Quasiclassical analysis of laser cooling by velocity-selective coherent population trapping

Abstract

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 influence of momentum diffusion on laser cooling of atoms

“…So the contradiction arises between the physical nature of the phenomenon and the description of it. There are no indications in the literature that both approaches [5,9] and [6,7,10] study the same phenomenon.…”

“…It is well known [13] that the A-atom is the simplest quantum system in which coherent population trapping manifests under the condition of the Doppler-shifted twophoton resonance [10,15]:…”

“…In particular, the nonlinear dependence of the radiation force on atomic velocity results in a friction force which in a certain velocity range can be anomalously high for some cooling configurations, leading to a strong narrowing of the atomic velocity distribution [4,6,7,10]. At the same time, diffusion is considered to play a destructive role in the cooling process, broadening the distribution continously.…”

“…A great variety of applications of atomic ensembles with the narrow momentum distribution is known, (see, e.g. [ 1,2]), and some mechanisms of laser cooling have been applied, such as Doppler cooling [3], polarization-gradient cooling [4] and cooling by the velocity-selective coherent population trapping [5][6][7][8][9][10].…”

Sub-Doppler cooling of three-level Λ atoms in space-shifted standing light waves

“…These mechanisms are based on coherent phenomena in multilevel atoms, resulting, in principle, in deep cooling of the atoms. For example, coherent population trapping [2] allows temperatures below T~, as well as below the temperature Ttt = R/ks [1], determined by the recoil energy R = 52k2/2M, to be obtained (M is the atomic mass and hk is the photon momentum).…”