Multiphoton Emission Enhancements for High Repetition Rate Photoinjectors

The development of high quality, high power electron beam photoinjectors is of great interest to free electron lasers and energy recovery linac facilities. One major hurdle is the achievement of high quantum efficiency (QE) from photoinjector cathodes. Semiconductor cathodes offer high efficiency, yet require ideal vacuum conditions and cryogen cooling. Metal cathodes are more prompt and robust with eased vacuum requirements but have not matched the QE of semiconductors. A novel scheme using multiphoton emission enhancement based on using infrared laser light (rather than ultraviolet) has recently demonstrated suitable equivalent quantum efficiency. Enhancement of this effect by exploring cathode coatings of Cesium-Bromide and different thicknesses of Magnesium- Flouride is expected to increase the efficiency. Additionally, other schemes to enhance the surface plasmon efficiency may increase the efficiency to levels of semiconductors or better. Commercial Applications and Other Benefits: The industrial applications of high-power free electron lasers (FEL) based on the multiphoton enhanced photoinjector include polymer surface processing, metals and ceramics micromachining, metal surface processing, and non-destructive testing. In addition, UV sources may be applied to lithography (i.e. for semiconductor fabrication). Defense applications include high power FELs for naval defense. The injector is an ideal source for monochromatic X-ray production via laser backscattering; such an X-ray source would have wide-ranging medical applications, including high contrast, low dose diagnostic imaging and new radiation therapy modalities