Showing papers on "Collimated light published in 2013"

Terahertz single pixel imaging with an optically controlled dynamic spatial light modulator

Abstract: We present a single pixel terahertz (THz) imaging technique using optical photoexcitation of semiconductors to dynamically and spatially control the electromagnetic properties of a semiconductor mask to collectively form a THz spatial light modulator (SLM). By co-propagating a THz and collimated optical laser beam through a high-resistivity silicon wafer, we are able to modify the THz transmission in real-time. By further encoding a spatial pattern on the optical beam with a digital micro-mirror device (DMD), we may write masks for THz radiation. We use masks of varying complexities ranging from 63 to 1023 pixels and are able to acquire images at speeds up to 1/2 Hz. Our results demonstrate the viability of obtaining real-time and high-fidelity THz images using an optically controlled SLM with a single pixel detector.

A six-degree-of-freedom surface encoder for precision positioning of a planar motion stage

Abstract: This paper presents a multi-axis surface encoder that can measure six-degree-of-freedom (six-DOF) translational displacement motions and angular motions of a planar motion stage. The six-DOF surface encoder is composed of a planar scale grating and an optical sensor head. A blue laser diode with a wavelength of 405 nm and an output power of 25 mW was employed as the light source of the sensor head. The light rays from the laser diode were collimated to a parallel beam with a diameter of 1.8 mm. The collimated beam was divided by a beam splitter into two beams, which were projected onto the scale grating and a reference grating with an identical grating period of 0.57 μm, respectively. The three-DOF translational displacement motions of the scale grating with respect to the sensor head along the X -, Y - and Z -directions were detected from the interference signals generated by superimposition of the first-order diffraction beams from the two gratings. A part of the zeroth-order and the negative first-order diffraction beams from the scale grating were employed for detection of the three-DOF angular motions about the X -, Y - and Z -axes. The sensor head was designed to have a dimension of 95 mm ( X ) × 90 mm ( Y ) × 25 mm ( Z ) so that it can be mounted on a previously developed planar motion stage. The grating area of the scale grating was designed to be 60 mm ( X ) × 60 mm ( Y ), which was larger than the stage moving ranges of 40 mm ( X ) × 40 mm ( Y ). Experiments were carried out to test the basic performances of the surface encoder.

Microrod compression of laser beam in combination with transmit lens

Abstract: A LIDAR device may transmit light pulses originating from one or more light sources and may receive reflected light pulses that are detected by one or more detectors. The LIDAR device may include a lens that both (i) collimates the light from the one or more light sources to provide collimated light for transmission into an environment of the LIDAR device and (ii) focuses the reflected light onto the one or more detectors. Each light source may include a respective laser diode and cylindrical lens. The laser diode may emit an uncollimated laser beam that diverges more in a first direction than in a second direction. The cylindrical lens may pre-collimate the uncollimated laser beam in the first direction to provide a partially collimated laser that diverges more in the second direction than in the first direction.

Collimated plasmon beam: nondiffracting versus linearly focused.

Abstract: We worked out a new group of collimated plasmon beams by the means of in-plane diffraction with symmetric phase modulation. As the phase type changes from 1.8 to 1.0, the beam undergoes an interesting evolution from focusing to a straight line. Upon this, an intuitive diagram was proposed to elucidate the beam nature and answer the question of whether they are nondiffracting or linear focusing. Based on this diagram, we further achieved a highly designable scheme to modulate the beam intensity (e.g., ``lossless'' plasmon). Our finding holds remarkable generality and flexibility in beam engineering and would inspire more intriguing photonic designs.

Light emitting device and related projection system

Abstract: A light-emitting device and a related projection system. Light-emitting devices (300, 400) comprise: a light source unit (1) and focusing lenses (330, 430). The light source unit (1) comprises laser units (310, 410) and collimating lenses (320, 420) corresponding to the laser units (310, 410). The light-emitting surface of the laser units (310, 410) is a rectangle, and the light divergence angle of laser passing through the cross-section of the long side of the rectangle is smaller than the light divergence angle of same passing through the cross-section of the short side of the rectangle. The collimating lenses (320, 420) are used for focusing the laser from the laser units (310, 410) on a target surface to form a predetermined light spot. The laser units (310, 410) are located on the light axis of the collimating lenses (320, 420) in a predetermined position deviating from the focal point thereof, so that the predetermined light spot has a predetermined length-width ratio. The light-emitting device and the related projection system have the advantages of relatively small regulation quantity and relatively high assembly efficiency.

