Dispersion-free amplification and oscillation in phase-conjugate four-wave mixing in an atomic vapor doublet

This paper presents theoretical and experimental descriptions of a novel application of the dispersion-free point associated with a pair of adjacent doublet transitions in atomic and molecular systems. At this point it is possible to observe enormous pulse amplification of a phase-conjugated wavefront and intense visible oscillation without mirror feedback in the degenerate four-wave parametric mixing in sodium vapor doublet at the characteristic wavelength of 5894 Å. At the dispersion-free point one also observes an ac Stark-free condition which permits the generation of a new type of coherent optical radiation called "cooperative phased-array radiation" (COPAR) from a phased-array system of coherently excited atoms in the medium at the wavelength.