Brewster Transmission Research Articles

Stray light suppression for Thomson scattering diagnostic on linear magnetized plasma device

In Thomson scattering (TS) diagnostic system, the stray light greatly affects the signal-to-noise ratio (SNR). The suppression issue is particularly severe for the low density and low temperature plasma due to very few scattered photons and narrow line broadening. The traditional methods, such as Brewster window, beam dump and transmission pipe with black-coated internal surface, have been adopted in the stray light suppression system on our Linear Magnetized Plasma (LMP) device. Moreover, an assembly of tapered apertures are placed in the optical path. Via numerical simulation, the optimal configuration of the adjustable aperture tube (size, location, and orientation) that provide the best suppression has been found. Numerical results show that the optimal aperture group with 6 mm and 8 mm tapered apertures can maintain over 97% transmission rate of the main laser energy while reducing stray light by 99.6%.

Generalized Brewster effect using bianisotropic metasurfaces.

We show that a properly designed bianisotropic metasurface placed at the interface between two arbitrary different media, or coating a dielectric medium exposed to the air, provides Brewster (reflectionless) transmission at arbitrary angles for both the TM and TE polarizations. We present a rigorous derivation of the corresponding surface susceptibility tensors based on the generalized sheet transition conditions and demonstrate by full-wave simulations the system with planar microwave metasurfaces designed for polarization-independent and azimuth-independent operations. The proposed bianisotropic metasurfaces provide deeply subwavelength matching solutions for initially mismatched media. The reported generalized Brewster effect represents a fundamental advance in optical technology, where it may both improve the performance of conventional components and enable the development of novel devices.

The complex refractive index of crude oils determined by the combined Brewster–transmission method

The complex refractive index of crude oils is an essential parameter for the study of radiative properties, which has important and wide applications in remote sensing analysis and identification of oil pollution. In this paper, a combined Brewster–transmission method for determining the complex refractive index was proposed. The method has a good performance for both strong and weak absorption liquids. The root-means-square error is less than 0.2% for the refractive index, and 10.0% for the absorption index. Furthermore, the complex refractive index of two crudes was measured by this method and the radiative properties of oil droplets and coated oil droplets were calculated using MIE theory. The research shows that the droplets exhibit significant forward scattering characteristics, and the scattering develops to further forward with size parameter increase. The coating significantly affects the radiative properties of droplets, causing the absorption efficiency to increase, and the scattering efficiency to decrease.

Plasticity or elasticity? Relating elastic moduli with secondary structural features of mixed films of polypeptides at air/fluid and fluid/solid interfaces

Viscoelastic properties of molecular assemblies formed by mixing poly (l-lysine) (PLL) and poly (l-glutamic acid) (PGA) at pH = 7.5 have been studied using Quartz crystal microbalance with dissipation (QCM-D). The inter-molecular complex between PLL and PGA arising from strong electrostatic interaction, leads to local changes in secondary structure resulting in intra-molecular complexes. ATR-FTIR analysis of the Secondary structural features of PLL, suggest an abundance of anti-parallel beta sheet that causes a significant change in the morphology of the self-assembled structures. A combination of spectroscopy, Brewster angle microscopy (BAM), Transmission electron and scanning electron microscopy show that an inverse relationship exists between the elasticity of the different PLL + PGA mixed films and the % anti parallel beta sheet conformation. The elastic moduli for the mixtures change from about 0.913 ± 0.01 GPa for pure PLL to about 0.764 ± 0.01 GPa in the mixture when PGA increases. The localized breaking and reformation of the ion pairs in the complex control their sizes and show an inverse relationship with the elastic moduli. The rheological profiles of the films, elastic moduli, together with their surface morphology from microscopy (TEM) and (SEM) confirmed their increasing propensity to self-assemble in one dimension to form tapes, colloidal particles and their composite assemblies.

