One exciting route to the formation of ultracold plasma is through a cold, dense cloud of highly excited Rydberg molecules — states for which a loosely bound electron interacts substantially with its neighboring molecules. In a custom-built vacuum chamber, a molecular beam composed of nitric oxide in a rare gas carrier is directed past a laser-interaction region to a distant micro-channel plate detector that is sensitive to charged particles. Nitric oxide molecules undergo a two-photon, resonant excitation to yield a high density of Rydberg states, which evolve into stable ultracold plasma. In this project, microwave radiation is used as a direct and selective tool to study Rydberg populations and ultracold plasma. Resonant microwave fields allow the signal corresponding to different quantum numbers to be selectively enhanced in both the pulsed-field ionization (PFI) and the action spectrum of plasma. We demonstrate that two frequencies are resonant to each optically bright Rydberg state, and that they correspond to the energy spacing between adjacent quantum numbers, n. Microwave fields appear to substantially enhance the lifetime of excited molecules that exhibit rapid dissociation in field-free conditions. Finally, the results are compared to the microwave field effect in the presence of small dc electric fields, which, depending on the magnitude, either intensify or dramatically diminish the observed enhancements.

Microwave spectroscopy of ultracold molecular plasma

255th National Meeting (2018)

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