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Ultra-Precise Measurement of Distance by Fabry-Perot Resonator

Length measurements in the region of nanometers by help of laser interferometers are influenced by the nonlinearity of their scale, which is usually ten or more nanometers. We developed and experimentally verified a new method, which has the resolution and linearity of the scale in the order of hundredth part of a nanometer. This method uses an optical Fabry-Perot resonator as a measuring element and by its help it is possible to measure small lengths and to test the nonlinearity of any interferometer with an uncertainty smaller than 0.1 nm The method takes advantage of a direct conversion of the relative changes of the optical path in measuring the arm of the Michelson interferometer to relative changes of the resonant optical frequency of the Fabry-Perot resonator. Frequency changes of the resonator resonance frequency have been monitored by a beat-frequency comparison between tunable He-Ne or semiconductor ECL (Extended Cavity Laser) laser and He-Ne-I2 optical frequency standard at 633 nm.