Background Gas Species and Pressure Dependence of Plasma Fluorescence and RF Emissions of Laser Driven Filament Plasmas

The Air Force Research Lab is investigating RF emissions generated by filaments of femtosecond lasers. We employed an 800 nm, terawatt class laser focused with a 3m focal length mirror to produce a filament inside of a quartz vacuum chamber to observe the effects of pressure and background gas on the filament. Background gases investigated at Argon, Helium, Krypton, Neon, and Nitrogen. A 4 Quik E camera was used to image 2 ns exposures of the plasma along the length of the plasma to observe the development of the plasma fluorescence from the multifilament regime into the single filament regime and to measure the width of the filament. In addition to the optical data, RF measurements of filaments will be presented. The effects of background gas and pressure on the characteristics of the filament will be detailed. This optical and RF data will aid in developing a deeper understanding of the plasma mechanisms responsible for the generation of the RF.