Angular Intensity Profile Research Articles

Polarization property of light scattered on dielectric nanorods at oblique incident angle

We report the study of light polarization property upon scattering off a dielectric nanorod in which the direction of the incident light is at an angle with respect to the cylinder main axis. The numerical work is done on the basis of the cylindrical Mie theory. It is shown that for incident light with different polarization, the resulted scattering cross-section spectra will also show different characteristics with varying incident angles. For TE case, resonance splitting is observed due to excitation of a new resonance mode, while for TM case, resonance merging is observed. An interference effect between different resonance modes due to variation of incident angle is then resulted in suppression of backward scattering intensity for TM case. Meanwhile, for TE case, at illumination angle approaching grazing angle, a spectral range exists whereby the scattered wave’s angular intensity profile forms a perpendicular dipolar feature with different polarization. The reported results may be useful for aplication of nanoantenna, photovoltaic, and polarization conversion.

Fourier series-based optimization of LED angular intensity profiles for displays and backlighting

A method using a Fourier series is demonstrated to optimize an LED array for local dimming applications in liquid crystal display backlighting. The same optimization method is also suitable for LED displays in which the Moire effect must be suppressed during photography with a minimum loss of spatial resolution. Initially, the angular intensity profile of a Lambertian LED is modelled when backlighting a Lambertian rear projection screen and compared to experimental data. An array of optimized LEDs and the resulting screen intensity pattern is then derived such that an intensity distribution with an intensity deviation of less than 2% is achieved. The angular intensity profile of the LED is modified using adjustable Fourier coefficients optimized according to an algorithm. The algorithm is designed to achieve an illuminated screen area of maximum size for a bounded LED backlight array to appear uniform in intensity to an observer. This Fourier series approach provides an elegant method to optimize the intensity profile of LED backlight arrays without the use of ray tracing.

The X-ray dust-scattered rings of the black hole low-mass binary V404 Cyg

We report on the first detection of X-ray dust scattered rings from the Galactic low mass X-ray binary V404 Cyg. The observation of the system with Swift/XRT on June 30 2015 revealed the presence of five concentric ring-like structures centred at the position of V404 Cyg. Follow-up Swift/XRT observations allowed a time-dependent study of the X-ray rings. Assuming that these are the result of small-angle, single X-ray scattering by dust grains along the line of sight, we find that their angular size scales as $\theta \propto\sqrt{t}$ in agreement with theoretical predictions. The dust grains are concentrated in five dust layers located at about 2.12, 2.05, 1.63, 1.50 and 1.18 kpc from the observer. These coincide roughly with locations of enhanced extinction as determined by infrared photometry. Assuming that the grain size distribution is described by a generalized Mathis-Rumpl-Nordsieck model, we find that the power-law index of the most distant cloud is $q\sim 4.4$, while $q \sim 3.5-3.7$ in all other clouds. We constrain at a $3\sigma$ level the maximum grain size of the intermediate dust layers in the range $0.16-0.20\,\mu$m and set a lower limit of $\sim 0.2\,\mu$m in the other clouds. Hints of an exponential cutoff at the angular intensity profile of the outermost X-ray ring suggest that the smallest grains have sizes $0.01 \mu{\rm m}\le \alpha_{\min} \lesssim 0.03\,\mu$m. Based on the relative ratios of dust column densities we find the highest dust concentration at $\sim 1.6$ kpc. Our results indicate a gradient in the dust properties within 1 kpc from V404 Cyg.

Vortex-based all-optical manipulation of stored light at low light levels.

We exploit the giant cross-Kerr nonlinearity of electromagnetically induced transparency (EIT) system in ultracold atoms to implement vortex-based multimode manipulation of stored light at low light levels. Using image-bearing signal light fields with angular intensity profiles, sinusoidal grating structures with phase-only modulation can be azimuthally imprinted on the stored probe light field, where the nonlinear absorption loss can be ignored. Upon retrieval of the probe light, collinearly superimposed vortex modes can be generated in the far field. Considering the finite size of atomic gas, the Fraunhofer diffraction patterns of the retrieved probe fields and their spiral spectra are numerically investigated, where the diffracted vortex modes can be efficiently controlled by tuning the weak signal fields. Our studies not only exhibit a fundamental diffraction phenomenon with angular grating structures in EIT system, but also provide a fascinating opportunity to realize multidimensional quantum information processing for stored light in an all-optical manner.

