Generation And Applications Of New Optical Frequencies By Filamentation Of Femtosecond Laser

With the development of ultrashort laser technology, plasma filaments generated by femtosecond laser propagation in nonlinear transparent media have been widespread concerned these years, especially some nonlinear phenomena formed with the filaments, because of their important meaning in applications.In this thesis, we explain the physics mechanism of filamentation in theory, and the physical models of filaments transmission are also introduced. Then some nonlinear phenomena accompanied with filamentation are illustrated in detail, such as generation of optical new frequencies, conical emission, formation of multifilamentation and THz emission.In the part of experiment, deterministic wavelength-dependent multifilamentation is controlled in fused silica by adjusting the diffraction pattern generated by a loosely focusing2D periodic lens array. By simply translating the sample along the propagation axis, the number and distribution of filaments can be controlled and are in agreement with the results of linear diffraction simulations. The effect of incident energy and polarization on filament number is also studied. On this basis, we research how to get supercontinuum with high output power and wide spectral range. By changing the media, BBO angles, distance between microlense array and the media, the energy and spectrum of supercontinuum in different experiment parameters are researched. We also do a comparison between spectra generated with microlense and ordinary lens. And the stabilities of the spectra are tested in the last of the thesis.