Calibration of a multiwavelength co-phase measurement system for a segmented solar telescope

The segmented solar telescope described in this study employs a simultaneous dual-wavelength measurement technique to achieve co-phase alignment. To meet measurement requirements with a 20 μm range, 5 nm root mean square (rms) precision, and edge jump rates below 10<sup>-6</sup>, this study focuses on calibrating the dual-wavelength measurement system for the segmented-mirror solar telescope. Analysis of relative error sources in the measurement system revealed that assembly-induced errors, such as defocus, translation, scaling, and rotation, significantly degrade measurement accuracy. To address these issues, we propose a defocus error compensation algorithm based on the light intensity distribution of the point spread function (PSF) and an affine transformation model to calibrate spatial pose deviations across two measurement channels. A dual-wavelength measurement system was implemented on a segmented-mirror experimental platform for calibration. Experimental results demonstrate that the mean relative error decreased from -0.6423 nm to -0.0345 nm after calibration, improving the reliability and stability of co-phase measurements.