Speckle-based curvature optical metrology

Area of Science:

• Optical Metrology
• Surface Characterization
• Advanced Optics

Background:

• Interferometric techniques are standard for optical surface height map measurement.
• These methods face limitations with strongly curved or freeform surfaces due to high fringe density.
• Advanced metrology is crucial for meeting stringent quality standards in high-performance optics.

Purpose of the Study:

• To develop an alternative metrology technique for characterizing complex optical surfaces.
• To address the limitations of interferometric methods for steep slope surfaces.
• To enable precise measurement of 2D surface curvature maps.

Main Methods:

• Development of a laser Speckle-based Curvature Optical Metrology (SCOM) instrument.
• Utilizing digital image correlation to extract curvature information from speckle patterns.
• Employing speckle patterns as effective wavefront markers for curvature measurement.

Main Results:

• Demonstrated effectiveness in measuring strongly curved mirrors (radius of curvature from 10m down to 100mm).
• Successfully applied the technique to online deterministic figuring of optical surfaces.
• Utilized for in-situ stress measurements during multilayer deposition and characterization of deformable mirrors.

Conclusions:

• The SCOM technique provides a promising alternative for high-precision metrology of complex optical surfaces.
• It is suitable for X-ray mirrors in synchrotron radiation facilities, free-electron lasers, and observatories.
• Shows potential for characterizing freeform optical components in advanced industrial applications.