Effect of finite size cavity on $nS$ Rubidium Rydberg state lifetimes*

In this work, we present lifetime measurements of $nS$ states of Rb as a function of the principal quantum number (40 $\leq$ n $\leq$ 70) using a sample of cold atoms held in a magneto-optical trap, which is performed in a finite size metal vacuum chamber. The Rydberg states are excited through a two-photon transition, and detected by pulsed field ionization. Our measurements are larger than the predictions by well established theoretical model. We have implemented a theoretical model, which considers the vacuum chamber as a lossy Fabry-Perot cavity with a discrete spectrum, and compared with experimental results. Such comparison indicates that the blackbody radiation contribution on Rydberg state lifetime can be decreased by using a small size metal cavity, without the need of cryogenic environment. This effect may have application in experiments where longer Rydberg lifetimes are required.