The Nonlinear Optical Response of Sodium Vapor when Pumped to a Two Photon Resonance.

Richard Wunderlich, W. R. Garrett, Roger C. Hart +2 more

The nonlinear response of sodium vapor with a laser tuned near the 4D two-photon resonance is investigated over a large range of sodium concentrations and pump intensities with emphasis on the influence of coherent cancellation effects on the induced polarizations and the primary mechanism for the generation of the new frequencies. Over a wide range of circumstances, the response of the medium is dominated by parametric four-wave mixing as compared to amplified spontaneous emission or stimulated electronic hyper-Raman scattering. Secondary four-wave-mixing fields are generated by stimulated Raman scattering of one parametric four-wave-mixing field and a coupling of these fields with the driving laser field. A sharp onset of saturation of the parametric four-wave-mixing signals with sodium number density and a transition from a quadratic to a linear power dependence is observed. Both effects are explained in terms of the two-photon cancellation effect.

Syed Golam Rabbani

Dieter Suter, Tilo Blasberg

Optical pumping of atomic vapors can lead to self-focusing of resonant laser beams. The saturation of the optical pumping process at low intensity allows the study of transverse solitons in the form of self-trapped laser beams, using low-power cw lasers. The long lifetime of the optically pumped atoms allows the atomic diffusion to transport the excitation away from the interaction region. Numerical simulations show that the resulting nonlocal response of the medium represents an important mechanism that stabilizes the self-trapped beam. The theoretical predictions are confirmed by experimental results from sodium vapor.

M. Squicciarini

Richard L. Sutherland

Yu A Galaĭchuk, Vladimir A. Kudryashov, V. L. Strizhevskiǐ +2 more

A systematic analysis was made of the spectral characteristics of resonance four-photon parametric conversion of infrared radiation as a result of two-photon resonance pumping of the 3S–3D and 3S–5S transitions in sodium and the influence of these characteristics on the threshold sensitivity of a parametric conversion detector was investigated. An experimental study was made of the characteristics of the noise radiation generated as a result of hyperparametric scattering. The results obtained can be used to select the optimal parameters of high-sensitivity detectors of weak infrared signals by parametric conversion in alkali metal vapors.