Angle Of Incident Light Research Articles

Evaluating fingerprint-like patterns in the healthy Henle fiber layer using enface OCT imaging

PurposeEnface OCT may disclose a distinct “fingerprint-like' pattern within the HFL in various macular disorders. This study aims to investigate the frequency and characteristics of this pattern in healthy eyes and identify potential factors influencing its visibility. MethodsTwo, independent masked reading center graders evaluated for the presence and prominence of a fingerprint pattern in the Henle fiber layer (HFL) on enface OCT images from 33 healthy subjects (66 eyes). The prominence of the pattern was rated qualitatively using a 0–3 scale, with 3 indicating the strongest prominence. Tilt angles (relative to the normal/perpendicular at the center) of the retina were measured on horizontal and vertical B-scans, and the retinal curvature was assessed using ImageJ, in order to determine the impact of the incident light angle on the visibility and prominence of the fingerprint pattern. Inter-grader agreement using Cohen's kappa and the frequency and percentage of patterns in the entire enface image and in each quadrant were calculated and compared using the Friedman test with Dunn's post-test. A generalized estimating equation (GEE) was used to analyze the association between these metrics and fingerprint prominence. ResultsSubstantial inter-grader agreement was observed (Cohen's kappa = 0.71) for assessing the prominence of the fingerprint pattern. Over 70% of eyes exhibited some evidence of the pattern (score ≥1). Significant difference in pattern prominence across quadrants was detected (p < 0.05), with lowest prominence in the temporal quadrant (p < 0.001 for pairwise comparisons against all other quadrants). The GEE analysis to account for the extent of the effect of scan tilt angle and RPE curvature was not able to predict the prominence of the fingerprint pattern, highlighting that angle of incidence (of the scanning laser light) alone could not explain the pattern. ConclusionsThis study confirms that a fingerprint-like pattern within the HFL can also be observed in healthy eyes, challenging the notion that this finding is only manifest in the setting of disease. In addition, the lack of correlation with angle of incident light suggests that the pattern may be related to other intrinsic characteristics of the HFL.

An ultra-wide-angle metasurface absorber operating in the ultraviolet to visible range

Here, we propose an ultra-wide-angle metasurface absorber. It consists of a one-dimensional titanium grating periodic array with dislocation distribution. The average absorptivity of the absorber exceeds 94% in the ultraviolet to visible light band (200–760 nm) under normal TM-polarized incident wave. This benefits from the coupling of propagating surface plasmon resonance, local surface plasmon resonance, and hybrid mode resonance. For normal TE-polarized incident wave, the absorber achieves perfect narrowband absorption (>99.22%) in the ultraviolet light region because of the excitation of cavity-mode resonance. The absorber exhibits broadband absorption with an average absorptivity exceeding 85% in the visible light band because of the excitation of slot mode. These excellent absorption properties are well retained at 70° oblique incidence. The structural symmetry of the absorber dramatically expands the flexibility of device applications. It can achieve great absorption performance in an ultra-wide-angle range of 280° along the incident light direction. In addition, the absorber is sensitive to the polarization angle and incident angle of ultraviolet light, which can be used for ultraviolet detection and sensing. The proposed ultra-wide-angle metasurface absorber has potential application in the field of optical communication, photoelectric detection, and solar energy harvesting.

Angular dispersion and diffraction imaging analysis in a light wave oblique incident two-dimensional crossed grating

Based on the vector diffraction theory, the angular dispersion and diffraction imaging are analyzed in parallel light oblique incident two-dimensional crossed gratings. The results show that the angular dispersion presents a kind of increase-decrease-increase oscillatory change, and the maximum value of diffractive polar angle dispersion and total dispersion present an abrupt point. The angular dispersion is limited by the light wave incidence angle and two-dimensional gratings crossed angle. In addition, some obvious pincushion distortion has been formed in some cases. The angular dispersion increases with the increase of grating crossed angle in the permissible range, leading to enhancement of the diffraction imaging distortion. The results imply that there is an inherent relationship between the angular dispersion and the diffraction imaging in parallel light oblique incident crossed gratings.

