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Physical Review A

Degenerate four-wave-mixing intensity noise fluctuations as a spectroscopic tool

H. Failache, Marcos Oriá, A. Lezama

Published Jul 1, 1995• 2 citations
Publisher

Abstract

We explore the use of degenerate four-wave-mixing (DFWM) intensity noise fluctuations as a spectroscopic tool for the study of atomic dynamics. Experimental results obtained from the spectral analysis of the intensity noise of the DFWM signal produced by a free running diode laser in a rubidium vapor cell are presented. For low exciting field intensities, the spectra are single peaked with a linewidth comparable to the atomic natural linewidth while at higher intensities a structure devleops revealing the existence of a dynamic Stark effect. The results are compared with numerical simulations of the power spectrum of the DFWM signal produced by a phase-diffusing field incident on two-level atoms.

DOI
10.1103/physreva.52.699

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We explore the use of degenerate four-wave-mixing (DFWM) intensity noise fluctuations as a spectroscopic tool for the study of atomic dynamics. Experimental results obtained from the spectral analysis of the intensity noise of the DFWM signal produced by a free running diode laser in a rubidium vapor cell are presented. For low exciting field intensities, the spectra are single peaked with a linewidth comparable to the atomic natural linewidth while at higher intensities a structure devleops revealing the existence of a dynamic Stark effect. The results are compared with numerical simulations of the power spectrum of the DFWM signal produced by a phase-diffusing field incident on two-level atoms.
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We report measurements of the effect of laser fluctuations on a strong-field degenerate four-wave mixing interaction, carried out in a nearly Doppler-free, two-level system using a single laser with statistically well-defined phase fluctuations. The counterpropagating pump beams and the probe beam, each split from this phase-noise-modulated source, were fully correlated. The nonlinear medium was an optically-pumped diffuse beam of atomic sodium. By time-delaying the probe with respect to the pump beams, the composite field becomes non-Markovian. Four-wave mixing results in the generation of a phase-conjugate beam anti-parallel to the probe beam. With the laser field spectrum nearly Lorentzian in shape, and with a field linewidth greater (and, for comparison, much narrower) than the natural linewidth of the sodium, we measured the intensity of the phase-conjugate beam as the pump and probe beams were tuned through the D2 resonance, as a function of intensity of die pump beam (up to intensities several times the saturation intensity), and for varying delay between the pump and probe fields. This experiment provides a cleaner measurement of this interaction than any previously available.
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Degenerate four-wave mixing (DFWM) spectroscopy is a potentially powerful technique for quantitative measurement of minor species in gas-phase media [1-3]. In this paper we compare the DFWM signal levels and lineshapes obtained using two different phase-matching geometries: the phase-conjugate geometry and the forward phase-matched geometry. DFWM signal levels are calculated by solving the time-dependent density matrix equations using direct numerical integration (DNI) [4, 5] for a two-level system interacting with three laser beams. This numerical analysis includes the effects of molecular motion, intermolecular collisions, and high laser intensities, all of which have been shown to affect the DFWM signal level.
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