Different Angles Of Light Incidence Research Articles

Application of Plasmonic Nanoantennas in Enhancing the Efficiency of Organic Solar Cells

It is known that the periodic use of silver nanoantennas in organic solar cells increases the efficiency of light absorption. In this study, we performed a geometric parametric analysis of nanoantennas using the finite element method. Based on the study of the convex truncated cone nanoantenna, we have found that a nanoantenna arrangement formed by the convex truncated cone nanoantenna along with a pyramidal nanoantenna provides a better solution for different angles of light incidence compared to a single nanoantenna. We obtained a mean increase in the absorption efficiency of this organic solar cell, both for the TM and TE polarizations, compared to the use of the conventional nanoantenna in the wavelength range of 300–800 nm.

Wet Imprinting of Channel-Type Superstructures in Nanostructured Titania Thin Films at Low Temperatures for Hybrid Solar Cells.

Hierarchically structured titania films, exhibiting interconnected foam-like nanostructures and large-scale channel-type superstructures, were achieved in an energy-saving way at low temperatures by a polymer template-assisted sol-gel synthesis in combination with a wet-imprinting process. The surface morphology was probed with scanning electron microscopy and atomic force microscopy, whereas the inner morphology was characterized with grazing incidence small-angle X-ray scattering measurements. Compared to the initial hybrid films, the titania films showed reduced structure sizes caused by removal of the polymer template. UV/Vis measurements showed an additional light-scattering effect at various angles of light incidence in the hierarchically structured titania films, which resulted in higher light absorption in the wet-imprinted active layer. To give proof of viability, the titania films were evaluated as photoanodes for dye-free hybrid solar cells. The dye-free layout allowed for low-cost fabrication, avoided problems related to dye bleaching, and was a more environmentally friendly alternative to using dyes. Under different angles of light incidence, the enhancement in the short-circuit current density was in good agreement with the improvement in light absorption in the superstructured active layer, demonstrating a positive impact of the superstructures on the photovoltaic performance of hybrid solar cells.

HfO2 Nanorod Array as High‐Performance and High‐Temperature Antireflective Coating

Antireflective (AR) coating with both high antireflectance and omnidirectional characteristic is desired for many advanced optical device applications and photovoltaic thin‐film solar cells. The application of double‐layer antireflective (DLAR) coating to reduce reflectance is largely constrained at wide wavelength range due to refractive index variation within individual layer and between the air–substrate interfaces. In this article, high performance gradient refractive index double‐layer AR coatings with periodically patterned hierarchical porous hafnia nanorods that mimic moth compound eyes are fabricated on a dense hafnia matrix layer using glancing angle deposition technique. The refractive indices for the top and bottom layers of the DLAR hafnia coatings are 1.36 and 1.87. The fabricated films possess high transparency showing zero reflectance at calculated wavelength of 550 nm but also give <1% reflectance over broad range of visible spectrum at different angles of light incidence displaying its omnidirectional characteristic. The shifting and tuning of reflectance to nearly <1% in visible, infrared, and ultraviolet regions was achieved for wide range of substrate materials by tailoring refractive index through porosity and film thickness of the two layers. Moreover, the DLAR hafnia thin films show high thermal stability at high temperatures up to 300 °C.

Iridescent (angle-dependent reflectance) properties of dorsal coloration in Podarcis muralis (Laurenti, 1768)

Iridescence is a visual property of those surfaces that change in colour with viewing angle. Iridescence has been rarely reported in reptiles, but some snakes and lizards show this type of coloration. Here we study the effect of different angles of light incidence and observation on the spectrophotometrically assessed reflectance of dorsal coloration in the lizard Podarcis muralis. The results demonstrate clear angle dependence of several colour parameters. In particular, different angles of light incidence and observation result in changes in hue of more than 30 nm. This suggests that lizard dorsal coloration may be perceived, depending on viewing geometry, as being of different colours by a wide range of potential observers. Functional implications of iridescence in dorsal coloration are discussed.

