Laser cooling without spontaneous Emission
Monday, 15 Jun. 2015, 17:30 - 19:00
Presenter: Harold Metcalf
Host: Arno Rauschenbeutel
Where: ATI, Lecture Hall, Stadionallee 2, Wien
The notion of laser cooling in the absence of spontaneous emission has generated considerable controversy because of entropy transport concerns. However, energy conservation is an even more significant consideration because stimulated emission at the same frequency as the cooling light cannot provide for energy removal. This conundrum is resolved by using more than one frequency of light. The talk will begin with a discussion of energy and entropy removal using two light frequencies. It will present our observation of laser cooling without spontaneous emission using the bichromatic force. The experiment works by restricting the atom-light interaction to a time short compared to a cycle of absorption followed by spontaneous emission. The momentum exchange between atoms and light is restricted to a well-defined velocity range resulting from nonadiabatic transitions at a velocity that can be understood from simple energy conservation. Our results comprise a compression in phase space because the velocity distribution is narrowed and the spatial expansion of the atoms is negligible. We have also done various simulations of the motion of atoms under the bichromatic force and they compare well with our data. This accomplishment is of interest to direct laser cooling of molecules or in experiments where working space or time is limited. See Phys. Rev. Lett. 114, 043002 (2015).