title: Sub-shot-noise high-sensitivity spectroscopy with optical parametric oscillator twin beams.
abstract: Nondegenerate optical parametric oscillators generate above-threshold signal and idler beams that have intensity fluctuations correlated at the quantum level (twin beams). We describe what is to our knowledge the first high-sensitivity spectroscopy experiment using twin beams emitted by a cw optical parametric oscillator: a very weak two-photon absorption signal, in the 10(-7) range, is recorded on the 4S(1/2)-5S(1/2) transition of atomic potassium with a noise background that is reduced by 1.9 dB with respect to the shot-noise limit of the light used in the experiment.
authors.forename: P H
authors.initials: PH
authors.lastname: Ribeiro
authors.forename: C
authors.initials: C
authors.lastname: Schwob
authors.forename: A
authors.initials: A
authors.lastname: Maître
authors.forename: C
authors.initials: C
authors.lastname: Fabre