Absolute surface metrology using gradient descent-optimized multi-surface phase-shifting interferometry for...

Area of Science:

• Optical Engineering
• Metrology
• Surface Science

Background:

• Conventional surface measurement relies on relative methods, offering speed but suffering from inherent interferometer errors.
• Absolute measurement is crucial for calibrating system errors, but existing methods like rotation-based or rotation-translation have limitations.
• Traditional rotation methods struggle to separate rotationally symmetric surface components and can introduce rotational errors.

Purpose of the Study:

• To develop a novel, accurate, and convenient absolute surface measurement method for calibrating interferometers.
• To overcome the limitations of traditional rotation-based and rotation-translation methods.
• To improve the accuracy of surface detection by eliminating system errors.

Main Methods:

• Combines multi-surface phase-shifting interferometry with a gradient descent algorithm.
• Incorporates redistribution of rotationally symmetric terms to address limitations of traditional methods.
• Utilizes two rotational measurements of an auxiliary test lens without requiring constant rotation angles.

Main Results:

• The proposed method automatically identifies rotation angles and eliminates rotationally symmetric errors.
• Achieves a surface root mean square (RMS) error on the order of 10^-4λ.
• Successfully detected and corrected system errors in a self-built 4-inch aperture interferometer.

Conclusions:

• The novel rotation-based method provides accurate and convenient absolute surface measurement.
• Validates the accuracy of the proposed scheme through comparison with a commercial interferometer.
• Offers a significant advancement in calibrating interferometric systems for precise surface metrology.