Ray-tracing Calculations Research Articles

Changes in monkey crystalline lens spherical aberration during simulated accommodation in a lens stretcher.

The purpose of this study was to quantify accommodation-induced changes in the spherical aberration of cynomolgus monkey lenses. Twenty-four lenses from 20 cynomolgus monkeys (Macaca fascicularis; 4.4-16.0 years of age; postmortem time 13.5 ± 13.0 hours) were mounted in a lens stretcher. Lens spherical aberration was measured in the unstretched (accommodated) and stretched (relaxed) states with a laser ray tracing system that delivered 51 equally spaced parallel rays along 1 meridian of the lens over the central 6-mm optical zone. A camera mounted below the lens was used to measure the ray height at multiple positions along the optical axis. For each entrance ray, the change in ray height with axial position was fitted with a third-order polynomial. The effective paraxial focal length and Zernike spherical aberration coefficients corresponding to a 6-mm pupil diameter were extracted from the fitted values. The unstretched lens power decreased with age from 59.3 ± 4.0 diopters (D) for young lenses to 45.7 ± 3.1 D for older lenses. The unstretched lens shifted toward less negative spherical aberration with age, from -6.3 ± 0.7 μm for young lenses to -5.0 ± 0.5 μm for older lenses. The power and spherical aberration of lenses in the stretched state were independent of age, with values of 33.5 ± 3.4 D and -2.6 ± 0.5 μm, respectively. Spherical aberration is negative in cynomolgus monkey lenses and becomes more negative with accommodation. These results are in good agreement with the predicted values using computational ray tracing in a lens model with a reconstructed gradient refractive index. The spherical aberration of the unstretched lens becomes less negative with age.

Surface profiling of X-ray mirrors for shaping focused beams.

Grazing incidence mirrors are a standard optic for focusing X-rays. Active mirrors, whose surface profile can be finely adjusted, allow control of beam shape and size at the sample. However, progress towards their routine use for beam shaping has been hampered by the strong striations in reflected beams away from the focal plane. Re-entrant (partly concave and partly convex) surface modifications are proposed for shaping X-ray beams to a top-hat in the focal plane while reducing the striations caused by unavoidable polishing errors. A method for constructing such surfaces with continuous height and slope (but only piecewise continuous curvature) will be provided. Ray tracing and wave propagation calculations confirm its effectiveness. A mirror system is proposed allowing vertical beam sizes in the range 0.5 to 10μm. A prototype will be fabricated and is expected to have applications on many synchrotron X-ray beamlines.

Damage Evaluation of the Human Eye for Different Laser Sources–Connecting Ray Tracing and Finite Volume Calculations

Damage Evaluation of the Human Eye for Different Laser Sources–Connecting Ray Tracing and Finite Volume Calculations

Dependency on Beamwidth in an SD Method Utilizing Two-Ray Fading Characteristics

Using ray-tracing propagation calculation, we clarify the dependency on antenna element beamwidth of the channel capacity of a spatial division (SD) transmission method utilizing the characteristics of two-ray fading. It was clarified that the SD transmission method can be effectively applied to microstrip antennas or horn antennas with beamwidth of more than 10 ${^\circ}$ , but that it is not effective when applied to narrow-beam antennas with less than 10 ${^\circ}$ beamwidth. In such cases, simple parallel transmission is a better way to utilize the narrow beam to increase channel capacity .

Recent Upgrading of ECRH System and Studies to Improve ECRH Performance in the LHD

This paper reports the recent status of the ECRH system in the LHD and introduces the experimental results that suggest the reasonable effects of the wave-plasma interaction in the plasma boundary including outside the LCFS. With increasing the available ECRH power, ECRH/ECCD have been performed in higher density target plasmas where the mode coupling between the O-mode and the X-mode caused by the magnetic shear occurs for long distance in the low density region of the plasma boundary including the ergodic layer outside the LCFS. In such a case, the incident polarization should be set by taking into account the mode coupling effect. Moreover, the refraction in the boundary region should be considered for accurate numerical prediction of the wave trajectory and power absorption with use of the ray-tracing calculation.

