Yuval Tsur

Arbitrary holographic spectral shaping of plasmonic broadband excitations

We demonstrate a new method for controlling the broadband excitations of surface plasmons. This method is based on computer-generated holographic gratings and enables not only the coupling of the broadband illumination with surface plasmons, but also the arbitrary shaping of their spectra. As an example, we demonstrate several spectral shapes numerically and measure them experimentally, finding a good agreement with the simulation results. In addition, we show the potential for shaping the plasmonic spatial profile simultaneously with its spectral profile. This method may be useful for on-chip communication and light filtering as well as for sensing and temporal manipulation of ultrashort pulses.

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.

Self-similar propagation of Hermite-Gauss water-wave pulses.

We demonstrate both theoretically and experimentally propagation dynamics of surface gravity water-wave pulses, having Hermite-Gauss envelopes. We show that these waves propagate self-similarly along an 18-m wave tank, preserving their general Hermite-Gauss envelopes in both the linear and the nonlinear regimes. The measured surface elevation wave groups enable observing the envelope phase evolution of both nonchirped and linearly frequency chirped Hermite-Gauss pulses, hence allowing us to measure Gouy phase shifts of high-order Hermite-Gauss pulses for the first time. Finally, when increasing pulse amplitude, nonlinearity becomes essential and the second harmonic of Hermite-Gauss waves was observed. We further show that these generated second harmonic bound waves still exhibit self-similar Hermite-Gauss shapes along the tank.

On-chip plasmonic spectrometer.

We report a numerical and experimental study of an on-chip optical spectrometer, utilizing propagating surface plasmon polaritons in the telecom spectral range. The device is based on two holographic gratings, one for coupling, and the other for decoupling free-space radiation with the surface plasmons. This 800 μm×100 μm on-chip spectrometer resolves 17 channels spectrally separated by 3.1 nm, spanning a freely tunable spectral window, and is based on standard lithography fabrication technology. We propose two potential applications for this new device; the first employs the holographic control over the amplitude and phase of the input spectrum, for intrinsically filtering unwanted frequencies, like pump radiation in Raman spectroscopy. The second prospect utilizes the unique plasmonic field enhancement at the metal-dielectric boundary for the spectral analysis of very small samples (e.g., Mie scatterers) placed between the two gratings.

Propagation Dynamics of Nonspreading Cosine-Gauss Water-Wave Pulses.

Linear gravity water waves are highly dispersive; therefore, the spreading of initially short wave trains characterizes water surface waves, and is a universal property of a dispersive medium. Only if there is sufficient nonlinearity does this envelope admit solitary solutions which do not spread and remain in fixed forms. Here, in contrast to the nonlinear localized wave packets, we present both theoretically and experimentally a new type of linearly nondispersive water wave, having a cosine-Gauss envelope, as well as its higher-order Hermite cosine-Gauss variations. We show that these waves preserve their width despite the inherent dispersion while propagating in an 18-m wave tank, accompanied by a slowly varying carrier-envelope phase. These wave packets exhibit self-healing; i.e., they are restored after bypassing an obstacle. We further demonstrate that these nondispersive waves are robust to weakly nonlinear perturbations. In the strong nonlinear regime, symmetry breaking of these waves is observed, but their cosine-Gauss shapes are still approximately preserved during propagation.

Iron doped silver halide crystals and their potential as middle infrared solid state lasers

The spectroscopic properties of Fe2+:AgClxBr1−x crystals were investigated in the near and the middle infrared. Broad absorption bands were observed at low temperatures in the 1.3–2.5 μm range, and broad emission bands were observed in the 2.5–4.4 μm range. Luminescence lifetimes of up to 160 μs were measured at 3.6 μm. These results indicate that Fe2+:AgClxBr1−x crystals can be used as gain media for middle infrared solid-state lasers, operating continuously at 80 K. These doped silver halide crystals can be extruded to form optical fibers, possibly introducing another family of fiber lasers for this spectral range.

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.

Compensating Plasmonic Losses by Wavefront Manipulation

We demonstrate experimentally the generation of unique surface-plasmon beams, which compensate the inherent losses of plasmons without using gain media, and show that these beams can extend the limited propagation length of surface-plasmons.