Abstract

Measurements were made of the time evolution of the photorefractive signals and of the two-beam coupling gain of doped and undoped KNbO₃ for both picosecond pulse and continuous excitation. The major features of the time response are a very fast spike and a slower signal that builds up in milliseconds. The characteristics of each of these components depend on doping, laser power, and sample orientation. The slow signal has the characteristics of the photorefractive response seen in KNbO₃ for continuous excitation. One possible origin of the fast signal is scattering from the lattice mode associated with the oscillation of the Nb ions between equivalent sites in the unit cell; a model based on this proposition is discussed. No gain was observed for picosecond pulse excitation. For continuous excitation, the two-beam coupling gain was greater in the undoped sample than in the Ta-doped sample. By analyzing the measured gain vs crossing angle of the laser beams the trap concentrations and effective electrooptic coefficients were determined.

© 1989 Optical Society of America