Direct measurement of refracted trajectory of transmitting electron cyclotron beam through plasma on the Large Helical Device

The electron-cyclotron (EC) -beam refraction due to the presence of plasma was investigated in the Large Helical Device. The transmitted-EC-beam measurement system was constructed and the beam pattern on the opposite side of the irradiated surface was measured using an IR camera. Clear dependence of the EC-beam refraction on the electron density was observed and the beam shift in the toroidal direction showed good agreement with the ray-trace calculation of TRAVIS. The influence of the peripheral density profile and the thermal effect on the beam refraction were discussed.

가열-냉각 사출성형 방식을 적용한 집광형 프레넬렌즈

A Fresnel lens is an optical component which can be used as a cost-effective, lightweight alternative to conventional continuous surface optics. Fresnel lens solar concentrators continue to fulfill a market requirement as a system component in high volume cost effective Concentrating Photovoltaic (CPV) electricity generation. The basic principles of the fresnel lens are reviewed and some practical examples are described. To investigate the performance space of the Fresnel lens, a fast simulation method which is a hybrid between raytracing and analytical computation is employed to generate a cache of simulation data. Injection molders are warming up to the idea of cycling their tool surface temperature during the molding cycle rather than keeping it constant. Heat and cool process are now also finding that raising the mold wall temperature above the resin’s glass-transition or crystalline melting temperature during the filling stage and product performance in applications from automotive to packaging to optics. This paper deals with the suitability of Fresnel lenses of imaging and non-imaging designs for solar energy concentration. The concentration fresnel lens confirmed machinability and optical transmittance and roughness measure through manufactured the prototype.

Acoustical Design Study on Application of Absorption Materials

Taipei Top Church Auditorium is a hall primarily intended for praise and worship. A three dimensional ray tracing computer simulation was used to provide sound energy distribution on the audience area of the hall, realistic design have been performed. The volume of the hall is 24600m3, which is occupied for 2200 people and equipped the hall with acoustical curtains by modifying its acoustical characteristics. Objective measurements of impulse response are reported, and background noise control and noise isolation are also be considered in the design phase. Reinforcement system is conducted to meet all the activity for the acoustical environments.

Nano- and microlenses as concepts for enhanced performance of solar cells

Both metallic nanoparticles exhibiting plasmonic effects and dielectric nanoparticles coupling the light into resonant modes have shown successful applications to photovoltaics. On a larger scale, microconcentrator optics promise to enhance solar cell efficiency and to reduce material consumption. Here, we want to create a link between the concentrators on the nano- and on the microscale. From metallic nanospheres, we turn to dielectric ones and then look at increasing radii to approach the microscale. The lenses are investigated with respect to their interaction with light using three-dimensional simulations with the finite-element method. Resulting maps of local electric field distributions reveal the focusing behavior of the dielectric spheres. For larger lens sizes, ray tracing calculations, which give ray distributions in agreement with electric field intensities, can be applied. Calculations of back focal lengths in geometrical optics coincide with ray tracing results and allow insight into how the focal length can be tuned as a function of particle size, substrate refractive index, and the shape of the microlens. Despite the similarities we find for the nano- and the microlenses, integration into solar cells needs to be carefully adjusted, depending on the goals of material saving, concentration level, focal distance, and lens size.

Analysis of Reference Sources for the Characterization and Calibration of Infrared Cameras

This paper gives an analysis of the radiometric properties of different types of reference sources applied for the characterization and calibration of infrared cameras. For the absolute radiance measurement with an infrared camera, a metrological characterization and calibration of the instrument are essential. Similar to the calibration of radiation thermometers, this calibration is generally performed with reference sources of known radiance. As infrared cameras are optically and electronically more complex than radiation thermometers, which are equipped with a single element detector, the applied reference sources have to be carefully characterized and limitations in their performance have to be considered. Each pixel of the image measured with an infrared camera should depict correctly the desired physical quantity value of the projected object area. This should be achieved for all relevant conditions of observation, e.g., at different distances or at different incident angles. The performance of cavity radiators and plate radiators is analyzed based on ray-tracing calculations and spatially and angularly resolved radiance measurements with radiation thermometers and cameras. Relevant components of a calibration facility for infrared cameras at PTB are presented with their specifications. A first analysis of the relevant characteristics of the applied infrared calibration sources and infrared cameras is presented as the essential basic information for the realization of the calibration of infrared cameras.

