P-polarized Incident Light Research Articles

Free carrier plasma edge and plasmonic excitations in heavily doped surface grated n-type Si

Infrared spectroscopic ellipsometry (SE) in the MID IR region was applied at room temperature to heavily doped n++-Si to obtain information about the free carrier plasma edge and plasmonic excitations before and after the Si surface was grated with a period Λ of 294 nm to a nominal depth of 20 nm by using laser lithography. Besides, SE measurements were performed in the NIR-VIS-UV spectral range to validate the optical models for non-grated and grated Si. In the latter case a thin grated layer on silicon surface was alternatively modelled either within Bruggeman effective medium approximation (BEMA) or by treating this layer as an anisotropic thin film (ATF). A model that included SiO2 (2.1 nm), n++-Si substrate and a 24.5 nm-thick ATF for grated layer was found to be good enough to reproduce the obtained ellipsometric parameters in the accessed spectral range. Intraband optical transitions are shown to overwhelmingly contribute to the MID IR dielectric function (DF) below the free carrier plasma edge (FCPE) of non-grated n++-Si. The parameters obtained for conduction electrons from Drude fit to this function agree well with the relevant data reported for Si so far. FCPE of non-grated n++-Si is positioned at 1416 cm−1. For graded layer this value is preserved within determination accuracy. The life time of plasmonic excitations that appeared as a single peak with a perfect Lorentz line-shape in the dielectric energy loss function of non-grated Si and grated Si layer is about 70 fs. Shape induced optical anisotropy, along with presumably conical diffraction that identified itself through a distinct angle-dependent upturn in the reflection spectra of p-polarized light incident upon surface in the plane perpendicular to Λ is behind the whole set of ellipsometric data obtained for n++-Si with subwavelength grating on the surface.

Linear mode conversion of terahertz radiation into terahertz surface plasmon wave over a graphene-free space interface

Abstract We analyzed the linear mode conversion of incident terahertz (THz) radiation into THz surface plasmon waves (SPWs) over a surface of graphene deposited on the rippled dielectric substrate. Obliquely incident p-polarized laser light imparts oscillatory velocity to the electrons in ripple layer regime. Electron oscillatory velocity beats with ripple surface density to produce a linear current density. We examine the tunable response of mode conversion of incident terahertz radiation with respect to change in Fermi energy of graphene and incident angle. A suitable surface ripple wave number resonantly drives the THz SPW. We observe the THz SPW generation tunability with respect to Fermi energy of graphene and incident angle. The amplitude of THz SPW is increased by lowering the Fermi energy of the graphene sheet.

Обобщенная нуль-эллипсометрия в схеме "поляризатор-образец-анализатор"

The null-method in generalized ellipsometry with the use of the compensator-free “polarizer ‒ sample ‒ analyzer” scheme is considered for the case of s- and p-polarized incident light on an anisotropic system. Analytical expressions are given that connect the measured angular value — the analyzer azimuth at the detected radiation intensity minimum — with the (2x2) anisotropic Jones matrix elements. To determine the optical and geometric parameters of the studied anisotropic systems, it is proposed to use this value’s dependence on the sample orientation (azimuth). The method sensitivity is estimated. It was found that it is comparable to the sensitivity of the “polarizer‒compensator‒sample‒analyzer” scheme. A comparative analysis of this method and the known photometric method of generalized ellipsometry in the “polarizer-sample-analyzer” scheme based on measuring the dependence of the reflected light intensity on the sample azimuth at the fixed polarizer and analyzer positions is carried out. It is estimated that, to obtain the same sensitivity of these two methods, the one arc minute error in the proposed method corresponds to the 0.05% relative error in determining the energy reflection coefficient in the photometric method.

