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Raman and NMR Relaxation Studies of Molecular Dynamics in Liquids

Description: Raman vibrational bands are sensitive to fluctuations in the molecular environment. Variations in the bandwidth and peak position can then be utilized to monitor molecular forces and interactions present in condense phases. Nuclear Magnetic Resonance (NMR) provides a convenient probe for the study of molecular reorientation in liquids since nuclear spin relaxation times are dependent on the details of molecular motion. Presented here is the solvent study of the Raman bandwidths and frequency displacements of the mode of the compounds CH3MCI3 (M = C, Si, Ge, Sn) in a number of solvents of widely varying molecular structure. Also, a detailed isotope dilution study of the modes in CH2CI2/CD2CI2 mixtures is presented. In this set of experiments, I observed broadening of the v1 mode of CH2C12 upon dilution,which is the first experimental observation of such behavior. The temperature-dependent carbon-13 relaxation times and nuclear Overhauser enhancements in neat dichloromethane were measured. In this study we found that the molecular reorientation of this molecule was highly anisotropic, but could be well characterized assuming quasi-symmetric top behavior. In addition, in order to gain a more complete understanding of the reorientational dynamics in dichloromethane, we analyzed the 13-C NMR relaxation of CH2CI2 both in "inert" solvents of differing viscosities and in interactive solvents of varying Lewis basicities. Various theoretical models were also applied in order to characterize dichloromethane1s reorientational dynamics.
Date: August 1987
Creator: Rodriguez, Arturo A. (Arturo Angel)
Partner: UNT Libraries

Cryptography, quantum computation and trapped ions

Description: The significance of quantum computation for cryptography is discussed. Following a brief survey of the requirements for quantum computational hardware, an overview of the ion trap quantum computation project at Los Alamos is presented. The physical limitations to quantum computation with trapped ions are analyzed and an assessment of the computational potential of the technology is made.
Date: March 1, 1998
Creator: Hughes, Richard J.
Partner: UNT Libraries Government Documents Department

Intensity dependent waiting time for strong electron trapping events in speckle stimulated raman scatter

Description: The onset of Stimulated Raman scatter from an intense laser speckle is the simplest experimentally realizable laser-plasma-interaction environment. Despite this data and recent 3D particle simulations, the controlling mechanism at the onset of backscatter in the kinetic regime when strong electron trapping in the daughter Langmuir wave is a dominant nonlinearity is not understood. This paper explores the consequences of assuming that onset is controlled by large thermal fluctuations. A super exponential dependence of mean reflectivity on speckle intensity in the onset regime is predicted.
Date: January 1, 2009
Creator: Rose, Harvey; Daughton, W & Yin, L
Partner: UNT Libraries Government Documents Department


Description: Vibrational spectra provide one of the most direct methods for the study of composition and structure of simple covalently bound species. In molten salts, where the presence of complex ionic species is debated, the application of the powerful techniques of infrared and Raman spectroscopy was hampered by severe experimental difficulty. The literature from 1925 to the present time is reviewed, and unusual aspects of experimental techniques as well as tue results obtained are covered. The discussion is limited to ionic salts except where the spectra of molecular liquids make a direct contribution to the understanding of related ionic liquids. Literature references number 62. (auth)
Date: July 26, 1963
Creator: James, D.W.
Partner: UNT Libraries Government Documents Department

Interpreting X-ray and auger resonant Raman spectra

Description: We discuss resonant Raman Scattering in atoms within the context of conservation of energy, arguing that energy conservation determines the principal features of spectra taken at a resolution comparable to the natural widths of the transitions involved. Example systems applicable to atoms or solids are calculated using the model by Tulkki and Aberg, and the model is discussed in terms of energy conservation. Finally, results for X-ray resonant Raman scattering in Xe and Auger resonant Raman scattering in Ar are presented and the two processes are contrasted.
Date: December 31, 1996
Creator: Lebrun, T.
Partner: UNT Libraries Government Documents Department

Observation of stimulated raman scattering in an optical fiber at the Fermilab A0 photoinjector

