Beamlike twin-photon generation by use of type II parametric downconversion.

Beamlike twin-photon generation by use of type II spontaneous parametric downconversion is demonstrated. The intensity distribution of each beam is round, and the emission angle is very small (0.9 degrees ). As a result, a high coincidence-count rate per unit of pump power was recorded. The ratio of coincidence-count rate to single-count rate was estimated to be 80% in this experiment. These features suggest that this method is useful for generation of a single-photon state and is applicable to bright, entangled twin-photon sources.