Tunable dual-band composite metasurface absorber in the mid-infrared region based on LSPs-SPPs interaction

Mid-infrared (MIR) region includes many important fingerprint signals about of particular chemical molecules and functional groups, which is an important band for compact optical sensing system. Controlling the localized surface plasmons (LSPs) and surface plasmon polariton (SPP) modes is an effective approach to achieving perfect absorption in plasmonic metasurfaces. In this work, we systematically investigate the interaction between LSP and SPP within a composite plasmonic metasurface absorber, as well as the impact of this interaction on its absorption characteristics. The absorber achieves absorptivity 99.2 % at 2.39 μm and 98.8 % at 3.61 μm. The detailed absorption mechanism and tunability of the absorber are discussed associated with a physical model based on quantum electron dynamics (QED) theory. Our analysis also explores the effect of incident angle, identifying a Rabi splitting at 40° and 3.61 μm due to the interaction between cavity modes and LSPs, while the absorption peak at 2.39 μm experiences a redshift with an increasing angle. These peaks show minimal dependence on the polarization angles of incident light. Furthermore, we investigate the impact of the SiO2 spacer's refractive index using an admittance model, observing a redshift in the absorption peaks with an increase in refractive index. Our findings not only introduce a metasurface absorber for the MIR spectrum, applicable in sensing and detection, but also establish a foundation for further research.

Multifunctional terahertz device based on plasmon-induced transparency

Enhancing light-matter interaction is crucial in optics for boosting nanophotonic device performance, which can be achieved via plasmon-induced transparency (PIT). In this study, a polarization-insensitive PIT effect at terahertz frequencies is achieved using a novel metasurface composed of a cross-shaped graphene structure surrounded by four graphene strips. The high symmetry of this metasurface ensures its insensitivity to changes in the polarization angle of incident light. The PIT effect, stemming from the coupling of graphene bright modes, was explored through finite difference time domain (FDTD) simulations and coupled mode theory (CMT) analysis. By tuning the Fermi level in graphene, we effectively modulated the PIT transparent window, achieving high-performance optical switching with a modulation depth (88.9% < MD < 98.0%) and insertion losses (0.17 dB < IL < 0.51 dB) at a carrier mobility of 2 m2/(V·s). Furthermore, the impact of graphene carrier mobility on the slow-light effect was examined, revealing that increasing the carrier mobility from 0.5 m2/(V·s) to 3 m2/(V·s) boosts the group index from 126 to 781. These findings highlight the potential for developing versatile terahertz devices, such as optical switches and slow-light apparatus.

Enhancing mid-infrared surface phonon polariton modes: optimization of structural parameters in Nb-doped SrTiO3 with hole array structures for advanced infrared sensors

This study utilized the finite difference time domain method to investigate the mid infrared surface phonon polaritons and localized surface phonon resonances in undoped and niobium (Nb)-doped SrTiO3 (STO) with planar and holes array structures. Research has shown that Nb-doped STO operates in the Reststrahlen band of 8.06–18.48 µm, providing a wider spectral response than undoped STO (12.58–18.26 µm) and effectively covering the atmospheric window of long wave infrared. This indicates that the increase in virtual permittivity has the least impact on spectral broadening, indicating that the new infrared sensor technology has broad prospects. The optimization of structural parameters, including the period, filling factor, and depth of STO holes array, as well as the response to changes in incident light angle, is crucial for guiding the design of high-performance optoelectronic devices. In addition, this study explored the excitation of four resonant modes within a holes array and analyzed their relationship with array parameters to enhance the design of optoelectronic applications.

Overall performance evaluation of a novel optical truncation method for compound parabolic concentrated photovoltaic-thermal system

