Absolute surface metrology by rotational averaging in oblique incidence interferometry

Area of Science:

• Optical metrology
• Surface characterization
• Interferometry

Background:

• Accurate measurement of large optical surfaces is critical for high-precision applications like synchrotron radiation facilities.
• Existing methods may face limitations in accuracy or complexity for large-scale optics.

Purpose of the Study:

• To present a modified, simple method for measuring the absolute figure of large optical flat surfaces.
• To enable high-accuracy surface error determination using a small aperture interferometer.

Main Methods:

• The method involves two main procedures: oblique incidence measurement and multiple rotating measurements.
• Analysis utilizes functions symmetric and antisymmetric with respect to vertical axis reflections.
• N-position rotational averaging is employed to remove mirror antisymmetric errors.

Main Results:

• The developed method allows for the determination of absolute deviations of large flat surfaces.
• Formulas for rectangular flats were derived and experimentally verified on high-accuracy samples.
• Detailed uncertainty analysis was performed to quantify measurement precision.

Conclusions:

• The modified interferometry method provides a straightforward and accurate approach for absolute surface figure measurement.
• The technique is effective for large optical flats, particularly in synchrotron radiation applications.
• Experimental validation confirms the reliability and precision of the proposed measurement strategy.