On the excess photon noise in single-beam measurements with photo-emissive and photo-conductive cells

Abstract

In this paper the so-called excess photon noise is theoretically considered with regard to noise power measurements with a single, illumined photo-emissive or photo-conductive cell. Starting from a modification of Mandel's stochastic association of the emission of photo-electrons with wave intensity, the frequency dependence of the excess noise power with photo-emissive cells is derived in Sect. 2. Use is made of formulas given by Rice for square-law detectors. In Sect. 3 a new hypothesis is introduced in order to calculate the excess photon noise effect with photo-conductive cells, in which the statistics of both the excitation and of the recombination have to be considered. It is shown that in the case of an ideal photo-conductor in thermodynamic equilibrium with the radiation field the result obtained is consistent with the expected Fermi-statistics for the electron gas. It is shown in Sect. 4 that under certain experimental conditions the excess photon-noise effect is detectable in noise-power measurements with a single photocell. This applies especially to the case of an infra-red sensitive photo-conductive or photo-emissive cell with a quantum-yield near to unity.