PRISMS & RETROREFLECTORS

Prisms

Prisms are solid optical glass that is ground and polished into geometrical and optically significant shapes. The angles, position, and number of surfaces help define the type and function. One of the most recognizable uses of prisms, as demonstrated by Sir Isaac Newton, consists of dispersing a beam of white light into its component colors

This application is utilized by refractometer and spectrographic components. Since this initial discovery, prisms have been used in "bending" light within a system into a smaller space, changing the orientation of an image, as well as combining or splitting optical beams with partial reflecting surfaces. These uses are common in applications with telescopes, binoculars, surveying equipment, and a host of other applications. A notable characteristic of prisms is their ability to be modeled as a system of plane mirrors in order to simulate the reflection of light within the prism medium.

Replacing mirror assemblies is perhaps the most useful application of prisms, since they both bend or fold light and change image parity. Often, multiple mirrors are needed to achieve results similar to a single prism. Therefore, the substitution of one prism in lieu of several mirrors reduces potential alignment errors, increasing accuracy and minimizing the size and complexity of a system.

Retroflectors 

Retroreflectors function by reflecting a beam or image 180° back toward its original direction. Depending on the coating, a prism does this through specular reflections or total internal reflections (TIR). 

A corner reflector is a retroreflector made of up 3 mutually perpendicular, square shaped intersecting surfaces which translate and reflect waves directly towards the source. Corner cubes or cube corners (also known as optical corner reflectors) are made up of 3 sided glass prisms, and are commonly utilized in laser ranging and surveying. When used for surveying, these retroreflector prisms are most often implemented as targets for long-range electronic distance measurement using a total station. In optics, corner reflectors are often made up of 3 reflective prism faces, or mirrors, which oppositely reflect an incident light beam.

Applications that require difficult or tedious precision alignment can utilize retroflection prisms to reflect incident light back to the light source. Retroreflection prisms will always reflect incident light back to the source, no matter the orientation of the prism. Unlike an optical mirror that requires a normal angle, retroflection prisms can be oriented in any position as long as the incident light hits an entrance face. The retroflection prisms total internal reflections enable it to function effectively even at extreme angles of incidence.