Model-Based Wavefront Sensorless Control with Magnetic Fluid Deformable Mirror for Large Aberration Corrections

Adaptive optics (AO) systems are used to enhance the performance of optical systems. A classical AO system consists of the wavefront corrector with the wavefront sensor (WFS). Wavefront correctors are able to compensate for aberrations in real-time with the measured aberrations. Compared with traditional wavefront correctors, the major advantage of the magnetic fluid deformable mirror (MFDM) features large deformation strokes that can be easily up to more than 100 m. both for the single actuator or inter-actuators. However, the measuring range of WFS is normally small, which could limit its usage in the applications with large aberrations. Considering the idea of taking full advantages of the MFDM's stroke strengths and the limitations of the AO system with the WFS, this paper proposes a model-based wavefront sensorless control algorithm for the adaptive optics systems with magnetic fluid deformable mirror. Compared with the model-free wavefront sensorless AO systems, the model-based control algorithm for the wavefront sensorless AO systems features faster convergence without dropping into the local optima. The model-based control approach is developed based on a relationship between the second moments of the wavefront gradients and the far-field intensity distribution by taking Zernike polynomials as the predetermined bias functions, therefore, the unknown aberrations can be corrected without the wavefront measurement in the closed-loop AO control system. The control algorithm is evaluated in a wavefront sensorless AO system setup with a prototype MFDM, where a parallel laser beam with unknown aberrations is supposed to produce a focused spot on the CCD. Experimental results show that the model-based control method can effectively make the MFDM to compensate for unknown aberrations in an imaging system.