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21 June 2019 Differential displacement measurements along a single beam using range-resolved interferometry
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Many applications of precision interferometry suffer from uncertainties in knowing the values of the air refractive index or the laser wavelength and often require the use of complex setups or costly components to mitigate these effects. In this work, using range-resolved interferometric measurements, we show how differential measurements along a single optical beam can be used to perform displacement measurements with drastically reduced systematic errors. In a proof-ofprinciple experiment, a semi-transparent target mounted on a moving stage is placed centrally between a window and a mirror, forming two air paths around the target that are arranged to be of nominally equal length. The evaluation of the interferometric phase signals at multiple locations along the measurement beam then allows the simultaneous measurement of changes in the length of the two air paths on either side of the target. The difference of the air path length changes yields the desired target displacement measurement, while influences that are common to both air paths such as air refractive index changes or laser wavelength drift are strongly suppressed.
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Thomas Kissinger and Ralph P. Tatam "Differential displacement measurements along a single beam using range-resolved interferometry", Proc. SPIE 11056, Optical Measurement Systems for Industrial Inspection XI, 110560E (21 June 2019);

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