Roei Remez

Super-narrow frequency conversion

The spectral width of a nonlinear converter is usually thought to be inversely proportional to the length of the nonlinear crystal. We present a method to overcome this limitation using the concept of super-oscillations, thus creating an arbitrarily narrow converter. A “super-narrow” frequency doubler was fabricated by appropriate modulation of its quadratic nonlinear coefficient, showing spectral and thermal response that are narrower by 39% and 69% compared to the side lobes and main lobe of the sinc function response of a standard frequency doubling crystal with the same length. This is accompanied by corresponding reduction of the efficiency to 14% and 0.79% with respect to those of the first side lobe and the main lobe. We propose more advanced modulation patterns, and discuss implications such as nonlinear filtering with higher resolution than the standard crystal.

Prospects for electron beam aberration correction using sculpted phase masks

Technological advances in fabrication methods allowed the microscopy community to take incremental steps towards perfecting the electron microscope, and magnetic lens design in particular. Still, state of the art aberration-corrected microscopes are yet 20-30 times shy of the theoretical electron diffraction limit. Moreover, these microscopes consume significant physical space and are very expensive. Here, we show how a thin, sculpted membrane is used as a phase-mask to induce specific aberrations into an electron beam probe in a standard high resolution TEM. In particular, we experimentally demonstrate beam splitting, two-fold astigmatism, three-fold astigmatism, and spherical aberration.

Superoscillating electron wave functions with subdiffraction spots

Almost one and a half centuries ago, Ernst Abbe [1] and shortly after Lord Rayleigh [2] derived the minimum, diffraction-limited spot radius of an optical lens to be 1.22{\lambda}/(2sin{\alpha}), where {\lambda} is the wavelength and {\alpha} is the semi-angle of the beams convergence cone. Here, we show how to overcome this limit and realize the first super-oscillating massive-particle wave function, which has an arbitrarily small central spot that is much smaller than the Abbe-Rayleigh limit and theoretically even smaller than the de Broglie wavelength. We experimentally demonstrate an electron central spot of radius 106 pm, which is more than two times smaller than the diffraction limit of the experimental setup used. Such an electronic wave function can serve as a probe in scanning transmission electron microscopy, providing improved imaging of objects at the sub-{\AA}ngstrom scale.

Generation of intensity-controlled two-dimensional shape-preserving beams in plasmonic lossy media

Two-dimensional surface-plasmon polariton waves, which propagate at a metal/dielectric interface, exhibit unique and attractive properties. These extraordinary properties, however, are accompanied by fundamentally inherent losses. The latter is probably the most pronounced challenge in the field of plasmonics and a true bottleneck for many applications. Shape-preserving beams, on the other hand, are unique solutions of the wave equation; they maintain their shape with propagation and also possess the ability to self-reconstruct. Here, we study the first realization of surface-plasmon shape-preserving beams, which maintain their shape and intensity over long distances, even when subjected to plasmonic losses. Moreover, their intensity distribution along propagation can be arbitrarily tailored. This is achieved without the use of any gain media, but rather by strictly controlling the initial plasmonic wavefront. This approach can be valuable for a variety of plasmonic applications, such as surface particle trapping and manipulation, on-chip communication, nonlinear optics, and more.

Spherical aberration correction in a scanning transmission electron microscope using a sculpted thin film

Nearly eighty years ago, Scherzer showed that rotationally symmetric, charge-free, static electron lenses are limited by an unavoidable, positive spherical aberration. Following a long struggle, a major breakthrough in the spatial resolution of electron microscopes was reached two decades ago by abandoning the first of these conditions, with the successful development of multipole aberration correctors. Here, we use a refractive silicon nitride thin film to tackle the second of Scherzers constraints and demonstrate an alternative method for correcting spherical aberration in a scanning transmission electron microscope. We reveal features in Si and Cu samples that cannot be resolved in an uncorrected microscope. Our thin film corrector can be implemented as an immediate low cost upgrade to existing electron microscopes without re-engineering of the electron column or complicated operation protocols and can be extended to the correction of additional aberrations.

Observation of linear plasmonic breathers and adiabatic elimination in a plasmonic multi-level coupled system

We provide experimental and numerical demonstrations of plasmonic propagation dynamics in a multi-level coupled system, and present the first observation of plasmonic breathers propagating in such systems. The effect is observed both for the simplest symmetric case of a thin metal layer surrounded by two identical dielectrics, and also for a more complex system that includes five and more layers. By a careful choice of the permittivities and thicknesses of the intermediate layers, we can adiabatically eliminate the plasmonic waves in all the intermediate interfaces, thus enabling efficient vertical delivery and extraction of plasmonic signals between the top layer and deeply buried layers. The observation relies on controlling the excited mode by breaking the symmetry of excitation, which is crucial for obtaining the results experimentally. We also observe this breathing effect for transversely shaped plasmonic beams, with Hermite-Gauss, Airy and Weber wavefronts, that despite the oscillatory nature of propagation in such systems, still preserve all their unique wavefront properties. Finally, we show that such approaches can be extended to plasmonic propagation in a general multi-layered system, opening a path for efficient three-dimensional integrated plasmonic circuitry.

Electron-Beam Shaping

In recent years, advances in nano-machining are thriving, allowing microand nano-scaled elements to be fabricated. Specifically, the authors have fabricated computer-generated holograms using nano-scale phase-masks [1], and demonstrated their operation in a standard TEM. Here, we continue to investigate applications for such phase-masks by imprinting the electron beam with familiar aberrations such as tilt, astigmatism, trefoil, and a spherical phase.

Unveiling the OAM and Acceleration of Electron Beams

Electron beams, specifically in a transmission electron microscope (TEM), are mainly used to investigate biological samples and materials. It was not until recently that investigation of special kinds of beams, namely vortex beams, has begun [1,2]. These beams are especially interesting because they carry orbital angular momentum (OAM) which may be coupled to the atomic wave-function, thus enabling probing of magnetic dichroism [3], for example. In light-optics these beams have long been known, and research into other types of beams, such as accelerating beams, is flourishing. Here we study the well known Airy beam [4,5] in the electron microscope – a shape-invariant, multi-lobed, nonspreading beam whose nodal trajectory follows a parabolic dependence, which has already been exploited in light-optics to overcome the diffraction limit implementing a “super-resolution” technique [6]. Where for the case of vortex beams the OAM property is of utmost importance, in this work we develop a tool for easy measurement of the Airy’s nodal trajectory coefficient, which is the defining property of the Airy beam, derive an elegant analytic model and verify it by fabrication of the relevant amplitude masks and consequent measurement and analysis. Our results agree completely with the proposed model, which is derived without approximations, and nicely relates lightto electron-optics via the geometric ray-tracing technique.

Super Oscillating Nonlinear Crystal

The spectral acceptance bandwidth of a standard nonlinear crystal is inversely proportional to the crystal length. We experimentally show that much narrower width is reached by modulating the nonlinear coefficient with a super-oscillation function.