Spectral shifts and spectral switches of partially coherent light passing through an aperture

Within the Fresnel approximation, we investigate the spectral characteristics in the near zone when a certain class of partially coherent light is incident on a circular aperture. It is shown that, as the distance z between the aperture and the on-axis observation point decreases, the spectral shifts show gradual change. However, when z approaches a critical value, a rapid spectral switch occurs. The evolution from a gradual spectral shift to a rapid spectral switch is illustrated. The effect of the coherence on the spectral switch is also presented. (C) 1999 Elsevier Science B.V. All rights reserved.