Showing papers on "Collimated light published in 2003"

Beam steering in planar-photonic crystals: from superprism to supercollimator

Abstract: We utilize the anomalous dispersion of planar-photonic crystals (PhCs) near the dielectric band edge to control the wavelength-dependent propagation of light. Light beams with up to 20/spl deg/ divergence were collimated over a 25-nm (1285 nm to 1310 nm) bandwidth using a triangular lattice. The "superprism" phenomenon is demonstrated in the same configuration, simply by tuning the wavelength. Sources of loss are discussed. Both the plane-wave expansion calculation and finite-difference time-domain simulation match well with the experimental results. This is the first experimental demonstration of self-collimating phenomena in a PhC configuration.

Resistive collimation of electron beams in laser-produced plasmas.

Abstract: Intense relativistic electron beams, produced by high-intensity short-pulse laser irradiation of a solid target, have many potential applications including fusion by fast ignition. Using a unique Fokker-Planck code, supported by analytic calculations, we show that fast electrons can be collimated into a beam even when the fast electron source is not strongly anisotropic, and we derive a condition for collimation to occur.

Spectroscopy illuminator with improved delivery efficiency for high optical density and reduced thermal load

Abstract: An improved illuminator for generating broadband light, and for delivering the light to a sample with an improved delivery efficiency, for higher optical density and/or reduced thermal transfer, than achieved with conventional halogen bulb sources. The illuminator enables spectroscopic analysis in thermally-sensitive or spatially-constrained environments. A phosphor-coated broadband white LED (105) and integrated collimating optics (107) produces a continuous, collimated broadband light beam from 400 nm to 700 nm, which is then transmitted through space to a sample region (125), such as a living tissue in vivo. This results in a high net efficient delivery of light to the tissue sample. An efficient conversion of power to light, and the high delivery efficiency, keeps both the illuminator and sample cool during operation, allowing the illuminator to be integrated into the tip of a medical probe or into monitoring systems.

Backward Monte Carlo Simulations in Radiative Heat Transfer

Abstract: Standard Monte Carlo methods trace photon bundles in a forward direction, and may become extremely inefficient when radiation onto a small spot and/or onto a small direction cone is desired. Backward tracing of photon bundles is known to alleviate this problem if the source of radiation is large, but may also fail if the radiation source is collimated and/or very small. Various implementations of the backward Monte Carlo method are discussed, allowing efficient Monte Carlo simulations for problems with arbitrary radiation sources, including small collimated beams, point sources, etc., in media of arbitrary optical thickness

Methods and systems for laser based real-time structured light depth extraction

Abstract: Laser-based methods and systems for real-time structured light depth extraction are disclosed. A laser light source (100) produces a collimated beam of laser light. A pattern generator (102) generates structured light patterns including a plurality of pixels. The beam of laser light emanating from the laser light source (100) interacts with the patterns to project the patterns onto the object of interest (118). The patterns are reflected from the object of interest (118) and detected using a high-speed, low-resolution detector (106). A broadband light source (111) illuminates the object with broadband/light, and a separate high-resolution, low-speed detector (108) detects broadband light reflected from the object (118). A real-time structured light depth extraction engine/controller (110) based on the transmitted and reflected patterns and the reflected broadband light.

Projection light source from light emitting diodes

Abstract: The light emitted from a bank of light emitting diodes is converted through a set of lenses into parallel light beams, which, in turn, is focused or diversified as projection light source Such a light source can replace traditional incandescent bulb Reflection mirrors can be used to deflect or reflect the light beams Phosphorescent material can be added in the transmission path to convert blue or ultraviolet short wave light into white light

System for detecting anomalies and/or features of a surface

Abstract: A cylindrical mirror or lens is used to focus an input collimated beam of light onto a line on the surface to be inspected, where the line is substantially in the plane of incidence of the focused beam. An image of the beam is projected onto an array of charge-coupled devices parallel to the line for detecting anomalies and/or features of the surface, where the array is outside the plane of incidence of the focused beam.

