Improved straightness interferometer for nanometrology

Chien-Ming Wu

doi:10.1117/12.570183

10 February 2005 Improved straightness interferometer for nanometrology

Chien-Ming Wu

Proceedings Volume 5638, Optical Design and Testing II; (2005) https://doi.org/10.1117/12.570183
Event: Photonics Asia, 2004, Beijing, China

Abstract

The interferometers which measure the displacement parallel to the measurement axis are called linear interferometers, while those measure the displacement orthogonal to the measurement axis are called straightness interferometers. Theoretically, the orthogonal characteristic between the displacement and the measurement axis does not introduce optical path difference (OPD) and thus, makes null signal. These lead to the straightness interferometer difficult to be implemented. A generalized laser interferometer system based on three design principles, the heterodyne frequency, the avoiding mixing, and the perfect symmetry, is described. These design principles give rise to the interferometer a highly stable system with no periodic nonlinearity. A novel straightness sensor, consisting of a straightness prism and a straightness reflector, is incorporated into the generalized system to form a straightness interferometer. With the help of a Hewlett-Packard commercial linear interferometer, the validity of the developed straightness interferometer has verified. Based on the present design, the interferometer has a gain of 0.348, a periodic nonlinearity of less than 40 picometers, and a displacement noise of 4 pm/√Hz at bandwidth 7.8 kHz. This system is useful in precision straightness measurement.

Citation Download Citation

Chien-Ming Wu "Improved straightness interferometer for nanometrology", Proc. SPIE 5638, Optical Design and Testing II, (10 February 2005); https://doi.org/10.1117/12.570183

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