We describe techniques for laser spectroscopy in the vacuum ultraviolet (VUV) spectral region that combine high spectral resolution with high absolute accuracy. A nearly transform-limited nanosecond laser source at 120 nm is constructed using difference-frequency missing. This source is used to perform the first Doppler-free VUV measurement. We measure the inherently narrow 11S - 21S two-photon transition in atomic helium with a spectral resolution of 7 parts in 108 (180 MHz). The narrowest line width so far observed at such short wavelengths. Careful measurements of optical phase perturbations allow us to determine the absolute frequency of the line center to a fractional uncertainty of 1 part in 108. Improvements now in progress should reduce this uncertainty to 2 parts in 109.
Citation: Journal of the Optical Society of America B-Optical Physics
Issue: No. 9
Pub Type: Journals
Doppler-free spectroscopy, helium, lamb shift, multiphoton ionization, QED Energy shift, VUV laser spectroscopy