Brewster Effect Research Articles

Optical Brewster interfaces enabled object identification and 3D reconstruction

Efficient and accurate object identification and 3D reconstruction are crucial for processing image information in visual imaging. Here, we propose a novel scheme for all-optical 2D contour identification and 3D reconstruction based on optical Brewster interfaces. It is revealed that 2D amplitude and phase contours for high-contrast and low-contrast objects can be identified, which is attributed to the 1D and 2D light fields manipulated by the photonic spin Hall and the Brewster effects. The 3D model can be reconstructed by rotating or slicing the high-contrast objects and by inverting the thickness of the low-contrast objects. The study potentially opens up opportunities in applications such as intelligent driving and microscopic imaging.

Dielectric metamaterials with effective self-duality and full-polarization omnidirectional brewster effect

Conventional dielectric solid materials, both natural and artificial, lack electromagnetic self-duality and thus require additional coatings to achieve impedance matching with free space. Here, we present a class of dielectric metamaterials that are effectively self-dual and vacuum-like, thereby exhibiting full-polarization omnidirectional impedance matching as an unusual Brewster effect extended across all incident angles and polarizations. With both birefringence and reflection eliminated regardless of wavefront and polarization, such anisotropic metamaterials could establish the electromagnetic equivalence with “stretched free space” in transformation optics, as substantiated through full-wave simulations and microwave experiments. Our findings open a practical pathway for realizing unprecedented polarization-independence and omnidirectional impedance-matching characteristics in pure dielectric solids.

Observation of zero-transmission dip in a single-layer electric metamaterial with finite non-radiative loss

We propose a theory for realizing a zero-transmission dip in the transmission spectrum of a reflectionless single-layer metamaterial designed based on the Brewster effect by variably controlling the radiative loss of the metamaterial in response to the non-radiative loss. The radiative loss can be controlled while maintaining broadband zero reflection by varying the relationship between the orientation of the constituent meta-atoms and the incident electromagnetic fields. As a verification of the proposed theory, we design a reflectionless metamaterial by arranging meta-atoms that exhibit a simple electric dipole resonance in a two-dimensional lattice. The numerically calculated and experimentally measured transmission spectra of this metamaterial demonstrate that the radiative loss can be controlled by changing the arrangement of the meta-atoms without altering their structure, and that a zero-transmission dip can be observed for a certain arrangement of the meta-atoms. This study could lead to the development of material sensing, especially for lossy materials based on resonant metamaterials.

Modulation of classical non-separability of vector vortex beams using Brewster effect

The vector vortex beams are generated by the superposition of two orthogonal orbital angular momentum (OAM) beams having orthogonal polarization states using a stable common path technique. The degree of non-separability of the generated vector vortex beams is controlled by changing the input polarization state and Brewster effect using a dielectric prism. We have estimated the linear entropy (SL) of the classical non-separable beams by measuring the reflection coefficients for different input polarization states at each rotation angle of the prism. The shifting of the peak value of SL for different input polarization states at the particular rotation angles of the prism is observed. The usefulness of the proposed scheme is demonstrated in sensing the refractive index variations of the prism.

Method for remote measurement of specific conductivity and moisture of subsurface soil horizons

The aim of the research is to develop a radar method for determining the physical and chemical parameters of subsurface soil horizons, providing rapid determination of moisture and specific conductivity in the area of the plant root system. The proposed method is based on a set of Fresnel equations which describe reflection of electromagnetic waves from the interface between dielectric media in vertical and horizontal polarization of the probing signal. For the practical implementation of the method, it is proposed to use two unmanned aerial vehicles that form a bistatic radar system which irradiates the Earth's surface obliquely in order to create the Brewster's effect and increase the fraction of the radio signal reflected from subsurface horizons. The percentage of moisture and the specific conductivity of soil are calculated from the measured values of the imaginary part of the complex permittivity. The required accuracy of moisture and conductivity measurements is achieved by two-step calibration of the measuring device. The values of the moisture content and specific conductivity of soil obtained by radar at a frequency of 469 MHz are in good agreement with the results of measuring these parameters using the soil moisture meter TDR 150 Spectrum Technologies, Inc.

