Laser/microstructure interaction and ultrafast heat transfer

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Heltzel, Alexander John

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The industrial demand for smaller structures required for the manufacture of quantum devices, high-density recording media, etc., have resulted in the need for fabrication technology at the nanometer scale. However, most lithography and milling techniques are limited either by their inability for large-area fabrication or by the diffraction limit and in most cases the high manufacturing costs. To overcome the diffraction limit and to spatially-control matter on a nanometer scale, near-field optics techniques have been employed. It has been shown that laser/microstructure interaction can create surface modifications below the diffraction limit in both localized and parallel fashions. This dissertation investigates laser/microstructure interaction using both numerical and analytical tools for computation. Two fundamental problems required for predictive optical nanolithography are addressed: the electrodynamic response of the laser energy in the vicinity of micro/nanostructures, and the resulting energy transport through the target material. The dissertation first concentrates on the interaction between lasers and dielectric microspheres. Analytical solutions provided by near-field Mie theory and numerical solutions to Maxwell’s equations are obtained. Three-dimensional electromagnetic fields are resolved in the near-field of these spheres and functional dependencies on several experimental parameters are uncovered. Energy transport through the substrate is modeled numerically in both two and three dimensions using conventional conduction formulae and ultrafast electron density evolution for the case of femtosecond pulse irradiation. The combined electrodynamic/heat transfer solutions generate final lithographic predictions which are compared to experimental characterizations. The final segment of this dissertation investigates the interaction between lasers and gold, silver, and carbon nanotube structures for the purposes of optical lithography and photonic signal propagation. Fundamentals of surface plasmons, coupled electron/photon waves at conductor/dielectric interfaces, are explored computationally. Practical lithographic and photonic applications are optimized theoretically in an effort to advance knowledge in this area.