Femtosecond ultraviolet laser pulse induced lightning discharges in gases

Ultraviolet pulses of 200 fs duration and low energy (/spl ap/0.2 mJ) have a sufficiently high peak power to ionize oxygen and nitrogen by three- and four-photon ionization, respectively. It is shown that the resultant ionization channel induces a lightning like discharge at half of the natural self-breakdown voltage in nitrogen or air. The laser triggered discharging process is studied by monitoring the voltage between two planar electrodes. The effects of oxygen on the induced breakdown is investigated. A complete theoretical model is presented to simulate: (1) the electron seeding; and (2) the evolution of the plasma of electron-ion in the applied field. The results of the theory verified by small scale experiments-are used to simulate the process of laser triggered lightning in atmosphere, and helps to define the parameters of a laser system for lightning protection.>