Optical Transmission in Arrayed Asymmetric Multilayered Ultra-Thin Metal Stripes

An arrayed structure of asymmetric multilayered ultra-thin metal stripes is proposed to achieve a narrow transmission peak in an ultra-broad transmission valley, which is formed due to the destructive multiple-interference tunneling existed in an ultra-thin metal and dielectric multilayers. The transmission peak is influenced by two resonant modes. One is the coupled gap surface plasmon (cg-SP) resonance mode confined in entire multilayered ridges, the other is the modified gap surface plasmon (g-SP) mode within metal-dielectric layers. Furthermore, the transmission mode and the stopband are tunable in a wide range through designing the dimension parameters. The proposed plasmonic structure is promising for wideband filters.     

Optical Bifacial Transmission by Asymmetric Charge-Oscillation-Induced Light Transmission Through a Plasmonic Structure

From first-principles computation, we reveal that optical bifacial transmission can be induced within an asymmetric metallic subwavelength structure. This phenomenon can be explained by a concrete picture in which the intensity of the driving forces for surface plasmon or charge wave is asymmetric for the two incident directions. Two distinguished different numerical methods, finite difference time domain (FDTD), and rigorous coupled wave analysis (RCWA) are utilized to verify that optical bifacial transmission can exist for linear plasmonic metamaterial. Previous results are also reviewed to confirm the physical meaning of optical bifacial transmission for a planar linear metamaterial. The incident light can provide direct driving forces for surface plasmon in one direction. While in the opposite direction, forces provided by the light diffraction are quite feeble. With the asymmetric driving forces, the excitation, propagation, and light-charge conversion of surface plasmon give the rise of bifacial charge-oscillation-induced transmission. In periodic a structure, the excitation of surface plasmon polariton can lead to the spoof vanish of such phenomenon. The transmissions for two incident directions get the same in macroscopic while the bifacial still exists in microscale.     

A Tunable on-Chip Integrated Plasmonic Filter and Router Based on Metal/Dielectric Nanostructures

An on-chip integrated wavelength filter and router device is realized using two-dimensional metal/dielectric nanostructures. The device can filter wavelengths of light from an incident broadband beam, and further route the filtered signals to different ports on the same chip. The footprint of the entire device is only 3.4 μm × 7.3 μm. Both the number of wavelength channels and the central wavelength of each channel can be tuned by adjusting the structure parameters, or by using a pumped laser. This work demonstrates an ultracompact and robust integrated multifunctional device, and provides a novel and flexible method for the integration of nanophotonic devices.     

Tunable Broadband Optical Responses of Substrate-Supported Metal/Dielectric/Metal Nanospheres

Using the image charge theory and finite element methods, we present the first comprehensive study on the optical properties of substrate-supported, three-layer, metal/dielectric/metal nanospheres. By adopting dipolar and quadrupolar approximations of the quasistatic image charge theory, we derive analytical expressions for the polarization-dependent polarizabilities of a three-layer nanosphere near a substrate and use them to find the nanosphere’s plasmon resonance wavelengths as functions of the geometric and material parameters of the nanosphere–substrate system. By calculating the resonance wavelength of substrate-supported gold/silica/gold nanosphere over a sufficiently large domain of the nanosphere’s dimensions, we show that this wavelength can be tuned from visible to infrared regions by altering only the size of the nanosphere’s core. We also show that the resonance position as well as the enhancement and confinement of the near-field can be dynamically tuned over broad ranges by changing the polarization of the excitation light. Of significance for the applicability of our results in practice is that we employ size-dependent permittivity of gold, which allows experimentalists to readily produce these substrate-supported nanospheres with desired optical responses. Upon comparing our analytical results with the results of numerical simulations, we reveal the range of the nanospheres’ outer radii within which the dipolar and quadrupolar approximations adequately describe the nanosphere–substrate interaction. Since majority of the optical functions are realized with light polarized parallel to the substrate, our results allow one to readily engineer the broadband optical responses of substrate-supported metal/dielectric/metal nanospheres for applications in resonance-enhanced sensing, in light harvesting, and in biomedicine.     

