Linear Light Source Research Articles

Effects of source shape on the numerical aperture factor with a geometrical-optics model.

We study the effects of an extended light source on the calibration of an interference microscope, also referred to as an optical profiler. Theoretical and experimental numerical aperture (NA) factors for circular and linear light sources along with collimated laser illumination demonstrate that the shape of the light source or effective aperture cone is critical for a correct NA factor calculation. In practice, more-accurate results for the NA factor are obtained when a linear approximation to the filament light source shape is used in a geometric model. We show that previously measured and derived NA factors show some discrepancies because a circular rather than linear approximation to the filament source was used in the modeling.

Linear light source reflectometry

This paper presents a technique for estimating the spatially-varying reflectance properties of a surface based on its appearance during a single pass of a linear light source. By using a linear light rather than a point light source as the illuminant, we are able to reliably observe and estimate the diffuse color, specular color, and specular roughness of each point of the surface. The reflectometry apparatus we use is simple and inexpensive to build, requiring a single direction of motion for the light source and a fixed camera viewpoint. Our model fitting technique first renders a reflectance table of how diffuse and specular reflectance lobes would appear under moving linear light source illumination. Then, for each pixel we compare its series of intensity values to the tabulated reflectance lobes to determine which reflectance model parameters most closely produce the observed reflectance values. Using two passes of the linear light source at different angles, we can also estimate per-pixel surface normals as well as the reflectance parameters. Additionally our system records a per-pixel height map for the object and estimates its per-pixel translucency. We produce real-time renderings of the captured objects using a custom hardware shading algorithm. We apply the technique to a test object exhibiting a variety of materials as well as to an illuminated manuscript with gold lettering. To demonstrate the technique's accuracy, we compare renderings of the captured models to real photographs of the original objects.

Measurements of the temperature profile of a two-dimensional slot burner using a Lau phase interferometer with linear gratings

We have investigated the utility of a Lau phase interferometer with linear gratings and white light source to measure the temperature and temperature profile of a flame produced by a slot burner used in an atomic absorption spectrophotometer. The temperature values measured using a Lau phase interferometer and a thermocouple and multilogger are in good agreement. The effect of aspirating water through a nebulizer on the temperature profile and details of theoretical analysis and experimental investigations are also presented.

Start-to-end simulation of self-amplified spontaneous emission free electron lasers from the gun through the undulator

It is widely appreciated that the performance of self-amplified spontaneous emission free-electron lasers (FELs) depends critically on the properties of the drive beam. In view of this, a multi-laboratory collaboration has explored methods and software tools for integrated simulation of the photoinjector, linear accelerator, bunch compressor, and FEL. Rather than create a single code to handle such a system, our goal has been a robust, generic solution wherein pre-existing simulation codes are used sequentially. We have standardized on the use of Argonne National Laboratory's Self-Describing Data Sets file protocol for transfer of data among codes. The simulation codes used are PARMELA, elegant, and GENESIS. We describe the software methodology and its advantages, then provide examples involving Argonne's Low-Energy Undulator Test Line and Stanford Linear Accelerator Center's Linac Coherent Light Source. We also indicate possible future direction of this work.

Visible-infrared self-amplified spontaneous emission amplifier free electron laser undulator

The visible-infrared self-amplified spontaneous emission amplifier (VISA) free electron laser (FEL) is an experimental device designed to show self-amplified spontaneous emission (SASE) to saturation in the near infrared to visible light energy range. It generates a resonant wavelength output from 800\char21{}600 nm, so that silicon detectors may be used to characterize the optical properties of the FEL radiation. VISA is designed to show how SASE FEL theory corresponds with experiment in this wavelength range, using an electron beam with emittance close to that planned for the future Linear Coherent Light Source at SLAC. VISA comprises a 4 m pure permanent magnet undulator with four 99 cm segments, each of 55 periods, 18 mm long. The undulator has distributed focusing built into it, to reduce the average beta function of the 70\char21{}85 MeV electron beam to about 30 cm. There are four FODO cells per segment. The permanent magnet focusing lattice consists of blocks mounted on either side of the electron beam, in the undulator gap. The most important undulator error parameter for a free electron laser is the trajectory walk-off, or lack of overlap of the photon and electron beams. Using pulsed wire magnet measurements and magnet shimming, we were able to control trajectory walk-off to less than $\ifmmode\pm\else\textpm\fi{}50\ensuremath{\mu}\mathrm{m}$ per field gain length.

