6D20.XX Diffraction Through Money

Concepts

Diffraction, interference

Overview

Modern Canadian plastic money has a diffractive element in it as a security feature. When a laser beam shines through the maple leaf on the bill, it produces a diffracted image telling you what the value of the bill is. Another way to see this is by looking at a point source of light through the maple leaf; this works with the naked eye.

Details

Equipment

  • [1] Canadian plastic bill
  • [1] Red laser pointer
  • [1] Green laser pointer
  • [1] Desk lamp

Classroom Assembly

  1. Plug in the desk lamp.

Important Notes

  • Lasers can cause blindness. Use with caution.
  • This demo is untested in a large class.

Script

  1. Turn off the lights.
  2. Shine a laser pointer through the maple leaf grating onto a prominent wall.
  3. Turn on the desk lamp and point it at the class for students to try on their own money.
  4. Turn off the lamp and turn on the lights.

 

Additional Resources

References

  • PIRA 6D20.XX
  • CCL Industries makes the substrate on which Canada's plastic bills are printed. They have an advertising-ish promotional journal called Specimen with some details about the money:
    Specimen, Issue 1 (December 2012)
    They call their diffraction grating technology "Eclipse." 

Disclaimer

  • Don't attempt this at home!

Last revised

  • 2020

Technicals

  • Red lasers seem to give a more legible pattern. The pattern may be bigger, and red light is likely less sensitive to imperfections in the grating.
  • The grating is probably a phase grating.

Related AV

Related demos

 

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.