An electron multiplier amplifies a signal by accelerating incoming electrons into surfaces that emit additional secondary electrons. Repeating this process at successive stages produces a measurable charge packet from a small initial signal.
A photomultiplier adds a photosensitive input that converts incident light into a photoelectron; its dynodes then perform multiplication. In a simple equal-stage model with mean secondary yield , stages give mean gain . The output fluctuates because emission is stochastic, and saturation can invalidate constant gain. Multiplication increases the signal scale but cannot recreate input events that were never detected.
