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This paper presents a comprehensive investigation into the quantum efficiency (QE) of metallic photocathodes used in modern high-performance radio frequency (RF) and superconducting radio frequency (SRF) guns. The study specifically examines how laser cleaning treatment impacts the QE of these photocathodes, providing detailed insights into their performance and potential improvements for accelerator applications, and assesses the chemical and environmental factors affecting the surface composition of metallic laser-photocathodes used in modern high-performance radio frequency (RF) and superconducting radio frequency (SRF) electron guns. This paper overviews the photocathode rejuvenation effects of laser cleaning treatment. Laser cleaning removes the oxides and hydrides responsible for the deterioration of photocathodes, increases the photoelectron emission quantum efficiency (QE) and extends the operational lifetime of high-brightness electron injectors. QE enhancement is analyzed with the aim of parametric cleaning process optimization. This study excludes semiconductor and thermionic cathodes, focusing solely on the widely used bulk and thin-film photocathodes of Cu, Mg, Y, Pb and Nb. Laser cleaning enhancement of QE in Cu from 5 × 10−5 to 1.2 × 10−4, in Mg from 5.0 × 10−4 to 1.8 × 10−3, in Y from 10−5 to 3.3 × 10−4, in Pb from 3 × 10−5 to 8 × 10−5, and in Nb from 2.1 × 10−7 to 2.5 × 10−5 is demonstrated. The analysis concludes with a specialized practical guide for improving photocathode efficacy and lifetime in RF and SRF guns.

This paper presents an innovative exploration of advanced configurations for enhancing the efficiency of metallic and superconducting photocathodes (MPs and SCPs) produced via pulsed laser deposition (PLD). These photocathodes are critical for driving next-generation free-electron lasers (FELs) and plasma-based accelerators, both of which demand electron sources with improved quantum efficiency (QE) and electrical properties. Our approach compares three distinct photocathode configurations, namely: conventional, hybrid, and non-conventional, focusing on recent innovations. Hybrid MPs integrate a thin, high-performance, photo-emissive film, often yttrium or magnesium, positioned centrally on the copper flange of the photo-injector. For hybrid SCPs, a thin film of lead is used, offering a higher quantum efficiency than niobium bulk. This study also introduces non-conventional configurations, such as yttrium and lead disks partially coated with copper and niobium films, respectively. These designs utilize the unique properties of each material to achieve enhanced photoemission and long-term stability. The novelty of this approach lies in leveraging the advantages of bulk photoemission materials like yttrium and lead, while maintaining the electrical compatibility and durability required for integration into RF cavities. The findings highlight the potential of these configurations to significantly outperform traditional photocathodes, offering higher QE and extended operational lifetimes. This comparative analysis provides new insights into the fabrication of high-efficiency photocathodes, setting the foundation for future advancements in electron source technologies.

Technology of creation effective photocathode based on the InP/InGaAs heterostructures is given. The results of an experimental study of pin-diode, which was used as the receiver of photoelectrons, are presented. Arrangement of the vacuum photoelectronic device with InP/InGaAs photocathode is proposed.

The present study reports the fabrication of CdSe quantum dot (QD)-sensitized photocathodes on NiO-coated indium tin oxide (ITO) electrodes and their H₂-generating ability upon light irradiation. A well-established spin-coating method was used to deposit CdSe QD stock solution onto the surface of NiO/ITO electrodes, thereby leading to the construction of various CdSe QD-sensitized photocathodes. The present report includes the construction of rainbow photocathodes by spin-coating different-sized QDs in a sequentially layered manner, thereby creating an energetically favorable gradient for charge separation. The resulting rainbow photocathodes with forward energetic gradient for charge separation and subsequent electron transfer to a solution-based hydrogen-evolving catalyst (HEC) exhibit good light-harvesting ability and enhanced photoresponses compared with the reverse rainbow photocathodes under white LED light illumination. Under minimally optimized conditions, a photocurrent density of as high as 115 μA·cm−2 and a Faradaic efficiency of 99.5% are achieved, which is among the most effective QD-based photocathode water-splitting systems.

The technology of creation the photocathode with quantum efficiency at the level of 5% based on the InP/InGaAs heterostructures is given. The effect of decreasing the quantum efficiency of the photosensitive structure on radiant sensitivity is considered. Several variants of realization of vacuum photoelectronic device with InP/InGaAs photocathode for special purposes are represented.

To realize practical solar hydrogen production, a low‐cost photocathode with high photocurrent density and onset potential should be developed. Herein, an efficient and stable overall photoelectrochemical tandem cell is developed with a Cu3BiS3‐based photocathode. By exploiting the crystallographic similarities between Bi2S3 and Cu3BiS3, a one‐step solution process with two sulfur sources is used to prepare the Bi2S3–Cu3BiS3 blended interlayer. The elongated Bi2S3‐Cu3BiS3 mixed‐phase 1D nanorods atop a planar Cu3BiS3 film enable a high photocurrent density of 7.8 mA cm−2 at 0 V versus the reversible hydrogen electrode, with an onset potential of 0.9 VRHE. The increased performance over the single‐phase Cu3BiS3 thin‐film photocathode is attributed to the enhanced light scattering and charge collection through the unique 1D nanostructure, improved electrical conductivity, and better band alignment with the n‐type CdS layer. A solar‐to‐hydrogen efficiency of 2.33% is achieved under unassisted conditions with a state‐of‐the‐art Mo:BiVO4 photoanode, with excellent stability exceeding 21 h. A novel solution‐processed Bi2S3–Cu3BiS3 mixed phase is fabricated for photoelectrochemical photocathodes generating high photocurrents and onset potential. By exploiting the unique dual‐sulfur‐source chemistry, unique nanostructure is obtained. The Bi2S3–Cu3BiS3 photocathode demonstrates synergetic effects of enhanced light absorption and superior charge transport, enabling 2.33% unassisted solar‐to‐hydrogen conversion efficiency when coupled with Mo:BiVO4 photoanode.

We developed, constructed and commissioned novel photocathode lasers for the X-ray FELs European XFEL and FLASH which allow emittance optimization via beam shaping. Both facilities operate continuously with those lasers since Jan. 2024 with high uptime and excellent performance.

A single-channel, two-spectral image receiver of objects emitting in UV radiation, made in the image intensifier tube architecture, was proposed and investigated. With the help of the COMSOL Multiphysics software package, search optimal measurements of the potential on the elements of the image receiver (silicon membrane, germanium and diamond photocathode, MCP input and output sensors) were implemented, which provides the possibility of registering and presence of UV objects in relation to the terrain.