Enhanced cooling of rubidium atoms in two-frequency diffuse lights

In this paper we describe an experiment of efficient cooling of ${}^{87}$Rb atoms in two-frequency diffuse laser lights. Compared with single frequency diffuse light, two-frequency diffuse lights have wider velocity capture range and thus can cool more atoms. In our experiment, the maximum number of cooled atoms can reach up to $3.9\times {10}^9$. Such a result is quite useful in building a compact cold atom clock.