Focal Plane Diffraction Anomalies in Telescopic Systems*

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Abstract
A description is given of an anomaly in the form of the Fraunhofer diffraction pattern which is usually characteristic of a rectangular aperture. The anomaly is created by allowing two plane polarized monochromatic light waves of different amplitudes and phases, with their electric vectors polarized at various azimuth angles with respect to each other, to be incident on the upper and lower halves of the diffracting aperture and then combining these two waves in the usual way with a focusing lens. It was found that the forms and spacings of the diffraction bands parallel to the dividing line of the aperture could be changed quite markedly while those perpendicular to the dividing line were unaffected. The forms of these bands are calculated theoretically, and are also observed experimentally by a unique utilization of the Michelson interferometer. These experiments not only make it possible to change the resolving power of a telescope in directions perpendicular to each other, but also suggest the possibility of measuring linear distances in terms of changes in diffraction patterns instead of the usual shift of interference fringes. The forms of the diffraction bands in unpolarized light were also considered both theoretically and experimentally.

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