Velocity-selective coherent population

A. Aspect, E. Arimondo, R. Kaiser, N. Vansteenkiste, C. Cohen-Tannoudji, Laser cooling below the one-photon recoil energy by velocity-selective coherent population trapping. J. Opt. Soc. Am. B 6, 2112 (1989)... 

To date, two specific phase-space optical-pumping schemes have been demonstrated. One uses a two-photon Raman transition and the other is based on the velocity-selective coherent population-trapping (VSCPT) effect. 

Velocity-selective coherent population trapping of ultracold atoms... 

Fig. 5. 15 (a) Three-level yl-scheme describing the interaction of and a circularly polarized laser waves with an atomic transition J = l —J = l. The dashed and wavy lines show the ways by which the atoms are pumped into the yl-system after a few cycles of absorption and spontaneous emission, (b) Atomic momentum distribution following a velocity-selective coherent population-trapping process. (Reprinted from Aspect et al. 1988 with courtesy and permission of the American Physical Society.)... 

Laser cooling below the one-photon recoil energy by velocity-selective coherent population trapping. Physical Review Letters, 61, 826 829. 

Our studies of the effect of velocity-changing collisions in an rf-laser double resonance experiment contribute to a new vista into the role of collisictis in laser spectroscopy of sub-level structures the limitation of the observation time of the active atoms due to narrow-bandwidth optical excitation and simultaneous velocity diffusion can be of importance for a variety of spectroscopic techniques that use a velocity-selective excitation and detection of either sublevel populations or sublevel coherence. On the other hand, the collisional velocity diffusion of sublevel coherence within an optical Doppler distribution can also give rise to new and surprising phenomena as will discussed in the next section. 

The coherent population-trapping effect occurs only in atoms that have a zero projection of their velocity onto the propagation direction, that is, under exact resonance conditions. Therefore, the atomic velocity selectivity of this effect can be used to select atoms with ultralow velocities (Aspect et al. 1988) for use with counterpropagating laser waves. 

---