Radiometry of partially coherent radiation

Bukshtab, Michael (2019) Radiometry of partially coherent radiation. In, Photometry, Radiometry, and Measurements of Optical Losses. (Springer Series in Optical Sciences, 209) Second edition ed. Singapore. Springer, pp. 129-212. (doi:10.1007/978-981-10-7745-6_3).

Abstract

The origin of the photometric and radiometric concept is associated with the desire to observe and quantify radiation and to measure physical parameters of light beams via energy and power extents. Owing to the finiteness of the dimensions and time constants of visual and radiometric detectors, the observation and the measurement processes are defined not only by wave amplitudes of the electromagnetic oscillations observed, but also by the detector’s response to the squared amplitude of the wave averaged by detector time and space constants. The properties of the actual detectors define the space–time averages of radiant or luminous parameters of optical radiation and cause high-frequency filtration for observable radiation, leading to an evident lack of correlation between radiometric observation and the description of wave oscillations by electric and magnetic vector amplitudes (Rosenberg, Sov Phys Usp 20(1):55–79, 1977). Only in the electromagnetic field of a plane monochromatic wave, with the phase of its oscillation being an amplitude-invariable function of time, is it possible to construct a single-valued square correlation between the field intensity and its amplitude. Light waves emitted by sources are not strictly monochromatic owing to the finiteness of source dimensions and a great number of elementary dipoles affecting one another. Each light excitation made by a physical source is always given by a sum of Fourier decompositions to infinitely long individual monochromatic groups. Therefore, the wave amplitudes and phases of light in any actual wave field undergo certain irregular fluctuations within spectral width Δν of effective radiating frequency ν.

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