Microwave diagnostics of plasma filaments left in the wake of high power femtosecond laser pulse

Summary form only given. We present a simple non-intrusive experimental method allowing a complete single shot time resolved measurement of the relaxation of laser induced plasma filaments. The method is based on filament interaction with low intensity microwave radiation in a rectangular single mode waveguide. The suggested diagnostics allow a complete single shot temporal analysis of filament plasma decay with temporal resolution better than 0.3 ns and high spatial resolution along the filament. This experimental method does not require prior knowledge of filament dimensions or control over its exact spatial location. The experimental results are compared to numerical simulations of air plasma chemistry. Results reveal the role of various decay mechanisms including the importance of O₄⁺ molecular levels. Microwave diagnostics was used to study plasma lifetime prolongation by properly timed irradiation of the filament with a relatively love intensity nanosecond laser pulse. Lifetime prolongation of high density plasma filament by more than an order of magnitude has been demonstrated. The experimental results are in good agreement with our theoretical model that follows the evolution of the temperature and density of various molecules, atoms and ion species. The results point to the possibility of generating extremely long time duration, stable high density plasma filaments in air.