Birefringence changes are induced in a cubic potassium tantalate niobate crystal with an external electric field by two−photon absorption of picosecond optical pulses. The recording sensitivity of 100 &mgr;J/cm2for elementary holograms with a few percent reconstruction efficiency is comparable to the sensitivity of holographic silver halide emulsions. The high sensitivity of KTN is shown to be due to efficient charge transport of photoexcited carriers.