Electron sources utilizing negative electron affinity photocathodes with ultra-small emission areas

An electron source comprising:

• a negative electron affinity photocathode on a light-transmissive substrate, said photocathode having a conduction band;
• a light beam generator for directing a light beam through said light-transmissive substrate at said photocathode for exciting electrons into the conduction band of said photocathode, said light beam having a cross-sectional area at said photocathode that is selected to produce an active area for emission of electrons with a dimension less than about two micrometers;
• electron optics for forming the electrons emitted from the active area of said photocathode into an electron beam;
• and
• a vacuum enclosure for maintaining said photocathode at high vacuum such that electrons in the conduction band of said photocathode have higher energies than electrons in the vacuum enclosure adjacent to said photocathode and have a high probability of emission into the vacuum enclosure from the active area of said photocathode.

An electron source comprising:

• a negative electron affinity photocathode on a light-transmissive substrate, said photocathode having a conduction band and at least one predefined active area of less than about 2 microns in at least one dimension for emission of electrons;
• a light beam generator for directing a light beam through said light-transmissive substrate at the predefined active area of said photocathode for exciting electrons into the conduction band of said photocathode;
• electron optics for forming electrons emitted from the active area of said photocathode into an electron beam;
• and
• a vacuum enclosure for maintaining said photocathode at high vacuum such that electrons in the conduction band of said photocathode have higher energies than electrons in the vacuum enclosure adjacent to said photocathode and have a high probability of emission into the vacuum enclosure from the predefined active area of said photocathode.

An electron beam system comprising:

• an electron source comprising:
• a negative electron affinity photocathode on a light-transmissive substrate, said photocathode having a conduction band and at least one active area for emission of electrons, said active area having one or more dimensions less than about two micrometers;
• a light beam generator for directing a light beam through said light-transmissive substrate at the active area of said photocathode for exciting electrons into the conduction band of said photocathode;
• electron optics for forming the electrons emitted from the active area of said photocathode into an electron beam;
• and
• a vacuum enclosure for maintaining said photocathode at high vacuum such that electrons in the conduction band of said photocathode have higher energies than electrons in the vacuum enclosure adjacent to said photocathode and have a high probability of emission into the vacuum enclosure from the active area of said photocathode;
• a main vacuum enclosure for receiving said electron beam from said electron source and for holding a workpiece for processing by said electron beam, and
• main electron optics located within said main vacuum enclosure for directing said electron beam to said workpiece.