Determination of stem and calyx location on apples using automatic visual inspection

Automatic surface blemish detection systems for apples can be confused by the stem, calyx, and concavities. If the stem and calyx are incorrectly classified as blemishes, a false grade will be assigned to a fruit. A new method to determine the location of these concavities is described. The apples were illuminated by blue linear light sources and a standard colour video camera was employed to detect the reflection patterns. Blue lights were employed because they were outside the spectrum of interest for blemish detection. This enables the technique to be used simultaneously with blemish detection. The reflection patterns were in the form of light stripes, with a shape dependent on the shape and orientation of each apple. Analysis of these patterns made it possible to identify the location of stem and calyx regions. Details of a laboratory implementation of the acquisition system and an outline of the algorithms, are presented together with some preliminary results.

A new technique for measuring dispersion of optical fibers using a frequency‐shifted feedback fiber laser. part I: Measurement of group velocity dispersion

AbstractWith the continually improving performance of long‐distance optical communication systems, it becomes important to administer and control wavelength dispersion of the optical fiber. In this paper, a method of measurement of the group velocity dispersion (GVD) of an optical fiber using optical frequency domain reflectometry is proposed. In this scheme, frequency‐chirped light is used as a light source and the total dispersion of the GVD of the optical fiber is measured from the variations of the optical frequency chirp rate after transmission through the fiber. In this method, the GVD value versus the optical wavelength can be measured directly. Another characteristic is that the effect of measurement error due to fluctuations of the fiber under test can be neglected. An experimental verification of the present scheme was performed with a frequency‐shifted feedback laser, which is an ideal linear chirped light source. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(2): 1–7, 2002

On numerical solutions to one-dimensional integration problems with applications to linear light sources

Many key problems in computer graphics require the computation of integrals. Due to the nature of the integrand and of the domain of integration, these integrals seldom can be computed analytically. As a result, numerical techniques are used to find approximate solutions to these problems. While the numerical analysis literature offers many integration techniques, the choice of which method to use for specific computer graphic problems is a difficult one. This choice must be driven by the numerical efficiency of the method, and ultimately, by its visual impact on the computed image. In this paper, we begin to address these issues by methodically analyzing deterministic and stochastic numerical techniques and their application to the type of one-dimensional problems that occur in computer graphics, especially in the context of linear light source integration. In addition to traditional methods such as Gauss-Legendre quadratures, we also examine Voronoi diagram-based sampling, jittered quadratures, random offset quadratures, weighted Monte Carlo, and a newly introduced method of compounding known as a difficulty driven compound quadrature .We compare the effectiveness of these methods using a three-pronged approach. First, we compare the frequency domain characteristics of all the methods using periodograms. Next, applying ideas found in the numerical analysis literature, we examine the numerical and visual performance profiles of these methods for seven different one-parameter problem families. We then present results from the application of the methods for the example of linear light sources. Finally, we summarize the relative effectiveness of the methods surveyed, showing the potential power of difficulty-driven compound quadratures.

線光源による灯火の不快グレアの抑制

線光源による灯火の不快グレアの抑制

Effects of beam-tube roughness on x-ray free electron laser performance

In an x-ray free electron laser like the Linear Coherent Light Source being designed at SLAC, electron bunches about $70\ensuremath{\mu}\mathrm{m}$ FWHM long are sent into a beam tube only 5 mm in internal diameter and more than 100 m in length. Because of the surface roughness of the beam tube, wakefields can be generated that catch up to the bunch and interact with it, causing energy spread and emittance growth. The strength of this effect depends on the details of the roughness of the surface. We present here a study in which the roughness of the beam tube was measured and the longitudinal impedance of the tube was calculated. Our result shows that a commercially available beam tube can be made smooth enough so the resulting wakefield effects are within the tolerance determined by the requirement that the induced relative energy spread of the beam be less than $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$.

Concentration of diffuse linear light sources with continuous optical elements

A new technique for geometric transformation of a diffuse linear light source into a two-dimensional symmetric virtual source is proposed and demonstrated. It involves two cylindrical lenses and a single holographic element that is optically recorded with a simple and single step. The results for a specific arrangement that transforms a 40 mm x 0.4 mm source, with diffusive angle of 0.1 rad, into a 1 mm x 1.2 mm nearly symmetric spot are presented. The lack of sharp boundaries in either the beam or the optical elements suppresses any diffraction losses, relaxes alignment tolerances, and improves stability.

