No description available.

In this study, we study the polarization dependence, gain property, and amplified spontaneous emission in Cr4+: YAG crystal fibers. Cr4+: YAG crystal has an ultra-wide bandwidth of 300 nm. Cr4+: YAG crystal fibers fabricated through laser heated pedestal growth technique are suitable for the applications of fiber amplifiers, fiber lasers, and broadband light sources. The experiment results showed that the polarization-dependent loss has a severe variation as the optical wavelength change. The maximum polarization-dependent loss was up to 18 dB. The main reason of such a large polarization-dependent loss is the combination of multimode interference and the birefringence induced by the non-uniformity of optical waveguide structure and residue strain in Cr4+: YAG crystal fibers. Thus, the results of polarization-dependent loss can be used as a feedback parameter to improve the fabrication process. In the experiment of gain property, bi-directional pump and double-pass transmission scheme was adopted and a 0.2 dB net gain was obtained for the first time at signal wavelength of 1400 nm, pumping wavelength of 1060 nm, and total pumping power of 2.8 W. It shows that Cr4+: YAG crystal fiber has potential to be developed as a broadband fiber amplifier. In the measurement of amplified spontaneous emission spectrum, a wide bandwidth of amplified spontaneous emission of 300 nm with total power of 50 £gWwas obtained at 0.2W pumping power condition. The coupling efficiencies from amplified spontaneous emission to single mode fibers and multimode fibers were 1.5 % and 9.9 %, respectively. This result reveals that it has potential to be developed as a broadband light source. To improve the optical properties of Cr4+: YAG crystal fiber in the future, improving the uniformity of optical fiber waveguide and reducing the residue strain in Cr4+: YAG crystal fiber may suppress the polarization-dependent loss; increasing the fiber length, decreasing the mode number, and employing a cladding pump technique with a well-distributed pump power in the crystal fiber to alleviate the excited state absorption may raise the gain performance and the amplified spontaneous emission power.

According to the regulation announced by Bureau of Standard, Metrology & Inspection (BSMI) of Ministry of Economic Affairs (MOEA), lamp fixtures must follow safety and electromagnetic compatibility (EMC) standards. However, the self-ballasted fluorescent lamps in the fixture should only be approved by the safety test but not regulated by EMC standard. Obviously, fixtures without light bulbs do not generate any electromagnetic noise. Electromagnetic interference (EMI) comes from the fluorescent light bulb embedded with an electronic ballast which included an inverter with high-frequency switching. A variety of tests demonstrate evidently that a fixture with different self-ballasted compact fluorescent lamps may possibly violate the EMC standard, revealing the absurdity of the regulation. In fact, self-ballasted fluorescent lamps use mostly self-excited electronic ballasts. The operating frequencies for this kind of electronic ballasts can not be precisely controlled due to the influence of many factors. They are not operated at a specified frequency but in a frequency range. This means that the generated EMI spectrum is hardly predicted, especially when a fixture is fitted by light bulbs from several manufacturers. This research inducts the worst cases from numerous measurements on a fixture with 1 piece to 8 pieces of light bulbs, and then attempts to design an EMI filter for all cases. As a result, a lamp fixture with the filter at the line input terminal can suppress the EMI. As long as the consumer buys the lamp fixture which are installed with the EMI filter together with any bulb in use, EMI noise can comply with standard limits.

In this work, interference and coherence phenomena, appearing in atomic and molecular ensembles interacting with coherent light sources, as electromagnetically induced transparency (EIT), coherent population trapping (CPT), and slow group velocity of light are investigated. The goal of the project is to make the steps towards various applications of these phenomena, first, by studying them in solid media (which are the most advantageous for applications), second, by suggesting some novel applications such as CPT-based plasma diagnostics, and realization of new types of solid-state lasers (based on suppression of excited-state absorption via EIT). The third goal of the project is extension of coherence and interference effects well-known in optics to the gamma-ray range of frequencies and, correspondingly, from atomic to nuclear transitions. A particular technique of chirped pulse compression applied to M??ossbauer transitions is considered and the possibility of compression of M??ossbauer radiation into ultrashort gamma-ray pulses is analyzed. The theoretical treatment of the interference and coherence effects is based on the semiclassical description of atom-light interaction, which is sufficient for correct analysis of the phenomena considered here. Coherent media are considered in two-, three-, and four-level approximations while their interaction with light is studied both analytically and numerically using the Maxwell-Bloch set of equations.

