IDBR: Agile Electronic Focus and Aberration Control for Live Animal Microscopy

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A grant has been awarded to Dr. David Dickensheets at Montana State University to develop a light microscope with agile electronic focus control. This project addresses a major technological barrier for in vivo microscopy: controlling the focus and managing aberrations when imaging through thick, unprepared specimens. We will investigate a method that adjusts the location of the focus in the sample under electronic control while maintaining the objective lens in a fixed position. This instrument will be compatible with CCD-based or scanned beam (confocal and two photon) types of microscopes, and will give the user fast, full-range focus control when imaging thick specimens at high numerical aperture, without requiring z-translation of the specimen stage. Of the several possible technologies for beam focus control, MEMS deformable membrane mirrors are attractive for their precision, speed and potential low cost. However, previous implementations have suffered from limited range of motion, such that full range focus control at high NA was not possible. This project will develop new MEMS membrane mirrors capable of an order of magnitude more displacement than current devices and able to correct spherical aberration to maintain high Strehl ratio throughout the image volume. The improvement is achieved through the use of new membrane materials, accurate mechanical modeling and a new closed loop control technique for stable electrostatic actuation. This project will develop the new mirrors and control techniques, and demonstrate their use in a new instrument for two different confocal microscopy applications: microscopy of the developing chick embryo, and microscopy of human skin in vivo. The scope of potential use for this technology is quite broad. The new instrument could support many sophisticated image acquisition schemes including oblique sectioning, enhanced depth of focus at high NA, and image feature tracking and stabilization. The technology is also critical for future miniaturized microscopes designed for laparoscope, endoscope or catheter platforms that presently have extremely limited ability to adjust focus in situ. Finally, advances made in this project will be relevant for a broad class of electrostatic MEMS actuators and the deformable mirrors will be of interest for applications in astronomy, photography, optical data storage and others. In addition to its scientific impact the project embraces integration of research and education, training two engineering Ph.D. students in cross disciplinary research and engaging 6 undergraduate students in engineering design teams. This project will also participate in an established summer internship program for students and faculty from Montana?s tribal colleges.