Perfect Brewster transmission through ultrathin perforated films

We address the perfect transmission of a plane acoustic wave at oblique incidence on a perforated, sound penetrable or rigid, film in two-dimensions. It is shown that the Brewster incidence θ∗ realizing so-called extraordinary transmission due to matched impedances varies significantly when the thickness e of the film decreases. For thick films, i.e.ke≫1 with k the incident wavenumber, the classical effective medium model provides an accurate prediction of the Brewster angle independent of e (this Brewster angle is denoted θB). However, for thinner films with ke<1, θ∗ becomes dependent of e and it deviates from θB. To properly describe this shift, an interface model is used (Marigo et al., 2017) which accurately reproduces the spectra of ultrathin to relatively thick perforated films. Depending on the contrasts in the material properties of the film and of the surrounding matrix, decreasing the film thickness can produce an increase or a decrease of θ∗; it can also produce the disappearance of a perfect transmission or to the contrary its appearance.

Epsilon-near-zero enhanced plasmonic Brewster transmission through subwavelength tapered metallic gratings

Recently, epsilon-near-zero (ENZ) materials have been employed to stimulate light funnelling enhancement through a subwavelength metallic channel. In this paper, we present a study of enhanced optical transmission through subwavelength metallic gratings deposited on ENZ material and gallium-arsenide (GaAs) substrate. We propose to carve periodically tapered slits on the metallic grating to enable the impedance matching at the entrance and exit faces and thus enhance the light transmission at the plasmonic Brewster angle. The optimal grating geometry provides around 80% average transmission over a broad bandwidth from 5 THz to 20 THz at the incident Brewster angle of 76°. Our study extends potential practical applications of ENZ materials for integrated photonics.

Broadband THz radiation through tapered semiconductor gratings on high-index substrate

We numerically demonstrate an extraordinary optical transmission (EOT) through semiconductor gratings with plasmonic properties on a high-index substrate over a broad terahertz (THz) bandwidth at the plasmonic Brewster channel. The THz EOT is due to impedance matching, an inherently non-resonant mechanism, at the grating entrance and exit faces, which are periodically carved with tapered slits. The optimal grating geometry provides a transmission of over 85% over a broad 0.2–1.0 THz bandwidth at a Brewster angle of incidence of 75°. In addition, we introduce a perfect THz absorber with low-loss and metal-free properties over a broad operating bandwidth based on the plasmonic Brewster transmission concept.

Physics of broadband Brewster transmission through square array of rectangular metallic pillars

The physics behind the broadband Brewster transmission through square arrays made of rectangular metallic pillars is explored by appealing to the effective medium theory. First, an analytical solution is given for the principal electromagnetic mode propagating between the pillars, and then, the mode matching technique is invoked to extract the parameters of the effective medium model. In this fashion, the pillars are homogenized via a diagonal anisotropic tensor and the effects of higher diffracted orders are included in the effective medium theory by attributing a surface conductivity to the surface boundary of the array. It is shown that the former effectuates the wideband Brewster effect while the latter causes the narrowband spoof surface plasmon resonances. The accuracy of the proposed model is verified by full-wave numerical simulations.

Enhanced plasmonic Brewster transmission through metascreens by tapered slits

The recently introduced plasmonic Brewster transmission through free-standing perforated metallic screens (metascreens), which offers ultrabroadband total light transmission has been demonstrated both theoretically and experimentally. This anomalous phenomenon is attributed to impedance matching between the guided modes supported by ultranarrow straight slits and transverse-magnetic impinging waves at a specific oblique incidence. However, this impedance matching mechanism is significantly influenced by the presence of realistic substrates leading to reduce the plasmonic Brewster transmission. To circumvent this substrate influence, the author proposes to carve periodically tapered slits on metascreens to enable the impedance matching at the input and output surface and thus enhance transmission at the Brewster angle. This finding is applied to realize ultrathin perfect absorbers with a broad bandwidth of operation.

