Page 214 - High Power Laser Handbook
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182   So l i d - S t at e   La s e r s     Intr oduction to  h igh-Power Solid-State Lasers      183


                                   Deformable
                                     mirror                   Aberrated
                                                             wavefront in



                                                                  Clean
                             Piezoelectric                     wavefront out
                              actuators
                                                   Wavefront
                                                    sensor
                      Figure 7.11  Closed-loop adaptive optics (AO) system for laser wavefront
                      correction.

                      loops and actuators. An AO system involves actively, or adaptively,
                      controlling the shape or orientation of optics in the beam path so as to
                      reduce or eliminate OPD on the high-power output beam. Most often,
                      the actuated optics are integrated with active sensing of the output
                      beam wavefront as part of a continuous feedback loop. However, AO
                      systems  can  also  be  configured  as  feed-forward  devices  based  on
                      such laser operating parameters as pump power levels.
                         A simple example of a closed-loop AO system is shown in Fig. 7.11.
                                                                              33
                      An aberrated, high-power beam is incident on a deformable mirror
                      (DM). The DM’s optical surface consists of a thin, polished face sheet
                      with a low-absorption high-reflectivity (HR) coating. The face sheet
                      changes  its  shape  in  response  to  stress  imposed  by  individually
                      addressable piezoelectric actuators attached to its rear surface (Fig. 7.12).
                      The beam reflected from the DM is sampled and its wavefront mea-
                                                       32
                      sured using a Shack-Hartmann sensor.  This wavefront information





















                      Figure 7.12  Deformable mirror for high-power SSL beam correction
                      (Xinetics, Inc.). Individual actuators can be seen through the 1064-nm high-
                      reflection coated face sheet, which is transparent at visible wavelengths.
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