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Measurement and fabrication process for a reference concave mirror with NA 0.9 is explained. The mirror's surface figure error is measured by using a Fizeau interferometer and a computer-generated hologram (CGH). The result is compared with a stitched figure error using a small NA transmission sphere. Also, the system error is calibrated by a Random Ball Test (RBT). Ion beam figuring (IBF) is employed to enhance the surface figure of the reference mirror. Achieving a high NA of 0.9 opens new opportunities in advanced metrology and optics applications.
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Kihm et al. (2024) studied this question.
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