A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
Browse
2 results
Search Results
Item Controlling light Propagation in complex media for Imaging, focusing and Brillouin measurements(2018) Edrei, Eitan Y; Scarcelli, Giuliano; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Imaging and focusing light through turbid media are two fundamental challenges of optical sciences that have attracted significant attention in recent years. Traditional optical systems such as confocal microscopy, optical coherence tomography and multi-photon microscopy utilize ballistic photons traveling in straight trajectories to generate an image; however, with increasing depth, the signal to noise ratio (SNR) decreases as the number of ballistic photons decays exponentially. In the first part of this thesis I present two novel techniques for imaging through scattering medium by decoding seemingly random scattered light patterns and demonstrate the highest resolution and acquisition speed to date. For point scanning applications I also study methods to focus light through scattering materials and report on a fundamental trade-off between the focal point intensity and the focal plane in which it is generated. In the second part of the thesis I investigate how the ability to control light propagation within turbid media can be used to enhance point scanning measurements such as Brillouin scattering spectroscopy, a technology recently developed in our lab to characterize material stiffness without contact. To do this, I first present a novel optical system (“spectral coronagraph”) which yields an improved extinction ratio when inserted into Brillouin spectrometers to enable the spectral separation in the presence of scattering or close to interfaces. Additionally, to enhance the Brillouin signal, I apply adaptive optics techniques, first developed for astronomy applications, where the incident wave front is shaped to circumvent for optical phase aberrations. Using adaptive optics, I show signal enhancement in artificial and biological samples, an important feature in the context of Brillouin microscopy to promote high SNR imaging in practical scenarios.Item Characterizing Atmospheric Turbulence with Conventional and Plenoptic approaches(2017) Ko, Jonathan; Davis, Christopher C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atmospheric turbulence is a phenomenon of interest in many scientific fields. The direct effects of atmospheric turbulence can be observed in everyday situations. The twinkling of stars is an indicator of weak atmospheric turbulence while the shimmering of objects above a hot surface is an indicator of strong atmospheric turbulence. The effects of atmospheric turbulence are generally considered a nuisance to optical applications. Image blurring effects are often present when observing distant objects through atmospheric turbulence. Applications that require maintaining the coherence of a laser beam, such as in free space optical communication, suffer from poor link quality in the presence of atmospheric turbulence. Attempts to compensate for the effects of atmospheric turbulence have varied in effectiveness. In astronomical applications, weak cases of atmospheric turbulence have been successfully compensated with the use of a Shack-Hartmann wavefront sensor combined with adaptive optics. Software techniques such as “Lucky Imaging” can be useful when clear images briefly appear through the presence of weak turbulence. However, stronger cases of atmospheric turbulence often found in horizontal or slant paths near the Earth’s surface present a much more challenging situation to counteract. This thesis focuses primarily on the effects of strong or “deep” atmospheric turbulence. The process of compensating for the effects of strong atmospheric turbulence begins with being able to characterize it effectively. A scintillometer measures the scintillation in the intensity of a light source to determine the strength of current turbulence conditions. Thermal fluctuation measurements can also be used to derive the strength of atmospheric turbulence. Experimental results are presented of a developed large aperture scintillometer, thermal probe atmospheric characterization device, and a transmissometer. While these tools are effective in characterizing atmospheric turbulence, they do not provide for a means to correct for turbulence effects. To compensate for the effects of atmospheric turbulence, the development of the Plenoptic Sensor is presented as a wavefront sensor capable of handling strong turbulence conditions. Theoretical and experimental results are presented to demonstrate the performance of the Plenoptic Sensor, specifically in how it leads to adaptive optics algorithms that can rapidly correct for the effects of turbulence.