Lirong Qiu

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 mum and 2 nm, respectively, when lambda=632.8 nm, epsilon=0.5, uM=6.95, and with a 0.85 numerical aperture.

Tri-heterodyne confocal microscope with axial superresolution and higher SNR

Based on the characteristic of a confocal microscope (CM) that the offset of a pinhole along an optical axis changes the axial intensity response phase, a novel tri-heterodyne confocal microscope is built up by dividing the CM measurement light path into three paths, and using three sets of focusing lenses, detectors and pinholes placed behind, on and before the focal plane to form three detection systems, thereby achieving the axial superresolution imaging and high Signal Noise Ratio (SNR) through pairwise heterodyne subtraction of three intensity signals with given phases received by the three detection systems and data processing. Simulation and experimental results indicate that the new tri-heterodyne confocal microscope reduces the full width at the half maximum of CM axial response curve by more than 50%, results in the significant improvement of CM anti-interference capability, and enables CM to be more suitable for high accuracy bipolar absolute measurement of 3D microstructures and surface contours.

A new laser heterodyne confocal probe for ultraprecision measurement of discontinuous contours

In order to further improve the lateral resolution required for ultraprecision measurement of discontinuous surface contours, a new laser heterodyne confocal probe (LHCP) has been proposed for use in making ultraprecision bipolar absolute measurements. The new probe follows the principle of reflection confocal microscopes (RCM), and uses the property of RCM light intensity curves being almost invariant with the offset of a pinhole. It also uses a heterodyne confocal light path arrangement and intensity normalization technique to improve the linearity and resolution of RCM and to suppress the common-mode noise caused by the disturbance in light source intensity, different environmental conditions and electric drifts of detectors. Analyses and experimental results indicate that, when a microscope objective of 40 ? 0.65 is used, the LHCP has a measurement range of 7 ?m and a resolution of better than 2 nm. After nonlinear compensation, its residual nonlinear error is less than 13 nm in the full range. The application of the LHCP to ultraprecision measurement of discontinuous contours made it possible to measure the inner and outer contours of a groove in a revolving body at higher precision.

Enhancing laser beam directional stability by single-mode optical fiber and feedback control of drifts

A system, which uses a single-mode optical fiber to suppress the laser beam drifts, and uses feedback control to further reduce the drifts of a primary collimated beam, is proposed to enhance the directional stability of laser beams. The linear and angular drifts of laser beams are separated through light path arrangement and detected using quadrant position detectors, and are controlled using two-dimensional linear and angular drift feedback control systems according to their magnitudes detected. Theoretical analyses and experimental results indicate that the collimation accuracy of 0.7×10−7rad can be achieved at a collimation distance of 500 mm using single-mode optical fiber and separate control of linear and angular drifts.

Approach to higher spatial resolutions in a laser probe measurement system using a phase-only pupil filter

Phase-only pupil-filtering differential confocal measurement, a new approach, is proposed to improve the spatial resolution of a laser probe measurement system (LPMS) for ultraprecise measurement of microstructural workpieces. The proposed approach uses a lateral superresolution pupil filter for sharpening the main lobe of the Airy spot to improve the LPMS lateral resolution and uses the differential confocal measurement method to improve the LPMS axial resolution, thereby improving the LPMS spatial resolution. In addition to improving the spatial resolution, linearity, and antiinterference capability of a confocal measurement system, the proposed approach can be used for bipolar absolute measurement and improvement of the measurement range. Experimental comparison and analyses indicate that the lateral resolution of a phase-only pupil-filtering differential confocal system can be improved by 50% over that of an LPMS with the same parameters, and a lateral resolution better than 0.27 μm and an axial resolution better than 3 nm can be achieved when the wavelength of the incident beam is λ=632.8 nm, the numerical aperture of the measuring lens is NA=0.65, and μ M =4. It is therefore concluded that the phase-only pupil filtering differential confocal measurement method is a new approach to a higher spatial resolution of LPMSs and can be used for ultraprecise measurement of surface microcontours and microdimensions.

Confocal measurement approach for enhancing lateral resolution using a phase-only pupil

Confocal measurement approach is recently widely used as important tools for measurement of three-dimensional microstructures and surface contours because of its good 3D chromatographic imaging capability. But its lateral resolution is limited by the diffraction effect to about 0.4 ?m only while the axial resolution has reached the nanometer level. A phase-only confocal measurement approach is therefore proposed to enhance the lateral resolution. In this paper, an optimized superresolution phase-only filter is used in a confocal microscopy system to improve the lateral resolution, and the pinhole in the confocal microscopy system effectively eliminates the disturbance of ambient lighting and improves the imaging quality. Simulation results indicate that, an optimized three-zone pupil with GL = 0.8375 and GA = 0.99 can make the lateral resolution of CMS 1.18 times better while the axial resolution is almost invariable. So it therefore can improve the applicability of confocal microscopy system.