Broadband Brewster transmission through 2D metallic gratings

Recently, we have introduced a mechanism to achieve ultrabroadband light funnelling and total transmission through 1D narrow metallic gratings at a specific incidence angle, the so-called plasmonic Brewster angle. This phenomenon is based on impedance matching between the guided modes supported by ultranarrow linear slits and transverse-magnetic waves at oblique incidence. In this paper, we demonstrate that such phenomenon, representing the equivalent of Brewster transmission for plasmonic screens, can also occur in 2D metallic gratings of various structural forms and shapes, and that it may be made insensitive to the azimuthal, or polarization, angle φ. This finding may have relevant implications to realize large funneling, absorption and squeezing of light in perforated metallic screens.

Matching and funneling light at the plasmonic Brewster angle

The ultrabroadband impedance matching of metallic gratings at the plasmonic Brewster angle [A. Al\`u et al., Phys. Rev. Lett. 106, 123902 (2011)] is analyzed here in several realistic scenarios and configurations, and in the case of nonmonochromatic excitation. This phenomenon is the analogy of the well-known Brewster transmission for dielectric slabs but, when applied to plasmonic gratings, has the remarkable property of funneling and concentrating light within subwavelength slits. We analyze here how the presence of absorption and of realistic substrates and/or superstrates may influence the phenomenon, its beamwidth and angular selectivity, and its overall performance in the case of broadband, ultrashort incident pulses in the time domain. We prove that broadband signals may be concentrated and transmitted almost unaffected through narrow apertures, even in the presence of absorption, very different from conventional extraordinary optical transmission based on resonant phenomena.

Tensile strained Ge quantum wells on Si substrate: Post-growth annealing versus low temperature re-growth

Abstract We investigate tensile strained Ge/Si 1 − x Ge x ( x = 0.87) multiple quantum wells (MQW) on a Ge virtual substrate abruptly grown on Si for integration in CMOS technology. Two schemes are discussed – Scheme A in situ growth of the MQW stack combined with post-growth rapid thermal annealing (RTA) and Scheme B re-growth of the MQW stack on an RTA strain optimized Ge-VS. Samples are characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning transmission electron microscopy, Brewster transmission and photo-reflectance spectroscopy. The strain in the as-grown virtual substrate of Scheme A , measured with Raman spectroscopy and XRD, increases from 0.17% to 0.24% after RTA to 850 °C. XRD reveals an activated inter-diffusion of the MQWs and, at the highest temperatures ( T RTA > 750 °C), a structural relaxation. The MQWs of Scheme B appear to be of inferior quality. The inter-band transitions in this material are comparatively blue shifted and broad, which is attributed to relaxation induced dislocations at the interface between the virtual substrate and the multiple quantum wells.

Quantum-confined direct-gap transitions in tensile-strained Ge/SiGe multiple quantum wells

Tensile-strained Ge/Si1−xGex (x = 0.87) multiple quantum wells (MQWs) on a Ge-on-Si virtual substrate are investigated with Brewster transmission and photo-reflectance, to identify quantum-confined direct-gap transitions and their light/heavy-hole splitting. Strain is deduced from optical splitting and x-ray diffraction measurements. As-prepared MQWs have an exciton at ≈ 820 meV, close to the 810 meV edge of the telecommunication C-band. The effect of rapid thermal annealing, to red-shift this feature into the C-band via increased strain, is investigated and interpreted with a tight-binding model. Annealing is observed to red-shift bulk absorption, but MQW transitions experience a net blue-shift due to interdiffusion.

Plasmonic Brewster Angle: Broadband Extraordinary Transmission through Optical Gratings

Extraordinary optical transmission through metallic gratings is a well established effect based on the collective resonance of corrugated screens. Being based on plasmonic resonances, its bandwidth is inherently narrow, in particular, for thick screens and narrow apertures. We introduce here a different mechanism to achieve total transmission through an otherwise opaque screen, based on an ultrabroadband tunneling that can span from dc to the visible range at a given incidence angle. This phenomenon effectively represents the equivalent of Brewster transmission for plasmonic and opaque screens.