A variable geometric concentration ratio (VGCR) truncation method was proposed to enhance the performance of compound parabolic concentrated photovoltaic-thermal (CPC-PVT) system in this study. Based on a multi-physics field model of optical-thermal-electrical coupling, numerical investigations using Monte Carlo ray tracing (MCRT) and finite volume method (FVM) were conducted to analyze the effects of the variation rate of truncation ratio (k) and light incident angle (θin) on the overall performance (optical efficiency (ηop), instantaneous thermal efficiency (ηth), instantaneous electrical efficiency (ηele,total), instantaneous electrical power (P), instantaneous exergy efficiency (ηu,total) and economic performance) of CPC-PVT system. Also, the overall performance between the VGCR-CPC-PVT system and the full CPC-PVT (FCPC-PVT) system was compared. The results indicate that, when θin is smaller, there is little disparity in the overall performance between the two systems. However, as k increases, ηop, ηele,total, ηth and ηu,total of VGCR-CPC-PVT system monotonically increase, and the area of the high-temperature region on the PV panel surface decreases. When θin is larger, the VGCR-CPC-PVT system has a smaller shaded area, ηop, ηele,total, P and ηu,total are significantly improved compared with the FCPC-PVT system. Additionally, k has a significant impact on the overall performance of the system, and P, ηu,total and saved reflective surface area (S) are the criteria for selecting k. When using P and ηu,total as the selection criteria, the optimal k value is 0.04. For 0°≤θin≤38°, the average ηop, average ηele,total, average ηth, average P and average ηu,total of the VGCR-CPC-PVT system with k = 0.04 are relatively improved by 1.91 %, 4.59 %, 2.42 %, 3.12 % and 4.04 %, respectively, while the reflector area decreases by 17.5 %, compared with the FCPC-PVT system. The cost-effectiveness of concentrator increases significantly with k.

Effect of DNA serial dilution on the highly precise broadband plasmonic signature of a BALB/c rat’s dried DNA deposited on gold thin film

An investigation was made to detect the DNA samples of BALB/c rats, exploiting the technique of broadband plasmonic response in the visible spectral regime. In experiments, a non-coherent light beam was physically designed and practically implemented to study the spectral effect due to serial dilution of BALB/c rat’s dried DNA. In particular, three different diluted DNA samples (with ratios of 1:10, 1:20, and 1:40) dried on the surface of a nanolayer gold thin film were considered to retrieve the plasmonic conditions under which the reflectance becomes minimum. The results indicate the most diluted DNA sample exhibits prominent plasmonic conditions, and the resonance wavelengths undergo redshifts with increasing incidence angle (of the p-polarized light). Also, the sensitivity of the configuration is enhanced in the presence of a DNA sample (as compared to the case of non-existence of measurand), which is further increased for larger incidence angles.

Protecting against micropollutants in water storage tanks using in-situ TiO2 coated quartz optical fibers

Photocatalyst-coated optical fibers (P-OFs) using UV-A LEDs offer a highly promising solution for the degradation of micropollutants within municipal, reuse, industrial or home distribution systems, by integrating P-OFs into water storage tanks. P-OFs have photocatalysts attached to bundles of optical fibers, enabling their direct deployment within tanks. This eliminates the necessity for photocatalyst slurries, which would require additional membrane or separation systems. However, a current limitation of P-OFs is light management, specifically light oversaturation of the coated photocatalysts and short light transmission distances along fibers. This study overcomes this limitation and reveals strategies to improve the light dissipation uniformity along P-OFs, and demonstrates the performance of P-OFs on degrading a model micropollutant, carbamazepine (CBZ). Key tunable variables of fibers and light emission conditions, including photocatalyst coating patchiness (p), minimum light incident angles (θm), radiant flux launched to fibers (Φi), and fiber diameters (D), were modeled to establish their relationships with the light dissipation uniformity in TiO2-coated quartz optical fibers (TiO2-QOFs). We then validated modeling insights by conducting experiments to examine how these variables influence the generation of evanescent waves which are localized energy on fiber surfaces, leading to either photocatalyst activation or the recapture of unused light back into fibers. We observed substantial enhancements in evanescent waves generation by decreasing p and increasing θm, resulting in uniform light dissipation which reduces light oversaturation and improves light transmission distances. Moreover, these optimizations led to a remarkable three-fold improvement in CBZ degradation rates and a 65% reduction in energy consumption. Such improvement substantially reduces the capital and operational cost and enhances practicality of energy-efficient photocatalysis without additional chemical oxidants for micropollutant degradation in water storage tanks.

