Deformable mirrors (DMs) are needed in optical systems for compensation of aberrations using a control technique known as adaptive optics (AO). DMs are generally comprised of a mirror face sheet supported by an array of underlying actuators that can shape the face sheet with nanometer-scale precision. A challenge in fabrication of such devices is that the adhesive assembly process that is generally used to attach surface-normal actuators to the face sheet results in undesirable stress and strain, leading to uncorrectable deformation of the face sheet. The work described in this dissertation presents an innovative mechanical design that effectively solves that problem. The dissertation details design, fabrication, assembly, and control of an electromagnetically actuated DM comprised of a bulk-micromachined single crystal silicon face sheet, an array of single crystal silicon posts that are integrally attached to the face sheet, and an electromagnetic actuation system. Actuation is achieved using an array of fixed permanent magnets adhesively attached to the distal ends of the posts, which are attracted to or repelled by an array of fixed electromagnetic coils, each of which can be independently controlled.
An analysis of the stress-reducing mechanical design for DM assembly is described, along with simulations and experimental results. The approach entails a direct application of St. Venant’s Principle to transform the complex and elevated stress state at the adhesion interface between magnet and post to a smaller and simpler and stress state at the face sheet, resulting in more than an order of magnitude reduction in stress-induced deformation.
Two electro-magnetic actuation approaches were explored. The first uses a surface micromachined and then electroplated planar copper coil array, while the second uses an array of three-dimensional coils made from precision wound copper wire, assembled in an aluminum housing. Multiple DMs based on these designs were produced in a design and assembly process that precisely attached magnets to posts, aligned that subassembly with the actuator array, and controlled the gap between the magnets and the actuation coils. An electronic driver circuit was developed to control the actuator array using a commercial DM driver and a custom designed voltage-to-current amplifier array. Measurements of static and dynamic performance of the DM in response to actuation were made using a partitioned aperture wavefront (PAW) surface mapping microscope and a high bandwidth single point fiber-optical displacement probe. The prototype DMs had 19 actuators spaced
1.5 mm apart, supporting a 12 mm diameter, 10 µm thick face sheet. Actuation of up to +/-10 µm was achieved and dynamic performance was evaluated. This new DM design and shows promise in applications of optical aberration correction and high-power laser beamforming. / 2025-05-23T00:00:00Z
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/48866 |
| Date | 24 May 2024 |
| Creators | Man, Wenkuan |
| Contributors | Bifano, Thomas G. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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