Spectral shifts and spectral switches in diffraction of partially coherent light by a circular aperture

When a particular class of partially coherent light is incident upon a circular aperture, the on-axis spectrum of the light in the far zone is different from the spectrum of the light at the aperture. An explicit expression describing the on-axis spectrum of the light in the far zone is obtained and the numerical calculation is performed. It is shown that by measuring the spectral shifts against some parameter, such as a/(L) over bar (a is the radius of the aperture and (L) over bar is the effective correlation length of the light at the aperture at the central frequency of the source spectrum), we find that the spectral shifts show a gradual change. However when a/(L) over bar is' equal toparticular values, the spectral shifts exhibit a rapid transition, i.e., spectral switches occur Some parameters, such as the half-width at half-maximum of the Source spectrum Gamma and the ratio of the central obstruction of the source epsilon (s) affect the spectral switch positions and the spectral switch performance. The generation of multi-spectral lines in the far zone from a single spectral line is also shown.