Ultrasensitive Sub-Nanosecond Time-Gated Detection Using a Single Photon Avalanche Diode

Ultrasensitive detection and spectroscopy experiments require single photon detectors with sub-nanosecond timing jitter. Since the first experiments demonstrating the detection of single chromophore dye molecules in solution,1 a significant improvement in the signal rate from each molecule has been achieved by using a high quantum efficiency single photon avalanche diode (SPAD). The EG&G SPCM-200 SPAD with custom-modified passivelyquenched bias circuit has been characterized for this purpose2 and has been found to provide a quantum efficiency of 55% at 532 nm and a single photon timing jitter of 168 ps when the input light is focused to a spot of diameter < 20 µm.