Reflective Fourier ptychographic microscopy using a parabolic mirror

Area of Science:

• Optical microscopy
• Phase retrieval algorithms
• Surface inspection technologies

Background:

• Fourier ptychography (FP) reconstructs high-resolution, wide field-of-view images using phase retrieval.
• Reflective-type FP (FPM) is promising for surface inspection but faces limitations in current methodologies.
• Existing FPM techniques struggle with signal-to-noise ratio and illumination geometry.

Purpose of the Study:

• To propose and validate a novel darkfield illuminator for reflective Fourier ptychographic microscopy.
• To enhance the signal-to-noise ratio and achievable numerical aperture (NA) in reflective FPM.
• To demonstrate the system's effectiveness for high-resolution surface inspection.

Main Methods:

• Designed a darkfield illuminator using a parabolic mirror and a flat LED panel.
• Implemented a reflective FPM system incorporating the novel illuminator.
• Collimated LED light via the parabolic surface for efficient object illumination.

Main Results:

• Achieved a synthesized numerical aperture (NA) of 1.06, the highest reported for reflective FPM.
• Demonstrated significantly increased signal-to-noise ratio in acquired images.
• Successfully reconstructed high-resolution images of a USAF reflective resolution target, resolving features down to 488 nm.

Conclusions:

• The proposed darkfield illuminator substantially improves reflective FPM performance.
• The system enables high-resolution surface inspection, validated by imaging integrated circuits.
• This advancement offers a powerful tool for detailed surface analysis and quality control.