Active optics: A new technology for the control of light

TLDR

Active optical systems use real‑time wavefront control to optimize performance amid random disturbances, with applications ranging from maximizing laser power density to enhancing telescope resolving power through turbulence. The paper reviews the basic concepts and historical evolution of active optics systems, from early low‑bandwidth figure‑control to modern high‑bandwidth atmospheric compensation. It compares coherent and incoherent wavefront sensing, describes correction devices such as Bragg cells, segmented mirrors, deformable mirrors, and analyzes closed‑loop performance using two basic models. The paper concludes by reviewing five current experimental active optical systems and discussing potential future applications.

Abstract

Active optical systems are those in which real-time control over optical wavefronts is employed to optimize system perference in the presence of random distrurbances. Applications include 1) outgoingwave systems for maximizing the power density of a laser beam on a target and 2) received-wave systems for maximizing the angular resolving power of a telescope viewing a distant object through a turbulent atmosphere. In this tutorial-review paper, the basic concepts of active optics systems and their historical evolution are discussed, from early figurecontrol systems with a servo bandwidth of less than 1 Hz to the recently developed high-bandwidth systems for atmospheric compensation with bandwidths of several hundred hertz. A critical comparison of the various approaches to wavefront sensing is then made covering both coherent (laser) and incoherent (white-light)systems. Current techniques for wavefront correction including Bragg cells, segmented mirrors, thin-plate deformable mirrors, monolithic mirrms, and membrane mirrors are described. The performance analysis and optimization of closed loop systems is covered using two basic models. The paper concludes with a review of the design and performance of five current experimental active optical systems, with some comments on future applications.