High precision radially-polarized-light pupil-filtering differential confocal measurement

A new method, high precision radially-polarized light pupil-filtering differential confocal measurement (RPDCM), is proposed to improve the 3D measurement resolution of confocal system. SPDCM uses the property that the radially-polarized-light can produce a strong longitudinal field component after being focused by a high numerical aperture objective to reduce the lateral size of the focus spot, and relies on the pupil-filtering technique to optimize the pupil function of the optical system by the designed pupil filter, which therefore improves the lateral resolution of confocal system, and it uses the differential confocal technology to improve the axial measurement resolution of the confocal system, thereby improves the 3D measurement resolution of the confocal system. Based on RPDCM, we developed a high precision radially-polarized light pupil-filtering differential confocal setup, and use it to verify the effectiveness of RPDCM by experiments. The theoretical analysis and experimental results show that the RPDCM can reach the lateral and axial measurement resolutions of 150 nm and 1 nm, respectively, which are an improvement of 20–32% and 3.7 times compared with a confocal system.