Physics Dept. Demonstration Manual

DOP25 - CD Diffraction


To use a compact disc as a Diffraction Grating.

  • Compact Disc
  • He-Ne Laser
  • Lab Jacks, 2
  • Screen


Arrange the laser on a lab jack, so that it strikes the compact disc about halfway up the radius. Observe the various orders of diffraction on the screen. The pattern is similar to a diffraction grating.

The distance between rows of pits can be calculated using:

d =  L/x

where:  =

6.328 x 10-7 m, for He-Ne


L  =

distance from point of incidence to the first order spot


x  =


distance between the central bright spot and the first order spot. (the accepted value = 1.6 x 10-6 m)


This demo was set up by using the very disc that contains this concept! (Physics Infomall)