Corner Cube Prisms
A corner cube prism, also called corner cube retroreflector or corner reflector, consists of 3 mutually perpendicular flat faces and has the unique property of reflecting back light input into the entrance face. The returned light is deviated by 180 degrees +/- 5 arcseconds, irrespective of the incidence angle. These very precise retroreflectors have even been placed on the moon for scientific applications and are used in optical systems to measure tilt and displacement. Corner cubes received their name because they are shaped like the corner of a box and have many features, such as constant path length inside no matter where the input is located. Corner cubes can be used to fold and offset a beam path instead of using multiple mirrors and the return image is rotated in-plane by 180 degrees.