The aim of the thesis was to complete the development of the Czech version of the extremal ultraviolet (XUV) argon capillary laser working at the wavelength 46.9 nm and its adaptation for the first practical applications. A multi-discipline complex of mutually interconnected problems was analyzed and studied: The reasons for a capillary low life-time were investigated using defectoscopic methods, a pre- pulse regime influence was studied with the help of spectroscopy on a physical model. By performing necessary construction and technology changes as well as by the multi-parametric optimisation of working regime, the indicated weaknesses were suppressed. The XUV laser was focused into a footprint of the size about 100 µm and the apparatus was extended by a set of practical aids and accessories for special applications, especially for exposition of the samples at extreme temperatures. As practical applications of the XUV laser, measurements of multilayer mirror reflectivity and filter transmissivity were performed. Using the XUV laser for a thin layer deposition and radiation resistance testing was verified to be practicable in principle. Probably a first temperature dependence of an XUV laser ablation rate was measured, in the temperature range from -180 deg.C to +200 deg.C, on BaF2.

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archives@tulane.edu / Metal whisker formation has been an unwanted byproduct in electronics for the past 70 years. However, in that period, no one has come up with one mechanism that can explain all the collected data. This dissertation focuses on copper whisker formation in the presence of a sulfur-containing compound. Pulsed laser deposition is used to create a molybdenum disulfide thin film, and the resulting whiskers are analyzed with scanning electron microscopy and x-ray photoelectron spectroscopy. The copper whiskers are proven to be pure copper and can be several millimeters in length. The collected data supports a recrystallization-based mechanism, where the copper vapor on the surface recrystallizes at the base of the copper whisker, therefore, adding to the length of the whisker. / 1 / Megan Elizabeth Woods

Bibliography: p. 153-170. / The nature of optical whispering-gallery-mode resonances in a layered microcylinder is investigated numerically by studying the scattering characteristics and the internal electromagnetic fields of a normally-illuminated cladded dielectric fiber calculated using the boundary-value method. Computed resonant mode configurations are compared to the better-known results for homogeneous spheres and cylinders and coated spheres. It is shown that high-Q whispering-gallery-mode resonances can be supported by the curved interface between the core and cladding regions of a layered fiber if the core refractive index is sufficiently greater than that of the outer layer, and that these modes can be directly related to the so-called morphology-dependent resonances of a homogeneous cylinder of the same size and relative refractive index as the fiber core. The implications of these resonant modes for inelastic optical processes are made clear by developing a model for optical emissions from a molecule in the core of a capillary fiber. The results of the model show that the transition rates of molecules in the fiber core and near to the core/cladding interface are enhanced at frequencies corresponding to cavity resonances. It is shown experimentally that these high-Q cavity modes can be excited to above the threshold for laser emission by providing gain in the fiber core material. We have used a refractive dye-doped solvent as a gain medium and a fused-silica capillary to form the resonant cavity. Upon optical excitation of the dye by illuminating the fiber normally with the green beam from a frequency-doubled Nd:YAG laser, laser emission is emitted from the fiber core in the plane perpendicular to the fiber axis. We explain the novel spatial and spectral dependences of the laser emission in terms of the calculated frequencies and Q-values of the resonant cavity modes and the bulk properties of the cavity medium. We show that the thresholds observed in the laser system can be explained using a simplified rate-equation approach, and that this also explains some of the other observed features of the emissions. The heating of the dye solvent during a laser pulse has an observable effect on the resonance mode locations due to the temperature dependence of the refractive index. We demonstrate the use of observed laser spectra to determine the size and taper of the capillary fiber core.

Includes bibliographical references. / This thesis deals specifically with the operation of the Ti:Sapphire laser. The laser was obtained from BMI Industries in a kit form. The component parameters were first determined to use in theoretical models of the laser's operation. The laser was then assembled and optimized in order to get the most efficient output. Runs of shots were recorded at various tuned wavelengths and energies. This allowed accurate comparisons with the models and assessment of the practicability of use of the laser as the Stokes beam in a CARS system. The shot-to-shot noise was also measured and an attempt made to identify the major sources of this noise. Finally a comparison of the noise values for the Ti:Sapphire laser was made with the values for the dye laser presently used in CARS.

Laser-induced breakdown spectroscopy (LIBS) is an efficient tool for identification of elemental composition and characterization of materials. The concept of this technique is to focus a laser pulse of sufficiently high power on to a sample to create a plasma plume of atoms, ions, and molecules. The measurement of the resulting optical emission from these species provides the basis of the spectral analysis. Spectroscopic analysis of the plasma generated by Nd:YAG laser irradiation of wheat flour tortillas was carried out. A careful selection of spectral lines of Ca, Na and K which do not suffer from spectral interference was made. Among the spectral lines selected for analysis, the Na I 589.00 and 589.60-nm doublet lines were found to show the same intensity ratio values. A study on combustion was carried out with the use of LIBS. The main focus of this study was to compare results previously obtained using a rectangular slot burner with new results using a McKenna burner for equivalence ratios measurement in atmospheric premixed methane-air flames with ungated LIBS and also obtaining a temperature profile for our new burner. The Mckenna burner has a steady and less turbulent flame. Fortyive equivalence ratios were calculated. LIBS spectra of helium, argon and nitrogen were acquired using samples of pure gases at low pressures. The spectra from the three species showed continuum contributions which differ from one gas to the other. To better understand LIBS of gaseous samples, we have performed a study of the laser-induced plasmas in three gases, i.e., Ar, He, N2 and their mixtures. The evolution of plasma intensity and electron density, with time was studied at different laser pulse energies. Samples containing cerium, cesium and strontium were made with known concentrations and analyzed using laser-induced breakdown spectroscopy (LIBS). Powder samples are more challenging to analyze using LIBS than pellets. Spectra resulting from these samples under various experimental conditions were compared for possible interferences and other properties, placing particular interest in Ce II 418.65-nm, Cs I 852.11-nm and Sr I 460.73-nm atomic emission spectra lines because these were outstanding strong lines of these three aforementioned elements.

This thesis describes the design and construction of a portable laser induced fluorescence sensor. The objective was to create a low-cost, versatile, and modular laser induced fluorescence sensor for agricultural remote sensing. The sensor module should able to be integrated with different pieces of hardware. The objective was successfully accomplished with the creation of a sensor module that met all of the requirements. The sensor module integrates with a handheld unit for reading and visualizing the data that was constructed and is described in this work. Performance testing and experiments were carried out with the sensor module in the handheld device with a focus on plant physiology. In particular, chlorophyll fluorescence related to stress and ripeness was studied and fungal toxins found in corn were detected with this device. Ongoing work consisting of mounting the sensor module to an unmanned aerial vehicle and testing in flight is described.

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