LASER COMPONENTS has been manufacturing avalanche photodiodes since 2004 and these detectors are the heart of the photon counting instruments. The COUNT series is a portfolio of single photon counting modules with the performance optimised in the wavelength range 500-900nm. The COUNT series has an unrivalled quantum efficiency, over 70% in the red region of the spectrum with dark count rates at less than 10cps on some units, providing a level of performance that often outperforms photomultiplier tubes.
These modules feature a simple robust design combining the low noise APD with specially developed quenching and signal processing electronics.
Incoming photons generate corresponding electrical pulses which are read out as a TTL signal. The device can also be supplied with an optional fibre connector providing a convenient method for sampling from a multimode optical fibre.
Confocal Imaging of biological samples ensures that light is only collected from the part of the specimen which is in focus, regions not in the focal plane of the objective appear black eliminating all unwanted glare.
This approach results in very low levels of light reaching the sensor requiring that the detector has a high level of photon conversion efficiency and responsivity.
Photomultipliers have been widely used in this application but have low photon detection efficiency which means about two thirds of the incident light does not contribute to the signal. The COUNT module with its much higher level of photon conversion efficiency ensures that this additional signal is not wasted.