Fabry - Perot Etalon

Holmarc's Fabry-Perot etalon is made of plate beamsplitters separated by 3mm distance. The beamsplitters are made by coating thin aluminum films on optically polished N-BK7 substrates. The reflecting surfaces are kept inside the assembly. The etalon has optical resonating properties similar to that of laser. A translucent screen is provided with vernier and needle to take the readings of the fringes directly.

Etalons transmit light as a series of periodic frequencies and their narrow bandwidth makes them well-suited for wavelength selection, measurement and line-narrowing. The properties of an etalon are largely determined by its thickness, index of refraction and the reflectivity of it’s surfaces. The finesse is a measure of the interferometer's ability to resolve closely spaced spectral lines.

An etalon is an optical interferometer in which a beam of light undergoes multiple reflections between two reflecting surfaces and it’s resulting optical transmission (or reflection) is periodic in wavelength. In other words, an etalon is a narrow band wavelength filter.

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