# Microwave spectroscopy of the $1\mathrm{s}n\mathrm{p}\,^3\mathrm{P}_J$ fine structure of high Rydberg states in $^4$He

## TL;DR

This study measures the fine structure of high Rydberg states in helium using microwave spectroscopy, providing experimental data that aligns well with theoretical predictions and analyzing systematic uncertainties.

## Contribution

First precise microwave measurements of the $1snp^3P_J$ fine structure in high Rydberg helium states across a range of principal quantum numbers.

## Key findings

- Good agreement with theoretical predictions.
- Resolved fine structure intervals for specific $n$ ranges.
- Quantified systematic uncertainties from residual fields.

## Abstract

The $1\mathrm{s}n\mathrm{p}\,^3\mathrm{P}_J$ fine structure of high Rydberg states in helium has been measured by microwave spectroscopy of single-photon transitions from $1\mathrm{s}n\mathrm{s}\,^3\mathrm{S}_1$ levels in pulsed supersonic beams. For states with principal quantum numbers in the range from $n=34$ to 36, the $J = 0 \rightarrow 2$ and $J = 1 \rightarrow 2$ fine structure intervals were both observed. For values of $n$ between 45 and 51 only the larger $J = 0 \rightarrow 2$ interval was resolved. The experimental results are in good agreement with theoretical predictions. Detailed characterization of residual uncancelled electric and magnetic fields in the experimental apparatus, and calculations of the Stark and Zeeman structures of the Rydberg states in weak fields, were used to quantify systematic contributions to the uncertainties in the measurements.