Effect of Source Size and Spectral Width on the Irradiance Distribution in the Defocused Image of a Grating

An expression is derived for the irradiance distribution in the neighbourhood of the geometrical image plane of a grating. The illuminating source has finite dimensions and emits over a large spectral width. Only two or three diffracted orders are used to form the grating image. A knowledge of three-dimensional irradiance distribution is of particular importance in estimating the tolerance in the setting of the receiving plane in an image forming system.