Fresnel Reflection Research Articles

High-Transmission Biomimetics Structural Surfaces Produced via Ultrafast Laser Manufacturing.

Inspired by periodically aligned micro/nanostructures on biological surfaces, researchers have been fabricating biomimetic structures with superior performance. As a promising and versatile tool, an ultrafast laser combined with other forms of processing technology has been utilized to manufacture functional structures, e.g., the biomimetic subwavelength structures to restrain the surface Fresnel reflectance. In this review paper, we interpret the biomimetic mechanism of antireflective subwavelength structures (ARSSs) for high-transmission windows. Recent advances in the fabrication of ARSSs with an ultrafast laser are summarized and introduced. The limitations and challenges of laser processing technology are discussed, and the future prospects for advancement are outlined, too.

Nonlinear optical properties of gold with intense femtosecond laser excitations above the damage threshold

The nonlinear optical properties of gold thin films have been studied under the irradiation of destructive laser pluses. The transmissivity and the reflectivity of a 100-nm-thick gold film are measured with femtosecond laser irradiations up to 106 J/m2 fluence, which is much higher than the damage threshold of gold. The nonlinearity is calculated with Fresnel loss equations. The real part of the complex refractive index is calculated to have a peak at ∼10 kJ/m2, which is close to the damage threshold. The complex third-order nonlinear susceptibility χ3 is estimated to be (4.95 − 2.02i) × 10−21 m2/V2, which agrees with the trend in previous reports that it decreases as the pulse duration decreases. This nonlinearity is further studied with a plasmon-photon exchange (PPE) model, where laser induced plasmons and absorbed photons are strongly correlated. The result of the simulation with the PPE model is in good agreement with the experimental transmissivity above the damage threshold. The model predicted an interaction time between photons and plasmons to be about 500 fs. This model is found to be essential in understanding such nonlinear optical processes under both extremely high and conventionally low laser irradiations.

Simplified setup for Brillouin scattering observation using variable reflectivity mirror and its polarisation characteristics

AbstractThe authors present a streamlined setup for Brillouin scattering observation, which negates the need for an independent reference path by incorporating a variable reflectivity mirror at the terminus of the sensing fibre. The authors’ study uncovers an optimal reflectivity point, specifically at −9 dB, where the signal‐to‐noise ratio (SNR) of the observed Brillouin gain spectrum (BGS) reaches its zenith, approximately doubling the SNR of a conventional simplified setup that utilises Fresnel reflection. Furthermore, the authors elucidate that this setup inherently mitigates the polarisation‐dependent fluctuations of the BGS.

Efficient laser emission at 1191 nm based on Ho3+-doped fluoroaluminate glass in a compact fiber configuration

Efficient laser emission at a wavelength of approximately 1.2 μm in Ho3+-doped AlF3-based glass fiber is reported for the first time. Lasing was achieved through in-band pumping at 1150 nm. The laser cavity's front-end feedback was facilitated by a (High reflectivity, HR) HR-FBG written in Corning HI1060 fiber, spliced to one end of the Ho3+-doped AlF3-based fiber. Fresnel's reflection of the gain fiber provided the other end feedback. The laser performance was characterized by different fiber lengths, and a 31 cm-long fiber achieved a maximum slope efficiency of 70.5 % and a maximum output power of 8.3 W. Furthermore, a series of (Low reflectivity, LR) LR-FBGs written in HI1060 fiber with different reflectivity values were used to replace the Fresnel reflection at the emission end of the gain fiber. The maximum slope efficiency was found to be 54.2 % for a LR-FBG with a reflectivity of 10 %. These results confirm that AlF3-based fiber can potentially serve as gain fiber for higher-power fiber lasers.

On pseudo-Riemannian quartics in Finsler geometry

Finsler geometry usually describes an extension of Riemannian geometry into a direction-dependent geometric structure. Historically, the well-known Riemann quartic length element example served as the inspiration for this construction. Surprisingly, the same quartic expression emerges as a fundamental dispersion relationcovariant Fresnel equationin solid-state electrodynamics. As a result, it is possible to conceive of the Riemann quartic length expression as a mathematical representation of a well-known physical phenomenon. This paper provides a number of Riemann quartic examples that show Finsler geometry to be overly constrictive for many applications, even when the signature space is positive definite in the Euclidean sense. The strong axioms of Finsler geometry are broken down on many more singular hypersurfaces for the spaces having an indefinite (Minkowski) signature. We suggest a more flexible definition of a Finsler structure that only has to hold for open subsets of a manifold’s tangent bundle. We demonstrate the distinctive singular hypersurfaces connected to the Riemann quartic and discuss the potential physics explanations for them. As an illustration of the pseudo-Riemannian quartic, we took into consideration the dispersion relation that appears in electromagnetic wave propagation in uniaxial crystal. Our analysis suggests that the signature of the Finsler measure may be altered for large anisotropy factors.

