Unimodality of the Distribution of the Number of Pulses for Gaussian Optical Fields

The statistics of detected pulses is considered when recording optical radiation. On the basis of Mandel's formula for the probability $P(n)$ to detect $n$ photons during an observation time interval, it is shown that the probability distribution $P(n)$ is unimodal provided the radiation field is Gaussian. The unimodality property makes it possible to apply the theory of statistical decisions that makes use of a unique threshold to the design of optical information transmission systems.