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A graded buffer Bragg reflector (GBBR) is a bifunctional device component that provides the reflection of a distributed Bragg reflector and the adjustable lattice constant of a compositionally graded buffer. Prior work showed that these properties can be combined with low threading dislocation density and high reflectivity. Here, we design and demonstrate complex GBBRs for specific metamorphic solar cell applications. We design buffers that provide (1) high reflectivity over a narrow bandwidth, for quantum well solar cells, (2) reflectivity over a wide bandwidth, for optically thin solar cells, and (3) low sidelobe reflection, for multijunction devices that demand low out-of-band reflection. Apodized and triple GBBRs are demonstrated, and transparency is always considered, requiring designs with carefully engineered material combinations. A GBBR with a reflection of 99% is demonstrated, as well as a triple GBBR that has over 80% reflection for 100 nm of the spectrum around 800 nm. We also analyze potential deviations in a baseline GBBR from that of a perfect DBR using transmission electron microscopy to analyze imperfections in the material and modeling to analyze the impact of imperfect refractive index data for lattice-mismatched AlGaInAs. Minimal crosshatch roughness and unintentional thickness variation occur throughout the buffer, which likely influences reflection slightly. Small deviations between the calculated AlGaInAs and utilized AlGaAs refractive index exist, giving methods for future GBBR improvement. While the GBBR designs are intended for metamorphic solar cells, the broad and high reflection may also be useful for other optoelectronic devices such as light-emitting diodes or lasers. [ABSTRACT FROM AUTHOR]

A metal–insulator-metal (MIM) structure consisting of a semi-circular resonant cavity (SCRC) and a circular split-ring resonator (SRR) is proposed and designed for optical sensing applications. The coupling between the SCRC and SRR can create dual Fano resonances in the visible range. The optical responses of the structure including transmittance spectra and magnetic field distributions are investigated using finite-difference time-domain (FDTD) method. According to the calculated transmittance spectra, the proposed optical sensor can support double Fano resonances as a result of the interaction between the narrow-band mode of SRR and broadband mode of SCRC. The light-matter interaction at the Fano resonance frequencies is highly enhanced so that a maximum sensitivity and figures of merit (FOM) of 579 nm/RIU and 12.46 are obtained, respectively. Our proposed design also exhibits a great linearity R2 value of 0.999987. For the sake of completeness, it is shown that the structure can result in an optical delay of about 0.05 ps corresponding to a group index of 14.6 that is potentially useful for plasmonic nanosensors and slow-light devices in the visible range of the spectrum. [ABSTRACT FROM AUTHOR]

This paper will focus on studying the effects of external electric field, hydrostatic pressure, impurity position, as well as the geometrical size on the electromagnetically induced transparency of a spherical Gaussian quantum dot. To this end, we discuss absorption coefficient, refractive index, and the group velocity of the probe light pulse under the influence of the above-mentioned agents. Our results reveal that the electromagnetically induced transparency occurs in the system and the geometrical size of the spherical Gaussian quantum dot system, confinement potential, hydrostatic pressure, and impurity position impact strongly on its frequency, transparency window, and group velocity of the probe field. Obtained results indicate that compared to the atomic system, one can control electromagnetically induced transparency and the group velocity of light through the confinement potential, external agents, and geometrical size of the dot. [ABSTRACT FROM AUTHOR]

Emerging tactile sensing devices mimic biological functions of human mechanoreception. By introducing the feature of optical transparency, it can lead to a combined capacities of tactile and visual intelligence into single system. Yet, it is difficult to realize ultrahigh level of optical transparency and device sensitivity in single structure, for the widely used methods for sensitivity improvement, such as elevating the interfacial roughness, may further reduce the transparency. By utilizing a transparent ionic material with tunable surface topologies, as well as introducing a strategy of refractive index matching, we have proposed a transparent iontronic sensing (TIS) device based on the iontronic sensing mechanism, simultaneously offering combined high device sensitivity (83.9 kPa−1), with ultrahigh optical transparency (96.9%), the highest reported value in literature. Benefiting from its comprehensive performance in sensing and optical characteristics, the TIS devices hold enormous potential for the human-machine interfaces for industrial and medical applications. [ABSTRACT FROM AUTHOR]

Here we report a transparent dual‐phase ZnO·2.7Al2O3 ceramic. The composite is pore‐free and consists of thin nanosheets with a spinel phase and a hexagonal phase, while the two phases match closely in both lattice and refractive index. Such features result in excellent optical transmittance (maximum value >80% in the visible spectrum) at comparable phase volume. This work may provide a new thought for the rational structural design of optical nanocomposites. [ABSTRACT FROM AUTHOR]

