Triple Evaporation of Bialkali Antimonide Photocathodes and Photoemission Characterization at the PhoTEx Experiment

The development of high-performance photocathodes is essential for generating high-brightness electron beams required by existing and future accelerators. This work introduces a state-of-the-art triple evaporation growth system designed for bialkali antimonide photocathodes. By enabling the simultaneous deposition of all three materials, this system significantly enhances vacuum stability and the reproducibility of photocathode fabrication. Complementing this, the novel characterization system PhoTEx allows spatially and spectrally resolved measurements of key photocathode parameters, such as quantum efficiency (QE), mean transverse energy (MTE), reflectance and lifetime. Crucially, all measurements are performed within a single compact setup, without moving the sample, preserving ultra-high vacuum conditions. The spectral resolved measurement of the reflectance allows the investigation of the color. Photocathode colorimetry may provide valuable insights into material homogeneity and aging. A Na-K-Sb photocathode was grown using the triple evaporation method, achieving an initial QE of $5.5\,\%$ at $520\,$nm. The photocathode was characterized at PhoTEx over two months, demonstrating consistent MTE measurements and a dataset with spectral response, reflectance and colorimetry data. Together, the triple evaporation growth system and PhoTEx mark a significant advancement in optimizing photocathodes with exceptional performance, paving the way for brighter and more stable electron sources for next-generation accelerator facilities.