Spectral and temporal measurements of the third-order nonlinear susceptibility were performed over 700 ${\mathrm{cm}}^{\mathrm{-}1}$ in ${\mathrm{LiNbO}}_3$ with use of Raman-induced phase-conjugation spectroscopy. Strong resonant enhancement was observed at six known vibrational frequencies, exhibiting relaxation times of less than 2 psec. These measurements show that ${\mathrm{LiNbO}}_3$ has the potential to be used in ultrafast real-time optical processing systems, which require a large and fast $X^{\mathrm{}\left(3\right)\mathrm{}}$ optical nonlinearity.

• Received 13 March 1989

DOI:https://doi.org/10.1103/PhysRevB.40.1885