First Open Loop Control Experiments, April, 2008

Open Loop Control uses measurements of the uncorrected wavefront and drives the MEMS DM without the benefit of optical feedback. It relies upon accurate and high dynamic range (full seeing) wavefront sensing and an accurate model of the DM response to voltage commands. After calibration, laboratory tests showed the MEMS mirror was capable of "going to" a desired wavefront shape to within 15 nm surface (30 nm phase). On sky tests in April 2008 with the Villages system were successful, with diffraction-limited images in R, I, and 900 nm bands (V band would have been if not for a pesky telescope vibration). Essentially: open loop Strehls and system performance were as good or better than closed loop performance.

• SPIE Telescopes Meeting (2008) Paper LAO Library Card - PDF file
• SPIE Telescopes Meeting (2008) Presentation (powerpoint)
• Paper on Open Loop Control of MEMS (Photonics West, January, 2008) LAO Library Card - see this for a full explanation and diagrams of the controller data flow, non-linear lookup tables, and calibration procedure for open loop control.

-- DonaldGavel - 15 Jul 2008