Radiation from Quantum Electrons in Strong Fields

The generation of electromagnetic radiation via the controlled movement of electrons has played a key role in technological development for over a century. It is through the simple process of accelerating electrons that we produce this radiation [1]. Recent developments in photon-induced near field electron microscopy (PINEM) [2,3] have provided novel techniques for engineering electric fields in or near the surface of nanomaterials. Through these designer electromagnetic environments we can control with high precision the quantum dynamics of electrons passing through it, and their subsequent radiation [4].

Here we develop the formalism to predict and analyze the radiation from quantum electrons in strong fields, and reveal a new opportunity for high harmonic generation from free electrons. We exploit the sub-nanometer resolution and (moderately) relativistic energies available in electron microscopes to precisely control the electron’s quantized photon exchange with the background electric field – thus controlling the radiation emitted during this process. Importantly, we further find significant radiation enhancement when the electron-field interaction occurs in or near a medium. By controlling the background field we can tune the frequency spectrum of outgoing Cherenkov radiation as well as enhance the electron-field interaction by modulating the electron with radiation that a priori satisfies the Cherenkov condition. These capabilities show the prospects of shaping light-matter interactions by the precise control of the electrons’ quantum nature.

[1] Levi Schachter, Beam-wave interaction in periodic and quasi-periodic structures (particle acceleration and detection), Springer, 2011.

[2] Brett Barwick, David J. Flannigan, and Ahmed H. Zewail, Photon-induced near-field electron microscopy, Nature, 2009.

[3] Sang Tae Park, Milo Lin and Ahmed H Zewail, Photon-induced near-field electron microscopy (PINEM): theoretical and experimental, New Journal of Physics, 2012.

[4] Armin Feist et. al., Quantum coherent optical manipulation in an ultrafast transmission electron microscope, Nature, 2015.