‘Tweeter’ and ‘woofer’ deformable mirrors to work together on GPI

The Gemini Planet Imager (GPI) is an adaptive opticsinstrument now under construction that will be installed at Gemini South, an 8 m telescope located atop Cerro Pachon in the Chilean Andes. The GPI will enable imaging of extrasolar giant planets in Jupiter-like orbits. The instrument’s adaptive optics include high-order “tweeter” and low-order “woofer” deformable mirrors, which will correct for atmospheric turbulence by producing a Strehl ratio of greater than 90%. But to do so, the microelectromechanical-systems (MEMS)-based tweeter must have enough stroke (physical travel) to handle the high-order atmospheric turbulence.

Scientists at the National Science Foundation Center for Adaptive Optics (University of California, Santa Cruz) have lab-tested a 1024-actuator 1.5-µm-stroke MEMS device to see whether and how much it saturated under realistic conditions. When placed under the influence of a software-generated Kolmogorov turbulence screen, the tweeter by itself saturated 4% of the time; in combination with a woofer, the tweeter saturated less than 1% of the time. However, mid-to-high-spatial-frequency stroke in the tweeter saturated more than expected, leading the researchers to conclude that analytical studies underpredict the MEMS stroke requirements, and thus empirical studies are key. Contact Katie Morzinski at [email protected].