The film-forming behavior on the interface between air and hydrosol of Fe2O3 nanoparticles

The film forming behavior on the interface between air and hydrosol of Fe2O3 nanoparticles was investigated by the surface pressure-time isotherms, the surface pressure-trough area isotherms, Brewster angle microscopy and transmission electron microscopy. It is found that the freshly prepared hydrosol of Fe2O3 nanoparticles is not stable. The surface pressure increases with the aging time and finally approaches a constant, and the smaller the concentration is, the smaller the surface pressure is stabilized at and the shorter the time the hydrosol reaching stable needs. The surface pressure also increases with compression until collapsed, and the longer the hydrosol is aged, the higher the collapsing pressure is. A uniform and compact film composed of nanoparticles with an average diameter of about 2–3 nm on the air-hydrosol interface is observed by Brewster angle microscope and transmission electron microscope.

Monolayer aggregation of a series of atypical amphiphilic β-diketone rare earth complexes at air/liquid interface

Monolayer aggregation of a series of atypical amphiphilic rare earth complexes REL 3Phen [RE=Eu(III), Sm(III), Tb(III); L=acac (acetylacetone), TFA (trifluoroacetylacetone), HFA (hexafluoroacetylacetone), TTA (thenoyltrifluoroacetone); Phen=1, 10-phenanthroline] were investigated at the air/liquid interface by π- A isotherms, Brewster angle microscopy (BAM) and transmission electron microscopy (TEM). When the complexes were mixed with arachidic acid (AA), respectively, stable monolayers could be formed. The rare earth complexes could be divided into two classes according to the π- A isotherm shape that whether there was a plateau period or not. Complexes with β-diketones acac, TFA and HFA were in one class, while complexes with the β-diketone TTA were in another. All the rare earth complexes formed microcrystals at the air/liquid interface. However, the former complex microcrystals oriented with the same crystal plane facing to all directions upon compression; while the latter complex microcrystals oriented with the same crystal plane facing to the same direction. Differences between monolayer behaviors of the two classes of complexes were discussed by comparing the structure of β-diketone ligands. A possible structural model of the rare earth complexes in the mixed monolayers with AA at air/liquid interface was proposed.

Mono- and multiparticulate Langmuir-Blodgett films prepared from surfactant-stabilized silver particles

Oleic-acid-stabilized 100 Å diameter silver particles have been spread at air-water interfaces in a Langmuir film balance. Surface pressure vs. surface area isotherms, reflectivity measurements, and Brewster angle and transmission electron microscopy demonstrated that increasing surface pressure resulted in the transition from gaseous and liquid phases of mixed oleic acid silver particle domains to closely packed, well-separated monoparticulate silver domains which ultimately collapsed to multiparticulate layers. Sequential transfer to solid substrates by the Langmuir-Blodgett technique led to the formation of multiparticulate layers of silver clusters.

An intrinsic tensor technique in Minkowski space with applications to boundary value problems

This article describes an intrinsic tensor technique for solving boundary value problems in electrodynamics of moving media, which entails considerable notational simplification and calculational advantages. On the basis of generalized impedance and characteristic matrix methods, the reflection and transmission operators of a multilayer structure consisting of anisotropic media uniformly moving with different velocities are found. A general solution to the problem of reflection and transmission at the interface between two moving isotropic media is obtained, and explicit expressions for Doppler shifts, Snell’s laws, critical and Brewster angles, reflection and transmission coefficients, and the radiation pressure force are found. The material tensor of a uniformly moving linear medium is expressed through its reflection and transmission operators.

Brewster anomaly and transmission of light through one-dimensional random layered system

The transmission of light through a one-dimensional random layered system is considered. The localization length depends on light polarization and goes to infinity approaching the Brewster angle for p-polarized light. The theory is in agreement with the results of Monte-Carlo simulation by Sipe et al. The angle of rotation of the polarization and the ellipticity of the light in a magnetic field are calculated in terms of the density of states and transmission.