Showing papers on "Collimated light published in 2006"

Magnetic Reconnection and Plasma Dynamics in Two-Beam Laser-Solid Interactions

Abstract: We present measurements of a magnetic reconnection in a plasma created by two laser beams (1 ns pulse duration, 1 x 10(15) W cm(-2)) focused in close proximity on a planar solid target. Simultaneous optical probing and proton grid deflectometry reveal two high velocity, collimated outflowing jets and 0.7-1.3 MG magnetic fields at the focal spot edges. Thomson scattering measurements from the reconnection layer are consistent with high electron temperatures in this region.

Eye tracker device

Abstract: Two collimated light beams (LB1 , LB2) are directed towards an eye (100) to provide two reflection spots (G1 , G2). The collimated light beams (LB1 , LB2) are advantageously provided by a diffractive beam expander (400). The reflection spots (G1 , G2) and the pupil (120) of the eye (100) are monitored by an imaging unit (200). The collimated beams (LB1 , LB2) are at different angles (α1 , α2) with respect to the imaging unit (200). The gaze direction (α3) is determined based on said angles (α1 , α2), the positions of the reflections spots (G1 , G2), and the position of the pupil (120). Thanks to the use of the two collimated beams (LB1 , LB2), the detected gaze direction is substantially independent of the size of the eye (100), independent of the lateral position of the eye (100), and independent of the distance (L2) between the imaging unit (200) and the eye (100). The detected gaze angle may be used for selecting between options displayed by a virtual display (500).

Optically oriented three-dimensional polymer microstructures

Abstract: A method and system of creating one or more waveguides and/or patterning these waveguides to form a 3D microstructure that uses mask and collimated light. In one embodiment, the system includes at least one collimated light source selected to produce a collimated light beam; a reservoir having a photo-monomer adapted to polymerize by the collimated light beam; and a mask having at least one aperture and positioned between the at least one collimated light source and the reservoir. Here, the at least one aperture is adapted to guide a portion of the collimated light beam into the photo-monomer to form the at least one polymer waveguide through a portion of a volume of the photo-monomer.

Strehl ratio and scintillation theory for uplink Gaussian-beam waves: beam wander effects

Abstract: First-order weak-fluctuation Rytov theory predicts that the longitudinal (on-axis) component of the scintillation index of an uplink collimated beam will become significantly smaller as the size of the transmitter aperture increases up to around 100 cm. However, the results of recent computer simulations are at odds with this behavior, and we believe that this discrepancy is due to the fact that the conventional Rytov theory does not correctly account for the effects of beam wander on the scintillation index. We present a theoretical structure that accurately describes far-field irradiance fluctuations caused by uncorrected beam wander. This new theory is validated by demonstrating excellent agreement between the predicted scintillation index and computer code results for both tracked and untracked beams. For many applications of practical interest, such as free-space optical communications, a good understanding of the time-average Strehl ratio is also essential simulation results for this parameter are presented and shown to be in good agreement with the theory.

Illuminators using reflective optics with recycling and color mixing

Abstract: Various optical techniques are described for obtaining a specified light output from an LED source. One technique uses a parabolic reflector surrounding an LED or LED array to create a collimated beam, and the light exit opening of the parabolic reflector is defined by a reflective disc with an opening of the desired size. Any generated light that is outside of the opening is reflected back into the parabolic reflector and re-reflected until the light exits the opening. For mixing different light colors from different LEDs or energized phosphors, a mixing tunnel is used. The mixing tunnel includes angled dichroic mirrors or angled polarizer mirrors that selectively reflect and pass selected colors or polarizations of light to a single output port of the mixing tunnel. Efficient and compact ways to energize phosphors are also described. Other optical techniques are also described.

Monochromator beamline for FLASH

Abstract: The design of a high resolution monochromator for the vacuum ultraviolet free electron laser at Hamburg (FLASH), DESY, is described. The monochromator is constructed as a plane grating monochromator using collimated light. Modifications have been made to take into account the free electron laser (FEL) beam characteristics, in particular, the extremely high peak power density of the radiation. Ray tracing simulations yield a resolving power in the range of 10 000–70 000 depending on the photon energy and the grating in use. Our monochromator is equipped with a 200line∕mm grating for the energy range of 20–200eV—the operation regime of FLASH—and a high resolution 1200line∕mm grating for the energy range of 100–600eV, covering the higher harmonic radiation of the FEL.

Full-field swept-source phase microscopy

Abstract: We present a full-field phase microscopy technique, motivated by swept-source Fourier-domain optical coherence tomography, for quantitative nanoscale two-dimensional profiling of sample surfaces and internal structures. The optical configuration consisted of a common path interferometer, illuminating the sample with a collimated beam and detecting the back-scattered light on a 2D CCD camera. A tunable fiber Fabry Perot filter was used to sweep a narrow band (0.07nm) through the 47nm FWHM bandwidth of a superluminescent diode source. The full field of view was recorded for each discrete wavelength step, generating a spectrally indexed interferometric data cube mapping each pixel to a point on the sample. A three dimensional volume was generated by performing the discrete Fourier transform along the spectral axis. Sub-coherence length variation across a depth slice was obtained by examining the phase of the Fourier transformed data set at the selected depth. The phase stability of the system was measured to be 1.3nm for high SNR surface features. The nanoscale imaging potential of this system was demonstrated by measuring the height of patterned chrome on a USAF resolution target, the location of receptor sites on a DNA assay biochip, and the surface topography of erythrocytes in a blood smear.

