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Surging interests in point-of-device miniaturization have led to the development of metasurface-based optical components. Here, we demonstrate an electrically-driven ultracompact beam controller in the infrared spectral range. The effect benefits from diffraction gratings consisting of the commercially available conductive polymer PEDOT:PSS, which exhibits metal-to-insulator transition characteristics upon electrical biasing. By combining several metagratings with different superlattice periods in electrically isolated areas, our device enables diffraction beams at 16 and 33.5° when applying voltages of only ±1 V. Furthermore, no diffraction is realized by switching off the plasmonic property of the gratings. Dynamic control of electromagnetic wave via the presented platforms could be transformative for sensing, imaging, and communication applications.

We present an electrically switchable, compact metasurface device based on the metallic polymer PEDOT:PSS in combination with a gel polymer electrolyte. Applying square-wave voltages, we can reversibly switch the PEDOT:PSS from dielectric to metallic. Using this concept, we demonstrate a compact, standalone, and CMOS compatible metadevice. It allows for electrically controlled ON and OFF switching of plasmonic resonances in the 2–3 µm wavelength range, as well as electrically controlled beam switching at angles up to 10°. Furthermore, switching frequencies of up to 10 Hz, with oxidation times as fast as 42 ms and reduction times of 57 ms, are demonstrated. Our work provides the basis towards solid state switchable metasurfaces, ultimately leading to submicrometer-pixel spatial light modulators and hence switchable holographic devices.

Spectroscopic photoemission microscopy is used to detect and quantify a ponderomotive shift in the energy of electrons that are emitted from a surface plasmon polariton focus. The focus is formed on an atomically flat Au(111) surface by an Archimedean spiral and is spatiotemporally separated from the circularly polarized light pulse used to excite the spiral. A spectroscopic analysis of electrons emitted from the focus exhibits a peaked above-threshold electron emission spectrum. From the shift of the peaks as function of laser power the field strength of the surface plasmon polariton was quantitatively determined without free parameters. Estimations of the Keldysh parameter γ = 4.4 and the adiabaticity parameter δ = 4700 indicate that electron emission occurs in a regime of multiplasmon absorption and nonlocalized surface plasmon fields.

The influence of the charge-transfer state on the photogeneration of free charges in alpha-sexithienyl is reassessed. The femtosecond differential transmission spectroscopy on an alpha-sexithienyl film at low temperature is performed by covering a broad range of excitation energies.

Electron beams in electron microscopes are efficient probes of optical near-fields, thanks to spectroscopy tools like electron energy-loss spectroscopy and cathodoluminescence spectroscopy. Nowadays, we can acquire multitudes of information about nanophotonic systems by applying space-resolved diffraction and time-resolved spectroscopy techniques. In addition, moving electrons interacting with metallic materials and optical gratings appear as coherent sources of radiation. A swift electron traversing metallic nanostructures induces polarization density waves in the form of electronic collective excitations, i.e., the so-called plasmon polariton. Propagating plasmon polariton waves normally do not contribute to the radiation; nevertheless, they diffract from natural and engineered defects and cause radiation. Additionally, electrons can emit coherent light waves due to transition radiation, diffraction radiation, and Smith-Purcell radiation. Some of the mechanisms of radiation from electron beams have so far been employed for designing tunable radiation sources, particularly in those energy ranges not easily accessible by the state-of-the-art laser technology, such as the THz regime. Here, we review various approaches for the design of coherent electron-driven photon sources. In particular, we introduce the theory and nanofabrication techniques and discuss the possibilities for designing and realizing electron-driven photon sources for on-demand radiation beam shaping in an ultrabroadband spectral range to be able to realize ultrafast few-photon sources. We also discuss our recent attempts for generating structured light from precisely fabricated nanostructures. Our outlook for the realization of a correlative electron-photon microscope/spectroscope, which utilizes the above-mentioned radiation sources, is also described.

Periodically arranged metallic nanowires on top of a waveguide layer show a strong coupling between the particle plasmon of the wires and the waveguide mode. By introducing a dielectric spacer layer between the metallic structures and the waveguide layer, this coupling can be reduced. Here, the thickness of this spacer layer is varied and the coupling strength is determined for each spacer layer thickness by fitting an effective energy matrix to the energy positions of the resonance peaks. It is found that the coupling strength can be very well described by the electric field amplitude of the waveguide mode at the location of the nanowires. We carried out experiments and found very good agreement with theory and our simple model. Using this method, we achieved experimentally an extremely small mode splitting as small as 25 meV leading to very sharp spectral features. Our pathway and design for tailoring the coupling strength of plasmonic Fano resonances will enable the design of highly sensitive plasmonic sensor devices and open the door for narrow plasmonic spectral features for nonlinear optics and slow light propagation.