The Application of Four-Wave Mixing to Cold and Ultra-Cold Atom Imaging

In this project, I investigated a new imaging technique for cold and ultra-cold atoms based on the four-wave mixing (FWM) process. In theory, this technique will provide more precise measurements of the number and spatial density distribution of cold atoms than fluorescence or absorption imaging. Since FWM is usually studied in high optical depth vapor cells but cold atoms have low optical depths, I first studied the dependence of FWM on optical depth. Results showed that Stokes field emission due to FWM decreases exponentially with decreasing optical depth, and that it can still be observed at optical depths of approximately 1. After determining the optimal conditions for Stokes field emission, I tried observing FWM with cold atoms. Absorption and emission-like features were observed on the probe and Stokes fields which depended on the interaction of the control field, the probe field, and the trapped atoms. There is significant reason to believe that these features are associated with the FWM process, although further studies need to be undertaken to determine more definitively the nature of these features, how they depend on various parameters of the experimental setup, and how they may be related to the number and density of the cold atoms