Modeling LED street lighting.

LED luminaires may deliver precise illumination patterns to control light pollution, comfort, visibility, and light utilization efficiency. Here, we provide simple equations to determine how the light distributes in the streets. In particular, we model the illuminance spatial distribution as a function of Cartesian coordinates on a floor, road, or street. The equations show explicit dependence on the luminary position (pole height and arm length), luminary angle (fixture tilt), and the angular intensity profile (radiation pattern) of the LED luminary. To achieve this, we propose two mathematical representations to model the sophisticated intensity profiles of LED luminaries. Furthermore, we model the light utilization efficiency, illumination uniformity, and veiling luminance of glare due to one or several LED streetlamps.

Grazing angle X-ray fluorescence from periodic structures on silicon and silica surfaces

Various 3-dimensional nano-scaled periodic structures with different configurations and periods deposited on the surface of silicon and silica substrates were investigated by means of the grazing incidence and grazing emission X-ray fluorescence techniques. Apart from the characteristics which are typical for particle- and layer-like samples, the measured angular intensity profiles show additional periodicity-related features. The latter could be explained by a novel theoretical approach based on simple geometrical optics (GO) considerations. The new GO-based calculations were found to yield results in good agreement with experiment, also in cases where other theoretical approaches are not valid, e.g., periodic particle distributions with an increased surface coverage.

Characterization of High-k Nanolayers by Grazing Incidence X-ray Spectrometry

The accurate characterization of nanolayered systems is an essential topic for today’s developments in many fields of material research. Thin high-k layers and gate stacks are technologically required for the design of current and future electronic devices and can be deposited, e.g., by Atomic Layer Deposition (ALD). However, the metrological challenges to characterize such systems demand further development of analytical techniques. Reference-free Grazing Incidence X-ray Fluorescence (GIXRF) based on synchrotron radiation can significantly contribute to the characterization of such nanolayered systems. GIXRF takes advantage of the incident angle dependence of XRF, in particular below the substrate’s critical angle where changes in the X-ray Standing Wave field (XSW) intensity influence the angular intensity profile. The reliable modeling of the XSW in conjunction with the radiometrically calibrated instrumentation at the PTB allows for reference-free, fundamental parameter-based quantitative analysis. This approach is very well suited for the characterization of nanoscaled materials, especially when no reference samples with sufficient quality are available. The capabilities of this method are demonstrated by means of two systems for transistor gate stacks, i.e., Al2O3 high-k layers grown on Si or Si/SiO2 and Sc2O3 layers on InGaAs/InP substrates.

Noise and analyzer-crystal angular position analysis for analyzer-based phase-contrast imaging

The analyzer-based phase-contrast x-ray imaging (ABI) method is emerging as a potential alternative to conventional radiography. Like many of the modern imaging techniques, ABI is a computed imaging method (meaning that images are calculated from raw data). ABI can simultaneously generate a number of planar parametric images containing information about absorption, refraction, and scattering properties of an object. These images are estimated from raw data acquired by measuring (sampling) the angular intensity profile of the x-ray beam passed through the object at different angular positions of the analyzer crystal. The noise in the estimated ABI parametric images depends upon imaging conditions like the source intensity (flux), measurements angular positions, object properties, and the estimation method. In this paper, we use the Cramér–Rao lower bound (CRLB) to quantify the noise properties in parametric images and to investigate the effect of source intensity, different analyzer-crystal angular positions and object properties on this bound, assuming a fixed radiation dose delivered to an object. The CRLB is the minimum bound for the variance of an unbiased estimator and defines the best noise performance that one can obtain regardless of which estimation method is used to estimate ABI parametric images. The main result of this paper is that the variance (hence the noise) in parametric images is directly proportional to the source intensity and only a limited number of analyzer-crystal angular measurements (eleven for uniform and three for optimal non-uniform) are required to get the best parametric images. The following angular measurements only spread the total dose to the measurements without improving or worsening CRLB, but the added measurements may improve parametric images by reducing estimation bias. Next, using CRLB we evaluate the multiple-image radiography, diffraction enhanced imaging and scatter diffraction enhanced imaging estimation techniques, though the proposed methodology can be used to evaluate any other ABI parametric image estimation technique.

