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A proposed design for an optical interferometer with sub-nanometric resolution

The limitations to the accuracy achievable by optical interferometers when they are used to measure sub-nanometric path differences are discussed, and techniques for realising the optimum performances from these instruments are described. An optical design for a two-beam interferometer is proposed that would maintain the accuracy of the instrument when resolving with subnanometric sensitivity and, in addition, facilitate the alignment of the optical and mechanical axes of the measurement system.