Wave Vector Of Incident Light Research Articles

Metamaterial grating for colorimetric chemical sensing applications

We propose and demonstrate a metamaterial grating sensor (MGS) composed of gold (Au) nanograting on a silver (Ag) thin-film and then encapsulated with a polydimethylsiloxane (PDMS) microfluidic chip for colorimetric chemical sensing applications. MGS is sensitive to the wavevector of incident light owing to the surface plasmonic resonance of metamaterial grating results in specific reflected colors of MGS affected by background refractive index (n) and incident angle (θ). The measured reflection spectra of MGS exhibit angle-dependence characteristic by changing θ value from 10° to 45°, whose resonances are blue-shifted 80 nm from the wavelength of 691 nm–611 nm and 88 nm from the wavelength of 671 nm–583 nm by injecting isopropyl alcohol (IPA) and deionized (DI) water solutions into MGS, respectively. This angle-dependence characteristic of MGS is visual in ambient light. Moreover, by injecting IPA solution with different concentrations, the maximum sensitivity of reflected resonance to n value is 1474 nm/RIU at θ = 45°. Similarly, the reflected color shows green, yellow, dark yellow, and cyan colors for MGS covering with DI water, acetone, 1 ppm lapatinib in acetone, and IPA solutions, respectively in the ambient light environment. The proposed MGS proves the potential applications in portable and convenient biochemical sensing without spectrometers.

Polarization-Resolved and Helicity-Resolved Raman Intensity of Monolayer and Bilayer β-InSe

The structural and vibrational properties along with the polarization-resolved and helicity-resolved Raman spectra of monolayer and bilayer β-InSe excited by two commonly used laser lines (532 and 633 nm) in experiments are investigated by first-principles calculations so that we can establish the correlation between layer stacks and optical features in two-dimensional InSe. The stability of both monolayer and bilayer InSe are examined and confirmed by phonon dispersion. The monolayer and bilayer InSe are found to exhibit different point group symmetries and thereby the Raman properties due to the symmetry breaking of bilayer structure caused by interlayer van der Waals interaction. All Raman-active modes for monolayer (bilayer) InSe are listed, and the polarization-angle-dependent Raman intensities are accordingly discussed separately in terms of the configuration of the incident light (parallel or perpendicular to certain planes). By calculating the Raman tensor of each Raman-active mode, we obtained polarization-angle-dependent Raman intensities and discussed the location of each maximum under different polarization configurations, as well as the nonpolarized Raman intensity. The helicity-resolved Raman intensity is also obtained. It is found that more Raman-active modes can be observed under helical excitation when the incident light wave vector is in the y-direction. Among all of the Raman-active modes, the Raman intensity of A′1(A1g) is the strongest. Our work might help material scientists to characterize monolayer and bilayer InSe in experiments.

Vibrational properties and Raman spectra of 2‐D octagon‐structure nitrogen

AbstractWe studied the vibrational properties and Raman spectra of two‐dimensional (2‐D) octagon‐structure nitrogen with density functional theory (DFT). There are 10 Raman active modes whose irreducible representations are A1g, B1g, B2g, and Eg. By calculating Raman tensor of each Raman active mode, we obtained polarization angle‐dependent Raman intensities. The results show that B1g and B2g modes can show polarization angle‐dependent Raman intensities when the incident light wave vector is perpendicular to the plane of the nitrogen monolayer, which is different from some other isotropic 2‐D materials. We also discussed polarization angle‐dependent Raman intensities when the incident light wave vector is parallel to the plane of the monolayer. We found that the Raman spectra have seven peaks when the incident light wave vector is perpendicular to the monolayer, while there are four distinct peaks when the incident light wave vector is parallel to the monolayer. Our results will help experimentalists to identify the existence and orientation of octagon‐structure nitrogen monolayer when they are growing it.

2D Octagon-Structure Carbon and Its Polarization Resolved Raman Spectra.

