THE EFFECT OF AN APERTURE ON THE SPECTRUM OF PARTIALLY COHERENT-LIGHT

It is shown, for a particular class of partially coherent fields, that when such a field is incident upon a circular aperture, the spectrum of the light at an on-axis observation point in the far zone of the aperture is different from the spectrum of the light in the aperture. An explicit expression for the spectrum at such observation points is obtained, and it is shown that the difference between the two spectra is determined by the ratio of the radius of the aperture to the effective correlation length of the light in the aperture. Numerical examples are presented. Our results support a recent suggestion by Kandpal, Vaishya and Josi that the origin of the discrepancies found in the intercomparison of spectroradiometric scales maintained by standards laboratories may be due to such changes in the spectrum. © 1990.