Shift of Brewster's angle with two-dimensional materials and structures

The Brewster effect has a number of applications in antireflection coatings, spectroscopy, and polarization optics, but its tunability is still of high demand. In this Letter, we discover a method of Brewster angle control with two-dimensional conducting layers. Namely, we analyze the angular shift of Brewster's angle depending on the surface conductivity of a two-dimensional layer. First, we derive the analytical model with exact conductivity-dependent solution. Then, we investigate the Brewster angle shift in the cases of monolayer graphene and plasmonic metasurface. Finally, we support our analytical results by the full-wave numerical simulations. The results obtained may find a plethora of applications in flat optical and planar photonic devices. Published by the American Physical Society 2024

Numerical analysis of the Brewster-electrical duo-effect for multi-resonance tuning in THz absorber

The excitation and tuning of multiple resonances with narrow spectral width based on Brewster's effect is possible in an ultrathin dual-band terahertz absorber. The angular variation establishes a monotonic relation with the frequency of some generated resonances offering tunability. Moreover, burying a graphene ring resonator beneath the metallic ring splits the resonance for providing the triple narrow absorption windows. The electrical modulation offers the feature of independent tunability in the generated third absorption band. Thus, the frequency ratio of the upper to lower spectral absorption peak can be modulated by the electrically tunable Fermi energy of graphene. Engraving the graphene resonator also enhances the incident angle based tunability by affecting a greater number of Brewster generated resonance peaks. The narrow line shape of the triple band absorption can enable refractive index sensing and the detection of extraneous elements in localized analyte samples. The detection of imidacloprid pesticide in wheat flour is performed by the implemented sensor. The numerical analysis is done for the design and analysis of the absorber structures to report the above facts.

Directional Thermal Emission Covering Two Atmospheric Windows

AbstractControlling directional thermal emission to match the ultra‐broadband atmospheric window is a long‐standing scientific challenge. Here, a strategy is introduced for achieving ultra‐broadband directional thermal emission matching the atmospheric window by combining Fabry–Perot resonances and the Brewster effect. The planar system, comprising a thin dielectric film (Ge) on a radiative substrate, exhibits high p‐polarized emissivity (> 0.9) at specific directions (76°–84°) covering the entire atmospheric window (3–5 and 8–14 µm) and high omnidirectional emission (> 0.7) in the non‐atmospheric window (5–8 µm) for simultaneous efficient radiative cooling. Moreover, it can integrate independent dual‐band (visible–IR) information encryption and the infrared information anti‐snooping function. The approach offers unique insights into controlling thermal emission using planar films, with broad implications in camouflage, thermal management, and encryption.

Controlling the polarization dependence of the complex transmission spectrum using the Brewster effect in metafilms.

We propose a method for controlling the polarization dependence of the complex transmission spectrum using the Brewster effect in a two-dimensional array of meta-atoms with finite thickness, which we refer to as a metafilm. We show that the complex transmission spectra of the orthogonal linear polarization components can be controlled independently without reflection by stacking multiple metafilms that exhibit only an electric dipole resonance. As a proof-of-concept numerical demonstration, we design several broadband waveplates with high transmission efficiency based on simple design principles. The proposed method would enable us to easily design anisotropic metamaterials with various complex transmission spectra.

Conversion of THz refractive index variation to detectable voltage change realized by a graphene-based Brewster angle device.

The Brewster effect has been previously reported as an essential mechanism for terahertz (THz) wave sensing application. However, generally in a sensing application, a complex rotation apparatus is required for detecting the slight change in Brewster angle. Here, we propose a graphene-based Brewster angle device operating at a specific terahertz frequency capable of sensing the refractive index at a fixed incident angle. In other words, our sensing device could avoid the impact of Brewster angle shift and eliminate the need for high-precision rotating equipment, which is usually required in traditional sensing applications. The conversion from the refractive index to a Volt-level detectable voltage roots from the tunability of graphene's Fermi level in the external electrical field. A linear correlation between the output voltage and the background refractive index is observed and theocratically analyzed. Furthermore, we present the improvement of our device in terms of sensing range and sensitivity by adjusting the permittivity of the dielectric substrate. As a demonstration of our proposed device, a detection range of 1.1-2.4 and a sensitivity of 20.06 V/RIU for refractive index is achieved on a high-resistance silicon substrate operating at 0.3 THz.