Here, a novel plasmon-induced transparency (PIT) sensing platform based on a Kretschmann–Raether configuration with graphene/J-aggregate materials is proposed. The J-aggregate material, despite its dielectric optical properties, can strongly confine the surface wave-like metal layers. These features promise to highly enlarge the range of plasmonic sensing devices. Therefore, the sensing parameters have been numerically and experimentally investigated using the finite-difference time-domain (FDTD) method and atomic force microscopy (AFM). The results show that the PIT resonance of the structure has a sharp reflection, in turn, leads to high sensitivity. To deep benchmark the structure, the effects of the structural parameters and environmental variables such as temperature and magnetic field on the sensing properties of the device are analyzed in detail. The maximum sensitivity is obtained as high as 1400 angle per refractive-index unit (RIU) with an extra high figure of merit of 36 RIU−1 around the PIT resonance angle of 53°. By considering the magnetic field of 0.01 T and graphene chemical potential of μ = 0.4 eV and environmental room temperature, the proposed structure may potentially be applied in advanced off-chip PIT sensors. [ABSTRACT FROM AUTHOR]

Based on Dirac semimetal metamaterials, the tunable plasmon induced transparency (PIT) is investigated elaborately in this work. The designed unit cell consists of a strip and a square bracket, which is periodically aligned on the dielectric substrate. Our numerical results illustrate that a pronounced transparency window exists due to near field coupling between two bright modes, which can be dynamically tuned with Fermi energy. Namely, the transparency window demonstrates a distinct blue shift with a larger Fermi energy. Moreover, an on-to-off switch of the PIT transparency window is realized with different polarization angles. In addition, the accompanied slow light property is examined with the calculation of phase and group delay. Finally, a small variation of the refractive index of the substrate can induce a clear movement of the PIT transparency window which delivers a guidance in the application of optical sensing. Thus, this work provides us a new strategy to design compact and adjustable PIT devices and has potential applications in highly tunable optical switchers, sensors, and slow light devices. [ABSTRACT FROM AUTHOR]

The development of new materials for obtaining ophthalmic lenses is a subject of great interest due to the great necessity of corrective lenses uses. The application of the lenses based on polymeric material that guarantees greater lightness and less risk of breakage, ensuring greater comfort to users of glasses. The use of nanoparticles in polymer nanocomposites can generate different properties in the final material, mainly when used in hybrid systems in which synergistic effects can be produced. Thus, the present work aimed to evaluate the optical properties of systems with poly(methyl methacrylate) and oxide nanoparticles (silica, zinc, zirconium, and titanium). The systems were characterized in terms of their optical behaviors (refractive index, transmittance, and color change) and mechanical behaviors (nanoindentation, and tensile strength). The results showed that silica-based systems tended to have greater transparency but generate lower refractive indexes. Systems containing zirconia, titanium, and zinc have a higher refractive index and smaller transparency than systems containing silica. Besides, the use of zirconia and titanium increases the nano-hardness and elastic modulus. The results showed that the use of these nanoparticles in binary systems leads to obtaining materials with higher refractive index, greater transparency, and best mechanical behavior. The combination of the nanoparticles also led to a better dispersion, reducing the impact on the color system and improve transparency. In this way, the materials developed using small amounts of fillers and present highly promising for the development of thinner, more resistant to scratching due to high hardness and higher transparent lenses. [ABSTRACT FROM AUTHOR]

We report a novel type of electromagnetically induced transparency (EIT) analogue based on metamaterials (MMs) with hybrid structures, in which spiral and cut-wire structures serve as bright-mode resonators with the spoof electric localized surface plasmons and electric dipole resonance. With the simulations and experiments, the EIT analogue generated by the frequency detuning and hybridization between the resonators is verified. The simulated surface charge density and electric and magnetic field distributions, together with the theoretical analysis based on the Lorentz oscillator model, reveal the principle of the EIT analogue. Moreover, the transmission window of the MM demonstrates linear dependence on the refractive index’s change of surrounding media, showing the potential as a tool for environmental detection. [ABSTRACT FROM AUTHOR]

Novel materials, with enhanced light–matter interaction capabilities, play an essential role in achieving the lofty goals of nonlinear optics. Recently, epsilon‐near‐zero (ENZ) media have emerged as a promising candidate to enable the enhancement of several nonlinear processes including refractive index modulation and harmonic generation. Here, the optical nonlinearity of ENZ media is analyzed to clarify the commonalities with other nonlinear media and its unique properties. Transparent conducting oxides as the family of ENZ media with near‐zero permittivity in the near‐infrared (telecom) band are focused on. The instantaneous and delayed nonlinearities are investigated. By identifying their common origin from the band nonparabolicity, it is shown that their relative strength is entirely determined by a ratio of the energy and momentum relaxation (or dephasing) times. Using this framework, ENZ materials are compared against the many promising nonlinear media that are investigated in literature and show that while ENZ materials do not radically outpace the strength of traditional materials in either the fast or slow nonlinearity, they pack key advantages such as an ideal response time, intrinsic slow light enhancement, and broadband nature in a compact platform making them a valuable tool for ultrafast photonics applications for decades to come. [ABSTRACT FROM AUTHOR]