Optical model enabling the use of Abbe-type refractometers on turbid suspensions

We derive a simple model for the angular-intensity profiles of diffuse light transmitted from a turbid colloid into a transparent medium of higher refractive index (RI) near the critical angle. Adjusting this model to experimental profiles obtained with an Abbe-type refractometer offers a sensitive and robust way of measuring the complex effective RI of highly scattering media.

SU-GG-T-98: Pencil Beam for Electron Intraoperative Radiotherapy. Early Results from Profile and Percentage Depth Dose Modelling

Purpose: To evaluate the feasibility and the accuracy of pencil beam modelling for electron intraoperative radiotherapy (IORT). Methods and materials: A complete set of dose measurements in water have been performed. They have been made with different source‐to‐applicator‐end distance, bevel angle, applicator size and beam energy. Dose measurements in air have also been made with one applicator size and bevel 0° to obtain initial pencil beam angular spread and fluence intensity profile. An Elekta Precise and a Varian 21 EX linacs have been used. Modelling has been carried out by Tecnicas Radiofisicas (Zaragoza, Spain) adapting a modified Hogstrom's pencil beam implemented in TPS PCRT3D for external Radiotherapy.Results: Different profiles have been obtained according to different machine and applicator design. Lack of accuracy has been kept within 2% or 3% in most of the reference profiles modelled. Nevertheless, it rose to more than 5% for little applicator size, 30° and 45° bevel angle and high energy when modelling Varian beams. Discrepancies for Elekta modelling data have appeared when increasing bevel angle. Additional difficulties have been found when modelling beam edges for little applicators. Besides, percentage depth dose have been modelled for both machines and discrepancies are under investigation. Conclusions: Pencil beam is able to model IORT beams in water for dose delivery calculation. A trade‐off between accuracy and linac time expense should be achieved. Thus, accuracy could be increased if taking extra dedicated data for each combination of energy and applicator size. Then, an improvement of modelling at beam edges should be expected, especially for large bevel angles. The authors expect that further research will lead to calculate absorbed dose in an IORT patient, turning an IORT virtual simulator developed by GMV (Madrid, Spain), Radiance, into a treatment planning system. Supported by grant PSE‐300000‐2009‐5. Ministerio de Ciencia e Innovacion. Spanish Government.

Saturated and efficient blue phosphorescent organic light emitting devices with Lambertian angular emission

The authors employ a microcavity to optimize the color of a phosphorescent organic light emitting device (OLED) based on the-sky blue phosphor FIrpic. The output of the OLED is filtered by scattering media to correct the angular emission intensity profile and eliminate the angular dependence of the color. With a holographic diffuser as the scattering medium, the microcavity OLED achieves an external quantum efficiency of (5.5±0.6)%, as compared to (3.8±0.4)% for a conventional structure. The color coordinates of the microcavity OLED with holographic diffuser are (x,y)=(0.116±0.004,0.136±0.010) with minimal angular color shift and a nearly ideal Lambertian angular emission profile.

Study of converging neutron guides for the cold neutron double-chopper spectrometer at J-PARC

Performance of converging neutron guides was studied for the cold neutron double-chopper spectrometer proposed for the spallation neutron source at J-PARC. Intensity, spatial distribution, and angular distribution of a neutron beam at a sample are compared for linearly tapered and elliptic geometries by Monte Carlo simulation. For low-energy neutrons, the flux on the sample is much increased by an elliptic geometry whose focal points are on the moderator and on the sample in compensation for the angular resolution. To keep a substantial gain for a wide energy range, an elliptic guide with one of the focal points far behind the moderator is better. It also gives good spatial and angular intensity profiles at the sample.

