Non-planar illumination deflectometry for axicon metrology

Area of Science:

• Optical metrology
• Precision engineering
• Surface characterization

Background:

• Axicons possess steep, convex geometries, posing significant challenges for traditional metrology techniques.
• Accurate measurement of axicon parameters is crucial for applications in beam shaping and optical systems.

Purpose of the Study:

• To introduce and validate an on-axis deflectometry test configuration for precise axicon metrology.
• To demonstrate a method for high-resolution surface measurement of axicons, overcoming geometric challenges.

Main Methods:

• An on-axis deflectometry setup was designed, aligning the axicon coaxially with a camera and a cylindrical illumination source.
• Light from a temporally modulated source was directed to deflect off the axicon's conical surface into the camera's entrance pupil.
• The method captured the full axicon aperture, excluding a small central tip, enabling detailed surface analysis.

Main Results:

• Measurements of 100° and 140° axicons demonstrated holistic cone angle agreement within 0.035° compared to touch probe data.
• The mean square difference from a best-fit cone was up to 7.93 root μm, indicating high surface accuracy.
• The technique successfully measured axicons with arbitrary apex angles.

Conclusions:

• The proposed on-axis deflectometry configuration offers a viable and accurate method for axicon metrology.
• This approach provides high-resolution surface data, addressing limitations of existing measurement techniques for challenging axicon geometries.
• The study validates the effectiveness of deflectometry for characterizing conical optical elements.