6C10.15 Adjustable Slit and Laser


Interference, diffraction


A He-Ne laser shines on an adjustable single slit to make a diffraction pattern. The slit can be adjusted in two dimensions.



  • [1] Single slit
  • [1] He-Ne tube laser
  • [1] Optical rail
  • [2] Saddle
  • [1] Lab jack
  • [1] Extension cord (if necessary) 

Classroom Assembly

  1. Mount the laser and slit 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 slit, maximizing the intensity of the diffraction pattern.
  3. Use the lab jack to elevate the fringe pattern to a screen, if necessary.
  4. Turn off the laser.

Important Notes

  • Lasers can cause blindness. Use with caution.


  1. Turn off the lights.
  2. Turn on the laser. Point out spacing of the diffraction minima.
  3. Adjust the size of the slit. Remark on how this changes the diffraction pattern.
  4. Turn off the laser.
  5. Turn on the lights.


Additional Resources


  • PIRA 6C10.15


  • Don't attempt this at home!

Last revised

  • 2020


Related AV

Related demos

  • Diffraction plate


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.