Measurement of Absolute Wavelength Stability of Lasers

Abstract
A technique was devised to measure the absolute wavelength stability of a gas laser by direct interferometric comparison with a mercury 198 standard lamp. The apparatus used is described; its limits of precision are discussed.The wavelength fluctuations of a free-running, unstabilized helium-neon laser were measured and found to be several parts in 107. They are attributed to thermal and mechanical instabilities of the laser cavity.Manual control of the laser was seen to yield a wavelength constancy of a few parts in 108, comparable to the limits of accuracy of interferometric standard sources.

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