Photoelastic and Acousto-optic Properties of KDP Crystal Applied in Wide Angle Tunable Filters

The paper presents results on calculation and measurement of acousto-optic properties of KDP crystals applied in imaging tunable acousto-optic filters operating in the ultraviolet region of electromagnetic light. Effective photoelastic coefficients and acousto-optic figures of merit are evaluated in the mode of wide angle diffraction. The carried out analysis is based on results of measurements of the efficiency of Bragg diffraction at the same frequency of ultrasound but at two different angles of light incidence in the KDP crystal. We used the crystal in an imaging acousto-optic tunable filter operating at the wavelengths of light 405, 532 and 633nm. The filters apply a slow shear acoustic wave propagating at the angles α=90 and α=120 relatively to the [100] axis in (010) plane of the crystal. Differences between the measured data on the photoelastic coefficients and those found in literature are discussed in the presentation.

Abandoned Functionality of Thin‐Film Opal Photonic Crystals

Angle‐resolved polarized transmission spectra of thin‐film opals are studied experimentally and theoretically as a function of the azimuthal rotation of the plane of incidence at different angles of light incidence. In such 3‐dimensional lattices, the refraction acquires the form of diffraction orders, each with a distinct spectrum, that propagate simultaneously along different directions. The corresponding continuous and patchy stop‐bands in the photonic energy band structure of the opal photonic crystal are determined numerically. For diffraction at high Miller index planes, the diffraction pattern is often distorted due to multiple‐wave diffraction. The finite stacking of hexagonally close‐packed layers leads to an intrinsic 3‐fold rotation symmetry of these spectra, which is particularly pronounced in transmission for frequencies that correspond to wave vectors within the 1st Brillouin zone. Despite the cubic symmetry of the opal lattice, cross‐polarization coupling effects occur in the volume of the opal crystal. These effects are associated with the fact that, the opal eigenmodes are Bloch waves whose electromagnetic field distributions and dispersion relations are markedly different from plane waves.

DESIGN AND ANALYSIS OF COLORED SOLAR SELECTIVE ABSORBING FILMS WITH THREE-LAYER STRUCTURE

Using glasses with 200-nm Cu films as substrates, the colored solar energy selective absorbing films with three-layer structure had been designed by optical multilayer design software. The three layers materials were Fe doped AlN and AlN . The optical constants of Fe doped AlN films with different Fe volume fractions were calculated by the effective medium theories. The color of the absorbing films includes orange yellow, purplish pink, pink, purple, and green. The solar absorptance of each colored film is between 0.89 and 0.96. The thermal emittance is lower than 0.1. The green film has the highest brightness. The purplish pink film has the highest absorptance, while the orange yellow and purple films have the lowest emittance. The color, absorptance, emittance, and brightness of the green film at different angles of light incidence had been analyzed. When the incident angle increases from 0° to 50°, the color of the green film changes from green to blue, and its absorptance and emittance decrease.

Depth-profiling of elastic and optical inhomogeneities in transparent materials by picosecond ultrasonic interferometry: Theory

The theoretical backgrounds for the depth-profiling of the optically transparent materials by picosecond ultrasonic interferometry are developed. The mathematical description of the light reflection from inhomogeneous transparent films or coatings is proposed. The inhomogeneity can be caused both by the film synthesis (intrinsic stationary inhomogeneity) and by the short acoustic transients launched in the film (time-dependent inhomogeneity). The theory indicates that the measurements of the complex optical reflectivity time evolution, caused by acoustic strain pulse propagation in such films, offer various possibilities to extract the depth profiles of intrinsic inhomogeneous distributions of mechanical/acoustical, optical, and acousto-optical parameters of the films. In particular it is proposed how the measurements of the transient complex optical reflectivity by the femtosecond optical interferometers, operating with light of different polarizations and probing the tested samples at different angles of light incidence, can be used. The spatial resolution of the method is limited by the acoustic spatial scale which, for picosecond acoustic pulses, is much shorter than optical wavelength.

