Numerical Aperture Measurement Based on Ronchi Lateral Interferometry

The light source is a monochromatic light-emitting diode (LED) with λ = 532 nm. The objective lens under test has a magnification of 5× and a NA of 0.3.

The periods of the object-plane grating and the image-plane grating are 75.2 μm and 15.04 μm, respectively. The image-plane grating is moved along the axial direction (z direction) in the study, and the x-sheared and y-sheared wavefront at the corresponding positions are measured using the (3N+1)-frame algorithm, then calculated the x-tilt coefficients of Zernike terms (Z2) of x-sheared wavefront and the y-tilt coefficients of Zernike terms (Z3) of y-sheared wavefront. The original measurement data were collected on July 23, 2021.