R-3 Repository :: Browsing by Author "Kim, Dae M."

Browsing by Author "Kim, Dae M."

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A classical approach to the critical equilibrium in a binary sustem
(1976) Kwon, O'Dae; Kobayashi, Riki; Kim, Dae M.
Recently extensive investigations have been directed toward the critical phenomena occurring in the liquid column of binary mixtures in a manner similar to the case of a pure component. This thesis presents a self-consistent analytic theory concerning these phenomena for "simple" binary systems. In particular, this thesis discusses, (1) a detailed derivation of the equation of state concerning the gravity-induced inhomogeneity (2) power law dependence of the coexistence curve (3) geometrical realization of the coexistence curve in a miscibility gap (4) thermodynamic stabilities in a binary system. In addition, the possibility of applying the present theory to thermodynamic measurements and the analogy between unitary and binary critical equilibria are discussed.
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.
Computer controlled intracavity second harmonic generation in a CW Dye Ring Laser
(1980) Marshall, Charles McAlister; Tittel, Frank K.; Wilson, William L.; Kim, Dae M.
The purpose of this research has been to develop a source of high power narrowline ultraviolet radiation suitable for spectroscopic applications. This was accomplished by using intracavity second harmonic generation in a computer controlled continuous wave dye ring laser. A DEC POP 11/3 minicomputer was used to control laser tuning elements and nonlinear crystal temperature to provide constant UV output powers of over 1 mW with a short term linewidth of + 5 MHz at the peak of the Rh6G gain curve. The computer system with a CAMAC interface provided control of laser calibration and scanning as well as data acquisition and storage over the wavelength range from 285 to 35 nm. The spectrometer development included the design-of an astigmatically compensated ring laser to provide optimal conversion of intracavity fundamental power to second harmonic UV output. Both Brewster cut and normal incidence crystals were analyzed to determine the most efficient insertion technique. The Brewster cut crystal was found to provide the highest output powers with the fewest complications. The system development also included techniques for long range temperature tuning of the nonlinear crystal to provide constant UV output over continuous frequency intervals of 32 GHz. The performance of the spectrometer was evaluated through studying the absorption spectra of SO around 3 nm. A simultaneous visible output at 6 nm was used to provide a reference spectra of the well documented fluorescence of I2.
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.
Nonlinear Dynamic Theory for Photorefractive Phase Hologram Formation
(1976-01-20) Kim, Dae M.; Shah, Rajiv R.; Rabson, Thomas A.; Tittel, Frank K.
A nonlinar dynamic theory is developed for the formation of photorefractive volume phase holograms. A feedback mechanism existing between the photo-generated field and free electron density, treated explicitly yields the growth and saturation of the space charge field in a time scale characterized by the coupling strength between them. The expression for the field reduces in the short time limit to previous theories and approaches in the long time limit the internal or photovoltaic field. Additionally, the phase of the space charge field is shown to be time dependent.
Phase holographic studies of the conductivity of Fe-doped LiNbO¿
(1979) Bienvenu, Michael Patrick; Rabson, Thomas A.; Kim, Dae M.; Tittel, Frank K.; Wilson, William L.
The writing process involved in volume phase holographic storage in LiNbO3 has been extensively studied, but no quantitative work exists concerning the decay of holograms. Since direct electrical conductivity measurements are difficult, if not impossible, decay rate measurements can provide an accurate figure for the material's conductivity. A coupled-wave theory developed by Kogelnik is presented describing diffraction by a phase grating with unslated fringes in a lossy medium. Next, a dynamic theory of hologram grating developed by Kim is presented. Using classical E-M theory, the hologram decay is predicted to be a sum of exponentials. Experimental data on writing and decay processes is presented which agree well with Kim's theoretical predictions, but which differ markedly from the expected decay behaviour. An excellent fit to the experimental decay curves was obtained by assuming a time dependent conductivity of the form a(t) = CJQ + e. The data show that T, the time constant involved, varies with the iron doping level in the crystal. A model is proposed to explain the phenomenon, involving metastable trapping centers releasing electrons into the conduction band.
Photovoltaic effect and photoconductivity in triode-sputtered thin-films of Hgl-XCdXTe
(1980) Lopez, Jorge Luis; Wilson, William L.; Kim, Dae M.; Dodds, Stanley A.
