We describe the construction and calibration of a low cost confocal scanning Fabry-Perot interferometer with a free spectral range of 382.3±1.1MHz, which is suitable for use as a frequency reference in laser locking and for spectroscopy experiments. The calibration of the free spectral range is performed using the longitudinal modes of a commercial helium–neon laser.

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Test Laser 1 is a Spectra-Physics model 155, and Test Laser 2 is a Melles Griot 05-LNP-925.

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