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We investigate silicon waveguides with subwavelength-scale modulation for applications in free-electron-photon interactions. The modulation enables velocity matching and efficient interactions between low-energy electrons and co-propagating photons. Specifically, we design a subwavelength-grating (SWG) waveguide for interactions between 23-keV free electrons and ≈1500-nm photons. The SWG waveguide and electron system exhibit a coupling coefficient of |gQu| = 0.23, and as we corroborate with time-domain, particle-in-cell simulations, the system operates as a backward-wave oscillator. Overall, our results show that modulated waveguides could open the door to strong, extended interactions between photons and low-energy (10-keV-scale) electrons, like those typically present in scanning electron microscopes. Additionally, our SWG waveguide design suggests that periodic waveguides could offer intriguing dispersion engineering opportunities for tailoring these interactions.
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Subwavelength-Structured Waveguides for Free-Electron-Photon Interactions
The interaction between free electrons and photons in electron microscopes offers unique opportunities for microscopy and quantum science. For example, modulating electron beams with multiple laser excitations, researchers have demonstrated a novel near-field electron microscope, capable of probing electromagnetic excitations on the nanometer spatial scale and in the attosecond (10 −18 s) temporal range [see D. Nabben et al., Nature, 619, 63 (2023)]. Additionally, it has recently been demonstrated that the interaction between free electrons and photons in an electron microscope can be quantum coherent, and furthermore, this quantum coherence could potentially be leveraged for heralded sources of single electrons and photons [see A. Feist et al., Science, 377, 777 (2022)]. Although promising, these innovations in free-electron-photon interactions have thus far suffered a significant limitation: they require high-energy (>100-ke V) electron beams. Accordingly, these demonstrations have taken place in energetic (and expensive) transmission electron microscopes (TEMs). TEMs are a logical setting for these experiments, as their high-energy electrons can be velocity-matched to co-propagating photons in dielectric waveguides. However, achieving such velocity-matching between photons in conventional dielectric waveguides and electrons is not feasible for the low electron energies (<30-keV) in more common scanning electron microscope (SEMs).
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- Award ID(s):
- 2110556
- PAR ID:
- 10550546
- Publisher / Repository:
- IEEE
- Date Published:
- ISBN:
- 978-1-946815-19-4
- Page Range / eLocation ID:
- 410 to 410
- Format(s):
- Medium: X
- Location:
- Boulder, CO, USA
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.23919/USNC-URSINRSM60317.2024.10464701
