Wavelength Of Incident Light Research Articles

Sensitivity Improvement of a Surface Plasmon Resonance Sensor Based on Two-Dimensional Materials Hybrid Structure in Visible Region: A Theoretical Study.

In this paper, we propose a surface plasmon resonance (SPR) sensor based on two-dimensional (2D) materials (graphene, MoS2, WS2 and WSe2) hybrid structure, and theoretically investigate its sensitivity improvement in the visible region. The thickness of metal (Au, Ag or Cu) and the layer number of each 2D material are optimized using genetic algorithms to obtain the highest sensitivity for a specific wavelength of incident light. Then, the sensitivities of proposed SPR sensors with different metal films at various wavelengths are compared. An Ag-based SPR sensor exhibits a higher sensitivity than an Au- or Cu-based one at most wavelengths in the visible region. In addition, the sensitivity of the proposed SPR sensor varies obviously with the wavelength of incident light, and shows a maximum value of 159, 194 or 155°/RIU for Au, Ag or Cu, respectively. It is demonstrated that the sensitivity of the SPR sensor based on 2D materials’ hybrid structure can be further improved by optimizing the wavelength of incident light.

Measurements of angle-resolved reflectivity of PTFE in liquid xenon with IBEX

Liquid xenon particle detectors rely on excellent light collection efficiency for their performance. This depends on the high reflectivity of polytetrafluoroethylene (PTFE) at the xenon scintillation wavelength of 178 nm, but the angular dependence of this reflectivity is not well-understood. IBEX is designed to directly measure the angular distribution of xenon scintillation light reflected off PTFE in liquid xenon. These measurements are fully described by a microphysical reflectivity model with few free parameters. Dependence on PTFE type, surface finish, xenon pressure, and wavelength of incident light is explored. Total internal reflection is observed, which results in the dominance of specular over diffuse reflection and a reflectivity near 100% for high angles of incidence.

Light intensity-induced photocurrent switching effect

A better control over processes responsible for the photocurrent generation in semiconductors and nanocomposites is essential in the fabrication of photovoltaic devices, efficient photocatalysts and optoelectronic elements. Therefore, new approaches towards photochemical properties tuning are intensively searched for. Among numerous parameters, the photocurrent polarity is of great importance to the overall performance of a device. Usually, the polarity is controlled through an alignment of electronic states/bands, tailoring of applied potential or suitable selection of incident light wavelengths. In most scenarios though, the influence of light intensity is somehow neglected and either some arbitrarily chosen, natural conditions are mimicked or this parameter is varied only in a narrow range. Here we present a ternary nanocomposite in which the persistent photocurrent polarity switching is achieved through changes in the light intensity. We also present arguments suggesting this behaviour is of a general character and should be considered also in other photochemical systems.

Isosbestic light absorption by metallic dimers: effect of interparticle electromagnetic coupling.

Isosbestic plasmonic nanostructures, which feature an invariance of optical absorption and heat generation upon varying the incident light polarization, have broad application in many fields such as nanochemistry, optical nanoantennas, and microbubble formation. In this study, we focus on the isosbestic optical absorption by metallic dimers and systematically investigate the coupling between two interacting particles by using both the superposition T-matrix method and dipole approximation model. We observe that the interparticle coupling effects on particle absorption can be both positive and negative, compared to an isolated particle. Meanwhile, the optical absorption properties of spheres with small size parameters can realize more flexible control through changing the sphere size, interparticle distance, and incident light wavelength. For illuminations with incident light propagating perpendicularly to the line joining the centers of the two spheres, isosbestic conditions will be satisfied as long as the absorption efficiencies for transverse and longitudinal illuminations are equal. For transverse illuminations along the dimer axis, the ratio of absorption efficiency of the two metallic spheres presents the fluctuation change with the interparticle distance. Owing to the strong interparticle coupling effects, it even leads to the absorption efficiency of the far sphere being higher than that of the near sphere. Our results are aimed at expanding our understanding of the interparticle electromagnetic coupling effects on isosbestic light absorption in plasmonic nanoparticle systems.

