A high-yield single photon source using gated spontaneous parametric   down conversion
  The construction of a single photon source using gated parametric fluorescence is reported with the measurement results of the photon number distribution. A beamlike twin-photon method is used in order to achieve high collection efficiency. The estimated probability P(1) to find a single photon in a collimated output pulse is 26.5 % at a repetition rate of 10 kHz when the effective quantum efficiency of 27.4 % in the detection setup is compensated. 
Shigeki Takeuchi, Ryo Okamoto and Keiji Sasaki