| In this dissertation, supercontinuum generations in sapphire fibers under various conditions are investigated, and their corresponding effects are analyzed. Main motivation to use sapphire fibers as optical media for supercontinuum generation is that they have characteristics of good transparency in mid-IR, high laser damage threshold, and high melting temperature compared to conventionally utilized fibers including silica-based fibers and infrared fibers. As an introductory step, the general theories of supercontinuum generation including derivation of Schrodinger equation and explanation of various nonlinear effects are covered. Also, laser systems including a femtosecond laser system and an optical parametric amplifier in our lab are explained since they are key equipments for most experiments performed in this dissertation. Sapphire fibers are pumped at various wavelengths to verify their ability to generate supercontinuum in wide wavelength regions since they are known to be transparent from visible to 4∼5mum. Since nonlinearity, dispersion, and fiber length play important roles on nonlinear interactions in sapphire fibers, corresponding nonlinear effects are also investigated and explained. The core diameter of sapphire fibers we used for experiments is quite large that its nonlinear coefficient inversely proportional to mode area is quite small even though its nonlinear refractive index is comparable to silica fiber. To overcome small nonlinear coefficient due to large mode area, sapphire fibers are pumped by three pumping sources to have very wide spectrum ranged from UV to mid-IR region, which can be predicted by the superposition of three different spectra. As application purposes, experiments of IR spectroscopy and remote sensing are performed. Finally, several future works to solidify this dissertation are discussed. |
