Browsing by Author "Kelly, Kevin F"

Now showing 1 - 6 of 6
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    Compressive Foveation and Spectrally Multiplexed Microscopy
    (2020-04-23) Giljum, Anthony T; Kelly, Kevin F
    Current hyperspectral imaging and video is limited due to optical hardware as well as challenges in the sheer amount of data that needs to be acquired. Compressive sensing presents a viable alternative for simplifying hardware and allows for the subsampling of the high-dimensional datacube, but is limited by long L1 reconstruction times. Therefore, here we demonstrate new approaches in reducing the time required to acquire and reconstruct the data for compressive hyperspectral images and video in multiplexing cameras. In the first method, we develop and utilize a procedure to reduce the reconstruction time in spatially-multiplexing single-pixel cameras using compressive foveation, Setting it apart from previous single-pixel foveation procedures is that our method actually allows for the selection of a region of interest after all measurements have been acquired and without any need for adaptive sensing. In addition, we provide a proof-of-concept method of hyperspectral microscopy based in spectral multiplexing that is capable of capturing hyperspectral images of the sample in a matter of seconds with over 100 bands while maintaining a megapixel spatial resolution. Both results presented represent significant advances in compressive hyperspectral imaging.
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    Compressive imaging systems and algorithms to extend machine vision beyond the visible spectrum
    (2018-06-21) Chen, Jianbo; Kelly, Kevin F
    Machine vision finds its importance in today’s most revolutionary technologies from artificial intelligence that surpasses humans in playing Go and chess to automobiles that drive themselves. For many of these tasks the key component that makes superior machine vision possible is the image sensor technology development that has paralleled the equally rapid development of processing power. However there is still a dilemma between the pursuit of higher resolution images that require a focal plane array (FPA) with more pixels on the front end, and the demands on acquisition for embedded systems restrained by power, transmission bandwidth, and storage. To overcome these challenges, the works presented in this thesis aim to seek solutions in solving particular machine vision tasks with compressive imaging system and advanced algorithms. The first strategy focused on achieving more robust infrared object classification utilizing measurements directly from the single-pixel camera without reconstruction with a multiscale compressive matched filter algorithm. Secondly, a multi-pixel hybrid optical convolutional neural network machine vision system was designed and validated to perform high-speed infrared object detection. Lastly, an approach to accomplish super-resolution beyond the resolutions of both the spatial light modulator and FPA in a compressive imaging system will be demonstrated by exploiting a coded point spread function to obtain sub-pixel information. Both simulation and experiment results were presented and analyzed to demonstrate the result of super-resolving an image with 4 times more of it original resolution. Resolving images beyond 4 times of their original resolutions is also possible by extending the idea of this work.
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    Development of a Terahertz Leaky-Wave Antenna using the Parallel- Plate Waveguide
    (2014-07-23) McKinney, Robert Warren; Mittleman, Daniel M.; Kelly, Kevin F; Natelson, Douglas
    Because of a growing bandwidth problem within wireless communications, the terahertz (THz) spectrum is being investigated as a possible technology for short-range, high-bandwidth communications. For this reason, it is worth implementing known communications technologies within the radio frequency (RF) and microwave bands, such as antennas, in the terahertz band. One such technology is the leaky-wave antenna. Leaky-wave antennas have been in use within the RF and microwave bands since the 1940’s. The leaky-wave antenna is a travelling wave antenna in which a fast wave with a phase velocity greater than the speed of light, c, propagates through a waveguide. This fast wave is allowed to leak out of the waveguide via an opening along the length of the waveguide. A THz leaky-wave antenna is implemented using the TE1 mode of a parallel-plate waveguide (PPWG). Various plate separations are used during this project in order to show the leaky-wave effect for different dispersion relations. Using a commercial THz time domain spectroscopy (THz-TDS) system, the input of the waveguide is a broadband THz signal. The expected output from such an input would be dispersed in the frequency domain. This is particularly interesting because it would allow the leaky-wave antenna to act as a THz demultiplexer by separating a broadband signal into individual frequency components that vary with angle. Our measured experimental results show that the waveguide indeed produces a dispersed output matching the analytical result. The propagation angle of lower frequencies is closer to perpendicular to the waveguide, with the cutoff frequency of the PPWG at the normal. Higher frequencies are transmitted closer to the axis of the waveguide. Since the phase-matching condition for a leaky-wave antenna can work in either direction, this THz leaky-wave antenna can also receive radiation. Our results show that when operating in this orientation, the receiving angle matches the angle of transmission from the transmitter setup for each frequency. This again shows agreement with the analytical result froe leaky-wave antennas. Using the leaky-wave antenna in this manner, we see the potential for THz frequency domain multiplexing. Varying the plate separation of a PPWG changes the dispersion relation. Since the angle of leaky-wave propagation depends on the dispersion, by varying the plate separation, one can vary the angle of the leaky-wave along the length of the waveguide. We implement such a waveguide in order to focus a chosen frequency to a point. Simulations of the field intensity show that this is possible. By mapping out the field intensity for each design frequency, our results validate this concept by showing that the field focuses within the plane of propagation. To the best of our knowledge, this work shows for the first time that these types of antennas can be implemented within the THz spectrum in order to transmit and receive THz signals.
