1 February 1979 Phase-Locked Interferometry
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A technique is described which converts in real time the fringe pattern resulting from two interfering beams into a wavefront map. The interferometer incorporates, as part of a servo system, a piezoelectrically driven mirror that is capable of applying both a known optical phase offset and a periodic optical phase modulation to one beam. The ac signal detected by a single photodiode is processed to generate an error signal for the servo system and a signal proportional to the optical phase difference between the two beams. Three instruments built on this principle will be discussed. The instruments are capable of detecting phase differences with a precision approaching A/100 and may be used for measuring surface topography (roughness, irregularity) or transparent phase objects such as biological samples, microballoons and gradient index materials.
Glen W. Johnson, Dennis C. Leiner, Duncan T. Moore, "Phase-Locked Interferometry," Optical Engineering 18(1), 180146 (1 February 1979). https://doi.org/10.1117/12.7972318 . Submission:

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