a device sensitive to electromagnetic radiation, consisting of a photocathode, from which electrons are released by incident photons, and an electron multiplier, which amplifies and produces a detectable pulse of current
photomultiplier in American English
(ˌfoʊtoʊˈmʌltəˌplaɪər)
noun
a photoemissive photoelectric cell which amplifies emitted electrons and converts them into brighter light, an electric signal, etc.