Broadband reflectors with a disordered layered structure: statistical properties of high performing configurations selected via genetic algorithm

Disordered multilayers consisting of alternating layers of two lossless dielectric materials with random thicknesses can behave as good reflectors in wide wavelength ranges except for narrow bands where the transmittance is significative. We use a dedicated genetic algorithm to select different configurations (thickness sequences) of such structures which exhibit very low transmittance in the entire visible wavelength range, showing that broadband disordered reflectors with very high performance can be designed. A statistical analysis of the thickness sequences selected by the genetic algorithm reveals that such sequences are characterized by correlated disorder and that the degree of autocorrelation is a key parameter in determining the reflection performance.

Optically Transparent and Highly Conductive Electrodes for Acousto-Optical Devices

The study was devoted to the creation of transparent electrodes based on highly conductive mesh structures. The analysis and reasonable choice of technological approaches to the production of such materials with a high Q factor (the ratio of transparency and electrical conductivity) were carried out. The developed manufacturing technology consists of the formation of grooves in a transparent substrate by photolithography methods, followed by reactive ion plasma etching and their metallization by chemical deposition using the silver mirror reaction. Experimental samples of a transparent electrode fabricated using this technology have a sheet resistance of about 0.1 Ω/sq with a light transmittance in the visible wavelength range of more than 60%.

Improved Imaging Model in the Presence of Multiplicative Spatially Extended Cloaking Interference

The paper proposes an improved imaging model in the presence of multiplicative spatially extended cloaking interference. The model take into account the effect of multiplicative masking interference. To simplify the calculations of the image brightness in the distorted region the diagram technique is used. Unlike the known ones, the model takes into account the concentration of the distorting medium in a narrow squat layer, the primary reflection of solar radiation from the upper boundary of the distorting layer and subsequent multiple re-reflections of the transmitted radiation of the visible wavelength range from the earth’s surface and the upper boundary of the distorting medium layer. A technique for finding and taking into account the reflection and re-reflection coefficients of radiation to restore distorted images is proposed. The results of experimental studies are presented. For the experiment, the image of the territory of Iraq during the 2003 "Freedom for Iraq" hostilities was selected. Keywords— image, model, multiplicative, extended cloaking interference, spacecraft, reflection, coefficient

Clustering in thin silver films upon heating

The kinetics of the formation of silver clusters Ag from nanoscale continuous films of Ag on the surface of silicate glass and composite structures from films of Ag with carbon in the form of a continuous film and individual nanoparticles upon annealing in air at temperatures up to 670K is investigated. In the course of the work, the dependences of the surface morphology of silver clusters and absorption spectra in the visible wavelength range were obtained by the methods of atomic force microscopy and optical spectrophotometry.

Snapshot multicolor fluorescence imaging using double multiplexing of excitation and emission on a single detector

Fluorescence-based multispectral imaging of rapidly moving or dynamic samples requires both fast two-dimensional data acquisition as well as sufficient spectral sensitivity for species separation. As the number of fluorophores in the experiment increases, meeting both these requirements becomes technically challenging. Although several solutions for fast imaging of multiple fluorophores exist, they all have one main restriction; they rely solely on spectrally resolving either the excitation- or the emission characteristics of the fluorophores. This inability directly limits how many fluorophores existing methods can simultaneously distinguish. Here we present a snapshot multispectral imaging approach that not only senses the excitation and emission characteristics of the probed fluorophores but also all cross term combinations of excitation and emission. To the best of the authors’ knowledge, this is the only snapshot multispectral imaging method that has this ability, allowing us to even sense and differentiate between light of equal wavelengths emitted from the same fluorescing species but where the signal components stem from different excitation sources. The current implementation of the technique allows us to simultaneously gather 24 different spectral images on a single detector, from which we demonstrate the ability to visualize and distinguish up to nine fluorophores within the visible wavelength range.

Colored Surfaces Made of Synthetic Eumelanin

The polymerization of 3,4-dihydroxy-L-phenylalanine leads to a carboxylic acid-rich synthetic melanin-like material (poly-L-DOPA). Synthetic melanin most resembles natural eumelanin in chemical structure. However, its deposition on surfaces leading to colored surfaces by interference is not as easy to accomplish as in the case of the preparation of colored surfaces by dopamine hydrochloride polymerization. This study deals with the preparation of new colored surfaces made from poly-L-DOPA displaying vivid colors by interference. These surfaces were obtained by depositing thin films of poly-L-DOPA on a reflective silicon nitride substrate. A high ionic strength in the polymerization medium was essential to accomplish the coating. The effect of ionic strength on the resulting surfaces was studied via reflectance, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The refractive index was determined by ellipsometry, and was nearly constant to 1.8 when λ > 650 nm. In the visible spectral region, the imaginary part of the refractive index becomes relevant. The refractive index in the visible wavelength range (400–600 nm) was in the range 1.7–1.80.

