Study of the Femtosecond Dynamics and Spectroscopy of Laser Ionized Plasmas

Title of Document: STUDY OF THE FEMTOSECOND DYNAMICS AND SPECTROSCOPY OF LASER IONIZED PLASMAS. JJennifer Anne Elle, Doctor of Philosophy, 2015 Directed By: Professor Howard Milchberg Department of Physics Ultra-short laser pulses are used to ionize gas in different configurations and study the plasma and ionization dynamics. The variation in non-linear index of refraction as a function of time is used to diagnose laser-plasma interactions. First, a proposed novel method to stimulate lasing in the atmosphere is studied. A few mJ pulse is used to ionize nitrogen gas in a long column without dissociating the molecular nitrogen. A 140ps laser is used to heat the resulting electron population in an attempt to generate a population inversion between the CPu and BPg states of molecular nitrogen. No evidence of lasing from this transition is observed. Next, a few mJ pulse is used to ionize xenon gas, creating Xe plasma. Ionization in Xe is observed far below the threshold predicted by multiphoton ionization theory due to resonant multiphoton ionization of collisionally excited states. To my knowledge, this is the first observation of resonant ionization involving multiple resonances. Finally, construction of an experiment to detect predicted birefringence in a relativistic laser-plasma interaction is described, with preliminary testing of diagnostics included. STUDY OF THE FEMTOSECOND DYNAMICS AND SPECTROSCOPY OF LASER IONIZED PLASMAS.