In the case of degenerate four-wave mixing in a cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) crystal, it is found that the transmission grating is dominant when the incident beams are extraordinarily polarized, the crystal response is more rapid, and the conjugate beam is more intense. Furthermore, the variation of the conjugate beam intensity forms a loop as the fringe modulation of the transmission grating varies. Based on this observation, we have implemented edge enhancement of an image and edge-enhanced optical correlation via four-wave mixing in a Ce:KNSBN crystal without the requirement of reversal of the signal–pump-beam intensity ratio.
Liang, B-L., Wang, Z-Q., Guan, J-H., Mu, G., & Cartwright, C. M. (2000). Four-wave mixing and edge-enhanced optical correlation in a Ce:KNSBN crystal. Optics Letters, 25(15), 1086-1088. https://doi.org/10.1364/OL.25.001086