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The work presented considers a new coherent phenomenon, i.e. the influence of the phases of electromagnetic fields interacting with a multilevel system on the character of excitation of this system. On the basis of analysing the equation for an N-level quantum system density matrix, it was established that in multilevel systems containing a closed contour of transitions, resonantly interacting with the field, stationary populations always depend on the total interaction contour phase Phi . For the simplest multilevel systems, i.e. three-level, the authors have obtained analytical expressions, connecting populations with the relative field phase in such systems. Thus, for a Lambda system, interacting with three resonant electromagnetic fields, it is discovered that, depending on the total phase value of the transition contour, both destruction and successive restoration of a coherent trapping state can take place. The work provides qualitative explanations of phase effects and suggests some possibilities for their application.

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Laser cooling based on velocity-selective coherent population trapping is investigated theoretically. Quasiclassical treatment is used to identify the conditions for optimal cooling and to study the dynamics of the cooling process in detail. For different cooling schemes we give the analytical expressions for the temperature of the cold atoms, which can be much lower than the Doppler cooling limit. The effect of the degree of incompleteness of coherent population trapping on dynamics and the limits of laser cooling are revealed.PACS number(s): 32.80.Pj, 42.50.Vk

The paper deals with the action of light pressure on a double-Λ system in case of four travelling optical waves. We find that light pressure effects are completely determined by the relative phase Φ of exciting fields. The time evolution of the velocity distribution for different values of Φ is obtained. The dependence of the transversal temperature of the double-Λ-atom beam on the phase Φ is calculated and it is shown that under certain conditions T can reach ∼ 3 μK.