Infinite deflectometry enabling 2π-steradian measurement range.

Area of Science:

• Optical Metrology
• Surface Characterization
• Freeform Optics

Background:

• Measuring freeform optical surfaces, especially highly convex ones, presents significant challenges for traditional metrology techniques.
• Existing methods often struggle with dynamic range limitations and full aperture coverage for complex optical designs.

Purpose of the Study:

• To introduce and validate a novel deflectometry technique, Infinite Deflectometry, for comprehensive surface reconstruction of freeform optics.
• To demonstrate the capability of Infinite Deflectometry in measuring challenging optical components, including highly convex surfaces and freeform Alvarez lenses.

Main Methods:

• Infinite Deflectometry utilizes a virtual source enclosure to achieve a 2π-steradian measurement range.
• The technique reconstructs a full aperture surface sag map of the tested optic.
• Performance is validated by measuring a fast f/1.26 convex surface and a freeform Alvarez lens.

Main Results:

• Infinite Deflectometry achieved an absolute RMS surface accuracy of 16.26 nm for a convex surface, outperforming a commercial interferometer (18.48 nm RMS).
• A freeform Alvarez lens was measured with 22.34 𝜇m surface sag RMS, showing good agreement with a profilometer (488 nm RMS deviation).
• Standard interferometry failed to measure the Alvarez lens due to its non-nulled wavefront dynamic range limitation.

Conclusions:

• Infinite Deflectometry provides a robust and accurate solution for metrology of challenging freeform and convex optical surfaces.
• The technique overcomes limitations of conventional interferometry, enabling precise characterization of complex optical systems.