Abstract
In order to achieve high-accuracy measurement of radius of curvature of optical sphere, ultra-high accuracy radius of curvature testing device is developed by dual-frequency laser interferometer and Fizeau interferometer based on cat’s eye and confocal method. Through analyzing the error source models of radius of curvature testing, optical configuration of the testing device has been optimized. Precise environment control and real-time monitoring system is also established to reduce the errors caused by environment. Through the above processes, the radius of curvature measurement relative accuracy is better than 2 ppm. One optical sphere, R88.5 mm, test aperture 59 mm, has been tested. Testing result is 88499.465 ± 0.176 μm, meeting the design requirement. The method has high accuracy and practical advantages.
Highlights
For high precision spherical optical elements are widely used in the fields of lithography, metrology, inertial confinement fusion, synchrotron radiation, etc., measurement accuracy requirements of radius of curvature of optical sphere continue to increase
Coordinate Measuring Machine (CMM) has a relative accuracy about 4× 10−6, but there is the risk of scratches due to contact measurement
Laser tracker with laser interferometer method is always used in low accuracy and large radius of curvature measurement
Summary
For high precision spherical optical elements are widely used in the fields of lithography, metrology, inertial confinement fusion, synchrotron radiation, etc., measurement accuracy requirements of radius of curvature of optical sphere continue to increase. There are several methods of measuring radius of curvature, including spherometer, mechanical measurement by a Coordinate Measuring Machine (CMM), cat’s eye and confocal method, laser tracker with laser interferometer method and so on. Laser tracker with laser interferometer method is always used in low accuracy and large radius of curvature measurement. Cat’s eye and confocal method based on dual-frequency laser interferometer and Fizeau interferometer is suitable for high precision applications since it is non-contact and high accuracy [5]-[7]. (2016) Measuring Method of Radius of Curvature Based on Dual-Frequency Laser Interferometer. High-accuracy testing device measuring radius of curvature based on cat’s eye and confocal method is described in this paper. The testing device is developed based on dual-frequency laser interferometer and Fizeau interferometer. Compared with other non-contact radius of curvature test methods, the method used in this paper has high accuracy and practical advantages
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