Browsing by Author "Rabson, Thomas A."

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    A method for measuring the conductivity of high resistivity semiconductor materials
    (1964) Lee, Shi Kyu; Rabson, Thomas A.
    A simple method of measuring the conductivity of semiconductor materials is studied both analytically and experimentally. The basic method utilizes two pairs of coils, operating as transformers, and excited with a source of sinusoidal voltage. The two primary coils are connected in series, so that they have the same current flowing through them; the secondary coils are connected in series, in such a manner that the induced voltages tend to cancel. An approximate null in the secondary circuit is produced by positioning of the coils. A sample (usually small) of semiconductor material is placed between one pair of coils. A voltage proportional to the bulk conductivity of the sample is induced in the secondary winding for that pair, disturbing the voltage balance in the secondary circuit. Because this voltage is 90 degrees out of phase with the original voltage, it may be detected by methods that take account of the phase relations. In the preliminary experimental studies reported in this thesis, the out-of_-phase voltage component was determined by simple trigonometric relations. A practical laboratory instrument would use a phase sensitive detector excited in such a manner that it responds to the desired component. The experimental study verified the essential correctness of the theoretical analysis and demonstrated the potential usefulness of a practical instrument based upon the principles utilized. Certain refinements and simplifications of design for a practical instrument are indicated.
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    A resonant cavity for a microwave maser
    (1962) Emery, Frank Edward; Wetsel, Grover C., Jr.; Rabson, Thomas A.
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    A thin film lithium niobate ferroelectric transistor
    (1991) Rost, Timothy Alan; Rabson, Thomas A.
    The incorporation of a thin film of LiNbO$\sb3$ in a conventional MOS (metal-oxide-semiconductor) structure gives the possibility of two fundamentally different types of computer memory architectures. One, based on ferroelectric switching, involves the reorganization of charge in the transistor channel to compensate for the change in surface polarization. Another, based on the bulk photovoltaic effect, creates a change in the threshold of the transistor when exposed to incident light. With the use of a molybdenum liftoff process, such ferroelectric transistors have been realized. The properties of these transistors have been measured before and after exposure to laser illumination, and before and after the application of voltage pulses.
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    An investigation of the rise times of output pulses of semiconductor nuclear radiation detectors
    (1963) Harris, David Allen; Rabson, Thomas A.
    This paper is a report of the investigations carried out to determine whether or not the rise time of the output pulses of semiconductor nuclear particle detectors is influenced by the type of ionizing particle striking the detector. Charge collection rise times are calculated in the customary fashion, neglecting interaction between the lines of charge produced by the ionizing particle. A model of the detector is developed on which rise time calculations may be carried out taking into account charge interaction. The calculations are carried out for several different types of ionizing particles. Comparing the calculated rise times shows no difference between the rise time calculated taking into account charge interaction and those neglecting charge interaction: to within the accuracy of the method of calculation. The design of a vide-band amplifier is discussed: and the performance characteristics of the system used to observe detector charge collection rise times are presented. Resistivity and junction capacitances of several detectors were measured. In only one of the available detectors could the charge collection time be observed. Using an eight m.e.v. alpha source, the charge collection time of the detector was measured and found to be several times longer than was predicted. No other types of particle sources were readily available: so it was not possible to determine if this effect varied with the type of ionizing particle striking the detector. This effect (i.e. an apparent lengthening of the charge collection time) has, however, been observed by others: who have determined experimentally that the effect does not depend on the particle type. The conclusion then, of this paper is that there is a definite lengthening of the charge collection time over that calculated by usual methods. This effect does not vary with different types of ionizing particles. No explanation for this effect is offered.
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    Analysis of passive mode-locking in lasers
    (1975) Smayling, Michael C.; Rabson, Thomas A.
    The passively mode-locked laser is modeled as a regenerative oscillator. An organic dye used as a saturable absorber is treated as the only nonlinear element in the feedback loop. Using a transcendental equation to represent the transfer function of the inhomogeneously broadened, "energy saturated" dye, numerical analysis shows that a Gaussian pulse is a steady state solution. For the example considered, in which an NdsYAG laser is mode-locked by an Eastman 974 dye, the initial shortening of the pulse by the dye is .6%, and approximately 1 to 2 passes are required to reach steady state.
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    Characterization of Iron Doped Lithium Niobate for Holographic Storage Applications
    (1976-06-20) Shah, Rajiv R.; Kim, Dae M.; Rabson, Thomas A.; Tittel, Frank K.
    A detailed study of eight systematically chosen Fe:LiNb03 crystals is presented. Correlation between the photorefractive sensitivity and various chemical properties of Fe:LiNb03 is investigated in order to ascertain optimum performance of Fe:LiNb03 crystals in holographic storage and display applications. Concentrations of Fe2+ and Fe3+ ions have been determined from optical and EPR spectra while impurities have been detected from x-ray emission and infrared spectra. Particular emphasis is placed on investigating the dependence on Fe3+ ion concentrations of the photorefractive sensitivity. The photorefractive sensitivity is shown to depend primarily on the concentration of Fe2+ ions in Fe:LiNb03. This fact seems to suggest that Fe2+ ions are the impurity centers responsible for the photorefractive effect in Fe:LiNb03. Spectral dependence of the photorefractive sensitivity and its modification due to oxygen annealing are also reported. Our results indicate that an unannealed Fe:LiNb03 crystal containing 0.05 mole % Fe with 20-25% of the ions in the Fe2+ state and the remainder in the Fe3+ state possesses the most favorable photorefractive sensitivity.
