The absolute calibration of remote sensing systems is based upon radiometric standards. The irradiance standards are currently 1000-watt quartz tungsten-halogen lamps that are traced to National Institute of Standards and Technology standards by a middle party at a significant cost. Lamp instability, short lifetime and calibration inaccuracy present problems. A detector-based absolute calibration technique is described here to replace the lamp calibration in the visible portion of the spectrum (approximately 400 to 700 nm). The system utilizes a quantum efficient QED-200 trap detector in an automated facility to absolutely characterize lamp spectral irradiances or reflectance panel spectral radiances. The measured irradiance of a directly-viewed standard lamp compared favorably (within 0.8%) to the original calibration. Standard-reflectance-panel radiance measurements could not be accurately compared (within 5%) to the illuminating standard lamp irradiance because of excessive stray light in the calibration facility.

One promising way to calibrate a satellite sensor in flight is to place a sun-illuminated white diffuser panel in front of it. However, even if the panel is only deployed for brief periods, it may degrade in the space environment. A ratioing radiometer to monitor the panel changes is described and an error analysis associated with the use of the radiometer is presented. The procedures used to test the optical properties of different candidate panel materials are described. Results of spectral directional-hemispherical reflectance, bidirectional reflectance, polarization and depolarization measurements are presented for nine panel candidate materials before and after exposure to proton and ultraviolet radiation. In this preliminary evaluation it was found that, although polytetrafluoroethylene materials exhibited the most desirable characteristics before proton and UV irradiation, IITRI paint YB-71 withstood proton and UV irradiation the best and is the choice among the nine materials tested.

Theoretical calculations have predicted the importance of two-photon absorptions in the third order optical nonlinearities of polydiacetylenes. We have used electro-absorption techniques to make these two-photon transitions slightly one-photon allowed and therefore observable in the one-photon absorption spectrum. Our findings, although unable to ascertain the existence of below-gap two-photon states, nevertheless provide an unexpected view of the conduction band in conjugated chain polymers. The observation of a field induced oscillatory change in the absorption around the vicinity of the band edge and comparison of this signal with theoretical calculations leads to the conclusion that the conduction band is composed of both one-photon and two-photon states. This oscillatory signal cannot be solely explained by one-photon or two-photon states but must include both types for this high energy signal to be reproduced in the theoretical calculations.

A digital-electronic video-rate reconstruction system for Magnetic Resonance Imaging (MRI) has been designed to first order. The maturation of ultra-fast acquisition techniques in MRI has produced the need for a reconstruction system that will enable dynamic processes to be viewed on-line. Conventional reconstruction hardware is not configured for real-time reconstruction and previous developments are limited in accuracy and flexibility. The real-time reconstruction system presented here consists of three main subsystems. A digitizer interfaces with an MR scanner to digitize data matrices of resolutions up to 256 x 256 at arbitrary rates up to video rates. A Fourier processor performs either 2D Fourier transformation or projection filtering on the digitized data at video-rates. A backprojector performs the backprojection operation on filtered-projection data at video-rates. The complete system would be able to reconstruct data acquired from nearly any acquisition technique. True real-time MRI is then possible.

In optical data storage, intersymbol interference (ISI) is one of the limiting factors for high storage density. To reduce ISI, we need to understand its characteristics and use appropriate signal processing techniques. In this thesis, we characterize ISI for various data patterns and compare Signal to Noise Ratio (SNR) with and without ISI equalization. To characterize ISI, we sample the readback waveforms and use a computer program for data processing. To compare SNR with and without equalization, we record a pseudo random sequence and compare the detected marks with original marks. We also compute SNR using the additive interleaving detection (AID) technique without ISI equalization. From our studies, ISI is found to be more significant as mark widths become smaller. We also found that SNR can be increased by 3-9 db with equalization. More interestingly, we found that AID gives good SNR even without ISI equalization. This indicates the simplicity of using AID for higher storage density.

In this paper a novel, radially varying birefringent output coupler is analyzed both theoretically and experimentally. This output coupler, a dimpled half waveplate, is designed to obtain better beam quality from unstable ring resonators. A theoretical model for its transmission when followed by a polarizer is developed. Since the transmission of the dimpled waveplate is a function of various parameters such as the birefringent material, dimple diameter, radius of curvature, and wavelength, the effect of these parameters on the transmission is studied. Using the theoretical equations, the dimpled waveplate design parameters are determined to achieve the necessary transmission. Two experimental procedures used to characterize the dimpled waveplates are described. One is designed to investigate its average transmission and the other to plot its transmission profile. The experimental results are within 5% error of the theoretical calculations for the peak and average transmissions. Finally, the unstable ring laser with the novel dimpled waveplate output coupler is demonstrated.

