Soviet Journal of Quantum Electronics

Collimation and compression of atomic beams under conditions of coherent population trapping

D. V. Kosachev, Boris G. Matisov, Yu. V. Rozhdestvenskiǐ

Published Jul 31, 1992• 1 citation

Abstract

A theoretical investigation was made of the collimation and compression of atomic beams under two-frequency cooling conditions. It was possible to reach cooled atom temperatures right down to TR = 2k2/2MkB ≈ 10−6 K, determined by the recoil energy of the atom. The dependences of the temperature on the frequency difference between the light waves were investigated, for velocities near zero, and these were found to be in qualitative agreement with those observed experimentally. An expression for the beam diameter after compression by diverging waves was derived. Estimates of these effects are given for cases of practical importance.

DOI: 10.1070/qe1992v022n07abeh003566

Related papers

Radiative collimation of atomic beams through two-dimensional cooling of atoms by laser-radiation pressure

V. I. Balykin, Vladilen S Letokhov, Vladimir G. Minogin +2 more

The transverse cooling of a beam of sodium atoms in an axisymmetric light field formed by a reflecting axicon is studied. It is shown that transverse cooling leads to a decrease in angular divergence (collimation) of the atomic beam. The transverse velocities of the beam are reduced from 5.5 × 102 to 1.6 × 102 cm/sec, which corresponds to the decrease in effective transverse temperature of the beam from T = 42 to T = 3.3 mK. The spatial and velocity distributions of the atomic beam are calculated numerically. It is found that theory and experiment are in good agreement.

Journal of the Optical Society of America BNov 1, 198537 citations

Laser cooling of atoms below the single-photon classical limit

Vladimir G. Minogin, M. A. Ol'shanyi, S. U. Shulga

We describe a new mechanism for the laser cooling of atoms. The mechanism is based on the damping of the motion of three-level atoms by laser light pressure under the condition of coherent atomic population trapping. Because of the action of this mechanism, three-level atoms can be cooled below the temperature of the single-photon classical limit, Tγ = ℏγ/kB, to a temperature corresponding to the recoil energy, TR = ℏ2k2/2MkB. It is probable that the mechanism described has a part in the recently observed laser cooling of sodium atoms below the temperature ℏγ/ kB.

Journal of the Optical Society of America BNov 1, 198911 citations

Laser control of atomic motion

V. I. Balykin, Vladilen S Letokhov, Vladimir G. Minogin +1 more

This paper presents the results of experimental and theoretical investigations on the control of atomic beam motion by light pressure of laser radiation. Collimation, focusing, and compression of an atomic beam are considered. Collimation of an atomic beam was achieved under the interaction of laser radiation with atoms when the light pressure force depended only on the atoms’ velocity. A similar regime of atomic beam interaction with radiation was performed under transversal irradiation of a beam by the axisymmetric field. The latter was formed by laser radiation reflected from the conical mirror surface of a reflecting axicon. The axis of an atomic beam coincided with that of the axicon. The collimation regime was reached under negative detuning of the laser radiation frequency from that of the atomic transition one by a value equal to a few homogeneous widths. Under positive detuning by the same value beam decollimation was observed.

International Laser Science ConferenceJan 1, 19860 citations

Laser cooling below the one-photon recoil energy by velocity-selective coherent population trapping: theoretical analysis

Alain Aspect, E. Arimondo, Robin Kaiser +2 more

We present a theoretical analysis of a new one-dimensional laser-cooling scheme that was recently demonstrated on a beam of metastable 4He atoms. Both internal and translational degrees of freedom are treated quantum mechanically. Unlike semiclassical approaches, such a treatment can be applied to situations in which the atomic coherence length is of the same order of or larger than the laser wavelength, which is the case for atoms cooled below the one-photon recoil energy. We introduce families of states that are closed with respect to absorption and stimulated emission, and we establish the generalized optical Bloch equations that are satisfied by the corresponding matrix elements. The existence of velocity-selective trapping states that are linear combinations of states with different internal and translational quantum numbers is demonstrated, and the mechanism of accumulation of atoms in these trapping states by fluorescence cycles is analyzed. From a numerical solution of the generalized optical Bloch equations, we study in detail how the final atomic-momentum distribution depends on the various physical parameters: interaction time, width of the initial distribution, laser detuning, laser power, and imbalance between the two counterpropagating waves. We show that the final temperature decreases when the interaction time increases, so that there is no fundamental limit to the lowest temperature that can be achieved by such a method. Finally, possible extensions of this method to two-dimensional cooling are presented.

Journal of the Optical Society of America BNov 1, 1989293 citations

Collimation of Atomic Beam

V. I. Balykin, Vladilen S Letokhov

The need to collimate a beam of particles arises whenever one has to increase their phase space density (the goal is to compress a spatial and a velocity distributions of the atoms) and to increase a spatial coherence of atomic beam. The method of increasing the spatial coherence by using special scheme of collimation is only one so far known for atomic beam. There is optimal laser detuning when the atomic beam collimation is maximum. As the detuning is decreased, the degree of collimation drops drastically. Near zero detuning the broadening of the atomic beam can be clearly seen, and its intensity is decreased. The collimation of atomic beam by the retarding force was first observed with a cesium than with sodium atoms. The collimation of atomic beams by polarization gradient force was demonstrated as in one-dimensional and two-dimensional cases.

CRC Press eBooksApr 23, 20200 citations

Complement 8A: Cooling to sub-recoil temperatures by velocity-selective coherent population trapping

G. Grynberg, Alain Aspect, Claude Fabre +1 more

In Section 8.3.9, we mentioned that the recoil temperature was not the ultimate barrier to cooling. Several mechanisms have been conceived and implemented to concentrate the atomic velocity distribution in a range of values of width less than V R . In contrast to Doppler or Sisyphus cooling, these mechanisms do not appeal to a friction force, but rather to an optical pumping process (see Complement 2B), able to accumulate the atoms in this narrow range of velocities. We now present one such mechanism called ‘velocity-selective coherent population trapping’, considering only the case where the motion occurs in one space direction (the O z -axis). Note, however, that the method generalizes to two or three dimensions. Coherent population trapping Coherent population trapping is a phenomenon that occurs when an atom has a system of three energy levels in the ∧ configuration shown in Figure 8A.1, where each leg of the ∧ interacts with a laser L − or L + . This was discussed in detail in Section 2D.2 of Complement 2D. Here we consider the case where the two ground states g + and L − , have exactly the same energy, and the two lasers have frequencies ω + and ω − , very close to the resonance frequency ω 0 . In this situation, the selectivity of the interactions is obtained via the polarization selection rules (see Complement 2B): if g − , g + and e have magnetic quantum numbers m = −1, +1 and 0, respectively, the laser wave L − is right-circularly polarized (σ + polarization), while the laser wave L + is left-circularly polarized (σ − polarization).

Cambridge University Press eBooksSep 2, 20100 citations