Reflective microelectrical mechanical structure (mems) optical modulator and optical display system

Abstract: A MEMS optical display system includes an illumination source for providing illumination light, a collimating lens for receiving the illumination light and forming from it collimated illumination light, and a microlens array having an array of lenslets for receiving the illumination light from the collimating lens. The converging microlens array directs the illumination light through an array of pixel apertures in an aperture plate to a microelectrical mechanical reflector array positioned opposite the aperture plate. The microelectrical mechanical reflector array includes an array of microelectrical mechanical actuators that support reflectors in alignment with the array of pixel apertures and selectively orients the reflectors to direct the illumination light back through the pixel apertures (to form part of a display image) or against the aperture plate (to be blocked). The illumination light passing back through the pixel apertures passes through the microlens array and a beamsplitter to a display screen.

Exploiting the x-ray refraction contrast with an analyser: the state of the art

Abstract: Besides attenuation, x-ray refraction occurs in an x-ray beam passing through an object containing details of different refractive indices or of non-uniform thicknesses. The emerging x-rays present characteristic angular deflections, which are on the microradian scale. Different refraction directions can be resolved by using an angular analyser, for instance a perfect crystal, which can then be revealed by a detector placed behind it. By varying the alignment of the analyser with regard to the incoming x-ray beam, the unrefracted x-rays can either be recorded on a detector or rejected, thus, either contributing or not contributing to the image contrast. The x-ray refraction contrast can greatly exceed the absorption contrast, for instance in imaging low Z materials, where the potentialities of the technique have been exploited from the beginning. An analyser-based imaging technique has been presented in various versions also assuming different names. An important variation, based on an algorithm that differentiates the separation of the refraction contrast from the absorption contrast in an image, has been introduced with the name `diffraction enhanced imaging' (DEI). The interest in the potential medical application of the diffraction imaging technique has given origin to many projects utilizing analyser-based refraction imaging. Initiated with conventional x-ray generators, it has been rapidly developed in synchrotron radiation sites thanks to the highly intense collimated beams available that permit fast projection and tomographic imaging. Mammographic in vitro protocols and cartilage characterization are the most exploited applications of DEI. The potential medical application has refocused the interest towards the utilization of presently available conventional high-power x-ray generators that can open the doors to large-scale utilization. The aim of this paper is to present a review of the technique in its theoretical and practical aspects; an abundant bibliography, highlights the most significant and recent results.

Fiber dispersion in time domain measurements compromising the accuracy of determination of optical properties of strongly scattering media

Abstract: Limitations in the accuracy of measurements of optical properties (absorption and scattering coefficients) of strongly scattering media that are due to temporal dispersion inside the detection fibers of a time-of-flight setup were investigated for a tissue-like phantom. It is shown that the absorption and reduced scattering coefficients may be overestimated by up to 90% (depending on length and numerical aperture of the fibers) if the instrumental response measurements for the setup are performed by direct illumination of the tip of the detection fibers with collimated short laser pulses. However, the accuracy can be improved significantly if a thin layer of scattering media is used in front of the detection fibers during the response measurements. The relevance of the investigated dispersion effects is discussed with respect to frequency-domain measurements as well.

One-dimensional transient radiation heat transfer modeling using a finite-volume method

Abstract: This article presents a finite-volume method to calculate transient radiative transfer in a one-dimensional slab. The fully implicit scheme is used to discretize the transient term. The step and CLAM spatial differencing schemes are used in this study. The procedure is validated with available published results. The capabilities of the procedure are then examined using three additional test problems. In these test problems, one of the walls is subjected to a single-pulse collimated beam and a repeated-pulse collimated beam. The effects of the two spatial differencing schemes are discussed.

A surface micromachined optical scanner array using photoresist lenses fabricated by a thermal reflow process

Abstract: This paper presents the design, fabrication, and operation of a newly developed micromechanical optical scanner array using a translating microlens. We have used photoresist reflow technique to form a microlens on a surface micromachined XY-stage of the scratch-drive actuation mechanism. The lens scanner is placed at the focal length from an incident optical fiber to collimate the transmitting light. The collimated beam is steered two-dimensionally by the XY-motion of the microlens with respect to the incident fiber. We also have developed a theoretical model to predict appropriate initial resist thickness and diameter for the scanning lens. An optical scanning angle of /spl plusmn/7/spl deg/ has been demonstrated by sliding a microlens of 670-/spl mu/m focal length at a physical stroke of /spl plusmn/67 /spl mu/m. Typical angular positioning resolution has been estimated to be 0.018/spl deg/.

