Towards a photoionization-based technique for measuring radiation trapping in highly resonant ultracold gases.

Ultracold atom traps are an excellent environment in which to explore how radiation builds up within and propagates through highly absorptive matter. Here we present a novel technique for measuring the light build-up during the absorption/emission process by which light diffuses through ultracold gases. This technique should have a high signal-to-noise ratio and allows us to conduct radiation trapping measurements in a new way and also probe parameter spaces that prior measurement techniques have not been able to access. Using a tapered amplifier, we create a MOT of 85Rb vapor with a large optical depth and shine on/near resonant light through one side of the cloud. At chosen times during the light's propagation, we will use a Nd:YAG pulse to illuminate the cloud. By choosing an ionization laser frequency that only ionizes excited state atoms we will produce Rb ions correlated with the position where light radiation energy has been trapped within the gas. These ions will then be swept to a microchannel detector to provide a signal proportional to the radiative energy trapped within the sample.