Breaking the mid-spatial-frequency noise floor to sub-nanometer in Fizeau interferometry via anisotropic...

Area of Science:

• Optical Engineering
• Metrology
• Interferometry

Background:

• Mid-spatial-frequency (MSF) noise is a significant challenge in high-precision optical metrology.
• Existing methods often struggle with full-aperture measurement and noise suppression across all spatial frequencies.

Purpose of the Study:

• To demonstrate anisotropic spatial-coherence engineering for selective MSF noise suppression in interferometry.
• To introduce a quantitative framework for assessing noise suppression performance.

Main Methods:

• Utilized illumination modulation to engineer anisotropic spatial coherence.
• Employed a 3D spatial-coherence model to analyze Fizeau systems with synthetic ring sources.
• Developed a noise transfer function (NTF) as a complement to the instrument transfer function (ITF).

Main Results:

• Demonstrated selective suppression of MSF noise in a Fizeau interferometer.
• Achieved NTF < 0.4 and ITF > 0.8 within 9.1 lp/mm.
• Reduced MSF noise floor to sub-1 nm for high-precision optical surfaces.

Conclusions:

• Anisotropic spatial-coherence engineering provides an effective solution for MSF noise reduction.
• The proposed NTF-ITF framework enables quantitative noise assessment.
• This technique offers a rapid, full-aperture measurement solution for optical surface errors.