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    Coherence and polarization measurements of light
    (1968) Underwood, Clarence Roy; Rabson, Thomas A.
    A technique for measuring the coherence properties of a light beam was proposed and verified. By performing certain operations on the beam, the coherence measurement reduces to a simple measurement of percent polarization. Measurements using this technique were performed on a beam from a He-Ne laser. Extensions of the presented experimental method were suggested.
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    Deposition, characterization, and applications of thin film lithium niobate
    (1990) Baumann, Robert Christopher; Rabson, Thomas A.
    Ferroelectric thin films of lithium niobate have been epitaxially grown on a variety of silicon and gallium arsenide substrates by reactive r.f. sputtering. The deposition process was optimized by independently varying the substrate temperature, oxygen-argon ratio, target mixture, substrate type, and deposition times. The results of these tests are presented. The lithium niobate thin films were structurally analyzed using Bragg x-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques to determine their orientation, grain size, and domain structure. Electrical characterization included C-V measurements utilized to calculate the permittivity, I-V to obtain the resistivity, and photocurrent measurements to verify the existence of a bulk photovoltaic and pyroelectric effect in the thin films. In addition, preliminary results on prefabricated devices are presented as well as a review of the pertinent effects and potential device applications based on thin films of lithium niobate.
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    Development of a computer controlled continuous wave ultraviolet-visible dye laser spectrometer
    (1979) Pollock, C. R. (Clifford R.); Tittel, Frank K.; Dunning, F. Barry; Rabson, Thomas A.
    The goal of this research was to design and develop a computer-controlled source of coherent, narrowline radiation, tunable in the ultraviolet range from 26 to 4 nm. This was accomplished by using a DEC LSI-11 minicomputer with CAMAC interface to control a single frequency dye laser, a second harmonic generation (SHG) crystal, beam directing optics, and diagnostic equipment. The computer system provided control of initialization, fine and coarse resolution scanning, wavelength calibration, and the acquisition and processing of data. Because of the number of interrelated adjustments necessary to tune a single-frequency ultraviolet source, computer control was needed for both convenient operation and optimum ultraviolet power. A new dye ring laser was designed for high single mode in the visible and ultraviolet regions. The motivation for this research came from the increasing need for a convenient, high-resolution, ultraviolet source of radiation for spectroscopic studies of molecules and atoms. This research has achieved i) a new level in resolution and power for CW ultraviolet radiation sources, and ii) has developed the software to conveniently control a CW visible-ultraviolet spectrometer.
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    Electrical and switching characteristics of lithium niobate thin films
    (1996) Chen, Jing; Rabson, Thomas A.
    C-V and I-V measurements combined with pulse application were employed to study the electrical characteristics of lithium niobate thin film samples. Though the C-V measurements showed some classical features, a lithium drifted n-i-p junction model was postulated to explain the low nominal dielectric constant in C-V characteristics. The I-V characteristics were analyzed and the field dependence was determined to be Frenkel-Poole emission at low field and possibly Fowler-Nordheim at high field. A four-pulse dual-polarity pulse train was then used to study the switching kinetics of these thin films. The resulting transient current was captured and unstable switching was found in some samples. The polarization reversal was found to be dominated by forward domain growth with virtually no sideways motion. Finally, some important time constants such as nucleation time and domain wall growth time were determined and analyzed.
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    Electrical characterization of thin-film lithium niobate
    (1985) Fabiny, Larry; Rabson, Thomas A.; Wilson, William L.; Rau, Carl
    The electrooptic properties of a thin film of lithium niobate were studied. The film was deposited on an n-type silicon substrate by RF sputtering. The short circuit photocurrent was measured as a function of time, and the voltage dependence of current and capacitance under light and dark conditions was measured. Photocurrents up to 16.1 pA were obtained with a light intensity of .5 mW/cm . With one exception, all photocurrent flowed from the A1 contact to the Si substrate. The current was linear for | Vapp | < .5 volts. At higher voltages, a thermal current was generated. It was found that the current required several minutes to reach its steady state value when the applied voltage was changed. The film was shown to possess some of the ferroelectric properties present in bulk crystals. Although no crystallographic studies have been done, the electrical measurements indicate that the LN film is polycrystalline.
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    Electrical characterizations of lithium niobate thin films in a metal-ferroelectric-semiconductor capacitor
    (2002) Wang, Xuguang; Rabson, Thomas A.