Water-Dispersible Triplet-Triplet Annihilation Photon Upconversion Particle: Molecules Integrated in Hydrophobized Two-Dimensional Interlayer Space of Montmorillonite and Their Application for Photocatalysis in the Aqueous Phase.

Green incident light (λ = ∼500 nm) is converted to blue light (λ = 400-450 nm) in air using bulky alkylammonium (DMDOA+), 9,10-diphenylanthracene (DPA), and Ru(dmb)32+ (dmb = 4,4'-dimethyl-2,2'-bipyridine) intercalated in a layered clay compound called "montmorillonite" [MMT-DMDOA+-DPA-Ru(dmb)32+]. The two-dimensional interstitial space has an interlayer spacing of a few nanometers. Emitter DPA is present in this interlayer spacing, having an intermolecular distance of approximately 3.0 nm at a high concentration. Sensitizer Ru(dmb)32+ is relatively dilute, having an intermolecular distance of 47 nm. The emission decay measurements and quantitative evaluation of the emission intensity demonstrate that blue light emission is induced by sequential processes, which consist of a triplet-triplet (T-T) energy transfer reaction from Ru(dmb)32+ to DPA and T-T annihilation of DPA molecules. From thermogravimetry and Fourier transform infrared spectra measurements, we observe that the cointercalated alkylammonium acts as a waterproof agent to prevent quenching of the molecules in the excited triplet states by H2O. Finally, we demonstrate a photocatalytic decomposition of Rhodamine B dissolved in H2O-containing MMT-DMDOA+-DPA-Ru(dmb)32+ and Pt-deposited WO3 photocatalyst, where wavelength of incident light (λ > 440 nm) is longer than the absorption edge of WO3 photocatalyst. The mechanism of photocatalytic decomposition is the following: (i) the incident long wavelength light is upconverted to 400-450 nm light by MMT-DMDOA+-DPA-Ru(dmb)32+, and then, (ii) WO3 photocatalyst is excited by the generated 400-450 nm light, and finally, (iii) Rhodamine B is decomposed on the Pt cocatalyst induced by the holes in a valence band of WO3.

Nanoparticle trapping and routing on plasmonic nanorails in a microfluidic channel.

Plasmonic nanostructures hold great promise for enabling advanced optical manipulation of nanoparticles in microfluidic channels, resulting from the generation of strong and controllable light focal points at the nanoscale. A primary remaining challenge in the current integration of plasmonics and microfluidics is to transport trapped nanoparticles along designated routes. Here we demonstrate through numerical simulation a plasmonic nanoparticle router that can trap and route a nanoparticle in a microfluidic channel with a continuous fluidic flow. The nanoparticle router contains a series of gold nanostrips on top of a continuous gold film. The nanostrips support both localised and propagating surface plasmons under light illumination, which underpin the trapping and routing functionalities. The nanoparticle guiding at a Y-branch junction is enabled by a small change of 50 nm in the wavelength of incident light.

Specific properties of light localisation in the cholesteric liquid crystal layer. The effects of layer thickness

ABSTRACT We investigated the effect of the thickness of the cholesteric liquid crystal (CLC) layer on the light energy and the density of the localised light energy in a CLC layer, as well as on the photonic density of states (PDS). It was shown that strong light localisation takes place on edge modes and that the amount of stored energy in the CLC layer depends on the value of refractive index of CLC layer surroundings. The dependences of the density of the localised light energy and PDS versus CLC layer thickness both for different wavelengths of incident light and edge modes are investigated. The effect of the thickness of the CLC layer on the total (integral) light energy and the density of the total localised light energy in the cholesteric liquid crystal (CLC) layer is discussed. It was shown that the total energy density is maximum for very small thicknesses of the CLC layer. We investigated the effect of the thickness of the CLC layer on absorption, the total field (aroused in CLC layer) amplitude, ellipticity and azimuth, too.

