Generating mutual coherence from incoherence with the help of a phase-conjugate mirror.

Abstract

Although the signal and idler light beams produced in the process of spontaneous parametric downconversion are mutually incoherent and exhibit no one-photon interference, interference effects should be observable after either the signal or the idler is reflected by a phase-conjugate mirror. The degree of coherence can, in principle, be as large as unity. We refer to the relationship between the signal and the idler produced by down-conversion as anticoherent and introduce a natural measure for the degree of anticoherence.