SABCMS, a new approach to higher lateral resolution of laser probe measurement system

Abstract

In order to achieve a high lateral resolution required for ultraprecision measurement of microstructural workpieces, shaped annular beam confocal measurement system (SABCMS), a new approach is proposed for ultraprecision measurement of 3D microstructures. SABCMS uses a binary optical element based on the diffraction principle to shape a Gauss laser beam into an annular beam, and optimizes the normalized inner radius of annular beam aperture ɛ to decrease the main lobe of airy spot, to increase the lateral resolution and measurement range. In comparison with an annular beam shaping technique used in a conventional annular lens confocal measurement system, the annular beam shaping technique used in SABCMS reduces the energy loss, and eliminates the effect of the inner ring edges diffraction of annular lens on the measurement system and improves the defocused property. Experimental comparison and analysis indicate that, as ɛ increases, both the lateral resolution and measurement range of SABCMS increase, and the spatial resolution improves, too, while the axial resolution of SABCMS reduces; the lateral resolution of SABCMS is better than 0.2 μm when wavelength of incidence laser beam λ = 632.8 nm, numerical aperture of measuring lens NA = 0.85, and ɛ = 0.5. It is therefore concluded that SABCMS is a new approach to further improvement of lateral resolution in laser probe measurement systems.