Phase conjugation

Phase conjugation is a physical transformation of a wave field where the resulting field has a reversed propagation direction but keeps its amplitudes and phases.
Description.
It is distinguished from Time Reversal Signal Processing by the fact that phase conjugation uses a holographic or parametric pumping whereas time reversal records and re-emits the signal using transducers.
Both techniques allow an amplification of the conjugate wave compared to the incident wave.
As in time reversal, the wave re-emitted by a phase conjugation mirror will auto-compensate the phase distortion and auto-focus itself on its initial source, which can be a moving object.
Propagation of a time reversal replica demonstrates a remarkable property of phase-conjugated wave fields.
Phase conjugation of wave field means the inversion of linear momentum and angular momentum of light.
Phase conjugation methods exist in two main domains: