Photocathodes are key elements in high-brightness electron sources and ubiquitous in the operation of large-scale accelerators. In this work, we propose the use of ultrafast laser nanostructuring techniques on copper photocathodes as a way to enhance the quantum efficiency of metallic photocathodes and enable their use in next-generation electron photoinjectors. When the surface is nanoengineered with patterns and particles much smaller than the optical wavelength, it can lead to the excitation of localized surface plasmons that produce hot electrons, ultimately contributing to the overall charge produced. To quantify the performance of laser nanopatterned photocathodes, we measured their quantum efficiency in a typical electron gun setup. Our experimental results suggest that plasmon-induced hot electrons lead to a significant increase in quantum efficiency, showing an overall charge enhancement factor of at least 4.5 and up to 25. We demonstrate laser nanopatterned plasmonic photocathodes outperform standard metallic photocathodes, and can be directly produced in-situ at the electron gun level in vacuum environments and without any disruptive intervention.
We study the propagation of coherent broadband light through laser induced periodic surface structures (LIPSS) fabricated in diamond, by comparing the performance of the laser generated nanostructures with sinusoidal ideal structures in the near-IR. The simulations were carried out for a variety of LIPSS morphologies, including nanostructure aspect ratio and the irregularities arising from the LIPSS technique. The results show that these irregularities produce substantial diffraction compared to the ideal structures, meaning that their use for some optical applications may be limited.
We have recently demonstrated high repetition rate tabletop lasers operating at wavelengths as short as 10.9 nm
based on collisional transient excitation of ions in plasmas created by laser heating of solid targets. As a further step in
the development of these lasers into very high brightness and fully coherent soft x-ray sources, we have demonstrated
injection seeding of the amplifiers with high harmonic seed pulses. We report results of an experiment in which a 32.6
nm Ne-like Ti amplifier was used to amplify a seed pulse from the 25th harmonic of Ti:Sapphire into the gain saturation
regime. Simultaneous amplification of the 27th harmonic at 30.1 nm was also observed. The seeded soft x-ray laser beam
was measured to approach full spatial coherence. We have demonstrated that this scheme is scalable to shorter
wavelengths and that is capable of producing extremely bright soft x-ray laser pulse with essentially full coherence.
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