Digital Holography And Wavefront Sensing PDF Download

"The work presented in this dissertation explores the use of several unconventional imaging and wavefront sensing modalities in the presence of distributed-volume, or "deep," atmospheric turbulence. This dissertation focuses on the propagation of coherent light from laser sources through the atmosphere, and imaging/wavefront sensing at optical and infrared laser wavelengths. Such wavelengths are negatively affected by deep turbulence. We use a coherent detection method known as digital holography to (1) coherently image distant objects and (2) to sense and correct for aberrations due to turbulence along the propagation path. We showed that compensated-beacon adaptive optics can be used with a digital holographic wavefront sensor or a Shack-Hartmann wavefront sensor to improve the performance of beam projection to distant objects over uncompensated beacon adaptive optics. We saw performance gains of 17% for the Shack-Hartmann wavefront sensor and 26% for the digital holographic wavefront sensor on average for several turbulence scenarios. We explored multi-wavelength 3D imaging with digital holography along with two speckle decorrelation mechanisms that degrade 3D imaging performance in a theoretical framework. Upon establishing this framework, we simulated multi-wavelength 3D imaging of distant objects through deep turbulence and reconstructed the imagery using sharpness metric maximization for 3D data. The results showed that the reconstruction process was more successful if using more corrective phase screens along the digital propagation path. Additionally we showed that sharpness metric maximization suffered in performance in the presence of scintillated illumination patterns, also known as uplink scintillation. Finally we explored motion compensated, multi-wavelength 3D imaging with digital holography and a pilot tone in theory. Our theoretical framework predicted that one would see increased noise in range images, known as range chatter, over highly-sloped object facets relative to the optical axis, and simulations bore this out explicitly. We showed that range chatter increases as a function of object facet slope, optical illumination bandwidth, optical frequency spacing, and turbulence. Going further we used sharpness metric maximization to improve the range chatter that was brought about by turbulence."--Pages xiv-xv.