Description: We have observed stimulated Raman scattering in a 2 km long optical fiber injected with an 81 MHz train of {approximately}80 ps pulses from a modelocked Nd:YLF oscillator operating at {lambda} = 1054 nm.
Date: September 1, 1998
Creator: Fry, A.R.; Taylor, B.; Fitch, M.J. & Melissinos, N.C., Fermilab
Partner: UNT Libraries Government Documents Department

Observation of multiple mechanisms for stimulating ion waves in ignition scale plasmas. Revision 1

Description: The laser and plasma conditions expected in ignition experiments using indirect drive inertial confinement have been studied experimentally. It has been shown that there are at least three ways in which ion waves can be stimulated in these plasmas and have significant effect on the energy balance and distribution in the target. First ion waves can be stimulated by a single laser beam by the process of Stimulated Brillouin Scattering (SBS) in which an ion acoustic and a scattered electromagnetic wave grow from noise. Second, in a plasma where more than one beam intersect, ion waves can Lie excited at the `beat` frequency and wave number of the intersecting beams,, causing the side scatter instability to be seeded, and substantial energy to be transferred between the beams [R. K. Kirkwood et. al. Phys. Rev. Lett. 76, 2065 (1996)]. And third, ion waves may be stimulated by the decay of electron plasma waves produced by Stimulated Raman Scattering (SRS), thereby inhibiting the SRS process [R. K. Kirkwood et. al. Phys. Rev. Lett. 77, 2706 (1996)].
Date: March 3, 1997
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Interaction between stimulated raman scattering and ion acoustic waves in ignition relevant plasmas

Description: We have observed that the scattering of light by stimulated Langmuir waves (SRS) in ignition scale plasmas is dependent on the properties of the ion acoustic wave, indicating that a nonlinear coupling between the two waves limits the scattered energy.
Date: June 1, 1997
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Raman study of phonons in Sr{sub 3}Mn{sub 2}O{sub 6.54} and Sr{sub 3}Mn{sub 2}O{sub 7} layered manganites

Description: Polycrystalline Sr{sub 3}Mn{sub 2}O{sub 6.54} and Sr{sub 3}Mn{sub 2}O{sub 7} layered manganites were studied at room temperature using Raman spectroscopy. While the phonon spectrum of the stoichiometric Sr{sub 3}Mn{sub 2}O{sub 7} sample is consistent with the group theoretical analysis for the 14/mm structure, three additional modes are observed in the phonon spectrum of the oxygen deficient Sr{sub 3}Mn{sub 2}O{sub 6.54} sample. Based on an analysis of the temperature dependence of the Raman spectrum of Sr{sub 3}Mn{sub 2}O{sub 6.54} and a comparison with the Raman spectrum of LaSr{sub 2}Mn{sub 2}O{sub 7}, the authors conclude that the extra modes should be viewed as disorder induced Raman scattering.
Date: April 27, 2000
Creator: Guedes, I.; Mitchell, J. F.; Argyriou, D. & Grimsditch, M.
Partner: UNT Libraries Government Documents Department

Solid hydrogen structure

Description: The J=0{minus}>2 Raman signal from solid J=0 D{sub 2} or H{sub 2} reveals HCP structure when deposited at a rate 0.1 {le} R({mu}/min) {le} 40 onto MgF{sub 2} at T{sub d}/T{sub tp} > 0.3, a mixture of HCP and FCC crystals at 0.2 < T{sub d}/T{sub tp} < 0.3 and possibly a randomly stacked close packed structure at T{sub d}/T{sub tp} < 0.2, where T{sub tp} is the triple point temperature. Non-HCP crystals transform to HCP continuously and irreversibly with increasing T. Finally, the crystal size decreases with decreasing T{sub d} and increasing R, from {approximately} 1 mm at T{sub d} {approximately} 0.8 T{sub tp} and R {approximately} 2 {mu}/min to {approximately} 1 {mu}m at 0.25 T{sub tp} and R {approximately} 40 {mu}/min.
Date: November 1, 1994
Creator: Collins, G.W.; Unites, W.G.; Mapoles, E.R.; Magnotta, F. & Bernat, T.P.
Partner: UNT Libraries Government Documents Department

