Electrons interacting with metamaterials: from few-photon sources to electron optics

Abstract

Controlling the trajectory of moving electrons by means of highly efficient aberration-corrected magnetic lenses1 has paved the way toward ultrahigh resolution microscopy and diffraction. Additionally, the advent of ground-potential monochromators has pushed electron spectroscopy into a new era (i.e., where electron energy-loss spectroscopy achieves an unprecedented energy resolution, as high as a few meV).2 Moreover, teaming up electron guns and lasers has enabled a number of new technologies, including ultrafast characterization of optical near fields,3 dielectric laser accelerators,4, 5 and photon-induced near-field electron microscopy.6 As in optics, ultrafast electron microscopy could be further advanced by exploiting time-frequency analysis.7 An example of methods that could stand to benefit from this approach are interferometry techniques, which provide unprecedented knowledge of the spatial profile of electron-induced optical near-field and electronic states in the time-energy phase space. Such insight could enable an understanding of the transition between states and of temporal evolutions (e.g., dephasing). To achieve this in optical studies, the time resolution has generally been increased (i.e., to the attosecond era). This is not feasible with today’s photoemission electron guns, however, due to time jitter. We have developed a new technique for overcoming these shortcomings by enabling the electron to create its own conjugate photons.8 A fast electron (i.e., traveling at 70% of the speed of light) can interact with a precisely designed metamaterial-based electron-driven photon source (EDPHS) to create broadband, coherent, and focused transition radiation: see Figure 1. Figure 1. A fast electron interacting with the electron-driven photon source (EDPHS) can create an ultrafast optical pulse with an energy range of 1–6eV. The EDPHS emission can excite the sample (here a silver disc) and interfere with the electron-induced excitations in the sample. e-: Electron. h̄!: Photon energy.