Showing papers on "Collimated light published in 2004"

Substrate-guided optical devices

Abstract: There is provided an optical device, having a light-transmitting substrate (20) having at least two major surfaces parallel to each other and edges; a display light source; optical means for coupling light from the light source into the substrate (20) by internal reflection, and at least one partially reflecting surface (22) located in the substrate (20) which is non-parallel to the major surfaces of the substrate wherein the source emits light waves located in a given field-of-view, that the light waves are collimated, that an angular resolution is defined for the optical device, and wherein the angular deviation between any two different rays located in one of the collimated light waves, is smaller than the angular resolution.

Refractive transmission of light and beam shaping with metallic nano-optic lenses

Abstract: We have performed finite-difference time-domain (FDTD) analysis of optical transmission through a nanoslit array structure formed on a metal layer with tapered film thickness. The analysis result shows refractive transmission of light through the nanoslit array, opening up the possibility of creating metallic lenses that resemble glass lenses in their shape. Metallic lenses with curved surfaces are designed such that each nanoslit element transmits light with phase retardation controlled by the metal thickness in the aperture region. The FDTD analysis result demonstrates a focusing or collimating function of convex-shaped metal lenses.

A flux- and background-optimized version of the NanoSTAR small-angle X-ray scattering camera for solution scattering

Abstract: A commercially available small-angle X-ray scattering camera, NanoSTAR from Bruker AXS, has been modified to optimize its use for weakly scattering solution samples. The original NanoSTAR is a pinhole camera with two Gobel mirrors for monochromating and making the beam parallel, and with a two-dimensional position-sensitive gas detector (HiSTAR) for data collection. The instrument has one integrated vacuum. It was constructed for position-resolved studies and thus has a small beam size at the sample position. In the present work, the instrumental configuration has been optimized by numerical calculations based on phase-space analysis and Monte Carlo simulations in order to obtain a higher flux. This has led to a setup in which the beam at the sample is larger and the collimation part of the instrument is longer, so that divergence of the beam is similar to that of the original camera. An extra pinhole is included after the Gobel mirrors to make the beam size well defined after the mirrors. The camera thus has genuine three-pinhole collimation. The use of electron-microscope pinholes minimizes parasitic scattering. At the University of Aarhus, the modified camera is installed on a powerful rotating-anode X-ray source (MacScience 6 kW Cu with a 0.3 × 0.3 mm effective source size). Measurements have been performed on a wide variety of weakly scattering samples, such as surfactant micelles, homopolymer solutions, block copolymer micelles, proteins etc. The data are routinely converted to absolute scale using the scattering from water as a primary standard. The standard configuration covers the range of scattering vectors from 0.01 to 0.35 A−1 with a flux of 1.7 × 107 photons s−1 for Cu Kα radiation at a generator power of 4.05 kW. The camera is easily converted to a high-resolution version covering 0.0037 to 0.22 A−1 with a loss of flux of about a factor of 10, as well as to a position-resolved version.

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 converging microlens array having an array of lenslets that converge the collimated illumination light. The converging microlens array directs the illumination light to a microelectrical mechanical system (MEMS) optical modulator. The MEMS optical modulator includes, for example, a planar substrate through which multiple pixel apertures extend and multiple MEMS actuators that support and selectively position MEMS shutters over the apertures. A MEMS actuator and MEMS shutter, together with a corresponding aperture, correspond to pixel. The light from the converging microlens array is focused through the apertures and is selectively modulated according to the positioning of the MEMS shutters by the MEMS actuators, thereby to impart image information on the illumination light. The light is then passed to a diffused transmissive display screen by a projection microlens array.

Side-emitting collimator

Abstract: A side-emitting collimator employs a combination of refraction and internal reflection to organize light from a light source into oppositely directed collimated beams. A light source chamber over the light source is defined by substantially cylindrical and aspheric refracting surfaces positioned to gather light into the collimating lens. The aspheric refracting surfaces redirect a portion of the light from the light source into a direction perpendicular to the optical axis of the light source. The substantially cylindrical surfaces refract light from the light source onto an aspheric upper reflecting surface. Light incident upon the aspheric upper reflecting surface is collimated into a direction perpendicular to the optical axis of the light source. The side-emitting collimator includes mirror image collimator halves, each producing a collimated beam. The collimator halves are rotationally symmetric about a common axis of symmetry above a plane including the axis of symmetry.

Vehicle display system

Abstract: System for displaying an incident image for an operator of a vehicle, the system including an optical assembly receiving the incident image from an image source, and a planar optical module optically coupled with the optical assembly, the optical assembly producing a collimated light beam according to the incident image, the planar optical module being located in a line of sight of the operator, the planar optical module displaying a set of output decoupled images, each of the output decoupled images being similar to the incident image, and each of the output decoupled images having a focal point substantially located at an infinite distance from the operator.

