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. Optical metrology is a critical and complex technique for the fabrication of precision optics in which the surface figure is better than peak-to-valley 1  /  10λ or RMS 1  /  30λ. Careful calibration of the intrinsic system errors of the experimental setup, including the alignment error of the metrology tool and the manufacturing error of the reference optics, should be performed. However, any surface deformation caused by the mounting supporter or a gravity effect can result in an incorrect surface figure correction, especially in mid-to-large optics. The system error of the experimental setup and deformation by external conditions of the optics, such as temperature drift, air turbulence, and vibration, affect the measured result. In the proposed method, the magnitude and phase of all nonrotationally symmetrical Zernike coefficients were obtained through multiple measurements by rotating the optics. These coefficients were used to analyze absolute low-spatial frequency figures. To verify the reproducibility of the proposed method, three metrology tools with distinct measurement methods were used to obtain surface figures and the results were then compared.

Comparison of absolute low-spatial frequency surface figure measurement for spherical surfaces