A TIP-TILT ADAPTIVE OPTICS SYSTEM FOR AMATEUR ASTRONOMERS AND OPTIMUM PLACEMENT OF ACTUATORS

A major concern in the design of a tip-tilt adaptive optics system, for amateur astronomical telescopes, is to find optimum positions of the actuators that result in least distortions of the mirror surface. A semi-analytical approach has been used, wherein the mirror is modelled as a thin circular plate with a peripheral ring mass and an elastic edge support. Modal analysis is performed to determine the natural frequencies and mode shapes of the system. The results of the modal analysis are incorporated in the subsequent harmonic analysis, where the response of the system to harmonic forces, applied by the three actuators, is expressed in terms of the Green functions. For various positions of the actuators, the maximum distortions on the mirror surface are evaluated, and from these results, the optimum positions of the actuators are located. The semi-analytical results are vertified by purely numerical results obtained from finite element analysis.