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Ultrafast photoexcitation of semiconducting photocathode materials

Hilde Bellersen1,2,*, Michele Guerrini1,†, and Caterina Cocchi1,2,‡

  • *Contact author: hilde.bellersen@uni-jena.de
  • †Contact author: michele.guerrini@uni-oldenburg.de
  • ‡Contact author: caterina.cocchi@uni-jena.de
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Phys. Rev. B 112, 024314 – Published 22 July, 2025

DOI: https://doi.org/10.1103/449c-nn6y

Abstract

Cs-based semiconductors like Cs3Sb and Cs2Te are currently used as photocathodes in particle accelerators. Their performance as electron sources critically depends on their interaction with intense laser sources. However, detailed studies on their strong-field excitation dynamics are currently missing. In this work, we employ real-time time-dependent density functional theory to investigate from first principles the time-dependent response of Cs3Sb and Cs2Te to ultrafast pulses of varying intensities, ranging from 1GW/cm2 to 1PW/cm2. Our analysis reveals that nonlinear effects, including high-harmonic generation, emerge with intensities of 100GW/cm2 in Cs3Sb and 200GW/cm2 in Cs2Te. We show that beyond these thresholds, the excitation mechanisms evolve from one-photon absorption saturation to increasingly dominant multiphoton absorption (above 1TW/cm2 for Cs3Sb and 5TW/cm2 for Cs2Te). Under the highest field intensities (>10TW/cm2), the onset of tunnel ionization is identified through occupation analysis. These findings offer material-specific insights into the nonlinear optical properties and nonequilibrium electron distributions in the femtosecond regime of these photocathode materials, providing valuable indications to optimize their performance and stability as high-brightness electron sources.

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Phys. Rev. B 112, 024314– Published 22 July, 2025
  • Received 12 March 2025
  • Revised 28 May 2025
  • Accepted 1 July 2025
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