The Study of the Third Order Nonlinear Susceptibility in GaSe

The generation of the third harmonic of the neodymium laser radiation in reflection from GaSe is observed for the first time. The third harmonic signal is studied as a function of the exciting radiation intensity and of the angle between the light wave field and the perpendicular to the optical axis of the crystal. Similar dependences are obtained for the etalone GaAs crystal. A comparison of the calculated and experimental curves shows that the experimental data correspond to the generation of the third harmonic for the γ-polytype of GaSe. The coefficients of the third order nonlinear susceptibility are C11(3ω) = 1.1 × 10−18 m2/V2; C31(3ω) = 6.7 × 10−21 m2/V2. This value of C11(3ω) is in agreement with the theoretical one calculated from the bound charge model when dispersion is taken into account. The correspondence is noted of nonlinear susceptibilities to the second and third orders for the same frequency of the exciting radiation.