Detection of biochemical interactions on a biosensor using tunable filters and tunable lasers

Abstract: An apparatus and method for detection of peak wavelength values of colorimetric resonant optical biosensors using tunable filters and tunable lasers is provided. Biomolecular interactions may be detected on a biosensor by directing collimated white light towards a surface of the biosensor. Molecular binding on the surface of the biosensor is indicated by a shift in the peak wavelength value of reflected or transmitted light from the biosensor, while an increase in the wavelength corresponds to an increase in molecular absorption. A tunable laser light source may generate the collimated white light and a tunable filter may receive the reflected or transmitted light and pass the light to a photodiode sensor. The photodiode sensor then quantifies an amount of the light reflected or transmitted through the tunable filter as a function of the tuning voltage of the tunable filter.

Optical-CT gel-dosimetry II: Optical artifacts and geometrical distortion

Abstract: There is a clear need for technology that enables accurate, high-resolution, three-dimensional (3D) measurement of intricate dose distributions associated with modern radiation treatments. A potential candidate has emerged in the form of water-equivalent "3D gel dosimetry" utilizing optical-computed-tomography (optical-CT). In a previous paper we presented basic physical characterization of an in-house prototype optical-CT scanning system. The present paper builds on that work by investigating sources of optical artifacts and geometric distortion in optical-CT scanning. Improvements in scanner design are described. Correction strategies were developed to compensate for reflection and refraction, imperfections in the water-bath, signal drift, and other effects. Refraction and reflection were identified as the principal factors causing inaccurate reconstruction of absolute attenuation coefficients. A correction specific to a given flask was developed utilizing prescans of the flask when filled with water-bath fluid, thereby isolating the refractive and reflective components for that flask. Residual artifacts were corrected by fitting a theoretical model to the well-behaved portion of these prescans and extrapolating to regions of lost data, enabling reconstruction of absolute optical-CT attenuation coefficients to within 4% of corresponding spectrophotometer values. Needle phantoms are introduced to quantify geometric distortion under a range of conditions. Radial distortion of reconstructed needle positions was reduced to < 0.3 mm (0.27% of the field of view) through adjustment of the water-bath refractive index. Geometric distortion in polymer gel due to radiation-induced refractive index changes was found to be negligible under the conditions examined. The influence of scattered light on reconstructed attenuation coefficients was investigated by repeat optical-CT scans while varying the aperture of a scatter-rejecting collimator. Significant depression of reconstructed attenuation coefficients was observed, particularly under conditions of poor scatter rejection collimation. The general conclusion is that the first-generation optical-CT technique can be made insensitive to geometrical distortion, but can be susceptible to scatter effects. For accurate reconstruction of absolute attenuation coefficients, correction strategies are essential.

Analysis of splitters for self-collimated beams in planar photonic crystals

Abstract: In this paper, we present methods for beam splitting in a planar photonic crystal, where the light is self-guided as dictated by the selfcollimation phenomenon. We present an analysis of a one-to-two and one-to-three beam splitter in a self-guiding photonic crystal lattice and validate our design and simulations with experimental results. Moreover, we present the first one-to-three splitter in a self-guiding planar photonic crystal. Additionally, we discuss the ability to tune the properties of these devices and present initial experimental results.

Projection display systems utilizing color scrolling and light emitting diodes

Abstract: A projection display system has at least one light-recycling illumination system, a color scroller and an imaging light modulator. The light-recycling illumination system includes a light source that is enclosed within a light-recycling envelope. The light source is a light-emitting diode that emits light, and a fraction of that light will exit the light-recycling envelope through an aperture. The light-recycling envelope recycles a portion of the light emitted by the light source back to the light source in order to enhance the luminance of the light exiting the aperture. The fraction of the light that exits the aperture is partially collimated and is directed to a color scrolling means. The color scroller scans the partially collimated light across the face of the imaging light modulator. The imaging light modulator spatially modulates the scrolled beam of light to form an image.

Projection display systems utilizing light emitting diodes and light recycling

Abstract: A projection display system has at least one light-recycling illumination system and at least one imaging light modulator. The light-recycling illumination system includes a light source that is enclosed within a light-recycling envelope. The light source is a light-emitting diode that emits light, and a fraction of that light will exit the light-recycling envelope through an aperture. The light-recycling envelope recycles a portion of the light emitted by the light source back to the light source in order to enhance the luminance of the light exiting the aperture. The fraction of the light that exits the aperture is partially collimated and is directed to the imaging light modulator. The imaging light modulator spatially modulates the partially collimated light to form an image.

