Precision Microwave Measurement of the 23P1−23P0 Interval in Atomic Helium: A Determination of the Fine-Structure Constant

Abstract

The $2^3{P}_1$-to- $2^3{P}_0$ interval in atomic helium is measured using a thermal beam of metastable helium atoms excited to the $2^{3}P$ state using a $1.08-\mu \mathrm{m}$ diode laser. The $2^3{P}_1$-to- $2^3{P}_0$ transition is driven by 29.6-GHz microwaves in a rectangular waveguide cavity. Our result of $29616950.9\pm 0.9\mathrm{kHz}$ is the most precise measurement of helium $2^{3}P$ fine structure. When compared to precise theory for this interval, this measurement leads to a determination of the fine-structure constant of $1/137.0359864\left(31\right)$.