Our goal is to develop a single-photon emission computed tomography (SPECT) system for dynamic cardiac imaging so that heart disease may be more accurately evaluated. We have developed multiple, stationary, modular scintillation cameras that allow for dynamic imaging because of large detector area, large collection efficiency, high count-rate capability, and no motion of detector, collimator, or aperture. We make use of coded-aperture pinhole arrays because they increase photon-collection efficiency. The coded apertures allow for overlapping projections or multiplexing of an object onto the detector face. We have designed a novel collimation system that allows for an increased number of pinhole projections without substantial multiplexing. This new method is called "subslicing". We verified the subslice concept both in computer simulation and with our 16-module ring imaging system. Comparison of results with and without subslicing shows that the new approach substantially reduces artifacts in the image reconstruction. (Abstract shortened with permission of author.)

<p> Terahertz (THz) heterodyne receiver systems are required by NASA to monitor gas concentrations related to the Earth's ozone depletion. To this end, NASA needs compact, solid state, tunable THz local oscillators. THz LOs have been developed using three means: 1) All-electronic LOs using mixers in combination with Gunn oscillators, 2) Hybrid Photo-electronic LOs using a cw analog of the Auston switch, and 3) All-photonic THz LOs using coherent sources, such as vapor lasers or solid-state Quantum Cascade Lasers, and down converting lasers using nonlinear crystals. In this dissertation, we began with two frequency stabilized Nd:YAG lasers, locked to a common reference cavity, as a starting point to having a stable input into a nonlinear optical frequency conversion system. Following this, we explored the nonlinear crystals useful for THz generation, and the phasematching schemes that could be employed by each. We concluded by settling on highly insulating III-V semiconductor crystals as the proper choice of nonlinear element, and put together a new phasematching method that is most useful for them.</p>

<p> In this dissertation, we describe, characterize, and demonstrate the operation of a dual-in, dual-out, all-optical, fiber-based quantum switch. This "cross-bar" switch is particularly useful for applications in quantum information processing because of its low-loss, high-speed, low-noise, and quantum-state-retention properties. </p><p> Building upon on our lab's prior development of an ultrafast demultiplexer ^[1-3] , the new cross-bar switch can be used as a tunable multiplexer <i> and</i> demultiplexer. In addition to this more functional geometry, we present results demonstrating faster performance with a switching window of &ap;45 ps, corresponding to >20-GHz switching rates. We show a switching fidelity of >98%, i. e., switched polarization-encoded photonic qubits are virtually identical to unswitched photonic qubits. We also demonstrate the ability to select one channel from a two-channel quantum data stream with the state of the measured (recovered) quantum channel having >96% relative fidelity with the state of that channel transmitted alone. We separate the two channels of the quantum data stream by 155 ps, corresponding to a 6.5-GHz datastream. </p><p> Finally, we describe, develop, and demonstrate an application that utilizes the switch's higher-speed, lower-loss, and spatio-temporal-encoding features to perform quantum state tomographies on entangled states in higher-dimensional Hilbert spaces. Since many previous demonstrations show bipartite entanglement of two-level systems, we define "higher" as <i>d</i> > 2 where <i> d</i> represents the dimensionality of a photon. We show that we can generate and measure time-bin-entangled, two-photon, qutrit (<i>d</i> = 3) and ququat (<i>d</i> = 4) states with >85% and >64% fidelity to an ideal maximally entangled state, respectively. Such higher-dimensional states have applications in dense coding ^[4] , loophole-free tests of nonlocality ^[5] , simplifying quantum logic gates ^[6] , and increasing tolerance to noise and loss for quantum information processing ^[7] .</p>

A fundamental quantum-mechanical problem on the phase of quantum harmonic oscillators, which has remained an enigma for more than sixty years since the first treatment by Dirac, is completely solved. Contrary to the common belief that no Hermitian phase operators can be found to describe the phase properties of a quantum harmonic oscillator, a well-defined Hermitian phase operator with an appropriate classical limit is constructed unambiguously. The approach is different in nature from those of many previous attempts which were more or less based on the idea of polar decomposition of the annihilation operator. The fundamental difference between the quantum phase and the classical phase in spite of their conceptual consistency is pointed out and explained. The eigenvalue spectrum and eigenstates of the phase operator are obtained. Some important properties of the phase operator and phase states are investigated. / The rest of this research is devoted to the studies of multimode Gaussian squeezed states of quantum harmonic oscillators. Multimode squeeze operators and rotation operators are defined such that they have extremely similar algebraic properties as those of their single-mode counterparts. It is shown that the introduction of N-mode squeeze operators provides a convenient set of parameters to describe squeezing in multimode Gaussian squeezed states. The disentangling, normal ordering, and some other properties of N-mode squeeze operators are investigated. It is also shown that the time-evolution operator for a general N-mode quadratic Hamiltonian can be conveniently expressed as an operator product containing an N-mode squeeze operator, an N-mode rotation operator, and an N-mode displacement operator. As an application of this result, the dynamics of N-mode harmonic oscillators with time-dependent normal coordinates and frequencies is investigated and formulated by the use of these N-mode unitary operators. A general expression for the time-dependent transition amplitudes between two arbitrary N-mode boson number states is obtained and explicit results are given for the case of sudden changes in normal coordinates and frequencies. / Source: Dissertation Abstracts International, Volume: 50-12, Section: B, page: 5703. / Major Professor: William Clifford Rhodes. / Thesis (Ph.D.)--The Florida State University, 1989.