among the crystals considered here. The streng ths of the anisotropic nonlinear response in Si and Ge are of the same order of magnitude.