Mechanical Hanle effect on the sodium D1line

Abstract

We present an experimental and theoretical analysis of the mechanical Hanle effect, i.e., the modification of the atomic trajectories following the interaction with laser fields in the Hanle configuration. The case of open transitions is examined. In our experiment a thermal sodium atomic beam is crossed perpendicularly by a single-mode linearly polarized laser beam. The laser field is tuned to resonance with an Fg Fe transition of the sodium D1 line. A static magnetic field B is applied collinear to the laser light propagation direction. The atomic beam flux at the position corresponding to its maximum in the absence of laser light is studied as a function of the applied magnetic field. For the Fg = F Fe = F,F-1 transitions the atomic flux shows a sharp increase at B = 0, as a result of the coherent trapping of the population into the ground state. For the Fg = 1 Fe = 2 transition this effect is absent and no significant variation of the atomic flux with the magnetic field is observed. A theoretical description of the mechanical Hanle effect in open transitions is given and it is clarified why in our experiment the mechanical Hanle/CPT-resonances associated to different hyperfine transitions have different contrasts.