5S−5D two-photon transition in rubidium vapor at high densities

Abstract

The rubidium $5S\text{\ensuremath{-}}5D$ Doppler-free two-photon transition has been observed in a thermal vapor cell by detecting the infrared radiation emitted during the decay from the $5D$ excited level to the $5P$ intermediate level. Different to the usual detection scheme based on blue light emission this approach does not suffer from reabsorption and still works at high densities. This not only allows for a dramatically enhanced detectable emission rate but also for investigating collisional effects such as collisional broadening and collisional energy transfer. Furthermore, we observe a yet unknown temperature dependence of the resonance linewidth for transitions into the states of the $5{D}_{\text{5/2}}$ level. Consequences for the design of an optical Rb-frequency standard are discussed.