Multiple strong impacts of anion doping Λ (Λ = oxygen vacancy, nitrogen, or hydrogen) on the optical properties in the near-infrared to vacuum ultraviolet spectral range are experimentally revealed in cube-on-cube-type epitaxial perovskite BaTiO3−δΛδ films (δ ≤ 0.01) grown on (001)SrTiO3 substrates. Compared to the reference undoped films and bulk crystal, the anion-doped films exhibit massive changes of the index of refraction in the transparency range Δn of ∼0.1 to 0.2, a profound bandgap widening ΔEg of ∼0.3 eV to 0.4 eV, a dopant-specific near-edge absorption, and doping-induced interband transitions. Both the conduction-band uplift and the changes in the index of refraction are ascribed to the internal stress and electric field, which result from epitaxially controlled dopant locations in the [Ba–O](001) planes. The dopant-induced in-gap states are responsible for the near-edge absorption, whereas the dopant-induced conduction-band states are suggested to modify the interband transitions and the intrinsic elasto- and electro-optic coefficients. [ABSTRACT FROM AUTHOR]

A new technique to measure the refractive index of shocked materials is reported. The arrival of a transparent shock at the free surface of an optical window generates a discontinuity in the observed interferometry record. In this work, we show that the magnitude of that discontinuity is simply defined by the shock velocity, the shocked refractive, and the free-surface velocity. This new technique, to measure the high-pressure refractive index of a transparent material, is demonstrated. [ABSTRACT FROM AUTHOR]

In this work, we report numerical research concerning a planar electromagnetically induced transparency (EIT) terahertz metamaterial capable of exhibiting refractive index sensing with high sensitivity. The unit cell of the proposed EIT metamaterial is consisted by metal cut wires with staggered H-shaped arrangement, and can display a sharply narrow transmission transparency peak at 2.653 THz with high quality-factor (Q-factor) valued 48.3. Through analysis of the extracted surface current distributions on metallic structures, it is confirmed that the EIT-like resonance results from the destructive interference of the electric quadrupole excited by the strong radiation of electric dipole. Furthermore, the EIT-like effect shows highly sensitive response to the refractive index of the covered layer. When it covered by 3 μ m -thickness analyte layer, the EIT metamaterial can yield a sensitivity of 0.2695 THz/refractive index unit (RIU) and a figure of merit (FOM) of 5.39. Meanwhile, it is also found that the sensitivity S is inversely proportional to the dielectric constant of the substrate material, and effective sensing capability maintains when the coverage thickness within 15 μ m. The proposed EIT metamaterial design provides great potential application for refractive index sensing performance. [ABSTRACT FROM AUTHOR]

A bright–bright coupling mode Plasmon-induced transparency (PIT) system composedof two Dirac semimetal blocks (DSBs) with different sizes is proposed in this paper. The electromagnetic mechanism of this PIT system and its modulation property at mid-infrared band is analyzed by finite-difference time-domain (FDTD) method. Numerical results show that the transparent window, transparent peak and quality factor can be precisely controlled by the geometric parameters of the PIT system, the Fermi energy (E F) of the DSB and refractive index (RI) of the superstrate. The advantage of DSBs grating structure is that its permitivity functions can be adjusted handily by E F through doping or bias voltage. Compared to the PIT system based on bulk Dirac semimetals, our proposed PIT system has much smaller structure size and wider tunability. The resonant frequency of the transparent peak can shift from 17.59 THz to 34.79 THz when E F changing from 40 meV to 80 meV. The second-order nonlinearity of this DSBs system is also investigated by introducing the second-order nonlinear source. This developed Dirac semimetal PIT structure may pave the way to the development of novel THz active devices for light modulation devices, switches, biosensors and other mid-infrared devices. [ABSTRACT FROM AUTHOR]

Electromagnetically induced transparency like effect, which can form a sharp transmission window within a broad spectrum, has been widely studied due to its potential in many optical devices. In this work, unlike traditional couple-ring resonator structure, we propose a new scheme to achieve electromagnetically induced transparency using only one hole-ring resonator. Thus, the proposed scheme can greatly miniaturize the device. At the wavelength of about 1550 nm, the structure can form multiple transparency windows and can behave as a refractive index sensor with high resolution, the figure of merit can reach larger than 530. The proposed scheme can pave the way for many practical applications such as optical sensors, optical switches and slow light devices. [ABSTRACT FROM AUTHOR]

Highlights • Electromagnetically induced transparency is studied in a GaAs/InAs/GaAs parabolic quantum well in the presence of magnetic field strength. • The three atomic sub-levels are considered and the system is considered using a density matrix approach. • Magnetic field related optical susceptibilities, Rabi frequency and the detuning parameters are computed in the present work. • Magnetic field induced refractive index and the group velocity of the probe light pulse are investigated. • The variation of group index as a function of probe field energy, with the application of magnetic field, is reported. [ABSTRACT FROM AUTHOR]

