Laser Waterfall

Overview: Total Internal Reflection or TIR allows us to send data via light through optical fibers, aka the internet. The laser waterfall gives us a clear medium (water) to observe TIR at work.

​​Supplies: Laser waterfall kit that includes 3 small tanks and 1 large one, water pump, 3 laser pointers, and waterfall stand. Water

Objectives: Look for the total internal reflection or TIR in the stream of water

Setup:

  • Place the smaller containers one on each level making sure the spouts face the container below it
  • Place the large container on the table
  • Fill the bottom large container about 3/4 full with water
  • Hook the end of the pump tubing over the edge of the top container
  • Turn on the pump and as it starts pumping water into the top container, fill the three containers about 3/4 full
  • Turn on the 3 laser pointers and attach them to their mounting points on each level
  • Align the laser pointers so they are aligned with the container spouts

How to run the demo:

  • Point out the TIR visible at the top of the stream of water
  • Point out the pool of green at the end of the stream of water
  • Discuss TIR and how it relates to fiber optic communication

What’s Happening?

As the water flows from one level to the next, the laser stays within the stream of water due to Total Internal Reflection (TIR).  This can occur when light reaches a boundary between materials with a higher index of refraction (water, in this case) and a lower index of refraction (air). If the light approaches this boundary at the critical angle, then the light will reflect and stay within the material.

This is a demonstration of how optical fibers work! Light reflects along the inside of the fiber, so the light stays completely contained within the fiber and can be guided and detected at the other end.

Try this:

  • Try placing your finger in the stream of water. Do you see the light on your hand?

Learn more: (external links)