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Sub-bandgap photodetection based on plasmonic excitations represents a promising route for expanding the spectral range of photodetectors, enabling, for instance, silicon-based devices to be employed at telecom wavelengths. This approach harnesses internal photoemission, where hot carriers are generated via nonradiative plasmonic decay and are subsequently emitted from the metal to a semiconductor, yielding a photocurrent not spectrally limited by the bandgap. However, many schemes based on this approach suffer from low responsivities that hinder their uptake in real-world technologies. Here, we demonstrate a cavity-based platform for both enhancing the generated photocurrent and providing a means for dynamic reconfiguration of the operating wavelength. The proposed device is composed of an optical cavity where one of the mirrors is patterned with a nanoscale grating and interfaced at the other side with a semiconductor. Fabry–Perot resonances supported by the cavity provide resonant excitation of plasmonic modes at the metal/semiconductor interface, leading to augmented hot-carriers and photocurrent generation compared to the non-resonant case. By employing this cavity-grating geometry, we experimentally demonstrate a fivefold increase in photocurrent due to the presence of cavity resonances. Electromechanical reconfiguration of the photodetector cavity length is also achieved, illustrating dynamic control over the detection wavelength. This cavity-based architecture is compatible with a variety of plasmonic nanostructures, including nanoparticles and nanoantennas, thus providing a flexible means of significantly increasing the photoresponse and hence bringing on-chip plasmonic hot-carrier technologies closer to realization for sub-bandgap photodetection, energy harvesting, and sensing.

We designed a metasurface made of a monolayer of spherical nanoparticles embedded in a dielectric slab, which exhibits transmission properties independent of the incidence angle. Adjusting the electromagnetic coupling between high-index dielectric and hybrid core-shell nanoparticles enables the metasurface to operate in low-pass, bandpass, as well as band-stop regimes in the visible and near-infrared spectral ranges. We demonstrate how symmetric properties of spherical nanoparticles determine the response of the metasurface, resulting in a spectral filter with a wide angular acceptance range. We study transmission characteristics of the metasurface, such as frequency selectivity, the slope of filtering at cutoff frequencies, and the robustness of the metasurface against experimental variations in geometrical parameters. Our analyses show that the proposed approach can be used to design angular-independent spectral filters with the same material platform and approach to operate in different regimes and spectral ranges.

Lead-free piezoelectrics are becoming increasingly important in view of environmental problems of currently used lead-based perovskites such as lead zirconate titanate (PZT). One of the recent candidates for PZT replacement, solid solutions of BaZr0.2Ti0.8O3 and Ba0.7Ca0.3TiO3, are investigated in this work by piezoresponse force microscopy. Coexistence of the tetragonal and rhombohedral phases in this material is observed, which probably gives rise to easy polarization switching due to multiple domain states. The period of observed domain lamella scales with the grain size obeying well-known square root dependence characteristic of BaTiO3 ceramics. Domain switching and relaxation are investigated at the nanoscale as a function of the applied voltage and duration of the applied voltage pulses. The observed distortion of piezoresponse hysteresis loops near grain boundaries is attested to the increased concentration of defects. Nanoscale piezoelectric properties of these materials are discussed. (C) 2015 AIP Publishing LLC.

The principles of magnetic domain image formation in second-harmonic near-field microscopy have been investigated in the case of in-plane magnetic anisotropy. Due to the electromagnetic interaction between a probe and a surface, magnetic contrast can be achieved by observing near-field intensity variations of the SH light for both polarizations of the fundamental light in the longitudinal and transverse illumination configurations without polarization analysis. Domains in thin ferromagnetic films of Ni and Co exhibiting in-plane magnetization have been imaged using the developed approach.

