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Optics Letters

Phase conjugation by degenerate four-wave mixing in barium vapor

Tassos A. Mikropoulos, S. Cohen, Μιχάλης Κομπίτσας, S Goutis, C. Baharis

Published Sep 17, 1990• 0 citations
Publisher

Abstract

We report what is to our knowledge the first observation of phase-conjugate waves by degenerate four-wave mixing in Ba vapor near its 6s(2)(1)S(0) ? 6s6p(1)P(1) resonance transition. A maximum reflectivity of 36% at 10 mbars of Ar buffer gas pressure is observed together with a temporal pulse shortening of 50%. Conical emission in the two pump waves after their passage through the nonlinear medium is also observed. The dependence of the phase-conjugate signal on the pressure of the Ar buffer gas shows a small state-changing collisional decay rate.

DOI
10.1364/ol.15.001270

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We report what is to our knowledge the first observation of phase-conjugate waves by degenerate four-wave mixing in Ba vapor near its 6s(2)(1)S(0) ? 6s6p(1)P(1) resonance transition. A maximum reflectivity of 36% at 10 mbars of Ar buffer gas pressure is observed together with a temporal pulse shortening of 50%. Conical emission in the two pump waves after their passage through the nonlinear medium is also observed. The dependence of the phase-conjugate signal on the pressure of the Ar buffer gas shows a small state-changing collisional decay rate.
The phase-conjugate signal observed in resonant degenerate four-wave mixing on the 6/sup 3/P/sub 2/ to 7/sup 3/S/sub 1/ transition of atomic mercury in a Hg-Ar discharge is investigated. At a fixed argon pressure the variation of the signal with pump powers is explained by a model that includes the effects of velocity-changing collisions (VCCs). As the argon pressure was varied from 0 to 1 torr an increase in the phase conjugate signal was observed and is ascribed to a change in the discharge dynamics with argon pressure and to the influence of VCCs. To further clarify the role of collisions and optical pumping, degenerate four-wave mixing spectra are examined as a function of pump power. Line shapes are briefly discussed.>
Nondegenerate four-wave mixing on the j=0\ensuremath{\rightarrow}j=1 transition, in a ``V '' system, using orthogonal, circularly polarized pump beams is used to study theoretically the generation of the phase-conjugate signals. The efficiency of generation of the conjugate wave is studied as a function of the various system parameters such as pump-probe detuning, Zeeman splitting, pump-atom detuning, collisional parameters, and the intensities of the pump beams. The origin of the various resonances in the reflectivity is explained. For weak pump fields, some resonances are shown to have subnatural linewidths. In the degenerate case, the reflectivity as a function of pump-atom detuning has, in contrast to a two-level system, a doublet structure for moderate absorption-length parameters and field strengths. The reflectivity is shown to have additional resonances due to pump imbalance. The phase-conjugate signal is also shown to exhibit the pressure-induced extra resonances.
Continuous wave (cw) phase conjugation of a HF laser beam has been observed using resonant degenerate four-wave mixing in a HF gas absorption cell. A HF laser was operated in the P1(8) transition to provide total (forward plus backward) pump beam and probe beam intensities of about 400 and 30 W/cm2, respectively, in the cell. Conjugate reflectivities were measured as a function of HF pressure and frequency detuning from line center. Reflectivities of the order of 10−4 were measured at HF gas pressures of the order of 2 Torr when the laser frequency was tuned near line center.