Diffractive optical coupling element for surface plasmon resonance sensors

Abstract: Design, technological features, and performance of polymeric diffractive optical coupling elements (DOCEs), developed for surface plasmon resonance (SPR) sensors are reported. The concept is based on input and output coupling of collimated and perpendicularly incident light beams to exchangeable SPR sensor chips. In the SPR sensor chips, one DOCE couples the input light beam to a (bio-)chemical sensor surface and another DOCE images the output light beam onto a detector array. The manufacturing technique is based on an injection moulding process similarly to the manufacturing process of compact discs allowing precision manufacturing and reproduction of the grating topography of the DOCEs. The DOCE-based SPR sensor chip is specifically suitable for miniaturisation and large scale production, while maintaining high optical quality and performance.

High pulse-energy, eye-safe lidar system

Abstract: An eye-safe atmospheric aerosol lidar featuring high transmit pulse energy to generate strong backscatter from long ranges in a single pulse together with an optically efficient receiver is disclosed. The transmitter employs a gas cell and non-focused laser beam geometry to convert short wavelength laser light to substantially safer and longer wavelength light by stimulated Raman scattering. The longer wavelength light is substantially safer than the shorter wavelength light thereby allowing the safe transmission of high energy pulses. The transmitter also features a diode injection seed and a beam expander which are effective to reduce the divergence of the long wavelength light below the field-of-view of the receiver. The receiver employs a telescope, collimating lens, interference filter, focusing lens, avalanche photodiode detector, amplifier and analog to digital converter. The transmit beam and receiver field of view are coaxial. Initial results demonstrate the ability of such technology to elucidate the structure of the atmosphere with high temporal and spatial resolution.

Illumination system with LEDs

Abstract: The luminance of a system that includes a light emitting diode (LED), such as a projection system, may be increased by using an LED chip that has a light emitting surface that emits light directly into any medium with a refractive index of less than or equal to approximately 1.25. For example, the LED chip may emit light directly into the ambient environment, such as air or gas, instead of into an encapsulant. The low refractive index decreases the etendue of the LED, which increases luminance. Moreover, without an encapsulant, a collimating optical element, such as a lens, can be positioned close to the light emitting surface of the LED chip, which advantageously permits the capture of light emitted at large angles. A secondary collimating optical element may be used to assist in focusing the light on a target, such as a micro-display.

Annular Gaussian beams in turbulent media

Abstract: A laser beam with a different irradiance profile may have favorable scintillation and diffraction characteristics, which are important qualities in the area of optical wireless communication. The propagation in random media (atmosphere) of a laser beam with an annular, donut-shaped, irradiance cross section was examined. Annular beams are created by unstable optical resonators, which are used as resonant cavities in high power lasers, and by beam expanders that consist of telescopes where the second mirror obstruct the central portion of the circular aperture. The annular beam was modeled as the difference of two collimated Gaussian beams, with different spot sizes. Diffraction and scintillation characteristics of the annular beam, for horizontal near ground propagation (i.e. constant refractive-index structure parameter Cn2), were compared to one collimated and one focused Gaussian beam. The Rytov approximation was used to calculate the on-axis scintillation index in weak atmospheric turbulence for both the annular and the Gaussian beams. The extended Huygens-Fresnel integral was solved to obtain the mean irradiance, from which the fraction of power in half aperture diameter was calculated.

Active correction of thermal lensing through external radiative thermal actuation

Abstract: Absorption of laser beam power in optical elements induces thermal gradients that may cause unwanted phase aberrations. In precision measurement applications, such as laser interferometric gravitational-wave detection, corrective measures that require mechanical contact with or attachments to the optics are precluded by noise considerations. We describe a radiative thermal corrector that can counteract thermal lensing and (or) thermoelastic deformation induced by coating and substrate absorption of collimated Gaussian beams. This radiative system can correct anticipated distortions to a high accuracy, at the cost of an increase in the average temperature of the optic. A quantitative analysis and parameter optimization is supported by results from a simplified proof-of-principle experiment, demonstrating the method’s feasibility for our intended application.

Opthalmic talbot-moire wavefront sensor

Abstract: A system for measuring the eye comprising a light source (10) which sends a narrow collimated beam of light (12), to reflect from a beam splitter (14). The beam of light (12) enters the eye (16) through the pupil (17) where it is focused to a point (20) on the retina (18). The light (12) is reflected from the retina (18) where it passes through a series of relay lenses (22, 24). The light then passes through one or more reticles (26, 28). A CCD camera (30) records the shadow pattern formed by reticles (26, 28). The shadow pattern is digitized into a computer and algorithms are created to calculate the distortions. As a result of the above steps being performed, the refractive power of the eye, with or without corrective lenses in place, can be measured at many points, simultaneously.

