Time-Resolved Shadowgraphy of Electrical Discharges Triggered by Laser in Air

Laser-triggered electric discharges were diagnosed using fast time-resolved shadowgraphy. A focused laser beam produced a plasma between two parallel plates connected to a high-voltage supply. This plasma, in turn, triggers the main arc between the plates. It was found that arcing occurs at about 400 after laser firing. The breakdown mechanism responds to a rarefaction of the air between the electrodes rather than to laser ionization.