A mathematical model of the single freeform surface design for collimated beam shaping

Abstract: Incoherent collimated beam has a wide application, and reshaping the collimated beam with freeform optics has become a popular and challenging topic of noniamging design. In this paper, we address this issue, embedded in three-dimensional space without any symmetry, with a freeform surface from a new perspective. A mathematical model is established for achieving the one-freeform surface design based on the problem of optimal mass transport. A numerical technique for solving this design model is disclosed for the first time, and boundary conditions for balancing light are presented. Besides, some key issues in achieving complex illuminations are addressed, and the influence of caustic surface on this design model is also discussed. Design examples are given to verify these theories. The results show elegance of the design model in tackling complex illumination tasks. The conclusions obtained in this paper can be generalized to achieve LED illumination and tackle multiple freeform surfaces illumination design.

Direct Electron Acceleration with Radially Polarized Laser Beams

Abstract: In the past years, there has been a growing interest in innovative applications of radially polarized laser beams. Among them, the particular field of laser-driven electron acceleration has received much attention. Recent developments in high-power infrared laser sources at the INRS Advanced Laser Light Source (Varennes, Qc, Canada) allowed the experimental observation of a quasi-monoenergetic 23-keV electron beam produced by a radially polarized laser pulse tightly focused into a low density gas. Theoretical analyses suggest that the production of collimated attosecond electron pulses is within reach of the actual technology. Such an ultrashort electron pulse source would be a unique tool for fundamental and applied research. In this paper, we propose an overview of this emerging topic and expose some of the challenges to meet in the future.

Astrophysics of Magnetically Collimated Jets Generated from Laser-Produced Plasmas

Abstract: The generation of astrophysically relevant jets, from magnetically collimated, laser-produced plasmas, is investigated through three-dimensional, magnetohydrodynamic simulations. We show that for laser intensities I∼10(12)-10(14) W cm(-2), a magnetic field in excess of ∼0.1 MG, can collimate the plasma plume into a prolate cavity bounded by a shock envelope with a standing conical shock at its tip, which recollimates the flow into a supermagnetosonic jet beam. This mechanism is equivalent to astrophysical models of hydrodynamic inertial collimation, where an isotropic wind is focused into a jet by a confining circumstellar toruslike envelope. The results suggest an alternative mechanism for a large-scale magnetic field to produce jets from wide-angle winds.

Optical system generating a structured light field from an array of light sources by means of a refracting or reflecting light structuring element

Abstract: An optical system for the generation of a structured light field comprises an array of light sources and a structuring unit separate from said array of light sources, said structuring unit being refractive or reflective and transforming the output of that array of light sources into a structured light illumination by collimating the light beam of each individual light source and directing each beam into the scene under vertical and horizontal angles that can be arbitrarily chosen by refraction or reflection.

X-ray luminescence optical tomography imaging: experimental studies

Abstract: We present a hybrid imaging modality, x-ray luminescence optical tomography (XLOT), in which collimated x-ray beams are used to excite phosphor-based contrast agents. Images are reconstructed from the optical signals, using the known x-ray beam location and spatial extent as priors. We demonstrate XLOT using phantom experiments with deep targets and show that the reconstructed signal varies by <12% when the depth changes from 4.2 to 7.7 mm. For simple source distributions, we find as few as two orthogonal projection measurements are sufficient for XLOT reconstruction.

Directionally illuminated waveguide arrangement

Abstract: Disclosed is a light guiding valve apparatus comprising an optical valve, a two dimensional light source array and a focusing optic for providing large area collimated illumination from localized light sources. A stepped waveguide may be a stepped structure, in which the steps may be extraction features optically hidden to guided light, propagating in a first forward direction. Returning light propagating in a second backward direction may be refracted, diffracted, or reflected by the features to provide discrete illumination beams exiting from the top surface of the waveguide. A two dimensional array of viewing windows may be produced. Such controlled illumination may provide for efficient, multi-user autostereoscopic displays with wide viewing freedom and low cross talk and near-eye displays that are substantially transparent.