We predict a new phase of two-dimensional carbon with density functional theory (DFT). It was found to be semimetal with two Dirac points. The vibrational properties and the polarization resolved Raman spectra of the carbon monolayer are predicted. There are five Raman active modes: 574 cm−1 (Eg), 1112 cm−1 (B1g), 1186 cm−1 (B2g), 1605 cm−1 (B2g) and 1734 cm−1 (A1g). We consider the incident light wave vector to be perpendicular and parallel to the plane of the carbon monolayer. By calculating Raman tensor of each Raman active mode, we obtained polarization angle dependent Raman intensities. Our results will help materials scientists to identify the existence and orientation of octagon-structure carbon monolayer when they are growing it.

β-As Monolayer: Vibrational Properties and Raman Spectra.

Recently, semiconducting and other extraordinary properties of the monolayer of the V-group element have attracted a broad interest and attention. The success of experimentally growing antimonene and black phosphorus makes the arsenic monolayer a reasonable candidate for two-dimensional semiconductors. By using DFT calculation, we investigate the vibrational properties and Raman spectra of the buckled honeycomb monolayer of arsenic (β-As) for four commonly used laser lines. By calculating Raman tensor of each active modes of the β-As monolayer, we obtained polarization angle-dependent Raman intensities when the wave vector of incident light is parallel and perpendicular with the plane of the β-As monolayer. We found that the nonresonant Raman spectra have two peaks at 235 and 305 cm–1 that correspond to the in-plane vibrating mode Eg and out-of-plane vibrating mode A1g, which is similar to germanene, blue phosphorene, and β-Sb monolayer Raman spectra. There are two (four) minima and two (four) maxima when the polarization direction of scattered light is parallel (perpendicular) to that of the incident light and the wave vector of the incident light is parallel to the β-As monolayer. The Raman intensities of neither parallel polarization configuration nor perpendicular polarization configuration depend on the polarization direction when the wave vector of incident light is perpendicular to the β-As monolayer. The relation between shapes of the polar plots and relative values of Raman tensor elements is found. The Raman intensities decrease with increasing wavelength of incident laser lines in most cases. Our results will help experimentalists to identify the existence and the orientation of the β-As monolayer while they are growing the β-As monolayer.

Plasmon Hybridization in Individual Gold Nanocrystal Dimers: Direct Observation of Bright and Dark Modes

We apply a nanomanipulation technique to assemble pairs of monodispersed octahedral gold nanocrystals (side length, 150 nm) along their major axes with a varying tip-to-tip separation (25-125 nm). These pairs are immobilized onto indium tin oxide coated silica substrates and studied as plasmonic dimers by polarization-selective total internal reflection (TIR) microscopy and spectroscopy. We confirm that the plasmon coupling modes with the scattering polarization along the incident light direction result from the transverse-magnetic-polarized incident light, which induces two near-field-coupled dipole moments oriented normal to the air-substrate interface. In such cases, both in-phase (antibonding) and antiphase (bonding) plasmon coupling modes can be directly observed with the incident light wave vector perpendicular and parallel to the dimer axis, respectively. The observation of antiphase plasmon coupling modes ("dark" plasmons) is made possible by the unique polarization nature of the TIR-generated evanescent field. Furthermore, with decreasing nanocrystal separation, the plasmon coupling modes shift to shorter wavelengths for the incident light perpendicular to the dimer axis, whereas relatively large red shifts of the plasmonic coupling modes are found for the parallel incident light.

Vertical Birefringence Characterization for Optical Polymer Films

This paper introduces a technique for precisely measuring the vertical birefringence of an optical polymer film. Analytical equations are derived to relate the phase retardation to the optical film birefringence. In the measurement, we first measure the in-plane birefringence of the film and locate the principal axes of refractive index ellipsoid. The film is then rotated with its normal at an angle to the incident light wave vector. The vertical birefringence is calculated from the retardations measured at several angles. Using the procedure, the vertical birefringence can be measured to a precision of 0.2 ×10-3.

