Spectral response of rejuvenated Cs-Te photocathodes for optimized production control

Precise control of the Cs-Te stoichiometric deposition ratio during the photocathode fabrication process is essential to optimize the resulting quantum efficiency (QE) and emittance of electron sources. For example, an excess of Cs or the formation of another Cs - Te phase can lead to a sub-optimal electron bunch energy spread or a decrease in overall quantum yield. This study investigates the spectral response characteristics of Cs - Te photocathodes rejuvenated by co-depositing a Cs - Te layer over a degraded one. For this, the QE of the photocathodes was measured using a 10 Hz 5 ns pulsed OPO in the wavelength range from 240 to 430 nm. This experiment allows comparison of the spectral response of rejuvenated photocathodes with non-rejuvenated ones reported in the literature, facilitates the estimation of the photoemission threshold for the photoemissive phase present on the cathode, and allows comparison with the expected spectral response predicted by Spicer's Three-Step Model. Our results contribute to a deeper understanding of the fabrication of Cs-Te photocathodes and provide practical insights for optimizing production to improve performance.