Doppler-free phase-conjugate reflection.

It is shown that the reflection from a phase-conjugate mirror does not exhibit a Doppler shift in frequency. The physical basis for this phenomenon is discussed, and it has been verified experimentally by using four-wave mixing with photorefractive Bi12SiO20 (BSO) in a phase-conjugate Michelson interferometer. The same measurement is also used to determine the response time of the nonlinear material to moving spatial holograms. This response time is 7.3 msec in BSO.