This invention describes a device and method to help protect a given avalanche photo diode (APD) from excessive light or photon counts without modification to the APD itself or the associated power for the APD. High photon count rate to a reference frequency and rapidly shutting down the APD if a threshold is exceeded. The design also can be interfaced with a laser interlock /label warning system in which a laser shutter can isolate the APD from an excessive source.
Avalanche photodiodes (APDs) are highly sensitive single photon counters and are used in fluorescence lifetime measurements, medical devices, safety equipment and optical communication devices among many other applications. They function by placing a high voltage across an optically sensitive semiconductor. When a photon strikes the semiconductor, excited charge carriers initiate an avalanche of current which results in an electrical pulse at the output. A potential problem with using APDs is the possibility of overloading the input, resulting in excessive dead time and/or damage to the photodiode. This invention provides a way to protect APDs by sensing the count rate, comparing it to a reference frequency, and then rapidly shutting down the device before damage can be done if the reference frequency is exceeded.
Protects photon counters from bright light damage; Works on multiple device types – APDs, Photomultipliers, Multi-Pixel Photon Counters; Novel concept: compares random photon rate to adjustable periodic reference frequency; If photon rate > ref frequency --> protect!