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    Enhanced super-resolution microscopy by phase modulation
    (2016-08-12) Wang, Wenxiao; Landes, Christy F; Kelly, Kevin F
    Super-resolution microscopy typically achieves high 2D spatial resolution but the detection of depth is always difficult. At the same time the temporal resolution remains low and obstructs most biological and chemical researches. In this thesis, I firstly introduced the depth detection method via phase modulation with a 4f system. In the Fourier domain, a phase mask encodes the depth information with a specific phase pattern, double helix phase mask. The final point spread functions deviates from the standard Gaussian point spread functions and the depth information can be measured with high precision by fitting the corresponding double helix point spread functions. Based on the 4f system, I modified the instrument and propose a novel technique Super Temporal-Resolved Microscopy (STReM) to improve the temporal resolution of 2D super-resolution microscopy. The fundamental basis for STReM is the utilization of a double helix phase mask which is rotated at fast speeds to encode temporal information in Fourier domain. The signal can be analyzed either by single emitter fitting or a l_1norm constrained optimization process, which is based on dynamic properties of emitter movement. STReM has been verified using both simulated and experimental 2D data for adsorption/desorption and 2D transport. The temporal resolution has been improved roughly 20 times when comparing traditional methods to that of the novel method of STReM presented in this thesis.
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    Imaging Plasmons with Compressive Hyperspectral Microscopy
    (2015-04-23) Lu, Liyang; Kelly, Kevin F; Baraniuk, Richard G; Landes, Christy
    With the ability of revealing the interactions between objects and electromagnetic waves, hyperspectral imaging in optical microscopy is of great importance in the study of various micro/nano-scale physical and chemical phenomena. The conventional methods, however, require various scanning processes to acquire a complete set of hyperspectral data because of its 3-dimensional structure. As such the quality and efficiency of the data acquisition using these conventional scanning techniques is greatly limited by the detector sensitivity and low signal light intensity from the sample. To overcome such limitations, we applied compressive sensing theory to the hyperspectral imaging. The compressive imaging enhances the measurement signal-to-noise ratio by encoding and combining the spatial information of the sample to the detector, and a recovery algorithm is used to decode the detector outputs and reconstruct the image. A microscopy system based on this compressive hyperspectral imaging scheme was designed and implemented. Further analysis and discussion on the diffraction and interference phenomenon and a solution to the spectral distortion in this compressive sensing microscopy system are also presented. Experimental results of compressive dark-field scattering from gold nanobelts are presented, followed with an analysis on signal-to-noise ratio and a comparison with conventional scanning methods in measuring the plasmon resonances.
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    Single-particle absorption spectroscopy by photothermal contrast
    (2014-11-21) Nizzero, Sara; Link, Stephan; Landes, Christy F; Nordlander, Peter J; Kelly, Kevin F
    Independent characterization of absorption of nano-objects is fundamental to the understanding of non-radiative properties of light matter interaction. To resolve heterogeneity in the response due to local effects, orientation or rare interactions, a single particle approach is necessary. Currently, there are very few methods that attempt to do so. Furthermore, they are limited in the type of structures and the spectral range for which they succeed. This work presents the first general and broad band method to measure the pure absorption spectrum of single particles. Photothermal microscopy is combined with a supercontinuum pulsed fiber optic tunable laser to detect a signal proportional to the pure absorption cross section of single particles at different excitation wavelengths. For the first time, a method is available to measure the pure absorption spectra of single nano-structures that exhibit spectral features from the visible to the near IR. This method is used to resolve the radiative and non-radiative properties of simple gold nanostructures, revealing the heterogeneity present in the response.