Diode-pumped chirped pulse amplification to the joule level

Abstract: The POLARIS project aims at the development of an all-diode-pumped, high-peak-power femtosecond laser system reaching the petawatt level. The laser amplifiers are based on pumping Yb3+-doped fluoride phosphate glass at 940 nm. Recently, stable operation of the first three amplifiers was achieved. Pulses with a bandwidth of 12 nm, which supports 135 fs pulses with energies up to 1.25 J, were generated in the third amplifier with a 12-pass configuration. The amplifier was pumped by 150 collimated high-power laser diodes. Successive polarization maintenance is used for a compact, stable, and convenient adjustable setup. Thermally induced abberations of lowest order were compensated by adaptive mirrors.

Parallel-beam scanning for surface patterning of materials

Abstract: A system and method for parallel-beam scanning a surface. An energetic beam source emits an energetic collimated beam which is received by an optical device, comprising: one or more optical media, operable to receive the emitted beam, such as two pairs of coordinated mirrors or a right prism, and at least one actuator coupled to the one or more optical media, and operable to rotate each of the one or more optical media around a respective axis to perform a parallel displacement of the beam in a respective direction, wherein the respective direction, the beam, and the respective axis are mutually orthogonal. The optical device is operable to direct the beam to illuminate a sequence of specified regions of a surface.

Light guide array, fabrication methods and optical system employing same

Abstract: A light guide array (30) for outputting light with improved uniformity and collimation includes a supporting material (35) and a plurality of light guides (32) formed in the supporting material. Each of the light guides (32) has an entrance aperture for receiving light and an exit aperture for outputting light. The light guides (32) can be solid pipes or hollow tunnels passing through the supporting material (35). The supporting material (35) can be a metal, such as Al, Au, Ni, a semiconductor material, such as silicon, poly-silicon, SiC, GaAs, or an optically transparent material. Semiconductor fabrication techniques can be used to build the array. The array can be incorporated into an optical projection system (125) to improve performance.

Optical interrogation system and method for using same

Abstract: An optical interrogation system and method are described herein that are capable of generating light beams that have desired optical properties which are directed towards a specimen array. In one embodiment, the optical interrogation system includes a light source, a diffractive element and a collimating optic (e.g., simple lens(es), f-θ lens(es), segmented mirror, fiber array). The light source emits a light beam to the diffractive optic which receives the light beam and outputs an array of light beams to the collimating optic. The collimating optic receives and conditions the light beams emitted from the diffractive optic and then outputs the conditioned light beams which have desired optical properties towards a specimen array. Several other embodiments of the optical interrogation system are also described herein.

Method and apparatus for object viewing, observation, inspection, identification, and verification

Abstract: In an object verifier having a housing and an object holder, an object may be placed in the object holder for observation by an operator. The object is illuminated using a collimated beam of white light that is generated by a light generator. The collimated beam of white light is passed through a beam splitter with the two portions of the collimated beam of white light presented to the object at a 90 degree angle one from the other. The interior of the housing includes a reflective surface for maximal illumination of the object. The observer may view the illuminated object through a viewing window and/or through a magnification window. The magnification window provides for the viewing of the object in greater detail.

Study of light transmittance from layers of Fricke-xylenol-orange-gel dosimeters

Abstract: In-phantom absorbed dose is imaged by measuring the optical transmittance through ferrous-sulphate and xylenol-orange infused gel, in form of layers. Images are acquired with a CCD camera provided with a suitable optical filter. The dependence of dosimeter sensitivity and of linearity range on the amount of xylenol orange and on parameters of optical analysis has been inspected. In order to check the capability of the method, dose profiles in the central axis of a phantom irradiated with a collimated γ-beam have been compared with the results obtained with a ionisation chamber.

Potential of a Compton camera for high performance scintimammography.

