Research On Bias - Like Aspheric Profile Measurement Based On White Light Interference Microscope

Contact probe in traditional swing arm profilometer may possibly damage aspheric surface and introduce measurement error because of its tip size. In order to measure asphere without contacting aspheric surface, non-contact optical probe based on white-light interferometric microscope was proposed. Scanning the sampling points on the outline to obtain their curvatures so as to reconstruct surface profiles from curvature values.Firstly, the accuracy of curvature measured by white-light interferometric microscope was studied. Least squares calculation method was proposed to fit the 3D surface contour. Different radius of curvature (ROC) of standard spherical mirrors and probe which is used on profilometer were measured. The test results indicate that ROC measured by white-light interferometric microscope is accurate.Secondly, in order to generate reference results for non-contact swing element profilometry of asphere testing. Several surface contours of standard spherical mirror and aspheres were acquired by contact profilometer Taylor-Hobson PGI840. The results are of good coincidence of the nominal values of these mirrors.Thirdly, non-contact swing element profilometry based on white-light interferometric microscope was proposed. Abscissa values of sampling points on surface profile were modified with coordinate compensation method while surface profile was reconstructed with integral method or fitting method according to curvature values and their abscissa values. Compared to the profile results of contact profilometer, the results measured by non-contact swing element profilometry show that ROC of standard spherical mirror is 49.97mm with PV of 95.2nm and RMS of 27.6nm in surface profile deviation while ROC of hyperboloid asphere at vertex is approximately 29.93mm with PV of 73.3nm and RMS of 21.6nm in surface profile. The results measured by non-contact swing element profilometry based on white-light interferometric microscope are accurate.Finally, error analysis was done for the purpose of explanation why the results of paraboloid asphere measured by non-contact swing element profilometry based on white-light interferometric microscoe were inaccurate. It was found that the elements which led to inaccurate key values of paraboloid asphere mainly included ROC of mirror exceeding the threshold value regardless of the non-contact swing element profilometry itself. Accurate results of hyperboloid asphere and standard spherical mirror generated a indirect proof of the feasibility of the non-contact swing element profilometry based on white-light interferometric microscope. The range of application is presented that ROC of asphere should be within the curveture range of which white-light interferometric microscope can measure.