Abstract

In optical lattices,¹ atoms are located in a periodic structure of micron-size optical potential wells. We present here a situation where the location is found in momentum space. The results described below correspond to an experiment performed with cesium atoms in a four-beam lin ⊥ lin lattice² (angle between the beams 2θ_x = 2θ_y = 76°) operating on the blue side of the 6S_l/2(F = 3) − 6P_3/2(F′ = 2) transition (frequency detuning Δ = 4Γ). However, we checked that similar results are found on the red side of the 6S_1/2(F = 4) − 6P_3/2(F' = 5) transition. A static magnetic field B₀ is applied along the Oz symmetry axis of the lattice, which lays in the horizontal plane. The velocity distribution along the x axis is measured by a time-of-flight method. An example of signal is shown in Fig. 1. The peak p = 0 corresponds to atoms having a velocity v_x ≅ 0. The other peaks are associated to nonzero velocities. For example, we show in Fig. 1 the shift of the velocity group associated with the peak p = −1 with B₀. A linear variation is observed. Actually a bunching of atoms around nonzero velocity groups was reported in the case of one-dimensional molasses with magnetic field.³ The bunching occurs close to values for which a Raman or a Rayleigh transition is resonant in the atomic frame. Such a condition in the three-dimensional case can be written.

© 1998 Optical Society of America