An indispensable process of geotechnical modeling with transparent soils involves capturing and analyzing images, in which favorable transparency is required for optical measurements. This paper proposes an objective framework for quantification of transparency in transparent soil based on its transmittance. Specifically, transparent soil with fused quartz serves as the soil sample for the detection of transmittance, and transmittance’s impact on imaging quality in geotechnical modeling with transparent soil is investigated through an evaluation function of image clarity. According to the results of research about transparent soil with fused quartz, viewing depth and refractive index matching are the dominant factors that affect variations in transmittance of transparent soil, and the variations of transmittance are subjected to exponential decay regarding viewing depth or refractive index matching based on the theoretical modeling’s function of curve fitting. Moreover, experimental results indicate that imaging quality of geotechnical modeling with transparent soil is enhanced with increasing transmittance, and imaging quality shows a remarkable improvement when transmittance is greater than 90%. [ABSTRACT FROM AUTHOR]

A nanoscale structure which comprises metal-insulator-metal (MIM) waveguide, stub resonator, and hexagonal resonator is proposed to realize plasmon-induced transparency (PIT) response. The characteristics of the device are numerically investigated with different geometrical parameters. Benefitting from the narrow transparency window and long coupling length between two resonators, the proposed devices are able to act as a nanosensor for refractive index (RI) sensing with figure-of-merit (FOM) of 178 and 140 RIU near RI of 1 and 1.33, respectively. Furthermore, the FOM can be further improved by employing symmetric structure. [ABSTRACT FROM AUTHOR]

Electromagnetic-induced transparency (EIT) is a transparent window phenomenon with high transmittance in atomic systems, which has a broad application in the sensing field. We propose a compact graphene metamaterial sensor and analyze its mechanism of EIT-like effect. The unit cell is composed of an octagonal star graphene ring and a rectangular graphene ring and excites EIT-like effect through the strong coupling of the light mode and the dark mode. The compact graphene structure design improves the area utilization rate and contributes to the miniaturization of devices, and the EIT window is actively tunable by the change of the Fermi level of graphene to improve the applicable range of the sensor. The numerical simulation demonstrates that the refractive index sensitivity can reach 2.828 THz/RIU, meaning that the transmission curves of the sensor shift 2.828 THz per unit change of refractive index of the surrounding medium and its figure of merit can reach 5.34. The proposed structure can be applied to the high-sensitivity refractive index sensing in the terahertz band and has great application potential in the biological and chemical sensing field. [ABSTRACT FROM AUTHOR]

ABSTRACT Trisilanolphenyl-polyhedral oligosilsesquioxane (trisilanolphenyl-POSS) structure is introduced into a polysiloxane network in an attempt to produce thermally stable material with improved transparency. A series of organic-inorganic resins comprised of diphenylsilanediol, 3-methacryloxypropyl trimethoxysilane, and varying content of trisilanolphenyl-POSS were copolymerized through condensation followed by curing using phenyltris(hydrogendimethylsiloxy)silane as curing agent. Fourier transform infrared spectroscopy (FTIR), proton-nuclear magnetic resonance spectroscopy (1H-NMR), and silicon-nuclear magnetic resonance spectroscopy (29Si-NMR) were used to confirm the synthesized product. Excellent thermal stability, improved glass transition temperature ( Tg), and lower coefficient of thermal expansion with the increasing POSS content were observed from thermomechanical analysis. Its extreme thermal degradation stability was attributable to the crosslinked network as well as the heavily substituted aromatic ring present in the system. Steric hindrance effect is noticeable beyond 5.66 mol % trisilanolphenyl-POSS content. Incorporation of POSS substituent in methacrylate-based polysiloxane give excellent transparency and improved thermal discoloration resistance as deduced from UV/vis Spectrophotometer, making it a potential material to be used in optoelectronics. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45285. [ABSTRACT FROM AUTHOR]

As an important optical constant of optical properties for spectacle lens, the refractive index measurement is studied using V prism refractometer. In the experiment, according to various factors inducing measurement error, the experimental results are analyzed, which include right angle deviation, contact liquid, curvature, and focusing accuracy. The study results show that focusing accuracy is the most important factor of influence for measurement, consists of contact liquid wettability, sample shape, and effective width of light transmission. In addition, the refractive index measurement is less affected by angle deviation of sample and the refractive index deviation of contact liquid. On the basis of the experimental data analysis, it is possible to relax the deviation of right angle of the sample to 1' or 2'. [ABSTRACT FROM AUTHOR]

In this paper, the effect of impurities on the phenomenon of electromagnetically induced transparency in a spherical quantum dot with parabolic potential is examined. It is assumed that spherical quantum dot has configuration four levels model M. First, consider the polarization Z for light; rotating wave approximation approach, rotating coordinate system, as well as the density matrix approach, we examine the phenomenon of electromagnetically induced transparency in spherical quantum dot. Finally, with regard to impurities of the disorder, we review electromagnetically induced transparency and Changes resulting from the presence of impurities. [ABSTRACT FROM AUTHOR]

