PHOTOREFRACTIVE PROPERTIES OF KNBO3

Several experimental techniques were used to characterize the photorefractive properties of KNbO3. Continuous-wave excitation was used to study two-beam coupling and creation times of photorefractive gratings for both undoped and doped samples. The results show how different types of dopants affect the photorefractive sensitivity and material properties relevant to the photorefractive effect such as carrier mobility, trapping time, effective trap density, effective electro-optic coefficient, Debye length, and the sign of the dominant photocarrier. Picosecond pulse excitation was used to study fast nonlinear responses of undoped KNbO3. Along with the trapped-charge photorefractive response observed at long times after the excitation pulses, it was also possible to observe nonlinear responses due to absorptive changes at intermediate times and an ultrafast response that may have contributions associated with bound-electron nonlinearities and with scattering from Nb5+ -ion hopping modes.