Shaped annular beam differential confocal measurement with higher spatial resolution

A novel shaped annular beam heterodyne confocal measurement system (SABHCMS) is proposed. The shaped annular beam confocal measurement method for sharpening the main lobe of Airy spot is used to improve the lateral resolution of a laser probe measurement system (LPMS), and the heterodyne confocal measurement method is used to improve the axial resolution of LPMS, thereby the spatial resolution of LPMS is improved. Experimental comparison and analyses indicate that both lateral resolution and measurement range of SABHCMS are improved as the normalized radius of the annular beam inner aperture ε increases; the lateral resolution of SABHCMS is better than 0.2μm and the axial resolution of SABHCMS is better than 2nm when the wavelength (λ) of the incident beam is 632.8nm, the numerical aperture (NA) of the objective lens is 0.85 and the normalized inner radius (ε) of the annular beam is 0.5. It is therefore concluded that SABHCMS is a new approach to higher spatial resolution of LPMS and can be used for ultra-precise measurement of microstructural workpieces.