Quadrupolar susceptibility modeling of substrated metasurfaces with application to the generalized Brewster effect.

We derive generalized sheet transition conditions (GSTCs) including dipoles and quadrupoles, using generalized functions (distributions). This derivation verifies that the GSTCs are valid for metasurfaces in non-homogeneous environments, such as for practical metasurfaces fabricated on a substrate. The inclusion of quadrupoles and modeling of spatial dispersion provides additional hyper-susceptibility components which serve as degrees of freedom for wave transformations. We leverage them to demonstrate a generalized Brewster effect with multiple angles of incidence at which reflection is suppressed, along with an "anti-Brewster" effect where transmission is suppressed.

Propagation of Dirac waves through various temporal interfaces, slabs, and crystals

We investigate the influence of the temporal variations of various medium parameters on the propagation of Dirac-type waves in materials where the quasiparticles are described by a generalized version of the pseudospin-1/2 Dirac equation. Our considerations also include the propagation of electromagnetic waves in metamaterials with the Dirac-type dispersion. We focus on the variations of the scalar and vector potentials, mass, Fermi velocity, and tilt velocity describing the Dirac cone tilt. We derive the scattering coefficients associated with the temporal interfaces and slabs analytically and find that the temporal scattering is caused by the changes of the mass, Fermi velocity, and vector potential, but does not arise from the changes of the scalar potential and tilt velocity. We also explore the conditions under which the temporal Brewster effect and total interband transition occur and calculate the change in total wave energy. We examine bilayer Dirac temporal crystals where parameters switch between two different sets of values periodically and prove that these systems do not have momentum gaps. Finally, we assess the potential for observing these temporal scattering effects in experiments.

Antireflection Spatiotemporal Metamaterials

AbstractReflection occurs when light impinges on an interface between two distinct media. Suppression of the reflection is of paramount significance to practical applications in information transfer and conversion. While technologies such as the Brewster effect and material coatings are widely adopted to eliminate the wave reflection from purely spatial or temporal interfaces, how to eliminate the reflection from a spatiotemporal interface remains elusive. Here, a new type of spatiotemporal metamaterial that functions as a global and generalized perspective of quarter‐wave impedance transformers is presented. With the proper geometric design, the proposed spatiotemporal metamaterial can fully suppress the reflection, applicable to arbitrary modulation velocities. Importantly, the tunability of modulation velocity in the spatiotemporal metamaterial allows flexible frequency conversions in high efficiency, indicating that the spatiotemporal metamaterials are much more powerful than the purely spatial or temporal counterparts. These findings not only enhance the controllability of electromagnetic waves but also can be adapted to other classes of physical dynamics, including water surface waves, acoustic, and elastic.

Optical axis-driven tunable Brewster effect in anisotropic materials.

The Brewster effect, which is known as a notable physical law, has promising prospects in perfect absorption and angular selectivity transmission. The Brewster effect in isotropic materials has been investigated extensively in previous works. However, the research on anisotropic materials has been rarely carried out. In this work, we theoretically investigate the Brewster effect in quartz crystals with tilted optical axes. The conditions for the occurrence of the Brewster effect in anisotropic materials are derived. The numerical results show that by changing the orientation of the optical axis, we have effectively regulated the Brewster angle of crystal quartz. The reflection of crystal quartz versus the wavenumber and incidence angle at different tilted angles is studied. In addition, we discuss the effect of the hyperbolic region on the Brewster effect of crystal quartz. The Brewster angle negatively correlates with the tilted angle when the wavenumber is 460c m -1 (Type-II). In contrast, when the wavenumber is 540c m -1 (Type-I), the Brewster angle positively correlates with the tilted angle. Finally, the relationship between the Brewster angle and wavenumber at different tilted angles is investigated. The findings in this work will broaden the research field of crystal quartz and open the door for tunable Brewster devices based on anisotropic materials.

