Beam Pointing Techniques Based On Achromatic Risley Prisms

Within a single and simple structure, the beam steering control mechanism of risley prisms can achieves the performances of wide scan angular range, fast response frequency and high pointing precision simultaneously. In application scenarios where target pointing direction don’t change extensively, it poses strong comparative advantages and obvious potential for substitution over those traditional beam steering control mechanisms, especially the gimbal one. Thus it shows a growing and spreading prospect of development. However, the complexity of the rules in beam steering has hindered its further research and application. Aimed at the risley prisms with optical components for eliminating chromatic aberration, this issue solves and improves some engineering difficulties in whose beam steering control technologyInitially, this paper focuses on the beam pointing solution of the achromatic risley prisms. Based on the method of first order paraxial approximation, the method of vectorial refraction and the method of vectorial refraction with coordinate transformation, the analytic formulae of the forward beam pointing solution is derivated. Using the solution data from Zemax as baseline, the correctness of the three formulae is verified. And comprehensive comparisonamong them is also finished in aspects of applicative angular range, solution precision and calculation complexity. Then through depicting and analyzing the curve characteristics betweenorientations of the two-prism groups and spatial pointing of the outgoing beam, solving method for the backward beam pointing solution is proposed as well.Subsequently, this paper deals with the scan pattern optimization of the achromatic risley prisms. The regulation of its beam movement is concluded, so does to its common scan patterns. The advantages of isometric spiral scan pattern is analyzed, considering it matching the motion character of this mechanism itself, its trajectory distributing uniformly in all scanning direction, and its easy adjustment of parameters like size of scan blind area or repeat coverage rate of the instantaneous field of view over the same space. Then the mathematic relationship used to avoid scan blind area and reduce the repeat coverage rate mentioned before is summarized, with which the distance between discrete scan points and the interval between adjacent spiral trajectories in isometric spiral can be adjusted. Furthermore, relevant experimental devices of the achromatic risley prism system involved by this issue are introduced. Tested by experiments, the correctness and effectiveness of those mathematic relationship are proved.Eventually,this paper work on eliminating the target imaging deviation caused by distortion of system parameters in the achromatic risley prisms. Benefit from those correlative conclusion obtained in former steps, the method managed to decouple how rotation of the two-prism groups affect movement of the target imaging is offered. Then an algorithm for target imaging alignment which based on closed loop feedback is induced. Its correctness and effectiveness are verified though simulation and experiment as well.