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Articles 31 - 39 of 39
Full-Text Articles in Optics
Performance Comparison Of Shearing Interferometer And Hartmann Wave Front Sensors, Timothy L. Pennington
Performance Comparison Of Shearing Interferometer And Hartmann Wave Front Sensors, Timothy L. Pennington
Theses and Dissertations
The resolution of optical imaging systems is severely degraded from the diffraction limit by the random effects of the atmosphere. Techniques exist to compensate for the atmospheric turbulence, one of which is adaptive optics. A critical component in the adaptive optics system is the wavefront sensor. Presently, two types of sensors are being used-the Hartmann-Shack Wavefront Sensor and the Shearing Interferometer. Previous studies have compared these two sensors and found them to perform identically for a point source. However, to date, no comparison has been performed for an extended source and subaperture spacing larger than the correlation length of the …
Improved Quality Of Reconstructed Images Through Sifting Of Data In Statistical Image Reconstruction, Craig A. Stoudt
Improved Quality Of Reconstructed Images Through Sifting Of Data In Statistical Image Reconstruction, Craig A. Stoudt
Theses and Dissertations
The U.S. Air Force employs adaptive optics systems to produce images of exo-atmospheric objects. Typically, a large set of short exposure images are collected, re-centered to compensate for random image motion, averaged together to improve the signal to noise ratio, and then processed to form a reconstructed image. It is known that some short exposure images will be better than others, so some researchers have suggested that image quality can be improved by selecting a subset of the short exposure images according to some quality criterion, and then processing the average of this subset to form a single, high quality …
Performance Impacts For Actuator Misalignments And Failures In Large- Aperture Adaptive-Optic Telescopes, Timothy D. Hogan
Performance Impacts For Actuator Misalignments And Failures In Large- Aperture Adaptive-Optic Telescopes, Timothy D. Hogan
Theses and Dissertations
Large-aperture telescopes require adaptive optics in order to compensate for atmospheric turbulence which would otherwise negate the resolution advantages of using large apertures. This investigation analyzes the impacts of misalignments and failures, in the deformable mirror actuators, upon the performance of such systems. A numerical simulation of a standard adaptive optics system is used to generate characteristic optical transfer function OTF and signal-to-noise ratio SNR performance metrics. The performance impacts of the misalignments are shown to be dependent upon the Fried parameter effective telescope diameter, the source object brightness, and the control system time delay. The degree of performance degradation …
Characterization Of Laboratory Generated Turbulence By Optical Phase Measurements, Eric P. Magee
Characterization Of Laboratory Generated Turbulence By Optical Phase Measurements, Eric P. Magee
Theses and Dissertations
The resolution achieved by an optical imaging system in the presence of the random effects of the atmosphere is severely degraded from the theoretical diffraction limit. Techniques exist for recovering near diffraction limited performance of an imaging system in the presence of atmospheric turbulence. As opposed to laboratory testing, testing image enhancement techniques in the Earth's atmosphere imposes many limitations. Unfavorable weather conditions could result in the loss of time and money invested in conducting the experiments. With a properly characterized turbulence generator, with statistics that match those of the atmosphere, experimental testing of image enhancement techniques can be conducted …
Increasing The Corrected Field Of View Of An Adaptive Optical Telescope, Dustin C. Johnston
Increasing The Corrected Field Of View Of An Adaptive Optical Telescope, Dustin C. Johnston
Theses and Dissertations
Current adaptive optical telescope designs use a single deformable mirror (DM) to compensate for atmospheric distortion. The corrected field of view (FOV) of an adaptive optics system could be increased through the use of multiple DMs optically conjugated to corresponding planes which sample the turbulence region in altitude. Often, the atmospheric turbulence responsible for the degradation of telescope images is concentrated in several layers. Each DM would correct for the component of the total wavefront in the pupil contributed by one or more layers. If the atmosphere does not possess a layered structure, the best fit of the turbulence profile …
The Effect Of An Adaptive Optical System's Spatio-Temporal Response On Imaging Performance, Patrick M. Harrington
The Effect Of An Adaptive Optical System's Spatio-Temporal Response On Imaging Performance, Patrick M. Harrington
Theses and Dissertations
Ideally, an adaptive optical control system would have instantaneous temporal response and infinite spatial bandwidth. In real systems, the response time of the adaptive optical control system is limited by the integration time of the wave front sensor, the computational time of the control algorithm, and the actuator response time. Additionally, finite inter actuator spacing limits the deformable mirror's ability to reproduce spatial frequencies having a period less than twice this spacing. Although analyses general enough to account for both the temporal and spatial characteristics of the adaptive optical system exist, they are complex and require detailed information regarding the …
Lqg Control Of A Deformable Mirror Adaptive Optics System With Time- Delayed Measurements, David J. Anderson
Lqg Control Of A Deformable Mirror Adaptive Optics System With Time- Delayed Measurements, David J. Anderson
Theses and Dissertations
This thesis proposes a linear quadratic Gaussian (LQG) control law for a ground-based deformable mirror adaptive optics system. The incoming image wavefront is distorted, primarily in phase, due to the turbulent effects of the earth's atmosphere. The adaptive optics system attempts to compensate for the distortion with a deformable mirror. A Hartman wavefront sensor measures the degree of distortion in the image wavefront. The measurements are input to a Kalman filter which estimates the system states. The state estimates are processed by a linear quadratic regulator which generates the appropriate control voltages to apply to the deformable mirror actuators. The …
An Investigation Of The Application Of Artificial Neural Networks To Adaptive Optics Imaging Systems, Andrew H. Suzuki
An Investigation Of The Application Of Artificial Neural Networks To Adaptive Optics Imaging Systems, Andrew H. Suzuki
Theses and Dissertations
Recurrent and feedforward artificial neural networks are developed as wavefront reconstructors. The recurrent neural network studied is the Hopfield neural network and the feedforward neural network studied is the single layer perceptron artificial neural network. The recurrent artificial neural network input features are the wavefront sensor slope outputs and neighboring actuator feedback commands. The feedforward artificial neural network input features are just the wavefront sensor slope outputs. Both artificial neural networks use their inputs to calculate deformable mirror actuator commands. The effects of training are examined.
Design Of A Linear Gaussian Control Law For An Adaptive Optics System, Mark Alan Von Bokern
Design Of A Linear Gaussian Control Law For An Adaptive Optics System, Mark Alan Von Bokern
Theses and Dissertations
This thesis considers the design of a linear quadratic Gaussian (LQG) controller for a ground-based adaptive-optics telescopes. The incoming aberrated image is reflected from a 97-element piezoelectric mirror, then measured with a Hartmann-type wavefront sensor. A Kalman filter processes the outputs of the wavefront sensor and obtains estimates of system states. A linear quadratic regulator processes these state estimates and determines an appropriate set of commands for the deformable mirror. Atmospheric distortion is modeled as a set of fourteen Zernike coefficients whose dynamic behavior is produced by excitation of a set of shaping filters by zero-mean Gaussian white noise. The …