The ASALT lab has been investigating the use of a segmented MEMS DM in adaptive optics systems. One of the anticipated benefits of a segmented device is that in monochromatic light the throw is essentially infinite due to the modulo 2Pi nature of the device. Earlier work demonstrated how this modulo 2Pi behavior interacts unexpectedly with a standard proportional integral controller. Here we present experimental data on this effect to ...
We propose a sensor that measures the number, strength, altitude and velocity of atmospheric turbulence layers. Recent research has shown that pupil plane branch points contain four independent and measureable parameters and that these four parameters can be used to estimate four independent turbulence layer parameters--number, strength, altitude and velocity--for each atmospheric turbulence layer. Here, we summarized previous results and then demonstrate how these results allow for construction of a ...
One of the problems associated with the use of the sodium laser guide star as a beacon for an adaptive optics system is the changes in the sensitivity of the wavefront sensor caused by the extended nature of the sodium layer. Shack-Hartmann wavefront sensors use quad cell detectors to estimate the amount of x- and y- gradients in each sub-aperture. The gradients are multiplied by a constant gain factor that ...
In earlier work we have shown that pupil plane branch points carry information about the conditions of the atmospheric turbulence. Experiments in the Atmospheric Simulation and Adaptive-optic Laboratory Test-bed (ASALT) at the Air Force Research Laboratory. Directed Energy Directorate's Starfire Optical Range have shown that branch points can provide the number and velocity of turbulence layers. Here we demonstrate that these measurements can further be used to estimate the turbulence ...
This paper is the 3rd in a series of papers discussing characterization of a Micro-Electrical-Mechanical-System (MEMS) deformable mirror in adaptive optics. Here we present a comparison between a conventional adaptive optics system using a Xinetics continuous face sheet deformable mirror with that of segmented MEMS deformable mirror. We intentionally designed the optical layout to mimic that of a conventional adaptive optics system. We present this initial optical layout for the ...
The use of a laser guidestar (LGS) for the purpose of a beacon in an adaptive-optics (AO) system is prone to perspective elongation effects on the spots of a Shack-Hartmann wavefront sensor. The elongated spots can vary in size over the subapertures and affect the gradient sensitivity of the sensor. The Air Force Research Laboratory (AFRL) has developed a LGS model that outputs gradient gains which represent the effects of ...
The atmospheric turbulence simulator used in testing in the atmospheric simulation and adaptive-optic laboratory test-bed at Starfire Optical Range is configured based on three characteristics: Fried's parameter, the Rytov number and the Greenwood Frequency. All three may be estimated from open loop data as a means of verifying the simulated turbulence conditions for a given test configuration. However, unlike Fried's parameter and the Greenwood Frequency the Rytov number isn't directly ...
The conventional adaptive-optics (AO) system configuration consisting of a Shack-Hartmann wavefront sensor using the Fried geometry is prone to an unsensed waffle mode because of an inability to have discrete point reconstruction of the phase at the actuator positions. Techniques that involve filtering and/or projecting out the waffle mode in the reconstructor have been shown to be effective at not allowing the unwanted mode to occur, but come at the ...
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