Self-calibrated BFP-type apertometer for both dry and immersion lenses via grating projection reference

Area of Science:

• Optical Metrology
• Microscopy Instrumentation
• Nanotechnology

Background:

• Accurate measurement of objective numerical aperture (NA) is crucial for high-resolution microscopy.
• Existing back focal plane (BFP)-based apertometers have limitations in measurement range and accuracy, especially for high-NA objectives.

Purpose of the Study:

• To propose and experimentally validate a novel BFP-type apertometer scheme.
• To achieve a wider measurement range and higher accuracy for objective NA determination.
• To enable measurement of objectives with NA exceeding unity using a virtual Fourier plane.

Main Methods:

• Generating "multi-references" on the BFP using grating projection.
• Implementing a self-calibration mechanism based on these multi-references.
• Utilizing a "virtual" Fourier plane for measurements, particularly for high-NA objectives.

Main Results:

• Demonstrated a wider measurement range for both dry and immersion objectives.
• Achieved higher accuracy through the self-calibration of multi-references.
• Successfully measured objectives with numerical aperture (NA) across unity, a first for BFP-type apertometers.

Conclusions:

• The proposed multi-reference BFP-type apertometer offers superior performance in terms of range and accuracy.
• This novel approach enables the measurement of high-NA objectives previously challenging to characterize.
• The experimental verification confirms the feasibility and effectiveness of the self-calibrated multi-reference apertometer system.