Multiple surface plasmon waves in [prism/Ag/SiO2 helical thin film] Kretschmann configuration

Two surface plasmon resonance dips in reflectance angular spectrum for a p-polarized incident beam of a [prism/Ag/SiO₂ helical thin film] Kretschmann configuration are measured and compared with simulations. The simulation also shows that the angular positions of resonances due to surface plasmon waves in reflectance spectrum are sensitive to the variation of principal refractive indices of helical films. It indicates that multiple surface plasmon waves at the [Ag/SiO₂ helical thin film] interface is more attractive than the traditional method of producing only one surface plasmon wave for chemical- and bio-sensing applications.     

Optical and topographical properties of selective black chrome

The optical and surface topographical properties of black chrome deposited onto differently treated substrates were investigated to study the effect of substrate surface roughness. Coatings with a solar absorptance α_s of 0.94 and a thermal emittance ε of 0.14 at 100 °C were obtained on steel substrates with dull nickel overlayers and anodically etched nickel overlayers. A polarimetric technique was employed to study the angular dependence of the reflectance of the coatings.     

Experimental and simulated angular profiles of fluorescence and diffuse reflectance emission from turbid media

Given the wavelength dependence of sample optical properties and the selective sampling of surface emission angles by noncontact imaging systems, differences in angular profiles due to excitation angle and optical properties can distort relative emission intensities acquired at different wavelengths. To investigate this potentiality, angular profiles of diffuse reflectance and fluorescence emission from turbid media were evaluated experimentally and by Monte Carlo simulation for a range of incident excitation angles and sample optical properties. For emission collected within the limits of a semi-infinite excitation region, normalized angular emission profiles are symmetric, roughly Lambertian, and only weakly dependent on sample optical properties for fluorescence at all excitation angles and for diffuse reflectance at small excitation angles relative to the surface normal. Fluorescence and diffuse reflectance within the emission plane orthogonal to the oblique component of the excitation also possess this symmetric form. Diffuse reflectance within the incidence plane is biased away from the excitation source for large excitation angles. The degree of bias depends on the scattering anisotropy and albedo of the sample and results from the correlation between photon directions upon entrance and emission. Given the strong dependence of the diffuse reflectance angular emission profile shape on incident excitation angle and sample optical properties, excitation and collection geometry has the potential to induce distortions within diffuse reflectance spectra unrelated to tissue characteristics.     

High reflectance materials for photovoltaics applications: analysis and modelling

The paper involves reflectance structures fabricated with application of sol–gel method. High reflectance was obtained through the fabrication of one-dimensional photonic crystals on glass substrate. The paper presents both the results of theoretical analysis as well as the results of experimental studies. Using the 2 × 2 transfer matrix method, we determined reflectance and transmittance characteristics of the analyzed structures as well as power distributions in the photonic crystals. The one-dimensional photonic crystals were fabricated by the successive deposition of quarter-wave layers of silica and titania on glass substrate using the dip-coating method. For the fabricated reflectance structures with four bilayers (TiO₂/SiO₂), for the wavelength ~500 nm we have obtained the reflectance value equal to 0.933, and for the structures with five bi-layers the reflectance was equal to about 0.967. The uniformity of the fabricated structures and the repeatability of the technological process are discussed. We discuss also some slight divergence between theoretical predictions and experimental results.     

Angle resolved color of bulk scattering media

The angle resolved reflectance factor of matte samples is measured with a goniophotometer and simulated using radiative transfer theory. Both measurements and simulations display the same characteristic dependence of the reflectance factor on the observation angle. The angle resolved reflectance spectra are translated to CIELAB color coordinates and the angular color differences are found to be surprisingly large. A chromatic adaptation that is dependent on the observation angle is suggested, in which a nonabsorbing opaque medium is used as the reference white, and the angular color differences are then reduced. Furthermore, the use of an undyed paper as the reference white is evaluated. The angular lightness differences are then reduced further, but the angular differences in chroma are still large. It is suggested that smaller variations in perceived color could be explained by angle dependent chromatic adaptation and a limited sensitivity of the human visual system to changes in chroma.     

