Application Note: Dynamic Range - Photon Counting Mode

Under low light intensity conditions the output signals from an SPM can be treated as discrete pulses and counted. The number of single photoelectron pulses is then proportional to the incident photon flux and the technique is known as photon counting. Photon counting has a number of advantages over analogue mode, including signal-to-noise ratio and stability, where the current from all the pulses is averaged.

In photon counting mode the dynamic range is determined by the ability to resolve successive pulses and is therefore determined by the time resolution of the signal processing circuit and the width of the output pulses.