Ultrasensitive Optical Temperature Transducers Based on Surface Plasmon Resonance Enhanced Composited Goos-Hänchen and Imbert-Fedorov Shifts

The spatial and angular Goos-Hänchen and Imbert-Fedorov shifts occur simultaneously for the light beam reflected from a lossy surface (e.g., metal surface). The mixture of spatial and angular Goos-Hänchen (Imbert-Fedorov) shifts, referred to as composited Goos-Hänchen (Imbert-Fedorov) shift, has been experimentally confirmed in recent years. The temperature-dependent composite Goos-Hänchen and Imbert-Fedorov shifts for a light beam reflected from the prism-gold interface in the Kretschmann-Raether configuration are theoretically investigated. The spatial and angular Goos-Hänchen and Imbert-Fedorov shitfs of p-polarized incident light are significantly enhanced around the resonant angle with the generation of surface plasmon resonance. The ultrahigh temperature sensitivities of 0.79 cm/K and 188 μm/K are obtained with the composite Goos-Hänchen and Imbert-Fedorov shift, respectively, which are about 5 orders higher than those obtained with a bare gold surface. The ultrahigh temperature sensitivity is mostly contributed by the angular shift effect. Our results demonstrated the importance of angular shift effect in achieving an ultrahigh sensitivity. This work can serve as a guidance for the design of temperature sensor, chemical sensor and biosensor based on composite Goos-Hänchen and Imbert-Fedorov shifts.

Surface phonon resonance enhanced Goos-Hänchen shift and its sensing application in the mid-infrared region.

The effect of surface phonon resonance (SPhR) and long range SPhR (LRSPhR) on the Goos-Hänchen shift (GHS) in the mid-infrared wavelength region are investigated. The GHS is significantly enhanced around the resonant angles of SPhR and LRSPhR with the p-polarized incident light. A highly sensitive refractive index sensor based on the enhanced GHS is proposed. The LRSPhR shows higher GHS and sensitivity than those of SPhR. The GHS and refractive index sensitivity can be further enhanced by engineering the damping rate of the phononic material. These results provide a potential route toward the large GHS and high refractive index sensitivity, thus opening up new opportunities for high sensitivity optical sensors based on GHS at the mid-infrared wavelength range.

Gap plasmon modes resolved by ultraflat nanogap and linear polarization in terrace-stepped hexagonal boron nitride spacer sandwiched by Ag nanowire and metal substrates

We investigate the nanogap and polarization-resolved excitation of gap plasmon modes using terrace-stepped hexagonal boron nitride (hBN) sandwiched between Ag nanowires and Au substrates for a metal–insulator–metal gap structure. The gap plasmon modes in the proposed hybrid structure are dominantly excited by a P-polarized incident light, which is supported by full-wave numerical simulations. Plasmon mode evolution for various hBN spacer thicknesses ranging from 5 to 90 nm shows that optical signals acquired via unpolarized dark-field mapping spectroscopy are primarily due to the optical scattering of the P-polarized incident light. Moreover, this plasmonic mode changes significantly from gap plasmon mode to Fabry–Perot-type resonance in a hBN thickness of 50–90 nm. Our analysis reveals that the proposed hybrid structure based on Ag nanowires and stepped hBN provides a well-defined gap thickness and is a robust platform for analyzing gap plasmon modes.

A Simple Simulation of Surface Plasmon Resonance in The Kretschmann Configuration Using Google Sheets

This article describes a simple numerical simulation of three-layer surface plasmon resonance (SPR) in the Kretschmann configuration. The calculation was performed in Google Sheets, a web-based spreadsheet environment that functions similarly to Microsoft Excel where it is easily accessible for students via the internet. Specifically, Fresnel’s equations were utilized to calculate the intensity of the reflected light for the p-polarized incident light on a three-layer system. The complex functions were utilized to plot the SPR curves. We examined the change of the resonance angle by the influence of the incident wavelength. The simulation was also performed for different thicknesses of the gold film layer. To demonstrate the sensitivity, we obtained the SPR curves with the variation of the refractive index in the sensitive medium. The SPR accuracy was analysed by comparing our obtained result with the published work. It is intended to incorporate into undergraduate instrumental analysis courses.

