Nikolai Berkovitch

Nano-plasmonic antennas in the near infrared regime

Plasmonic nano-antennas constitute a central research topic in current science and engineering with an enormous variety of potential applications. Here we review the recent progress in the niche of plasmonic nano-antennas operating in the near infrared part of the spectrum which is important for a variety of applications. Tuning of the resonance into the near infrared regime is emphasized in the perspectives of fabrication, measurement, modeling, and analytical treatments, concentrating on the vast recent achievements in these areas.

Nonlocal ponderomotive nonlinearity in plasmonics

We analyze an inherent nonlinearity of surface plasmon polaritons at the interface of Fermi-Dirac metal plasma, stemming from the depletion of electron density in high-intensity regions. The derived optical nonlinear coefficients are comparable with the experimental values for metals. We calculate the dispersion relations for the nonlinear propagation of high-intensity surface plasmon polaritons, predicting a nonlinearity-induced cutoff and vanishing group velocity.

Controlling absorption enhancement in organic photovoltaic cells by patterning Au nano disks within the active layer.

We show experimentally and theoretically enhancement of external quantum efficiency in the green-NIR spectrum for organic photovoltaic device, by the incorporation of patterned Au nano-disk arrays that extend from the front electrode into the active layer. Enhancement mechanisms and design rules are extracted by comprehensive simulations which match the experimental findings. The enhanced efficiency is shown to stem from field enhancement originating from both localized plasmonic resonances and periodic nano patch antennas configuration.

Plasmonic Nanoantennas for Broad-Band Enhancement of Two-Photon Emission from Semiconductors

We demonstrate experimentally and theoretically a broad-band enhancement of the spontaneous two-photon emission from AlGaAs at room temperature by plasmonic nanoantenna arrays fabricated on the semiconductor surface. Plasmonic structures with inherently low quality factors but very small effective volumes are shown to be optimal. A 20-fold enhancement was achieved for the entire antenna array, corresponding to an enhancement of nearly 3 orders of magnitude for charge carriers emitting at the near field of a plasmonic antenna.

Resonances on-demand for plasmonic nano-particles.

A method for designing plasmonic particles with desired resonance spectra by exploiting the interaction of local geometry with surface charge distribution and applying evolutionary algorithm is presented. The method is based on repetitive perturbations of an initial particles shape while calculating the eigenvalues of the various quasistatic resonances. Novel family of particles with collocated dipole-quadrupole resonances was designed, as an example for the unique power of the method.

Concave Plasmonic Particles: Broad-Band Geometrical Tunability in the Near-Infrared

Optical resonances spanning the near-infrared spectrum (1-2 microm) were exhibited experimentally by arrays of plasmonic nanoparticles with concave cross-section. The concavity of the particle was shown to be the key component for enabling the broad band tunability of the resonance frequency, even for particles with dimensional aspect ratios of order unity. The atypical flexibility of setting the resonance wavelength is shown to stem from a unique interplay of local geometry with surface charge distributions.

Efficient coupling and field enhancement for the nano-scale: plasmonic needle.

Theoretical demonstration of efficient coupling and power concentration of radially-polarized light on a conical tip of plasmonic needle is presented. The metallic needle is grown at the center of radial plasmonic grating, engraved in a metal surface. The electromagnetic field distribution was evaluated by Finite Elements and Finite-Difference-Time-Domain methods. The results show that the field on the tip of the needle is significantly enhanced compared to the field impinging on the grating. The power enhancement exhibited a resonant behavior as a function of needle length and reached values of approximately 10(4). Test samples for few types of characterization schemes were fabricated.

Light emission rate enhancement from InP MQW by plasmon nano-antenna arrays

Arrays of gold single-strip and double-strip nano-antennas, with resonance in the wavelength range of 1200-1600 nm, were fabricated on the top of InGaAs/InP multi quantum well structure. Photo-luminescence from the quantum-wells was measured and shown to be enhanced by a factor of up to 9, with maximum enhancement wavelength corresponding to the nano-antennas resonance. Emission enhancement is attributed to the coupling of emitting charge-carriers to the plasmonic nano-antennas, causing an estimated increase in the radiative recombination rate by a factor of ~25, thus making it dominant over non-radiative recombination. This effect will enable fast modulation of InP-based nano-emitters spontaneously emitting at telecom-wavelength.

Novel complex modes in asymmetrical nanoscale plasmonic waveguides.

Highly asymmetrical plasmonic waveguides exhibit guiding even below the expected cut-off dimensions. A new family of discrete complex guided modes of asymmetrical waveguides with losses--which may assist in nano plasmonic guiding, is found by employing the effective index method. These modes having a real effective index lower than the substrate index of refraction can be exhibited also in regular (lossy) photonics.

Coupling of nano-stripe and nano-slot plasmonic waveguides

Coupling effects between two types of surface-plasmon-polariton waveguides in the subwavelength regime (stripes and slots) are measured experimentally at ¿ = 1.55¿m using near field microscopy and validated by finite element modal calculations.