ПОЛЯРИЗАЦИОННЫЕ ЭФФЕКТЫ ПРИ ОТРАЖЕНИИ СВЕТА ОТ ГРАНИЦЫ ОДНООСНОГО КРИСТАЛЛА

In this paper, the boundary conditions for plane electromagnetic waves at the interface between an isotropic medium and a uniaxial crystal have been obtained and analyzed. Elements of the reflection matrix that relates components of the electric field of the reflected wave back to those of the incident electromagnetic wave have been determined. Using the elements of the reflection matrix, we show that the possibility exists for polarization of light to be preserved upon reflection at the interface with anisotropic media. The conditions for the Jones vectors conservation upon reflection from the surface of a uniaxial crystal are obtained. The existence of the Brewster effect at the interface with such an anisotropic medium has been studied and verified. The Brewster’s polarizations have been shown to be almost p-polarizations with just little admixture of s-polarization.

The Implementation and Application Progress of the Generalized Brewster Effect

The Implementation and Application Progress of the Generalized Brewster Effect

Brewster differential microscopy

Imaging of transparent samples such as cells is important in the biomedicine field; however, insignificant absorption and weakly scattering limit the imaging contrast of phase objects. Here, we propose and demonstrate Brewster differential microscopy based on simple optical reflection at the glass interface. The combination of spin–orbit interaction of light and the Brewster effect can perform two-dimensional differentiation to the incident light distribution and, thus, achieves isotropic edge-enhanced imaging of pure phase objects, which overcomes the limitation of traditional one-dimensional imaging. Furthermore, by introducing bias retardation, we also reconstruct the original phase distribution. The proposed microscopic imaging mechanism does not involve any complex modulation devices and takes advantages of simple and low-cost structure. The results indicate that our research shows promising applications for nondestructive imaging of biological cells.

Brewster metasurfaces for ultrabroadband reflectionless absorption at grazing incidence

Previous reflectionless metasurfaces based on balanced electric and magnetic responses in engineered resonant meta-atoms become ineffective at oblique incident angles and usually have strong reflection at grazing incidence, where the impedance becomes near-zero or divergent. Here, by introducing the concept of anomalous generalized Brewster effect to metasurfaces, we demonstrate an exceptional resonance-free Brewster metasurface that exhibits ultrabroadband zero reflection at grazing incidence. The anomalous generalized Brewster effect is obtained via combining the mechanisms of the generalized Brewster effect and the anomalous Brewster effect, which are both resonance-free and thus enable ultrabroadband functionalities. As a practical application, Brewster metasurfaces exhibiting ultrabroadband reflectionless perfect absorption at grazing incident angles are constructed and demonstrated by full-wave simulations and microwave experiments. Our work could enable reflectionless wave manipulation at grazing incidence with an ultrawide working bandwidth.

Broadband Control of Group Delay Using the Brewster Effect in Metafilms

We propose and verify a method for controlling the frequency dependence of the group delay of electromagnetic waves over a broad frequency range using the Brewster effect in single-layer metamaterials with finite thickness, here referred to as metafilms. When the metafilm's reflectance vanishes regardless of the incident frequency, the group delay can be large near its resonance frequency while maintaining the transmittance close to unity regardless of the incident frequency. Furthermore, when several reflectionless metafilms are stacked together, the total group delay should be given as the sum of the individual group delays. In this study, we realize reflectionless metafilms by arranging the meta-atoms so that the Brewster effect occurs regardless of the incident frequency. We evaluate in numerical simulations and experiments the frequency dependence of the transmittance and of the group delay of a three-layer metamaterial composed of reflectionless metafilms with different resonance frequencies, and find that the total transmittance and group delay of this metamaterial agree respectively with the product of the transmittances and the sum of the group delays of the constituent metafilms.

Optical interface engineering with on-demand magnetic surface conductivities

Optical interfaces with arbitrary magnetic and electric surface conductivities can enable the design of photonic devices with new functionalities, but practical approaches to date are nonexistent. Regular interfaces, such as those with graphene, are optically interesting due to their tailorable electric surface conductivity. However, their magnetic surface conductivity is negligible since the magnetic response in natural materials is generally weak from the terahertz frequency onward. The quest for artificial magnetic response has recently triggered the development of magnetic metasurfaces that, however, can only provide the interface with a limited value of magnetic surface conductivity. Herein we find that vertical heterostructures based on regular nonmagnetic metasurfaces have a direct correspondence to an optical interface with both magnetic and electric surface conductivities, whose desired values can be structurally engineered. Moreover, we identify several unique photonic and plasmonic responses at optical interfaces with specific magnetic surface conductivities, including a polarization-insensitive Brewster effect and pure magnetic surface waves.