Strontium ${}^1{S}_0\to {}^1{P}_1$ transition frequency measurements assisted by a photonic grating chip

Abstract

We measure the absolute frequency of the ${}^1{S}_0\to {}^1{P}_1$ transition in strontium using two methods: fluorescence spectroscopy of a thermal atomic beam source from a compact low-power oven and velocity measurements of a slow atomic beam from a two-dimensional grating magneto-optical trap (2D gMOT). The measurements for both methods are performed in the same ultra-high vacuum chamber containing a diffraction grating chip which is placed below the strontium atoms that are being interrogated. The first method uses a probe laser beam incident on the grating chip such that the grating acts as an end mirror, with the first-order diffracted beam providing a retro-reflected probe beam. The counter-propagating laser beams traverse an atomic beam emitted from an oven, enabling spatially resolved fluorescence spectroscopy through CCD imaging and hyperfine-constrained multi-isotope fitting. The second method relies on a large profile cooling laser beam normally incident onto the grating chip which laser cools strontium atoms for a slow atomic beam source. The velocity of the atoms exiting the 2D gMOT is measured as a function of the laser detuning and intensity from which the resonance frequency can be estimated. The two methods are consistent within their quoted uncertainties. Using three datasets based on retro-beam spectroscopy measurements, and one dataset using slow atom beam velocity measurements, we determine the ${}^1{S}_0\to {}^1{P}_1$ transition frequency to be $650.503815(5)\mathrm{THz}$. Our result provides a re-evaluation of this $461$ nm transition demonstrated on a compact laser cooling apparatus based on a diffraction grating platform.

15 pages, 9 figures