Multilayer coated grazing incidence condenser for large numerical aperture objective at wavelength of 4.5 nm.

A grazing incidence condenser is developed for objectives with large numerical aperture working in Carbon-window wavelength region (λ=4.4-5.0 nm) with the use of a point light source. The condenser is composed of four pieces of toroidal mirrors and a piece of the mirror was fabricated to evaluate the performance of the mirror. The radii of the toroidal mirror are determined by ray-trace calculation, and each radius of the mirror substrate and the roughness of the polished surface were evaluated to satisfy the designed parameter. A Co/C reflection multilayer is also designed to reflect soft x-ray light at 4.5 nm wavelength, and the reflection multilayer was deposited on the mirror surface. Measured reflectance of the toroidal mirror with the reflection multilayer is higher than 0.32 at 4.5 nm wavelength.

A scalable plant-resolving radiative transfer model based on optimized GPU ray tracing

A new model for radiative transfer in participating media and its application to complex plant canopies is presented. The goal was to be able to efficiently solve complex canopy-scale radiative transfer problems while also representing sub-plant heterogeneity. In the model, individual leaf surfaces are not resolved, but rather vegetation is aggregated into isothermal volumes. Using the leaf angle distribution and leaf area density functions, the volumes realistically augment the radiation field through absorption and anisotropic scattering and re-emission. The volumes are grouped to form individual plants, and individual plants are grouped to form entire canopies. The model increases efficiency by performing ray tracing calculations on graphics processing units (GPUs) using the NVIDIA® OptiX™ and CUDA™ frameworks, and through efficient algorithms for radiation reflection, scattering, and emission. This efficiency allows for realistic representation of heterogeneity, while also allowing for the solution of problems with very large domains (∼105 trees) quickly on an inexpensive desktop workstation. Problem execution time scaled nearly linearly with the number of discrete elements in the domain. Model results are compared with experimental data collected from an array of radiation sensors within and above a grapevine canopy and an isolated tree. Agreement between simulated and measured values of shortwave and longwave radiation were very good, with model predictions generally within the expected measurement accuracy.

Particle simulation of lower hybrid wave propagation in fusion plasmas

Global particle simulations of the lower hybrid (LH) waves have been carried out using fully kinetic ions and drift kinetic electrons with a realistic electron-to-ion mass ratio. The LH wave frequency, mode structure, and electron Landau damping from the electrostatic simulations agree very well with the analytic theory. Linear simulation of the propagation of a LH wave-packet in the toroidal geometry shows that the wave propagates faster in the high field side than the low field side, in agreement with a ray tracing calculation. This poloidal asymmetry arises from the non-conservation of the poloidal mode number due to the non-uniform magnetic field. In contrast, the poloidal mode number is conserved in the cylindrical geometry with the uniform magnetic field.

Improvement and Upgrade of Small-Angle X-ray Scattering Beamlines at the Photon Factory

