This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Earth's atmosphere is turbulent and as light passes through it the resulting images become distorted. Solar astronomers who study the sun, our local star, use the techniques of Adaptive Optics (AO) to correct for these distortions. To do this they analyze the distortions of a small patch of sunlight very close to the region being studied. The corrections necessary to remove the distortions are then made by passing the telescope's incoming light through special deformable mirrors. This works very well when the region of the sun they want to study is small. However, sunspots and other interesting phenomena on the sun are large enough that such techniques will only deliver an undistorted image of a small part of the region of interest. More sophisticated techniques, called Multi-Conjugate Adaptive Optics (MCAO) have been developed to increase the distortion-free field of view. Newer, and larger, solar telescopes are capable of delivering sharper images than their smaller counterparts. But in order to take advantage of this the atmospheric distortion corrections must be improved even further. Dr. Philip Goode of the New Jersey Institute of Technology and Director of the Big Bear Solar Observatory in Big Bear Lake, California, leads a team that is developing an enhanced MCAO system that will deliver exquisite images of a much larger area of the sun using the new 1.6-meter New Solar Telescope there. This new system will provide scientists with a much clearer picture of the physical processes that give rise to "space weather" that originates in the sun and affects earth's climate and environment. Dr. Goode's project is funded by NSF's Major Research Instrumentation program through the NSF Division of Astronomical Sciences.
Adaptive Optics (AO) is revolutionizing solar astronomy by enabling diffraction limited observations of our nearest star with more powerful telescopes having sufficient aperture to resolve what is regarded as the fundamental scale of the Sun. The stunning successes of solar AO have come from systems with a single deformable mirror (DM), but only a small part of the field of view can be corrected compared to the field over which the dynamical events like fleares and coronal mass ejections occur. Dynamical solar phenomena, like flares and coronal mass ejections (CMEs) are quite non-local, with nearly simultaneous, somehow interconnected manifestations of the dynamics spread over the entire field-of-view (FOV), which is typically an order of magnitude larger in angular extent than what can be corrected by a single deformable mirror. Thus, multi-conjugate AO (MCAO) is the holy grail for understanding the fundamental dynamics of our star. The Sun is an ideal target for research on, and development of MCAO technology. While stellar MCAO systems need either multiple bright natural guide stars or artificial high-power laser guide stars for wavefront tomography, the Sun offers enough information to reconstruct the optical turbulence in Earth's atmosphere even though it is a single star. This is due to proximity of the Sun to the Earth, which makes the Sun an extended observational target in contrast to a point-source like distant star. Further, since the Sun is not a uniform radiator but exhibits a fine structure---its ubiquitous granular field---that offers sufficient information to reconstruct the requisite wavefront information with necessary speed. Big Bear Solar Observatory (BBSO) has built, and now operates the highest resolution solar telescope ever built - the NST (New Solar Telescope). The NST is the first facility-class solar telescope built in the U.S. in a generation. The NST is an off-axis, 1.6~m clear aperture telescope that has been in operation for more than four years. Its third generation AO system has been deployed and it is today's most powerful and most flexible solar MCAO system. In detail, under NSF-MRI-0959187 support, the MCAO system on the NST was built in a close collaboration with our partners in that proposal -- the National Solar Observatory (NSO), and the German Kiepenheuer-Institute fur Sonnenphysik (KIS). NST's MCAO is strongly based on the concepts of the MCAO system of the German GREGOR telescope, which are the result of the pioneering and continuous solar MCAO research at KIS and NSO. NST's MCAO system is not only today's most powerful solar MCAO system, but it is purposely flexible. It features three deformable mirrors, each having 357 actuators, and a total of 669 image registration fields, which are distributed to 19 guide regions spanning 85’'. NST's MCAO was designed to offer maximum flexibility for addressing the outstanding issues in maturing the MCAO technology for solar observations. By shifting and exchanging each DM and its dedicated flat folding mirror, a conjugation range from 2km to 8km can be covered almost continuously by both DMs. First light in Ground Layer AO (GLAO) has been obtained, which corrects only the ground layer and is an essential step in MCAO. The NST MCAO setup has undergone extensive testing and we expect first light in the Spring of 2014. A less robust setup has already worked on the KIS GREGOR telescope using the same basic hardware, so we expect success in Big bear very soon.