Polarization-dependent nonlinear optical response in GeSe<sub>2</sub>

Germanium diselenide (GeSe<sub>2</sub>), a layered IV-VI semiconductor, has an in-plane anisotropic structure and a wide band gap, exhibiting unique optical, electrical, and thermal properties. In this paper, polarization axis Raman spectrum and linear absorption spectrum are used to characterize the crystal axis orientation and energy band characteristics of GeSe<sub>2</sub> flake, respectively. Based on the results, a micro-domain I scan system is used to study the optical nonlinear absorption mechanism of GeSe<sub>2</sub> near the resonance band. The results show that the nonlinear absorption mechanism in GeSe<sub>2</sub> is a superposition of saturation absorption and excited state absorption, and is strongly dependent on the polarization and wavelength of incident light. Under near-resonance excitation (450 nm), the excited state absorption is more greatly dependent on polarization. With different polarizations of incident light, the modulation depth can be changed from 4.6% to 9.9%; for non-resonant excitation (400 nm), the modulation depth only changes from 7.0% to 9.7%. At the same time, compared with saturation absorption, the polarization-dependent excited state absorption is greatly affected by the distance away from the resonance excitation wavelength.

Bisulfone-Functionalized Organic Polymer Photocatalysts for High-Performance Hydrogen Evolution.

Conjugated polymers show great potential in the application of photocatalysis, particularly for the photoreduction reaction of water to generate hydrogen. Molecular structure design is a key part for building a high-performance organic photocatalyst. Herein, two bisulfone-containing conjugated polymer photocatalysts were constructed with 1D or 3D polymer structures, and the effect of polymer geometry on photocatalytic activity was studied. It was found that the linear polymer PySEO-1 exhibited increased photocatalytic performance compared with the 3D polymer network PySEO-2 because the enhanced coplanarity of the polymeric chain in PySEO-1 promoted the photogenerated charge-carrier transmission along the 1D main chain. As a result, an attractive hydrogen generation rate of 9477 μmol h-1 g-1 was obtained with PySEO-1 under broadband light irradiation. PySEO-1 also exhibited a high external quantum efficiency of 4.1 % at an incident light wavelength of 400 nm, demonstrating that the bisulfone-containing polymers are attractive as organic photocatalysts for hydrogen production.

Double-cladding optical fiber design and optimization for simplifying the STED system

Abstract A special double-cladding optical fiber with three-layer step-index structure was introduced for simplifying the stimulated-emission-depletion (STED) microscopy. With this special fiber, a dark hollow beam with decent doughnut-shaped focal spot can be generated for incident light in a specific wavelength range. At the same time, a Gaussian-like beam can be generated when the wavelength of incident light is out of (either longer or shorter than) the specific range. An all-fiber STED illumination system has been achieved by this special fiber. For special cases, a semi-fiber solution based on this special fiber has also been realized.

Augmenting sensitivity of surface plasmon resonance (SPR) sensors with the aid of anti-reflective coatings (ARCs)

Surface plasmon resonance (SPR)-based biosensors are an integral and indispensable aspect of present-day pathology, owing to its efficient real-time and label-free detection capabilities. Enhancing the sensitivity of these sensors is of paramount importance as it indirectly affects the detection limits of biomolecules. In this simulation work, we make use of antireflective coatings (ARCs) (double and multi-layered), made up of nanomaterials with alternating high and low refractive indices (R.I.) (TiO2/SiO2, TiO2/MgF2, Nb2O5/SiO2 and Nb2O5/MgF2); to enhance the sensitivity of Si-Transition Metal Dichalcogenides (TMDCs)-based SPR sensors. To summarize the entire outcome, our simulation predicts the sensitivity of the TiO2-SiO2-Au-Si-TMDC configuration to be 284 degRIU-1 at 633 nm of incident light wavelength.

Flexible Solar-Blind Ga2O3 Ultraviolet Photodetectors With High Responsivity and Photo-to-Dark Current Ratio

In this work, flexible solar blind Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ultraviolet photodetectors with high responsivity and photo-to-dark current ratio are demonstrated. The Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films are obtained by the RF magnetron sputtering method on flexible polyimide (PI) substrates and the results demonstrate that all the films grown under various temperatures are amorphous. When the incident light wavelength is less than 254 nm, the incident light is effectively absorbed by the Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film. By controlling the growth temperature of the material, the responsivity and photo-to-dark current ratio of the corresponding metal-semiconductor-metal photodetectors are significantly improved. At growth temperature of 200 °C, the current under 254 nm illumination obtains 396 nA at voltage of 20 V (corresponding responsivity is 52.6 A/W), the photo-to-dark current ratio is more than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , and the external quantum efficiency reaches 2.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> %, which is among the best reported Ga2O3 ultraviolet photodetectors including the devices on the rigid substrates. After the bending and fatigue tests, the flexible detectors have negligible performance degradation, showing excellent mechanical and electrical stability.

