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The Response of Molecular Gases and Modulated Plasmas to Short Intense Laser Pulses

dc.contributor.advisorAntonsen, Thomas Men_US
dc.contributor.authorPearson, Andrewen_US
dc.description.abstractIn this thesis we study the response of two systems to short, intense laser pulses. The first system is a gas of diatomic molecules whose ensemble-averaged alignment features rotational revivals. We analyze the effect of a background plasma on the revival peaks. Both the revivals and the plasma are the result of a laser pulse passing through the gas. The second system is a density-modulated plasma channel. We study the generation of electromagnetic radiation by a laser pulse passing through this structure. The molecules in the gas are modeled as rigid rotors that interact first with the cycle-averaged electric field of the laser pulse, and second with the fluctuating electric field of the background plasma. The laser pulse generates a broad superposition of angular momentum eigenstates, resulting in the transient alignment of the molecules. Because of the time evolution properties of the angular momentum states, the alignment re-occurs periodically in field-free conditions. The alignment is calculated using a density matrix, and the background plasma is modeled using dressed particles. The result is decoherence between the phases of the basis states of the wavefunction, which causes decay of subsequent alignment peaks. We find that field-induced decoherence is competitive with collisional decoherence for small ionization fractions. The corrugated plasma channel is modeled using linear plasma theory, and the laser pulse is non-evolving. Corrugated channels support EM modes that have a Floquet dispersion relation, and thus consist of many spatial harmonics with subluminal phase velocities. This allows phase matching between the pulse and the EM modes. Since the pulse bandwidth includes THz frequencies, significant THz generation is possible. Here we consider realistic density profiles to obtain predictions of the THz power output and mode structure. We then estimate pulse depletion effects. The fraction of laser energy converted to THz is independent of laser pulse energy in the linear regime, and we find it to be around one percent. Extrapolating to a pulse energy of 0.5 J gives a THz power output of 6 mJ, with a pulse depletion length of less than 20 cm.en_US
dc.titleThe Response of Molecular Gases and Modulated Plasmas to Short Intense Laser Pulsesen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.subject.pqcontrolledPlasma Physicsen_US
dc.subject.pquncontrolledCorrugated plasma channelen_US
dc.subject.pquncontrolledLaser plasmaen_US
dc.subject.pquncontrolledRotational revivalsen_US
dc.subject.pquncontrolledTeraHertz generationen_US

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