On-axis reverse Hartmann test in aspheric optical surface test with the optical flat calibration
2016
The Reverse Hartmann test is developed rapidly, robustly, and accurately in measuring precision aspheric surface. The onaxis
design provides better control of the astigmatism in the test. We use an on-axis Hartmann test in reverse to measure
the aspheric optical mirrors. In the configuration, the LCD with a light pattern on the screen illuminates to the tested surface,
and a 2μm-thick pellicle beam splitter is employed to obtain the coaxial light model. An optical flat with 1/20λ surface
precision is used to calibrate the rays which pass through the external pinhole and image at the detector, and the data are
processed to obtain the direction vectors of arbitrary reflected rays. The surface gradients are determined by the spatial
equations of incident and reflected rays which have been calibrated. The shape of surface is finally reconstructed by
Zernike polynomial fitting. The experiments include measuring a 76.2mm off-axis parabolic mirror and a 76.2mm
spherical mirror. The experimental results show coaxial reverse Hartmann test system may allow for accurate
measurements with uncertainties in the micrometer range using cost-effective equipments.
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