Effects of pulsed photoemission in plasma breakdown

Photoemission of electrons by pulsed laser light 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, for example, through multiphoton absorption, above threshold ionization, and photo-assisted tunneling, where the dominant process depends on the work function of the material, photon energy and associated fields, surface heating, and background fields. 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. The quantum model of photoemission is incorporated into a simple global model to study the transient current-voltage behaviors of the plasmas measured in experiments.