Two-photon-excited fluorescence spectroscopy of Rb atoms in a magneto-optical trap

Abstract

We report the results of two-photon-excited fluorescence (TPEF) measurements of the $5{\mathrm{S}}_{1/2}\to 5{\mathrm{D}}_{5/2}$ transition of ${}^{85}$Rb and ${}^{87}$Rb cooled in a magneto-optical trap (MOT). We observe TPEF at excitation powers as low as 1 $\mu$W or fluxes as low as $2.98_{-0.94}^{+1.37}\times 10^{18}\text{photons}{\text{cm}}^{-2}{\text{s}}^{-1}$ (${}^{85}$Rb) and $3.31_{-1.33}^{+2.21}\times 10^{18}\text{photons}{\text{cm}}^{-2}{\text{s}}^{-1}$ (${}^{87}$Rb). Our results demonstrate that optically cooled Rb is a promising platform for observing sensitive two-photon spectral signatures at low photon fluxes.