One-dimensional stitching interferometry assisted by a triple-beam interferometer.

Area of Science:

• Optical Engineering
• Metrology
• Surface Metrology

Background:

• Stitching interferometry is crucial for measuring large optical surfaces.
• Classical stitching methods like least-squares can be limited by accuracy and repeatability.
• Interferometer errors can propagate into the final stitched surface map.

Purpose of the Study:

• To propose a novel stitching interferometry method using a triple-beam interferometer.
• To improve the accuracy and repeatability of surface measurements compared to classical methods.
• To reduce the impact of interferometer errors on the final stitched topography.

Main Methods:

• Utilizing a triple-beam interferometer to measure distance and tilt for all sub-apertures.
• Calculating relative piston between adjacent sub-apertures using overlapping area data.
• Comparing the proposed method with the classical least-squares stitching principle.

Main Results:

• The proposed method enhances accuracy and repeatability, especially with numerous sub-aperture measurements.
• Simulations and experiments on flat and spherical mirrors confirm reduced influence of interferometer error.
• Achieved a root mean square comparison of approximately 2 nm with Fizeau interferometry data.
• Demonstrated repeatability within ± 2.5 nm peak to valley.

Conclusions:

• The triple-beam interferometer approach offers superior performance for stitching interferometry.
• This method effectively mitigates systematic errors inherent in classical stitching techniques.
• The findings are validated through simulations and experimental results on optical components.