Photomolecular effect: Visible light interaction with air–water interface

Although water is almost transparent to visible light, we demonstrate that the air-water interface interacts strongly with visible light via what we hypothesize as the photomolecular effect. In this effect, transverse-magnetic polarized photons cleave off water clusters from the air-water interface. We use 14 different experiments to demonstrate the existence of this effect and its dependence on the wavelength, incident angle, and polarization of visible light. We further demonstrate that visible light heats up thin fogs, suggesting that this process can impact weather, climate, and the earth's water cycle and that it provides a mechanism to resolve the long-standing puzzle of larger measured clouds absorption to solar radiation than theory could predict based on bulk water optical constants. Our study suggests that the photomolecular effect should happen widely in nature, from clouds to fogs, ocean to soil surfaces, and plant transpiration and can also lead to applications in energy and clean water.

Spatial wavefront shaping with a multipolar-resonant metasurface for structured illumination microscopy [Invited

Structured illumination microscopy (SIM) achieves superresolution in fluorescence imaging through patterned illumination and computational image reconstruction, yet current methods require bulky, costly modulation optics and high-precision optical alignment, thus hindering the widespread implementation of SIM. To address this challenge, this work demonstrates how nano-optical metasurfaces, rationally designed to tailor the far-field optical wavefront at sub-wavelength dimensions, hold great potential as ultrathin, single-surface, all-optical wavefront modulators for SIM. We computationally demonstrate this principle with a multipolar-resonant metasurface composed of silicon nanostructures that generate versatile optical wavefronts in the far field upon variation of the polarization or angle of incident light. Algorithmic optimization is performed to identify the seven most suitable illumination patterns for SIM generated by the metasurface based on three key criteria. We quantitatively demonstrate that multipolar-resonant metasurface SIM (mrm-SIM) achieves resolution gain that is comparable to conventional methods by applying the seven optimal metasurface-generated wavefronts to simulated fluorescent objects and reconstructing the objects using proximal gradient descent. Notably, we show that mrm-SIM achieves these resolution gains with a far-field illumination pattern that circumvents complex equipment and alignment requirements of comparable methodologies. The work presented here paves the way for a metasurface-enabled experimental simplification of structured illumination microscopy.

Optical Analysis Method for Turbid Media Based on Wedge-Shaped Cells at Different Angles.

The wedge-shaped sample cell, by offering a comprehensive representation of scattering information in turbid media, significantly enhances the informational content conveyed by spectral images compared to flat sample cells. To further refine the accuracy of turbid medium component detection utilizing wedge-shaped sample cells, this work undertakes modeling and analysis of the influence of different wedge angles on detection precision. In this study, employing a 5° gradient in the incident angle of light, we investigate the impact of incident angles ranging from 10 to 45° on the turbid medium component analysis. Validation experiments are performed by utilizing solutions of Indian ink and fat emulsion at varying ratios. Experimental findings demonstrate that under identical experimental conditions, the wedge-shaped sample cell model at an incident angle of 35° yields optimal analysis results. Utilizing partial least-squares regression (PLSR) for the corresponding optical parameters, the highest value of Rp reached 0.980, with an RMSEP of 0.002. When compared to the model with a 30° incident angle, Rp increased by 0.033, and RMSEP decreased by 0.008. In comparison to the flat sample cell model, Rp increased by 0.041, and RMSEP decreased by 0.004. This study, through continuous variation of wedge angles and PLSR modeling and prediction, further enhances the accuracy of turbid medium component detection, laying an experimental foundation for subsequent analysis of turbid medium components based on wedge-shaped sample cells.

Incident angle optimization with multiple conflicting objectives based on BP-MOPSO in oblique laser interferometry

The oblique incident phase-shifting interferometric measurement method is an effective technique for assessing gear tooth form deviation. In the measurement process, the tooth flank incident angle is a crucial factor determining the quality of interferograms. Addressing the challenge in traditional optical path design, where the selection of the tooth flank incident angle encounters a trade-off among quality features such as measurable tooth area (MTA), interference fringe density (IFD) and interferogram compression ratio (ICR), this paper proposes an optimized method for the tooth flank incident angle. Firstly, a comprehensive evaluation model is established to calculate and analyze the MTA, IFD and ICR of the helical gear. Secondly, by integrating BP neural network and Multi-Objective Particle Swarm Optimization (MOPSO) algorithm, a tooth flank incident angle optimization method is devised to simultaneously optimize the measurement light incident angle γ and the rotation angle of the gear axis β. Finally, simulation analyses and physical experiments are employed to demonstrate the feasibility of the proposed method, compared to before optimization, the pseudocorrelation (PSD) value has increased by an average of 34%, and the residual points have decreased by an average of 80%, confirming its capability to improve quality interferogram and measurement accuracy.

