Two-photon cooling of calcium atoms

TL;DR

This paper demonstrates a novel two-photon cooling method for calcium atoms that achieves temperatures below the Doppler limit, offering advantages like adjustable linewidth and high transfer efficiency.

Contribution

It introduces a two-photon cooling scheme for calcium atoms, providing an alternative to standard Doppler cooling with improved control and efficiency.

Findings

Achieved temperatures as low as 260 μK in a calcium MOT.

Observed no reduction in MOT lifetime with the new scheme.

Good agreement between experimental results and theoretical simulations.

Abstract

We demonstrate sub-Doppler cooling of calcium atoms using a two-photon transition from the ${^1}S_0$ ground state to the upper $4s5s~{^1}S_0$ state via the ${^1}P_1$ intermediate state. We achieve temperatures as low as $260~\mu\text{K}$ in a magneto-optical trap (MOT), well below the Doppler limit ($T_{\text{D}} = 0.8~\text{mK}$) of the ${^1}P_1$ state. We characterize temperature, lifetime and confinement of the MOT over a range of experimental parameters, observing no reduction in lifetime due to coupling to the higher state. We perform theoretical simulations of the cooling scheme and observe good agreement with the experimental results. The two-photon cooling scheme presented in this work provides an alternative to the standard Doppler cooling applied to alkaline-earth atoms, based on a sequence of two magneto-optical traps. The advantages of our scheme are the possibility of varying the effective linewidth of the ${^1}P_1$ state, a higher transfer efficiency (close to 100$\%$), and a more straightforward experimental implementation.