Bipolar absolute differential confocal approach to higher spatial resolution

By use of a superresolution pupil filtering technique to achieve a lateral optical superresolution and a differential confocal microscopy technique to achieve an axial resolution at the nanometer level, we propose a high spatial resolution bipolar absolute differential confocal approach for the ultraprecision measurement of three-dimensional microstructures. The feasibility of the proposed approach has been proved by use of a shaped annular beam differential confocal microscopy system. The experimental results indicate that the lateral and axial resolutions of the shaped annular beam differential confocal system are better than 0.2 μm and 2 nm, respectively, when λ=632.8 nm, ε=0.5, u_M=6.95, and with a 0.85 numerical aperture.