Trapping and Cooling of Neutral Atoms with the Dipole Force of a Laser Beam

Abstract

Publisher Summary This chapter discusses a novel method of trapping and cooling neutral atoms with the dipole force of a laser beam. This method allows the cooling of neutral atoms to a temperature much lower than the Doppler limit. Further cooling even beyond the recoil limit is feasible because cooling with the dipole force is free from fluctuations of the photon recoil. The chapter illustrates a proposed trap, in which the laser beam is concave upwards. Precooled atoms fall freely in the gravitational field and are reflected by the dipole force exerted by the gradient of the laser beam. Then atoms will be repeatedly rebounding on the laser beam. The potential of the dipole force is given by –α' U, where α' is the real part of the atomic polarizability at the frequency of the laser and U is the electric energy density of the laser beam. The value of α' is negative at positive detuning so that the dipole-force potential increases with the light intensity. On the other hand, the gravitational potential for the atom of mass μ is Mgz, where g is the gravitational acceleration and z is the vertical coordinate. The resulting potential has a valley. The falling atoms are repelled by the potential hill as if elastically reflected by the laser beam. Thus these atoms are trapped around the valley between the hill and the gravitational slope. In order to prevent atoms spilling over at either end of the valley, the three-dimensional profile of the laser beam may be formed in shape of a shallow tray.