LED-based NIR spectrometer module for hand-held and process analyser applications

This paper discusses an electronically scanned, small size 32-wavelength NIR spectrometer unit developed for use as a building block in hand-held composition meters as well as in spectroscopic sensors for process automation. The design relies on a linear LED array light source and a fixed grating monochromator. The benefits of the LED spectrometer unit are a highly accurate wavelength scale, with fixed precalibration for subnanometer tolerances and compatibility with a wide operating temperature range, thanks to internal temperature stabilisation. A series of LED spectrometer modules was manufactured for short wave near infrared (SW-NIR) specifications, covering the range from 832 to 1048 nm and a testing program was arranged to characterise typical performance and the spread of the key optical parameters. Potential applications for this SW-NIR wavelength scale can be seen in food, agricultural and petrochemical analysis. The design can also be modified for other wavelengths, for which LEDs are currently available, i.e. from 400 nm to beyond 2 μm, which will further widen the scope of possible applications in the field of NIR spectroscopy and colour analysis.

Light-intensity distribution in eccentric photorefraction crescents.

We try to improve the accuracy of eccentric photorefraction by taking more information into account than just the size and tilt of the crescent. Based on Gaussian optics and the assumption of an isotropic scattering retina, a theoretical analysis of the light-intensity distribution in the pupils of astigmatic eyes is presented. The method is applied to different photorefractor setups (point light source, long linear light source, knife-edge aperture, and circular aperture). In the case of a knife-edge aperture the crescent structure can be formulated analytically. In the case of a circular aperture an analytic description is possible only for spherical refractive errors, but astigmatic refractive errors can be determined from crescent parameters with neural networks.

Nonlinear theory of short-wavelength free-electron lasers.

The nonlinear evolution of free-electron laser (FEL) amplifiers is studied for infrared and shorter wavelengths. The configuration of interest consists in the propagation of an energetic electron beam through a drift tube in the presence of a periodic wiggler magnetic field with planar symmetry. A three-dimensional formulation is derived in which the electromagnetic field is represented as an expansion of Gaussian optical modes. Since the wiggler model is characterized by planar symmetry, the Gauss-Hermite modes are used for this purpose. A set of nonlinear differential equations is derived for the evolution of the amplitude and phase of each mode, and they are solved simultaneously in conjunction with the three-dimensional Lorentz force equations for an ensemble of electrons in the presence of the magneto-static wiggler, self-electric and self-magnetic fields due to the charge and current distributions of the beam, and the electromagnetic fields. It is important to note that no wiggler average is used in the integration of the electron trajectories. This permits the self-consistent modeling of effects associated with (1) the injection of the beam into the wiggler, (2) emittance growth due to inhomogeneities in the wiggler and radiation fields as well as due to the self-fields, (3) the effect of wiggler imperfections, and (4) betatron oscillations. The optical guiding of the radiation field is implicitly included in the formulation. This approach has important practical advantages in analyzing FELs, since it is necessary only to characterize the beam upon injection into the wiggler, and the subsequent evolution is treated self-consistently.Numerical simulations are performed for two examples corresponding to an infrared FEL at wavelengths near 3.5 \ensuremath{\mu}m, and an x-ray FEL operating in the neighborhood of 1.4 \AA{} wavelengths corresponding to the proposed linear coherent light source (LCLS) at the Stanford Linear Accelerator Center. Results for both cases indicate that the more severe limiting factor on the performance of the FEL is the beam emittance. For the infrared example, the transition to the thermal regime occurs for an axial energy spread of \ensuremath{\Delta}${\ensuremath{\gamma}}_{\mathit{z}}$/${\ensuremath{\gamma}}_{0}$\ensuremath{\approxeq}0.19%, and optimal performance is obtained for \ensuremath{\Delta}${\ensuremath{\gamma}}_{\mathit{z}}$/${\ensuremath{\gamma}}_{0}$0.1% and \ensuremath{\gamma} is the relativistic factor. This restriction is more severe for the LCLS parameters, for which the thermal transition is found for \ensuremath{\Delta}${\ensuremath{\gamma}}_{\mathit{z}}$/${\ensuremath{\gamma}}_{0}$\ensuremath{\approxeq}0.05% and optimal performance requires \ensuremath{\Delta}${\ensuremath{\gamma}}_{\mathit{z}}$/${\ensuremath{\gamma}}_{0}$\ensuremath{\le}0.01%. Wiggler imperfections are found to be a much less important constraint on FEL design. Simulations indicate that there is no coherent ``walkoff'' of the beam from the symmetry axis due to wiggler imperfections, and that the radiation field is sufficiently guided by the interaction that no severe degradation is found in the extraction efficiency or growth rate for moderate levels of wiggler fluctuations.