Plasmon-Induced Nearly Null Transmission of Light Through Gratings in Very Thin Metal Films

Based on numerical simulations, we show that a very thin metal (Ag) film, otherwise transmissive partially, becomes opaque for transverse magnetic-polarized light in a certain spectrum band when perforated with grating-like slits. Positions of the nearly null transmission band are dependent on the various structure dimensions, particularly on the ridge width for gratings with relatively narrow slit width. Our analyses show that the nearly null transmission is related to resonant excitation of anti-symmetric bound surface plasmon waves at the ridges of the thin metal film gratings and further resulted from destructive interference of waves evolved from the fields at the ridges and slits that are in opposite phase. It is also found that for 2D gratings, the nearly null transmission band appears only for disk array-type gratings and not for the hole array-type gratings. This structure may be applied in novel photonic devices to enhance their performances and functionalities.     

Modeling of Hybrid Plasmonic Ring Resonator Based on Dielectric Filled Subwavelength Metal Grating

Plasmonics - A nanophotonic dual ring Cu-SiO2-Si-Cu-SiO2 plasmonic switch with subwavelength metal grating as switching element is designed and simulated in this paper. The 2D finite element method...     

A Tunable Slow Light Device with Multiple Channels Based on Plasmon-Induced Transparency

Slow light devices with buffering capability play a critical role in all-optical signal processing. In this paper, multiple slow light phenomena are implemented based on plasmon-induced transparency (PIT) in our device. The device mainly consists of dual tooth cavities coupled with stub resonators, respectively. Temporal coupled-mode theory model illustrates that the triple PIT phenomena can be achieved based on different formation mechanisms. The simulation results calculated by the finite-difference time-domain method reveal that significant slow light response occurs at two wavelength regions. In addition, the parameters of structure have an important influence on PIT response and slow light characteristics. Moreover, the separate manipulation of wavelength, transmission and group index at transparency peak can be achieved in different slow light channels by adjusting the structural parameters. This plasmonic device is of great significance for the design of optical networks on chips.

     

Effect of Edge Rounding on the Extinction Properties of Hollow Metal Nanoparticles

The optical responses of metal nanoparticles induced by subtle variations in geometry, especially by the rounding of the edges and corners, have generated great interest at present due to the requirement of fabricating refined structures of metal nanoparticles and theoretical simulations of the real particles. We study the effect of both inner and outer edge rounding on the optical properties of gold nanobox and gold nanobox dimer with small interparticle distances by using the discrete dipole approximation method. The shift of extinction peaks, the electric field distribution, and the variation of refractive index sensitivities by changing the curvature of the inner and outer edges of gold nanobox are investigated. We demonstrate that the optical properties of nanobox are more sensitive to the outer edge rounding than the inner edge rounding. By edge rounding of two very close gold nanoboxes, the blue shift of the dipolar and the quadrupolar plasmonic resonances of nanobox dimer are shown. Comparing with the inner edge rounding of nanobox dimer, we find that rounding of the outer edges causes the larger shift of the quadrupolar mode and approximate shift of the dipole mode.     

Bidirectional chromosome replication in Bacillus subtilis

We have examined autoradiographically the pattern of DNA replication following the germination of Bacillus subtilis spores in [³H]thymidine. Thymine-requiring spores were germinated in low specific activity medium and diluted into higher specific activity medium soon after the first round of replication was expected to start. After a further short period, replication was stopped and the chromosomal structures examined by autoradiography. From the pattern of labelling within individual replicating loops it is clear that the majority (≥75%) expand by growth at two positions that are opposite, i.e. expand bidirectionally. The loops continue to expand at approximately equal rates in both directions until at least 20% of the chromosome has been replicated.From a consideration of the other structural forms that become visible, it seems likely that most chromosomes replicate bidirectionally.     

