Selection of a phase-conjugate wave in an oscillator based on a four-wave interaction with feedback in an extended nonlinear medium

A quasi-optical approximation without allowance for beam spreading over its envelope is used to show that selection of a conjugate wave occurs in a volume hologram whose dimensions are greater than the longitudinal correlation length of the fields forming the hologram. The condition under which the signal power exceeds the noise power is found. Phase conjugation of a speckle field with a divergence of 2×10^-2 by a four-wave interaction with feedback was achieved experimentally for neodymium-activated glass and the efficiency was 5%. The input energy threshold was 100 mJ and the maximum energy in the phase-conjugate wave was 10 mJ.