Shading with Curve Light Sources1

AbstractA new shading model for curve light sources is presented. It accounts for both diffuse reflection and specular reflection of the illuminated surface. By regarding a linear light source as a directional quadrilateral light source with very small width, a simple formula is derived first for calculating the diffuse reflection component due to the illumination of the linear segment. The diffuse reflection of the surface by direct illumination of a curve light source is then evaluated by approximating the curve light with a series of linear segments. The specular reflection component due to a curve light source is represented by an integration taking Phong's specular model as the kernel and evaluated by summing the contributions from the linear segments. Finally, an efficient shadow detection algorithm for curve light sources is proposed. The images rendered with the shading model are very photo‐realistic.

Fast Shadowing Algorithm for Linear Light Sources

AbstractThis paper presents a fast shadowing algorithm for linear light sources that uses a ray‐oriented buffer. Space segmentation by the buffer guarantees that if a point is included in a subspace, all light rays toward the point are also contained in the subspace. Each cell of the buffer stores a list of objects that lie within or intersect the subspace allocated to the cell. Therefore, candidate objects, those that may cast shadows onto a point, are determined by referring to the cell where the point is mapped. In addition, whether each candidate object actually casts shadows or not is tested with the bounding‐volume of the shadow space to reduce the number of objects subjected to expensive light clipping. The bounding‐volumes are also stored in the buffer. For efficiently generating the ray‐oriented buffer, we present the cylindrical scan‐conversion algorithm. The algorithm preconverts objects' surfaces to trapezia to decrease the light clipping cost, then connects the trapezia to the buffer cells.Due to the above improvements, our algorithm achieves over 10 times faster shadow generation compared to the conventional methods. Experimental results confirm that our method can generate realistic images with soft shadows in a few minutes.

Fast Shadowing Algorithm for Linear Light Sources

Fast Shadowing Algorithm for Linear Light Sources

Light-Source Modeling Using Pyramidal Light Maps

The diversity of lighting arrangements and fixtures in everyday life allows us great creative and functional control over the appearance of our environments. In computer graphics, the lack of realistic models of light sources does not permit the same level of control. To model a light source, one must (at least) be able to specify its geometry and its spatial intensity distribution. We describe a system that permits the interactive specification of point, linear, and area light sources having arbitrary and variable spatial intensity distributions across their domains. A continuous distribution of an extended light source is created by interpolating a set of sample distributions that are interactively placed on the light source. Rendering is accomplished by resampling the light source at a variable resolution. To speed up rendering, a pyramidal representation of the light source is created, allowing the dynamic selection of the resampling rate. We describe the theory, design, and implementation of our light-source modeling system. Pyramidal light-source models can be used in rendering environments such as conventional scanline or ray-tracing renderers, or renderers with programmable shaders.

Light-Source Modeling Using Pyramidal Light Maps

The diversity of lighting arrangements and fixtures in everyday life allows us great creative and functional control over the appearance of our environments. In computer graphics, the lack of realistic models of light sources does not permit the same level of control. To model a light source, one must (at least) be able to specify its geometry and its spatial intensity distribution. We describe a system that permits the interactive specification of point, linear, and area light sources having arbitrary and variable spatial intensity distributions across their domains. A continuous distribution of an extended light source is created by interpolating a set of sample distributions that are interactively placed on the light source. Rendering is accomplished by resampling the light source at a variable resolution. To speed up rendering, a pyramidal representation of the light source is created, allowing the dynamic selection of the resampling rate. We describe the theory, design, and implementation of our light-source modeling system. Pyramidal light-source models can be used in rendering environments such as conventional scanline or ray-tracing renderers, or renderers with programmable shaders.

Shading models for linear and area light sources

Two shading models that account for, respectively, both diffuse reflection and specular reflection caused by ideal diffuse linear light sources and ideal diffuse polygonal light sources are proposed. In both models, the diffuse reflection component is accurately represented in an analytic form, while the specular reflection component is represented by an integration taking Phong's specular model as the kernel. For linear light sources, a precise recursive formula is derived to calculate the specular reflection component analytically. For polygonal light sources, we adopt Taylor's series to approximate the integration. All the analytic representations of both diffuse and specular terms involve no complex coordinate transformation and the images generated by the shading models are very realistic. Finally, a shadow detection algorithm is presented for the polygonal environment, the precise umbra and penumbra can be produced. Results show great potential of our method.