We investigate the ultrafast photoelectric effect at sharp tungsten needles and find a considerable energy offset between thermally emitted and photoemitted electrons. Neither changes in temperature nor tuning the work function by the Schottky effect strongly affect the free-space energy of the photoelectrons. We explain these discoveries by a direct optical excitation within the band structure of tungsten, followed by scatter-free transport to the surface and emission into free space. Experiments at different photon energies support that the material and not the photon energy determines the primary properties of the electron beam.

We demonstrate multi-dimensional control of electrons in a transmission electron microscope using the electromagnetic field of terahertz single-cycle pulses.

Mit der Attosekunden‐Elektronenmikroskopie können optische Antworten und elektronische Reaktionsmechanismen in komplexen Materialien direkt in Raum und Zeit gefilmt werden. Wir erreichen dabei simultan eine räumliche Auflösung im Bereich einzelner Nanometer sowie eine Zeitauflösung im Attosekunden‐Bereich, schneller als die Oszillationen von Licht. Die Leistungsfähigkeit dieser Methode demonstrieren wir an einigen nanophotonischen Metamaterialien. Sie ist darüber hinaus zum Beispiel in der Katalysatorforschung oder der Entwicklung neuer elektronischer Schaltkreise anwendbar.

Ultrafast electron microscopy provides a movie-like access to structural dynamics of materials in space and time, but fundamental atomic motions or electron dynamics are, so far, too quick to be resolved. Here we report the all-optical control, compression and characterization of electron pulses in a transmission electron microscope by the single optical cycles of laser-generated terahertz light. This concept provides isolated electron pulses and merges the spatial resolution of a transmission electron microscope with the temporal resolution that is offered by a single cycle of laser light. Central to these achievements is a perforated parallel-plate metallic waveguide in which transverse velocity mismatch and magnetic forces are mitigated by electrically constructive and magnetically destructive interferences of incoming and reflected terahertz half-cycles from a displaced waveguide termination. Measurements of spatial chirp via energy-filtered imaging reveal flat pulses with no transversal deflection or temporal aberrations at the specimen. We also report the all-optical control of multi-electron states and discover a substantial two-electron and three-electron anti-correlation in the time domain. These results open up the possibility to visualize atomic and electronic motions together with their quantum correlations on fundamental dimensions in space and time.

Angular momentum and torque are important principles for basic and applied physics on any spatial scales, for example, in elementary particles, cold gases, optical tweezers, quantum information technology, metamaterials, gyroscopes or astrophysical entities. Investigating or controlling angular momentum in atoms or sub-atomic structures requires torque on femtosecond and picometer scales, far below the capabilities of laser light. Here we shape the electrons in an electron microscope into wave packets with a time-dependent chirality and internal torque. We intersect the electron beam with chiral laser light to create discrete energy sidebands by multiple helical photon absorptions that create a correlation between orbital angular momentum and kinetic energy. Dispersion of these partial waves due to the electron rest mass then converts each single electron into a wave function with internal torque. Under our control, a left-handed matter wave becomes right-handed in femtosecond times. Such quantum objects will facilitate research on angular momentum and chirality on atomic and sub-atomic scales.

Chirality is a phenomenon with widespread relevance in fundamental physics, material science, chemistry, optics, and spectroscopy. In this work, we show that a free electron can be converted by the field cycles of laser light into a right-handed or left-handed coil of mass and charge. In contrast to phase-vortex beams, our electrons maintained a flat de Broglie wave but obtained their chirality from the shape of their expectation value in space and time. Measurements of wave function densities by attosecond gating revealed the three-dimensional shape of coils and double coils with left-handed or right-handed pitch. Engineered elementary particles with such or related chiral geometries should be useful for applications in chiral sensing, free-electron quantum optics, particle physics or electron microscopy.

We study ultrafast charge and spin dynamics in magnetoplasmonic Au-Ni nanostructures. Experiments reveal modification of the ultrafast magnetization dynamics time induced by a strong plasmonic response, and the results are supported by numerical modelling.

