Diffraction by perfect and imperfect amplitude grating.

The paper presents theoretical formulas for calculation of diffraction by perfect infinite and finite amplitude gratings with Fresnel and Fraunhofer approximations. Further, general formulas for diffraction by an imperfect diffraction grating are derived where edges of the grating are described with general harmonic functions. Such a formalism provides enough power to accurately characterize imperfections of diffraction gratings, and it serves as a simple tool for a solution to a diffraction problem.