    A LiNbO3 thin film Metal-Ferroelectric-Semiconductor capacitor is analyzed with various electrical characterization methods for studying the polarization switching and the thin film conduction behavior. The polarization density vs. electric field (P-E) curve shows that the remnant polarization is 16.85muC/cm2 and the coercive field is 117.25 KV/cm when maximum applied field is 286.2KV/cm for a sinusoidal input waveform. The capacitance vs. voltage bias (C-V) curve further demonstrates that the polarization charge is the dominant charge in controlling the ferroelectric semiconductor interface property. The switching transient current curve from a dual polarity four pulses chain study (P-S) gives the switching time of the sample about 80--100ns. Current vs. voltage (I--V) curve is explained with a back-to-back Schottky barrier controlled conduction mechanism. These electrical characterization results demonstrate that LiNbO3 is a promising candidate for a Metal-Ferroelectric-Semiconductor-Field-Effect-Transistor (MFSFET) non-volatile non-destructive memory application.
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    GALLIUM-ARSENIDE SUBMILLIMETER PHOTOCONDUCTIVE DETECTION
    (1974) CROWLEY, JAMES DUANE; Rabson, Thomas A.
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    HIGH ELECTRIC FIELD CONDUCTION ANISOTROPIES IN SEMICONDUCTORS
    (1970) GAYLORD, THOMAS KEITH; Rabson, Thomas A.
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    Interferometric Studies of Mode Locked Nd3+: Glass Lasers
    (1975-03-20) Shah, Rajiv R.; Rabson, Thomas A.; Kim, Dae M.
    A general technique for measuring the electric field vector of the ultrashort pulses from mode locked laser systems is described. The technique is applied to perhaps the most difficult laser to analyze, the dye mode locked, Nd3+:glass laser whose pulses change rapidly in bandwidth and amplitude, are chirped, and can occur in quite short pulse trains. The results of these measurements indicate a rather rapid change in the phases between modes and a plot of the phase change as a function of mode frequency has been obtained.
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    Interferometric studies of ultrashort pulses
    (1974) Shah, Rajiv Rajaram; Rabson, Thomas A.
    The purpose of this work is to study the evolution of ultrashort pulses in mode-locked pulse trains generated by a Nd: glass laser (at 1.6 microns) mode locked by a saturable absorber. Using an infra-red sensitive image converter camera, streaked interference fringes and hence the fringe visibility curves have been obtained for the interference of picosecond pulses separated by zero, one, two and three cavity transit times. The pulses under observation were in the central region of the pulse-trains, typically 1-15 nanoseconds wide. The shape of the fringe visibility curves and the decrease in the region of coherence with the increase in the separation in the pulse train, of the pulses that overlap to give the interference fringes is a good measure of the correlation of the pulses in that region. Further information on the type of pulses being investigated by the interferometric method was obtained by monitoring the time and spectral structure of the pulse trains. This was achieved by using two-photon-fluorescence, a 3.6 meter diffraction spectrometer and a fast photodiode-oscilloscope combination. The main features of the experiment are: (1) a 17 meter optical delay path (55 nanoseconds) which enabled observation in the central region of the pulse train, and (2) an experimental set up that allowed the observation of (a) streaked interference fringes (b) two-photon-fluorescence (c) the spectrum and (d) the intensity profile simultaneously, and for every single shot of the laser.
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    Investigation into the polarization of the beams of a Nd≥+ -barium crown glass laser operated at liquid nitrogen temperature
    (1967) Huang, Kuo-Chao; Rabson, Thomas A.
    By designing a greatly improved high time-resolution polarimeter, measurements and calculations, at various pumping levels, of the time variation of polarization of the beams of a Nd34-barium crown glass laser have been made at liquid nitrogen temperature. It was found that, as far as the time-variation behavior of polarization is concerned, operation of the laser at 77°K or roam temperature makes no qualitative difference. Under normal pumping conditions, the majority of spikes have degrees of polarzation greater than 50%. The average degree of polarization per spike over one flash generally tends to go down with increasing pumping energy. Unfortunately the variation of polarization with time is so complicated that no preferred relation between polarization and time can be concluded. The sources of polarization have been discussed in detail, and the experimental results interpreted. The polarization properties of the polarized part of each spike ---e.g. the direction of rotation and orientation and ellipticity of the polarization ellipse-- have also been investigated. In addition, the existences of the multimode emission and the coherence between Ex and Ey of the light waves of this laser were justified by this experiment.
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    Klystron frequency stabilization with a pound discriminator
    (1962) Livingston, Robert McLean; Rabson, Thomas A.
    The problem involved in this thesis was to construct a source of microwave frequency electromagnetic energy to be used as the signal source of a microwave maser. The maser was intended to have a signal frequency of 9 - 10 kmc. and a pump frequency of 22 - 25 kmc. For this purpose it is necessary to have a signal source whose frequency is accurately known and will remain constant. The frequency-stabilized source constructed made use of a reflex klystron and a Pound discriminator. The components of the system, the klystron, the discriminator, and the amplifier, are analyzed and their calculated and actual performance presented. It is shown that the Pound discrimiator can be made more sensitive by allowing its crystal detectors to have unequal sensitivities, instead of the usual practice of equalizing their sensitivities. The actual performance of the system in stabilizing the frequency of oscillation is presented and compared with the expected requirements of the signal source of a microwave maser. The system was found to provide a frequency stability of 5 parts in 106, which will in general be adequate for the intended purpose.