Angular Distribution Of Light Research Articles

Operation Characteristics and Optical Emission Distribution of a Miniaturized Silicon Through-Substrate Split-Ring Resonator Microplasma Source

There are many new microplasma sources being developed for a wide variety of applications, each with different properties tailored to its specific use. Microplasma sources enable portable instruments for, e.g., chemical analysis, sterilization, or activation of substances. A novel microplasma source, based on a microstrip split-ring resonator design with electrodes integrated in its silicon substrate, was designed, manufactured, and evaluated. This device has a plasma discharge gap with a controlled volume and geometry, and offers straightforward integration with other microelectromechancial systems (MEMS) components, e.g., microfluidics. The realized device was resonant at around 2.9 GHz with a quality factor of 18.7. Two different operational modes were observed with the plasma at high pressure being confined in the gap between the electrodes, whereas the plasma at low pressures appeared between the ends of the electrodes on the backside. Measurement of the angular distribution of light emitted from the device with through-substrate electrodes showed narrow emission lobes compared with a reference plasma source with on-substrate electrodes.

Angular Dependence of Cathodoluminescence of Linear and Circular Au Gratings: Imaging the Coupling Angles between Surface Plasmon Polaritons and Light

We measured the wavelength-dependent angular light distribution upon cathodoluminescence of micrometer-sized linear and circular gold gratings to study the coupling of surface plasmon polaritons (SPP) to light. A point source of SPP was excited next to the gratings with an electron beam of a scanning electron microscope. Subsequent scattering of propagating SPP at the gratings led to emission of light. The observed angular emission pattern, i.e., the azimuthal and polar angles of the emitted light, could be well-explained within a simple model, considering momentum conservation upon the scattering process with the grating wave vector. Whereas the angular distribution of the emitted light was dependent on both grating period and shape, the spectral distribution was not significantly affected. Focusing of light coupled from SPP by sectors of circular gratings and narrow linear grating structures was also demonstrated.

Asymmetry of the angular distribution of Cherenkov photons of extensive air showers induced by the geomagnetic field

The angular distribution of Cherenkov light in an air shower is closely linked to that of the shower electrons and positrons. As charged particles in extensive air showers are deflected by the magnetic field of the Earth, a deformation of the angular distribution of the Cherenkov light, that would be approximately symmetric about the shower axis if no magnetic field were present, is expected. In this work we study the variation of the Cherenkov light distribution as a function of the azimuth angle in the plane perpendicular to shower axis. It is found that the asymmetry induced by the geomagnetic field is most significant for early stages of shower evolution and for showers arriving almost perpendicular to the vector of the local geomagnetic field. Furthermore, it is shown that ignoring the azimuthal asymmetry of Cherenkov light might lead to a significant under- or overestimation of the Cherenkov light signal especially at sites where the local geomagnetic field is strong. Based on CORSIKA simulations, the azimuthal distribution of Cherenkov light is parametrized in dependence on the magnetic field component perpendicular to the shower axis and the local air density. This parametrization provides an efficient approximation for estimating the asymmetry of the Cherenkov light distribution for shower simulation and reconstruction in cosmic ray and gamma-ray experiments in which the Cherenkov signal of showers with energies above 1014eV is observed.

47.4: Distinguished Paper: Realization of Outstandingly High Efficacy White OLED by Controlling Evanescent Mode and Wide Angular Incident Light

AbstractOptimization of angular light distribution in organic layer and light extraction structure based on high refractive index substrate were investigated. Due to advanced optical design for decreasing waveguide and evanescent modes, white OLED device with outstandingly high efficacy of 133 lm/W at 1,000 cd/m2 was realized.

57.4L: Late‐News Paper: Intelligent Backlight: A Controllable Illumination System for High Efficiency and Sunlight Readable Mobile Displays

AbstractA novel directional backlight system for transmissive LCD illumination is described for the first time. By controlling the angular light distribution from the display, very low power consumption can be achieved for a required display luminance, or the backlight can operate with a conventional luminance distribution. Additionally very high display luminance can be achieved at the same power consumption levels as conventional backlight designs. Such a display can achieve good readability in high illuminance conditions, for example in direct sunlight. The backlight optical stack comprises a stepped waveguide Directional Light Guide Plate (D‐LGP), a micro‐structured reflective film and a polarisation recirculation structure that cooperates with an LED array to direct viewing windows to an observer with high coupling efficiency. The system implementation is described and measured performance from demonstrator displays is presented.

