Focal-Plane Alignment Sensing

The method of phase diversity has been investigated for use in sensing piston and tilt misalignments in the Multipurpose Multiple Telescope Testbed MMTT, a phased-array telescope in operation at Phillips Laboratory, Kirtland Air Force Base. Misalignment parameters are estimated indirectly from focal-plane imagery. Accordingly, the hardware requirements for this approach are modest. Furthermore, the method relies on an external reference the object being imaged so that it is less susceptible to systematic errors than are direct-sensing approaches. Regularization is used to combat noise sensitivity, and strategies for selecting a regularization parameter have been developed. The probability of convergence to within a prescribed RMS phase error operational convergence was quantified for noisy imagery using Monte Carlo experiments and was found to be acceptable. Simulations were also performed using three diversity channels, in which the fidelity of estimates was shown to improve and the probability of operational convergence was observed to dramatically increase.... Phase diversity, Phased-array telescope, Regularization, Operational convergence, Multipurpose Multiple Telescope Testbed MMTT.