Optical excitation of surface plasma waves in an indium film bounded by dielectric layers

The method of attenuated total reflection (ATR) was used to excite optically surface plasma waves (SPWs) in thin indium films. Three successive layers of MgF₂/In/MgF₂ were evaporated onto the base of a glass prism which had a high refractive index. Continous thin films of indium were obtained by maintaining the substrate at liquid nitrogen temperature during deposition. The ATR angular spectra and associated resonant oscillations were studied at three different wavelengths in the visible region and good agreement was obtained between the experimental and the calculated spectra. The symmetric SPW of the indium film was more highly attenuated than the antisymmetric SPW. Owing to the high damping of the plasma in indium only the antisymmetric SPW could be excited via an optical reflectance resonance when the indium slab was isolated by thick dielectric layers. With thinner bounding dielectrics two SPW-type resonances were observed. Complete calculations of the magnetic field oscillations within the variousmedia, as well as calculations of the current distributions and surface charge densities of the indium film, showed resonant oscillations of mixed symmetry.     

K Correlations and Facet Models in Diffuse Scattering

The angular intensity distribution of radiation scattered by a wide range of random media can be accounted for by assuming effective source amplitude correlations involving modified Bessel functions K _v. We investigate how such correlations can be derived from physical models of stochastic scattering systems, namely facet models with suitable slope distribution, and consider the cases of constant and varying r.m.s. slope or facet size. We study the pertinent photon statistics of the radiation scattered by these model systems and look for a link between K correlations and K distributions. As an application we revisit the concepts and laws of diffuse reflectance and discuss the existence of lambertian scatterers.     

An inherent-optical-property-centered approach to correct the angular effects in water-leaving radiance

Remote-sensing reflectance (R(rs)), which is defined as the ratio of water-leaving radiance (L(w)) to downwelling irradiance just above the surface (E(d)(0?)), varies with both water constituents (including bottom properties of optically-shallow waters) and angular geometry. L(w) is commonly measured in the field or by satellite sensors at convenient angles, while E(d)(0?) can be measured in the field or estimated based on atmospheric properties. To isolate the variations of R(rs) (or L(w)) resulting from a change of water constituents, the angular effects of R(rs) (or L(w)) need to be removed. This is also a necessity for the calibration and validation of satellite ocean color measurements. To reach this objective, for optically-deep waters where bottom contribution is negligible, we present a system centered on water's inherent optical properties (IOPs). It can be used to derive IOPs from angular R_rs and offers an alternative to the system centered on the concentration of chlorophyll. This system is applicable to oceanic and coastal waters as well as to multiband and hyperspectral sensors. This IOP-centered system is applied to both numerically simulated data and in situ measurements to test and evaluate its performance. The good results obtained suggest that the system can be applied to angular R(rs) to retrieve IOPs and to remove the angular variation of R(rs).     

On the determination of the optical constants n(λ) and α(λ) of thin supported films

A general method was developed to determine the optical constants n(λ) and α(λ) for a thin semiconducting or metallic supported film from five or three measurements of the transmittance and the reflectance.Exact formulae were deduced for oblique incidence transmittance and reflectance considering multiple coherent reflections in the films and incoherent reflections in the non-absorbing substrate. A computer program was developed that, when used as a subroutine of a European Organization for Nuclear Research program called MINUIT, allowed the method to be tested for gold, silicon, CdS, Cu₂S (chalcocite) and Cu_1.96S (djurleite) polycrystalline films.A residual function shows good agreement between the calculated and measured values of the transmittance and the reflectance when a careful choice of the value of the thickness is made.     

Angular distribution of diffuse reflectance in biological tissue

We measured angular-resolved diffuse reflectance in tissue samples of different anisotropic characteristics. Experimental measurements were compared with theoretical results based on the diffusion approximation. The results indicated that the angular distribution in isotropic tissue was the same as in isotropic phantoms. Under normal incidence, the measured angular profiles of diffuse reflectance approached the Lambertian distribution when the evaluation location was far away from the incident point. The skewed angular profiles observed under oblique incidence could be explained using the diffuse model. The anisotropic tissue structures in muscle showed clear effects on the measurements especially at locations close to the light incidence. However, when measuring across the muscle fiber orientations, the results were in good agreement with those obtained in isotropic samples.     

