Adam Light with Kathy Kash

Laser Trapping and Cooling of Neutral Atoms

Laser trapping and cooling is a cutting edge research tool that has made possible the work of several recent Nobel laureates, including the production of Bose-Einstein condensates by Carl E. Wieman and Eric A. Cornell in 1995. In a trapping system, gas atoms absorb laser light from a particular direction and emit photons in a random direction, resulting in a net momentum transfer in the direction of the incoming laser beam. Because atoms of different velocities interact with monochromatic light at slightly different frequencies (Doppler effect), trapping lasers can be set to stimulate a transition only in slower atoms whose trajectory is opposite the direction of the laser beam. In addition to this velocity selection, a position-dependent interaction can be provided by using a non-uniform magnetic field to Zeeman-shift the energy levels of the atoms at the hyperfine level as a function of distance from the trapping center. According to selection rules for angular momentum, the polarizations of the trapping lasers can be adjusted to interact in these hyperfine transitions only with those atoms whose trajectory is pointed outward from the trapping center. With a simple magneto-optical trap, up to 10­ 7 atoms at micro-kelvin temperatures can be confined to a ~4 cm 3 volume for several seconds. Construction of a magneto-optical laser trapping and cooling system for use in the CWRU teaching laboratories will be completed and the system characterized. A suite of possible experiments for use in the senior lab, including measurements of temperature and emission spectra and demonstration of the quantization of angular momentum, will be explored.