ABSTRACT
When light propagates in a vacuum or in a transparent homogeneous medium, it moves along straight lines defined as light rays. Due to the electromagnetic nature of the radiation, can also define hypothetical surfaces, called wavefronts, which are the spatial loci where the electromagnetic field vibrates in phase. Light rays of a beam are everywhere normal to the wavefronts. The aim of optical visualization methods is to make visible the light ray deviations due to the refractive index heterogeneities in a transparent medium. To become visible, these deviations or wavefront deformations must involve changes in illumination or color on an observation screen. Visualization methods are often used only qualitatively. Even so, an image can contribute to the understanding of complex physical phenomena in a flow field and clarify the data acquired discontinuously by other metrological means. Shadowgraphy is the simplest technique for implementing flow visualization.
