6A44.45 Water Stream Light Pipe


Total internal reflection, rays


A laser beam undergoes total internal reflection inside a stream of water coming out of a punctured pop bottle.



  • [1] He-Ne tube laser
  • [1] Lab stand
  • [1] 90-degree clamp
  • [1] Plastic tub
  • [1] Lab jack
  • [1] Pop bottle
  • [1] Water
  • [1] Milk or cream
  • [1] Camera

Classroom Assembly

  1. Put a tiny amount of milk or cream in the water and fill the pop bottle with the water.
  2. Put the capped pop bottle on a lab jack in the tub.
  3. Mount the laser and align the beam with the hole on the side of the bottle. The laser should be shining off to the side, away from students.
  4. Turn off the laser.
  5. Set up the camera.

Important Notes

  • Lasers can cause blindness. Use with caution.


  1. Turn off the lights.
  2. Switch the projector to the camera view.
  3. Turn on the laser.
  4. Uncap the bottle.
  5. Adjust alignment of the laser, if required.
  6. Cap the bottle.
  7. Turn off the laser.
  8. Switch the projector to slide or document view.
  9. Turn on the lights.


Additional Resources


  • PIRA 6A44.45


  • Don't attempt this at home!

Last revised

  • 2024


  • The laser used should have a clean, fine beam.
  • The milk or cream is to introduce particles to scatter the laser light.
  • The usual demo document camera doesn't perform very well in low-light conditions. Cell phone cameras may work adequately. Stream cell phone video through Zoom.

Related AV

Related demos

  • Fibre optics


If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.