Laser plasmas from picosecond laser filamentation in the atmosphere and its application on guided high voltage discharges

Femtosecond laser filamentation in the atmosphere produces plasmas with densities on the order of 1016 cm−3 or less than 1% of air ionized [1]. Filamentation is a nonlinear process where a short laser pulse is propagating through a nonlinear medium while a dynamic balance between non-linear focusing, diffraction and plasma defocusing is established. The short lifetime and relative low temperature of the laser-generated plasma results in a high resistivity, making femtosecond filaments difficult to utilize for some applications including guiding high voltage electric discharges [2]. To achieve guided discharges with femtosecond filaments over several meters requires voltages larger than 100 kV between the electrodes. Alternatively nanosecond lasers have been used to create plasma sparks and trigger short discharges. The nanosecond laser plasma is denser and hotter in comparison to the femtosecond filament plasma. These properties result in a high conductivity and a fast trigger of the high voltage discharge [3]. However, the spatial extent of these plasmas is limited and only short discharges can be initiated. A recent experiment on picosecond laser filamentation [4] indicates the possibility of combining the properties of the two plasmas described above: an extended plasma channel with high conductivity. Here, we present experimental results that show the effect of picosecond laser filamentation on guiding high voltage discharges. The results indicate that higher conductivity plasma is produced in comparison to a femtosecond pulse. We achieved a reduction of threshold break down voltage by 20% with our experimental setup. The experiments are conducted using the COMET laser, at Jupiter Laser facility, Lawrence Livermore Laboratory.