Additive-Subtractive Two-Wavelength ESPI Contouring by Using a Synthetic Wavelength Phase Shift

Area of Science:

• Optical Metrology
• Interferometry
• Speckle Imaging

Background:

• Object contouring is crucial for dimensional measurement.
• Twyman-Green interferometry is a standard technique but sensitive to environmental vibrations.
• Speckle interferometry offers potential for non-contact measurements but often suffers from low fringe visibility.

Purpose of the Study:

• To develop a robust object contouring method using speckle interferometry.
• To enhance fringe visibility in speckle-based contour mapping.
• To provide a contouring technique suitable for unstable or noisy environments.

Main Methods:

• Utilizing the addition correlation of two speckle fields illuminated simultaneously at different wavelengths.
• Employing a Twyman-Green-type interferometer setup.
• Subtracting stochastic speckle background intensity for fringe visibility enhancement.
• Calculating the contour phase map using a phase-shift algorithm with synthetic wavelength.

Main Results:

• Achieved object contouring through simultaneous speckle field correlation.
• Demonstrated enhanced fringe visibility by subtracting modulated reference plane speckle intensity.
• Successfully calculated contour phase maps using a synthetic wavelength phase-shift algorithm.
• Compared the method with sequential illumination phase-difference techniques.

Conclusions:

• The proposed method provides effective object contouring with enhanced fringe visibility.
• The technique is robust against environmental instability, making it suitable for noisy applications.
• Simultaneous illumination and synthetic wavelength phase-shifting offer advantages over sequential methods.