Optical array and collimated light distribution

Abstract: High luminance display devices, typically utilized in applications requiring sunlight readability, require unique design methodologies as the thickness approaches a maximum of one-inch. The present invention relates to a high-intensity light generation engine and associated light transmission apparatus for transmitting the light generated by the engine to a remote location. The invention is especially applicable for use in constructing a back lighted display, such as a liquid crystal display (LCD), of minimal thickness, i.e., one-inch or less. A display of minimal thickness is achieved by separating a light source and other peripherals from the display device, using a remote enclosure. Such a display is most suited for use in high ambient lighting conditions where space is at a premium, such as in the cockpit of an aircraft.

Particle selection for laser-accelerated proton therapy feasibility study.

Abstract: In this paper we present calculations for the design of a particle selection system for laser-accelerated proton therapy. Laser-accelerated protons coming from a thin high-density foil have broad energy and angular spectra leading to dose distributions that cannot be directly used for therapeutic applications. Our solution to this problem is a compact particle selection and collimation device that delivers small pencil beams of protons with desired energy spectra. We propose a spectrometer-like particle selection and beam modulation system in which the magnetic field will be used to spread the protonsspatially according to their energies and emitting angles. Subsequently, an aperture will be used to select the protons within a therapeutic window of energy (energy modulation). It will be shown that for the effective proton spatial differentiation, the primary collimation device should be used, which will collimate protons to the desired angular distribution and limit the spatial mixing of different energy protons once they have traveled through the magnetic system. Due to the angular proton distribution, the spatial mixing of protons of different energies will always be present and it will result in a proton energy spread with the width depending on the energy. For 250 MeV protons, the width (from the maximum to the minimum energy) is found to be 50 MeV for the magnetic field configuration used in our calculations. As the proton energy decreases, its energy width decreases as well, and for 80 MeV protons it equals 9 MeV. The presence of the energy width in the proton energy distribution will modify the depth dose curves needed for the energy modulation calculation. The matching magnetic field setup will ensure the refocusing of the selected protons and the final beam will be collimated by the secondary collimator. The calculations presented in this article show that the dose rate that the selection system can yield is on the order of D=260 Gy/min for a field size of 1×1 cm2.

Production of high-quality electron beams in numerical experiments of laser wakefield acceleration with longitudinal wave breaking

Abstract: 121301-1 In 1998 Bulanov et al. [Phys. Rev. E 58, R5257 (1998)] proposed a novel scheme for the production of high-quality electron beams in laser wakefield acceleration in which a controlled longitudinal nonlinear wave breaking is induced by a tailored electron density profile. This proposal was supported by both analytical and numerical results in a spatially one-dimensional configuration. In this paper we present results of a particle-in-cell simulation, two-dimensional in space and three-dimensional in the fields, of the interaction of an ultraintense laser pulse with a preformed plasma where the electron density decreases steeply from a first to a second plateau. We show that in our regime two-dimensional effects play a relevant role, allowing the production of well collimated, short and almost monochromatic electron beam. Remarkably low values of transverse and longitudinal normalized beam emittance tr rms 9 10 2 mmmrad and lon rms 2 mmkeV are obtained.

CCD-area-based autocollimator for precision small-angle measurement

Abstract: An optical method for precision small-angle measurement based on CCD-area-based autocollimator is proposed in this article. The autocollimator utilizes CCD area—an interline CCD image sensor in a video camera as its detector. A collimated image is taken by the video camera and captured into the memory of a personal computer by an image board with high performance, then the image is transformed into a digital image and can be further processed by software with special arithmetic. A small angular displacement is magnified twice by the collimator objective with a long focal length and the camera lens of the video camera. By using a cold-light source and special data processing arithmetic, the measuring resolution of the autocollimator has been greatly improved. The method is proved to be reliable by a prototype experiment. Although some inexpensive materials were used in the experiment, two-axis angular displacement can be measured simultaneously and a measuring accuracy of 0.01 arcsec has been achieved. If some expensive materials with lower temperature expansion coefficient are used, a measuring accuracy of about 0.005 arcsec or a much higher measuring accuracy can be achieved. Until now, this has been the highest measuring accuracy.

