The three-level $5S_{1/2}\text{−}5P_{3/2}\text{−}5D_{5/2}$ cascade transition of ${}^{87}\mathrm{Rb}$ is widely used as a reference for optical frequency standards based on two-photon spectroscopy, implemented with either single-color excitation at 778 nm or two-color excitation at 780 and 776 nm. Although primarily exploited as a clock transition, its relatively large scattering rate enables significant radiation pressure. Here we theoretically investigate two-color laser cooling based on this optical clock transition. Using a semiclassical model, we calculate the radiation force, damping and diffusion coefficients, and equilibrium temperatures as a function of laser detunings and intensities. We show that sub-Doppler temperatures, below the Doppler limit of the $5S_{1/2}\text{−}5D_{5/2}$ transition, can be achieved with a weak probe field at 780 nm and a strong coupling field at 776 nm. We further demonstrate that, under appropriate cooling conditions, the ac Stark shift of the clock transition can be strongly reduced or canceled through suitable choices of laser detunings and power ratios. These results suggest a route toward incorporating laser cooling directly into two-color rubidium optical clocks using the same interrogation lasers, potentially improving stability while minimizing experimental complexity.

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• Atom & ion cooling
• Atomic, optical & lattice clocks
• Mechanical effects of light on material media