This paper presents results on the dependence of a phase conjugate signal in Bi12SiO20 (BSO) crystal on the frequency of an applied sinusoidal ac electric field. Large enhancement in the phase conjugate signal is observed for the ac field compared to that produced by the equivalent dc field. The conjugate signal shows a strong dependence on the ac field frequency. In addition, the variation of the diffraction grating signal with the ac field frequency is studied. © 1989.