Multilayer designs comprising zirconium nitride and perovskites as a novel angular plasmonic biomedical sensor

Abstract In this paper, a comparison between different configurations of surface plasmon resonance (SPR) biosensors has been theoretically conducted to improve the performance of the designed biosensor. The proposed biosensor configurations contain zirconium nitride (ZrN) as an alternative plasmonic material, which comprises different perovskite materials (KNbO3, LiTaO3, LiNbO3, SrTiO3, and BaTiO3) in the visible region. Depending on the study calculations, the reflection spectra of the suggested designs were studied under the angular interrogation mode based on Fresnel coefficients for the transverse magnetic polarized light. The numerical findings demonstrated that the SPR biosensor, which has the configuration of [Prism/BaTiO3/ZrN/BaTiO3/Biosensing medium], represents the best biosensor due to its higher sensitivity and minimum reflectivity values. Meanwhile, sensitivity could receive 179.58 (deg/RIU). Therefore, it is believed that the proposed SPR biosensor designs could be promising through wide-ranging applications, specifically in biomedical, chemical, and environmental protection.

Experimental study of a linear Fresnel reflection solar concentrating system

Introduction: In the field of solar energy utilization, the construction of low cost and easy to process large concentrated photothermal system is a scientific problem to be solved. A linear Fresnel reflection solar concentrator is proposed in this paper.Methods: The position, tilt angle and width of the glass mirrors placed in the same plane are different to ensure that all the reflected light falls on the flat focal plane or cylindrical focal surface. According to the focusing principle of the concentrator, two experimental system platforms ware built. When a flat focal plane is used to receive radiation from the sun, the intensity distribution of focal plane light spot is uniform in theory.Results: The CCD measurement method is used to analyze the concentrated light spot under experimental conditions, and it is proved that the energy flux density on the focal plane is uniform. Placing monocrystalline silicon cells on the focal plane, the experimental results of p-v power generation voltammetry show that the power generation efficiency of monocrystalline silicon cell does not decrease due to the uniform solar energy density, which can reach 17.1%. The photothermal experiment is carried out by using one-dimensional tracking mode of sunlight. The concentrator reflects the sun’s rays onto the vacuum collector tubes, heating the heat conduction oil flow in. The thermocouple measures the temperature of the heat conduction oil at the inlet and outlet of the vacuum collector tubes. The experimental photothermal conversion efficiency of this concentrator was analyzed and calculated through multiple groups of photothermal experiments, and compared with the theoretical concentrator efficiency. With two collector tubes in series, the theoretical photothermal conversion efficiency reaches 0.8 and the experimental photothermal conversion efficiency reaches about 0.74.Discussion: Because of its good concentrating performance and low cost, this type concentrator can be widely used in photothermal and photovoltaic applications.

Ultraviolet light scattering by a silicon Bethe hole

Abstract Bethe’s theory predicts that scattering by a small hole on a thin perfect electric conductor (PEC) is presented as radiation by an in-plane magnetic dipole of the incident magnetic field direction. Even in the near-infrared range where metals are no more PEC, the magnetic dipole radiation of Bethe holes has been demonstrated. However, such Bethe holes’ nature has not been addressed yet in the ultraviolet (UV) range where conductivity of metals becomes severely deteriorated. Meanwhile, UV plasmonics has been elevating its importance in spectroscopy and photochemistry, recognizing silicon (Si) as an alternative plasmonic metal featuring the interband transition in the UV range. In this work, we expanded the Bethe’s theory’s prediction to the UV range by investigating Si Bethe holes theoretically and experimentally in terms of the scattering pattern and polarization. Simulation results showed that the scattered field distribution resembles that of an in-plane magnetic dipole, and the dipole direction at oblique incidence is roughly given as the incident magnetic field direction with a deviation angle which can be predicted from the Fresnel equations. Simulation with various diameters showed that the magnetic dipole nature maintains with a diameter less than the quarter-wavelength and multipoles becomes noticeable for diameters larger than the half-wavelength. We performed scattering polarization measurement at 69-degree incidence, which confirms the theoretical analysis. The features of Si Bethe holes demonstrated here will be useful for designing UV plasmonic metasurfaces.

