When light passes from one medium to another of different density, its path of travel is bent. This phenomenon is known as refraction.
The word refraction is derived from the same origins as the word ‘fracture’. Both words are associated with the term ‘broken’, and, in the case of refraction, the light ‘breaks’ from its original path of travel when it enters the new medium.
Refractive Properties of Different Media
Different types of media have different refractive properties. The amount of refraction a given material causes is known as its refractive index.
For any interface between two materials, the incident and refracted light rays both lie in the same plane, with the path of the refracted ray being bent towards the normal in the medium with the higher refractive index.
Different materials can be ranked in order of their refractive indexes, with a vacuum taking the value of 1 (these lists are now widely published). Refractive indexes tend to be related directly to the density of a material, but they are also dependent on other material properties.
Nanotechnology and Refractive Index
New developments in nanotechnology have resulted in materials that would normally have high refractive indexes possessing an altered refractive index that is often dependent on the size of the nanoparticles. In some cases it has been possible to make so-called ‘metamaterials’ with negative refractive indexes that can bend the path of the incoming light back on itself.
This article was updated in May 2019 by Rebecca Ingle.