High-precision calibration of the DKDP modulator for polarization measurement in solar telescopes

DKDP modulators are widely employed in polarization measurements of solar telescopes. Accurate calibration of the DKDP modulator is essential to ensure reliable polarization measurements. In this paper, we propose a method for calibrating the DKDP modulators based on polarization rotation and the longitudinal Pockels effect. Using this method, both the fast-axis azimuth and retardance with the voltage of the DKDP modulator can be simultaneously obtained. The simulation results demonstrate that this method achieves calibration accuracies for both the azimuth angle and retardance better than 0.05°. An experimental calibration of a DKDP modulator is also conducted to verify the method's feasibility and stability. The experimental results align with the repeatability estimates from the simulations. By applying this method, the calibration of the DKDP modulator can be made to meet the requirements of next-generation telescopes, showing great potential for application in the polarization measurements for solar telescopes.