Interference photocathode

An interference photocathode comprising:

• a reflective substrate;
• and
• interference means disposed on said reflective substrate for selectively enhancing a first photoelectric yield of said photocathode when irradiated by radiation having a first wavelength relative to a second photoelectric yield of said photocathode when irradiated by radiation having a second wavelength;
• and
• wherein said interference means comprises a layer disposed on said reflective substrate such that the effective thickness of said interference means for radiation having said first wavelength is an odd multiple of a quarter of said first wavelength and an effective thickness for radiation having said second wavelength is an even multiple of a quarter of said second wavelength.

An interference photocathode comprising:

• a reflective substrate;
• and
• interference means disposed on said reflective substrate for selectively enhancing a first photoelectric yield of said photocathode when irradiated by radiation having a first wavelength relative to a second photoelectric yield of said photocathode when irradiated by radiation having a second wavelength;
• and
• wherein said first photoelectric yield is at least 1000 times greater than said second photoelectric yield when said first and second wavelengths are 834 and 1216 Angstroms, respectively.

An interference photocathode sensor comprising:

• interference means for selectively enhancing a photoelectric yield of a cathode when irradiated by radiation having a first wavelength relative to a photoelectric yield of said cathode when irradiated by radiation having a second wavelength;
• and
• detector means for detecting electrons yielded from said cathode;
• and
• wherein said interference means is an interference coating comprising alternating layers of electron emissive material and dielectric material.

An interference photocathode comprising:

• a reflective substrate;
• and
• interference means disposed on said reflective substrate for selectively enhancing a first photoelectric yield of said photocathode when irradiated by radiation having a first wavelength relative to a second photoelectric yield of said photocathode when irradiated by radiation having a second wavelength;
• wherein said interference means comprises a first layer and at least one second layer disposed between said first layer and said reflective substrate,
• wherein said first and second layers have a wavelength dependent composite effective thickness such that a composite effective thickness of said interference means for radiation having said first wavelength is an odd multiple of a quarter of said first wavelength and a composite effective thickness of said interference means for radiation having said second wavelength is an even multiple of a quarter of said second wavelength.