Next generation wavefront controller for the MMT adaptive optics system: Algorithms and techniques for mitigating dynamic wavefront aberrations

Abstract

Wavefront controller optimization is important in achieving the best possible image quality for adaptive optics systems on the current generation of large and very large aperture telescopes. This will become even more critical when we consider the demands of the next generation of extremely large telescopes currently under development. These telescopes will be capable of providing resolution which is significantly greater than the current generation of optical/IR telescopes. However, reaching the full resolving potential of these instruments will require a careful analysis of all disturbance sources, then optimizing the wavefront controller to provide the best possible image quality given the desired science goals and system constraints. Along with atmospheric turbulence and sensor noise, structural vibration will play an important part in determining the overall image quality obtained. The next generation of very large aperture telescopes currently being developed will require assessing the effects of structural vibration on closed loop AO system performance as an integral part of the overall system design. Telescope structural vibrations can seriously degrade image quality, resulting in actual spot full width half maximum (FWHM) and angular resolution much worse than the theoretical limit. Strehl ratio can also be significantly degraded by structural vibration as energy is dispersed over a much larger area of the detector. In addition to increasing telescope diameter to obtain higher resolution, there has also been significant interest in adaptive optics systems which observe at shorter wavelength from the near infrared to visible (VNIR) wavelengths, at or near 0.7 microns. This will require significant reduction in the overall wavefront residuals as compared with current systems, and will therefore make assessment and optimization of the wavefront controller even more critical for obtaining good AO system performance in the VNIR regime.