Adaptive optics

Adaptive Optics is a technique related to astronomical imaging. The maximum theoretical resolving power of ground-based telescopes is difficult to reach because of the presence of the atmosphere. Astronomical image resolution is severely limited by atmospheric turbulence that distorts the optical wavefront of the light coming from space. Adaptive optics helps compensating for this effect by means of a deformable mirror that partially cancels the wavefront distortion. The deformable mirror is controlled in real-time on the basis of the measurement of the wavefront that is provided by a wavefront sensor, making the AO system a feedback control loop, as shown in the figure. 

The control system is a key element for achieving sharp images. The subject of my research is to address the control challenges brought by the coming generation of wide-field AO systems, with a special attention to systems with a very large number of degrees of freedom. The aim is simultaneously to propose new methods to increase the imaging performance of AO instruments and to study the problem of optimal control in a the large-scale context, in view of applications to the future generation of extremely large telescopes, which will feature actuators and sensors in the numbers of the tens of thousands. A further aspect that will be addressed is the identification of the models of the turbulence from real observation data, as the use of precise models in the control design process implies a significant improvement of the performance.

References

P. Massioni, L. Gilles, B. Ellerbroek Adaptive Distributed Kalman Filtering with Wind Estimation for Astronomical Adaptive Optics Journal of the Optical Society America A, Volume 32, Issue 12, December 2015, pages 2353-2364. P. Massioni, C. Kulcsár, H.-F. Raynaud, J.-M. Conan An Approximation of the Riccati Equation in Large-Scale Systems with Application to Adaptive Optics IEEE Transactions on Control Systems Technologies, Volume 23, Issue 2, March 2015, pages 479-487.

L. Gilles, P. Massioni, C. Kulcsar, H.-F. Raynaud, B. Ellerbroek Distributed Kalman Filtering compared to Fourier Domain Preconditioned Conjugate Gradient for Laser Guide Star Tomography on Extremely Large Telescopes Journal of the Optical Society America A, Volume 30, Issue 5, May 2013, pages. 898-908.