Update on Improving the Precision of Helium Laser Spectroscopy

Precision measurements of the fine structure of the helium 2P state provides a proving ground for various experimental techniques as well as a test of the bound state quantum electrodynamics of the electron-electron interaction.  Additional applications are to nuclear few-body physics and possible input to the fine structure constant determination. We report on the performance of previously presented concepts.  (1) Circular polarized atomic beam preparation pumping, accomplished with a custom, miniature, annular, NdFeB magnet assembly and a variable retardance liquid crystal.  (2) 10x increased data collection rate via LabVIEW timing optimization.  (3) An alternative first-order Doppler shift minimization using picomotor-driven, sub-microradian “active” precision laser alignment, tailored optical mounts, and optical fiber switching.  In addition, we describe our in-house fiber laser developments for spectroscopy and atom-state preparation [1].  There was an unexpected discrepancy between the theoretical model and experiment.  Further modeling, revised physical parameters, and possible resolution to this discrepancy will be discussed.  Data collection to further identify sources of uncertainty which limit precision will be examined also.

1. Currey R, Khademian A, Shiner D. Development of a Thulium Fiber Laser for an Atomic Spectroscopy Experiment. Fibers 2020, 8, 12. https://doi.org/10.3390/fib8020012