Precision measurement sof the n = 2 phosphorus-3 intervals of atomic helium: A determination of the fine-structure constant

The fine-structure constant is a fundamental constant of nature and its value quantifies the strength of electromagnetic interactions of charged particles. Comparison of high-precision theory and experiment of the 23P fine-structure intervals of helium will allow for a determination of the fine-structure constant.;The 23P1-to-23P0 interval in atomic helium is measured using a thermal beam of metastable helium atoms excited to the 23P state using a 1083-nm diode laser. The 23P1-to-23P0 magnetic-dipole transition is driven by 29.6-GHz microwaves in a rectangular waveguide cavity. The result of 29 616 950.9 +/- 0.9 kHz is the most precise measurement of helium 23P fine structure. When compared to similarly precise theoretical determinations for this interval, this measurement allows for a determination of the fine-structure constant to 15 parts-per-billion precision.;A technique to determine the 2.29-GHz 23P1-to-2 3P2 interval in atomic helium to a precision of less than 300 Hz is detailed. A precise determination of this interval will allow for a high-level test of the theory required to predict the energy splitting of both the 23P1-to-23P2 and 23P1-to-23P0 intervals.