Femtosecond Z-scan measurements of nonlinear refraction in nonlinear optical crystals

We report an investigation of third-order optical nonlinearities in several nonlinear optical crystals using the Z-scan technique with femtosecond laser pulses at 780 nm wavelength. The crystals studied include LiNbO3:MgO, KTiOAsO4, KTiOPO4, beta -BaB2O4 and LiB3O5, which are extensively used for ultrashort-pulse second-harmonic generation and optical parametric oscillation. The nonlinear refractive index n(2) in these crystals has been determined to be in the range from 10(-16) to 10(-15) cm(2)/W. No two-photon absorption has been observed. The experimental results are compared with the two-band model for the bound electronic Kerr nonlinearity. It is shown that the measured n2 values in beta -BaB2O4 and LiB3O5 are one order of magnitude smaller than those of LiNbO3:MgO, KTiOAsO4, KTiOPO4, which is in agreement with the theoretical prediction. (C) 2001 Elsevier Science B.V. All rights reserved.