Large-area Photocathodes (LAP)

The LAP program seeks to develop large-area photocathodes. Photocathodes can be found in devices such as photomultiplier tubes, image intensifiers, high-power electronics, and even free electron lasers. Photocathodes typically use low-work function metals or semiconductors and are applied in sub-micron thicknesses on planar surfaces with millimeter to centimeter-scale areas. Photocathode performance can be characterized by attributes such as quantum efficiency (QE), lifetime, and mean transverse energy (MTE).

Metals such as copper and magnesium have low QE but are well-understood, robust, and easy to obtain. CsTe is a leading semiconductor used within the accelerator community with a reasonable balance of QE, lifetime, and MTE. Diamond has been examined for switching applications but may hold promise as a photocathode. Other materials, such as the alkali antimonides, could offer high QE operation at longer wavelengths but may have lifetime, process, and handling challenges.

In addition, recent work has also focused on increasing QE and lowering emittance through patterning techniques. , LAP seeks manufacturable photocathode material systems with high quantum efficiency that can be produced in large areas with substantial lifetimes and manageable handling requirements. LAP will develop and produce photocathodes that will be incorporated by the government team into a prototype system.