Mid-Infrared Single Photon Counting
  We report a procedure to detect mid-infrared single photons at 4.65 um via a two-stage scheme based on Sum Frequency Generation, using a Periodically Poled Lithium Niobate (PPLN) nonlinear crystal and a Silicon Avalanche Photodiode. An experimental investigation shows that, in addition to a high timing resolution, this technique yields a detection sensitivity of 1.24 pW with 63mW of net pump power. 
Guilherme Temporao (1), Sebastien Tanzilli (1 and 2), Hugo Zbinden   (1), Nicolas Gisin (1), Thierry Aellen (3), Marcella Gi...