Characterization and control of a multielement dual-frequency liquid-crystal device for high-speed adaptive optical wave-front correction

Abstract

Multielement nematic liquid-crystal devices have been used by others and ourselves for closed-loop adaptive control of optical wave-front distortions. Until recently the phase retardance of available devices could be controlled rapidly in only one direction. The phase retardance of the dual-frequency device can be controlled rapidly in both directions. Understanding the dynamics of the phase retardance change is critical to the development of a high-speed control algorithm. We describe measurements and experiments leading to the closed-loop control of a multielement dual-frequency liquid-crystal adaptive optic.

Liquid crystal wavefront corrector with modal response based on spreading of the electric field in a dielectric material

“…Commercially available LC phase modulators use electrodes that are in direct contact with the LC layer [2,3,4,5]. When the electrode size is larger than the thickness of the LC layer, the electric field is nearly constant over the actuated area, resulting in a step-like response, as shown in Fig.…”

Fast, large and controllable phase modulation using dual frequency liquid crystals

“…It is therefore only meaningful to quote switching speeds of phase shifting nematic LCs when also quoting the phase shift. Methods for improving the switching speed include pi-cells [2] and the transient nematic effect [3], but the method reported to give the fastest phase shift is the dual frequency effect [4,5,6].…”

“…Some of the problems associated with dual frequency control can be circumvented if the LC is used as a wavefront controller in an adaptive optics system [6,7], in which case high speed high dynamic range switching can occur. Similarly, results using a closed loop optical system [7] to compensate for vibrations in an interferometer have been reported.…”

“…Similarly, results using a closed loop optical system [7] to compensate for vibrations in an interferometer have been reported. However the results quoted in [6,7] are not suitable for non-closed loop adaptive optics applications requiring high speed high stroke phase shifting.…”

Modal liquid crystal wavefront corrector

“…It is the latter constraint which is the subject of this paper. The other two have been addressed elsewhere [6,7,8,9]. The alternative to LC technology is MEMS technology, which is a relatively undeveloped technology.…”