Photoemission induced plasma breakdown*

Laser-induced photoemission of electrons offers opportunities to trigger and control plasmas and discharges. However, the underlying mechanisms are not sufficiently characterized to be fully utilized. Photoemission is highly nonlinear, achieved through multiphoton absorption, above threshold ionization, photo-assisted tunneling, etc., where the dominant process depends on the work function of the material, photon energy and associated fields, surface heating, background fields, etc. To characterize these effects, Townsend breakdown experiments were performed and interpreted using a quantum model of photoemission. In the low-current regime considered, it is found that laser-induced photoemission is sufficiently de-coupled from space charge effects to be observable. The effect of laser heating of the electrode and the dominant photoemission mechanisms are characterized for different reduced electric fields and laser intensities and photon energies (<6.3 eV). Experiments were performed using a tunable picosecond laser that allowed the use of a two-temperature model for electrode heating.