Dynamically controlling local field enhancement at an epsilon-near-zero/dielectric interface via nonlinearities of an epsilon-near-zero medium

Abstract For p-polarized light incident on an interface between an ordinary dielectric and an epsilon-near-zero (ENZ) material, an enhancement of the component of the electric field, normal to this interface, has been shown to occur. This local field enhancement holds great promise for amplifying nonlinear optical processes and for other applications requiring ultrastrong local fields in epsilon-near-zero based technologies. However, the loss associated with the imaginary part of the dielectric constant of an epsilon-near-zero material can greatly suppress the field enhancement factor. In this study, we analyze, using density matrix formalism, the field enhancement factor for a saturable two-level system that exhibits second- and third-order nonlinearities. We show that, in such a system, an almost lossless ENZ response can arise as a consequence of saturable nonlinearity and that the local field enhancement factor can be readily controlled dynamically by adjusting the intensity of the incident electromagnetic wave. Our findings provide for the first time a pathway to design a material exhibiting an external field responsive epsilon-near-zero behavior for applications in nonlinear photonics.

Analysis of the Rigorous Coupled Wave Approach for [formula omitted]-polarized light in gratings

We study the convergence properties of the two-dimensional Rigorous Coupled Wave Approach (RCWA) for p-polarized monochromatic incident light. The RCWA is a semi-analytical numerical method that is widely used to solve the boundary-value problem of scattering by a grating. The approach requires the expansion of all electromagnetic field phasors and the relative permittivity as Fourier series in the spatial variable along the direction of the periodicity of the grating. In the direction perpendicular to the grating periodicity, the domain is discretized into thin slices and the actual relative permittivity is replaced by an approximation. The approximate relative permittivity is chosen so that the solution of the Maxwell equations in each slice can be computed without further approximation. Thus, there is error due to the approximate relative permittivity as well as the truncation of the Fourier series. We show that the RCWA embodies a Galerkin scheme for a perturbed problem, and then we use tools from the Finite Element Method to show that the method converges with increasing number of retained Fourier modes and finer approximations of the relative permittivity. Numerical examples illustrate our analysis, and suggest further work.

Excitation of surface plasmon–polariton waves in the prism-coupled configurations guided by reciprocal, uniaxially chiral, bianisotropic material

Excitation of the surface plasmon–polariton (SPP) waves guided by the planar interface of a metal and a reciprocal, uniaxially chiral, bianisotropic material was investigated. The characteristics of SPP waves in two prism-coupled configurations were observed and also verified by the spatial profiles when the waves were guided by the interface perpendicular to the direction of the chirality and uniaxiality. The SPP waves were found to be neither p- nor s-polarized in nature when the chirality parameter was large. The SPP wave was excited in the Turbadar–Kretschmann–Raether (TKR) configuration by p-polarized incident light only, that also when the real part of the chirality parameter was smaller than a threshold value. The excitation of SPP wave was not supported by s-polarized incident light in the TKR configuration. However, the excitation of SPP wave was found in the Turbadar–Otto configuration for both the p-polarized incidence and the s-polarized incidence.

Efficient planar plasmonic directional launching of linearly polarized light in a catenary metasurface

Efficient directional excitation of planar surface plasmon polaritons (SPPs) has important and wide applications in micro-nano photonic technology. Recently, by using the geometric phase and spin-orbit interaction, catenary structures have been applied to the directional control of SPPs and showed excellent performance. However, due to the need to use the chirality of the subwavelength catenary apertures, the previously studied systems were only suitable for circularly polarized light. Here, based on a catenary metasurface we theoretically design and experimentally demonstrate a SPP directional launcher used for linearly polarized light. The numerical calculation results show that the directional extinction ratio reaches up to 35 dB under the normal incidence of p-polarized light at 750 nm which is 5 dB higher than the maximum extinction ratio in the existing results as we know. The experimental results show that the resonant wavelength position, bandwidth and extinction ratio change trend well match the theoretical results. The physical mechanism is analyzed and it is found that the asymmetric quadrupole mode is the key factor leading to the directional SPPs which is completely different from the geometric phase modulation mechanism to excite the directional SPPs of circularly polarized light in the catenary metasurface. These principles and methods could open new doors for future chip-level photonic device or system design such as multi-directional beam splitters and polarization detectors.

Structural Evolution of Water on ZnO(10 0): From Isolated Monomers via Anisotropic H-Bonded 2D and 3D Structures to Isotropic Multilayers.

