| Abstract [eng] |
Supercontinuum Generation in Photonic Crystal Fiber and Highly Nonlinear ZnS Crystal Using Low-energy Femtosecond Pulses. In this Master’s thesis the principals of supercontinuum generation in different media are introduced. Nonlinear spectral broadening mechanisms and applications of supercontinuum as a unique source for the generation of new colors are reviewed. Types of photonic crystal fibers and their properties, also differences from bulk materials are mentioned. The aim of this work was to investigate supercontinuum generation in photonic crystal fiber and highly non-linear ZnS crystal using Yb-doped femtosecond fiber lasers with low-energy pulses as a pump. In this work we tried to determine a dependence of generated supercontinuum spectrum on various pump pulse energy and on parameters of the media. Stable broadband supercontinuum was successfully generated by pumping photonic crystal fiber in anomalous dispersion regime with nJ pulses. Spectral dependency on pump pulse energy, polarization and fiber length have been experimentally investigated. It was demonstrated that both higher energy and longer fiber leads to broader supercontinuum generation independent of polarization direction. Also, by optimizing the splicing between different fibers, all-in-fiber stable supercontinuum generation source was created, which allowed to generate wider supercontinuum spectrum compared to one produced by coupling pump into photonic crystal fiber through free space. On top of that, a more powerful femtosecond fiber laser has been assembled. It was used to generate much broader supercontinuum with the same fiber length. Bulk continuum generation with low-energy pulses was demonstrated. Supercontinuum spectra dependence on pump pulse energy and beam focusing conditions was investigated. Pulse and beam parameters was optimized to obtain the broadest supercontinuum generation. It was experimentally demonstrated that blueshifted broadening of the supercontinuum spectrum depended on the pump pulse energy. At first higher energy leads to broader supercontinuum, but at some point the maximum blueshift of the spectrum was achieved and spectral modulation ocuurred if energy was further increased. It was also shown that by reducing beam waist diameter the blue extent of the supercontinuum decreased significantly. It was found that broadest supercontinuum is generated, when beam was focused in the middle of crystal. |
