Abstract

Wechoes in a sample of 85Rb atoms confined in a magneto-optical trap. The trapped atoms are excited with two sets of simultaneous σ⁺ − σ⁻ orlin-perp-lin laser pulses separated by time T. These pulses are applied several milliseconds after turning off the trapping laser and magnetic field gradient. The pulses have wave vectors k₁ and k₂ at an angle 6 and are close to resonance with the 5S_1/3 F = 3 − 5P_3/2 F = 4’ transition. In the case of σ⁺ − σ⁻ excitation, the first pulse creates a spatially modulated coherence grating involving magnetic sublevels of the ground state separated by Δm = 2. The grating washes out as a result of the velocity distribution of the atoms and may be rephased by the second pulse at time t = 2T, Both the dephasing (free induction decay or FID) and rephasing (magnetic grating echo or MGE) are detected by applying a traveling wave pulse along k₂ and observing the coherent scattering along k₁ with use of a heterodyne technique (Fig. 1). We have used the FID and the MGE to measure the velocity distribution of cold atoms.

© 1997 Optical Society of America