Light interference - Theory and applications

It was Isaac Newton who, around 1750, first observed and described an interferential phenomenon. When a convex lens with a large radius of curvature is applied to an optical plane, a series of typical concentric rings - Newton's rings - is seen by reflection. We will describe these rings in relation to their modern application for the interferential measurement of large radii of curvature 7.2 . A proponent of a corpuscular theory of light, Newton went to great lengths to interpret phenomena according to his ideas, and his authority long stifled the chances of a wave-like conception of light phenomena. Nevertheless, Newton's theory of "accesses" contains many of the properties of a periodic wave in space, and Thomas Young, one of the discoverers of the wave nature of light, claims to have found many of his ideas in Newton's texts.

Light interference allows convenient observation of very small variations in distance, of the order of magnitude of the wavelengths involved, i.e. of the order of 0.5 µm. These are always differential measurements, giving a phase deviation in relation to a reference: displacement in relation to a supposedly fixed point, deformation in relation to a reference shape (plane, sphere or other). Both visual and radiometric techniques can achieve low fractions of a fringe (between 1/10 and 1/1,000), giving access to nanometric sensitivities (a nanometer is a billionth part of a meter). Since the advent of lasers and their extreme coherence, light interference has become a widely-used tool both in the optics workshop and in industrial testing. In this article, we'll review some of the basic properties of light interference and look at a few famous experiments. We'll then take stock of the main applications, not forgetting a few major projects currently under development, which illustrate the incredible possibilities of light in today's context of scientific instrumentation.