Deformable Mirror Characterization
We have carried out extensive computer modeling and simulations of deformable mirrors (DM) used in our AO systems, however a significant amount of computer power is required to carry out such in-depth modeling of this complicated system. A single simulation may result in only a few microseconds of DM behavior. Additionally, without observations of the actual behavior of a real deformable mirror, simulations cannot be effectively applied to or compared to realistic behavior.
We have obtained a high-speed camera and are creating an in-lab AO system to record the behavior of a real DM. We will be able to characterize the DM's behavior on time scales as short as 1/10,000th of a second, forwarding our understanding of this extremely important element of our AO systems.
Analytical Development of Topics in Curvature Adaptive Optics
While a lot of studies, resources, and support exists for Shack-Hartmann AO systems, curvature AO systems are far less understood and supported. Or AO lab is working to fill in the gaps in understanding and strive to develop resources for these systems.
Postdoc Aglae Kellerer at UH Hilo is, in particular, working to characterize curvature AO systems. Her work includes site testing, measuring curvature AO response to varying atmospheric conditions, streamlining curvature AO systems to result in the most effective seeing corrections, and more.
Developing New Hardware Systems
Our AO systems currently use avalanche photo-diode systems to noiselessly count photons with zero dark current and zero read noise. The measurement system incorporating these diodes is somewhat involved. We are looking into replacing avalanche photo diodes with electron multiplier CCDs in place of the expensive avalanch doides. This replacement would allow for a much more physically compact syste, reduce the number of components required within the sensing system, and potentially increase speed and efficiency in the sensing to DM adjustment process.
Currently, the mirrors that measure wavefront curvature in our AO systems are controlled by acoustic signals. A high-frequency tweeter causes a reflective membrane to oscillate between convex and concave shapes (thus allowing the mirror to measure phase in front of and behind the focal plane). One disadvantage of this set-up is that it is not possible to use the mirror in in a zero-curvature state during operations.
We are working to replace this acoustically controlled sensor with a piezoelectric membrane mirror. A piezoelectric mirror would afford a huge increase in control over the shape of the wavefront sensor during AO operations.
`IMAKA - AO System for CFHT
`IMAKA is an ambitious project to bring atmosphere-corrected high-resolution images over extremely large fields of view to the Canada-France- Hawaii Telescope. There are three key pieces to `IMAKA. First, we have found that the optical turbulence above Mauna Kea is (a) weak in the free atmosphere and (b) confined within a very thin turbulence layer close to the ground within the boundary layer. Second, the approach of ground-layer adaptive optics, correcting for just the local optical turbulence, has advanced and is now in operation at ground-based facilities. Finally, with the development of orthogonal-transfer CCDs by the IfA/PanSTARRs group, we now have the ability to correct for global tip/tilt on the focal plane of the cameras. With this, `IMAKA will correct for the local turbulence with a very wide-field ground-layer AO system and correct for the remaining high-altitude tip/tilt using a PanSTARRs-style CCD camera. The combination has the potential to deliver FWHM~0.3" images over a full one-degree field of view in the visible (e.g. r band) under median seeing conditions.
The IfA is leading the development of this instrument (PI - Chun) and pending funding approval from the CFHT Board will enter a Phase A design study in 2011. The `IMAKA web page is located at: