Feedback control of a piezo deformable mirror for a wavefront-sensorless AO setup

Feedback control of a piezo deformable mirror for a wavefront-sensorless AO setup

Kroese, H.

Verhaegen, M. (mentor)
Song, H. (mentor)

Mechanical, Maritime and Materials Engineering

Delft Center for Systems and Control

2009-12-18

This master thesis presentation concludes the research done on a wavefront-sensorless (WFSless) adaptive optics (AO) setup, where light intensity of a focussed beam behind a pinhole is measured. As wavefront compensator, a Piezo Deformable Mirror (PDM) was used. The goal of the research is to investigate which algorithms lead to the highest light intensity possible and the time needed to reach this optimum. The research consists out of two parts: compensation for the hysteresis of the PDM, which now causes inaccuracy of the actuator strokes; and implementation of theories on WFSless AO found in literature. To reduce the effects of hysteresis, compensation was developed, which uses a modified structure of the Coleman-Hodgdon equations (C-H eq.). The inverse model can directly be used and the number of variables was reduced. The optimization algorithms used to find light intensity are a Nelder-Mead (NM) simplex which directly optimizes PDM actuator voltages (VO), a NM, which controls 14 Zernike modes and a line search (LS) and quadratic optimization (QO) algorithm that optimize 14 individual Zernike modes coefficients. The OA and the hysteresis compensator were experimentally evaluated. From the experimental tests it can be concluded that the NM algorithms result in the highest light intensity. The use of Zernike modes increases the optimization speed. For the NM simplex a reduction of 59-66% in time was achieved before the algorithm reached 95% of its final light intensity value. If the NM simplex in Zernike mode optimization is compared with the QO, the QO only needs 60 steps to reach a photodiode value of 3V (about 80% of highest possible light intensity), whereas the NM simplex needs 129 steps. The use of hysteresis compensation led to an increase of the light intensity for the NM in VO and the LS and QO.

http://resolver.tudelft.nl/uuid:25c2ddea-6f9f-4f3c-b486-5cc801c4bd71

Student theses

master thesis

(c) 2009 Kroese, H.