Intracavity cold atomic ensemble with high optical depth.

We describe the apparatus of an optical cavity loaded with cold 85Rb atoms of high optical depth (OD) in the weak coupling regime. The relevant cavity-atom parameters are the single-photon Rabi frequency g0 = 2π × 0.25 MHz, the cavity power decay rate κ = 2π × 9.0 MHz, and the atomic excited state decay rate Γ = 2π × 5.75 MHz. In this bad-cavity configuration where the atomic natural linewidth (Γ/2π) is less than the cavity linewidth (κ/2π), the cavity enhancement factor for the longitudinal OD is about 188. We obtain a cavity enhanced OD up to 7600, corresponding to an atomic ensemble with a bare single-pass OD of 40, coupled to the cavity mode. Our intracavity cold atomic ensemble with high OD may have many applications in studying collective atom-light interaction inside an optical cavity.