Lifetime measurement of the 5s5p 1P1 state in strontium

We present a direct lifetime measurement of the $5s5p{}^1{P}_1$ state of strontium using time-correlated single-photon counting of laser induced fluorescence in a hot atomic beam. To achieve fast switch-off times and a high signal-to-noise ratio, we excite the strontium atoms with a femtosecond pulsed laser at $\approx$461 nm and collect the fluorescence onto a hybrid single-photon detector. Analysis of the measured exponential decay gives a lifetime of the ${}^1{P}_1$ state of $\tau =(5.216\pm {0.006}_{stat}\pm {0.013}_{sys})$ ns, where all the systematic effects have been thoroughly considered.