Surface plasmon polariton waveguide modes excited in mutually orthogonal line defects of a surface polaritonic crystal (two-dimensional photonic crystal on a metal surface) are observed to be extremely sensitive to the polarization state of excitation light. Full switching between orthogonal waveguides can be achieved with less than 10° variation of the polarization angle. For oblique incidence, the polarization sensitivity of switching is even higher but full switching cannot be realized. This effect can be considered as a polarization-domain analog of the photonic crystal superprism effect. It suggests the possibility of building actively controlled photonic crystal devices for optical signal processing.

Second-harmonic generation at a gold tip apex has been studied within the context of applications in apertureless scanning near-field microscopy. Polarization and distance dependencies of second-harmonic generation have been investigated and compared to respective dependencies for scattered fundamental light. The results shows that, in general, different topological features of a tip are responsible for scattering and second-harmonic generation in the far and near field. The near-field interaction between a probe tip and a surface significantly modifies enhancement of the electromagnetic field at the tip and results in different distance dependencies of near-field scattering and second-harmonic generation. The polarization contrast obtained with the second-harmonic signal significantly exceeds the polarization contrast of linear scattering from the tip.

Hyperbolic plasmonic metamaterials are important for designing sensing, nonlinear, and emission functionalities, which are, to a large extent, determined by the epsilon-near-zero behaviour observed close to an effective plasma frequency of the metamaterial. Here, we describe a method for tuning the effective plasma frequency of a gold nanorod-based metamaterial throughout the visible and near-infrared spectral ranges. These metamaterials, fabricated by two-step anodization in selenic acid and chemical post-processing, consist of nanorods with diameters of around 10 nm and interrod distances of around 100 nm and have a low effective plasma frequency down to a wavelength range below 1200 nm. Such metamaterials open up new possibilities for a variety of applications in the fields of bio- and chemical sensing, nonlinearity enhancement, and fluorescence control in the infrared.

Centimeter sized arrays of gold coaxial rod-in-a tube cavities have been fabricated using anodized aluminum oxide as a template. The etching process used to create the cavities enables the production of extremely small gaps between tube and rod, on the order of 5 nm, smaller than those created by standard fabrication techniques. Normal incidence spectroscopy reveals two extinction peaks in the visible and near infrared wavelength range associated with resonant plasmonic modes excited in the structure. Numerical simulations show that the modes are associated with in-phase and out-of-phase hybridization of transverse dipolar excitations in the nanorod and in the tube.

We demonstrate the application of plasmonic crystals for extracting light trapped in the substrate due to total internal reflection (TIR). The broadband transmission properties of one-dimensional plasmonic crystals have been investigated, both experimentally and numerically, beyond the TIR critical angle in order to reveal the role of plasmonic modes in this process. Through optimisation of the traditional square slit unit cell geometry of the crystals, transmission coefficients of up to 47% were obtained in the TIR regime. An U-shaped cell geometry with a few nm thick continuous film was found to significantly modify the plasmonic modes of the crystal in addition to exhibiting highly tuneable, structurally dispersive transmission peaks, further increasing transmission in the TIR regime up to 56%. Such structures exhibit better than glass transparency at the design wavelength when integrated over all incident angles.

A compact, four-level polarization discriminator based on a surface plasmon polaritonic crystal (SPPC) has been experimentally demonstrated. It is able to uniquely resolve and spatially separate four signals that have been linearly polarized at azimuth angles 0°, 45°, 90°, and 135°. It exploits the excitation of multiple surface plasmon polariton eigenmodes in nondegenerate directions when the SPPC is illuminated with monochromatic light. The device is planar and of micrometer scale, which makes it suitable for on-chip integration and miniaturization of photonic circuits.

We present three-dimensional numerical modeling of an active electronically controlled switching element for fully-functional plasmonic circuits based on dielectric-loaded surface plasmon polariton waveguides. It has been demonstrated that the transmission of the guided mode through a highly wavelength-selective waveguide ring resonator (WRR) can be efficiently controlled with very small refractive index changes of the order of 10−3, achievable through the electro-optic effect in nonlinear materials. Furthermore, we have introduced a figure of merit for such active plasmonic elements and optimized the active WRR performance in terms of its sensitivity and size. These results shows the potential to create high performance 600 nm radius plasmonic WRR switches.

