Perspectives on Designer Photocathodes for X-ray Free-Electron Lasers: Influencing Emission Properties with Heterostructures and Nanoengineered Electronic States

Abstract

The development of photoemission electron sources to specifically address the competing and increasingly stringent requirements of advanced light sources such as X-ray Free Electron Lasers (XFELs) motivates a comprehensive material-centric approach that integrates predictive computational physics models, advanced nano-synthesis methods, and sophisticated surface science characterization with in situ correlated study of photoemission performance and properties. Related efforts in material science are adopting various forms of nanostructure (such as compositionally graded stoichiometry in heterostructured architectures, and quantum features) allowing for tailored electronic structure to control and enhance opto-electronic properties. These methods influence the mechanisms of photoemission (absorption, transport, and emission) but have not, as yet, been systematically considered for use in photocathode applications. Recent results and near-term opportunities are described to exploit controlled functionality of nanomaterials for photoemission. An overview of the requirements and status is also provided.

High-Fidelity Prediction of Megapixel Longitudinal Phase-Space Images of Electron Beams Using Encoder-Decoder Neural Networks

“…However, beamdynamics simulations are typically carried out under different theoretical assumptions about collective effects such as space-charge forces, wakefields, and coherent synchrotron radiation. In addition, electron emission from a photocathode is governed by multiple physical processes and is even * jun.zhu@desy.de more difficult to simulate [14]. Moreover, aging of accelerator components affects the long-term operation of a facility but is generally not included in simulations.…”

Highly efficient photoelectric effect in halide perovskites for regenerative electron sources

“…For example, while metal-based electron sources exhibit excellent lifetime in operation (several months), their QE is typically of the order of 0.1% or less, which is more than two orders of magnitude lower than state-of-the-art semiconductorbased electron sources. On the other hand, the latter type of electron sources is more sensitive to degradation, and requires intensive material and device preparation [18][19][20][21] . The main advantage of non-metallic photocathodes is that they generate high free-electron currents (several milliamperes) due to their high QE spanning the ultraviolet and visible light spectrum range.…”

Optical-Resonance-Enhanced Photoemission from Nanostructured GaAs Photocathodes

“…The QE stability of a GaAs photocathode is largely dependent on the vacuum conditions under which the measurement occurs. Practical high voltage photoguns used at modern accelerators [5][6][7][8] can be expected to provide better vacuum and therefore better stability than reported here. The excellent NEA activation performance of NPA photocathodes can be also attributed to the larger effective active surface area compared to that of a flat wafer.…”