4.3 Deformable MEMS Mirror Device (DMD) 4.3.1 Device Capabilities Deformable mirrors have many applications that include microscopy, retinal imaging, laser communications, and wavefront correction in astronomy. The deformable mirror of interest is a MEMS device typically used as an integral part of wavefront correction mechanisms, as shown in Fig. 4.3. The MEMS device contains an array of 12 by 12 electrostatically driven actuators interacting with a deformable thin reflective surface and each actuator having a maximum stroke of 1.5μm driven at speeds of up to 3 kHz [12]. 4.3.2 Control System A multipurpose control software interface was developed to synchronize the motions of the DMD with HDHS acquisition. As shown in Fig. 4.4, the desired pattern and amplitudes for each piston are entered in the user interface and the camera is adjusted to have enough temporal and spatial resolution matching the desired MEMS operational frequency. The measurements presented herein were obtained with a camera set at 42 kHz with spatial resolution of 384 384 pixels and 3.9 μs exposure time. 4.4 Representative Results Transient response of the DMD under various loading conditions was investigated. First, the piston at location-1, shown in Fig. 4.5a, b, is activated by 90 % of its 1.5μm stroke. In the next step, the piston is deactivated to its original position and is followed by activating piston in location-4 to 80 % of its stroke. The transient motions at five specific locations are shown in Fig. 4.5c. In addition, six temporal instances of the transient motions from 571 to 2595 μs are shown in Fig. 4.6. 4.5 Conclusions and Future Work Some of the measuring capabilities of a HDHS under development were demonstrated by testing the transient response of a high-speed deformable MEMS device (DMD). High temporal and spatial (i.e., microseconds at >140,000 data points) resolutions of HDHS enables concomitant measurements at all points to quantify spatial and temporal motion parameters, including modal frequencies, time constants, Q-factors, changes in shapes, and surface strains. These measurements enable Fig. 4.3 MEMS deformable mirror of interest [12]: (a) schematic representation of a closed-loop wavefront correction system that includes adaptive optics in the form of a deformable mirror; (b) view of the reflective surface of the MEMS device of interest; and (c) schematic of the actuation mechanisms 44 P. Razavi et al.
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