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

Single Shot Ablation Craters with Ultra-Short Laser Pulses: A Comparative Study

Single Shot Ablation Craters with Ultra-Short Laser Pulses: A Comparative Study D. P. Weber1, *, V. Sudesh1, H. Kerrigan2, S. R. Fairchild2, M. C. Richardson2 1Physical Sciences Department, College of Arts and Sciences, Embry-Riddle Aeronautical University. Daytona Beach, FL, 32114, USA 2Laser Plasma Laboratory, College of Optics and Photonics, University of Central Florida, Orlando, FL 32816, USA *[email protected] (832) 533-1318 Laser ablation is a technique to remove material by irradiation. This work qualitatively studies the basic mechanisms of laser ablation on GaAs, Al, Ti, Cu, and ZnSe samples by two regimes: a focused 1064 nm, 14.6 mJ pulse of 8 ns duration from an Nd:YAG laser (ns regime) and a focused 800 nm, 4.2 mJ pulse of 50 fs duration from a Ti:Sapphire laser (fs regime). The materials were ablated in these two regimes to qualitatively investigate the extent of the dominating mechanisms, as seen clearly in their craters. By firing only single shots, the formations that were created remain intact. The following diagnostics were used to view the craters: a white light interferometric microscope to determine the crater topography, an optical microscope for a more general view, and a scanning electron microscope (SEM) to view the regions smaller than the resolution of the previous instruments. Significant thermo-mechanical stress in the nanosecond regime and a sub-surface boiling layer in the femtosecond regime have been identified. This investigation has concluded and is under final analysis and preparation for publication

Uv-Vis-Nir White Light Lidar Using Polarization-Controlled Laser Filamentation

White-Light LIDAR was performed using a unique polarization-controlled white light source generated by filamentation. The design and performance of this supercontinuum source will be shown as well as its importance for a novel LIDAR approach

Uv-Vis-Nir White Light Lidar Using Polarization-Controlled Laser Filamentation

White-Light LIDAR was performed using a unique polarization-controlled white light source generated by filamentation. The design and performance of this supercontinuum source will be shown as well as its importance for a novel LIDAR approach

Enhanced Ablation With A Femtosecond-Nanosecond Dual-Pulse

Single-shot ablation of GaAs samples by a collinear femtosecond-nanosecond (fs-ns) dual-pulse is investigated. Significantly enhanced material removal is achieved by optimally combining a single 8 ns pulse at 1064 nm and a single 50 fs pulse at 800 nm in time. The resulting ablation craters are examined for inter-pulse delays ranging from -50 ns (ns first) to +1 μs (fs first) as well as very long delays of ±30 s. Crater profilometry is conducted with white light interferometry and optical microscopy to determine the volume of ablated material and identify surface features that reveal information about the physical mechanism of material removal during fs-ns dual-pulse ablation

Transition From Linear- To Nonlinear-Focusing Regime Of Laser Filament Plasma Dynamics

Laser filament properties, including the plasma induced by the filamenting pulse in the medium, depend on the numerical aperture (NA) of the focusing optics used to create them. Recent studies of this dependence have revealed two distinct linear and non-linear filamentation regimes. High-resolution spatial and temporal electron density measurements are presented demonstrating the transition from the linear to nonlinear focusing regime. This study shows that the dominance of geometrical focusing in the linear (high NA) regime produces plasma with high peak densities and large plasma diameters, while filamentation in the nonlinear regime, equivalent to long distance filamentation, leads to low peak densities and small plasma diameters

Enhanced Supercontinuum Generation By Polarization Control Of Filamentation In Molecular Gases

Supercontinuum generation by filamentation in molecular gases is optimized by studying the ellipticity of the pulse polarization during the interaction with the species of the gas medium via strong field ionization and molecular alignment effects. © OSA 2015