Diffraction

Abstract

Diffraction can be used to describe the departure of radiation from its rectilinear path, such as may occur when it meets a slit or a circular aperture. The important parameter to be determined is the ratio wavelength λ: characteristic aperture size a; for a slit, a would be its width and for a circular aperture it would be the diameter. If λ/a is ⪡ 1, diffraction can be ignored and the transmitted wavefront propagates in the same direction as the incident wavefront. However, if λ/a is ⪢ 1 the energy of the incident wave is uniformly distributed in all directions (see Fig. 4.1).