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Thesis (Ph. D.)--Washington State University, December 2008. / Title from PDF title page (viewed on Apr. 13, 2009). "School of Mechanical and Materials Engineering." Includes bibliographical references.

Thesis (M.S.)--University of Michigan, 1963.

No description available.

No description available.

In this thesis, nanosecond pulsed lasers are used as the tools to generate microstructures on metal and glass. The applications of these structures are described too. The production of micro structures is demonstrated using diode-pumped solid state (DPSS) Nd:YVO4 lasers operating at wavelengths of 532nm or 1064 nm. The laser fluence and scanning speed are important parameters to control the results. The first part of thesis is on the laser generation of microstructures on metal surfaces. Copper (Cu) and titanium (Ti) have been studied. According to the reflectivity of metals, Cu is processed by a 532nm laser and Ti is processed by a 1064nm laser. It is shown that the periods of surface microstructures are highly dependent on the hatch distance (overlapping distance between laser scanning). Only if the laser fluence is greater than a threshold, may the microstructures on metals be induced. The thresholds are measured by the diameters of ablated areas at different fluence. Laser generated surface microstructures have been applied to modify the reflectivity of a Cu sample. It was found that laser induced surface microstructures on Copper can decrease the surface reflectivity by almost 97% between 250 nm and 700 nm. To find the mechanism of how to form microstructure on metal surface with laser, laser ablation and heating models have been studied. The 1D ablated numerical model is calculated in Matlab. The pressure of metal vapour is an important parameter, as it pushes the melted metal out of surface to form microstructures after re-solidification. The second part of thesis is on glass welding with microstructures on glass surfaces. The soda-lime glasses containing silver nanoparticles (from the company Codixx) have been studied and welded with Schott B270 glass. Compared with other techniques for welding glass, lasers offer the advantage of a relatively simple and flexible technique for joining the local area underneath the cover glass. Most of the laser energy is deposited in the Ag nanoparticle layer because of the large absorption coefficient at 532 nm. Expanded microstructures generated by the laser are applied to fill the gap between the glass surfaces. This is attributed to the formation of bubbles in the Ag nanoparticle layer after laser processing. The welded samples have the joint strength of 4.9 MPa and have great potential for industrial applications. A 3D analytical model is used to estimate the temperature of the glass after the laser pulse. The increase in temperature is about 129 °C. To induce the bubble in glass, many laser pulses are necessary. This is very different from the results for the metals.

The emphasis of this work has been in two areas of optical materials - the crystal-chemical development of new optical frequency converters and the synthesis and study of new hosts for Cr����� luminescence and lasing. A simple method has been developed to identify promising frequency-doubling materials containing triangular oxoanions by estimation of nonlinear susceptibilities. Implementation of this method and its results have generated predictive capabilities in determining the relationships among crystal structure, nonlinear properties, and threshold powers. The new noncentrosymmetric borate SrLiB���O������ is discussed; its structure is built from a 3-dimensional condensation of B���0��� units with channels alternately filled with Sr and Li atoms. From these studies, a prescription for new pyroborate frequency converters has been developed. The material CdC������C���H7NO���, has been synthesized and structurally characterized by single-ciystal X-ray diffraction. Three new alkaline-earth beryllium borates, built from unique 2- and 3- dimensional networks and frameworks, have been identified. The structure of SrBe���(B0���)��� consists of layers of composition [Be���(BO���)���] interleaved by Sr atoms. CaBeB���O��� is constructed from a Ca0��� polyhedral network and a beryllium borate network. In BaBe���(B0���)��� the structure is composed of a beryllium borate framework intermingled with a Ba-centered dodecahedral framework. Several materials with potential as hosts for Cr����� lasing have been analyzed. The structural study of the laser host LiSrAIF6 revealed the distortions at the Al site that contribute to the unique optical properties of the Cr����� -doped crystals. The family of solid state oxide A���MM'(B0���)��� is one of the largest families of oxide reported to date. Metal site preferences, disorder, solid solubility, and the interrelationship between this structure and the layered structure type of Ba���Sc(B0���)��� are detailed. An optimal synthetic procedure has been developed for these materials to provide pure, highly crystalline phases. Also, the structural and optical features of (Cr�����:) Sr���In(B0���)��� with A= Sr and M=M'= In have been studied. The material Sr���LilnB���O������, was discovered while searching for a suitable lithium borate flux for crystal growth of the compound Sr���In(B0���)���. / Graduation date: 1993

Graduation date: 1993

<p>The objective of this thesis has been to investigate novel host material configurations for high-power end-pumped Er-Yb co-doped, or Yb doped microchip lasers and try to increase their performance. In Er-Yb co-doped systems, the main limitation is the thermal shortcomings of the phosphate glass host material. The thesis presents some novel results that contribute to the search for a crystalline replacement. In Yb doped systems, most end-pumped schemes reported have been using relatively low-power single-emitter diodes. The thesis presents experiments with Yb:KGW microchips end-pumped by high-power diode bars. Another common limitation of end-pumped Yb microchip lasers is the thermal lens that destabilizes the cavity and decreases the beam quality. The approach to reduce the thermal lens by using an athermal propagation direction has been evaluated and the results are presented in the thesis.</p><p>In the search for a crystalline host material for Er-Yb systems, borates have been found increasingly interesting. Consequently, we started out by investigating Gadolinium-calcium-oxoborate, GdCOB, which could be grown in platinum crucibles. It was found that the cw performance of such monolithic microchips is quite comparable to glass hosts in terms of slope efficiency, but the threshold is significantly larger. As for Q-switched performance, which is essential to most Er-Yb applications, the first efficient Q-switched results with a crystalline host is presented in the thesis. Similar to the cw regime, the slope efficiencies are comparable to glass, while the threshold is quite high. However, the perhaps most important parameter, maximum output power before thermal fracture, is neither significantly improved nor worsened compared with phosphate glass. This is believed to be due to higher threshold and a stronger thermal expansion that negates the benefit of a thermal conductivity that is only 2-3 times higher. To find a host material that could withstand higher pump powers, we turned our attention to the double-tungstates KGW and KYW, which have higher thermal conductivity and higher cross-sections. They have, however, energy level lifetimes which differ significantly from glass or borates and as a consequence, a thorough spectroscopic investigation has been undertaken to optimize dopant concentrations. Laser experiments on crystals with dopant concentrations based on this investigation are expected in the near future.</p><p>When pumping Yb:KGW with a high-power diode bar, we achieved output powers of 9 – 12.4 W under different experimental conditions with incident powers of 18.3 – 26 W. The incident power of 26 W in one design was enough to fracture the crystal. Using a crystal cut for propagation along an athermal direction and comparing it with an identical b-cut crystal, we found that the thermal lens in the athermally oriented crystal was about a factor two weaker at the same absorbed power.</p>

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