Two-photon absorption and anisotropic transient energy transfer in BaTiO_3 with 1-psec excitation

We use a cross-polarized pump–probe technique and 1-psec pulses at 596 nm to measure a two-photon absorption coefficient of 0.1 cm/GW in BaTiO3. A long-lived absorption is also observed and is shown to be consistent with free-carrier absorption and charge redistribution between two separate impurity levels. We also observe an anisotropic transient energy-transfer process in which the p-polarized pump is scattered into the s-polarized probe. The energy transfer occurs when the c axis of the crystal is oriented along a grating vector equal to the difference between the pump- and probe-wave vectors.