Phase-only pupil filtering approach to higher spatial resolutions in a laser probe measurement system

The phase-only pupil filtering heterodyne confocal measurement method is a new approach for improving the spatial resolution of a laser probe measurement system(LPMS) for ultra-precise measurement of micro-structural workpieces. The proposed approach uses a phase-only pupil with lateral superresolution capability for sharpening the lateral main lobe of the Airy spot to improve the LPMS lateral resolution and uses the heterodyne confocal measuring method to improve the LPMS axial resolution, and thereby improving the LPMS spatial resolution. Experimental comparison and analyses indicate that the lateral resolution of a phase-only filtering heterodyne system can be improved by 50% that of an LPMS with the same parameters, and a lateral resolution better than 0.2 μm and an axial resolution of 2 nm can be achieved when the wavelength of the incident λ = 632.8 nm, the numerical aperture of the measuring lens NA = 0.85, and u_M = 4. It is therefore concluded that the approach proposed can be used for ultra-precise measurement of surface micro-contours and micro-dimensions.