Ultraviolet stimulated electron source for use with low energy plasma   instrument calibration
  We have developed and demonstrated a versatile, compact electron source that can produce a monoenergetic electron beam up to 50 mm diameter from 0.1 to 30 keV with an energy spread of <10 eV. By illuminating a metal cathode plate with a single near ultraviolet (UV) light emitting diode (LED), a spatially uniform electron beam with 15% variation over 1 cm2 can be generated. A uniform electric field in front of the cathode surface accelerates the electrons into a beam with an angular divergence of <1 degree at 1 keV. The beam intensity can be controlled from 10^9 electrons/cm2s. 
Kevin Henderson, Ron Harper, Herb Funsten, and Elizabeth MacDonald
physics.space-ph physics.ins-det