We present our investigation of two-photon absorption and self-focusing in second-harmonic-generation crystals on a picosecond 532-nm-wavelength beam using the z-scan technique. By measuring the crystal transmittance as a function of the crystal position with respect to the focus, the two-photon absorption coefficients were determined to be 0.041 plus or minus 0.008, 0.10 plus or minus 0.02, and 0.24 plus or minus 0.06 cm/GW for KTPA, KTA, and LiNbO3, respectively. With inserting an aperture in front of the detector that recorded the transmitted laser pulse energy, self-focusing effects manifested themselves in the z scans on the three crystals at input irradiances of higher than a few GW/cm2. The quantitative data confirm that the optical Kerr nonlinearity should be responsible for the observed self-focusing and n2 equals (4.6 plus or minus 0.9), 3.6 plus or minus 0.7), and 5.3 plus or minus 1.0) multiplied by 10-6 cm2GW in KTP, KTA and LiNbO3, respectively. The microscopic origin of the measured n2 can be understood in terms of bound electronic effects. The theoretical predictions are in agreement with our measurements. Finally, effects of the observed refractive nonlinearity on laser-induced damage are discussed.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.