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 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 depends on the ratio of the radius of the aperture to the effective correlation length of the light in the aperture. Numerical examples are presented, and the relevant limiting cases are discussed.