Photo-controlled deformable mirror for wavefront shaping

Wavefront shaping is of main interest in the field of Adaptive Optics for Astronomy, wide-field imaging in Microscopy and live cells/tissues imaging in Biology. We propose an innovative technology for a new type of membrane deformable mirror, made by coupling a reflective polymeric membrane with a monolithic non-pixelated photoconductive substrate. The device is called continuous photocontrolled deformable mirror (PCDM), actuated by sending a light flux with given shape and intensity distribution, on the back side of the photoconductor, opposite to the reflective side. Unlike the other actuation mechanisms, this allows to obtain a continuous actuation field, without the typical segmented actuators pattern. Furthermore, it leads to a strong simplification to the driving electronics, for example by eliminating hundreds of cables used for the deformation control. Fundamental is the role played by the photo-excitation dynamics of the photoconductive material, in fact the deformation is obtained through the electrostatic pressure exerted by the photo-generated charge carriers, on the thin reflective membrane. We have developed a device with a single crystalline semiconductor photoconductor wafer, either Silicon or Cadmium Sulfide. The actuation is controlled by a light pattern modulated by a DMD (Digital Micromirror Device) chip, generating a reprogrammable actuator pattern projected on the photoconductor. In order to test the performance of the PCDM, we are addressing two deformation regimes: static behavior and dynamical response. We are then able to measure the response with light actuation, as the influence function matrix with respect to the number of projected virtual actuators; the response with frequency, including response time, resonance frequency, with respect to the different applied patterns, and with respect to the number of virtual actuators; finally, the response in open/close loop.