The OSA 2005 Special Topical Meeting on “Adaptive Optics: Analysis and Methods” was held in Charlotte, North Carolina, on June 8th and 9th of that year. The papers presented during those two days provided an overview of recent progress in the theory and application of adaptive optics (AO) for real-time atmospheric turbulence compensation. This Focus Issue is devoted to a further exploration of seven of these topics, ranging from formal analytical treatments of optimal estimation and control methods for AO, to recent field tests of wave front sensing and reconstruction using multiple laser guide stars.
In the broadest perspective, adaptive optics has progressed through three phases since its introduction by Babcock in 1953 and the early field tests of the 1970’s. Initial system concepts and demonstrations were limited to correcting a single wave front propagating from (or to) a particular point-like object, using measurements of the light from the object itself as the error signal in the control loop. The requirement for a relatively bright, point-like source was a significant limitation for these early systems, and the concept of an artificially generated beacon (or “laser guide star”) was introduced in the 1980’s to greatly enlarge the fraction of the sky accessible to AO. Nearly two decades have now passed since the first successful field tests of real-time turbulence compensation using laser guide stars, and as of this writing such systems are in operation or the final stages of commissioning on four of the largest astronomical telescopes in the world. Finally, novel adaptive optics system concepts are now being developed for further performance improvements, including: (i) very high-order systems designed for use on even larger telescopes, (ii) three-dimensional atmospheric turbulence compensation using multiple wave front correctors to compensate for scintillation effects and/or enlarge the size of the corrected field-of-view; and (iii) “planet finding” systems designed to detect faint companions of nearby stars at contrast ratios of 10-6 to 10-9.
The contents of this focus issue describe highlights of the analytical and experimental efforts now underway to address these new challenges. The control of very high order AO systems requires the rapid solution of high dimensional inverse problems, and conventional solutions involving explicit matrix multiplications must be replaced by more computationally efficient methods such as sparse matrix techniques, frequency domain algorithms, or iterative solutions such as preconditioned conjugate gradients. High contrast imaging systems required new wave front sensor designs and system architectures to minimize standard both AO system error terms, such as noise, servo lag, and fitting errors, as well as systematic implementation errors, at unprecedented levels of accuracy. All such advanced concepts must eventually be demonstrated, first in the lab and then in the field. In my opinion, the papers presented here illustrate some of the fascination of these problems, the sophisticated tools now used to address them, and the strong prospects of important progress in the coming years.
The next OSA special topical meeting on adaptive optics is now scheduled for June 18th-20th in Vancouver, Canada. This next conference is likely to witness significant progress on all of these topics, as well as entirely new concepts only vaguely defined at the time of the last meeting in Charlotte.