• A self-supporting photonic composite film with response behavior is fabricated. • Quasi-amorphous PSN arrays are rationally integrated into the polymeric matrix. • Copolymer composite phase ensures the stability in practical applications. • Optical path control is guided by solvent-induced and thermal stimulation. • Self-encryption and decryption are designed based on stimulus parameter control. Artificial photonic composites can exhibit the structural colors of embedded colloidal arrays and the functionality of polymeric matrix, making them suitable for emerging applications, such as display, sensing, and information security. However, their ability to integrate flexibility, color visibility and stimulus-responsive macroscopic change has not been adequately harnessed. In this study, a self-supporting photonic composite film is constructed by incorporating isotropically arranged polysulfide nanoparticles (PSNs) into polyethylene glycol diacrylate and butyl acrylate copolymers. The inherent light-absorbing properties and high refractive index of PSNs impart the photonic composites with high structural color visibility. Furthermore, the flexible copolymer network enables sustainable optical capability of photonic pattern during deformation. Due to its unique hydrophobic and hydrophilic structures, tunable optical path control can be achieved through solvent-induced microphase separation and inverse transparency changes under thermal stimulation, resulting in self-encryption and decryption. The function of switching desired stimuli into visualized optical signals allows flexible photonic composites to present great prospects in smart materials for dynamic memory devices. [ABSTRACT FROM AUTHOR]

A Terahertz (THz) plasmonic frequency selection metasurface based on Na-GaAs complementary symmetrical split-ring (PFSM-NCSS) is demonstrated for bulk refractive index (RI) sensing. The sensing performances of the PFSM-NCSS is studied by finite element method (FEM). The results show that the PFSM-NCSS has reflection peaks at 9.25 and 4.4 THz for the TM and TE incident lights, respectively. The parameter optimizations indicate that the reflection peak moves towards lower frequency when P decreases or r increases, and shifts to higher frequency when w 1 or w 2 increases. The PFSM-NCSS with two loaded dielectrics has minimum relative frequency offset with various θ , which means it has good angular stability. The sensing structure based on the PFSM-NCSS has RI sensitivities of −969.8 and −651.1 GHz/RIU for the TM and TE incident lights, meanwhile DLs of 9.8 × 10−4 and 3.2 × 10−4RIU can be achieved. The PFSM-NCSS provides a feasible THz RI sensing scheme for the cost-effective, real-time biosensors and immunosensors, along with strong light–matter​ interaction, good electromagnetically induced transparency characteristics, and compatibility with the CMOS technology. [ABSTRACT FROM AUTHOR]

We designed all-dielectric π -shaped Si metamaterials and numerically demonstrated their electromagnetically induced transparency (EIT) behavior. Each unit of the metamaterial comprises one horizontal Si nanobar and two vertical Si nanobars with feed-nanogaps between them. A narrow EIT peak with a transmittance of 99% and a Q-factor of 2436 is observed due to the destructive interference between the horizontal bright and vertical dark mode resonators. The EIT can be tunable by changing the nanogap width, and the narrowest EIT window with the largest Q-factor is obtained as the nanogap width is 20 nm. Strong electric field enhancement exceeding 104 in magnitude is also realized inside the 20-nm nanogap. Theoretical fittings according to the coupled Lorentz oscillator model exhibit a well consistency with the simulation spectra, validating the accuracy of the numerical simulation. The designed metamaterial is sensitive to the surround refractive index change with a figure-of-merit of 460, which far exceeds Fano-resonant plasmonic metal sensors. The designed Si metamaterial with a sharp EIT response and a strong electric field enhancement is an ideal platform for applications in optical sensing, low-loss slow-light devices, fluorescence enhancement, and nonlinear optics. • EIT in a planar all-dielectric π -shaped Si metamaterial with two feed-nanogaps in a unit cell is numerically demonstrated. • A characteristic EIT peak with a high Q-factor of 2436 and a transmittance of 99% is obtained. • Electric field enhancement exceeding 104 is realized inside the 20-nm feed-gaps of the designed metamaterial. • The metamaterial can be applied in optical sensing, slow optical devices, fluorescence enhancement and nonlinear optics. [ABSTRACT FROM AUTHOR]

We present a new dual-wavelength quantitative measurement approach that can be employed for simultaneously measuring both the refractive index and the thickness of the homogenous specimen. This method is realized by dual-wavelength in-line phase-shifting digital holography, and then the phase images are obtained by using four-phase step algorithm for each wavelength separately. Based on computer simulation technology, the feasibility and the effectiveness of our proposed method are demonstrated by comparing our simulation results with the experimental results of the spherical silica bead and the red blood cell, respectively. Our work will provide some guidance in the experimental research for transparent phase objects. [ABSTRACT FROM AUTHOR]

There is an increasing demand for glass materials with better mechanical and optical properties for display and electronic applications. This paper describes the deposition of novel thin films of Mg Si O N onto float glass substrates. Amorphous thin films in the Mg Si O N system with high nitrogen and magnesium contents were deposited by reactive RF magnetron co-sputtering from Mg and Si targets in Ar/N 2 /O 2 gas mixtures. The thin films studied span an unprecedented range of compositions up to 45 at% Mg and 80 at% N out of cations and anions respectively. Thin films in the Mg Si O N system were found to be homogeneous and transparent in the visible region. Mechanical properties like hardness (H) and reduced elastic modulus (E r ) show high values, up to 21 GPa and 166 GPa respectively. The refractive index (1.87–2.00) increases with increasing magnesium and nitrogen contents. [ABSTRACT FROM AUTHOR]