The photodissociation and reaction dynamics of vibrationally excited molecules. Technical progress report

Description: The goal of this Department of Energy sponsored research is to discover the properties, behavior, and dissociation dynamics of vibrationally energized molecules, which are crucial participants in many chemical reactions. The authors study vibrationally energized molecules by using an optical excitation scheme to prepare them and a subsequent photon to dissociate them into fragments that they detect with a spectroscopic probe. This technique, vibrationally mediated photodissociation, provides new information on vibrationally energized molecules and even provides a means of controlling the course of a molecular decomposition. During the most recent period of Department of Energy support, the authors have advanced this work in three directions: they have used vibrational overtone excitation to control the decomposition pathways in the tetra-atomic molecule isocyanic acid (HNCO) and unravelled the decomposition pathways in hydroxylamine (NH{sub 2}OH), they have implemented stimulated Raman excitation as the vibrational state preparation technique in vibrationally mediated photodissociation, and they have tested the limits of transient grating spectroscopy as a means of obtaining electronic spectra of vibrationally excited molecules.
Date: September 1, 1995
Partner: UNT Libraries Government Documents Department

Fiber optic probe for light scattering measurements

Description: This invention is comprised of a fiber optic probe and a method for using the probe for light scattering analyses of a sample. The probe includes a probe body with an inlet for admitting a sample into an interior sample chamber, a first optical fiber for transmitting light from a source into the chamber, and a second optical fiber for transmitting light to a detector such as a spectrophotometer. The interior surface of the probe carries a coating that substantially prevents non-scattered light from reaching the second fiber. The probe is placed in a region where the presence and concentration of an analyte of interest are to be detected, and a sample is admitted into the chamber. Exciting light is transmitted into the sample chamber by the first fiber, where the light interacts with the sample to produce Raman-scattered light. At least some of the Raman- scattered light is received by the second fiber and transmitted to the detector for analysis. Two Raman spectra are measured, at different pressures. The first spectrum is subtracted from the second to remove background effects, and the resulting sample Raman spectrum is compared to a set of stored library spectra to determine the presence and concentration of the analyte.
Date: January 1, 1993
Creator: Nave, S.E.; Livingston, R.R. & Prather, W.S.
Partner: UNT Libraries Government Documents Department

Effect of crossed beams irradiation on parametric instabilities

Description: Modification of the growth of scattering processes in the case of multiple beam irradiation compared to single beam irradiation has been investigated in a preformed plasma using Thomson scattrering of a short wavelength probe beam, and spectral and temporal analysis of reflected and transmitted light. First observations of the reduction of the amplitude of ion acoustic waves associated with stimulated Brillouin scattering, amplification of the amplitude of electron plasma waves associated with stimulated Raman scattering, and transfer of energy between crqssing beams with same frequency in a flowing plasma under crossed beam irradiation are reported.
Date: April 27, 1998
Creator: Labaune, C., Ecole Polytechnique, France
Partner: UNT Libraries Government Documents Department

A study of non-equilibrium phonons in GaAs/AlAs quantum wells

Description: In this thesis we have studied the non-equilibrium phonons in GaAs/AlAs quantum wells via Raman scattering. We have demonstrated experimentally that by taking into account the time-reversal symmetry relation between the Stokes and anti-Stokes Raman cross sections, one can successfully measure the non-equilibrium phonon occupancy in quantum wells. Using this technique, we have studied the subject of resonant intersubband scattering of optical phonons. We find that interface roughness plays an important role in resonant Raman scattering in quantum wells. The lateral size of the smooth regions in such interface is estimated to be of the order of 100 {Angstrom}. Through a study of photoluminescence of GaAs/AlAs quantum wells under high intensity laser excitation, we have found that band nonparabolicity has very little effect on the electron subband energies even for subbands as high as a few hundred meV above the lowest one. This finding may require additional theoretical study to understand its origin. We have also studied phonon confinement and propagation in quantum wells. We show that Raman scattering of non-equilibrium phonons in quantum wells can be a sensitive measure of the spatial extent of the longitudinal optical (LO) phonons. We deduce the coherence length of LO phonons in GaAs/Al{sub x}Ga{sub 1-x}As quantum wells as a function of the Al concentration x.
Date: November 1, 1996
Creator: Su, Zhenpeng
Partner: UNT Libraries Government Documents Department

