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Modulated laser interferometer with picometer resolution for piezoelectric characterization

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Abstract

A modified double-beam interferometric measurement system is established and tested for displacement measurement of ferroelectric lead zirconate titanate bulk samples. To overcome the optical path-length drift or laser intensity instability, a modulation technique is introduced, and desired resolution (down to several picometers) and reliability are achieved without the complicated close loop servo system. This modified interferometer provides us a powerful yet easily accessible tool for piezoelectric thin/thick film characterization.

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... Optical Interferometry is mainly used in fine precision equipment, especially in cases which require both large range and fine resolution displacement measurement [37][38][39][40][41][42]. The basic form for this method of sensing relies on splitting coherent light into two beams, arranging the beam paths such that one path length is dependent on the displacement of interest and recombining the beams to generate an interference pattern [37,[42][43][44]. This pattern will vary with the displacement measurement, and can be measured to infer the change in the path length. ...
... Optical Heterodyne Interferometers are extremely sensitive to environmental conditions such as temperature and pressure, both of which change the optical properties of the medium through which the beam travels [37,42,44]. The range of measurement of an optical heterodyne interferometer is effectively decoupled from its resolution because the relative phase measurement cyclically shifts only through 0 to 2π as the displacement value changes. ...
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... While there are numerous examples of precision laser interferometry in the literature [4,5,6,7,8], these instruments are somewhat complex in their design and are therefore not optimally suited for a teaching environment. Below we describe a laser interferometer designed to demonstrate precision physical measurement techniques in a compact apparatus with a relatively simple optical layout. ...
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