Optical Studies of Partially Coherent Diffraction and the Ergodic Hypothesis

摘要

Diffraction by apertures illuminated by partially coherent light, diffraction by apertures containing random phase disturbances, experimental demonstration of the ergodic hypothesis, and the concept of cross spectral purity are considered. In diffraction experiments using partially coherent illumination, it is observed that as the ratio of aperture size to coherence interval increases (i.e., the illumination becomes less coherent) the sharp minima present in the diffraction pattern disappear and a shifting of the minima occurs. The results are compared with existing theories, and the agreement is excellent. It is experimentally shown that random phase disturbances placed in the diffracting aperture distort an individual diffraction pattern. In the corresponding ensemble-averaged experiment, the distortion is reduced and the diffraction pattern is more readily identified. A dynamical model of lycopodium particles suspended in water demonstrated the equivalence of time and ensemble averaging (ergodic hypothesis). The ensemble-averaged results agree quantitatively with theoretical calculations. In investigating the concept of cross spectral purity (J. Opt. Soc. Am. 51:1342 (1961)), it is shown that quasi monochromaticity is synonymous with spectral purity and that spectral impurity is synonymous with polychromaticity. (Author)