Nonlinear photoemission from organic cathodes excited by a pulsed near-ultraviolet laser

High current density electron beams with fast modulation capability can be generated using laser-driven photoemission. Organic film cathodes having a real intermediate energy level can work in a poor vacuum environment and with near ultraviolet (∼ 350 nm) illumination where temporal formats from CW to picosecond pulse are available. Measured nonlinear photoemission characteristics of several organic films are presented and compared to the response of a rate equation model. Pulse distortions for 5 ns and 5 ps pulses also have been computed. Current densitities above 30 A/cm²for 5 ns, 337 nm pulses have been measured: an increase up to 3 kA/cm³for 5 ps pulses is predicted by the model.