Bouncing Laser Beam - Physics Demonstrations - Bouncing Laser Beam | Physics Undergraduate Labs

Class 3R or higher lasers require appropriate safety protocols. Ensure the beam is contained within the tank and terminates on the black backing. Never allow reflections to exit the apparatus into the classroom. Students and instructor should avoid direct viewing of the beam source. For large classrooms, use camera projection rather than allowing students to approach the apparatus closely.

Purpose

A sugar density gradient in water creates a continuous variation in refractive index. A laser beam curves toward higher-density regions and undergoes total internal reflection, producing a visible bouncing path. Demonstrates gradient-index optics, Snell's law in continuous media, and wavelength-dependent refraction.

Green laser beam entering a rectangular water tank from the left, curving downward then bouncing back up through the sugar-gradient water, against a black background

Figure 1: A green laser beam curves and bounces through a water tank containing a sugar density gradient. The beam bends toward the higher-index water near the bottom, then undergoes total internal reflection back upward.

4 L Erlenmeyer Flask

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Safety Warnings

Warning: Laser Safety Requirements

Purpose