Right Angle Prisms

Right-angle prism is the most common type of prism. It is used to re-direct a beam of light at 90 degrees from the incident direction or used as a 180 beam retro-reflector. They are often coated with various optical coatings to form cubic beam splitters and color separation cubes used in various projection systems.

•    The right-angle prism possesses the simple geometry of a 45-degree right triangle and is one of the most commonly used prisms for redirecting light and rotating images. This interactive tutorial explores light reflection and image rotation, inversion, and reversion by a right-angle prism as a function of the prism orientation with respect to incident light.
•    In a right-angle prism, a parallel bundle of light waves entering one of the smaller prism faces (or legs) at a perpendicular angle is reflected from the hypotenuse (longest) face and exits through the other leg. Provided the prism is constructed from a material having a refractive index greater than the square root of 2 (approximately 1.414), the light will undergo total internal reflection at the glass/air boundary while inside the prism.
•    This feature renders prisms an excellent substitute for mirrors because there is no requirement for metallic or dielectric coatings on the reflecting surface, which serves as a nearly perfect reflector. The only light scattering and loss that occurs (usually only a few percents) are due to minute surface imperfections, absorption by the prism material, and reflections at the entrance and exit legs of the prism. Optical grade polishing of the surfaces and the application of a suitable anti-reflection coating to the legs will minimize even these small light losses. In this orientation, the right-angle prism acts as an image inverting system with the top face performing the duties of a plane mirror by producing left-handed images from right-handed images.