SBIR Phase I:Dielectric Coating of MEMS Deformable Mirrors

This small Business Innovation Research (SBIR) Phase I project will demonstrate the ability to coat a microelectromechanical systems (MEMS) deformable mirror (DM) array with high-reflectance dielectric coatings. Micromachined DMs provide unprecedented control over an optical beam, however, they cannot sustain operation with lasers of more than a few hundred milliwatts because of the relatively low reflectance of the typical metallic optical coatings. The dielectric coated MEMS DMs developed with this research will be able to handle tens of Watts of laser power commensurate with many laser machining applications. Normally, a dielectric coating would render a MEMS based mirror useless because residual stresses in these thick coatings warp the mirror surface. Even simple single-wavelength coatings with 99.75% reflectance are relatively thick (3-5 times the wavelength of interest) compared to typical MEMS layer thicknesses. To achieve a high-quality mirror surface, this research will fabricate novel MEMS DMs with a stress-compensation layer that balances residual stresses from the dielectric coatings. The stress compensation layer enables the DMs to be coated with well-established and readily available coatings. Mirrors with these coatings will be tested at high laser fluence to determine failure points and validate thermal models of the DM. The broader impact/commercial potential of this project is to enhance the capabilities of microelectromechanical systems (MEMS) deformable mirrors (DM) to make them suitable for use in industrial applications. Deformable mirrors offer high-resolution control of an optical beam spatially and temporally. This ability has led to tremendous technical and scientific advances in astronomy, retinal imaging, and microscopy. The research here will expand the capabilities of low-cost MEMS DMs to provide exquisite wavefront control to applications where relatively high power (1-100 W) lasers are employed. For astronomers, the DM will be used to pre-compensate laser guide star beams for atmospheric turbulence to improve AO performance of 10-30m class telescopes. These increases in performance will enable astronomers to probe deeper into the universe. The same technology can be employed to enhance laser-machining equipment for the electronics and semiconductor industries. Applications for this equipment include via drilling for ceramic packages, through- silicon vias (TSV), laser machining of high-density flex circuits, integrated-circuit trimming of resistors, and cutting of links in DRAMs. For these applications, the DM can provide fast focus corrections and on-the-fly beam shaping to tailor the beam for the task at hand.