Multilevel design and construction in nanomembrane rolling for three-dimensional angle-sensitive photodetection

Releasing pre-strained two-dimensional nanomembranes to assemble on-chip three-dimensional devices is crucial for upcoming advanced electronic and optoelectronic applications. However, the release process is affected by many unclear factors, hindering the transition from laboratory to industrial applications. Here, we propose a quasistatic multilevel finite element modeling to assemble three-dimensional structures from two-dimensional nanomembranes and offer verification results by various bilayer nanomembranes. Take Si/Cr nanomembrane as an example, we confirm that the three-dimensional structural formation is governed by both the minimum energy state and the geometric constraints imposed by the edges of the sacrificial layer. Large-scale, high-yield fabrication of three-dimensional structures is achieved, and two distinct three-dimensional structures are assembled from the same precursor. Six types of three-dimensional Si/Cr photodetectors are then prepared to resolve the incident angle of light with a deep neural network model, opening up possibilities for the design and manufacturing methods of More-than-Moore-era devices.

Lateral optical force on paired isotropic spherical particles in a linearly polarized plane wave

To generate lateral optical force (LOF) on a mirror-symmetric object is still challenging. Here, we demonstrate numerically and analytically that an extraordinary LOF can be induced on paired isotropic spherical particles under the illumination of an obliquely incident linearly polarized (LP) plane wave. Theoretical analysis reveals that the LOF arises from lateral asymmetric scattering between two particles induced by the linear polarization of obliquely incident LP light. The magnitude and sign of the LOF are tunable and reversible by changing the particle separation, incident angle and polarization angle of the incident light. Especially, the LOF shows a sinusoidal dependence on the polarization angle, which enriches the degree of freedom of optical manipulation. The proposed mechanism does not depend on complex structured light or interface and is expected to have practical applications in separating and sorting different dimers.

Design, preparation, and property analysis of metal/dielectric multilayer film with wavelength selectivity

Metal/dielectric multilayer films have important applications in energy-saving glass, stealth materials, solar energy utilization and other fields. In the current study, the thickness of each layer of TiO2/Ag/TiO2/Ag/TiO2 film is optimized. The effects of the number of metal/dielectric multilayer films and the incident light angle on their optical properties were investigated. The TiO2/Ag/TiO2/Ag/TiO2 film was prepared by electron beam evaporation coating technology, and their reflectance and transmittance were measured. The measurement results show that the visible light transmittance (380–780 nm) of the film can achieve 68.7%, and the infrared reflectance (780–2500 nm) can reach 95.9%. Compared with the traditional dielectric/metal/dielectric three-layer film, the visible light transmittance of the film is higher, and the solar infrared reflectance is greatly improved. In the solar radiation band (280–2500 nm), the average error between the experimental reflectance and transmittance and the theoretical prediction results is less than 0.03. The distribution of electric and magnetic fields inside the film was simulated by finite-difference time-domain method. The simulation results show that the high visible light transmittance is due to the interference resonance of electromagnetic waves inside the film. Taking Shanghai as an example, under our calculation conditions, compared with ordinary SiO2 glass, TiO2/Ag/TiO2/Ag/TiO2 film can reduce the total energy consumption of buildings by 14.3% and refrigeration energy consumption by 17.2%.

Graphene metamaterials-based plasmon-induced terahertz modulator for high-performance multiband filtering and slow light applications.

We proposed multilayered graphene (Gr)-based surface plasmon resonance-induced high-performance terahertz (THz) modulators with tunable resonance frequencies. Previously reported Gr metamaterials-based THz plasmonic modulators had small group delay, low extinction ratio (ER), and difficult-to-tune resonant frequency without changing structural parameters in the THz range. A comprehensive investigation employing the finite-difference time-domain (FDTD) simulation technique revealed high group delay, broad tunability independent of structural parameters, and large ER for our proposed quadband and pentaband plasmonic modulators. We obtained tunable group delays with a maximum of 1.02 ps and 1.41 ps for our proposed quadband and pentaband plasmonic modulators, respectively, which are substantially greater compared to previously reported Gr-based metamaterial structures. The maximum ER of 22.3 dB was obtained, which was substantially high compared to previous reports. Our proposed modulators were sensitive to the polarization angle of incident light; therefore, the transmittance at resonant frequencies was increased while the polarization angle varied from 0° to 180°. These high-performance plasmonic modulators have emerging potential for the design of optical buffers, slow light devices, multistop band filters, integrated photonic circuits, and various optoelectronic systems.

