6D20.15 Grating and Laser


Diffraction, interference


A laser pointer shining on a diffraction grating or CD creates a series of diffraction spots depending on the spacing of the lines or pits in the grating or CD and the wavelength emitted by the laser.



  • [1] Red laser pointer
  • [1] Green laser pointer
  • [1] Diffraction grating
  • [1] CD

Classroom Assembly

  1. Make sure you have a clear space to shine a laser without striking anyone in the eye, either with direct, diffracted, or reflected beams.

Important Notes

  • Lasers can cause blindness. Use with caution.


  1. Shine the green laser through the diffraction grating so that the diffracted beams are visible on a screen or wall.
  2. Remark on how the spacing of grating lines affects the diffracted dot spacing.
  3. Do the same with the red laser for comparison.
  4. While holding the CD, make a remark about the scourge of AOL CDs in the 90s.
  5. Reflect the green and red lasers off the CD's surface to get similar diffraction patterns for the CD.
  6. Remark on how the CD has a pattern of pits and grooves that also diffracts light like a grating.


Additional Resources


  • PIRA 6D20.15, 6D20.32


  • Don't attempt this at home!

Last revised

  • 2017


Related AV

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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.