6D20.XX Diffraction Through Money
Concepts
Diffraction, interference
Overview
Modern Canadian plastic money (specifically the Frontiers series) 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
- Plug in the desk lamp.
Important Notes
- Lasers can cause blindness. Use with caution.
- This demo is untested in a large class.
Script
- Turn off the lights.
- Shine a laser pointer through the maple leaf grating onto a prominent wall.
- Turn on the desk lamp and point it at the class for students to try on their own money.
- 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 call their diffraction grating technology "Eclipse."
- From personal communications with a Bank of Canada R&D scientist:
The grating is a volume holographic phase grating.
Disclaimer
- Don't attempt this at home!
Last revised
- 2023
Technicals
- Red lasers tend to give a more legible pattern. The pattern may be bigger, and red light is likely less sensitive to imperfections in the grating.
- Some of the special edition banknotes in circulation don't have the maple leaf diffraction 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.