A transmission line model for the optical simulation of multilayer structures and its application for oblique illumination of an organic solar cell with anisotropic extinction coefficient

A transmission line model for the calculation of optical interference phenomena in dielectric multilayered structures is adopted as an alternative option to the transfer matrix model (TMM). The method is based on the transmission line theory and is exact, easy to implement and uses closed iterative forms instead of the TMMs matrix formalism. The proposed model has been appropriately modified and then applied for performance evaluation of a typical organic photovoltaic device under inclined illumination. Optical field distribution, short-circuit photocurrent and reflectivity have been calculated under different angles of light incidence. The theoretical simulations have been discussed and compared with experimental photocurrent measurements, while the influence of the photoactive layer thickness on the device efficiency has been evaluated for different angles of light incidence, taking into account its extinction coefficient anisotropy.

Study of Surface Roughness of CsI:Tl Crystals Treated by Various Abrasives

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The study of the surface roughness of CsI:Tl scintillators processed by abrasives with different grain size was performed to obtain the surface characteristics that are important for simulation of light collection processes in scintillators. The degree of roughness of the surface was studied qualitatively, by optical microscopy, and quantitatively, by measuring reflectance distribution functions at different angles of light incidence on the samples. Micrographs of the sample surfaces, obtained by means of optical microscopy, allowed the estimation of the typical roughness for each abrasive. The micro-facet slope distribution functions were extracted from the measured reflectance distribution. It was found that these functions depend mainly on the grain size of the abrasive. For the same abrasive, the micro-facet slope distribution functions do not depend on the incidence angle, which is a good demonstration of the reliability of the results. To demonstrate how the variation of the surface roughness influences the light collection, the pulse-height spectra of the scintillator samples with different surface treatments were measured. Micro-facet slope distributions obtained for CsI:Tl can be used for the simulation of light collection processes in different scintillators with similar hardness and elastic properties. </para>

Optical characterization of thin chalcogenide films by multiple-angle-of-incidence ellipsometry

Optical properties of thin chalcogenide films from the systems As–S(Se) and As–S–Se were investigated as a function of the film composition, film thickness and conditions of illumination by light using multiple-angle-of-incidence ellipsometry. Thin films were deposited by thermal evaporation and exposed to white light (halogen lamp) and to monochromatic light from Ar + — ( λ = 488, 514 nm) and He–Ne- ( λ = 632.8 nm) lasers. The ellipsometric measurements were carried out at three different angles of light incidence in the interval 45–55°, at λ = 632.8 nm. An isotropic absorbing layer model was applied for calculation of the optical constants (refractive index, n and extinction coefficient, k) and film thickness, d. The homogeneity of the films was checked and verified by applying single-angle calculations at different angles. It was shown that the refractive index, n of As–S–Se films is independent of film thickness in the range of 50 to 1000 nm and its values varied from 2.45 to 3.05 for thin layers with composition As 2S 3 and As 2Se 3, respectively. The effect of increasing in the refractive index was observed after exposure to light which is related to the process of photodarkening in arsenic containing layers. The viability of the method for determining the optical constants of very thin chalcogenide films with a high accuracy was confirmed.

Photoemission along the surface normal of Cu(001): experiment and theory

Experimental normal photoemission spectra from Cu(100) were taken with linearly polarised synchrotron radiation at photon energies between 13 and 48 eV and at two different angles of light incidence. They are compared with intensity profiles calculated by nonrelativistic 'one-step-model' theory including a classical macroscopic radiation field inside the crystal. All direct transition features of the spectra are reproduced quite well, while agreement in detail is not yet perfect. Several possibilities for improving the agreement are discussed.

Electronic orbitals of Se bonded to Ni(100)

New angle-integrated UPS spectra are presented at different angles of light incidence for NeI radiation on Ni(100) c (2×2)Se. These spectra show that a Se-derived orbital lies in the energy range of the Ni d band as suggested by Fisher. The corresponding INS spectrum is also given and discussed. It is shown that the present Ni sample produces a two-domain c (2×5)Se structure at one-quarter monolayer as opposed to the p (2×4)Se structure observed on earlier samples.

Direct Optical Excitation of the Surface Photoelectric Effect

Measurements on Al of the ratio of the photoyields by $p$- and $s$-polarized light, $\frac{{Y}_{p}}{{Y}_{s}}$, and the absolute yield for $p$-polarized light ${Y}_{p}$, at different angles of light incidence and at energies near photoemissive threshold, give results which are in excellent agreement with the strength of the surface photoelectric effect implied in recent calculations.