Understanding the performance of Abbe-type refractometers with optically absorbing fluids**This paper was an invited article at the Sensors and Applications XVII conference.

We investigate the use of Abbe-type refractometers with homogeneous absorbing fluids. We derive a simple model based on electromagnetic optics to describe quantitatively the angular distribution of light around the critical angle and report some experimental tests. First, we verify experimentally that the diffusing film near the base of the prism does in fact deliver light that refracts up to the critical angle. Then we compare experimental profiles of refracted light around the critical angle with theoretical profiles, and find very good agreement. Finally, we use the model to analyze some requirements and limitations on using Abbe-type refractometers on absorbing fluids.

Computational Light Routing

Despite recent interest in digital fabrication, there are still few algorithms that provide control over how light propagates inside a solid object. Existing methods either work only on the surface or restrict themselves to light diffusion in volumes. We use multi-material 3D printing to fabricate objects with embedded optical fibers, exploiting total internal reflection to guide light inside an object. We introduce automatic fiber design algorithms together with new manufacturing techniques to route light between two arbitrary surfaces. Our implicit algorithm optimizes light transmission by minimizing fiber curvature and maximizing fiber separation while respecting constraints such as fiber arrival angle. We also discuss the influence of different printable materials and fiber geometry on light propagation in the volume and the light angular distribution when exiting the fiber. Our methods enable new applications such as surface displays of arbitrary shape, touch-based painting of surfaces, and sensing a hemispherical light distribution in a single shot.

Two-dimensional simulations of laser–plasma interaction and hot electron generation in the context of shock-ignition research

Laser–plasma interaction and hot electron generation play a crucial role in the context of inertial confinement fusion and in particular in the shock-ignition concept. Here we present a fully kinetic large-scale two-dimensional simulation studying laser–plasma interaction and hot electron generation in a relatively long and hot coronal plasma. The simulation shows saturation of the reflectivity of an intense spike pulse and absorption taking place close to a quarter critical density in particular, due to cavitation and stimulated Raman scattering. The signatures of steady two-plasmon decay are observed, but the hot electron number produced by this instability is low in comparison with the other two processes. The spectral and angular distribution of the back-scattered light is presented and the energy and angular characteristics of hot electrons due to individual absorption processes are studied.

Cherenkov light detection as a velocity selector for uranium fission products at intermediate energies

The in-flight particle separation capability of intermediate-energy radioactive ion (RI) beams produced at a fragment separator can be improved with the Cherenkov light detection technique. The cone angle of Cherenkov light emission varies as a function of beam velocity. This can be exploited as a velocity selector for secondary beams. Using heavy ion beams available at the HIMAC synchrotron facility, the Cherenkov light angular distribution was measured for several thin radiators with high refractive indices (n=1.9~2.1). A velocity resolution of ~10−3 was achieved for a 56Fe beam with an energy of 500MeV/nucleon. Combined with the conventional rigidity selection technique coupled with energy-loss analysis, the present method will enable the efficient selection of an exotic species from huge amounts of various nuclides, such as uranium fission products at the BigRIPS fragment separator located at the RI Beam Factory.

Virtual experiment for near-field goniophotometric measurements

Near-field goniometric measurements are employed to determine the photometric characteristics of light sources, i.e., the spatial and angular distribution of the emitted light. To this end, a complex measurement system consisting of a goniometer and a CCD-based imaging photometer is employed. In order to gain insight into the measurement system and to enable characterization of the whole measurement setup, we propose to apply a computer model to conduct virtual experiments. Within the computer model, the current state of all parts of the virtual experiment can be easily controlled. The reliability of the computer model is demonstrated by a comparison to actual measurement results. As an example for the application of the virtual experiment, we present an analysis of the impact of axial malpositions of the goniometer and camera.

Study of the Angular Distribution of Scintillation Photons

This paper presents a characterization method to experimentally determine the angular distribution of scintillation light. By exciting LYSO crystals with a radioactive source, we measured the light angular profiles obtained with samples of different geometries in different conditions of wrapping. We also measured the angular distribution of light emitting in glue and compared it with the one emitting in air. Angular distribution of light output of photonic crystals is also provided. Consistency of the measurements is verified with conventional light output measurements.

Plasmon-Enhanced Fluorescence Biosensors: a Review.