Photo-Responses of Silicon Photodiodes with Different ARC Thicknesses for Scintillators

We designed and fabricated silicon positive-intrinsic-negative (PIN) photodiodes coupled with a scintillator for radiation detection. The photodiodes were fabricated on an n-type double-sided polished silicon wafer with a diameter of 6-in., a high resistivity ( orientation. To increase the quantum efficiency (QE) of the photodiode, an anti-reflection coating (ARC) was provided on the side where light entered. It is difficult to realize an ARC with an uniform thickness in the sensor fabrication process. The effect of changes in the ARC thickness on the QE of the fabricated sensors was studied in detail. We measured the electrical characteristics and compared their quantum efficiencies as a function of the incident light wavelength for the photodiodes with different ARC thicknesses. In this paper, we present the design of the photodiodes and their measured electrical characteristics and photo-responses for different ARC thicknesses. From measurements of the wavelength-dependent QE, we determined the refractive index of the ARC layer to be 2.25 ± 0.15. The ARC layer improved the QE up to 56% and 63% at the wavelengths of 550 and 475 nm, which correspond to the wavelengths of the scintillation light from CsI(Tl) and CdWO4, respectively.

Design of Aluminum Bowtie Nanoantenna Array with Geometrical Control to Tune LSPR from UV to Near-IR for Optical Sensing

Plasmonic nanoantennas have earned strong recognition for their unique capability to confine light from free space into sub-wavelength dimensions with strong electric field (E-field) enhancement factor due to localized surface plasmon resonance (LSPR). Broad spectral tuning of LSPR from ultraviolet (UV) to near-infrared (NIR) is required for incident light wavelength and material sensitive plasmonic applications in different spectral regions. In this article, we introduced and designed a novel aluminum plasmonic platform consisting of a bowtie nanoantenna (BNA) array with metal-insulator-metal (MIM) configuration where LSPR peak position was broadband tunable from UV to NIR through geometric control of antenna parameters. Furthermore, we designed and numerically analyzed a plasmonic biosensor platform that detected concentration of glycerol in de-ionized (DI) water with a concentration in the range of 0 to 40 wt% (refractive index = 1.333 to 1.368) with a sensitivity of 497 nm/RIU (refractive index units). The designed plasmonic platform can also be used as a surface-enhanced Raman scatting (SERS) substrate with enhancement factor as high as 4.82 × 109 for 1042 nm excitation wavelength. The reported hybrid dielectric-metallic plasmonic nanostructured system is a universal plasmonic platform for a wide range of applications including single-molecule SERS, biosensing, fluorescence microscopy, plasmonic nanocavity, nanolasers, and solid-state lighting.

Surface modification of silicon solar cell using TiO2 and Ta2O5: fabrication and characterization

We report the fabrication and characterization of surface modified silicon solar cells with the deposition of amorphous tantalum oxide (Ta2O5) and crystalline titanium oxide (TiO2) nanolayers of thickness 54.9 nm and 69.82 nm, respectively, as antireflection coating (ARC) using RF-sputtering technique. The thickness of the films measured by variable angle spectroscopic ellipsometry and scanning electron microscopy is in close agreement. The transmittance measurement as a function of wavelength of incident light showed that the thin-films deposited have lowest effective reflectance in the wavelength range of 380 nm–570 nm indicating reduced light reflection and enhanced light trapping as observed from UV–Vis measurements. Illuminated current–voltage measurements showed an increase in the short circuit current density (Jsc) and an increase of 1.54% in the efficiency of the antireflection-coated cells. Results of the External Quantum Efficiency measurement as a function of wavelength for the solar cells with ARC is also presented in this paper.

