A compact apparatus for a two-photon optical clock

The Doppler- and recoil-free nature of two-photon transitions eliminates the need for atoms in optical clocks to be trapped at ultracold temperatures. The resulting technical simplicity makes atoms with narrow two-photon transitions attractive candidates for portable optical frequency standards. We report on progress towards the construction of a two-photon optical clock based on the 915 nm $4s^{2}\,^{1}S_{0} \rightarrow\rightarrow 4s3d\,^{1}D_{2}$ transition in calcium atoms. We demonstrate laser cooling of calcium in a compact and portable apparatus, and report on the performance of two narrow-linewidth 915 nm lasers.