A novel simulador for agile and graphical modeling of surface plasmon resonance based sensors

Surface plasmon resonance (SPR) sensor is a consolidated technology for analysis of biomolecular interaction, largely applied in biology and pharmaceutical research. The simulation of the surface plasmon optical excitation response is an important step in the development process of SPR based sensors. The structure, design and configuration of the desired sensor benefits from a previous simulated analyses of the generated responses, defining operational conditions and feasibility of the selected materials to composed the optical coupling layers. Here an online web-based SPR sensor’s simulator is presented. With a visual-oriented interface, enable drag & drop actions to easily and quickly model a variety of sensor arrangements. Presenting an embedded materials database for metals, glasses, 2D materials, nanoparticles, polymers, and custom substances, the simulator enables flexible configuration for sensors operating in angular and spectral modes, as well as localized SPR. The light propagation through the multilayer of materials is presented in terms of Fresnel coefficients, which are graphically displayed. The so-called SPR morphology parameters can be visualized. Moreover, sensor dynamic behavior could be knowledge by a Sensorgram simulation. Localized surface plasmon resonance (LSPR) in homogeneous and spherical nanoparticles is also present in the simulator. Simulated scenario’s in various configurations, designs and excitation were performed and compare with other simulator. The proposed simulator guarantees comparable results with low-code, agile, and intuitive flow of execution.

Unravelling keyhole instabilities and laser absorption dynamics during laser irradiation of Ti6Al4V: A high-fidelity thermo-fluidic study

A 3D multi-phase thermo-fluidic solver is implemented to investigate the laser-melt pool interaction dynamics and keyhole instabilities during stationary and moving laser irradiation. The physical phenomena such as phase changes, thermocapillary driven flow, multiple reflections of the Gaussian laser beam and beam trapping, vaporization recoil pressure, and heat losses (convective, radiative, and evaporative) have been incorporated in the model. A detailed parametric study has been carried out to investigate the influence of the laser beam spot diameter and the traversal speed on the laser absorption dynamics and melt pool characteristics. For both the stationary and moving laser irradiation, it is found that during the initial transient stage, the melt pool morphology belongs to the conduction melting mode with laser absorption according to the normal incidence condition of the Fresnel equation. Later, depending on the irradiating laser intensity, a melt transition occurs from conduction to the keyhole mode of melting, during which laser absorption rises sharply. The laser absorption and the vapor depression morphology in the keyhole regime show substantial oscillations (periodic and non-periodic) due to the complex hydrodynamics of the recoil pressure, the surface-tension dynamics, and convection-driven flow resulting in the opening and closing of the vapor depression. These oscillations are quantified, and a direct correlation of the laser absorptance with the keyhole depression depth has been observed for stationary laser irradiation. The keyhole closure mechanism and bubble trapping-ejection phenomena have been explored during the solidification stage. The numerically predicted melt pool dimensions match well with the in-house performed experimental measurements and published benchmarking experiments combining integrating sphere radiometry and in-situ X-ray radiography.

Preparation of NaYF4:Tm, Yb, and Gd Luminescent Nanorods/SiO2 Nanospheres Composite Thin Film and Its Application in Perovskite Solar Cells.

In this study, we aim to minimize light loss and achieve high power conversion efficiencies (PCE) in perovskite solar cells (PSCs) by employing a spectral conversion film component with antireflection properties. In our scheme, NaYF4:Tm, Yb, and Gd luminescent nanorod/silica nanosphere-based thin films are applied on CH3NH3PbI3 PSCs to improve the device efficiency. The film was fabricated by spin coating an aged silica sol containing NaYF4:Tm, Yb, and Gd luminescent nanorods. The size and the spectral conversion properties of the NaYF4:Tm, Yb, and Gd luminescent nanorods were controlled by tuning the Gd3+ ion concentration. The microstructure and the transmittance properties of the thin film were controlled by changing the concentration of NaYF4:Tm, Yb, and Gd luminescent nanorod in silica sol. The thin films have excellent spectral conversion properties while exhibiting a maximum transmittance. The photovoltaic performance of PSCs with NaYF4:Tm, Yb, and Gd luminescent nanorod/silica nanosphere-based thin films was systematically investigated. The light transmittance was optimized to 95.1% on a cleaned glass substrate, which resulted in an average increase of about 3.0% across the broadband range of 400-800 nm. The optimized films widen the spectrum of light absorbed by conventional PSC cells and reduce reflections across a broad range, enhancing the photovoltaic performance of PSCs. As a result, the PCE of the PSC increased from 14.51% for the reference device without a thin film to 15.67% for the PSC device with an optimized thin film. This study presents a comprehensive solution to the problem of Fresnel reflection and spectral response mismatch of the PSCs, which provides new ideas for the light management of PSCs.