Subcollinear acousto-optic tunable filter based on the medium with a strong acoustic anisotropy

We design and investigate the properties of acousto-optical tunable filter (AOTF) based on tellurium dioxide (TeO 2) single crystal. We use so-called “subcollinear” geometry of anisotropic acousto-optic interaction that occurs when the wavevector of incident light is collinear to acoustic energy vector. We have obtained the analytical formula of spectrum spread function of proposed AOTF and have found the condition determining the shape of that characteristic. Also we have designed and fabricated the experimental prototype of subcollinear AOTF. In our design we have used the reflection of acoustic wave that allowed to use crystal’s media more effectively and reduce the AOTF size. The main advantage of filter based on proposed geometry is extremely low value of electrical driving power (20 mW) that makes it a strong candidate in many applications.

Diffusing wave spectroscopy of dense colloids: Liquid, crystal and glassy states

Using intensity autocorrelation of multiply scattered light, we show that the increase in interparticle interaction in dense, binary colloidal fluid mixtures of particle diameters 0.115µm and 0.089µm results in freezing into a crystalline phase at volume fractionφ of 0.1 and into a glassy state atφ=0.2. The functional form of the field autocorrelation functiong(1)(t) for the binary fluid phase is fitted to exp[−γ(6k02Defft)1/2] wherek0 is the magnitude of the incident light wavevector andγ is a parameter inversely proportional to the photon transport mean free pathl*. TheDeff is thel* weighted average of the individual diffusion coefficients of the pure species. Thel* used in calculatingDeff was computed using the Mie theory. In the solid (crystal or glass) phase, theg(1)(t) is fitted (only with a moderate success) to exp[−γ(6k02W(t))1/2] where the mean-squared displacementW(t) is evaluated for a harmonically bound overdamped Brownian oscillator. It is found that the fitted parameterγ for both the binary and monodisperse suspensions decreases significantly with the increase of interparticle interactions. This has been justified by showing that the calculated values ofl* in a monodisperse suspension using Mie theory increase very significantly with the interactions incorporated inl* via the static structure factor.

Diffraction of light by a three-dimensional acoustic column

We solve the 3-D Bragg diffraction problem for a plane light wave, incident on a rectangular acoustic column, in the near zone of acousto-optic (AO) diffraction for the case of weak interaction. We show that the orientation of the boundaries of the acoustic column with respect to the incident light wave vector influences the direction of the diffracted light. It appears that the wave vector of the diffracted light is not necessarily coplanar with the wave vector of the incident light and the central wave vector of the sound column. The angle of deviation of the wave vector for the diffracted light is calculated. Conditions for applying the standard solution of the 2-D AO problem are studied. The problem is solved using the 4-D spectral representation of wave fields method.

Magneto‐Reflectance of the B‐Exciton of CdS

AbstractThe magneto‐reflectance of the B‐exciton of CdS is studied for fields up to 9.0 T. The spectra show a strong anisotropy of the Zeeman‐effect for H ⟂ c; the splitting is proportional to the sum of the g‐values of the valence and the conduction band for H parallel to the wave vector of incident light, but it is proportional to the difference of g‐values for H perpendicular to the wave vector. For the first time a change of the spectra with magnetic field inversion (pole‐changing effect) is observed; it appears for oblique incidence of light and results from the k‐linear term of the valence band. The spectra are discussed by lineshape analysis along the lines of excitonic polaritons. From the excellent agreement between experiments and calculations some new parameters of the B‐exciton can be determined: the g‐value of the B‐valence band g = 0.8 ± 0.1, the diamagnetic shift δdia = (2.0 ± 0.3) μe V/T2, and the different parts of the exchange interaction energy ΔLT = (1.4 ± 0.03) meV, Δ25 = (0.1 ± 0.05) meV and Δ21 = (0.15 ± 0.05) meV.