Observation of diminished specular reflectivity from phase-conjugate mirrors

We observe that the specular reflectivity from the input face of a ${\mathrm{BaTiO}}_3$ phase-conjugate mirror decreases by over 600% relative to the standard Fresnel reflectivity value upon the onset of phase conjugation, or wave-front reversal. Reasonable agreement is obtained using a model involving the destructive interference of the Fresnel-reflected beam with a series of phase-conjugate wave generated internal to the crystal. The basic diminishing effect should be universal and hence observable in other classes of self-pumped and externally pumped phase conjugators.