DEGENERATE 4-WAVE-MIXING LINE-SHAPES OF HYDROXYL AT HIGH PUMP INTENSITIES

The degenerate four-wave-mixing spectral profile of the R(1)(9) transi tion in the A (2) Sigma(+) --> X2 Pi(0, 0) band of OH has been measure d for various combinations of saturating pump beams. With increasing p ump-beam intensity the degenerate four-wave-mixing line shape changes dramatically near line center. In phase-conjugate geometry, three dist inct spectral line shapes were observed for the cases of (1) equally i ntense pump beams, (2) a strong forward pump and a weak backward pump, and (3) a weak forward pump and an intense backward pump. A significa nt saturation dip appears in the spectrum near line center for case (3 ). The measured spectra have been modeled by the use of nonperturbativ e numerical solutions of the density matrix equations, and agreement b etween the calculations and the experimental results is excellent. The differences in the saturated line shapes for cases (2) and(3) are exp lored theoretically, and the calculated results are compared with prev ious theoretical work [Bloch and Ducloy, J. Opt. Sec. Am. 73, 635 (198 5)] in which the line shapes were calculated in the limit of infinite Doppler broadening.