Retroreflector - Physics Demonstrations - Retroreflector | Physics Undergraduate Labs

Use only Class 2 or 3R lasers (< 5 mW) for classroom demonstrations. Never aim the laser at students or allow direct eye exposure. The retroreflector will return the beam directly toward the source - ensure the returned beam is captured by the aperture screen or a beam dump. Class 3B and Class 4 lasers require additional safety protocols and are not recommended for this demonstration.

Purpose

Demonstrates that three mutually perpendicular mirrors reflect light directly back toward its source regardless of incident angle. Students see image inversion (180° rotation) and the apparent corner-tracking effect unique to retroreflectors.

Corner cube retroreflector with reddish-brown wooden frame holding three perpendicular mirrors, showing reflected workshop environment with a clock visible, on a green surface

Corner cube retroreflector from a different angle showing three perpendicular mirror surfaces in wooden frame, with inverted reflections of the workshop including tripod and shelving

Figure 1: The corner cube retroreflector consists of three plane mirrors mounted at 90° to each other, creating a triangular aperture. Note the central corner where all three mirrors meet.

Figure 2: Alternate view showing the three-mirror geometry and reflected images. The corner appears to track the observer's position due to the retroreflective property.

Safety Warnings

Warning: Laser Safety

Purpose