All-optical realization of an atom laser.

Abstract: We demonstrate an atom laser using all-optical techniques. A Bose-Einstein condensate of rubidium atoms is created by direct evaporative cooling in a quasistatic dipole trap realized with a single, tightly focused CO2-laser beam. An applied magnetic field gradient allows the formation of the condensate in a field-insensitive m(F)=0 spin projection only, which suppresses fluctuations of the chemical potential from stray magnetic fields. A collimated and monoenergetic beam of atoms is extracted from the Bose-Einstein condensate by continuously lowering the dipole trapping potential in a controlled way to form a novel type of atom laser.

CdTe and CdZnTe X-ray and gamma-ray detectors for imaging systems

Abstract: This review paper presents the current state of the art imaging systems using room-temperature CdTe and CdZnTe X-ray and gamma-ray detectors. Imaging systems composed of both single elements and monolithic segmented CdTe and CdZnTe arrays are used in medical diagnostics, astronomy, research and industry. This paper is divided into three sections: The first section describes different types and configurations of CdTe or CdZnTe detectors used in imaging systems, with the emphasis on single charge carrier collection detectors and front-end read-out electronics in the form of Application Specific Integrated Circuits associated with these detectors. The second section discusses the advantages, disadvantages and limitations with respect to the efficiency and area of the imaging systems using CdTe and CdZnTe detectors compared to other types of X and gamma ray detectors. The third section describes several examples of imaging systems utilizing CdZnTe detectors: 1) A large area imaging telescope for the detection of gamma ray bursts using a coded aperture collimator. 2) A large area medical nuclear camera for cardiology and scintimammography using a parallel hole collimator. 3) A large field of view gamma camera based on a rotating slat collimator and 4) A prototype of an electronically collimated Compton camera.

Lighting device with adjustable spotlight beam

Abstract: A lighting device (10) has a light source, a light pipe (28), two convex magnifying lenses (40, 60) ,and an adjusting mechanism (20) for moving the two magnifying lenses (40, 60) relative to the light source. The light emitted from the light source is dispersed and directed into the light pipe (28) by a reflector (26). The light pipe (28) transfers collimated light through the first (40) and second (60) magnifier lenses which redirects the light to produce a circular spotlight beam having uniform intensity. The size of the spotlight beam is adjusted by an adjusting mechanism (20).

Speckle free laser probe beam

Abstract: The present invention contemplates a method and apparatus to generate a laser probe beam free of speckles. The present invention employs a holographic phase plate inserted in a laser beam path to modulate the relative phase across the beam. The holographic phase plate is designed to optimize the phase modulation across the beam while to minimize the degradation of the beam quality. The modulated laser beam has only a small and confined divergent angle and can then be refocused or collimated into a narrow and near collimated probe beam. The present invention further rotates the holographic phase plate to randomize the speckles in a time sequence. As a result, the probe beam preserves substantially the beam quality of a laser and produces substantially no speckles on image of its, intersection with a surface or material.

An optical spectrometer

Abstract: An optical spectrometer (1, 100, 200) has a collector (15) for collecting a reflected probe, and a separate collector (23) for collecting luminescence. In one spectrometer (200) the collimated luminescence and reflectance beams are routed through an optical subsystem (6), a monochromator (7), and further optical components (8). Thus reflectance (16), calibration (11), and luminescence (24) detectors receive inputs from the same optical subsystem (8). This arrangement allows calibration (spectral accuracy and even correction or repair), as well as modulation reflectance spectroscopy and luminescence spectroscopy to be simultaneously performed without the need for a filter such as a notch filter.