Surfaces of metallic films and metallic nanoparticles can strongly confine electromagnetic field through its coupling to propagating or localized surface plasmons. This interaction is associated with large enhancement of the field intensity and local optical density of states which provides means to increase excitation rate, raise quantum yield, and control far field angular distribution of fluorescence light emitted by organic dyes and quantum dots. Such emitters are commonly used as labels in assays for detection of chemical and biological species. Their interaction with surface plasmons allows amplifying fluorescence signal (brightness) that accompanies molecular binding events by several orders of magnitude. In conjunction with interfacial architectures for the specific capture of target analyte on a metallic surface, plasmon-enhanced fluorescence (PEF) that is also referred to as metal-enhanced fluorescence (MEF) represents an attractive method for shortening detection times and increasing sensitivity of various fluorescence-based analytical technologies. This review provides an introduction to fundamentals of PEF, illustrates current developments in design of metallic nanostructures for efficient fluorescence signal amplification that utilizes propagating and localized surface plasmons, and summarizes current implementations to biosensors for detection of trace amounts of biomarkers, toxins, and pathogens that are relevant to medical diagnostics and food control.

An Investigation of the Optical Analysis in White Light-Emitting Diodes With Conformal and Remote Phosphor Structure

An effective emission model of phosphor film is proposed by using bidirectional scattering distribution function system (BSDF), and the model is verified by white light-emitting diodes (LEDs) with conformal and remote phosphor structure. The emission model is built to clarify the optical characteristics by analyzing the angular-dependent distribution of emission and excitation behaviors in phosphor film. The white LEDs with conformal and remote phosphor structure are also fabricated for experimental comparison. The uniformity of angular correlated color temperature (CCT) in white LEDs can be determined by the angular distribution of blue and yellow light, which is in turns decided by the refractive index variation between chip a©nd phosphor layers. Finally, the experimental results are found to have good agreement with the simulation results performing by the Monte Carlo method.

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

Imperfect internal reflectance of near-bandgap light reduces the performance of all solar cells, and becomes increasingly detrimental as absorbers become thinner. We consider light incident on the silicon/dielectric/metal structure at the back of rear-passivated crystalline silicon solar cells with surface textures that are large enough for geometric optics. By calculating the absorbance in the metal as a function of the angle of incidence, we discover three results that are important for understanding and improving rear reflectors in many types of solar cells. First, significant parasitic absorption occurs in the metal layer in two cases: s- and p-polarized propagating modes (near-normal angles of incidence) when the dielectric thickness is adjusted to cause destructive interference of the reflected beams, and p-polarized evanescent modes (angles of incidence above the semiconductor/dielectric critical angle) that excite surface plasmon polaritons at the metal surface. Second, the latter loss dominates; a well-designed rear dielectric passivation layer must suppress the penetration of evanescent waves to the metal. Third, when used as an input in a simple analytical model, the average rear internal reflectance calculated by assuming a Lambertian angular distribution of light accurately predicts the total reflectance and absorbance of a solar cell.

Penetration of UV‐visible solar radiation in the global oceans: Insights from ocean color remote sensing

Penetration of solar radiation in the ocean is determined by the attenuation coefficient (Kd(λ)). Following radiative transfer theory, Kd is a function of angular distribution of incident light and water's absorption and backscattering coefficients. Because these optical products are now generated routinely from satellite measurements, it is logical to evolve the empirical Kd to a semianalytical Kd that is not only spectrally flexible, but also the sun‐angle effect is accounted for explicitly. Here, the semianalytical model developed in Lee et al. (2005b) is revised to account for the shift of phase function between molecular and particulate scattering from the short to long wavelengths. Further, using field data collected independently from oligotrophic ocean to coastal waters covering >99% of the Kd range for the global oceans, the semianalytically derived Kd was evaluated and found to agree with measured data within ∼7–26%. The updated processing system was applied to MODIS measurements to reveal the penetration of UVA‐visible radiation in the global oceans, where an empirical procedure to correct Raman effect was also included. The results indicated that the penetration of the blue‐green radiation for most oceanic waters is ∼30–40% deeper than the commonly used euphotic zone depth; and confirmed that at a depth of 50–70 m there is still ∼10% of the surface UVA radiation (at 360 nm) in most oligotrophic waters. The results suggest a necessity to modify or expand the light attenuation product from satellite ocean‐color measurements in order to be more applicable for studies of ocean physics and biogeochemistry.