The surface chemistry of water on zinc oxides is an important topic in catalysis and photocatalysis. Interaction of D2O with anisotropic ZnO(101‾ 0) surfaces was studied by IR reflection absorption spectroscopy using s‐ and p‐polarized light incident along different directions. Interpretation of the experimental data is aided using isotopologues and DFT calculations. The presence of numerous species is revealed: intact monomers, a mixed 2D D2O/OD adlayer, an anisotropic bilayer, and H‐bonded 3D structures. The isolated water monomers are identified unambiguously at low temperatures. The thermally induced diffusion of water monomers occurs at elevated temperatures, forming dimers that undergo autocatalytic dissociation via proton transfer. Polarization‐ and azimuth‐resolved IR data provide information on the orientation and strength of H‐bonds within the 2D and 3D structures. Ab initio molecular dynamics simulations reveal strong anharmonic couplings within the H‐bond network.

Novel single-frequency Nd:YAG ring laser by reducing the depolarization loss

A principle study on reducing the depolarization loss in a single-frequency Nd:YAG ring laser by a novel ring resonator configuration is reported. In the resonator, one cavity mirror with 99.5% reflectivity at 1064 nm for 45-degree incident s-polarized light and about 75% transmissivity for 45-degree incident p-polarized light was employed. Besides, the transmissivity for the 45-degree incident p-polarized and s-polarized light for the output-couple mirror were 32% and 3.5%, respectively. The cavity mirror and the output-couple mirror were utilized as the polarizer to enforce the s-polarized beam unidirectionally operating in the resonator. 2.1 W single-frequency output at 1064 nm with elliptical polarization was obtained from this ring resonator. Compare with the existent Nd:YAG ring resonator, this novel resonator has a potential advantage in reducing depolarization loss and increasing the efficiency.

Realizing Vibrant and High-Contrast Reflective Structural Colors from Lossy Metals Supporting Dielectric Gratings.

Despite their distinctive chemical properties, lossy metals are generally avoided in the design of structural colors because the optical losses can degrade the color vibrancy. Herein, we demonstrate a strategy that allows lossy metals supporting near-wavelength dielectric gratings to achieve high color vibrancy by benefiting from the optical loss rather than suffering from it. By exciting the grating rotated 45° relative to the incident field, s-polarized (s-pol) and p-polarized (p-pol) light each excites a spectrally distinct resonance, described by a treatment of coupled waveguide-array modes, that retards the phase over the wavelength. Owing to the birefringence, a cross-polarized reflection spectrum displays two sharp peaks from each component that decreases the monochromaticity. We show that lossy metals can minimize the p-pol contribution, leaving the sharp s-pol response to determine the spectrum and generate high color vibrancy. Through this scheme, we demonstrate that lossy metal substrates including Pt, a catalytically active metal, and W, a CMOS-compatible metal, can achieve larger sRGB gamut coverage ratios of 90% and 69%, respectively, than that of 55% from Ag, while maintaining similar pixel contrast ratios to that of Ag.

Influence of deposition angle on nano-structure, optical and electrical properties of copper azide (CuN3) thin films

Cu/glass films of 100 (nm) thicknesses were deposited at 0° and 40° and post annealed at three different temperatures with flow of nitrogen. XRD patterns of the films deposited at 40° confirmed formation of CuN3 phase which is due to higher void fraction in these films. Optical properties of the produced samples were obtained using the Bruggeman homogenization method. Results of optical properties of these films showed that the dispersion behavior is sensitive to the annealing temperature, polarization of the incident light and film deposition angle. Clear energy loss peak is obtained for film deposited at 0° and annealed at 350 °C using both s- and p-polarized incident lights with a shift to lower energies for p-polarized incident light. Appearance of these peaks are related to the values of the dielectric functions and the structure of the sample which consists of almost evenly distributed conical shapes with sharp tips leading to the enhancement of plasmon resonances and the corresponding frequency in this sample. The surface morphology of the produced samples was analyzed by means of field emission electron microscope and atomic force microscope. Variation of grain size with annealing temperature is observed which can be due to competition between two processes of diffusion and penetration of nitrogen atoms/molecules in the body of the grains.

