Fresnel Diffraction

Fresnel diffraction is discussed in terms of a description of waves traveling near the stationary point. That is the point that lies on a line connecting the source and the observation point. We discuss a rectangular aperture using Fresnel integrals or graphicly using the Cornu Spiral We discuss a circular aperture in terms of Fresnel zones and we develop a simple formula for the calculation of the radius of a Fresnel zone. Using the concept of Fresnel zones we develop an expalination of Fermat’s Principle and explain the origin of Poisson’t spot. The Fresnel zones generate an understanding of the operation of the pinhole camera.