Calibrating multispot illumination for asphere metrology using shear-interferometry

The use of aspherical and freeform optics is increasingly prevalent to overcome aberrations and facilitate compact optical systems. However, achieving simultaneously fast, flexible, and accurate measurements of such surfaces remains a challenge. Multiple Aperture Shear-Interferometry (MArS) utilizes multi-spot illumination to measure a wide spectrum of such surfaces without adjusting the measurement system. Using the wave vectors of wave fields reflected by the surface as well as the positions of the individual light sources, the surface form is reconstructed using an inverse ray-tracing approach. Hence, the accuracy of the measurement directly depends on knowledge of these entities. In this publication we present a calibration approach for wave vectors incident across the measurement plane. Secondly, we introduce a geometric and spectral calibration method for the multi-spot illumination, ensuring accurate and consistent measurements across diverse surfaces.