Improvement of pointing accuracy for Risley prisms by parameter identification.

Abstract

Risley prisms appear to be a promising solution to high-accuracy pointing and tracking. To improve the pointing accuracy of achromatic Risley prisms, an appropriate mathematical model is established, and the forward and inverse solutions are proposed. Focusing on the sources of systematic errors, an optimization method based on a genetic algorithm is proposed to identify the parameters of the physical model, including wedge angles, refractive indexes, and installations. Finally, the experimental platform is established. The pointing accuracy and the size of the blind zone are tested to prove the validity of the method. Experimental results show that the proposed method is effective to reduce the influence of manufacturing, installation, and measurement errors. The optimized pointing accuracy has been improved significantly. Within the maximum deflection angle of 3°, the maximum pointing error is reduced from 33 arcsec to less than 1 arcsec. And the angular dynamic range is found to be greater than 43 dB, able to meet the needs of the majority of applications. In addition, the test of the blind zone shows that the optimized parameters are consistent with the actual system.