Angle-resolved Transmission Measurements Research Articles

Experimental Observation of Acoustic Weyl Points and Topological Surface States

Weyl points emerge as topological monopoles of Berry flux in the three-dimensional (3D) momentum space and have been extensively studied in topological semimetals. As the underlying topological principles apply to any type of waves under periodic boundary conditions, Weyl points can also be realized in classical wave systems, which are easier to engineer compared to condensed matter materials. Here, we made an acoustic Weyl phononic crystal by breaking space inversion (P) symmetry using a combination of slanted acoustic waveguides. We conducted angle-resolved transmission measurements to characterize the acoustic Weyl points. We also experimentally confirmed the existence of acoustic "Fermi arcs" and demonstrated robust one-way acoustic transport, where the surface waves can overcome a step barrier without reflection. This work lays a solid foundation for the basic research in 3D topological acoustic effects.

Fabrication and characterization of silver mirror planar microcavity with dye J–aggregates

Silver mirror planar microcavity containing dye J–aggregates is fabricated by a vacuum deposition method. Characterization of the microcavity with the dye J–aggregates of lower concentration (7.70×10−4M) in comparison with the previous studies is performed. Optical strong coupling between excitons and confined photons within the microcavity is demonstrated from the anticrossing of exciton and photon modes. Angle-resolved transmission measurements give a Rabi-splitting energy of ~190meV for the upper and lower polariton splitting. The fabrication of such a simple metal–mirror–based microcavity (Q–factor ~13) leads to a progress of polaritonic characterization of organic media.

Terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes

We demonstrate time-resolved terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes. The angle-resolved transmission measurements reveal anisotropic characteristics of the terahertz electrodynamics in multi-walled carbon nanotubes. The anisotropy is, however, unexpectedly weak: the ratio of the tube-axis conductivity to the transverse conductivity, σz/σxy≅2.3, is nearly constant over the broad spectral range of 0.4–1.6 THz. The relatively weak anisotropy and the strong transverse electrical conduction indicate that THz fields readily induce electron transport between adjacent shells within multi-walled carbon nanotubes.

Optical transmission through two-dimensional arrays ofβ-Sn nanoparticles

We present measurements of the collinear optical transmission through arrays of $\ensuremath{\beta}$-Sn nanoparticles on fused silica substrates. The particles are cylinders or squares with side lengths of 120--520 nm, and heights of 26--118 nm placed in square-periodic arrays fabricated by electron-beam lithography. By placing the 120 nm cylinders in an index-matched environment peaks appear in the transmission spectrum at wavelengths where the diffracted light propagates at a grazing angle to the substrate. Angle-resolved transmission measurements show that the peak positions depend on the angle of incidence, and the shift of the peaks is in excellent agreement with theoretical calculations of the dipole lattice sum. The peak positions can also be matched by a simple wave-vector analysis. The larger square particles show resonant dips in the transmission even without index matching, and the depth of the dips depends on the particle height. By index matching the environment around the large particles, the dips are replaced by peaks.

Phase-shift, refraction and focusing based on the metamaterial technologies

Abstract We address the problem of positive phase-shifting, negative refraction and focusing via a flat lens on the basis of the metamaterial technologies. With this aim, three examples are considered which differ by the technology employed and the operating frequency. The first one concerns negative-zero-positive refraction by using a prism-shaped electromagnetic metamaterial which consists of omega-type inclusion arrays operating at microwaves. The experimental verification was done in this case by angle-resolved transmission measurements. Second, we report on the phase-shift properties of a negative index transmission line which operates at Terahertz frequencies. In order to experimentally demonstrate the left-handed character of the propagation along the line, resulting in a phase advance, we used time domain experiments. At last, focusing by double refraction in a flat negative index lens was demonstrated by the theoretical and experimental mapping of the intensity of the electric field. Such a mapping of the E-field was carried out at near infrared (∼1.5 μm) by analysis in the time domain and scanning by near field optical microscopy. To cite this article: D. Lippens, C. R. Physique 10 (2009).

Tailoring radiative and non-radiative losses of thin nanostructured plasmonic waveguides

Thin nanostructured metal films allow to control radiative and non-radiative losses of surface plasmon polariton modes without changing their group velocities. This effect is studied in plasmonic waveguides made of thin gold films drilled with very narrow slits and deposited on a GaAs substrate. The analysis is supported by high-resolution angle-resolved transmission measurements and rigorous electromagnetic calculations. We show that the excitation of air/gold and gold/GaAs surface waves leads to Fano-type resonances with specific light localization into the slits. As a result, gold/GaAs surface waves induce a modulation of radiative and non-radiative losses of air/gold surface waves. The minimum and maximum of the Fano-type resonance introduce two propagation regimes. In the radiative propagation regime, the losses due to the absorption are negligible, whereas an efficient inhibition of free-space coupling is demonstrated in low-loss propagation regime.

Optical characterization of photonic crystal slabs using orthogonally oriented polarization filters

We present an experimental method for direct analysis of guided-mode resonances in photonic crystal slab structures using transmission measurements. By positioning the photonic crystal slab between orthogonally oriented polarization filters light transmission is suppressed except for the guided-mode resonances. Angle resolved transmission measurements with crossed polarizers are performed to obtain the band structure around the Gamma-point. Results are compared to mode simulations. Spatially resolved measurements in a confocal microscope setup are used for homogeneity characterizations. Stitching errors and inhomogeneities in exposure dose down to 1.3% in photonic crystal slabs fabricated by electron beam lithography are observed using this method.

Negative-zero-positive metamaterial with omega-type metal inclusions

We report on a negative-zero-positive metamaterial based on an omega-type microstructure with special attention on the nonvanishing group velocity for a zero refractive index. We first investigate the dispersion characteristics by full wave analysis, by stressing the necessary conditions of equality between the electric and magnetic plasma frequencies which are characteristic of the dispersion of the effective permittivity and permeability. Also, tuning of the gapless transition frequency between the left and right-handed dispersion branches was analyzed when the permittivity of the host substrate is changed. Last, we demonstrate experimentally the balanced composite character of the dispersion by frequency and angle-resolved transmission measurements, carried out at centimeter wavelengths on slabs and wedge-type prototypes, respectively.

Toward tunable light propagation and emission in thin nanostructured plasmonic waveguides

High-resolution angle-resolved transmission measurements are carried out through nanostructured plasmonic waveguides made of thin gold films with very narrow slits deposited on GaAs substrates. They reveal transmission intensity modulations along the air/metal surface plasmon band, due to the presence of metal/substrate surface modes. Two propagation regimes have been identified. In this plasmonic waveguide, the radiative emission can be enhanced or inhibited by a slight modification of the refractive index of the substrate (δn∕n≃1%), allowing to control the propagation regime of surface plasmon waves along the air/metal interface.

Angle-resolved transmission measurements through anisotropic two-dimensional plasmonic crystals

We report on high-accuracy angle-resolved optical transmission measurements through anisotropic 2D plasmonic crystals made of gold films with large-area rectangular arrays of nanoscale square holes, deposited on GaAs substrates. The measurements reveal the dispersion relations of air-gold and gold-GaAs surface plasmon polaritons. The crystal anisotropy induces a separation between plasmonic modes propagating in different directions. Their symmetry and dispersion properties are discussed.