To realize high-performance thermoplastic camera lenses for compensating chromatic aberration in which lenses with large and small Abbe numbers were combined, novel poly(phenylene thioether)s with a fluorene-based cardo structure were developed with the potential for simultaneously realizing high transparency, a high refractive index, low birefringence, and small Abbe number. Excellent transmittance was observed in all polymer films because the interchain packing was effectively suppressed by the cardo structure (e.g., transmittance was as high as 90% at 400 nm), and furthermore, high refractive index values (1.6553-1.6762) were attained. The polymer with the highest content of cardo structure exhibited a low birefringence of 0.0014. The efficient cancellation of polarization anisotropy between the polymer backbone and the fluorene units directed perpendicular to the polymer backbone contributed to the low birefringence. These results indicate that promising materials for high-performance optical applications can be developed based on the well-suited incorporation of the cardo structure into the polymer backbone. [ABSTRACT FROM AUTHOR]

An optically transparent woven glass fiber-reinforced polyester composite has been fabricated. This composite has been used as an interlayer in the fabrication of a laminated glass-composite window panel for application in blast-resistant windows. The transparency of the glass fiber-reinforced composite was achieved by matching the refractive index of the polyester matrix with that of glass fibers. Various chemical additives have been investigated for their effectiveness in modifying the refractive index of the polyester matrix. The composite interlayer's mechanical properties under both quasi-static and dynamic loading conditions have been characterized in this study. The window panels were tested under various blast loading conditions. The panels perform well under U.S. General Services Administration (GSA) specified C, D, and E blast loading levels. [ABSTRACT FROM AUTHOR]

Hyperbranched polyvinylsulfides have been prepared through a facile, metal-free, radical induced 'A2+B3' thiol-yne polymerization of 1,3,5-tris(naphthalylethynyl) benzene and 1,4-dithiolbenzene with three different input ratios. The resulting polymers exhibit excellent optical properties like high transparency and very high refractive index (RI) of up to 1.7839, combined with high thermal stability ( Td5% up to 420 °C) and excellent solution processability. These properties make them ideal candidates as high RI polymeric materials (HRIP) in connection with light out-coupling schemes for organic light-emitting diodes (OLEDs). A series of hyperbranched HRIPs with varying monomer compositions have been compared in their optical properties. Finally, phosphorescent monochrome OLEDs are fabricated on top of HRIP layers to test the compatibility of HRIPs with state-of-the-art OLEDs. The results show that the HRIPs do not deteriorate the performance of the OLEDs while maintaining external quantum efficiencies of over 20% for phosphorescent red OLEDs. These results open a pathway toward alternative, low-cost, and scalable out-coupling concepts through refractive index matching of the OLED materials and the HRIPs presented. [ABSTRACT FROM AUTHOR]

A polarization-independent terahertz metamaterial based on hybrid graphene-gold structure with excellent refractive index sensing characteristics is proposed. The proposed structure exhibits a sharply narrow plasmon-induced transparency peak in the transmission spectrum at the terahertz regime. Obvious frequency shift in the transparency peak can be observed by varying the surrounding medium’s refractive index or the Fermi level in graphene, which can be well applied in bio-sensing technology. Moreover, an electrical RLC circuit model is used to provide a reasonable explanation for the optical response process in the proposed structure. Our work can offer reference value for the application of graphene technology as well as new idea for designing novel biosensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • We investigated the magnetic and optical properties of the WSe2/VSe 2 heterostructure. • The Curie temperature was substantially enhanced to 380 K in the heterostructure. • The refractive index in was greatly increased to 2.85. • We obtained the transmission coefficient larger than 0.7 in the heterostructure. An optically transparent low dimensional magnetic system has rarely been found in nature. Particularly, it is a real challenging issue to find an optically transparent two-dimensional magnetic material operating at room temperature with a high refractive index. Thus, we explored the magnetic and optical properties of the 1T-VSe 2 monolayer and WSe 2 /VSe 2 heterostructure. Both VSe 2 monolayer and WSe 2 /VSe 2 heterostructure showed ferromagnetic state ground state. The Curie temperature of the 1T-VSe 2 monolayer was 250 K, and this was substantially enhanced to 380 K due to the increased exchange parameter in the heterostructure. We also found that the WSe 2 /VSe 2 heterostructure displayed a refractive index of 2.85. Moreover, the optical transparency of the heterostructure reached more than 75 % in the visible range. The high refractive index and optical transparency of the heterostructure are comparable to those of bulk type TiO 2. Overall, we find that the WSe 2 /VSe 2 heterostructure can be used for potential device applications as an optically transparent magnetic system at room temperature. [ABSTRACT FROM AUTHOR]

In this study, novel thermally stable zirconia-containing polyimides (PI/ZrO2) with excellent optical properties have been prepared successfully. The obtained flexible PI/ZrO2 hybrid films revealed excellent optical transparency, a tunable refractive index and an Abbe number up to 1.804 and 32.18, respectively, which are crucial for optical devices. In addition, the PI/ZrO2 hybrid films also exhibit a higher Abbe number and transparency in the visible light region due to a larger energy band gap of ZrO2 than the corresponding PI/TiO2 system. [ABSTRACT FROM AUTHOR]

