6C10.10 Diffraction Plate


2-slit interference, 1-slit diffraction, multiple-slit interference, cross-slit diffraction


A He-Ne laser shines on a variety of aperture patterns to create interference fringes. Most of the aperture patterns are single- and double-slits. These are also the most-used.



  • [1] Diffraction plate
  • [1] Diffraction plate documentation
  • [1] He-Ne tube laser
  • [1] Optical rail
  • [1] Slide mount
  • [2] Saddle
  • [1] Lab jack
  • [1] Extension cord (if necessary)

Classroom Assembly

  1. Mount the laser and diffraction plate on opposite ends of the rail, making sure the laser is pointed away from people.
  2. Plug in the laser and aim it at the desired pattern, maximizing the intensity of the pattern.
  3. Use the lab jack to elevate the interference fringes to a screen, if necessary.
  4. Turn off the laser.

Important Notes

  • Lasers can cause blindness. Use with caution.
  • Manufacturer tolerance on the feature sizes of the plate is +/- 5 microns, but the smaller slits have likely deteriorated to be even smaller.


  1. Show students the diffraction plate documentation, if desired.
  2. Turn off the lights.
  3. Turn on the laser. Point out spacings of the interference fringes (maxima, minima, as appropriate).
  4. Change to a different aperture pattern. Observe the differences between the fringe formations.
  5. Turn off the laser.
  6. Turn on the lights.


Additional Resources



  • Don't attempt this at home!

Last revised

  • 2020


  • Original construction: purchased. The plate comes from Pasco.

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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.