The behavior of the phase conjugated light is very unique. It has the same wavefront as the incident light and travels back to the light source along the incident light path (see figures below). This can happen because, unlike the normal mirror which uses “reflection”, phase conjugate mirror (phase conjugator) utilizes “diffraction” to send back light. It should be noted that double-passing the phase object such as air turbulence cancels out the wavefront distortions automatically.

    Usually, phase conjugate light is generated through four-wave mixing that generates the fourth light (which is the phase conjugate light) from three other incident light beams. In four-wave mixing, interference between object and reference light in a nonlinear medium causes intensity-dependent modulation of property such as refractive index or transmission factor of the material, which searvs as diffraction gratings. Then, the diffracted readout light becomes the phase conjugate light.