High efficiency phase-conjugate reflection in germanium and in inverted CO2

The first observation of phase-conjugate reflection at 10.6 microns is reported. An intracavity technique was utilized which is of general utility for any oscillating laser system. Attention is given to an experiment in which germanium was placed in a TEA CO2 laser cavity to utilize the intracavity counterpropagating (strong) waves for degenerate 4-wave mixing, noting that reflectivities as high as 20% were obtained. In addition, in a second experimental arrangement, phase-conjugate reflection and amplification with an effective gain exceeding unity was obtained by redirecting the output of a TEA CO2 laser oscillator into the active gain medi2m. It is shown that the intense counter-propagating waves within the laser medium coupled with the saturated gain medium to provide the nonlinearity in a process analogous to degenerate four-wave-mixing.