Introduction

The propagation of light can be interpreted in terms of rays indicating the trajectory that is followed by the light. For example, in a transparent, homogenous and isotropic medium, light propagates in a rectilinear manner. This approach is useful for describing a wide array of light phenomena. Nevertheless, light interferences cannot be described through a geometrical approach, since light also propagates in the form of waves. In 1869, the English physicist Maxwell established that such waves can be described by electromagnetic waves made up of both an electrical field and a magnetic field . The interference phenomenon occurs when the energy, the illumination, or the intensity that results from the superposition of two radiations is not equal to the sum of their respective energies, illuminations, or intensities. Historically, this result was quite surprising to the point that we refer to the paradox of interferences, which is often provocatively expressed as light+light =darkness.

This course examines interferences between two waves, for both plane and spherical waves. It also analyzes the effects of the source's spectral and spatial width. The case studies and exercises use the Young slits model to demonstrate how interferences between two waves are produced.