DOPPLER COOLING OF ION-CYCLOTRON MOTION IN COUNTER-PROPAGATING LAGUERRE-GAUSSIAN BEAMS

We demonstrate theoretically that ions moving in the field of two axia l counter-propagating Laguerre-Gaussian (LG) light modes and a constan t axial magnetic field, exhibit novel cooling effects. When the beams have orbital angular momentum I of the same sign we find that in addit ion to an axial force similar to the conventional plane wave Doppler c ooling force, there is a velocity-independent quantised torque about t he common beam axis which significantly influences the subsequent moti on of the ion. The new effects are illustrated for the cooling of Mg-2 4(+) ions in the presence of an axial magnetic held.