Light intensity measurements

Any device built to measure the radiation power density, such as photocells, photomultipliers, takes relies on the absorption of radiation by matter. In this presentation, we are interested in the description of the incident radiation, in particular in how to express the number of photons and their fluctuations for different spectral compositions of light, such as laser or chaotic light. We investigate the temperature dependence of the photon number and the corresponding radiation power density, as well as their fluctuations. In case of coherent states such as in laser light, only one term appears in the expression for the energy fluctuations, characteristic also for particles. In case of chaotic light, there are two terms in the expression for the energy fluctuations of which one is characteristic of particles and the other of waves. This is a manifestation of the dual particle-wave nature of light.