Three small-angle X-ray scattering (SAXS) beamlines, BL-6A, BL-10C and new BL-15A2 are available at the Japanese synchrotron facility, Photon Factory (PF). We are recently improving and upgrading the SAXS beamlines at the PF in order to support new measurements and construct a high-throughput experimental system. BL-6A is a bending magnet beamline and the wavelength is fixed at 1.5 angstrom. This beamline had two detectors, PILAUS 300K (Dectris) for SAXS/GI-SAXS and PILATUS 100K (Dectris) for WAXD experiment, respectively, and the simultaneous measurement using these detectors are available. We installed a new experimental stage and replaced PILATUS 300K with PILATUS3 1M in this March. Therefore, the range of an applicable camera length spread to 0.25 ~ 2.5 m, and the detectable angle area expanded in the small-angle region. BL-10A is also a bending magnet beamline and the wavelength has been fixed at 1.488 angstrom. We replaced almost all the optical and experimental components of this beamline with new ones in this March. A fixed-exit double-crystal monochromator, a focusing mirror and a mirror bender were newly installed in this beamline. We will be able to change the energy from 6 to 14 keV. Although the photon flux at the sample position will not change after this upgrade, the area of the beam at the focal point will decrease to 40 % on the basis of the raytracing calculation. The camera length spread from 2 m to 3m in a new experimental stage with the camera tube. PILATUS3 2M and 200K (Dectris) were also installed as a detector. The commissioning will be started from this May, and the beamline will be re-opened from this June. In order to control all new devices and make the user-operation easier, we newly developed GUI software for the beamline control and the experiment. We are also developing the solution sample mixer and changer at BL-15A2 for the high-throughput Bio-SAXS measurement. We will present the current status of these beamline refurbishment.

Weather-Dependent Airport Noise Contour Prediction Concept Based on Ray Tracing

The most frequently used excess attenuation method for noise contour models is called the lateral attenuation correction. This empirical method disregards varying atmospheric conditions. It is known that varying atmospheric conditions can lead to large discrepancies for single-event cases. This paper studies these atmospheric effects for a longer period, thus involving multi-event calculations. A European Civil Aviation Conference Document 29 compliant noise model is used with the extended functionality to apply results from a ray-tracing excess attenuation calculation. Results are shown for monthly and yearly noise contours around an example airport using three different modeling options: the standard Document 29 methodology, the standard methodology augmented by varying atmospheric absorption, and the ray-tracing excess attenuation method. The differences found in excess attenuation between the standard Document 29 method and ray tracing are small. It is argued that the main differences are related to varying atmospheric absorption and ground attenuation. For the case considered, wind effects are of minor importance when modeling monthly or yearly contours. In conclusion, the empirical lateral attenuation model, used to estimate the average excess attenuation in a varying atmosphere, provides a practical and realistic estimate for yearly and monthly noise contours for the used atmosphere.

Acoustics Oribotics

There is a great demand in multipurpose elements design for use adaptation. This in turn requires great flexibility in design strategies, as well as a wider spectrum of space settings to achieve the required environment that special activities imply. Acoustics is an essential factor influencing cognitive acts and behavior as well as on the extreme end the physical wellbeing inside a space. The complexity of this constrain is fueled up by the extended geometric dimensions of multipurpose halls, making acoustic adequateness a great concern, that could not easily be achieved for each purpose. To achieve a performance oriented acoustic environment, various parametric shaped false ceilings based on origami folded notion are simulated. These parigamic shapes are able to fold and unfold forming an oribotic structure, and changing the mutual acoustic environment according to the geometric shapes position and its changing exposed surface areas. The mobility of the facets in the parigamic surface can stretch up the range from a complete plain surface to an unfolded element where a considerable amount of absorption is added to the space. The behavior of the parigamic shapes are being modeled employing a ray tracing computer simulation package for various shapes topology. Results revealed a divergence of results that is caused by the folded facets to shorten the mean free path thus introducing more reflections and consequently quicker decay curves.

Reflectance calculations of alkaline textured multicrystalline silicon: a new approach

Alkaline texture etching is a standard procedure for manufacturing solar cells with (100) oriented single-crystalline-silicon wafers as substrates. This is performed to reduce reflectance from the wafer surface. Alkaline etching, being anisotropic in nature, results in unique texture on the surface of each crystallographic orientation of silicon. Hence, the reflectance of each grain of a multicrystalline silicon (mc-Si) substrate can be treated as a signature of its crystal orientation. This provides an opportunity to ascertain the orientation of each grain in a mc-Si wafer by the shape of the textures formed on its surface and henceforth, its corresponding reflectance. A model has been developed that can predict and create surface textures for any arbitrary crystal orientation of silicon on anisotropic alkaline etching. This model has been implemented in a computer program written in C++ to perform rigorous ray-tracing computations to calculate reflectance curves for textured silicon of any crystal orientation, wafer thickness and texture height. A database of reflectance curves for multiple crystal orientations has been built. This has led to a new and ultrafast method for grain orientation characterization using reflectance of each grain, instead of time-consuming X-ray (Laue) and Electron-backscatter diffraction measurements. The model and the algorithm used for reflectance calculations, along with some calculated results, are presented to highlight the usefulness of this procedure for application in grain orientation mapping.

