To measure characteristics such as density and particle-size distributions of a medium that interacts with light, a polarimeter simultaneously develops all 16 elements of the Mueller matrix by modulating polarized monochromatic light with a quarter-wave retarder operating at a predetermined frequency before transmitting it to the medium and then modulating the light leaving the medium with another quarter-wave retarder which operates at a frequency five times that of the predetermined frequency of modulation of the light transmitted to the medium. The light is electrically detected and provides a signal which may, by Fourier analysis, be broken into 25 terms. The coefficients of those 25 terms, by relatively easy calculations, provide the 16 elements of the Mueller matrix. An electrical element is provided for optically simulating the rotation of a quarter-wave retarder.
Azzam, Rasheed M.A., "Polarimeter" (1981). University of New Orleans Patents. Paper 1.