PMT Gain & Signal Calculator
Calculate PMT gain, cathode/anode current, SNR, and NEP in analog and photon counting modes.
A photomultiplier tube amplifies a photocathode current through a cascade of dynodes, each producing secondary electrons with a multiplication factor δ. Total gain is G = δⁿ; for ten dynodes with δ = 5 the gain is nearly 10⁷. The tool operates in two modes. Analog mode computes cathode current from optical power and quantum efficiency, scales it by gain to anode current, then calculates shot-noise-limited SNR and noise-equivalent power (NEP) using the bandwidth and excess noise factor. Photon counting mode tracks discrete detected events: signal count rate, dark count accumulation over an integration window, dead-time correction fraction, and counting SNR = N_s / √(N_s + 2N_d). Photocathode presets cover bialkali (25%), super bialkali (35%), multialkali (20%), GaAsP (50%), and GaAs (12%) quantum efficiencies.