ITO Breakers: Highly Transparent Conducting Polymer/Metal/Dielectric (P/M/D) Films for Organic Solar Cells

Ormoclear/Ag/WO₃ (OAW) films with ultrahigh transparency are designed for application in organic solar cells (OSCs). When the thicknesses of Ag and WO₃ are fixed at 8 nm and 30 nm, respectively, excellent transparency that is independent of Ormoclear thickness is successfully achieved by employing soft materials instead of inorganic dielectrics. Oxygen plasma treatment prior to the deposition of Ag introduces the polar functional groups on the Ormoclear surface, which results in increasing the surface hydrophilicity, thereby enhancing the wettability of Ag. From the surface modification, OAW exhibits low sheet resistance (4.8 ohm sq^‐1), high transmittance of up to 96.3% at 535 nm, and enhanced efficiency of 7.63% of OSCs. Moreover, nanoimprint lithography is used to prepare a well‐ordered nanopatterned OAW with dimple diameter of 90 nm, leading to further increase in photocurrent density by 17%, compared to that with a planar indium tin oxide (ITO) electrode.     

Dielectric relaxation in lecithin/cholesterol/water-mixtures

The dielectric spectrum of aqueous solutions of dimyristoyl-l-3-phosphatidylcholine and dipalmitoyl-l-3-phosphatidylcholine with admixed cholesterol has been determined by means of a pulse reflection method which was used to measure the complex permittivity of the solutions as a function of frequency between 100 kHz and 50 MHz. Measurements have been performed at various concentrations of cholesterol in dependence of temperature around the crystal-line/liquid-crystalline phase transition temperature of the solutions.The measured dielectric spectra are treated in terms of a Debye-function. The dielectric relaxation strength and the relaxation time decrease distinctly with increasing cholesterol concentration. In addition, the data are treated on the basis of a theoretical solution model in order to allow for conclusions concerning the lecithin head group motion in the lipid bilayer surface. One important result is that increasing cholesterol concentration affects the interaction of the lecithin head groups and increases their mobility. These effects already occur at small concentrations of cholesterol.     

Tunable Absorption of Light via Localized Plasmon Resonances on a Metal Surface with Interspaced Ultra-thin Metal Gratings

We studied optical reflection properties of complex metal (Ag) surfaces with close-interspaced ultra-thin metal gratings. Prominent reflection minima were observed corresponding to enhanced absorption of light. Our analysis convinced us that the period-dependent mode is ascribed to Bloch-wave-like resonances of surface plasmon waves at the overall effective metal surfaces, and the ridge-width-dependent mode to Fabry-Pérot-like resonances of localized surface plasmon waves in micro-/nanocavities defined by regions of the grating ridges. The latter resonance mode is shown highly tunable with variation of the grating ridge width. Such structures may be applied in spectrum resolvable photovoltaic devices, bio-sensing, and studying optical properties of cavity-coupled molecules or functional nanomaterials.     

Self-Powered Wireless Carbohydrate/Oxygen Sensitive Biodevice Based on Radio Signal Transmission

Here for the first time, we detail self-contained (wireless and self-powered) biodevices with wireless signal transmission. Specifically, we demonstrate the operation of self-sustained carbohydrate and oxygen sensitive biodevices, consisting of a wireless electronic unit, radio transmitter and separate sensing bioelectrodes, supplied with electrical energy from a combined multi-enzyme fuel cell generating sufficient current at required voltage to power the electronics. A carbohydrate/oxygen enzymatic fuel cell was assembled by comparing the performance of a range of different bioelectrodes followed by selection of the most suitable, stable combination. Carbohydrates (viz. lactose for the demonstration) and oxygen were also chosen as bioanalytes, being important biomarkers, to demonstrate the operation of the self-contained biosensing device, employing enzyme-modified bioelectrodes to enable the actual sensing. A wireless electronic unit, consisting of a micropotentiostat, an energy harvesting module (voltage amplifier together with a capacitor), and a radio microchip, were designed to enable the biofuel cell to be used as a power supply for managing the sensing devices and for wireless data transmission. The electronic system used required current and voltages greater than 44 µA and 0.57 V, respectively to operate; which the biofuel cell was capable of providing, when placed in a carbohydrate and oxygen containing buffer. In addition, a USB based receiver and computer software were employed for proof-of concept tests of the developed biodevices. Operation of bench-top prototypes was demonstrated in buffers containing different concentrations of the analytes, showcasing that the variation in response of both carbohydrate and oxygen biosensors could be monitored wirelessly in real-time as analyte concentrations in buffers were changed, using only an enzymatic fuel cell as a power supply.     

