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CDs (compact disks) hold all kinds of audio, image, text and numerical information in a binary format. This information is encoded along a spiral track which is itself about a micron in width. This regular line spacing acts like and as a diffraction grating which can be used to resolve light into its component wavelengths.


In the picture to the left, a laser is directed onto a CD. It strikes the CD on the side nearest the laser at the bottom (red spot). The beam reflects from the CD to make a spot on the blue screen just above the CD. The light also diffracts to produce the second red spot above the CD. The position of the spot depends of the color of the light. This is why CDs have this shimmering color in the light of day. There are about five orders of diffracted spots coming off the CD.

CD Spectrometer