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Journal of Experimental and Theoretical Physics

Nonlinear resonance induced by the higher spatial coherence harmonics

Sergei A Babin, Evgeniy V. Podivilov, Vladimir V. Potapov, Dmitry V. Churkin, David A. Shapiro

Published Apr 1, 2002• 3 citations
Publisher

Abstract

The spectrum of a test field in a three-level ArII Λ scheme in the presence of a strong standing wave on the adjacent transition was measured. The known light-induced transparency peak was observed; the peak shifted as the detuning of the strong field was varied. In addition, a new resonance in the line center arose whose position was independent of the strong-field frequency. The resonance was caused by the higher spatial coherence harmonics on the test transition. Perturbation theory for a low and numerical calculations for a high standing wave intensity give qualitative agreement with experiment and substantiate the nature of the central transition.

DOI
10.1134/1.1477894

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The spectrum of a test field in a three-level ArII Λ scheme in the presence of a strong standing wave on the adjacent transition was measured. The known light-induced transparency peak was observed; the peak shifted as the detuning of the strong field was varied. In addition, a new resonance in the line center arose whose position was independent of the strong-field frequency. The resonance was caused by the higher spatial coherence harmonics on the test transition. Perturbation theory for a low and numerical calculations for a high standing wave intensity give qualitative agreement with experiment and substantiate the nature of the central transition.
The interaction of a two-level system with a strong standing wave is examined by the probe field resonant to the adjacent transition in the $\ensuremath{\Lambda}$ configuration of Ar II. The known peak of electromagnetically induced transparency is observed in the absorption spectrum at the detuning of the probe field proportional to the detuning of the strong field. Along with it, the different structure has been found at the line center, independently of the strong-field frequency. The calculations clarify that the central structure is induced by the higher-order spatial harmonics of the atomic coherence induced at the probe transition. The effect results in steep frequency dependence of the refractive index at the line center.
Coherent preparation of quantum states of atoms and ions by laser light can lead to electromagnetically induced transparency and related effects. In particular, the standing wave at the adjacent transition induces a new type of nonlinear resonance in the probe-field spectrum of a three-level system. The resonance is due to the effect of high-order harmonics of atomic coherence. However, the resonance is broadened and the reason of the broadening was unclear. The paper describes how the velocity changing collisions broaden the resonance. The analytic theory taking into account up to 4-th order of the perturbation theory is presented. The numerical calculations are described. The analytical formulas are shown to describe the experiment qualitatively while the numerical computation demonstrates quantitative agreement. The Coulomb dephasing is discussed as the physical mechanism of the broadening.
Coherent preparation of quantum states of atoms and ions by laser light can lead to electromagnetically induced transparency and related effects. In particular, the standing wave at the adjacent transition induces a new type of nonlinear resonance in the probe-field spectrum of a three-level system. The resonance is due to the effect of high- order harmonics of atomic coherence. However, the resonance is broadened in experiment and the reason of the broadening was unclear. The paper describes how the velocity changing collisions broaden the resonance. The analytic theory taking into account up to 4-th order of the perturbation theory is presented. The numerical solution of density matrix equations is discussed. The analytical formulas are shown to describe the experiment qualitatively while the numerical computation demonstrates quantitative agreement. The Coulomb dephasing is shown to be the physical mechanism of the broadening.
The probe field spectrum of a three-level A scheme with a strong standing wave at the adjacent transition is calculated numerically taking into account velocity-varying collisions. It is shown that even a small population of the upper level changes the shape of the spectrum and increases the absorption in the line center. Taking into account the excitation of the level and the saturation of the adjacent transition allows a quantitative explanation of the experiment on argon ions in plasma of a high-current discharge.
The effect of a double structure of saturated absorption resonance in the field of counterpropagating light waves interacting with an atomic gas is studied. The experimental observation of this effect was first reported in 2011 in a work by our colleagues at the P.N. Lebedev Physical Institute of the Russian Academy of Sciences (Laboratory of Frequency Standards). The essence of the effect lies in the fact that, on exciting an open dipole transition, another, narrower, resonance of an opposite sign can be observed at the center of the ordinary saturated absorption resonance. A theoretical analysis of this effect has also been performed in this work in terms of a simple spectroscopic model of an atom with two nondegenerate energy levels without taking into account higher spatial harmonics of atomic polarization and polarizations of light waves (scalar model). The present work is devoted to the development of a theory of the formation of a central narrow resonance for the example of a real F g = 1 → F e = 1 atomic transition and to the study of its main characteristics (amplitude, width, contrast, and amplitude-to-width ratio). In addition, the theoretical results obtained without taking into account the influence of higher spatial harmonics and with inclusion of the influence of first higher harmonics are compared. This comparison shows that their influence on the parameters of the new nonlinear resonance is strong even in moderately intense light fields (R ~ γ, where R is the Rabi frequency). The results of this study can be of interest for quantum metrology, as well as for many experiments in which the laser-radiation frequency is stabilized by the saturated absorption resonance on open dipole transitions in atoms and molecules.