Telecentric Scale Projection System for Real-Time In-Situ Surgical Metrology

Abstract: A system and method for determining endoscopic dimensional measurements including a projector assembly comprising a light source for projecting light through a telecentric lens and into a surgical site, and a mask coupled to the projector assembly. Light projected from the light source projects through the mask. The projected light through the mask may be a collimated pattern which does not significantly change in size as a function of the distance to a projected plane. The projected light patterns may include multiple wavelengths of light for measurements of different features of tissue and may be produced using a laser in conjunction with a light shaping optical diffuser, or using a light emitting diode in conjunction with a light shaping optical diffuser, or using a spatial filter. The projected light patterns may take the form of concentric rings with each ring representing a radius of a given dimension.

A Bragg beam splitter for hard x-ray free-electron lasers.

Abstract: We report a Bragg beam splitter developed for utilization of hard x-ray free-electron lasers. The splitter is based on an ultrathin silicon crystal operating in the symmetric Bragg geometry to provide high reflectivity and transmissivity simultaneously. We fabricated frame-shaped Si(511) and (110) crystals with thicknesses below 10 μm by a reactive dry etching method using atmospheric-pressure plasma. The thickness variation over an illuminated area is less than 300 nm peak-to-valley. High crystalline perfection was verified by topographic and diffractometric measurements. The crystal thickness was evaluated from the period of the Pendellosung beats measured with a highly monochromatic and collimated x-ray probe. The crystals provide two replica pulses with uniform wavefront [(<1/50)λ] and low spatial intensity variation (<5%). These Bragg beam splitters will play an important role in innovating XFEL applications.

Electro-optic system for crosswind measurement

Abstract: An electro-optic system, e.g., mounted to a weapon, measures down range winds and a range-to-target for compensating the ballistic hit point. The system may include an optical light source, collimated to generate a laser spot on the target. The system may include a wind measurement receiver that captures laser light scattered from the target. The captured light may be modulated by atmospheric scintillation eddies, producing optical patterns which change in time and move with the crosswind. These patterns may be analyzed by a processor using covariance techniques in either the time-domain or the frequency-domain to determine path-integrated crosswinds and associated errors. Ranging is done by measuring the time of flight of the laser pulse to the target collecting the scattered signal from the target. Compensated ballistic hit point, measurement errors and other data may be displayed on a micro-display digital eyepiece, or projected onto the direct view optics (DVO) of a riflescope so as to be overlaid in real-time on the optical image of the target.

Head-wearable display with collimated light source and beam steering mechanism

Abstract: A head-wearable display includes a collimated light source, a beam steering mechanism, and a synchronization controller. The collimated light source selectively emits collimated light. The beam steering mechanism is optically coupled to receive the collimated light and angularly scans the collimated light between beam steering states that each redirect the collimate light to a different angular direction along at least one angular dimension. The beam steering mechanism is coupled to scan the collimated light across an eyebox. The synchronization controller is coupled to the collimated light source and the beam steering mechanism to synchronize selective emission of the collimated light from the collimated light source with the beam steering states of the beam steering mechanism to repetitiously draw an image in the eyebox.

Backlight having collimating reflector

Abstract: A backlight includes a plate light guide to guide light, a light source to produce light, and a collimating reflector to substantially collimate the produced light. The collimating reflector also is to direct that collimated light into the plate light guide as guided light of the plate light guide. A portion of the guided light in the backlight is to be emitted from a surface of the backlight as emitted light.

Light source device and image display apparatus

Abstract: A light source device and an image display apparatus include a Blue Laser Diode (B-LD) light source unit, a dichroic mirror to reflect substantially collimated Blue (B) light from the B-LD light source unit, a lens to focus the B light reflected by the dichroic mirror, and a color wheel comprising a Green (G) fluorescent section which is excited by the collimated B light to emit and to reflect G light and a B mirror reflector to mirror-reflect the B light, wherein a center of a light flux of the B light reflected by the dichroic mirror is on other than an optical axis of the lens.

Detecting small low emission radiating sources

Abstract: In order to prevent influx of highly enriched nuclear material throu-gh border checkpoints, new advanced detection schemes need to be developed. Typical issues faced in this context are sources with very low emission against a dominating natural background radiation. Sources are expected to be small and shielded and hence cannot be detected from measurements of radiation levels alone. We consider collimated and Compton-type measurements and propose a detection method that relies on the geometric singularity of small sources to distinguish them from the more uniform background. The method is characterized by high sensitivity and specificity and allows for assigning confidence probabilities of detection. The validity of our approach can be justified using properties of related techniques from medical imaging. Results of numerical simulations are presented for collimated and Compton-type measurements. The 2D case is considered in detail.