Experiments and simulations of Ar scattering from an ordered 1-decanethiol–Au(111) monolayer

A study of the scattering of Ar from a well-ordered standing-up phase of 1-decanethiol adsorbed on Au(111) at surface temperatures from 110 to 185 K is presented. The final energies and intensities were measured as a function of incident polar and azimuthal angles using incident energies from 65 to 600 meV. These experimental results are compared to classical trajectory calculations. Scattering shows two distinct exit channels. The higher energies are due to direct inelastic scattering and have the greatest intensities at glancing incident and final angles. The lower energy channel is due to trapping-desorption; it has a Maxwell–Boltzmann energy distribution at the surface temperature and a cosine angular intensity profile. The simulations show that the timescale for normal momentum accommodation is very fast. The parallel momentum accommodation takes slightly longer, dependent on the initial conditions, but is still complete within only a few picoseconds. The result is that much of the Ar undergoes trapping-desorption, and the promptly scattered direct inelastic component, which interacts with the surface for ∼1 picosecond, retains more of its parallel than perpendicular momentum, leaving the surface preferentially at glancing polar angles. Another interesting observation is that the energy exchange between the surface and the directly scattered Ar has a dependence on the incident azimuthal angle. This is, in a sense, another type of structure scattering, where it is the anisotropic elastic response of the surface rather than the corrugation that leads to the angular dependence of the atom scattering.

Line shapes in triple-resonance ionization spectroscopy

Line shapes in high-resolution triple-resonance ionization spectroscopy have been calculated and compared with experimental measurements on the 4s2 1S0 --> 4s4p 1P1 --> 4s4d 1D2 --> 4snf 1F3 --> Ca+ system of calcium. Calculations based on the density matrix formalism integrated the fundamental equations over experimental atomic angular and velocity distributions and laser intensity profiles. The measurements reveal and confirm all predicted structures arising from the complex coupling of four atomic states with three laser fields and the Doppler distribution of the atomic ensemble. Effects of different laser beam geometries on the line shapes have been investigated. The agreement between calculated and experimental spectra is generally good over a dynamic range of 10 orders of magnitude. Thus these calculations can accurately predict optical isotopic selectivity in multistep resonance ionization, with a value of S(opt) approximately 10(10) expected for detection of the ultratrace isotope 41Ca.

Enhanced backscattering of light by aggregation of particles in an absorbing and dense colloidal suspension

The angular intensity profile of the enhanced backscattering of light (EBL) is investigated experimentally with regard to the spatial distribution of particles suspended in a disordered, dense and absorbing medium. Particle aggregation is induced by adding NaCl solution to a colloidal suspension of polystyrene latex particles. We show experimentally that a decay slope of the peak intensity profile decreases suddenly at a certain concentration of NaCl due to the formation of fractal clusters. Such behaviour is shown to be independent of absorption. The dimension of the medium defined as a measure of the particle distribution is estimated by applying the EBL decay slope to the empirical formulae obtained in the previous study by Ishii et al (Ishii?K, Iwai?T and Asakura?T 1997 Opt. Rev. 4 643). As a result, we confirm that the EBL is applicable to the in situ monitoring of the aggregation process of particles without dilution of the suspension or degradation of accuracy by changes in absorption.

Imaging enhanced energy transfer in a levitated aerosol particle

Energy transfer experiments are carried out at dilute concentrations of donors (10−4 M, coumarine 334) and acceptors (5×10−6 M, sulforhodamine 101) in a levitated microdroplet (diameter, 2a=19 μm), using an aerosol particle fluorescence microscope. Microphotographs in donor and acceptor luminescence show that the transfer mechanism is not of a Förster type, but is mediated by morphology dependent resonances (MDRs) of the microdroplet. The transfer is vanishingly small in the central region of the droplet (r<0.9a), and grows to a pronounced maximum beneath the surface (active region), consistent with the theory of MDR-enhanced energy transfer. The angular intensity profile of the acceptor image, along with current theory, suggests that the energy transfer is a maximum with the donor and acceptor at equal distances on opposite sides of the droplet center, ∼18 μm apart. From photometry we measure an overall ratio of acceptor to total luminescence of 7%. Within the active region the transfer efficiency is above 50%. This yield is ∼1000× that expected from Förster transfer. This effect may be understood from a modification in the photon density of states in this region, which leads to efficient photon emission into MDRs.

