Detection of individual 0.4–28 μm wavelength photons via impurity‐impact ionization in a solid‐state photomultiplier

A solid‐state device capable of continuous detection of individual photons in the wavelength range from 0.4 to 28 μm is described. Operated with a dc applied bias, its response to the absorption of incident photons consists of submicrosecond rise time pulses with amplitudes well above the electronic readout noise level. A counting quantum efficiency of over 30% has been demonstrated at a wavelength of 20 μm, and over 50% was observed in the visible‐light region. Optimum photon‐counting performance occurs for temperatures between 6 and 10 K and for count rates less than 1010 counts/s per cm2 of detector area. The operating principle of the device is outlined and its performance characteristics as a photon detector are presented.