Phase conjugation through Brillouin-enhanced four-wave mixing over an extended atmospheric path.

We report what is to our knowledge the first demonstration of Brillouin-enhanced four-wave mixing over a long atmospheric path. Weak laser light reflected from a remote retroreflector was input to a high-gain conjugate mirror. The resulting amplified output returns to the retroreflector owing to its phase-conjugate nature. Despite atmospheric effects the phase-conjugate return energy measured at the retroreflector increased by a factor of 10(4) over the initial weak beam.