Using ultraviolet femtosecond pulses with high irradiance stability, we measured the two-photon absorption (TPA) coefficients in a number of substances with a total accuracy of similar to10%. Six commercial fused-silica samples (KU-1, Corning 7940, SQ, Suprasil, Herasil, and Infrasil) possess TPA coefficients (beta values) of similar to2 x 10(-11) cm/W. For crystalline quartz and sapphire, the following beta values were obtained: (1.2 +/- 0.2) x 10(-11) and (9.4 +/- 1.2) x 10(-11) cm/W, respectively. In beta-barium borate crystal the TPA coefficient depends on crystal cut, beam polarization, or both and varies from (47 +/- 5) x 10(-11) to (68 +/- 6) x 10(-11) cm/W. For eight liquids that were studied (water, heavy water, ethanol, methanol, hexane, cyclohexane, 1,2-dichloroethane, and chloroform) the beta value lies from (34 +/- 3) x 10(-11) to (95 +/- 11) x 10(-11) cm/W. (C) 2002 Optical Society of America.