Phantom for evaluating nondosimetric functions in a multi-leaf collimated radiation treatment planning system

Abstract: A phantom for evaluating nondosimetric functions in radiation therapy installation having a patient couch and a gantry with a head thereon for generating a multi-leaf collimated beam, wherein the beam is directed toward the couch at an orientation dictated by relative orientations of the couch and gantry. The phantom comprises a base adapted for disposition on the couch, and a component mounted to the base for rotation in accordance with the relative orientations of the couch and gantry. The component incorporates a plurality of known geometrical structures corresponding in shape to the multi-leaf collimated beam. Upon imaging the component, nondosimetric functions may be evaluated by comparing the known geometrical structures with images of the structures and identifying discrepancies therebetween.

Angular domain imaging of objects within highly scattering media using silicon micromachined collimating arrays

Abstract: Optical imaging of objects within highly scattering media, such as tissue, requires the detection of ballistic/quasi-ballistic photons through these media. Recent works have used phase/coherence domain or time domain tomography (femtosecond laser pulses) to detect the shortest path photons through scattering media. This work explores an alternative, angular domain imaging, which uses collimation detection capabilities of small acceptance angle devices to extract photons emitted aligned closely to a laser source. It employs a high aspect ratio, micromachined collimating detector array fabricated by high-resolution silicon surface micromachining. Consider a linear collimating array of very high aspect ratio (200: 1) containing 51/spl times/1000 /spl mu/m etched channels with 102-/spl mu/m spacing over a 10-mm silicon width. With precise array alignment to a laser source, unscattered light passes directly through the channels to the charge coupled device detector and the channel walls absorb the scattered light at angles >0.29/spl deg/. Objects within a scattering medium were scanned quickly with a computer-controlled Z axis table. High-resolution images of 100-/spl mu/m-wide lines and spaces were detected at scattered-to-ballistic ratios of 5/spl times/10/sup 5/: 1, with objects located near the middle of the sample seen at even higher levels. At >5/spl times/10/sup 6/: 1 ratios, a uniform background of scattered illumination degrades the image contrast unless recovered by background subtraction. Monte Carlo simulation programs designed to test the angular domain imaging concept showed that the collimator detects the shortest path length photons, as in other optical tomography methods. Furthermore, the collimator acts as an optical filter to remove scattered light while preserving the image resolution. Simulations suggest smaller channels and longer arrays could enhance detection by >100.

Improving sensitivity of a small angle x-ray scattering camera with pinhole collimation using separated optical elements

Abstract: We show that a significant improvement in the sensitivity of a Huxley–Holmes design for a small angle x-ray scattering camera is obtained by separating the mirror and the monochromator. The design of the camera involves a long x-ray mirror close to a point x-ray source associated with a curved focusing crystal located close to the sample. The sample area is located at half the distance between the source and detector planes. Diffuse scattering produced by the mirror is not incident on the focusing crystal, thus reducing the background signal. Complete elimination of hard x rays allows precise calibration and hence absolute determination of sample cross section by means of a semitransparent beam stop. In pinhole geometry, the flux corresponds to a ∼107 photons/s through the sample, collimated to 10−2 A−1 in q range. This allows determination of scattered intensities on the order of 10−3 cm−1, corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. As a reference sample, the widely used Lupolen™, a semicrystalline polymer, is calibrated. The high-q limit (q≈4.5 nm−1) of a porous calcite sample can be used as a secondary standard for specific area determination of solid/solid or solid–liquid dispersions.

Standardized Collimated Beam Testing Protocol for Water/Wastewater Ultraviolet Disinfection

Abstract: Ultraviolet (UV) irradiation has emerged as a viable alternative for water/wastewater disinfection. Laboratory dose-response data from collimated-beam tests are commonly used as a basis for determining the necessary delivered UV dose for full-scale UV systems as measured by UV intensity and exposure time. While researchers often think that germicidal dose can be estimated confidently in a collimated beam system, the reported dose-response relationships vary considerably. Numerous factors may affect the test results to some extent. They include apparatus setup, column dimensions, UV lamp type and output, intensity measurement, shutter type and operation, petri dish specifications, sample volume and depth of the liquid, mixing condition, laboratory settings, microbial organism preparation and testing, and water quality. The methodology used to calculate the UV dose for collimated beam tests is also a critical factor. To ensure reproducibility or to have a meaningful comparison of results from different collimated beam tests, a standardized protocol for collimated beam testing and its dose calculation is necessary. The standardized collimated beam test can then serve as a tool to calibrate the dose calculation models for field-scale UV reactors and, consequently, to meaningfully compare the dose values derived from these models. A comprehensive standardized collimated beam testing protocol is warranted to advance applications of UV disinfection for water/wastewater. However, development of such a protocol is a significant research effort that will require input from researchers of various technical and disciplinary backgrounds. In addition, some technical issues still need to be clarified by further research. This paper presents important issues associated with collimated beam testing in the context of developing a standard protocol as well as future research needs. The main objective is to serve as a starting point for development of a standardized collimated beam testing protocol that is universally acceptable by researchers, industries, and regulatory agencies.

