Development and Characterization of Multi-Alkali Antimonide Photocathodes for High-Brightness RF Photoinjectors

Abstract

Due to their excellent photoemissive properties, especially low thermal emittance and high sensitivity in the green wavelength, multi-alkali antimonide photocathodes, in particular, cesium–potassium–antimonide, emerged as prominent photoemissive materials for the electron sources of high-repetition-rate FEL applications. To explore its feasibility of operating in a high-gradient RF gun, DESY collaborated with INFN LASA to develop multi-alkali photocathode materials. In this report, we describe the recipe of K-Cs-Sb photocathodes, which were grown on a Mo substrate by varying the foundational Sb layer thickness using sequential deposition techniques. This report also illustrates the information regarding the film thickness, substrate temperature, deposition rate, and its possible effects on the photocathode’s properties. In addition, the influence of temperature on the cathode degradation is also summarized. Furthermore, in the framework of density functional theory (DFT), we investigated the electronic and optical properties of the K₂CsSb material. The optical properties, such as dielectric function, reflectivity, refracting index, and extinction coefficient, were evaluated. The correlation between the calculated and measured optical properties, such as reflectivity, provides a better and more efficient strategy to rationalize and understand the photoemissive material’s properties.

Towards Implementation of 3D Amplitude Shaping at 515 nm and First Pulseshaping Experiments at PITZ

“…Another project is cathode development and characterization. Tests with new green photocathodes are ongoing [29], which would simplify the photocathode laser systems because no conversion to UV is necessary for them, relaxing the requirements for the laser system. In addition, pulseshaping schemes become directly available at green wavelengths, which are not working in UV due to high absorption or narrow spectral bandwidth.…”

“…Here, we propose a scheme that uses the same pulseshaping method as used for IR lasers [23,25] and adapt it for 515 nm wavelength, which has the advantage of being directly applicable to alkali antimonide photocathodes [29]. Working with green light is a good compromise regarding having powerful lasers and the availability of efficient pulseshaping devices for operation with 1 MHz repetition rate at several watts of average power.…”

Thermodynamic stability and vibrational properties of multi-alkali antimonides

“…Multi-alkali antimonides are semiconductors used as electron sources in particle accelerators [1][2][3]. Despite the persisting challenges in producing high-quality samples [4][5][6], the research on these materials is relentless.…”