APDs as single-photon detectors for visible and near-infrared wavelengths down to Hz rates

For the SPECTRAP experiment at GSI, Germany, detectors with single-photon counting capability in the visible and near-infrared regime are required. For the wavelength region up to 1100 nm we investigate the performance of 2 x 2 mm super(2) avalanche photo diodes (APDs) of type S0223 manufactured by Radiation Monitoring Devices. To minimize thermal noise, the APDs are cooled to approximately -170 degree C using liquid nitrogen. By operating the diodes close to the breakdown voltage it is possible to achieve relative gains in excess of 2.10 super(4). Custom-made low noise preamplifiers are used to read out the devices. The measurements presented in this paper have been obtained at a relative gain of 2.2.10 super(4). At a discriminator threshold of 6 mV the resulting dark count rate is in the region of 230 s super(-1). With these settings the studied APDs are able to detect singlephotons at 628 nm wavelength with a photo detection efficiency of (67 plus or minus 7)%. Measurements at 1020 nm wavelength have been performed using the attenuated output of a grating spectrograph with a light bulb as photon source. With this setup the photo detection efficiency at 1020 nm has been determined to be (13 plus or minus 3)%, again at a threshold of 6 mV.