Designing a new optical biosensing platform based on an insulator-metal-insulatornanostructure

The insulator-metal-insulator (IMI) structure is potential for the fabrication of biosensor platform devices because of its unique optical properties, especially surface plasmon resonance (SPR). In this study, the optical properties of the IMI structure in the visible wavelength range were calculated using the transfer matrix method. The results indicated that the IMI structure exhibited high absorbance at the proper wavelength due to the SPR. This phenomenon was resulted from the resonance of incident light and the free electrons in the metal surface. The SPR signal relied on the thickness of layers in the IMI structure and the refractive index of the surrounding medium. Based on calculation results, the IMI structure applied for the biosensor was designed and optimised with respects to optical properties. In addition, sensitivity calculation demonstrated that IMI structure was more sensitive than biosensor based on attenuated total reflection (ATR), SPR method while similar results were attained with the metal-insulator-metal (MIM) structure method.

High Q-Factor Hybrid Metamaterial Waveguide Multi-Fano Resonance Sensor in the Visible Wavelength Range

We propose a high quality-factor (Q-factor) multi-Fano resonance hybrid metamaterial waveguide (HMW) sensor. By ingeniously designing a metal/dielectric hybrid waveguide structure, we can effectively tailor multi-Fano resonance peaks’ reflectance spectrum appearing in the visible wavelength range. In order to balance the high Q-factor and the best Fano resonance modulation depth, numerical calculation results demonstrated that the ultra-narrow linewidth resolution, the single-side quality factor, and Figure of Merit (FOM) can reach 1.7 nm, 690, and 236, respectively. Compared with the reported high Q-value (483) in the near-infrared band, an increase of 30% is achieved. Our proposed design may extend the application of Fano resonance in HMW from mid-infrared, terahertz band to visible band and have important research value in the fields of multi-wavelength non-labeled biosensing and slow light devices.

POLY ORGANIC POLYMER (3-HEXYLTHIOPHENE) P3HT as LIGHT SENSITIVITY in PROTOTYPE DYE-SENSITIZED SOLAR CELLS (DSSC)

This research aims to review the characteristic of the nature of electricity polymer material poly(3-hexylthiophene) P3HT against increasing efficiency solar cells based on dye-sensitized solar cells (DSSC). The testing sample has done electricity P3HT el-kahfi 100/ I-V meter. The optical properties use spectrophotometer UV visible 1601 PC and characterizing IV DSSC use Keithley 2600 a type. The absorbance of P3HT polymer 1% has an absorption peak in the wavelength range of 300-650 nm. Thus the P3HT polymer material can absorb light in the visible wavelength range. The electrical properties of P3HT 1% indicate that the material has a response to light. In bright conditions, P3HT 1% shows a conductivity of 3.7x10-3Ω-1m-1 and in dark conditions 2.2x10-3Ω-1m-1. Meanwhile, Pt (Hexacloroplatinic IV) Platina as the opposing electrode can improve the performance of DSSC, which is because Pt (Hexacloroplatinic IV) functions as a catalyst to accelerate the redox reaction with electrolytes. The use of P3HT 1% can improve DSSC performance. DSSC using 1% P3HT and using Pt (Hexacloroplatinic IV) as the opposing electrode produced an efficiency value of 1.8x10-2%.

Design of Polarization-Independent Reflective Metalens in the Ultraviolet–Visible Wavelength Region

Flat lens or metalens, as one of the most important application branches of metasurfaces, has recently been attracting significant research interest. Various reflective and transmissive metalenses have been demonstrated in the terathertz, infrared and visible wavelength range. However, metalens operating in the ultraviolet (UV) wavelength range is rare. Moreover, the development of reflective UV metalens, the important counterpart of transmissive ones, falls far behind. In this work, with thorough investigation of material properties, we propose a reflective metalens based on silicon dioxide (SiO2) and aluminum (Al) that operates in the vacuum ultraviolet (VUV) to visible wavelength region. Four reflective metalenses were designed and optimized for wavelengths of 193, 441, 532 and 633 nm, and prominent focusing capability was observed, especially for the VUV wavelength of 193 nm. Dispersion characteristics of the metalenses were also studied within ±50 nm of the design wavelength, and negative dispersion was found for all cases. In addition, the SiO2 + Al platform can be, in principle, extended to the mid-infrared (IR) wavelength range. The reflective VUV metalens proposed in this work is expected to propel miniaturization and integration of UV optics.