Laser-driven generation of collimated ultra-relativistic positron beams

Abstract: We report on recent experimental results concerning the generation of collimated (divergence of the order of a few mrad) ultra-relativistic positron beams using a fully optical system The positron beams are generated exploiting a quantum-electrodynamic cascade initiated by the propagation of a laser-accelerated, ultra-relativistic electron beam through high-Z solid targets As long as the target thickness is comparable to or smaller than the radiation length of the material, the divergence of the escaping positron beam is of the order of the inverse of its Lorentz factor For thicker solid targets the divergence is seen to gradually increase, due to the increased number of fundamental steps in the cascade, but it is still kept of the order of few tens of mrad, depending on the spectral components in the beam This high degree of collimation will be fundamental for further injection into plasma-wakefield afterburners

Backlight having dual collimating reflectors

Abstract: A backlight to emit light from a surface thereof includes a light guide to guide light, first and second collimating reflectors and a light source to produce light. The first collimating reflector is at a first edge of the light guide to collimate the light from the light source in a vertical direction and to direct the collimated light into the light guide. The second collimating reflector is at a second edge of the light guide to further collimate the collimated light in a horizontal direction and to redirect the further collimated light back into the light guide.

Beam shaping of edge-emitting diode lasers using a single double-axial hyperboloidal micro-lens

Abstract: We report an innovative approach for beam shaping of edge-emitting semiconductor diode lasers using a single double-axial hyperboloidal micro-lens fabricated with femtosecond laser direct writing technology. The two hyperboloids of different axial lengths focus the light from fast and slow axes to an identical focal spot. The divergence angles were shaped from 60 and 9 to 6.9 and 32.3 mrad, respectively, and the single-end fiber coupling efficiency is measured higher than 80%. The device is simple in fabrication, robust in structure, and easy for operation, by which multiple reflections and absorptions at interfaces are reduced, and assembly errors are minimized. 2013 Optical Society of America.

Angular diversity approach to indoor positioning using visible light

Abstract: A system for indoor localization using partially collimated light from individual LEDs inside a luminary is proposed, simulated and tested experimentally. A simple biconvex lens provides angular diversity to the luminary and generates multiple spatially separated regions of overlapping light which can be resolved with a single detector receiver. This approach provides location information without relying on signal intensity measurements, time-of-flight data or complex imaging approaches. The multiple LEDs available in each luminary are exploited to create a large number of uniquely detectable regions, enabling both low positioning error and low complexity. Using a model based on experimental measurements, in a prototypical 5×5×3 m room the average positioning error is 26.0 cm using 4 luminaries and 12.9 cm with 9 luminaries.

Bimorph mirrors: The Good, the Bad, and the Ugly

Abstract: Bimorph mirrors are widely used by the X-ray, Laser, Space, and Astronomy communities to focus or collimate photon beams. Applying voltages to the embedded piezo ceramics enables the user to globally bend the optical substrate to a range of figures (including cylindrical, parabolic, and elliptical), and finely correct low spatial frequency errors, thus improving optical performance. Bimorph mirrors are employed on numerous synchrotron X-ray beamlines, including several at Diamond Light Source. However, many such beamlines were not achieving the desired size and shape of the reflected X-ray beam. Metrology data from ex-situ, slope measuring profilometry (using the Diamond-NOM) and in-situ, synchrotron X-ray “pencil-beam” scans, revealed sharp defects on the optical substrate directly above the locations at which the piezo ceramics are bonded together. This so-called “junction effect” has been observed on a variety of bimorph mirrors with different numbers of piezos, substrate length, and thickness. To repair this damage, three pairs of bimorph mirrors were re-polished at Thales-SESO. We review the re-polishing process, and show that it successfully removed the junction effect, and significantly improved beamline performance. Since the internal structure of the bimorph mirrors was not modified during re-polishing, it is hoped that the mirrors will retain their surface quality, and remain operational for many years. We also highlight the combination of super-polishing techniques with bimorph technology to create the “Ultimate” mirror, and discuss a next generation, bimorph mirror which is predicted not to suffer from the junction effect.

