Retrodirective reflector: Silvered right angle prism, using laser.

Retrodirective reflector: Silvered right angle prism, using laser. A laser beam is aimed at a 'retrodirective reflector' and the beam reflects back and hits a 6x6" white paper card mounted on the laser. Even when the laser is moved from one end of the lecture table to the other, when the laser is pointed at the reflector, the beam bounces back and hits the white card. The retrodirective reflector is a glass prism that has three reflecting surfaces that are like the corner of a cube. (The 3 silvered faces are mutually perpendicular.) A beam of light that enters the prism reflects off two and sometimes three of the surfaces in such a way that the exiting beam is parallel to the entering beam. Thus, a beam of light returns in the direction of the source.