Improving the energy spread and brightness of thermal-field (Schottky) emitters with PHAST—PHoto Assisted Schottky Tip

Using a relatively simple model of photoemission we derive an expression for the reduced on axis brightness of a thermal-photofield emitter. We then show that it is theoretically possible to reduce the energy spread of a Schottky (thermal field) emitter whilst increasing the reduced brightness. This can be achieved by the illumination of the tip with a high intensity laser light. We call the source PHAST—PHoto Assisted Schottky Tip. We find that due to the strong E-fields applied PHAST may operate at photon energies below the (Schottky reduced) work function. Thus removing the need for UV lasers, we will show that it is in fact preferable to work in the red, or in the green. The necessary laser intensities probably limit the application to pulsed operation.