Monte Carlo simulations of coherent backscatter for identification of the optical coefficients of biological tissues in vivo

A Monte Carlo model of light backscattered from turbid media has been used to simulate the effects of weak localization in biological tissues. A validation technique is used that implies that for the scatteringand absorption coefficients and for refractive index mismatches found in tissues, the Monte Carlo method is likely to provide more accurate results than the methods previously used. The model also has theability to simulate the effects of various illumination profiles and other laboratory-imposed conditions. A curve-fitting routine has been developed that might be used to extract the optical coefficients from theangular intensity profiles seen in experiments on turbid biological tissues, data that could be obtained in vivo.

(Ca, Sr)F 2 surface roughness effect on angle resolved XPS measurements

Nanometric scale surface morphology of layers on substrates can be investigated using angle dependent X-ray photoemission spectroscopy. Experimentally we differentiate the two typical surface forms of (Ca, Sr)F 2 for the (100) and the (111) orientations by means of angular photoemission intensity profiles. The surfaces of these fluorides are known to be terminated by facets in the case of the (100) orientation and to be flat in the case of the (111) orientation. We calculate the influence of an idealized triangular surface roughness of layers on photoemission intensity. The calculation is compatible with the measurements. We show that within certain conditions the intensity ratio ( I layer I substrate ) can be used as a measure of the substrate coverage.

Disordering of the (111) surface of germanium crystal near its bulk melting temperature

The reversible disordering transition of the Ge(111) surface near 1050 K (160 K below the bulk melting temperature) has been studied by low-energy electron diffraction (LEED). Measurements were made using a position-sensitive detection system with the following characteristics: maximum speed, ${10}^{5}$ electrons/sec; resolution, 256\ifmmode\times\else\texttimes\fi{}256 channels with up to ${2}^{16}$ counts per channel. LEED peak and total (integrated) intensities I were recorded for varying electron energy E [I(E) plots] or varying crystal temperature T [I(T) plots]. Angular intensity profiles and intensity contour plots were also recorded. The I(E) plots are interpreted to indicate that layerlike crystalline order is preserved in the transition, up to but possibly not including the outermost double layer. The angular intensity profiles are interpreted to rule out thermal roughening as a disordering mechanism. The ratios of nonspecular beam intensities to the specular beam intensity for T>1050 K are found to be incompatible with a surface-melting mechanism like that described by molecular-dynamics (MD) simulations. The I(T) plots exhibit features, such as ranges of positive slope, which cannot be explained by any previously proposed mechanism of surface disordering. The intensity contour plots for T near 1050 K reveal satellite peaks which also have no conventional explanation. A domain-disordering mechanism is proposed to explain the observations qualitatively. In this mechanism, the domains are laterally strained to a depth of one double layer of crystalline Ge(111). The disordering is described as a loss of registry between the strained domains and the substrate. The possible role of intrinsic lateral compressive stress at the Ge(111) surface is discussed with reference to the observations, the disordering mechanism, and relevant MD simulations. Experimental results for Ge crystal films and a theoretical treatment of LEED from strained domains are presented in the Appendixes.

Modeling of Non-Gaussian Beamlet Profile Based on Total-Beam Power Loss and Transmission

The angular intensity profile of a single beamlet is expressed as a sum of a main Gaussian and a bump-on-the-tail representing the optical aberration. Transmission of a total beam comprised of a large number of beamlets is then analytically derived. By an iterative matching of the calculated transmissions to the measured transmissions through at least two downstream openings, the parameters that describe the single beamlet angular profile are determined. Some of the neutral beam injectors employed for heating fusion plasmas are characterized by this modeling. Also presented is an improved algorithm for calculating the intensity distribution at a downstream plane.