Flat surface measurement using laser trackers and SMRs on motorized stages

In this paper, we propose a noncontact, high-precision method for measuring the flat surface of large-scale optics using laser trackers and spherically mounted reflectors (SMRs) placed on motorized stages. Accurate measurement of surface flatness is critical for the development of optical systems, especially for aligning large-scale astronomical telescopes and space-based instruments. The proposed method can capture high-resolution surface figure of large flat areas, generating dense spatial point clouds. The measurement system consists of laser trackers, SMRs on two-dimensional motorized stages, and a flat mirror. The laser tracker directly measures the position of an SMR and captures an image of the SMR through the reflection from a flat mirror. The motorized stage enables precise and repeatable movement of the optics, allowing for the measurement of the local slope and complete surface figure of the flat mirror. To demonstrate the effectiveness of the proposed method, we conducted a series of measurements using a large flat mirror. The results show that the proposed method can measure the surface figure of a flat mirror with six-degrees-of-freedom, accuracy, and precision. The measurement data obtained from the laser tracker and SMR were compared with those obtained using an interferometer-based measurement system with a parabolic mirror, and the results were found to be in excellent agreement. The proposed method offers a noncontact, high-precision solution for measuring the surface figure of large flat areas and has the potential to significantly improve the manufacturing and testing of large optical systems for astronomy and space-based applications.