Mie scattering from submicron-sized CO_2 clusters formed in a supersonic expansion of a gas mixture

A detailed mathematical model is presented for a submicron-sized cluster formation in a binary gas mixture flowing through a three-staged conical nozzle. By measuring the angular distribution of light scattered from the clusters, the size of CO(2) clusters, produced in a supersonic expansion of the mixture gas of CO(2)(30%)/H(2)(70%) or CO(2)(10%)/He(90%), has been evaluated using the Mie scattering method. The mean sizes of CO(2) clusters are estimated to be 0.28 ± 0.03 μm for CO(2)/H(2) and 0.26 ± 0.04 μm for CO(2)/He, respectively. In addition, total gas density profiles in radial direction of the gas jet, measuring the phase shift of the light passing through the target by utilizing an interferometer, are found to be agreed with the numerical modeling within a factor of two. The dryness (= monomer/(monomer + cluster) ratio) in the targets is found to support the numerical modeling. The apparatus developed to evaluate the cluster-gas targets proved that our mathematical model of cluster formation is reliable enough for the binary gas mixture.

Experimental and simulation study of thin film silicon solar cells with intermediate reflector

Optical and electrical simulations were carried out for thin film silicon solar tandem cells with intermediate reflector layer (IRL) between top and bottom cell and compared with experimental external quantum efficiency and current voltage characteristics results. Reference data were collected from a series of tandem cells with different thicknesses of the top cell absorber layer (160–240 nm), the bottom cell absorber layer (1750–2100 nm), and the transparent conductive oxides based IRL (10–80 nm). It turned out that for capturing correctly the influence of the IRL on the light management as a function of the IRL thickness, the conventional semicoherent approach is not sufficient. Whereas the optical properties of a very thin IRL are governed by interference effects that are best calculated using a fully coherent model, increasingly thicker IRL show a more and more incoherent behavior. By taking into account, the interface morphology and angular light distribution within the cell stack an algorithm for the effective IRL reflectivity was proposed that explains the experimental findings very well. The consecutive electrical simulations were carried out with the device simulator ASA. The dependence of short circuit current density jsc and fill factor FF on the thickness dIRL of the IRL is in qualitative agreement between simulation and experiment showing coincident extrema in jsc(dIRL) and FF(dIRL) at the current matching point. Copyright © 2013 John Wiley & Sons, Ltd.

Characterization of submicron-sized CO2 clusters formed with a supersonic expansion of a mixed-gas using a three-staged nozzle

The size of CO2 clusters, produced in a supersonic expansion of a mixed-gas of CO2/He or CO2/H2 through a three-staged conical nozzle designed based on the Boldarev's model, has been evaluated by measuring the angular distribution of light scattered from the clusters. The data are analyzed utilizing the Mie scattering theory, and the sizes of CO2 clusters are estimated as 0.22 μm and 0.25 μm for the cases of CO2/He and CO2/H2 gas mixtures, respectively. The results confirm that the Boldarev's model is reliable enough for the production of micron-sized clusters.

Two-dimensional modeling of optical transmission on the surface of a lenticular array for autostereoscopic displays

In this study, we suggest a customized model describing optical phenomena at the surface of a lenticular array for autostereoscopic displays in a mathematical form and analyzed the optical characteristics of lenticular array for the first time. We checked the validity of our mathematical model by examining and comparing our result with conventional lens theory. Monte Carlo simulations were performed to obtain the angular distribution of light from each sub-pixel corresponding to each views under actual design conditions. From the results, we think the optical model is very useful for designing optical parameters of autostereoscopic displays.

Yellow structurally modified fluorescence in the longhorn beetles Celosterna pollinosa sulfurea and Phosphorus virescens (Cerambycidae)

Celosterna pollinosa sulfurea and Phosphorus virescens are longhorn beetles which both have a sulphur-yellow pigmentary coloration and, more surprisingly, a yellow-green fluorescence coloration. In this study, we used a refined experimental examination to characterize the angular distribution of light and unveiled a different behavior between these reflection and emission processes. A key feature of these observations is the peculiar architecture of the scales (a three-dimensional photonic structure), which acts differently on each phenomenon. For reflection, this architecture can be viewed as a scattering device, while, for emission, it can be viewed as a waveguide. These effects were investigated by scanning electron microscopy (SEM), Bidirectional Reflectance Distribution Function (BRDF) diagrams and spectrophotometric measurements. Collection and analysis of data at every emergence direction was found to be crucial when studying optical properties in materials with spatial changes in composition at the scale of the light wavelength.