Approach to expansion measurement range of heterodyne confocal microscopy system

In order to achieve the larger measurement range of heterodyne confocal microscopy system (HC-MS) required for measurement of 3D microstructures and 3D surface profiles, a new approach based on annular pupil filter technique was proposed to expand HCMS measurement range. The method proposed uses binary optical shaping method to expand full width at half maximum of intensity response curve detected by two detectors in HCMS, thereby expanding the measurement range of the system. In comparison with the general method of measurement range expanded by decreasing objective numerical aperture of confocal microscopy system presently, the expansion method of shaping annular pupil used in HCMS expands the measurement range, improves HCMS resolution property, suppresses the effect of side lobe on the measurement, and avoids the reduction of HCMS lateral resolution caused by decreasing the objective numerical aperture. Analysis and experiments indicate that when ratio of inner aperture radius to outer aperture radius of the annular beam ε=0.5, annular pupil expansion technique of measurement range makes HCMS measurement range expanded one times, and makes HCMS lateral resolution improved and the side lobe suppressed.