Triggering and guiding HV discharge in air by filamentation of single and dual fs pulses.

The triggering and guiding of the stationary high voltage (HV) discharges at 5-40 kV are demonstrated by using plasma filaments generated by single and dual femtosecond(fs) laser pulses in air. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser pulse filamentaion was observed. The amount of free electrons of filaments generated by different pulse configurations was compared by sonography method. The lifetime of filaments is measured by using time-resolved fluorescence spectrum, and the lifetime of filaments generated by dual fs laser pulses was doubled due to the re-ionization by the succeeding pulse. The triggering ability of dual fs laser pulses was demonstrated to be enhanced due to the longer lifetime of filaments.