title: Two-photon optical Ramsey spectroscopy of freely falling atoms.
abstract: Using a simple semiclassical model, we explore ultrahigh-resolution optical two-photon spectroscopy of cold neutral atoms falling freely in a fountain. Considering atoms that interact with the same standing-wave laser field twice on their parabolic trajectories, and averaging over a Maxwellian velocity distribution, we predict a nearly Lorentzian line shape with just the natural linewidth. First-order Doppler shifts cancel even if the counterpropagating beams are slightly misaligned, and sub-Hertz resolution appears feasible with a fountain of modest dimensions.
authors.forename: R G
authors.initials: RG
authors.lastname: Beausòleil
authors.forename: T W
authors.initials: TW
authors.lastname: Hänsch