Improved laser triggering and guiding of meqavolt discharges with dual fs-ns pulses

We demonstrate that the capacity of ultrashort high-power laser pulses to trigger and guide high-voltage discharges can be significantly enhanced by a subsequent visible nanosecond laser pulse. The femtosecond pulse induces a bundle of filaments, which creates a conducting channel of low density and cold plasma connecting the electrodes. The subsequent laser pulse photodetaches electrons from $O2−$ ions in the electrode leader. The resulting electrons allow efficient heating by Joule effect in a retroaction loop, resulting in a 5% reduction of the breakdown voltage.