The Casimir Force between Two Graphene Sheets: 2D Fresnel Reflection Coefficients, Contributions of Different Polarizations, and the Role of Evanescent Waves

We consider the Casimir pressure between two graphene sheets and contributions to it determined by evanescent and propagating waves with different polarizations. For this purpose, the derivation of the 2-dimensional (2D) Fresnel reflection coefficients on a graphene sheet is presented in terms of the transverse and longitudinal dielectric permittivities of graphene with due account of the spatial dispersion. The explicit expressions for both dielectric permittivities as the functions of the 2D wave vector, frequency, and temperature are written along the real frequency axis in the regions of propagating and evanescent waves and at the pure imaginary Matsubara frequencies using the polarization tensor of graphene. It is shown that in the application region of the Dirac model nearly the total value of the Casimir pressure between two graphene sheets is determined by the electromagnetic field with transverse magnetic (TM) polarization. By using the Lifshitz formula written along the real frequency axis, the contributions of the TM-polarized propagating and evanescent waves into the total pressure are determined. By confronting these results with the analogous results found for plates made of real metals, the way for bringing the Lifshitz theory using the realistic response functions in agreement with measurements of the Casimir force between metallic test bodies is pointed out.

New Difference Schemes for Impedance Boundary Conditions of Wide-Angle Shift-Map PE

New impedance boundary conditions (IBC) difference schemes are proposed for wide-angle shift-map PE. A simple experiment is set up to check the accuracy of the PE. We explain the drawbacks of original boundary conditions (BCs) difference schemes. Some problems are caused by the PEC boundary. We use one-sided difference schemes for the BCs as substitutes. The proposed schemes not only meet the physical property but also perform well in numerical calculation. The numerical experiments are done on PEC and media boundaries to study the characteristic of the new BCs. The reflection calculated by PE are compared with Fresnel reflection. The numerical analysis reveals that the new BCs scheme errors are smaller than those of the original BCs. The new 1st-order PE is accuracy for the slope up to 14° with the reflection angle offset being less than 0.5°, where a horizontally spreading, 0.5° beamwidth levy source illuminates the slope. Under the same condition, the 2nd-order Claerbout PE is accurate when the slope is less than 16° and the 2nd-order Greene PE is accurate when the slope is less than 19°. In addition, the ripples caused by the 2nd-order PE with new BCs is smaller than the original one.

Theoretical Design of Highly Sensitive Ag-Ni-Thiol-based Hybrid SPR Biosensor for Viral Detection

In this work, a biosensor under Kretschmann configuration with enhanced sensitivity utilizing thiol on the bimetallic layers of magnetic material nickel (Ni) over silver (Ag) is proposed and analyzed numerically using the Fresnel equation and the Transfer Matrix Method (TMM). Results have shown that such a hybrid configuration with a well-optimized thickness of a bimetallic layer of Ni over Ag and the proper utilization of thiol with fixed thickness can increase the sensitivity substantially higher than the conventional sensor. The minimum reflectivity, FWHM of the Surface Plasmon Resonance (SPR) curve and sensitivity were examined in order to optimize the thickness of metal layers for the fixed thickness of the thiol. It is observed that sensitivity as high as 321º/RIU is obtained for the configuration consisting of 15 nm of Ni over 40 nm thickness of Ag added with a 4 nm thickness of thiol. Such high-sensitivity sensors can be used for protein-protein interaction and virus detection in the field of biosensing applications.

Does the degree of polarization of vector beams remain unchanged on atmospheric propagation?

All roads lead to Rome. In this article we propose a novel theoretical framework to demonstrate vector beams whose degree of polarization does not change on atmospheric propagation. Inspired by the Fresnel equations, we derive the reflected and refracted field of vector beams propagating through a phase screen by employing the continuity of electromagnetic field. We generalize the conventional split-step beam propagation method by considering the vectorial properties in the vacuum diffraction and the refractive properties of a single phase screen. Based on this vectorial propagation model, we extensively calculate the change of degree of polarization (DOP) of vector beams under different beam parameters and turbulence parameters both in free-space and satellite-mediated links. Our result is that whatever in the free-space or satellite-mediated regime, the change of DOP mainly fluctuates around the order of 10-13 to 10-6, which is almost negligible.

