Since the pinhole reduces the amount of signal, a photomultiplier tube detector (PMT) is used. A PMT is an extremely sensitive detector that can multiply the current produced by light by up to 100 times.

PMTs contain a photocathode, which when struck by an incoming photon of light, emits an electron. The electron is attracted to the positively charged anode and is multiplied many times as it hits a series of intermediate dynodes. This large number of electrons creates a current that can be recorded by the computer.