Purpose:Demonstrate interference of a laser beam by a type of grating.
Description:This demonstration uses a compact disc recording to produce an interference pattern with a laser beam. Hold the CD at an angle with respect to the incoming laser beam and look for the diffraction pattern on the wall or the ceiling. Note that the angle must be reasonably large because the spacing of the spiral "groove" on the disc is 1.6 microns, only about twice the wavelength of the laser light. You will see both the interference pattern and specular reflection off the shiny surface of the dics.