Feasibility study of a layer-oriented wavefront sensor for solar telescopes

Solar multiconjugate adaptive optics systems rely on several wavefront sensors, which measure the incoming turbulent phase along several field directions to produce a tomographic reconstruction of the turbulent phase. In this paper, we explore an alternative wavefront sensing approach that attempts to directly measure the turbulent phase present at a particular height in the atmosphere: a layer-oriented cross-correlating Shack-Hartmann wavefront sensor (SHWFS). In an experiment at the Dunn Solar Telescope, we built a prototype layer-oriented cross-correlating SHWFS system conjugated to two separate atmospheric heights. We present the data obtained in the observations and complement these with ray-tracing computations to achieve a better understanding of the instrument's performance and limitations. The results obtained in this study strongly indicate that a layer-oriented cross-correlating SHWFS is not a practical design to measure the wavefront at a high layer in the atmosphere.

Dart-ray: a 3D ray-tracing radiative transfer code for calculating the propagation of light in dusty galaxies

We present DART-Ray, a new ray-tracing 3D dust radiative transfer (RT) code designed specifically to calculate radiation field energy density (RFED) distributions within dusty galaxy models with arbitrary geometries. In this paper we introduce the basic algorithm implemented in DART-Ray which is based on a pre-calculation of a lower limit for the RFED distribution. This pre-calculation allows us to estimate the extent of regions around the radiation sources within which these sources contribute significantly to the RFED. In this way, ray-tracing calculations can be restricted to take place only within these regions, thus substantially reducing the computational time compared to a complete ray-tracing RT calculation. Anisotropic scattering is included in the code and handled in a similar fashion. Furthermore, the code utilizes a Cartesian adaptive spatial grid and an iterative method has been implemented to optimize the angular densities of the rays originated from each emitting cell. In order to verify the accuracy of the RT calculations performed by DART-Ray, we present results of comparisons with solutions obtained using the DUSTY 1D RT code for a dust shell illuminated by a central point source and existing 2D RT calculations of disc galaxies with diffusely distributed stellar emission and dust opacity. Finally, we show the application of the code on a spiral galaxy model with logarithmic spiral arms in order to measure the effect of the spiral pattern on the attenuation and RFED.

Long-distance flux mapping using low-cost collimated pyranometers

Concentrating solar thermal power tower plants with capacities of 100MWe or greater require large heliostat fields with heliostats over 1500m (nearly a mile) away from the tower. The accuracy and performance of these heliostats must be evaluated and understood as new heliostat designs emerge to reduce costs. Conventional beam characterization systems that use photographs of the reflected beam on a tower-mounted target are typically not large enough to capture the beam at long distances, and the magnitude of the irradiance for long-distance heliostats is quite low (only a fraction of a sun), which can make the beam image difficult to discern from the ambient lighting on the target. The Long-Range Heliostat Target (LRHT) implements a technique for mapping low density flux images from heliostats and reflectors at slant ranges up to approximately 1700m.The LRHT is a vertical array of collimated pyranometers deployed to a test site via flat-bed trailer and quickly erected on an aluminum truss tower. Once the sensors have been aimed at the heliostat, the heliostat beam is swept azimuthally across the array whereupon the data is stitched into a flux map indicating horizontal and vertical beam dimensions and flux intensities. The LRHT was used to evaluate and compare beam shape, peak flux, and total power of heliostats and single facet reflectors at distances from 300 to 1700m. Results were compared to theoretically rendered flux maps created by computational ray tracing algorithms, and to photographs taken on the beam characterization system (BCS) at the National Solar Thermal Test Facility at Sandia National Laboratories.