As indicated by the material in the first chapter, the diffraction equations are linear, i.e., the superposition principle is fulfilled for these equations. Considerable advances have been made in optics using the approach developed in the mathematical theory of linear systems with the distributed parameters . The important concepts will now be described.
To simplify considerations, it is assumed that the light is linearly polarised. The electrical field at the moment of time t at the point with the coordinates x = (x1, x2, x3), excited by a monochromatic light source, can be written in the complex form:
where is the frequency of the light ...