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Published on: July 5, 2016
Large step-height measurements using multiple-wavelength holographic interferometry with tunable laser diodes.
Atsushi Wada1, Makoto Kato, Yukihiro Ishii
1Department of Applied Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan. a24wada@nda.ac.jp
Summary
This study demonstrates accurate measurement of large step heights up to 18 mm using multiple-wavelength holographic interferometry with laser diodes. The method achieves high precision, with an RMS error of 0.04 mm, by utilizing tunable lasers for phase unwrapping.
Area of Science:
- Optics and Photonics
- Metrology
- Laser Technology
Background:
- Accurate measurement of large step heights is crucial in various industrial and scientific applications.
- Traditional interferometry methods face limitations in measuring large displacements due to phase ambiguity.
- Multiple-wavelength interferometry offers a potential solution to extend measurement range.
Purpose of the Study:
- To develop and validate a multiple-wavelength holographic interferometry technique for precise measurement of large step heights.
- To leverage the tunability of laser diodes to enhance measurement accuracy and range.
- To investigate the requirements for successful phase unwrapping in this system.
Main Methods:
- Utilized laser diodes with high-resolution wavelength tunability.
- Recorded pairs of holograms with a minimal wavelength difference (<0.01 nm).
- Extracted phase differences using a large synthetic wavelength, ranging from 2.5 to 73 mm.
Main Results:
- Achieved accurate measurement of an 18 mm step height with a root-mean-square (RMS) error of 0.04 mm.
- Demonstrated the extraction of phase differences across a wide range of synthetic wavelengths.
- Identified precise knowledge of recording wavelengths as critical for phase unwrapping.
Conclusions:
- Multiple-wavelength holographic interferometry with tunable laser diodes is a viable method for accurate large step height measurement.
- The technique overcomes limitations of conventional interferometry by employing large synthetic wavelengths.
- Successful phase unwrapping is contingent upon accurate wavelength determination.
