Multipoint gap measurement by low coherence tandem interferometry

Sheng-Hua Lu; Chi-Ying Chang; Ching-Fen Kao

doi:10.1117/12.858851

2 August 2010 Multipoint gap measurement by low coherence tandem interferometry

Sheng-Hua Lu, Chi-Ying Chang, Ching-Fen Kao

Proceedings Volume 7791, Interferometry XV: Applications; 77910L (2010) https://doi.org/10.1117/12.858851
Event: SPIE Optical Engineering + Applications, 2010, San Diego, California, United States

Abstract

Gap uniformity between two plates is an important parameter in many optical devices or instruments. The proposed method combines low coherence tandem interferometry and the concept of distributed fiber sensors for in-situ multipoint gap measurement. No gratins or special marks are required on the surfaces of the plates. A superluminescent diode (SLD) is used as the light source because of its low temporal coherence, high spatial coherence, and high optical power. Therefore, the proposed technique can also be easily implemented in free space. A collimated light beam from the SLD first passes through a scanning Michelson interferometer. The output of the interferometer is split into several separate beams, and then each beam is normally incident to the test sample at different positions. Gap distribution measurement is performed by sequentially opening the shutter behind each incident beam. A detector is employed to receive the reflected lights from the sample. The interferometric signal is recorded as a function of the arm-length difference of the scanning interferometer. The gap is eventually derived from the separation of the two side fringe packets, whose peak positions are determined by the centroid algorithm. Preliminary experimental results validate the feasibility of the presented method.

Citation Download Citation

Sheng-Hua Lu, Chi-Ying Chang, and Ching-Fen Kao "Multipoint gap measurement by low coherence tandem interferometry", Proc. SPIE 7791, Interferometry XV: Applications, 77910L (2 August 2010); https://doi.org/10.1117/12.858851

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KEYWORDS

Interferometers

Interferometry

Camera shutters

Sensors

Beam splitters

Light sources

Michelson interferometers

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