The vibrational potential energy surfaces in electronic ground and excited states of several ring molecules were investigated using several different spectroscopic methods, including far-infrared (IR), Raman, ultraviolet (UV) absorption, fluorescence excitation (FES), and single vibronic level fluorescence (SVLF) spectroscopies. Based on new information obtained from SVLF and millimeter wave spectra, the far-IR spectra of coumaran were reassigned and the one-dimensional ring-puckering potential energy functions for several vibrational states in the S0 ground state were determined. The barrier was found to be 154 cm-1 and the puckering angles to be ± 25°, in good agreement with the millimeter wave barrier of 152 cm-1 and puckering angles of ± 23°. Moreover, the UV absorption and FES spectra of coumaran allowed the one-dimensional ring-puckering potential energy functions in the S1 excited state to be determined. The puckering barrier is 34 cm-1 for the excited state and the puckering angles are ± 14°. Several calculations with different basis sets have been carried out to better understand the unusual vibrational frequencies of cyclopropenone. It was shown that there is strong interaction between the C=O and symmetric C-C stretching vibrations. These results differ quantitatively from a previous normal coordinate calculation and interpretation. The vapor-phase Raman spectrum of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene was analyzed and compared to the predicted spectrum from DFT calculations. The spectrum further shows it has D2h symmetry, in which the skeletons of both rings are planar. The infrared and Raman spectra of vapor-phase and liquid-phase 1,4-benzodioxan and 1,2,3,4-tetrahydronaphthalene were collected and the complete vibrational assignments for both molecules were made. Theoretical calculations predicted the barriers to planarity to be 4809 cm-1 for 1,2,3,4-tetrahydonaphthalene and 4095 cm-1 for 1,4-benzodioxan. The UV absorption, FES, and SVLF spectra of both molecules were recorded and assigned. Both one and two-dimensional potential energy functions of 1,4-benzodioxan for the ring-twisting and ring-bending vibrations were carried out for the S0 and S1(π,π*) states, and these were consistent with the high barriers calculated for both states. The low-frequency spectra of 1,2,3,4-tetrahydronaphthalene in both S0 and S1(π,π*) states were also analyzed.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

The research presented in this dissertation was performed in the Atomic, Molecular and Optical (AMO) physics laboratory at the University of Manitoba. Atomic beams of the two-valence-electron heavy atom systems, barium and ytterbium, were investigated with low energy electron scattering and optical emission studies. Both the ground states and laser excited states were investigated as a function of incident electron beam energy from 10 eV to 50 eV. Measurements of relative cross sections and polarization for 583 nm and 554 nm line emission from the (6s7p)1P1 and (6s6p)1P1 states of barium excited by electron impact from both the ground states and the optically pumped metastable (6s5d)1D2 are reported. Data are normalized to absolute cross sections for the ground state (6s2)1S0→(6s6p)1P1 state transition due to electron scattering, with corrections for branching ratios and cascading from higher states to deduce the total level excitation cross sections. Results are also presented for the first studies of the 399 nm line emission from laser-excited ytterbium, yielding an upper limit on the apparent cross section for the (6s6p)3P1→(6s6p)1P1 transition. Results are compared with the latest theoretical models and previous data, where available. / October 2015

No description available.

Brake squeal is a common noise problem encountered in the automotive industry. Higherfriction coefficients and weight reduction recently led to higher vibration levels in the audiblefrequency range. This quality issue becomes economic due to penalties imposed to the brakesupplier although no robust design method exists. The industrial practice thus relies on costlyprototyping and adjustment phases. The evolution of computational power allows computationof large mechanical assemblies, but non-linear time simulations generally remain out of reach.In this context, the thesis objective is to provide numerical tools for squeal resolution at earlydesign stages.Parameterized reduction methods are developed, using system real modes as Rayleigh-Ritzvectors, and allow very compact reduced models with exact real modes. The proposed ComponentMode Tuning method uses the components free/free modes as explicit degrees of freedom.This allows very quick sensitivity computation and reanalyzes of an assembly as function oflocal component-wise parameters. Non-linear time simulations are made possible through twoingredients. A modified non-linear implicit Newmark scheme and a fixed Jacobian are adaptedfor contact vibrations. The brake is reduced keeping a superelement with exact real modes anda local non-linear finite element model in the vicinity of the pad/disc interaction.A set of design tools is illustrated for a full industrial brake model. First, instant stabilitycomputations and complex mode trajectories are studied. Modal interactions and non-linearphenomena inside the limit cycles are thus well understood. Time/frequency correlations areperformed using transient modal identification and space-time decomposition. A time domainmodal damping model is also shown to be very useful. The modification of a critical componentfor squeal resolution is finally tested and validated.