New device measures curved mirrors' absolute shape to within 2 nanometers without touching them

Researchers at Japan's National Institute of Advanced Industrial Science and Technology (AIST) have developed a non-contact device capable of measuring the absolute surface profile of curved optical elements with exceptional precision. The device operates without physically touching the mirrors, which is crucial for maintaining their integrity during measurements.

High-precision curved mirrors play a vital role in various advanced technologies, such as extreme ultraviolet (EUV) lithography systems, synchrotron facilities, astronomical telescopes, and gravitational wave detectors. The accuracy of their surface profiles directly impacts the performance of these devices. During manufacturing, it is essential to determine not only the fine-scale surface topography but also the absolute surface profile, including the radius of curvature.

This information is then used to correct any deviations from the desired design. Traditionally, measuring the surface profile of curved mirrors with high precision without causing damage has been a significant challenge. However, the AIST researchers have overcome this hurdle by developing a system that measures the surface slope (local angle) at each point on the curved surface across a broad angular range.

By analyzing the direction of reflected light, the device can calculate the absolute surface profile with an impressive accuracy of just 2 nanometers. The key to this achievement lies in the integration of a high-precision angle measurement device called SelfA, which automatically corrects any errors in the angle scale. This innovative technology enables non-contact measurement of the absolute surface profile of curved mirrors, ensuring that advanced optical components maintain their performance and meet stringent design specifications.