Patent ID: 8779376

Claim:
A method of determining emission characteristics of a field electron source, comprising: sequentially extracting electrons from the field electron source using different extraction voltages; measuring the electron current at the multiple extraction voltages to determine a relationship between an angular intensity I′ and the extraction voltage; determining, from the relationship and beam geometry, work function and field factor β corresponding to a ratio of the applied electric field at the emission surface and the extraction voltage; determining an emission current density J from the angular intensity and beam geometry, J being defined at the emitter surface location; determining an intrinsic emission energy spread from the field factor, the extraction voltage, the work function, and the source temperature; determining an intrinsic virtual source size d v (int) from the beam geometry, source temperature, and extraction voltage; determining a corrected emission energy spread from the intrinsic emission energy spread and the angular intensity; determining a corrected virtual source size d v from the emission current density; and determining a beam brightness from the angular intensity, the corrected virtual source size, and the extraction voltage.