Collimator assembly having multi-piece components

Abstract: The present invention is directed to a collimator assembly defined by a series of multi-piece collimator elements or plates that extend along at least one dimension of a scintillator pack. Each collimator element has a collimating component and a shielding component that are structurally independent from one another. The collimating components may be connected to the shielding components or separated by a small air gap. The shielding components are wider than the collimating components but the collimating components have a greater height. With this construction, the collimator assembly optimizes collimation and shielding with lower material requirements and reduced overall size.

Micro X-ray fluorescence imaging without scans: toward an element-selective movie.

Abstract: Micro X-ray fluorescence imaging is a promising method for obtaining positional distribution on specific elements in a nondestructive manner. So far, the technique has usually been performed by a 2D positional scan of a sample against a collimated beam. However, the total measuring time can become quite long, since a number of scanning points are needed in order to obtain a high-quality image. The present report discusses a completely different way of performing imaging of elements much more quickly. A combination of grazing-incidence geometry using a rather wide beam and parallel optics for detecting X-rays can produce an X-ray fluorescence image with ∼1 M pixels and with ∼20-μm resolution in 1−2 min or less. The technique has the potential to open up new frontiers in X-ray imaging, particularly in element-selective movie applications.

Development of a high-precision straightness measuring system with DVD pick-up head

Abstract: Al ow-cost and high-precision straightness measurement system using a DVD pick-up head has been developed in this research. By removing its objective lens the pick-up head of a commercial DVD player possesses excellent properties of stable laser power, collimated laser beam, circular Gaussian distribution and sensitive photodetectors. A moving knife-edge piece is placed between the pick-up head and a plane mirror. According to the knife-edge principle, the non-shaded part of the laser beam will be reflected back and focused onto the four-quadrant photodetector of the pick-up head. The four-quadrant signals are added to measure the returned laser power. Theoretical analysis based on the circular Gaussian distribution theory and regression method can attain the straightness error of the knife-edge while it moves along the beam direction. This low-cost system can apply to the straightness measurement of precision coordinate measuring machines and NC machine tools. Experimental results showed the achieved accuracy is better than ±0.2 µ mw ithin the measuring range of 200 µm.

Image scanning device having a system for determining the distance to a target

Abstract: An image scanning device is provided which includes a system for determining the distance to a target to be scanned. The image scanning device includes an optical system and an image sensor array for focusing a light beam and imaging the target. The device preferably includes an automatic focusing system for adjusting the position of the optical system in order to adjust the focal point, and thereby focus the image of the target onto the image sensor array. In one embodiment of the image scanning device, the distance is determined by analyzing a collimated aiming pattern formed by collimating the light beam. In another embodiment, the distance is determined by analyzing a speckle pattern caused by the speckle effect upon the light beam hitting the target.

Confocal probe and confocal microscope

Abstract: PROBLEM TO BE SOLVED: To provide a confocal probe constituted so that any light beam made incident on a part to be observed may have nearly uniform power by restraining the loss of light quantity, and also made compact and thin in terms of diameter. SOLUTION: The confocal probe is provided with an optical fiber for guiding a beam radiated from a light source part and having wavelength of specified width into the confocal probe, a collimating lens for changing the beam emitted from the end face of the optical fiber to parallel beams, a dispersion prism for dispersing the parallel beams to multiple dispersed light beams in accordance with the wavelength, and a condensing means for condensing the multiple dispersed light beams so that the respective dot images of the dispersed light beams formed on the part to be observed may be arranged in a 1st direction. COPYRIGHT: (C)2004,JPO&NCIPI