We propose a two-wavelength interferometer that is used to a stroboscopic step height measurement. Different from most two-wavelength interferometers, in present experiment, two slightly different wavelengths are simultaneously oscillated by currently and thermally controlling a laser diode to work at mode hop region. By use of this two-wavelength laser source, a Twyman-Green interferometer, whose reference arm and object arm have known step height r and unknown step height h, respectively, is constructed. Three independent interference patterns corresponding to different OPDs are formed and they can be simultaneously taken by a CCD camera. Furthermore, tilting the reference, spatial frequencies are introduced into the interference patterns. Taking the Fourier transform of these patterns, three fringe amplitudes are obtained and their expressions can be solved for the unknown step height. As we can capture clear image of the interference patterns in a very short time by use of the high speed shutter function of the CCD camera, the error induced by the external disturbance is farthest reduced.

Date Published: 26 February 2004
PDF: 7 pages
Proc. SPIE 5265, Two- and Three-Dimensional Vision Systems for Inspection, Control, and Metrology, (26 February 2004); doi: 10.1117/12.518642

Published in SPIE Proceedings Vol. 5265:
Two- and Three-Dimensional Vision Systems for Inspection, Control, and Metrology
Bruce G. Batchelor; Heinz Hugli, Editor(s)