The formation of a columnar structure, different expansion directions of the luminous (monomers) and obscure (droplets) plume species, and gradual deflection of the luminous plume are found to be interrelated in special experiments on pulsed laser deposition of Si. The obscure species always expands in the direction of incidence, which leads to a characteristic skewed angular distribution of the deposition rate. These observations are explained by the change of the microscopic mechanism of laser ablation from monomer evaporation at low local fluences to phase explosion at higher local fluences.

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.

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.

In view of the demand for high-quality thermal neutron detectors, boron films have recently attracted widespread research interest because of their special properties. In this work, we report on the deposition of boron films on silicon substrates by sub-picosecond pulsed laser deposition (PLD) at room temperature. Particular emphasis was placed on the investigation of the effect of the laser energy density (fluence) on the ablation process of the target material, as well as on the morphological properties of the resulting films. In addition, based on the study of the ablation and deposition rates as a function of the fluence, the ablation/deposition mechanisms are discussed. We show that well-adherent and stable boron films, with good quality surfaces revealing a good surface flatness and absence of cracks, can be obtained by means of the PLD technique, which proves to be a reliable and reproducible method for the fabrication of thick boron coatings that are suitable for neutron detection technology.