Light Absorption and Recycling in Hybrid Metal Halide Perovskite Photovoltaic Devices

The production of highly efficient single‐ and multijunction metal halide perovskite (MHP) solar cells requires careful optimization of the optical and electrical properties of these devices. Here, precise control of CH₃NH₃PbI₃ perovskite layers is demonstrated in solar cell devices through the use of dual source coevaporation. Light absorption and device performance are tracked for incorporated MHP films ranging from ≈67 nm to ≈1.4 µm thickness and transfer‐matrix optical modeling is utilized to quantify optical losses that arise from interference effects. Based on these results, a device with 19.2% steady‐state power conversion efficiency is achieved through incorporation of a perovskite film with near‐optimum predicted thickness (≈709 nm). Significantly, a clear signature of photon reabsorption is observed in perovskite films that have the same thickness (≈709 nm) as in the optimized device. Despite the positive effect of photon recycling associated with photon reabsorption, devices with thicker (>750 nm) MHP layers exhibit poor performance owing to competing nonradiative charge recombination in a “dead‐volume” of MHP. Overall, these findings demonstrate the need for fine control over MHP thickness to achieve the highest efficiency cells, and accurate consideration of photon reabsorption, optical interference, and charge transport properties.     

Transcranial Red and Near Infrared Light Transmission in a Cadaveric Model

Background and Objective

Low level light therapy has garnered significant interest within the past decade. The exact molecular mechanisms of how red and near infrared light result in physiologic modulation are not fully understood. Heme moieties and copper within cells are red and near infrared light photoreceptors that induce the mitochondrial respiratory chain component cytochrome C oxidase, resulting in a cascade linked to cytoprotection and cellular metabolism. The copper centers in cytochrome C oxidase have a broad absorption range that peaks around 830 nm. Several in vitro and in vivo animal and human models exist that have demonstrated the benefits of red light and near infrared light for various conditions. Clinical applications for low level light therapy are varied. One study in particular demonstrated improved durable functional outcomes status post-stroke in patients treated with near infrared low level light therapy compared to sham treatment [1]. Despite previous data suggesting the beneficial effect in treating multiple conditions, including stroke, with low level light therapy, limited data exists that measures transmission in a human model.

Study Design/Materials and Methods

To investigate this idea, we measured the transmission of near infrared light energy, using red light for purposes of comparison, through intact cadaver soft tissue, skull bones, and brain using a commercially available LED device at 830 nm and 633 nm.

Results

Our results demonstrate that near infrared measurably penetrates soft tissue, bone and brain parenchyma in the formalin preserved cadaveric model, in comparison to negligible red light transmission in the same conditions.

Conclusion

These findings indicate that near infrared light can penetrate formalin fixed soft tissue, bone and brain and implicate that benefits observed in clinical studies are potentially related to direct action of near infrared light on neural tissue.     

波纹唇鱼鳃丝的光镜、扫描和透射电镜观察

应用光学显微镜、扫描电镜和透射电镜对波纹唇鱼(Cheilinus undulatus)鳃的组织结构、表面形态特征及鳃小片超微结构进行了观察.结果表明,波纹唇鱼有3对全鳃,1对半鳃和1对伪鳃,鳃丝呈梳状紧密排列在鳃弓上,鳃小片紧密地镶嵌排列在鳃丝两侧,入鳃动脉、出鳃动脉和鳃小片毛细血管网组成鳃的血液系统.鳃丝非呼吸区分布...     

Recovery of Lost Photons in Plasmon-Mediated Transmission Through Continuous Metal Film

The plasmon-mediated transmission across a subwavelength-undulated, nanometer-thick continuous metal film embedded in a polymer exhibits an, as yet, unexplained loss, reducing the resonant transmission to half its theoretical value, precluding practical applications of this interesting spatially resolved polarization- and wavelength-selective effect. Slow chemical dissolution of the surrounding polymer while measuring the transmission spectrum under floating conditions reveals near complete recovery of the missing photons. The excess losses originate in nanoclusters of overheated polymer spots at the metal interface giving rise to index and geometrical nonuniformities where the mediating plasmon modes have their field maximum.