Theoretical exploration of photoemission characteristics of GaAs nanowire array cathode based on photon-enhanced thermionic emission

The theoretical photoemission models of single GaAs nanowire and nanowire array cathode based on photon-enhanced thermionic emission (PETE) mechanism are respectively developed by utilizing two-dimensional continuity equations. Based on the built models in this work, the effect of several key factors on the quantum efficiency are also discussed. Results show that GaAs nanowire cathode exhibits the superiority of photoemission performance compared with GaAs film cathode at the spectral range of 300∼600 nm. Besides, the optimal wire diameter of GaAs nanowire cathode is in the range of 340∼360 nm. In addition, the nanowire cathode with low electron affinity of 0.3 eV achieves PETE effect under low temperature of 400 K, which is conducive to improve the stability of cathode. Moreover, increasing the incident light angle or decreasing the array spacing provides an effective method of obtaining high quantum efficiency of nanowire array cathode. Furthermore, the numerical difference between quantum efficiency and effective quantum efficiency implies that the low collection efficiency of emitted electrons is the main issue that hinders the application of PETE cathodes of GaAs nanowire array. The proposed GaAs nanowire array model would provide theoretical guidance for optimum design of PETE cathodes with nanoarray structure.

High Q-Factor, High Contrast, and Multi-Band Optical Sensor Based on Plasmonic Square Bracket Dimer Metasurface.

A high-performance resonant metasurface is rather promising for diverse application areas such as optical sensing and filtering. Herein, a metal-insulator-metal (MIM) optical sensor with merits of a high quality-factor (Q-factor), multiple operating bands, and high spectrum contrast is proposed using plasmonic square bracket dimer metasurface. Due to the complex square bracket itself, a dimer structure of two oppositely placed square brackets, and metasurface array configuration, multiple kinds of mode coupling can be devised in the inner and outer elements within the metasurface, enabling four sensing channels with the sensitivities higher than 200 nm/RIU for refractive index sensing. Among them, the special sensing channel based on the reflection-type surface lattice resonance (SLR) mechanism has a full width at half maximum (FWHM) of only 2 nm, a high peak-to-dip signal contrast of 0.82, a high Q-factor of 548, and it can also behave as a good sensing channel for the thickness measurement of the deposition layer. The multi-band sensor can work normally in a large refractive index or thickness range, and the number of resonant channels can be further increased by simply breaking the structural symmetry or changing the polarization angle of incident light. Equipped with unique advantages, the suggested plasmonic metasurface has great potential in sensing, monitoring, filtering, and other applications.

Strong circular dichroism absorbers using chiral metamaterials with circular polarization

We designed and characterized a chiral metamaterial circularly polarized strong circular dichroism absorber with dynamic tuning capabilities using graphene. The synergistic combination of strong circular dichroism and perfect absorption, coupled with the tunability afforded by graphene, positions this absorber as a promising candidate for advanced electromagnetic applications. Employing a frequency-domain solver in electromagnetic simulation software, the impact of parameters such as the thickness of a metal U-ring, a silica dielectric layer, and the polarization angle of incident light on circular dichroism is systematically analyzed. Strong circular dichroism can be achieved by adjusting the misalignment angle of the metal U-ring, reaching a value as high as 0.91. At an incident angle of 60°, left-circularly polarized (LCP) light demonstrates outstanding wide-angle absorption performance, absorbing over 80% in the x-z plane and more than 70% in the y-z plane. Transitioning from circular to linear polarization and changing the tilt angle of the metal U-ring also achieves a 99.99% absorption peak at 1.33 THz. Moreover, in comparison to conventional absorbers, the structure presented in this study offers enhanced controllability of absorption performance through external voltage manipulation. This research not only refines the existing concepts but also introduces novel ideas for the development of tunable chiral optical devices.