EFFECT OF KTA1-XNBXO3 CRYSTAL ORIENTATION ON THE NONLINEAR-OPTICAL RESPONSE IN THE PICOSECONDS DEGENERATE-4-WAVE MIXING

Nonlinear optical response signals on picosecond and nanosecond time s cales have been studied in the mixed-crystal system KTa1-xNbxO3 using transient degenerate-four-wave mixing (DFWM). The two distinct signal components, denoted as an instantaneous response (IR) and slow respons e (SR) in previous studies, changed intensity as the relative arriving time between two write pulses varied. The dependence of these signals on the crystal orientation was characterized. The results were consis tent with a lattice relaxation model based on the laser-induced dynami c displacement of the Nb ion. In this model the signal variations resu lt from the competition between the dynamic displacement and the intri nsic distortion associated with the spontaneous polarization along the optic axis.