Characterization of a SPECT pinhole collimator for optimal detector usage (the lofthole)

Abstract: In single-photon emission computed tomography (SPECT), multi-pinhole collimation is often employed nowadays. Most multi-pinhole collimators avoid overlap (multiplexing) of the projections on the detector. This can be done by using additional shielding or by spacing the pinholes far enough apart. Using additional shielding has the drawback that it increases weight, design complexity and cost. Spacing the pinholes far enough apart results in sub-optimal detector usage, the valuable detector area is not entirely used. This is due to the circular projections of pinholes on the detector; these ellipses can not be tiled with high detector coverage. To overcome this we designed a new pinhole geometry, the lofthole, that has a rectangular projection on the detector. The lofthole has a circular aperture and a rectangular entrance/exit opening. Sensitivity formulae have been derived for pinholes and loftholes. These formulae take the penumbra effect into account; the proposed formulae do not take penetration into account. The derived formulae are valid for geometries where the field-of-view and the sensitivity of the aperture are solely limited by the exit window. A flood map measurement was performed to compare the rectangular projection of a lofthole with the circular projection of a pinhole. Finally, measurements were done to compare the amount of penetration of pinholes with the amount of penetration of a lofthole. A square lofthole collimator has less penetration than a knife-edge pinhole collimator that irradiates the same rectangular detector area with full coverage. A multi-lofthole collimator allows high detector coverage without using additional shielding. An additional advantage is the lower amount of penetration.

Free-space to single-mode collection efficiency enhancement using photonic lanterns.

Abstract: We demonstrate single-mode collection efficiency enhancement for free space optical systems using a photonic lantern to collect scattered infrared light from diffuse objects at far- and near-field distances. A single-mode collection efficiency improvement of ∼8 dB is demonstrated in the near-field region relative to standard single-mode fiber. The insertion loss properties of the photonic lantern are also analyzed, and an additional insertion loss penalty is observed for near-field distances when the transmitted beam is collimated. The photonic lantern can be used for coherent detection systems such as light detection and ranging and free-space optical communication with improved collection efficiency and nearly perfect mode matching.

Analytical design of freeform optical elements generating an arbitrary-shape curve

Abstract: A method is proposed for designing refractive optical elements focusing a collimated incident beam into a curve with specified shape. A general relationship for the freeform surface of the optical element is derived as an envelope of a parametric family of hyperboloids of revolution that focuses the incident beam into the points on the curve. Using the thin optical element approximation, the calculation of the hyperboloid parameters providing required irradiance distribution along the curve is reduced to the solution of an explicit first order differential equation. Optical elements generating line segment focus and circular arc focus are designed. The simulation results demonstrate generation of high-quality curves.

Compact high-resolution gamma-ray computed tomography system for multiphase flow studies

Abstract: In this paper, a compact high-resolution gamma-ray Computed Tomography (CompaCT) measurement system for multiphase flow studies and tomographic imaging of technical objects is presented. Its compact and robust design makes it particularly suitable for studies on industrial facilities and outdoor applications. Special care has been given to thermal ruggedness, shock resistance, and radiation protection. Main components of the system are a collimated 137Cs isotopic source, a thermally stabilised modular high-resolution gamma-ray detector arc with 112 scintillation detector elements, and a transportable rotary unit. The CompaCT allows full CT scans of objects with a diameter of up to 130 mm and can be operated with any tilting angle from 0° (horizontal) to 90° (vertical).

Directional grating-based backlighting

Abstract: A directional grating-based backlight includes a light guide to guide light and three sets of diffraction gratings. The diffraction grating sets are to selectively couple out portions of light to be guided by the light guide. The light is to propagate within the light guide in three different propagation directions separated in angle by about 120 degrees. The sets of diffraction gratings are to couple out different portions of the guided light as substantially collimated light using diffraction coupling. The substantially collimated light is to be emitted from the directional grating-based backlight in substantially the same direction.

Three-coordinate digital autocollimator

Abstract: Studies have been carried out to determine the characteristics of a three-coordinate digital autocollimator under laboratory conditions. The results of the studies confirmed that the proposed autocollimator can efficiently determine the angular strains of large objects of the type of the primary mirror of a radio telescope.