Brewster angle optical reflection observation of self-limiting nanoparticle monolayer self-assembly at a liquid/liquid interface

Real-time optical reflection of incident p-polarized light near Brewster’s angle shows that after drop-casting iron oxide nanoparticles (NPs) in heptane on top of a diethylene glycol (DEG) liquid substrate, an iron oxide NP layer forms at the DEG/heptane interface, and it self-limits to a monolayer even when there are excess NPs dispersed in the upper heptane phase. Most modes of NP self-assembly do not self-limit growth after the formation of a single monolayer. Observations are compared to a reflection model incorporating the reflectances expected at each interface. An effective medium model of the dielectric constant is used to model the reflectance of the NP layer at the DEG/heptane interface.

Thermally Controllable High-Efficiency Unidirectional Coupling in a Double-Slit Structure Filled With Phase Change Material

We present the realization of a high-efficiency, compact, and thermally tunable unidirectional launcher of surface plasmon polaritons (SPPs) in a double-slit structure filled with phase change materials (PCMs). PCMs such as VO2 provide a feasible way for tailoring optical properties, particularly refractive index as a function of heat. By introducing a narrow hybrid dielectric layer beneath the slits, SPPs couple efficiently into waveguide mode and propagate within the slot waveguide with considerably high intensity. Our simulation results revealed up to 80% coupling efficiency into the slot waveguide with extinction ratio of 1:800 between the left and the right slots can be achieved at telecommunication wavelength for normally incident P-polarized light. By heating the coupler above the VO2 phase transition temperature, the coupling and consequently the crosstalk approaches zero. Propagation length and other properties of the structure are characterized to confirm the feasibility of the coupler. This approach of unidirectional coupling into slot waveguides may lead to the development of integrated plasmonic circuits and on-chip applications.

Investigations on sensitivity enhancement of SPR biosensor using tunable wavelength and graphene layers

Surface plasmon resonance (SPR) is a well-known, rapid and sensitive technique used for probing the biomolecular interactions in real time. Several new approaches have been suggested to improve the sensitivity of SPR sensors over the last two decades. Recently, there have been few reports on using graphene on a metal film based SPR sensor in order to improve the sensitivity. The role of incident light wavelength and graphene layers in sensitivity enhancement is unclear. This paper reports computational investigations on sensitivity enhancement of SPR biosensor using tunable wavelength and graphene layers. The reflectivity of p-polarized incident light has been calculated using the N-layer model for the most common Kretschmann configuration. Sensitivity enhancements over a conventional angular interrogated SPR sensor have been calculated within the wavelength range 600 -1600 nm and up to ten graphene layers. Results indicate that the sensitivity can be enhanced by the increasing the graphene layers on conventional gold coating based SPR biosensor. Sensitivity enhancement is highly dominated by the wavelength of interrogation used in this design. By tuning the wavelength and graphene layers sensitivity of the graphene-based SPR biosensor can be increased.

SO2 adsorption on rutile TiO2(110): An infrared reflection-absorption spectroscopy and density functional theory study

The adsorption of SO2 on single crystalline TiO2(110) has been investigated by means of polarized infrared reflection-absorption spectroscopy (IRRAS) experiments and density functional theory (DFT) calculations. IR absorption bands were detected at 1324 cm−1 and 985 cm−1 with p-polarized light incident along both the [11¯0] and [001] crystallographic directions at 123 K. When the temperature was increased to 153 K, the peak at 1324 cm−1 disappears, while a new, weak band appears at 995 cm−1. Simultaneously, a band at 995 cm−1 also emerges with s-polarized light along the [11¯0] direction. Based on the symmetry properties of the IRRAS spectra and accompanying ab initio simulations of the spectra employing a three layer model (vacuum-adsorbate-substrate), it is shown that the low temperature absorption IRRAS bands can be attributed to an SO3-like adsorbate structure. This is also the most stable adsorption structure (Ead = −0.58 eV) on the stoichiometric surface. The combined IRRAS and DFT results show that the band appearing at 995 cm−1 is associated with a surface sulfite specie which is stabilized by residual surface water. The DFT calculations also revealed that a stable adsorption structure exists on a reduced TiO2 surface, where SO2 binds strongly to an oxygen vacancy site. It is suggested that this is an intermediate that form surface sulfate upon further reactions with water, although it was not observed on the stoichiometric surface studied in this work.

Plasmonic Magnetooptic Structures for Visualization of Magnetic Information

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