Design of phase shifting algorithms: fringe contrast maximum

Area of Science:

• Optical Metrology
• Interferometry
• Surface Measurement

Background:

• Fringe contrast is critical in phase shifting interferometry, especially for low-reflectivity surfaces.
• Low signal contrast can lead to measurement abortion if it falls below a set threshold.
• Phase shifting algorithm design directly impacts fringe contrast and measurement accuracy.

Purpose of the Study:

• To derive conditions for maximizing fringe contrast in phase shifting interferometry.
• To develop error-compensating algorithms insensitive to harmonic components and phase shift errors.
• To provide practical algorithms for measuring highly-reflective surfaces.

Main Methods:

• Derivation of fringe contrast maximization conditions using linear equations of sampling amplitudes.
• Analysis of the minimum number of samples for error-compensating algorithms.
• Development of novel phase shifting algorithms, including 15-sample and (3N-2)-sample methods.

Main Results:

• Established the relationship between sampling amplitudes and maximum fringe contrast.
• Identified the minimum sample requirements for robust error compensation.
• Successfully derived two new algorithms tailored for challenging reflective surface measurements.

Conclusions:

• Optimized phase shifting algorithms enhance fringe contrast and measurement reliability.
• The developed algorithms effectively mitigate issues associated with low signal contrast and phase shift errors.
• These advancements are particularly beneficial for the metrology of highly-reflective surfaces.