High-precision and traceable equipment for measuring aspheric mirror surface

In recent years, the superior optical properties of complex aspherical elements have provided optical designers with greater flexibility, leading to an explosive growth in demand across various applications. High-precision and reliable profile measurement technology is crucial for ensuring the quality of aspherical processing and the proper functioning of optical systems. To achieve high-precision, traceable measurements of complex aspherical mirror surfaces, a non-contact coordinate scanning measurement equipment based on an independent metrological loop is proposed. This equipment incorporates a dedicated metrology frame and utilizes multiple interferometric systems for real-time, accurate measurements of aspheric surfaces, ensuring the results are traceable to the SI definition of the meter. Specifically, the equipment features three co-referenced interferometric systems: two for real-time tracking of the optical probe's spatial position, and the third integrated within the miniature interferometric probe for measuring the surface shape of complex aspherical mirrors. The measurement principles of the interferometric systems are explained in detail. Each interferometric system utilizes a highly integrated waveplate-array quadrant photodetector to minimize optical components, mitigate processing and installation errors, significantly reduce system volume and mass, and decrease equipment load. Partial surfaces of standard spheres and aspherical mirrors were tested. The results showed a measurement error of less than 0.2 μm and the repeatability of 70 nm, achieving sub-micron accuracy.