A relation of the effective refractive index $n* = \sqrt {n_1 n_2 } $ of a two-dimensional polycrystalline dielectric film in the transparency region to the refractive indices n and n of crystallites at the positions of axes 1 and 2, respectively, of refraction ellipsoids of the crystallites in the plane of the film has been obtained. This relation and the relation L* = ( L + L)/2 between the components of the Lorentz tensors for the film and crystallites have been confirmed by comparison with experimental data for conjugate-polymer films with uniaxial domains. [ABSTRACT FROM AUTHOR]

We proposed and numerically demonstrated an analog of electromagnetically induced transparency (EIT) in a Chinese character 王-shaped all-dielectric metasurface in the near-infrared region. Through asymmetric adjustment, the high transmittance EIT-like optical response of both single and double transparency windows can be realized. The EIT-like optical responses are clearly interpreted by the destructive interference between the bright dipolar moment and trapped magnetic dipolar mode through the asymmetric metasurface, and the dark dipolar moment causes the transparency window to split into two peaks. This all-dielectric structure shows a good application prospect in the field of refractive index sensors and slow-light transmission. [ABSTRACT FROM AUTHOR]

This paper presents time resolved quantitative evaluation of elastic stress waves in solid media by utilising an adaptation of the well-established laser Doppler vibrometry method. We show that the introduction of elastic stress waves in a transparent medium gives rise to detectable and quantifiable changes in the refractive index, which is proportional to stress. The method is tested for mechanical excitation at frequencies from 10 to 25 kHz in an acrylic bar. This refractometric quantification can measure internal strains as low as 1 X 10-11. Additionally, finite element analysis is conducted to gauge the validity of the results. In the presented work an acrylic bar is used, this method however should be applicable to any transparent solid. [ABSTRACT FROM AUTHOR]

Highlights: [•] Absorption and refractive index depend on the length of quantum dot for z-polarization. [•] Absorption and refractive index depend on the radius of quantum dot for x-polarization. [•] Transparency window and FWHM do no depend on the size of quantum dot. [•] By increasing Rabi frequency, transparency window is increased. [•] Maximum of transparency occurs at (Δ p /γ 02)max = n for Δ c /γ 02 = n. [ABSTRACT FROM AUTHOR]

Surfaces within a dielectric material, where the derivatives of a continuous and real refractive index profile are discontinuous, are shown to enhance reflection. To this end, the amplitude and phase representation of electromagnetic waves is used to model light propagating normally through a transparent medium with a continuous refractive index profile that varies only in one spatial direction. The amplitude equation is solved under the slowly varying refractive index approximation (SVRI). To isolate the effect of a single surface where the refractive index derivatives are discontinuous, an n(z) profile is proposed that is analytical, smooth and slowly varying except for a single piecewise junction. At this junction, n(z) is continuous but some of the mth order derivatives are not. Two different SVRI approximated solutions are joined at the discontinuity plane and, by demanding that boundary conditions are satisfied, a general complex reflection coefficient is obtained. By categorizing profiles according to the lowest order discontinuous derivative at the junction, a simple expression for the reflection coefficient can be written. Results are compared favorably with previous numerical solutions. Furthermore, a conjecture by the authors in a previous paper, ‘for a Cm−1 refractive index profile type, where m stands as the order of the lowest order discontinuous derivative, phase change upon reflection at the discontinuity plane is for an increasing lowest order discontinuous derivative and for the decreasing case’, is proved here. [ABSTRACT FROM AUTHOR]

Abstract: Imposing a phase random distribution in an interval larger than on a spatially coherent light beam transforms the beam into a diffuse one. However, if the required random phase distribution is imposed by a rough transparent plate immersed in a transparent liquid or covered by another transparent material of refractive index close to that of the plate, the diffused light is confined in a small cone around the light incident angle. This renders to fabricate diffusers with high transmission efficiency that has applications in computer displays, bar code scanners, and image forming systems including conventional optical microscopes. [Copyright &y& Elsevier]

It is shown that, on a surface of optical transparency of a medium with quasi-zero refractive index, surface optical waves traveling along the surface can be excited for different angles of incidence of external radiation. Expressions for the amplitudes of nonspecular reflection and transmission of light waves at an inhomogeneous boundary between two media are derived. Using these expressions, the boundary reflectance and transmittance for different angles of incidence and refraction can be calculated. [ABSTRACT FROM AUTHOR]

