Resonant Collisions of Potassium Atoms

This thesis discusses an approach to excite potassium atoms to very highly excited states (Rydberg states), and then tune their energy levels to induce resonant collisions between atoms. Potassium gas is super-cooled to 1 mK and confined to a small volume in a magnetooptical trap. A 405 nm laser diode, electronically locked to a potassium vapor cell via Doppler free spectroscopy, excites these atoms from the 4s1/2 state (ground state) to the 5p3/2 state. A 978 nm laser then excites the 5p3/2 to nd3/2 or nd5/2 transition, creating Rydberg atoms. Since there is no ground state reference for this transition, an alternative method must be used to lock the laser’s frequency. A scanning transfer cavity lock transfers the stability of a 632 nm HeNe reference laser to the unstable 978 nm laser diode by passing both lasers through a Fabry-Pérot interferometer. Once Rydberg atoms have been created, their energy levels are tuned with an external electric field so that collisions between atoms cause resonant atomic transitions to different Rydberg states. The Rydberg atoms are ionized with a second, stronger electric field, and detected by microchannel plate detectors. Rydberg atoms with different principal quantum numbers ionize at different electric field strengths, so a successful collision signal has multiple peaks from the microchannel plates.