High sensitivity two-photon spectroscopy of cold atoms in a dark optical trap, using an electron shelving scheme

Summary form only given. Utilizing cold and trapped atoms for precision spectroscopy of weak atomic transitions has two important advantages: the suppression of Doppler and time-of-flight broadenings and a combination of long interaction times, weak perturbations and tight confinement, which can be obtained using dark optical traps. We present a new and extremely sensitive method for measuring weak transitions with cold atoms in a dark optical trap, using electron shelving spectroscopy. Our scheme is based on a /spl Lambda/ system. Atoms with two ground states (for example, two hyperfine levels) are stored in the trap in a level that is coupled to the upper (excited) state, by an extremely weak transition. Atoms that undergo the weak transition may be shelved by a spontaneous Raman transition on the second ground level, which is uncoupled to the excited level by the measured photons. Finally, the detection scheme benefits from the multiply excited fluorescence of a strong closed transition from the uncoupled ground-state, that utilizes quantum amplification due to the electron shelving technique. We realized this scheme on a 5S/sub 1/2//spl rarr/5D/sub 5/2/ two-photon transition in cold and optically trapped /sup 85/Rb atoms.