Needle cathodes as sources of high-brightness electron beams

At the present time, the normalized brightness of electron beams available for use in free-electron lasers is of the order of 1011 A/m2-steradian. Needle cathodes emitting by field emission have demonstrated high current density, low electron temperature, and small emittance at peak currents exceeding 1 A. Photoelectric field emission can be used to control the pulse length. Measurements are underway to measure the emittance and electron energy spread of beams produced by photoelectric field emission. Using beams with very high brightness, as much as five orders of magnitude beyond those in use now, it is possible to construct compact free-electron lasers at wavelengths from the far infrared to the ultraviolet. Cerenkov and Compton lasers are discussed in detail