Investigation on third-order nonlinear optical properties of undoped LiNbO 3 by modified Z-scan technique

new method for measuring third-order nonlinear optical properties of photo refractive materials based on modified Z-scan technique in which employing focus-tunable lens was proposed. By this method, the nonlinear refractive index and the nonlinear absorption coefficient of an undoped LiNbO_3 crystal were investigated γ = - 1.48 ×10^ - 12 m^2/W and β = 0.33 mm/W , respectively. The investigation suggests that the calculated results keep agreement with the traditional Z-scan technique in the order of magnitude.