Transverse coherence length of down-converted light in the two-photon state

Abstract
Measurements of the Young interference pattern for down-converted light in the two-photon state are performed. Light in the two-photon state is generated at the output of a Hong-Ou-Mandel balanced interferometer. Two-photon interference patterns with visibilities up to 100% are obtained. Visibilities of the two-photon interference patterns as a function of the double-slit separation are obtained and show that the transverse coherence length of the two-photon light is much larger than the one-photon beam for the distances considered in the experiment.