Design and performance investigation of a novel self-adaptive radiative cooling module for thermal regulation in buildings

Daytime radiative cooling utilizes the process of reflecting sunlight and radiating heat through the atmospheric transparent window (8–13 μm) to achieve spontaneous cooling of an object. However, the existing challenge lies in the disparity between the cooling supply and demand, necessitating the development of self-regulating radiative cooling. This study introduces a novel design that combines paraffin wax with a radiative cooler, leading to the development of a self-adaptive radiative cooler (SRC) with two distinct modes based on dynamic optical properties. The spectral properties of the four SRCs were calculated by Fresnel equation, and it was found that the SRC possessed the ability to optimally absorb solar energy (Δα = 0.322) and automatically adjusted their thermal emittance (Δε = 0.552) in response to ambient temperature changes, facilitated by the liquid-solid transition, especially for Case 1. Therefore, the novel SRCs demonstrate a unique behaviour: they are warmer than static radiative coolers (ΔT = 3 K) in cold ambient conditions, while maintaining high cooling power in hot environments. Through extensive simulations for various cities and climates, this study demonstrates the superior energy-saving performance of the SRCs in building thermal regulation compared to that of static radiative coolers (Δδ1 = 9.6%).

All-fiber hollow-core fiber gas cell

We present a hollow-core fiber (HCF) gas cell with light launched and collected via standard solid-glass core single-mode fibers (SMFs). Gas delivery is realized via a 100μm gap between the SMF and HCF with light low-loss coupling optimized for such a gap. Coupling into higher-order modes as well as the Fresnel reflections at the SMF-HCF interface are strongly suppressed to minimize unwanted multi-path interference. The assembled HCF gas cell including the gas inlet is encapsulated in a conventional metallic T-piece for easy gas filling, venting, and sealing. Thanks to its numerous features, such as alignment-free design (once fabricated), above-described promising optical performance, and compactness, we believe it will be of interest for applications in gas sensing and as gas references.

Photosensitivity and optical nonlinearity in arsenic selenide planar waveguides [Invited

We present the first experimental observation of reversible 1550 nm-induced Bragg gratings and stimulated Brillouin scattering (SBS) in a planar waveguide made of high-index chalcogenide material, arsenic triselenide (As2Se3). The temporary grating is inscribed by the two-photon absorption (TPA)-induced refractive index change along the waveguide, facilitated by the high Fresnel reflection from the chip facet. Furthermore, our SBS measurements reveal a Brillouin gain coefficient gB of 7.14 × 10−10 m/W and a frequency shift vB of 7.8 GHz. The Brillouin linewidth ΔvB is measured to be 60 MHz at an input power of 144 mW, which is four times broader compared to As2Se3 fibers. We explain the observed broadening of the linewidth that is attributed to the presence of the photorefractive effect in this platform, which induces a non-uniform refractive index profile along the length of the waveguide. The investigation of photosensitivity and optical nonlinearity in this study holds paramount importance for the realization of reconfigurable nonlinear photonic applications utilizing As2Se3 glasses.

Topological Darkness in Optical Heterostructures: Prediction and Confirmation.

Topological darkness is a new phenomenon that guarantees zero reflection/transmission of light from an optical sample and hence provides topologically nontrivial phase singularities. Here we consider topological darkness in an optical heterostructure that consists of an (unknown) layer placed on a composite substrate and suggest an algorithm that can be used to predict and confirm the presence of topological darkness. The algorithm is based on a combination of optical measurements and the Fresnel equations. We apply this algorithm to ultrathin Pd films fabricated on a Si/SiO2/Cr substrate and extract four different points of topological darkness. Our results will be useful for topological photonics and label-free optical biosensing based on phase interrogation.

Influence of recoil pressure, mushy zone flow resistance and reflectivity on melt pool shape in laser powder bed fusion simulation

Melt pool dimensions (depth: D and width: W) are strongly correlated with defects generated in laser powder bed fusion. The melt pool dimensions have been evaluated by CFD simulation including solid–liquid–gas phase change and laser multiple reflection. Such a multi-physics simulation requires a large number of parameters. Preliminary simulations for parameter identification require a lot of time and effort. The parameter sensitivity to the melt pool dimensions is important; however, the systematic evaluations have hardly been found in the literature. In this study, we performed systematic parametric evaluation for three parameters related to recoil pressure, flow resistance in solid–liquid mushy zone and Fresnel laser reflection. As a result, the D values increased with increasing recoil pressure, but the W values did not. The flow resistance force influenced the velocities in the mushy zone but not the melt pool dimensions. The D increased with increasing reflectivity, but the W did not. The melt pool dimensions varying recoil pressure, flow resistance force and reflectivity were all inconsistent with the experimental melt pool dimensions. In order to agree with the experimental melt pool dimensions, the problems to be solved were discussed by comparing the previous studies.