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Quantum Electronics

Selective detection of polarisation components of a coherent population trapping signal in hot alkali metal atoms

К. А. Баранцев, Е. Н. Попов, A N Litvinov

Published Sep 1, 2017• 5 citations
Publisher

Abstract

A mathematical model of the interaction of bichromatic laser radiation with alkali metal atoms in an optically dense gas cell at above room temperature is constructed. Within the framework of the model, complete hyperfine and Zeeman structures of alkali metal atom levels are considered, which allows the propagation of radiation polarisation along the cell and the effect of a constant magnetic field to be correctly taken into account. It is found that the selective detection of polarisation radiation components carries additional information in comparison with a signal of total intensity.

DOI
10.1070/qel16447

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A mathematical model of the interaction of bichromatic laser radiation with alkali metal atoms in an optically dense gas cell at above room temperature is constructed. Within the framework of the model, complete hyperfine and Zeeman structures of alkali metal atom levels are considered, which allows the propagation of radiation polarisation along the cell and the effect of a constant magnetic field to be correctly taken into account. It is found that the selective detection of polarisation radiation components carries additional information in comparison with a signal of total intensity.
A theory of excitation of a coherent population trapping resonance in hot alkali-metal atoms in a cell with buffer gas is constructed, taking into account the finite spectral width of two-component radiation, its vector properties, and the hyperfine and Zeeman structures of atoms. The propagation of intermode correlations in an optically dense gas cell is studied. It is found that in the case of partially correlated input modes, their correlation degree at the output can increase. This effect can be used for filtering the incoherent part of radiation.
Abstract We report on a theoretical model of the effect of coherent population trapping in alkali atoms in an optically thin gas cell with a buffer gas at a nonzero temperature in a pulsed laser field. The shape of the Ramsey resonance is analysed for two different temperature ranges, i. e. for a ‘cold’ atomic ensemble and for an ensemble of ‘hot’ atoms in a cell with a buffer gas. The influence of the hyperfine structure of the excited level on the shift of the central Ramsey resonance is investigated.
We propose a scheme to achieve one-dimensional velocity-selective coherent population trapping in a five-level system under two-frequency laser excitation. It may be applied to either D line of alkali-metal atoms. The trapped state is a time-dependent superposition of three sublevels from two different hyperfine ground states. Stable trapping may be produced by correctly detuning the laser beams to compensate for different hyperfine and kinetic energies of these ground states. We present numerical results for a five-level model, as well as for the complete level systems appropriate for alkali-metal atoms.
Abstract We analyze the polarization of the total angular momentum of alkali atoms in a gas cell with a buffer gas under pumping by monofrequency circularly polarized laser radiation. The mathematical model takes into account the motion of atoms and collisions preserving the nuclear spin under the chaotization of the angular momentum of the outer electron shell, total hyperfine structure, and the Zeeman structure. We analyze the stationary solution to equations for the density matrix of alkali atoms and the effect produced on them by the fraction of inelastic collision in which the quenching of atomic excitation takes place. We consider the contribution of various hyperfine states to the polarization of alkali atoms. The results are compared with the results of the model of instantaneous mixing of populations in the excited state.
We report our study on coherent population trapping (CPT) in a $\ensuremath{\Lambda}$ configuration coupled by magnetic dipole interactions. The $\ensuremath{\Lambda}$ configuration is formed by bichromatic radio-frequency fields coupling a pair of Zeeman sublevels in one hyperfine level of an alkali-metal atom to another sublevel in the other hyperfine level. The Zeeman sublevel at the apex is coupled to a state in the nPnPnP manifold via an optical transition on one of the spectroscopic DDD lines to induce optical pumping to a dark state. The configuration is closed without leakage to other Zeeman sublevels. We use lithium atoms in an optical trap for our experimental study. The system allows independent control of the main parameters characterizing CPT, which include the upper-state decay rate and the decoherence rate as well as the Rabi frequencies. By turning off the applied fields, the system is frozen so that its quantum state can be measured precisely. We studied the line shapes and dynamics of the CPT system, and measured the phase relation of the dark superposition state to find excellent agreement with theory. The possible application of the scheme as a method to cool optically trapped atoms below the recoil limit in a manner analogous to velocity-selective coherent population trapping is discussed.