Designed for analytical and scientific applications such as confocal microscopes, adaptive optics, Lidar, particle sizing, and fluorescence microscopes, the SPCM-AQR actively quenched single photon counting module uses an avalanche photodiode capable of detecting single photons over a wavelength of 400 to 1060 nm with better than 70% Q.E. at 650 nm. This self-contained unit requires only 5V to operate.