Search for: All records

Abstract We analytically describe the noise properties of a heralded electron source made from a standard electron gun, a weak photonic coupler, a single photon counter, and an electron energy filter. We describe the sub-Poissonian statistics of the source, the engineering requirements for efficient heralding, and several potential applications. We use simple models of electron beam processes to demonstrate advantages which are situational, but potentially significant in electron lithography and scanning electron microscopy. 

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 |g_Qu| = 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. 

We investigate how free-electrons can excite modes in nearby photonic waveguides. Using particle-in-cell simulations, we explore how a free-electron packet can couple energy into multiple, velocity-matched modes of an adjacent silicon waveguide. 

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). 

We investigate dielectric waveguides with subwavelength-scale modulation for applications in free-electron-photon interactions. We show that such waveguides are capable of supporting low-loss modes that can efficiently couple to co-propagating, <10-keV electrons.