Self-pumped phase conjugation in KNSBN:Fe

Nonlinear optical phase conjugation in photorefractive crystals and other dynamic recording media have generated tremendous interest because of potential applications in restoration of distorted images. Self-pumped phase conjugation has been observed in several photorefractive crystals including BaTiO3, KNbO3, Sr1- x Ba x Nb2O6 (SBN), Ba2- x Sr x K1- y Na y Nb5O15 (KNSBN), and Bi12TiO20 (BTO). Phase conjugation reflectivity of up to 30% has been reported. In this work we report we believe for the first time self-pumped phase conjugation in Fe doped (K x Na1-x)0.4(Sr y Ba1- y ,)0.8Nb2O6 (KNSBN) crystals using the external ring geometry. The phase conjugation reflectivity has been measured as a function of the light wavelength, light intensity, and the angle between the incident beam and the crystal c-axis. Larger phase conjugation reflectivities are observed for higher light intensity and shorter light wavelength. Phase conjugation reflectivity of up to 37% has been measured. Phase conjugated images of high quality are observed. The rise time and decay time of the phase conjugate image are measured. Fast rise (decay) followed by a much slower rise (decay) is observed. These two time constants indicated that two photorefractive gratings are involved in the phase conjugation process.