A study was made of trîode sputtered thin films of Hg. Cd Te to determine their physical, electronic, and electrooptic characteristics. The films were sputtered from inhomogeneous targets made from HgTe enriched Hg CdTe onto glass substrates. The composition of the films was determined by electron microprobe. Electrical characteristics were determined by resistivity and Hall data, and electrooptic response by exposure to a black body source through a grating monochrometer. The films exhibited photoconductivity and photovoltaic response in the range from at least 2-1 g. The photovoltage was believed to be due to a graded-gap mechanism induced by a lateral compositional gradient. The frequency response of the detectors to a modulated input signal was found to cut off above 3.5 Hz for the photoconductivity and beyond 44 Hz for the photovoltaic effect. The difference is attributed to different lifetimes for electrons and holes. Best D (5,6) for the photoconductivity was 1 , and watts for the photovoltaic effect.
Remote detection of oil under ice using fluorescence
(1981) Rivet, Genevieve J.; Rabson, Thomas A.; Kim, Dae M.; Wilson, William L.
The first phase of a project devoted to the exploitation of laser induced fluorescence for detection of oil leaks under ice is presented. The basic principle is as follows: The radiation from a nitrogen laser, used as an excitation source, goes through the ice and irradiates a layer of oil under the ice. The oil fluorescence , which emits radiations in the range of about 5 nm, can pass back through the ice and be detected. Once the prominence of sea ice fluorescence was established and measured to be intense under certain conditions, it was shown that an absolute fluorescence detection could not be used to reveal leaks of oil underneath the ice. A detection technique based on spectral filtering which transmit mainly the fluorescent emission from oil is investigated and shown to be a feasible technique within certain limits.
RF sputtered Hg¿-XCdXTe infrared detectors
(1980) Thielsch, Donald Kurt; Wilson, William L.; Kim, Dae M.; Johnson, Don H.
Thin films have been prepared by RF sputtering from an inhomogeneous HggCdg 2Te target onto glass substrates. Both mercury and argon were used as sputter gases. Each film consisted of a Hall bar and a 2-element detector array. Electron microprobe analysis showed the existence of a lateral composition gradient. Electrical measurements provided resistivity, mobility, and carrier concentration information. The carrier concentration was found to vary with sputter deposition rate. The detectors exhibited both photoconductive and photovoltaic response. The photovoltage was believed to have been due to a graded band gap, induced by the composition gradient. Spectral response ranged from less than 4 microns to more than 14 microns. Best photoconductive D (5, 275) was 5.5 x 17 cm Hz1/2 W-1 and best photovoltaic D (5°, 275) was 1.22 x 17 cm Hz1/2 W-1 for detectors cooled to 125° K.
Study of the Equivalent Electron Drift Field Characteristics in LiNb0₃ by Phase Holography
(1976-06-20) Kim, Dae M.; Shah, Rajiv R.; Rabson, Thomas A.; Tittel, Frank K.
An analysis of the diffraction efficiency of photorefractive holograms in ferroelectric crystals is shown to provide a novel technique for determining the nature and magnitude of the equivalent electron drift field. For a Fe doped lithium niobate crystal (0.05% per mole) we find that the total field consists of an intensity independent internal field of 8.5 KV/cm and a photo-generated field given by the conversion factor 1.4Ã 10⁶ V-cm/W.
The effect of gain saturation on actively mode-locked laser pulses
(1983) Lekkas, Panayotis C.; Kim, Dae M.; Rabson, Thomas A.; Wilson, William L.
The goal of this thesis is to take into account the gain saturation that occurs within pulse duration for actively node-locked lasers and to discuss its effects on the generated pulses. The population inversion, obtained analytically using a perturbation scheme, has been found to vary considerably within pulse envelope. An assumingly Gaussian pulse has been followed along its round-trip in the laser cavity through the active medium and the modulator, and by incorporating the time-dependent gain for the first time in the analysis, self-consistency relations have been found. The resulting pulse characteristics* based on typical Nd:YAG laser parameters show a strong dependence of the output pulsewidths on the pump intensity. as well as of the interpulse spacing on the length of the active medium. The population inversion droped by two orders of magnitude within the duration of the incoming pulse and the extent of the depletion was increasing for increasing pump intensities. By varying the input field from 1 up to 1.5x1 V/m the pulsewidth was found to vary from 1.4 to 2.1 psec while the interpulse spacing jittered within 1.7 psec for variations of the length of the active medium from 1 cm to 5 cm.

Browsing by Author "Kim, Dae M."

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