Diffraction of Light from Sources of Finite Dimensions

Abstract

The distribution of light intensity in the diffraction pattern of continuous light sources is treated analytically for Fraunhofer diffraction phenomena. Sources and diffracting apertures of any dimensions are first discussed, and a result of general application is derived which relates the illumination and dimensions of the diffraction pattern to the dimensions of the source and aperture. A source consisting of a luminous strip is considered in more detail, the form of the pattern is derived for such a source, and tables are supplied to facilitate numerical evaluation. Consideration is given to the maxima and minima of intensity in the image, and the conditions under which these are observable are indicated. In particular, attention is drawn to certain diffraction effects which do not seem to have been previously recorded and which are in agreement with the theory. These effects consist of faint but visually discernible fringes associated with the image of a strip when viewed through a narrow slit. Applications to the optics of the telescope and spectroscope are discussed.