Optical Lattice in a High Finesse Ring Resonator

An optical lattice with rubidium atoms ($^{85}Rb$) is formed inside a ring resonator with a finesse of $1.8 \times 10^5$ and a large mode volume of 1.3 $mm^3$. We typically trap several times $10^6$ atoms at densities up to $10^{12} cm^{-3}$ and temperatures between 25 and 125 $\mu K$. Despite of the narrow bandwidth (17.3 kHz) of the cavity, heating due to intra--cavity intensity fluctuations is kept at a low level, such that the time evolution of the temperature is determined by evaporative cooling.