Real-time measurement of optical thickness by three-channel homodyne interferometry

Year: 1994

Authors: Greco V., Iemmi C., Ledesma S., Molesini G., Quercioli F.

Autors Affiliation: Istituto Nazionale di Ottica, Largo E. Fermi 6, 50125 Firenze, Italy

Abstract: A homodyne interferometer is described, using a He-Ne laser source and working in Twyman- Green configuration. By means of proper retardation plates and polarizing beam splitters, three signals at 90° phase lag are made available. Such signals are digitized and fed into a desktop computer. Fitting procedures and computing algorithms are then implemented working out a phase angle; monitoring such a phase provides information on the optical path difference between the two arms of the interferometer. The general features of the approach are reviewed; examples of application are given, monitoring the fine displacement of mechanical parts and measuring the optical thickness variation of a soap film in air.

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KeyWords: Algorithms; Computer aided analysis; Lasers; Optical variables measurement; Real time systems, Homodyne interferometer; Twyman-Green configuration; Interferometry; Soap films; Multichannel interferometr