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. (C) 2001 Optical Society of America.