Physics
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Item Modeling strong-field laser-atom interactions with nonlocal potentials(2017) Rensink, Thomas C.; Antonsen (Jr.), Thomas M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atom-field interactions in the ionization regime give rise to a wide range of physical phenomena, and their study continues to be an active field of research. However, simulation of atom-field dynamics is time-consuming and computationally expensive. In this thesis, a nonlocal model potential is used in place of the Coulomb potential in the time dependent Schrodinger equation, and examined for suitabil- ity of modeling strong field-atom dynamics while offering significant reduction in computation cost. Nonlocal potentials have been used to model many physical systems, from multi-electron molecular configurations to semiconductor theory. Despite their rel- ative success, nonlocal potentials have been largely unexplored for modeling high field laser-gas interactions in the ionizing regime. This work explores the theory and numerical results of a single state gaussian nonlocal model in intense, femtosecond laser pulses, with the main findings: nonlocal potentials are useful for obtaining the photoionization rate in the tunnel and multiphoton regimes, and qualitatively char- acterize the wavefunction dynamics of irradiated atoms. The model is also examined in the context of the two-color technique for producing Terahertz (THz) frequency radiation.Item Interaction of Lasers with Atomic Clusters and Structured Plasmas(2007-11-09) Palastro, John Patrick; Antonsen, Thomas M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We examine the interaction of intense, short laser pulses with atomic clusters and structured plasmas, namely preformed plasma channels. In examining the laser pulse interaction with atomic clusters we focus on the optical response of an individual cluster when irradiated by a laser. Our analysis of the laser pulse interaction with plasma channels focuses on the mode structure of a laser pulse propagating within the channel. We then present a novel application of these channels: quasi-phased match acceleration of electrons. The optical properties of a gas of laser pulse exploded clusters are determined by the time-evolving polarizabilities of individual clusters. In turn, the polarizability of an individual cluster is determined by the time evolution of individual electrons within the cluster's electrostatic potential. We calculate the linear cluster polarizability using the Vlasov equation. A quasi-static equilibrium is calculated from a bi-maxwellian distribution that models both the hot and cold electrons, using inputs from a particle-in-cell simulation [Taguchi, T. et al., Phys. Rev. Lett., 2004. 92(20)]. We then perturb the system to first order in field and integrate the response of individual electrons to the self consistent field following unperturbed orbits. The dipole spectrum depicts strong absorption at frequencies much smaller than omega_p/√2. This enhanced absorption results from a beating of the laser field with electron orbital motion. The properties of pulse propagation within plasma are determined by the structure of the plasma. The preformed plasma channel provides a guiding structure for laser pulses unbound by the intensity thresholds of standard wave guides. In particular, the corrugated plasma channel [Layer et al. Phys. Rev. Lett. (2007)] allows for the guiding of subluminal spatial harmonics. These spatial harmonics can be phase matched to high energy electrons, making the corrugated plasma channel ideal for the acceleration of electrons. We present a simple analytic model of pulse propagation in a corrugated plasma channel and examine the laser-electron beam interaction. Simulations show accelerating gradients of several hundred MeV/cm for laser powers much lower than required by standard laser wakefield schemes.