Ultrafast electron microscopy provides a movie-like access to structural dynamics of materials in space and time, but fundamental atomic motions or electron dynamics are, so far, too quick to be resolved. Here, we report the all-optical control, compression, and characterization of electron pulses in a transmission electron microscope by the single optical cycles of laser-generated terahertz light. This concept provides isolated electron pulses and merges the spatial resolution of a transmission electron microscope with the temporal resolution that is offered by a single cycle of laser light. We also report the all-optical control of multi-electron states and find a substantial two-electron and three-electron anticorrelation in the time domain. These results open up the possibility to visualize atomic and electronic motions together with their quantum correlations on fundamental dimensions in space and time.

The primary step of almost any interaction between light and materials is the electrodynamic response of the electrons to the optical cycles of the impinging light wave on sub-wavelength and sub-cycle dimensions 1 . Understanding and controlling the electromagnetic responses of a material 2 – 11 is therefore essential for modern optics and nanophotonics 12 – 19 . Although the small de Broglie wavelength of electron beams should allow access to attosecond and ångström dimensions 20 , the time resolution of ultrafast electron microscopy 21 and diffraction 22 has so far been limited to the femtosecond domain 16 – 18 , which is insufficient for recording fundamental material responses on the scale of the cycles of light 1 , 2 , 10 . Here we advance transmission electron microscopy to attosecond time resolution of optical responses within one cycle of excitation light 23 . We apply a continuous-wave laser 24 to modulate the electron wave function into a rapid sequence of electron pulses, and use an energy filter to resolve electromagnetic near-fields in and around a material as a movie in space and time. Experiments on nanostructured needle tips, dielectric resonators and metamaterial antennas reveal a directional launch of chiral surface waves, a delay between dipole and quadrupole dynamics, a subluminal buried waveguide field and a symmetry-broken multi-antenna response. These results signify the value of combining electron microscopy and attosecond laser science to understand light–matter interactions in terms of their fundamental dimensions in space and time.

Molecular polaritons are hybrid light-matter states that emerge when a molecular transition strongly interacts with photons in a resonator. At optical frequencies, this interaction unlocks a way to explore and control new chemical phenomena at the nanoscale. Achieving such control at ultrafast timescales, however, is an outstanding challenge, as it requires a deep understanding of the dynamics of the collectively coupled molecular excitation and the light modes. Here, we investigate the dynamics of collective polariton states, realized by coupling molecular photoswitches to optically anisotropic plasmonic nanoantennas. Pump-probe experiments reveal an ultrafast collapse of polaritons to pure molecular transition triggered by femtosecond-pulse excitation at room temperature. Through a synergistic combination of experiments and quantum mechanical modelling, we show that the response of the system is governed by intramolecular dynamics, occurring one order of magnitude faster with respect to the uncoupled excited molecule relaxation to the ground state.

We show a process for the fabrication of nanopores arrays via photocatalysis triggered by electromagnetic field enhancement in plasmonic structures immersed in metallic salt solutions and generating hotspots causing pore diameter reduction below 5 nm.

We show that plasmonic solid-state nanopores with tunable hole diameter can be prepared via a photocatalytic effect resulting from the enhanced electromagnetic field inside a metallic ring prepared on top of a dielectric nanotube. Under white light illumination, the maximum field intensity in these nanorings induces a site selective metal nucleation and growth. We used this approach to prepare bare Au and bimetallic Au-Ag nanorings and demonstrate the reduction of the initial inner diameter of the nanopore down to 4 nanometers. This process can be applied over large arrays with good reproducibility and good control on the nanopore diameter. The tunability of the nanopore diameter can be used to enable optimized detection of single entities with different size, such as single nanoparticles or biomolecules. As proof-of-concept, we demonstrate the versatility of the platform to perform single object detection of dsDNA, and Au nanoparticles with a diameter of 15 nm and 30 nm. We support our experimental findings with numerical simulations that provide insights into the electromagnetic field intensity distribution, showing that a field intensity enhancement of up to 104 can be achieved inside the nanopores. This strong field confinement inside the final nanopore can be used to perform enhanced optical measurements, and to generate local heating, thereby modifying the ionic conductance of the nanopore

Defects in 2D semiconductors present an exciting materials platform to engineer atomic quantum states in a robust, yet tunable solid-state system. In this contribution, we will present our efforts to probe the dynamics of point defects in transition metal dichalcogenides (TMDs) at picosecond time and atomic spatial resolution by means of an ultrafast THz pulse driven scanning tunneling microscope (THz-STM). We demonstrate an efficient, continuous carrier-envelope phase control, which enables state-selective tunneling into specific defect orbitals in our multi-MHz repetition rate system.