Self-cleaning organic solar cells based on micro/nanostructured haze films with optical enhancement effect

We present a self-cleaning organic solar cells (OSCs) with a light-trapping structure by introducing a groove-shaped micro/nanostructured haze thin films (GHFs). The GHF with periods larger than wavelengths of incident light can broaden the effective optical paths and promote the diffused lights, while keeping high (low) total transmission (reflectance) properties. When laminated GHF on top of the light-in side of OSCs, the power conversion efficiency of OSCs is improved more than 10%. Simultaneously, the superhydrophobic GHF composed of the groove structure allows the droplets to successfully remove dust particles from the polydimethylsiloxane (PDMS) surface during the roll-off process of the drop. Under 10 cycles of dust contamination and cleaning treatment, OSCs with GHF can still guarantee an initial efficiency of 84% (76%), showing great potentials of OSCs in practical applications.

Analytical calculation of diffraction order intensities for a hyperspectrometer

We employ a geometric optics approach to calculate the eikonal of a light field at the output of a diffraction grating in the immediate microrelief vicinity. Analytic relations to calculate the diffraction order intensities as functions of the grating step height, line spacing, wavelength of incident light, and incidence angle are deduced. By way of illustration, intensities of the diffraction orders for a blazed reflection grating with a 555-nm operating wavelength utilized in hyperspectrometers are calculated.

Photothermal modeling and characterization of graphene plasmonic waveguides for optical interconnect.

The photothermal properties of graphene plasmonic waveguides (GPWs) are numerically investigated, while most of existing studies focus on their optical properties. A three-dimensional (3D) coupled optical-thermal model based on finite element method (FEM) is presented. The graphene sheet is treated as an graphene equivalent impedance surface. Transient thermal responses and peak temperature of the GPWs are captured using time-domain FEM (TDFEM). The effectiveness of the proposed method is validated by two examples of hybrid GPWs. Numerical results present the main factors that influence the photothermal properties of the GPWs, including the conductivity of graphene, and the wavelength and power density of incident light. The findings unveil that the temperature increase is an underlying factor influencing the maximum integration density of GPWs in optical interconnect.

Analysis of Multiple Surface Electromagnetic Waves on the Planner Interface of Hyperbolic Medium and Rugate Filter Having Sinusoidal Refractive Index Profile

This paper presents a canonical boundary value problem to understand the behavior of electromagnetic surface waves propagated on the planar interface of rugate filter and hyperbolic material. The electromagnetic surface waves are generated on the planar interface of two different materials. The hyperbolic materials constructed by making a dyadic negative in columnar thin films. Multiple electromagnetic surface waves were investigated by varying phase of rugate filter form 0 to 180° and wavelength of incident light from 400 to 700 nm. Material’s manufacturing fault is also introduced by adding 0.001 i in refractive index of hyperbolic medium.Propagation of multiple electromagnetic waves were observed on the planar interface of rugate filter and hyperbolic material. In order to verify the existence of surface electromagnetic waves at the interface of hyperbolic medium and rugate filter, electric and, magnetic fields are plotted for different material specifications.

Visualization of UV by Nanopatterned Down‐Shifting Materials Mimicking Human Retinal Cone Cells

AbstractThe conversion of invisible ultraviolet (UV) light to visible light by down‐shifting (DS) materials has a variety of important applications in the fields of optoelectronics and photonics. The ability to control emission colors as a function of the wavelength of incident UV light would significantly advance scientific research and technological applications. A novel strategy for UV visualization is demonstrated that employs nanoimprint lithography combined with a sol–gel process. The principles of trichromacy of human vision are applied; three DS materials sensitive to three different ranges of UV light are nanopatterned to mimic the three types of cone cells in the human retina. Each DS material then emits a distinctive color that can be recognized by each type of cone cells for visualization. The nanopatterned structure significantly intensifies the light emission by Mie scattering and spatially separates the three DS materials, thereby minimizing unwanted optical interference among them. The deliberately designed triple‐nanopatterned DS materials exhibit various emission colors ranging from green, to orange, to pink depending on the wavelength of the incident UV light. The current work would contribute to the development of novel strategies for multicolor tunable emission that may lead to innovative applications.