Nanolaminate-based antireflection coatings for enhanced scratch and tribological performance.

Developing durable antireflection (AR) coatings with sapphire-like hardness and high transparency faces a significant challenge. Conventionally, achieving these requirements involves depositing thick, high-hardness nitride films. Here, we proposed an alternative approach that combines nanolaminate materials with optical design, overcoming the brittleness of thick nitride films. We selected Ta2O5/Si3N4 nanolaminates with similar refractive indices, improving tribological and optical performance through a unique optomechanical method. Our proposed AR coating exhibited a low reflectance of 0.8% (420-780 nm) and remarkable hardness of 22.8 GPa, and demonstrated the ability to withstand abrasion from steel wool up to 3,000 times on a glass substrate. This work successfully achieves a balance between hardness and toughness, opening new avenues for the development of highly durable coatings.

Wide-angle broadband antireflection coatings with nano-taper hydrated alumina film.

Wide-angle and broadband antireflection (AR) coating is of the essence in modern optical systems in many fields, which has a great influence on the stray light and imaging quality. A simple and convenient manufacturing method is proposed to address this issue based on a composite coating combining the nano-tapered Al2O3•xH2O (AH) structure and high-low index thin film stack. The optical properties of nano-tapered AH structure at various thickness are first studied and modeled in optics by several homogeneous sub-layers with the graded equivalent index. The designed composite AR coatings are manufactured by vacuum deposition and wet etching subsequently in the hot deionized water. Compared to the common dielectric multilayer antireflection stack, the composite coating presents excellent AR performance. The measured average reflectance values of the double-side coated BK7 glass are as low as 0.40%, 0.41%, 0.56% and 3.13% in 400-1100nm band at angles of incidence (AOI) of 6°, 20°, 40°, and 60°, respectively, while the measured average transmittance at normal incidence increases up to 99.3%. Finally, the process reproductivity, environmental reliability test including long term storage, high temperature annealing and 85°C-85% relative humidity storage of the composite coatings are evaluated. The proposed AR scheme provides a low-cost, efficient, wide-angle and broadband AR coating for kinds of large-curvature components and complex surfaces in fields of consumer electronics, automotive, security, etc.

Broadband absorption coating for large-curvature surfaces by atomic layer deposition.

For many applications, large curvature surfaces or complicated 3D structures are required to absorb light that falls on them to reduce stray light or energy collection. A novel, to the best of our knowledge, strategy with a metal-dielectric film stack by the atomic layer deposition technique is put forward to achieve broadband absorption coating covering both sides of a quartz tube completely. Absorptive metallic material of titanium-aluminum-carbon composite and dielectric material of aluminum oxide (Al2O3) is employed to realize high absorption (>99%) for the 400-780 nm band with the configuration of a six-layer metal-dielectric film stack. Good angle insensitivity up to 50° for P- and S-polarizations is demonstrated experimentally with the proposed structure on a glass slab. The average absorption of the coated quartz tube reaches as high as 99% for all curving areas on the inner and outer sides, while the nonuniformity is confined to 1.5% for the axial and circumferential directions. This presented approach has enormous potential in the fields of optical detection, optical imaging, optical sensing, and energy management.

Effective, angle-independent radiative cooler based on one-dimensional photonic crystal.

A simple and low-cost radiative cooler based on one-dimensional photonic crystal is proposed in this work, which has an average emissivity of 96% within the atmospheric transparency window (8-13µm). The ultra-broadband emissivity property is realized by constructing the strongly overlapped optical resonances with a tandem structure composed of two lossy materials while an additional lossless material is adopted as the top layer to reduce the Fresnel reflection of the whole structure. The maximum cooling power density of the fabricated radiative cooler can reach 113.0W/m2 at night. When integrated with an excellent solar reflector that can reflect 97% incident solar power, it theoretically has the maximum cooling power of 83.0 W/m2 in the case of solar irradiance up to 1000 W/m2 at noon.