We report a process for fabricating sub-10 nm nanopores via photocatalysis caused by electromagnetic field enhancement in plasmonic structures, which immersed in metallic salt solutions triggers hotspots for metallic deposition causing pore diameter shrinkage.

Frustrated internal reflection enables precise and efficient THz phase control for ultrafast scanning tunneling microscopy, allowing state-selective investigation of quantum dynamics with picosecond time and atomic spatial resolution at multi-MHz repetition rate.

Event-driven hybrid pixel detectors with nanosecond time resolution have opened up novel pathways in modern ultrafast electron microscopy, for example in hyperspectral electron-energy loss spectroscopy or free-electron quantum optics. However, the impinging electrons typically excite more than one pixel of the device, and an efficient algorithm is therefore needed to convert the measured pixel hits to real single-electron events. Here we present a robust clustering algorithm that is fast enough to find clusters in a continuous stream of raw data in real time. Each tuple of position and arrival time from the detector is continuously compared to a buffer of previous hits until the probability of a merger with an old event becomes irrelevant. In this way, the computation time becomes independent of the density of electron arrival and the algorithm does not break the operation chain. We showcase the performance of the algorithm with a 'timepix' camera in two regimes of electron microscopy, in continuous beam emission and laser-triggered femtosecond mode.

We advance transmission electron microscopy to attosecond time resolution and probe the electromagnetic near-fields of nanostructures in space and time.

In the past twenty years, we have reached a broad understanding of many light-driven phenomena in nanoscale systems. The temporal dynamics of the excited states are instead quite challenging to explore, and, at the same time, crucial to study for understanding the origin of fundamental physical and chemical processes. In this review we examine the current state and prospects of ultrafast phenomena driven by plasmons both from a fundamental and applied point of view. This research area is referred to as ultrafast plasmonics and represents an outstanding playground to tailor and control fast optical and electronic processes at the nanoscale, such as ultrafast optical switching, single photon emission and strong coupling interactions to tailor photochemical reactions. Here, we provide an overview of the field, and describe the methodologies to monitor and control nanoscale phenomena with plasmons at ultrafast timescales in terms of both modeling and experimental characterization. Various directions are showcased, among others recent advances in ultrafast plasmon-driven chemistry and multi-functional plasmonics, in which charge, spin, and lattice degrees of freedom are exploited to provide active control of the optical and electronic properties of nanoscale materials. As the focus shifts to the development of practical devices, such as all-optical transistors, we also emphasize new materials and applications in ultrafast plasmonics and highlight recent development in the relativistic realm. The latter is a promising research field with potential applications in fusion research or particle and light sources providing properties such as attosecond duration.

We study ultrafast dynamics of photocromic molecules both weakly and strongly coupled to plasmonic nanoantennas. Experiments, verified by quantum modelling, reveal subps collapse of molecular polaritons to intramolecular dynamics induced by interaction with the plasmons.

Plasmonic solid‐state nanopores with tunable hole diameters can be prepared via a photocatalytic effect resulting from the enhanced electromagnetic (EM) field inside a metallic ring on top of a dielectric nanotube. Under white light illumination, the plasmon‐enhanced EM‐field induces a site‐selective metal nucleation and growth within the ring. This approach is used to prepare Au and bimetallic Au–Ag nano‐rings and demonstrate the reduction of the initial inner diameter of the nanopore down to 4 nm. The tunability of the nanopore diameter can be used to enable optimized detection of single entities with different sizes. As a proof‐of‐concept, single object detection of double stranded DNA (dsDNA) and Au nanoparticles (AuNPs) with a diameter down to 15 nm is performed. Numerical simulations provide insights into the EM‐field distribution and confinement, showing that a field intensity enhancement of up to 10 4 can be achieved inside the nanopores. This localized EM‐field can be used to perform enhanced optical measurements and generate local heating, thereby modifying the properties of the nanopore. Such a flexible approach also represents a valuable tool to investigate plasmon‐driven photochemical reactions, and it can represent an important step toward the realization of new plasmonic devices.