High confinement of surface plasmon polaritons in graphene at infrared frequencies enhances the light-matter interaction and can be used for the sensing of the environment. The considered sensing platform consists of parallel graphene ribbons which enables efficient coupling of an electromagnetic field into localized surface plasmons. Changes in the environment are then detected by measuring the resulting frequency shifts of the plasmonic resonances. It is shown that the graphene ribbons have the sensitivity comparable to the sensitivity of noble metal nanoparticles at visible frequencies, which enable sensing of only several nanometers thick films at wavelengths around ten microns. At the same time, the tunability of graphene plasmons enables a design of broadband substrates for surface enhanced infrared absorption of thin films. By changing the Fermi level in graphene, the plasmonic resonance of graphene ribbons can be adjusted to desired vibrational mode which facilitates detection of multiple absorption bands.

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Engineering of a refractive index profile is a powerful method for controlling electromagnetic fields. In this paper, we investigate possible realization of isotropic gradient refractive index media at optical frequencies using two-dimensional graded photonic crystals. They consist of dielectric rods with spatially varying radii and can be homogenized in broad frequency range within the lowest band. Here they operate in metamaterial regime, that is, the graded photonic crystals are described with spatially varying effective refractive index so they can be regarded as low-loss and broadband graded dielectric metamaterials. Homogenization of graded photonic crystals is done with Maxwell-Garnett effective medium theory. Based on this theory, the analytical formulas are given for calculations of the rods radii which makes the implementation straightforward. The frequency range where homogenization is valid and where graded photonic crystal based devices work properly is discussed in detail. Numerical simulations of the graded photonic crystal based Luneburg lens and electromagnetic beam bend show that the homogenization based on Maxwell-Garnett theory gives very good results for implementation of devices intended to steer and focus electromagnetic fields.

In this work, we have examined the optical properties of exfoliated graphene on an Si/SiO2 substrate using spectroscopic imaging ellipsometry in the visible range (360–800 nm). Measured spectra were analyzed by an optical model based on the Fresnel coefficient equations. The optical model was supported by correlated Raman and atomic force microscopy measurements. The complex refractive index of graphene was obtained by inversion of the measured ellipsometry data. The Fano line-shape was used to parameterize the optical properties. Measurements were highly reliable due to the numerous advantages of the spectroscopic imaging ellipsometric technique combined with the proper choice of substrate and experimental set-up. Thickness maps of the graphene sample were obtained from spatially resolved imaging ellipsometry spectra with a spot size of 1 μm. The data showed the presence of a water layer on the surface of the sample, and the thickness was mapped showing the distribution of water over graphene in ambient conditions.

Liquid-crystal devices are a promising cheap alternative for terahertz light modulation, albeit they suffer from problems associated with thick cells. Here we describe a few-micron-thick polarization-independent nematic liquid-crystal metamaterial device displaying terahertz reflectance modulation depths above 23 dB, millisecond response times, low operating voltages, and a spectral tuning of more than 15%. The dramatic performance improvement is based on invoking critical coupling with external fields, which rests on a suitable choice of resonator geometry. We analyze the coupling mechanism to conclude that perfect absorption can be reached with a wide range of parameters and liquid-crystal materials. The proposed device performance, microscopic details, and the nematic molecule switching dynamics are evaluated with the use of a rigorous tensorial formulation of the Landau-de Gennes theory and shown to be robust to small parameter deviations.

Acrylate nanoanchors of subdiffraction-limited diameter are written with optical stimulated emission depletion (STED) lithography. After incubation, 98% of all nanoanchors are loaded quickly with fluorescently labeled antibodies. Controlling the size of the nanoanchors allows for limiting the number of the antibodies. Direct stochastic optical reconstruction microscopy (dSTORM) imaging, statistical distribution of fluorescence, quantitative fluorescence readout, and single molecule blinking consistently prove that 80% of the nanoanchors with a 65 nm diameter are carrying only one antibody each, which are functional as confirmed with live erythrocytes.

Large birefringence and its electrical modulation by means of Fréedericksz transition makes nematic liquid crystals (LCs) a promising platform for tunable terahertz (THz) devices. The thickness of standard LC cells is in the order of the wavelength, requiring high driving voltages and allowing only a very slow modulation at THz frequencies. Here, we first present the concept of overcoupled metal-isolator-metal (MIM) cavities that allow for achieving simultaneously both very high phase difference between orthogonal electric field components and large reflectance. We then apply this concept to LC-infiltrated MIM-based metamaterials aiming at the design of electrically tunable THz polarization converters. The optimal operation in the overcoupled regime is provided by properly selecting the thickness of the LC cell. Instead of the LC natural birefringence, the polarization-dependent functionality stems from the optical anisotropy of ultrathin and deeply subwavelength MIM structures. The dynamic electro-optic control of the LC refractive index enables the spectral shift of the resonant mode and, consequently, the tuning of the phase difference between the two orthogonal field components. This tunability is further enhanced by the large confinement of the resonant electromagnetic fields within the MIM cavity. We show that for an appropriately chosen linearly polarized incident field, the polarization state of the reflected field at the target operation frequency can be continuously swept between the north and south pole of the Poincaré sphere. Using a rigorous Q-tensor model to simulate the LC electro-optic switching, we demonstrate that the enhanced light-matter interaction in the MIM resonant cavity allows the polarization converter to operate at driving voltages below 10 Volt and with millisecond switching times.

Tapping mode atomic force microscopy (AFM) is employed for dynamic plowing lithography of exfoliated graphene on silicon dioxide substrates. The shape of the graphene sheet is determined by the movement of the vibrating AFM probe. There are two possibilities for lithography depending on the applied force. At moderate forces, the AFM tip only deforms the graphene and generates local strain of the order of 0.1%. For sufficiently large forces the AFM tip can hook graphene and then pull it, thus cutting the graphene along the direction of the tip motion. Electrical characterization by AFM based electric force microscopy, Kelvin probe force microscopy and conductive AFM allows us to distinguish between the truly separated islands and those still connected to the surrounding graphene.