Laser beam smoothing and backscatter saturation processes in plasmas relevant to National Ignition Facility hohlraums

Description: We have used gas-filled targets irradiated at the Nova laser to simulate National Ignition Facility (NlF) hohlraum plasmas and to study the dependence of Stimulated Raman (SRS) and Brillouin (SBS) Scattering on beam smoothing at a range of laser intensities (3{omega}, 2 - 4 10{sup 15}Wcm{sup -2}) and plasma conditions. We have demonstrated the effectiveness of polarization smoothing as a potential upgrade to the NIF. Experiments with higher intensities and higher densities characteristic of 350eV hohlraum designs indicate that with appropriate beam smoothing the backscatter from such hohlraums may be tolerable.
Date: October 1, 1998
Creator: Berger, R L; Cohen, B I; Decker, C D; Dixit, S; Glenzer, S H; Hinkel, D E et al.
Partner: UNT Libraries Government Documents Department

Characterization of plasma and laser conditions for single hot spot interaction experiments

Description: The LANL TRIDENT laser system is being used for fundamental experiments which study the interaction of self-focusing, stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in a single (diffraction limited) laser hot spot in order to better understand the coupling between these plasma instabilities. The diffraction limited beam mimics a single hot spot found in speckle distributions that are typical of random or kinoform phase plate (RPP or KPP) smoothing. A long scale length, hot plasma ({approximately} 1 mm, {approximately} 0.5 keV) is created by a separate heater beam, and the single hot spot beam is used to drive parametric instabilities. The focal plane distribution and wavefront of the single hot spot beam are characterized, and the intensity of the single hot spot can be varied between 10{sup 14}--10{sup 16} W/cm{sup 2}. The plasma density, temperature, and flow profiles are measured using gated imaging spectroscopy of collective Thomson scattering. Results of the laser and plasma characterization, and initial results of backscattered SRS, SBS, and beam steering in a flowing plasma are presented.
Date: November 1, 1998
Creator: Montgomery, D.S.; Johnson, R.P.; Cobble, J.A.; Fernandez, J.C.; Lindman, E.L.; Rose, H.A. et al.
Partner: UNT Libraries Government Documents Department

Regime for a Self-ionizing Raman Laser Amplifier

Description: Backward Raman amplification and compression at high power might occur if a long pumping laser pulse is passed through a plasma to interact resonantly with a counter-propagating short seed pulse [V.M. Malkin, et al., Phys. Rev. Lett. 82 (1999) 4448-4451]. One critical issue, however, is that the pump may be unacceptably depleted due to spontaneous Raman backscatter from intrinsic fluctuations in the amplifying plasma medium prior to its useful interaction with the seed. Premature backscatter may be avoided, however, by employing a gaseous medium with pump intensities too low to ionize the medium, and using the intense seed to produce the plasma by rapid photoionization as it is being amplified [V.M. Malkin, et al., Phys. Plasmas (2001)]. In addition to allowing that only rather low power pumps be used, photoionization introduces a damping of the short pulse which must be overcome by the Raman growth rate for net amplification to occur. The parameter space of gas densities, laser wavelengths, and laser intensities is surveyed to identify favorable regimes for this effect. Output laser intensities of 10(superscript ''17'') W/cm(superscript ''2'') for 0.5 mm radiation are found to be feasible for such a scheme using a pump of 10(superscript ''13'') W/cm(superscript ''2'') and an initial seed of 5 x 10(superscript ''14'') W/cm(superscript ''2'') over an amplification length of 5.6 cm in hydrogen gas.
Date: October 4, 2001
Creator: Clark, D.S. & Fisch, N.J.
Partner: UNT Libraries Government Documents Department