Polarization characterization of nonlinear laser propagation

High power laser pulses propagate nonlinearly in media transparent to their wavelength. Self-induced nonlinearities lead to strong modifications of the spatial, spectral as well as temporal characteristics of the pulse. The interaction of the high power laser pulses with the propagation medium leads to partial ionization of the latter. This highly complex and dynamic nonlinear process, induced by the high power laser pulses, with a narrow high intensity core that is maintained over long distances is known as "filamentation". Filaments created from a linearly polarized electric field have been studied by different research groups. However, it is interesting to know how the properties of the filament change with polarization and most importantly whether the polarization state is maintained during the nonlinear propagation of the laser pulse. This dissertation addresses the polarization evolution of a laser beam going through a nonlinear medium which can be expanded to filamentation. It is shown that the presence of the nonlinear interaction before the starting point of the filament, leads to polarization modification of an initially elliptically polarized light and the rotation of the polarization ellipse with propagation can be used to measure the intensity. Filaments generated in different gas media are also investigated to provide a better understanding of matter-light interaction when we deal with a highly nonlinear process such as filamentation. For gases such as N2 and O2, an extra component of optical nonlinearity due to the delayed rotational response (molecular alignment) is present which has been shown to have an effect on propagation and properties of the filament. Instabilities of the polarization of the filament lead to observation of an anomalous spectral broadening phenomenon due to molecular effects which is further investigated with a theoretical model. This dissertation leads to recognition of polarization as a new dimension to characterize nonlinear laser propagation and facilitates polarization dependent applications such as THz emission and supercontinuum generation.Optical Science and EngineeringDoctoralUniversity of New Mexico. Dept. of Physics & AstronomyDiels, Jean-Claude M.Arissian, LadanThomas, James L.Richardson, Martin C.Roach, William P