Highly efficient omnidirectional structural color tuning method based on dielectric-metal-dielectric structure.

A novel and convenient scheme is proposed to achieve angle insensitive color filtering across a large color gamut by simply altering the thickness of the dielectric layer of a dielectric-metal-dielectric grating structure. The plasmonic filter presents a great feature of angle resolved spectrum response up to 60° and is independent of the azimuthal angle and the polarization state as well so as to construct an omnidirectional filter for practical applications. The color tuning feature of the proposed filter with varied dielectric thickness is attributed to the modulation of the condition for the localized surface plasmon resonance, which bears responsibility for the omnidirectional property of this plasmonic filter. This color-tuning method with a single mold size required can have wide applications in fields of display, colorful decoration, printing, and so forth.

Dielectric multilayer beam splitter with differential phase shift on transmission and reflection for division-of-amplitude photopolarimeter.

Dielectric multilayer beam splitter with differential phase shift on transmission and reflection for division-of-amplitude photopolarimeter (DOAP) was presented for the first time to our knowledge. The optimal parameters for the beam splitter are Tp = 78.9%, Ts = 21.1% and Δr - Δt = π/2 at 532nm at an angle of incidence of 45°. Multilayer anti-reflection coating with low phase shift was applied to reduce the backside reflection. Different design strategies that can achieve all optimal targets at the wavelength were tested. Two design methods were presented to optimize the differential phase shift. The samples were prepared by ion beam sputtering (IBS). The experimental results show good agreement with those of the design. The ellipsometric parameters of samples were measured in reflection (ψr, Δr) = (26.5°, 135.1°) and (28.2°, 133.5°), as well as in transmission (ψt, Δt) = (62.5°, 46.1°) and (63.5°, 46°) at 532.6nm. The normalized determinant of instrument matrix to evaluate the performance of samples is respectively 0.998 and 0.991 at 532.6nm.

Design and simulation of omnidirectional reflective color filters based on metal-dielectric-metal structure.

We propose omnidirectional reflective color filters based on metal-dielectric-metal subwavelength grating structure. By particle swarm optimization, the structural parameters of three color filters (yellow, magenta, cyan) are obtained. The optimized filters can present the same perceived specular color at unpolarized illumination for a broad range of incident angles. The reflectance curves at different incident angles keep almost invariable and the color difference is less than 6 in CIEDE2000 formula up to 45°. Angle-insensitive properties including the incident angular tolerance, azimuthal angular tolerance and the polarization effect are investigated thoroughly to construct a real omnidirectional color filter. Through the analysis of the magnetic field, the physical origin is verified that the total absorption band at specific wavelength results from the localized surface plasmon resonance responsible for the angle insensitive spectral filtering.

Color-tuning method by filling porous alumina membrane using atomic layer deposition based on metal-dielectric-metal structure.

A novel and convenient color-tuning method by filling the porous alumina membrane (PAM) based on metal-dielectric-metal structure is proposed. The pore sizes of PAM as well as the thickness of TiO2 films, deposited by atomic layer deposition, causes various reflection colors due to multilayer interference effects. Overlapping films on top and within the PAM structure can be observed with a scanning electron microscope and will be used to show the change of the effective refractive index of the PAM composite layer. The color-tuning method resulting in changing the dynamics of the PAM layer can be widely applied in fields such as micro-optics, microstructures, nanomaterials, and micro/nanotechnology.

Design of reflective color filters with high angular tolerance by particle swarm optimization method.

We propose three color filters (red, green, blue) based on a two-dimensional (2D) grating, which maintain the same perceived specular colors for a broad range of incident angles with the average polarization. Particle swarm optimization (PSO) method is employed to design these filters for the first time to our knowledge. Two merit functions involving the reflectance curves and color difference in CIEDE2000 formula are respectively constructed to adjust the structural parameters during the optimization procedure. Three primary color filters located at 637nm, 530nm and 446nm with high saturation are obtained with the peak reflectance of 89%, 83%, 66%. The reflectance curves at different incident angles are coincident and the color difference is less than 8 for the incident angle up to 45°. The electric field distribution of the structure is finally studied to analyze the optical property.

