Patent ID: 6847164

Claim:
An electron beam source comprising: (a) a photocathode comprising a photoemitter material having a work function, the photocathode comprising a beam receiving portion and an electron emitting portion; (b) a first light source that generates a first light beam having a wavelength λ 1 that is directed onto the beam receiving portion of the photocathode to emit an electron beam from the electron emitting portion, the wavelength λ 1 having a value such that hc/λ 1 is at least the work function of the photoemitter material, where ‘h’ is Planck's constant and ‘c’ is the speed of light; and (c) a second light source that generates a second light beam having wavelength λ 2 that is directed onto the beam receiving portion of the photocathode, the wavelength λ 2 having a value such that hc/λ 2 is less than the work function of the photoemitter material.