Fabrication of vertically aligned CuInSe2 nanorod arrays by template-assisted mechanical approach

A facile, low cost, and vacuum free method for fabricating vertically aligned copper indium diselenide (CuInSe₂) nanorod (NR) arrays from pre-synthesized CuInSe₂ nanoparticles (NPs) by mechanical approach using porous anodic aluminum oxide (AAO) as a template was demonstrated. This approach utilizes a rubbing technique to fill CuInSe₂ NPs suspension into AAO template. X-ray diffraction and Raman spectroscopy study is employed to confirm the phase of CuInSe₂ NPs before and after the formation of NRs. The polycrystallinity and composition of NRs are confirmed by using transmission electron microscopy. Optical studies of CuInSe₂ NPs film reveal a reflectance of ∼9.8% while a significant reduction of the reflectance to ∼1.2% is observed after the formation of CuInSe₂ NR arrays. The observed low reflectance behavior is attributed to a concept of gradual refractive index with vertical array structures. From differential reflectance spectra of CuInSe₂ NRs, a band gap of ∼1.01 eV was observed, which is identical to its bulk value.     

Critical field and impurity scattering: Application to layered and 3D superconducting systems

An efficient and rigorous method of evaluating the critical fieldH _c2 is developed. The method allows one to consider in a regular way the angular dependence of the scattering cross-section. The method is applied to layered and 3D superconductors.     

Small-angle measurement by use of a single prism

A new method of angle measurement based on the internal reflection effect is proposed that uses a single right-angle prism. We measure the angular displacement between a laser beam and the prism by detecting the changes in reflectance as a function of the angle of incidence. We achieve high linearity of measurement by taking the inverse of reflectance as the output. The inverse of reflectance is obtained from the intensities of the reflected and the transmitted beams measured by two photodiodes. Experiments with a prototype device have demonstrated that angle measurement with a range of ?500 arc sec, a nonlinearity error of ?0.1%, and a resolution of 0.1 arc sec can be readily achieved. The measurement range can be further increased with some sacrifice of linearity.     

Molybdenum-doped vanadium dioxide coatings on glass produced by the aqueous sol-gel method

Thin films of vanadium dioxide (VO₂) on glass substrates were produced by the aqueous sol-gel method. Various levels of doping were achieved by adding small quantities of a water-soluble molybdenum compound to the sol. After dip coating, the substrates were reduced by heat treatment in a low-pressure carbon monoxide/carbon dioxide (CO/CO₂) atmosphere. The change in electrical conductivity with temperature, and optical reflectance in the semiconductor and metallic phases were measured and compared to undoped VO₂ films. Doping the VO₂ films with molybdenum lowered the transition temperature of the semiconductor-to-metal phase change; at a doping level of 7 at.% the transition temperature was measured at 24 °C, as indicated by the electrical conductivity. All the films showed a substantial change in reflectance upon heating through the transition. The optical reflectance in the semiconductor state increased slightly with additional dopant, while the reflectance in the metallic state remained constant.     

Parametric optimization of narrow bandstop optical filters using the self-suspended subwavelength grating for TE polarization

Instead of a conventional fixed multilayer grating, a self-suspended subwavelength grating (SSG) which consists of a single grating layer and possesses tunable functions, is investigated by the rigorous coupled-wave method in detail. Through optimizing various parameters including the incident wavelength, the grating period, the grating thickness and the grating filling factor, we demonstrate that the silicon dioxide (SiO₂) SSG owns a narrow reflectance linewidth in the case of TE polarization. For the SiO₂ SSG, the reflectance peak splits into two branches when the incident light deviates from normal incidence. In addition, the reflectance property of the SiO₂ SSG with unoptimized parameters is also presented for comparison, which exhibits a much larger reflectance linewidth. It is expected that the SiO₂ SSG should be used as narrow bandstop optical filters for TE polarization in micro optics systems.     