Vector-dispersion compensation and pulse pedestal cancellation in a femtosecond nonlinear amplification fiber laser system.

We report on a femtosecond nonlinear amplification fiber laser system using a vector-dispersion compressor, which consists of a transmission grating pair and multipass cell based Gires-Tournois interferometer mirrors. The mirror is designed with nearly zero group-delay dispersion and large negative third-order dispersion. As a result, the third-order dispersion of the compressor can be adjusted independently to compensate the nonlinear phase shift of amplified pulses to reduce the pulse pedestal. With this scheme, the system outputs 44 fs laser pulses with little wing at 26.6 W output average power and 531 nJ pulse energy, corresponding to 10.8 MW peak power.

Group delay dispersion measurement of a dispersive mirror by spectral interferometry: comparison of different signal processing algorithms.

We built a dispersive white-light spectral interferometer for precisely measuring the dispersion properties of a multilayer thin-film structure. A novel algorithm with improved robustness to measurement errors is presented by combining a windowed Fourier transformation with wavelet-based differentiation. Compared with previously published algorithms, this method shows substantial resistance to measurement errors. The group delay dispersion properties of bulk materials and a homemade chirped mirror are measured by our apparatus, and the measurement result manifests considerable accuracy and robustness. The technique shows reasonable potential for the characterization of ultrabroadband chirped mirrors.

Optical Device Based on a Nanopillar Array by the Pattern Transfer of an Anodic Aluminum Oxide Membrane.

A simple and convenient nanofabrication method is proposed to achieve nanopillar arrays by the pattern transfer of an anodic aluminum oxide membrane, profiting from the rapid and efficient preparation process and regular hexagonal lattice patterns of the anodic aluminum oxide template. The taper angle of the nanopillar is affected by the distribution of the vapor particles during the deposition process, which is highly dependent on the material and deposition power. Based on this method, a novel scheme employing aluminum nanopillar arrays is demonstrated to realize the color tuning feature by simply varying the thickness of the top dielectric layer within a large range. The nanopillar arrays are completely covered by the thick dielectric layer atop due to the great conformality of the atomic layer deposition method that is used for the dielectric deposition. In addition, the color devices present good angular insensitivity up to 45°, resulting from the excited localized surface plasmon resonance within the metallic patches. The simple fabrication method is of great advantage to produce periodic nanostructures over large areas, which are widely used in designs and verifications of optical metasurfaces for various applications, including optical communication, imaging, sensing, and so forth.

Omnidirectional narrow bandpass filter based on metal-dielectric thin films.

We show that a metal-dielectric Fabry-Perot (FP) structure can exhibit an omnidirectional transmission for p-polarized light, which means a passband is independent of the incidence angle of light. The omnidirectional passband occurs when the sum of the reflection phase shift at the metal-spacer interface and the propagation shift in the spacer region is almost 2pi for every incidence angle. We numerically and experimentally demonstrate such an omnidirectional narrow bandpass filter in an air/Ag/ZnS/Ag/glass structure. Moreover, we introduce an antireflection coating on both sides of the metal-dielectric FP structure. The transmittance will increase obviously, while the omnidirectional property remains the same.

Morphology-Conserved Transformations of Metal-Based Precursors to Hierarchically Porous Micro-/Nanostructures for Electrochemical Energy Conversion and Storage.

To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.

Rspo1-activated signalling molecules are sufficient to induce ovarian differentiation in XY medaka (Oryzias latipes).

