Next-generation Electron Sources

Abstract

Electron sources play a crucial role in electron microscopes, particle accelerators and novel light sources. In most cases, the electron source parameters determine the downstream parameters because it is non-trivial to compress or cool electron pulses. For many applications requiring transversely coherent electrons, needle tips have been the preferred electron source for decades, well-known in high-resolution electron microscopy. Recently, these sources have found significant interest in ultrafast applications, where electron pulses are emitted through the illumination of a needle tip with femtosecond laser pulses. We will give an overview of recent developments in ultrafast needle tip-based electron sources. In addition, we will show how the interaction of laser pulses with electron pulses downstream of the source element can help to shape electron beams with highly intriguing properties, such as attosecond pulses, high-energy beams or electron pulses with small energy widths. The most promising approach to accelerate and shape the electron pulses is based on near-field techniques, which, depending on the parameter range, can either be classified as dielectric laser acceleration or photon-induced near-field electron microscopy physics. Finally, we will provide details of the state-of-the-art in two-photon or ponderomotive schemes for temporal electron pulse shaping, before concluding this chapter with a brief review of applications and future outlook.