Influence of the angular shape of the volume-scattering function and multiple scattering on remote sensing reflectance

Scattering phase functions derived from measured (volume-scattering meter, VSM) volume-scattering functions (VSFs) from Crimean coastal waters were found to have systematic differences in angular structure from Fournier-Forand (FF) functions with equivalent backscattering ratios. Hydrolight simulations demonstrated that differences in the angular structure of the VSF could result in variations in modeled subsurface radiance reflectances of up to +/-20%. Furthermore, differences between VSM and FF simulated reflectances were found to be nonlinear as a function of scattering and could not be explained with the single-scattering approximation. Additional radiance transfer modeling demonstrated that the contribution of multiple scattering to radiance reflectance increased exponentially from a minimum of 16% for pure water to a maximum of approximately 94% for turbid waters. Monte Carlo simulations demonstrated that multiple forward-scattering events were the dominant contributors to the generation of radiance reflectance signals for turbid waters and that angular structures in the shape of the VSF at forward angles could have a significant influence in determining reflectance signals for turbid waters.     

Synthesis of ZnO/Zn2SiO4/SiO2 composite pigments with enhanced reflectance and radiation-stability under low-energy proton irradiation

ZnO/Zn₂SiO₄/SiO₂ composite pigments with nano-sized α-Zn₂SiO₄ interface phase were synthesized by a simple solid-state reaction method. It was found that the composite pigments exhibit significant improvement on the spectral reflectance and the proton radiation-stability compared with the pure ZnO pigment. The investigations have demonstrated that the enhancements on the spectral reflectance and the radiation-stability are attributed to the introduction of willemite Zn₂SiO₄ interface phase on the surface of ZnO matrix particles. In addition, the enhancement mechanisms of radiation-stability for ZnO/Zn₂SiO₄/SiO₂ composite pigments were discussed.     

Integrated three-dimensional shape and reflection properties measurement system

Creating accurate three-dimensional (3D) digitalized models of cultural heritage objects requires that information about surface geometry be integrated with measurements of other material properties like color and reflectance. Up until now, these measurements have been performed in laboratories using manually integrated (subjective) data analyses. We describe an out-of-laboratory bidirectional reflectance distribution function (BRDF) and 3D shape measurement system that implements shape and BRDF measurement in a single setup with BRDF uncertainty evaluation. The setup aligns spatial data with the angular reflectance distribution, yielding a better estimation of the surface's reflective properties by integrating these two modality measurements into one setup using a single detector. This approach provides a better picture of an object's intrinsic material features, which in turn produces a higher-quality digitalized model reconstruction. Furthermore, this system simplifies the data processing by combining structured light projection and photometric stereo. The results of our method of data analysis describe the diffusive and specular attributes corresponding to every measured geometric point and can be used to render intricate 3D models in an arbitrarily illuminated scene.     

Crystallization and spectroscopic studies of manganese malonate

The preparation of manganese malonate crystals by gel method and its spectroscopic studies are reported. X-ray diffraction (XRD) pattern reveals the crystalline nature. The FTIR and FT Raman spectra of the crystals are recorded and the vibrational assignments are given with possible explanations. Diffuse reflectance spectroscopy (DRS) is used to measure the bandgap (E _g) of the material.     

Modeling the bidirectional reflectance of emissive displays

The reflection properties of a display device influence the available contrast and affect the perception of subtle detail. The display reflection characteristics of flat-panel displays (FPDs) are appropriately described by a six-dimensional bidirectional reflectance distribution function (BRDF). I describe a Monte Carlo method for modeling the bidirectional reflectance of multilayer emissive structures used in electronic display devices. I estimate the complete BRDF using a one-dimensional angular distribution function of the luminance. I apply the method to model typical high-performance cathode-ray tube and FPD structures. I find that, for the BRDF signatures of cathode-ray tubes characterized by a specular and a quasi-Lambertian components, the estimated values for the specular and diffuse reflection coefficients agree well with low-resolution experimental measurements conducted with a rotation arm and a collimated probe. I show that emissive FPDs with thin-film organic layers on reflective substrates can exhibit a predominant specular peak broadened by short-range light scattering.