Abstract: In this paper, we present a novel approach to scintimammography that is based on the Compton camera principle. We analyse the performance of our scheme using Monte Carlo simulations. In particular, we evaluate the detection efficiency, spatial resolution and lesion visibility of the system at several gamma photon energies. The simulation results show that the proposed technique achieves an absolute detection efficiency of 0.03 and a full width at half maximum resolution of 3.8 mm at 141 keV photon energy for point sources 2.5 cm deep in a 5 cm thick breast phantom using 5 mm thick silicon detectors. Furthermore, our approach shows good performance in lesion detection, especially at high gamma photon energies, where mechanically collimated systems perform poorly due to severe septal penetration. With total collected counts of 1.35 million, equivalent to a 30 s acquisition time for an activity concentration level of 3.7 kBq ml(-1) (100 nCi cm(-3)) in normal breast tissue, and a tumour-to-background ratio of 8:1, our system can clearly reveal an 8 mm diameter tumour that is located 2.5 cm deep in a 500 ml breast phantom. We also present a simulation-based quantitative performance comparison between the proposed scintimammographic system and the compact collimated scintimammographic system in the task of lesion detection under a clinical imaging situation using a non-prewhitening matched filter observer model. Our comparison demonstrates that for the same imaging time, the two systems have a comparable performance in detecting an 8 mm tumour at 141 keV, with the proposed system performing marginally better. However, the proposed scintimammographic system clearly outperforms the compact collimated counterpart in the detection of a 5 mm tumour. We also investigate the contribution of scatter and direct radiation from adjacent organs. We find that the background contribution of liver to the right breast is 30% at 141 keV, which can be reduced to 4.8% with shielding.

Dichroic beam combiner utilizing blue LED with green phosphor

Abstract: A white beam (22W) with high color-rendering index is formed by uniting a collimated red beam (22R) and a collimated blue-green beam (22B), the latter having as it's source a blue LED (11) with a green phosphor (12). The white beam is formed by a prism (20)with an amber low-pass dichroic filter. The prism cross-section can be either a square or an equilateral triangle. The triangular prism can have one third of it's mass reduced by stepped facets. Both types of prisms can be elongated to accommodate multiple collimators. Switching between white, red, and blue-green allows application to police vehicles.

Production of ultrahigh-current-density ion beams by short-pulse skin-layer laser–plasma interaction

Abstract: We report experimental evidence, supported by a simple theory and numerical calculations, that the skin-layer subrelativistic interaction of a short (⩽1ps) low-energy (<1J) laser pulse with a thin preplasma layer in front of a solid target can produce a collimated fast ion flux of extremely high ion current density (⩾1010A∕cm2 close to the target), comparable to those predicted for ballistically focused ion beams from relativistic laser–plasma interactions.

Full forward Monte Carlo calculation of portal dose from MLC collimated treatment beams

Abstract: This work deals with a full Monte Carlo (MC) simulation of a radiotherapy treatment facility including a multi-leaf collimator (MLC) and electronic portal imaging device (EPID). A method for a planar calibration of the EPID response in terms of dose using the MC technique is presented. Calibration measurements and simulations with several blocks of attenuating material are carried out down to approximatively 5% of the open field transmitted dose. A linear relationship is shown between the squared EPID signal and the MC calculated dose. The calibrated EPID was used as a dosimetric system to validate a MC model for the MLC. Computations and measurements agreed within 2% of dose difference (or 2 mm in regions of high dose gradient). The technique described herein is not significantly limited by physics transport model constraints. Therefore it can potentially provide a more accurate verification of dose delivery to inhomogeneous anatomical regions in patients undergoing complex multi-field conformal or intensity-modulated radiation therapy.

Light direction from shad(ow)ed random Gaussian surfaces.

Abstract: Three human observers estimated the illumination direction for samples of random Gaussian surfaces illuminated by a collimated beam from random directions. These stimuli appear as ‘texture’ due to ...

A High Flux Source of Cold Rubidium

Abstract: We report the production of a continuous, slow, and cold beam of 87-Rb atoms with an unprecedented flux of 3.2 x 10^12 atoms/s and a temperature of a few milliKelvin. Hot atoms are emitted from a Rb candlestick atomic beam source and transversely cooled and collimated by a 20 cm long atomic collimator section, augmenting overall beam flux by a factor of 50. The atomic beam is then decelerated and longitudinally cooled by Zeeman slowing.

Modal power decomposition of beam intensity profiles into linearly polarized modes of multimode optical fibers.

Abstract: We calculate the modal power distribution of a randomly and linearly polarized (LP) multimode beam inside a cylindrical fiber core from knowledge of spatial-intensity profiles of a beam emitted from the fiber. We provide an exact analysis with rigorous proofs that forms the basis for our calculations. The beam from the fiber end is collimated by a spherical lens with a specific focal length. The original LP-mode basis is transformed by the spherical lens and forms another orthogonal basis that describes the free-space beam. By using this basis, we calculate the modal power distribution from the mutual-intensity profile. This is acquired by adopting a well-known mutual-intensity-profile-retrieving technique based on measurements of the intensity patterns several times after two orthogonal cylindrical lenses with varying separation. The feasibility of our decomposition algorithm is demonstrated with simulations.