Effect of the adhesive layer on the unimorph deformable mirror

As the thickness of the adhesive layer between the mirror and the actuator decreases and the performance requirements of the unimorph deformable mirror (DM) increase, stricter control on the adhesive layer thickness and Young's modulus is necessary. In this paper, a finite element model (FEM) for the unimorph DM with an adhesive layer is obtained. Based on the model, the influence of adhesive layer thickness and Young's modulus on the deformation is studied. Also their influence on the adhesive's maximum shear stress is analyzed. In the meantime, the design principles of the adhesive layer thickness and Young's modulus are established with the restrictions of shear failure and the maximum displacement. As a result, different adhesive Young's modulus has corresponding requirements for the upper and lower thicknesses (<20 μm) to obtain 85% maximum displacement. Then, DMs with four different mirror thicknesses are fabricated for verification experiments. The experiments results can be matched with the simulation results. Finally, the thickness in the spin coating process of adhesive layer is explored. The adhesive layer thickness can be controlled within 12.1 μm, and the deviation of uniformity is better than ±2%.