6C20.30 Pinhole Diffraction


Diffraction, interference


A laser beam is shone onto a small circular aperture and concentric circles about a central bright spot known as Airy’s disk appear.



  • [1] Slide with a small circular aperture (2 mm, A, or B)
  • [1] Laser with beam expander
  • [1] Optical rail
  • [1] Slide mount
  • [1] Saddle
  • [2] Lab jack
  • [1] Extension cord (if necessary) 

Classroom Assembly

  1. Place the laser on top of the lab jacks, making sure the laser is pointed away from people.
  2. Place the slide mount on the optical rail and insert the sample slide to the slide mount.
  3. Plug in the laser and aim it at the aperture, make necessary adjustments such that the intended diffraction pattern is visible. The aperture should be very close to the laser to maximize the incident intensity.
  4. Use the lab jacks to elevate the fringe pattern to a screen, if necessary.
  5. Turn off the laser.

Important Notes

  • Lasers can cause blindness. Use with caution.


  1. Turn on the laser.
  2. Turn off the room light to see the diffraction pattern more easily.
  3. Point out the Airy's disk diffraction pattern.
  4. Use a blank sheet of white paper as a screen at various distances from the laser to view transitions of the middle spot from bright to dark to bright etc.
  5. Turn off the laser.


Additional Resources


  • PIRA 6C20.30


  • Don't attempt this at home!

Last revised

  • 2017


Related AV

Related demos

  • Poisson's Bright Spot
  • Thin Wire Diffraction


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.