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Interference - Examples

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• Constructive - Destructive
• Young's 2-slit Experiment
• Diffraction Gratings
• Thin films and coatings

Interference

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The air wedge:

Two flat glass plates are brought together with a thin spacer at one edge so that an air-wedge is formed. The light reflected from the top and bottom of the wedge interferes.

Bright and dark fringes result. Note that the light reflected from the bottom of the wedge is reversed, so a dark fringe occurs at zero path difference.

The light reflected from the inside and outside of the water film interferes.

Different wavelengths have different fringe patterns, so you see colors in the bubble.
Eventually the top becomes thinner than a wavelength of visible light.

The inside and outside reflections are then exactly out of step and cancel for all wavelengths --- the top of the bubble becomes invisible.

A a thin film of transparent material is put on glass. The speed of light in this material is between that in air and in glass.

The thickness of the coating is 1/4 the wavelength of green light.

For green light at perpendicular incidence, the reflections cancel exactly.

For other wavelengths and other angles, the reflections are much reduced.

Examples --- What this is an example of

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