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Iterative least square phase-measuring method that tolerates extended finite bandwidth illumination
Florin Munteanu1, Joanna Schmit
1Veeco Instruments Inc., Tucson, Arizona, USA.
Applied Optics
|April 10, 2013
Summary
This study enhances iterative least squares phase-measuring techniques for phase-shifting interferometry. The modified algorithm achieves vibration-insensitive measurements even with varying fringe contrast, improving accuracy in laser interferometers.
Area of Science:
- Optical metrology
- Interferometry
Background:
- Phase-shifting interferometry (PSI) is sensitive to vibrations and scanner nonlinearity.
- Traditional PSI methods assume constant fringe contrast.
- Existing iterative least squares methods require precise phase step knowledge.
Purpose of the Study:
- To modify iterative least squares methods for vibration-insensitive PSI.
- To enable accurate measurements with spatially and temporally varying fringe contrast.
- To address limitations of PSI in systems with limited bandwidth light sources and non-zero numerical apertures.
Main Methods:
- Step-by-step modifications to the basic iterative least squares algorithm.
- Simultaneous determination of wavefront phase and phase steps from phase-shifted fringe frames.
- Algorithm validation using experimental data.
Main Results:
- The modified algorithm provides vibration-insensitive measurements.
- Successful compensation for fringe contrast variations across frames and fields.
- Theoretical analysis of the algorithm's tolerance to contrast variations.
Conclusions:
- The enhanced iterative least squares method overcomes limitations of traditional PSI.
- This technique improves the robustness and accuracy of optical metrology systems.
- The algorithm is effective even with challenging fringe contrast conditions.
