From instrumental design
to scientific exploitation
Home > News > Rami Gasmi’s thesis defense

Rami Gasmi’s thesis defense

Study and control of the dynamical behaviour of the wide deformable mirror of the E-ELT
» Monday 27 September 2010


  • François Hammer (Observatoire de Paris)

This thesis discusses the impact of the dynamical behaviour of the deformable mirror (DM) on the adaptive optics (AO) control loop. The study focuses on the prototype of the large DM of the E-ELT (European Extremely Large Telescope), which first light is planned for 2017. I present here a global approach to apprehend such structures and insert them in the AO loop. The modal parameters of the structure of a 1m prototype of the deformable mirror are firstly determined through a finite element model and through an experimental modal analysis. The frequency response of the mirror is then studied in the modal and in the Zernike base. The excitations are defined to simulate the behaviour of the deformable mirror while correcting the turbulent wave fronts. Finally, I present some active and passive ways to control the vibrations of the mirror.

The results show that the classical modelling of a deformable mirror in a single input single output way when studying the global adaptive loop behaviour no longer applies when the deformable mirror gets its own dynamics. A multi input multi output model is than necessary to represent these dynamics. The results also show that the control of the vibrations of such structures is possible if we have an accurate model of the dynamical behaviour of the deformable mirror.