Showing papers by "Katie M. Morzinski published in 2009"

Preliminary characterization of Boston Micromachines' 4096-actuator deformable mirror

Abstract: We present preliminary findings on the characteristic behavior and initial performance of Boston Micromachine Corporations' (BMC) 4096-actuator micro-electrical mechanical systems (MEMS) deformable mirror (DM). This device is examined for its application in the Gemini Planet Imager high-contrast adaptive optics (AO) system. It is also being considered for use in next generation AO systems on the extremely large telescopes. Testing of this device has been in progress at the Laboratory for Adaptive Optics (LAO) on the Extreme Adaptive Optics (ExAO) testbed in experiments designed to qualify performance for imaging extrasolar planets. In this paper we present first test results including actuator stroke (3.0 microns at 200 V), individual actuator RMS surface (10.3 nm surface), actuator yield for two DM arrays (94.4% and 98.8%), actuator crosstalk (no more than 32%), stroke at the highest spatial frequency (1.2 nm surface), and sub-nanometer closed loop flattening capabilities over a 30-actuator diameter.

Stroke saturation on a MEMS deformable mirror for woofer-tweeter adaptive optics.

Abstract: High-contrast imaging of extrasolar planet candidates around a main-sequence star has recently been realized from the ground using current adaptive optics (AO) systems. Advancing such observations will be a task for the Gemini Planet Imager, an upcoming "extreme" AO instrument. High-order "tweeter" and low-order "woofer" deformable mirrors (DMs) will supply a >90%-Strehl correction, a specialized coronagraph will suppress the stellar flux, and any planets can then be imaged in the "dark hole" region. Residual wavefront error scatters light into the DM-controlled dark hole, making planets difficult to image above the noise. It is crucial in this regard that the high-density tweeter, a micro-electrical mechanical systems (MEMS) DM, have sufficient stroke to deform to the shapes required by atmospheric turbulence. Laboratory experiments were conducted to determine the rate and circumstance of saturation, i.e. stroke insufficiency. A 1024-actuator 1.5-microm-stroke MEMS device was empirically tested with software Kolmogorov-turbulence screens of r(0) =10-15 cm. The MEMS when solitary suffered saturation approximately 4% of the time. Simulating a woofer DM with approximately 5-10 actuators across a 5-m primary mitigated MEMS saturation occurrence to a fraction of a percent. While no adjacent actuators were saturated at opposing positions, mid-to-high-spatial-frequency stroke did saturate more frequently than expected, implying that correlations through the influence functions are important. Analytical models underpredict the stroke requirements, so empirical studies are important.