Abstract: Optical characteristics of two novel copolyimides prepared from an alicyclic or a fluorine-based dianhydride combined with an aliphatic siloxane-based diamine and an aromatic one containing ether linkages, are compared. Ellipsometry data show that the reduced polarizability, provided by the aliphatic moieties, leads to copolyimides with low refractive index (1.53–1.57). The corresponding dielectric constants decrease from 2.71 to 2.57 as the polarization of the dianhydride unit is reduced by the presence of CF3 groups. The transmittance is of approx. 90% and the cut-off wavelengths are comprised between 336 and 380nm. The values of optical band-gap are higher for the fluorine-based copolyimide, namely 3.00eV comparatively to 2.34eV for the sample with alicyclic dianhydride sequences, indicating a lower probability of optical absorption transitions and thus a better transparency. The Urbach and Tauc energies changed in the range of 2295–2809meV and 893–1161meV, being smaller as the polarizability is diminished by the presence of CF3 groups. Optical properties are correlated with morphological aspects, namely surface roughness parameters and entropy of morphology, which varies in agreement with the refractive indices of copolymers. [Copyright &y& Elsevier]

Some novel semi-alicyclic polyimides based on epiclon and three aromatic diamines are investigated. The ellipsometry data reveal that the reduced polarizability provided by the alicyclic dianhydride moieties leads to polyimides with low refractive index, ranging from 1.64 to 1.72. The corresponding dielectric constants decrease from 2.97 to 2.71 as the polarization of the diamine part is lower. The transmittance is of appreciatively 90 % for polyimides containing methylene groups in the diamine residue. The cut-off wavelength decreases, as the backbone conjugation is smaller, being comprised between 305 nm and 317 nm - values comparable to that of a fully aliphatic PI. To obtain the optical energies describing absorption limits, the approach proposed by Tauc and Davis-Mott has been used, due to the similarity of the absorption edges. The values of optical band-gap are found from 3.51 to above 3.78 eV, indicating a low probability of optical absorption transitions and thus a good transparency. The Urbach and Tauc energies changed in the range of 480-806 meV and 1,453-2,786 meV, being smaller as the flexible sequence in the diamine moieties is longer. The novelty of this work consists in relating optical properties with morphological aspects, namely surface defects and entropy of morphology. These new results have a great impact in selecting the proper materials as liquid crystal alignment layers or as cell culture substrates. [ABSTRACT FROM AUTHOR]

A novel high refractive index and highly transparent silicone resin-type material for the packaging of high-power light-emitting diodes (LEDs) is introduced, which was synthesized by hydrosilylation of vinyl end-capped methylphenyl silicone resin and methylphenyl hydrosilicone oil catalyzed by Karstedt's catalyst. The vinyl end-capped methylphenyl silicone resins were prepared by hydrolysis−polycondensation method from methylphenyl diethoxysilane (MePhSi(OEt)2), phenyl triethoxysilane (PhSi(OEt)3), and vinyl dimethylethoxy silane (Me2ViSiOEt) in toluene/water mixture catalyzed by cation-exchange resin. The vinyl end-capped methylphenyl silicone resins were characterized by 1H-NMR and Fourier-transform infrared. The performances of the cured silicone resin-type materials for LED packaging have been examined in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present recent progress in the development of hydrophobic silica aerogel as a Cherenkov radiator. In addition to the conventional method, the recently developed pin-drying method for producing high-refractive-index aerogels with high transparency was studied in detail. Optical qualities and large tile handling for crack-free aerogels were investigated. Sufficient photons were detected from high-performance aerogels in a beam test. [Copyright &y& Elsevier]

Abstract: This study measured a wide range of the refractive index of transparent glass with low phase error using precision circular heterodyne interferometry. We determined precision measurement conditions with theoretical error analysis. The findings showed that minimum phase error could be achieved through appropriate selections of the incident angle and azimuth angle of the analyzer. Using the proposed method, phase error could be estimated at better than 1×10−4. Error in refractive index measurements for each sample could be estimated at better than 1×10−4 under precision measurement conditions. In addition, the proposed method has the advantages of simple optical configuration, easy operation, and a wide measurement range of the refractive index of transparent materials. [Copyright &y& Elsevier]

Abstract: Design and operation of three different optical designs based on the light intensity modulation for investigation of the humidity effects on the air index of refraction are described. The measurement variable is the transmitted power, which depends on the refractive index of the medium in the path of a fiber-to-fiber optical design. Three different probes (probe #1, #2, and #3) are tested in which probe #1 and probe #2 can also check the presence of water or any other transparent liquid in the gap between the two axial fibers. Performances of the new systems are tested as a refractive index monitoring mean and experimental results are given. The variations of the modulated powers as functions of the air humidity change in the light path are determined for the reported optical designs. For probe #1 for a power variation of 255–315nW, the relative humidity changes from 32% to 41%. For probe #2 for 5mm gap distance, for a power change of 2470–2754nW, the relative humidity changes from 54.95% to 90.39%. For probe #3 for the 10mm fiber gap, a power change 929.5–972.9nW is noted for the relative humidity change of 33.0–76.75%. Power variations as a function of the axial fiber gap distances are also given and the optimum condition for the highest sensitivity is obtained. Probe #3 shows a higher sensitivity compared to probe #1 and it is superior to probe #2 because it operates in a fog-free condition. Finally, the calibration curve for each probe is given that can be used for the operation of the probe as a humidity sensor. [Copyright &y& Elsevier]