A design of high optical throughput nanoscale light sources has been proposed based on plasmonic wedge waveguides. It provides localization of the 1500 nm wavelength light at the output of less than 30×30 nm2 area at about 80% coupling efficiency from a dielectric loaded surface plasmon polariton waveguide and nearly 90% efficient power deposition in the absorbing media placed at the output for an experimentally viable 10 nm apex radius of the wedge. Such nanoscale light sources can be useful for high-density data storage, scanning near-field optical microscopy, and sensing.

The opening of the light extraction cone of a high index substrate (GaP) is demonstrated using plasmonic gratings. We show that the excitation of surface plasmons on the metal grating leads to the extraction of light otherwise undergoing total internal reflection in the substrate with high efficiency. This effect has an immediate application in the context of light emitting diodes, where resonant metal gratings are promising for the design of dual purpose electric contact/extraction structures.

The electro-optic response of a cell consisting of a thin layer of liquid crystal deposited onto gold nanorods embedded in thin film alumina with a transparent top electrode has been investigated. For p-polarized light incident from the liquid crystal side, the extinction peak associated with the nanorod longitudinal plasmon resonance is completely suppressed. The peak could be recovered by applying an external electric field parallel to the long axis of the nanorods. No extinction peak suppression is observed when the light was incident from the nanorod side of the cell. The effect is explained by polarization properties of liquid crystal.

The authors present full three-dimensional numerical modeling of passive photonic elements based on dielectric-loaded surface plasmon polariton waveguides (DLSPPWs). They demonstrate that at telecom wavelengths a highly confined SPP mode can be guided in a single mode DLSPPW of subwavelength cross section and estimate the achievable density of photonic integration. The size of bending and splitting photonic elements based on DLSPPW can be as small as a few micrometers with pure bend loss less than 10% (0.4dB) and the transmission efficiency exceeding 70% (total loss of about 1.3dB). Such DLSPPW elements are important for implementation of photonic integrated circuits, guiding optical and electric signals in the same circuitry, and lab-on-a-chip applications.

International audience; For protons of energy up to a few MeV, the temporal evolution of etched latent tracks in CR-39 nuclear track detector has been numerically modeled by assuming that the electronic energy loss of the protons governs the latent track formation. The technique is applied in order to obtain the energy spectrum of high intensity laser driven proton beams, with high accuracy. The precise measurement of the track length and areal track density have been achieved by scanning short etched, highly populated CR-39 employing atomic force microscope.

Local restructuring of metallic nanorod arrays and the fabrication of metallodielectric microstructures using direct femtosecond laser writing technologies have been studied. Femtosecond laser ablation has demonstrated the possibility to create sharp boundaries (down to a single nanorod) on the nanorod array. Polymer structures on the nanorods can be used to control the resonance wavelengths and thus the effective refractive index of surface plasmons supported by the array. The structured nanorods and their polymer composites are important for applications in light guiding and the development of nonlinear optical nanodevices.

The principles and mechanisms of scanning near-field microscopy of second-harmonic generation from ferromagnetic films have been investigated. Magnetic domain image formation in near-field second-harmonic microscopy is discussed and the role of the probe tip is considered. It is shown that magnetic contrast can be achieved in the second-harmonic intensity measurements in both the transverse and longitudinal magnetization configurations for both polarizations of the fundamental light. This is related to the electromagnetic near-field properties in the vicinity of the probe tip and the electromagnetic interaction between a tip and a surface. The capabilities of this imaging approach have been illustrated using magnetic domain structures in thin Co and Ni films. The near-field second-harmonic distributions obtained with p-polarized excitation light are strongly correlated to the topography of the films. At the same time, the images obtained with s-polarized excitation light are much less sensitive to the top...