A Geiger-Mode APD Photon Counting System With Adjustable Dead-Time and Interchangeable Detector

A Geiger-mode avalanche photodiode (GM-APD) photon counting system is presented in this letter. The system provides a maximum counting rate of 35 Mcounts/s and is capable of directly displaying the counting rate and data logging to a PC. In this system, the detector can be easily changed to enhance its usefulness in different applications. A novel active quench and reset integrated circuit (AQR-IC) is designed for the system with adjustable hold-off time from several nanoseconds up to 1.6 μs with a setting resolution of ~6.5 ns. This facilitates optimal performance when using different types of APDs. The AQR-IC also registers each avalanche event as a TTL pulse that is processed by a microcontroller to calculate the photon-counting rate. The microcontroller can be interfaced with a PC over USB to record the measured data and to allow further processing. Software was also written to calculate the photon-counting rate, display the results and save the data to files.