Fabry-Perot Cavities

What is a Fabry-Perot cavity?

Fabry-Perot cavities are small devices about a millionth of an inch wide. They are built out of small, half-silvered mirrors. Light entering them gets trapped inside.

Once inside a Fabry-Perot cavity, certain wavelengths of light are positively reinforced, while most wavelengths destructively interfere with each other. (See the page on interference.)

In the illustration below, red light is passed, while other wavelengths are blocked.

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Why are Fabry-Perot cavities useful?

Fabry-Perot cavities can be used to isolate a single wavelength of light. Because they isolate only one wavelength of light, Fabry-Perot cavities are instrumental in making laser light, wavelength filters, or calibration instruments.

Fabry-Perot cavities can be built to pass almost any wavelength of light. Some Fabry-Perot cavities can be controlled by an electronic circuit to block / pass a variable wavelength.

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