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Optics and Spectroscopy

Analysis of the Spectral Composition of Fluorescence from Laser-Excited Cold Atomic Clouds

Sergey V. Bozhokin, Igor M. Sokolov

Published Dec 1, 2017• 4 citations
Publisher

Abstract

A consistent quantum approach is used to calculate the signal of fluorescence from a laser-excited cold atomic ensemble. The possibility of analyzing the spectral composition of this nonstationary signal is investigated. Application of wavelet transforms is shown to be a very efficient method that allows achieving a good spectral or temporal resolution, depending on specific problem. On the basis of this approach, the spectral composition of fluorescence and its dynamics after excitation are studied. The spectral properties of the secondary emission of the ensemble are compared for different directions and polarizations.

DOI
10.1134/s0030400x17120037

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A consistent quantum approach is used to calculate the signal of fluorescence from a laser-excited cold atomic ensemble. The possibility of analyzing the spectral composition of this nonstationary signal is investigated. Application of wavelet transforms is shown to be a very efficient method that allows achieving a good spectral or temporal resolution, depending on specific problem. On the basis of this approach, the spectral composition of fluorescence and its dynamics after excitation are studied. The spectral properties of the secondary emission of the ensemble are compared for different directions and polarizations.
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Abstract The fluorescence of cold atoms, cooled to ultra-low temperatures and excited by pulsed laser radiation, is calculated. The fluorescence of cold atoms is calculated based on the solution of the non-steady-state Schrödinger equation for a combined system of atoms and an electromagnetic field. A universal function is proposed in the work showing the deviation of the fluorescence decay at the end of the pulse from the single-exponential model. To analyze the dynamics of fluorescence, a Radon–Nikodym method has been used based on the studies on the eigenvalues of a matrix constructed on the basis of the fluorescence signal. It is shown that a correlation exists between the parameter of distribution asymmetry inherent in signal matrix eigenvalues, and the temporal law of fluorescence decay. As an alternative method of fluorescence analysis, a multistage relaxation model is used, caused by collective multiatomic effects. The values of characteristic amplitude and relaxation time both at short times (“superradiance”) and at long times (“subradiance”) have been found.
Abstract A fluorescence dynamics of a cold atomic cloud, laser–cooled to a very low temperature, optically excited by a short laser impulse is calculated by applying non–stationary Schrödinger equation to the system of atoms and electromagnetic field. The solution gives fluorescence time–relaxation dependence, with relaxation time distribution depending on the system itself and external electromagnetic field applied. The distribution of the relaxation rates changes, when an external electric field affecting the atomic ensemble is applied. To analyze the relaxation process a novel Radon–Nikodym approach is applied: the relaxation curve is not piece–wise interpolated, but instead is converted to a matrix, the eigenvalues of which provide relaxation rate distribution. In contrasts to the random matrix theory, where the weights, corresponding to an eigenvalue, are considered equal, in this work the weight, corresponding to an individual eigenvalue, is determined by the Lebesgue integral quadrature weights.
Abstract The fluorescence dynamics of optically dense but dilute atomic ensembles cooled to sub-Doppler temperatures and excited by resonant pulsed radiation is studied. Apart from total radiation intensity, the temporal variations of the spectral composition of fluorescence and its polarization, as well as the variation of the spatial distribution of excitation in the atomic ensemble, are analyzed. Based on this analysis, it is shown that the role of radiation trapping becomes smaller with time, and subradiance quantum states formed as a result of the resonant dipole–dipole interatomic interaction become the main factor determining the slow atomic excitation decay. The dependence of the subradiance form on the ensemble size is analyzed.