Measurement of the Lifetime of the 7s2s1/2 State in Atomic Cesium Using Asynchronous Gated Detection

We report a measurement of the lifetime of the cesium 7s 2S1/2 state using time-correlated single-photon counting spectroscopy in a vapor cell. We excite the atoms using a Doppler-free two-photon transition from the 6s 2S1/2 ground state, and detect the 1.47-μm photons from the spontaneous decay of the 7s 2S1/2 to the 6p 2P3/2 state. We use a gated single-photon detector in an asynchronous mode, allowing us to capture the fluorescence profile for a window much larger than the detector gate length. Analysis of the exponential decay of the photon count yields a 7s 2S1/2 lifetime of 48.28 ± 0.07 ns, an uncertainty of 0.14%. These measurements provide sensitive tests of theoretical models of the Cs atom, which play a central role in parity violation measurements