arXiv subjects
Publications and source records attributed to N. E. Bulleid.
Experiments with cold molecules usually begin with a molecular source. We describe the construction and characteristics of a cryogenic buffer gas source of CaF molecules. The source emits pulses with a typical duration of 240 $μ$s, a mean speed of about 150 m/s, and a flux of $5\times 10^{10}$ molecules per steradian per pulse in a single rotational state.
We present a combined experimental and theoretical study of beam formation from a cryogenic buffer gas cell. Atoms and molecules are loaded into the cell by laser ablation of a target, and are cooled and swept out of the cell by a flow of cold helium. We study the thermalization and flow dynamics inside the cell and measure how the speed, temperature, divergence and extraction efficiency of the beam are influenced by the helium flow. We use a finite element model to simulate the flow dynamics and use the predictions of this model to interpret our experimental results.
We demonstrate the deceleration of heavy polar molecules in low-field seeking states by combining a cryogenic source and a travelling-wave Stark decelerator. The cryogenic source provides a high intensity beam with low speed and temperature, and the travelling-wave decelerator provides large deceleration forces and high phase-space acceptance. We prove these techniques using YbF molecules and find the experimental data to be in excellent agreement with numerical simulations. These methods extend the scope of Stark deceleration to a very wide range of molecules.
The fluorescence spectrum resulting from laser excitation of the A^{2}Π_{1/2} - X^{2}Σ^{+} (0,0) band of ytterbium monofluoride, YbF, has been recorded and analyzed to determine the Franck-Condon factors. The measured values are compared with those predicted from Rydberg-Klein-Rees (RKR) potential energy curves. From the fluorescence decay curve the radiative lifetime of the A^{2}Π_{1/2} state is measured to be 28\pm2 ns, and the corresponding transition dipole moment is 4.39\pm0.16 D. The implications for laser cooling YbF are discussed.