In contrast to our understanding of testicular differentiation, ovarian differentiation is less well understood in vertebrates. In mammals, R-spondin1 (Rspo1), an activator of Wnt/ß-catenin signaling pathway, is located upstream of the female sex determination pathway. However, the functions of Rspo1 in ovarian differentiation remain unclear in non-mammalian species. In order to elucidate the detailed functions of Rspo/Wnt signaling pathway in fish sex determination/differentiation, the ectopic expression of the Rspo1 gene was performed in XY medaka (Oryzias latipes). The results obtained demonstrated that the gain of Rspo1 function induced femininity in XY fish. The overexpression of Rspo1 enhanced Wnt4b and ß-catenin transcription, and completely suppressed the expression of male-biased genes (Dmy, Gsdf, Sox9a2 and Dmrt1) as well as testicular differentiation. Gonadal reprograming of Rspo1-over-expressed-XY (Rspo1-OV-XY) fish, induced the production of female-biased genes (Cyp19a1a and Foxl2), estradiol-17ß production and further female type secondary sexuality. Moreover, Rspo1-OV-XY females were fertile and produced successive generations. Promoter analyses showed that Rspo1 transcription was directly regulated by DM domain genes (Dmy, the sex-determining gene, and Dmrt1) and remained unresponsive to Foxl2. Taken together, our results strongly suggest that Rspo1 is sufficient to activate ovarian development and plays a decisive role in the ovarian differentiation in medaka.

Angle Insensitive Color Filters in Transmission Covering the Visible Region.

Angle insensitive color filter based on Metal-SiOx-Metal structure is proposed in this paper, which can keep the same perceived transmitted color when the incidence angle changes from 0° to 60°, especially for p-polarization light. Various silicon oxide films deposited by reaction magnetron sputtering with a tunable refractive index from 1.97 to 3.84 is introduced to meet the strict angle insensitive resonance conditions. The angle resolved spectral filtering for both p-polarization light and s-polarization light are quite well, which can be attributed to the different physical origins for the high angular tolerance for two polarizations. Finally, the effect of SiOx absorption and Ag thickness on the peak transmittance are analyzed.

Compact multilayer film structure for angle insensitive color filtering.

Here we report a compact multilayer film structure for angle robust color filtering, which is verified by theoretical calculations and experiment results. The introduction of the amorphous silicon in the proposed unsymmetrical resonant cavity greatly reduces the angular sensitivity of the filters, which is confirmed by the analysis of the phase shift within the structure. The temperature of the substrate during the deposition is expressly investigated to obtain the best optical performance with high peak reflectance and good angle insensitive color filtering by compromising the refractive index of dielectric layer and the surface roughness of the multilayer film. And the outlayer of the structure, worked as the anti-reflection layer, have an enormous impact on the filtering performance. This method, described in this paper, can have enormous potential for diverse applications in display, colorful decoration, anti-counterfeiting and so forth.

High-temperature solid-state dye-sensitized solar cells based on organic ionic plastic crystal electrolytes.

Organic ionic plastic crystal, 1-ethyl-1-methyl pyrrolidinium iodide (P(12) I), is employed as the solid-state electrolytes for dye-sensitized solar cells. The fabricated solid-state devices show an overall power conversion efficiency of ~5.8% under AM 1.5 radiation (50 mW/cm(2) ) and excellent long-term stability at 80 °C.

Benzimidazolyl functionalized ionic liquids as an additive for high performance dye-sensitized solar cells.

Benzimidazolyl functionalized ionic liquids were synthesized and applied as additives for dye-sensitized solar cells. The fabricated devices show an overall power conversion efficiency of ~7.79% under AM 1.5 radiation (50 mW cm(-2)), and an excellent long-term stability.

Optical properties and residual stress of YbF3 thin films deposited at different temperatures.

The influence of deposition temperature on the optical properties, microstructure, and residual stress of YbF(3) films, deposited by electron-beam evaporation, has been investigated. The increased refractive indices and surface roughness of YbF(3) films indicate that the film density and columnar structure size increase with deposition temperature. At the same time, higher packing density reduces absorption of moisture. The residual stress is related to deposition temperature and to substrate. For the samples deposited on BK7, the residual stress mainly comes from intrinsic stress, however, for those on fused silica, thermal stress is the dominant factor of total residual stress.