Useful Concepts

• To create a laser, you need an active medium of atoms or molecules with an inverted population of excited states enclosed in an optical resonator. The laser light is generated by the stimulated emission of photons by the excited medium. Laser light is characterized by its monochromaticity and its coherence.

• The fringe visibility is

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• The coherence is

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• Holograms are made by recording the interference pattern of a reference beam and an object beam. The holographic images are reproduced by illuminating the hologram with a beam of light similar to the original reference beam.

• A full range of colors can be reproduced by the addition of primary colors of light (red, green, and blue). Colors can also be produced by passing white light through a combination of subtractive filters (the subtractive primaries of yellow, magenta, and cyan).