Radiative Lifetime of the A 2Π1/2 State in RaF with Relevance to Laser Cooling

The radiative lifetime of the A ^2 Π_1/2 (v=0) state in radiummonofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state is ofrelevance to the laser cooling of RaF via the optically closed A ^2Π_1/2← X ^2Σ_1/2 transition, which is an advantageousaspect of the molecule for its promise as a probe for new physics. Theradiative decay rate Γ = 2.9(2)× 10^7 s^-1 is extracted usingthe lifetime, which determines the natural linewidth of 4.6(3) MHz and themaximum photon scattering rate of 4.1(3)× 10^6 s^-1 of thelaser-cooling transition. RaF is thus found to have a comparablephoton-scattering rate with other laser-cooled molecules, while thanks to itshighly diagonal Franck-Condon matrix it is expected to scatter an order ofmagnitude more photons when using 3 cooling lasers before it decays to a darkstate. The lifetime measurement in RaF is benchmarked by measuring the lifetimeof the 8P_3/2 state in Fr to be 83(3) ns, in agreement with literature.