A Novel Approach to Multipinhole SPECT for Myocardial Perfusion Imaging

Abstract: Myocardial perfusion imaging with SPECT remains critically important for diagnosing, assessing, and evaluating treatment of coronary artery disease. However, conventional rotational SPECT suffers from prolonged study times because of relatively low detection efficiency. We therefore have investigated a multipinhole collimator that could improve the detection efficiency in cardiac SPECT by a factor 5, while providing image quality comparable to standard rotational SPECT techniques using parallel-hole collimation. Methods: We have measured the spatial resolution and efficiency of a 9-pinhole and a parallel-hole collimator mounted to a standard nuclear medicine γ-camera as a function of distance from the collimator with a point source array. The efficiency was derived by integrating the detected counts, and the spatial resolution was determined from the full width at half maximum of the detected point spread function. In addition, we generated and reconstructed projection data of a 9-pinhole collimator from a digital heart phantom with a basal lesion. We simulated 3 scenarios: single view from left anterior, 2 views from left anterior and left lateral; and 4 views that include the 2 previous views and left lateral and anterior views. Results: We found that the spatial resolution of the 9-pinhole collimator with 8-mm diameter pinholes was 30% poorer than that for the parallel-hole collimator, whereas the detection efficiency was increased by >10-fold. This predicts that a 9-pinhole collimator having the same spatial resolution as a parallel-hole collimator will have 5 times greater efficiency. Reconstructed data from 1 angular view of the 9-pinhole collimator showed the expected loss of spatial resolution in the longitudinal direction with reduced resolution of the basal lesion. In addition, the tomograms showed distortions in the apical region. In contrast, the reconstructed data from 2 and 4 views of the 9-pinhole collimator demonstrated good lesion definition and also produced images describing the shape and size of the heart more accurately. Conclusion: Our results indicate that myocardial multipinhole tomography with 2 or more views offers an image quality and spatial resolution comparable with current rotational SPECT techniques, but with the advantage of a 5-fold increase in efficiency.

Effective Elimination of Laser Interference Fringing in Fluorescence Microscopy by Spinning Azimuthal Incidence Angle

Abstract: Laser illumination used in both conventional widefield epi-fluorescence as well as in total internal reflection fluorescence (TIRF) microscopy is subject to nonuniformities in intensity that obscure true image details. These intensity variations are interference fringes arising from coherent light scattering and diffraction at every surface in the laser light's optical path, including the lenses, mirrors, and coverslip. We present an inexpensive technique for effectively eliminating these interference fringes based upon introduction of the excitation laser beam by oblique through-the-objective incidence coupled with rapid azimuthal rotation of the plane of incidence. Although this rotation can be accomplished in several ways, a particularly simple method applicable to a free laser beam is to use an optical wedge, spun on a motor, which diverts the beam into a hollow cone of fixed angle. A system of lenses converts this collimated beam cone into a focused spot that traces a circle at the objective's back focal plane. Consequently, a collimated beam with fixed polar angle and spinning azimuthal angle illuminates the sample. If the wedge is spun rapidly, then the different interference patterns at every particular azimuthal incidence angle average out over a single camera exposure to produce an effectively uniform field of illumination.

Systems, devices, components and methods for controllably configuring the brightness and color of light emitted by an automotive LED illumination system

Abstract: Disclosed are various embodiments of system, devices, components and methods for controllably configuring the brightness and color of light emitted by an automotive LED illumination system. The brightness and color of light emitted by LEDs, or clusters or groups of LEDs, may be varied smoothly or in step-wise fashion to produce virtually any desired pattern of collimated light. Such a pattern may be varied in respect of time or space, or both time and space. Light and other types of sensors may be employed to provide feedback control as a further means of controllably configuring the brightness and color of light emitted by such a system in response to changes in external and other conditions.

Compact mid-ir laser

Abstract: A compact mid-IR laser device utilizes a quantum cascade laser to provide mid-IR frequencies suitable for use in molecular detection by signature absorption spectra. The compact nature of the device is obtained owing to an efficient heat transfer structure, the use of a small diameter aspheric lens and a monolithic assembly structure to hold the optical elements in a fixed position relative to one another. The compact housing size may be approximately 20 cm×20 cm×20 cm or less. Efficient heat transfer is achieved using a thermoelectric cooler TEC combined with a high thermal conductivity heat spreader onto which the quantum cascade laser is thermally coupled. The heat spreader not only serves to dissipate heat and conduct same to the TEC, but also serves as an optical platform to secure the optical elements within the housing in a fixed relationship relative on one another. A small diameter aspheric lens may have a diameter of 10 mm or less and is positioned to provided a collimated beam output from the quantum cascade laser. The housing is hermetically sealed to provide a rugged, light weight portable MIR laser source.

Resonant absorption of electromagnetic fields by surface plasmons buried in a multilayered plasmonic nanostructure

Abstract: Next the top silver layer was etched by a focused ion beam to mill an array of identical slits covering an area of 0.75 mm 2 . This was undertaken in a manner that gave well-formed slits with minimal bridging, while at the same time minimizing the damage to the dielectric core. The width of each slit w50 nm is significantly less than the visible radiation wavelength, and the periodicity of the array is g =340 nm. The choice of these parameters was based upon initial modeling studies that took into account the resolution limitations of the fabrication process together with the requirement to observe well-defined resonances in the visible regime. The geometrical parameters of the structure are determined from scanning electron microscope SEM imaging Table I; an image of a typical region of the sample surface is presented in Fig. 1b. The dispersion of the modes is determined by recording the spectra of the specularly reflected beam as a function of the angle of incidence . A collimated beam from a tungsten halogen lamp was spectrally filtered by a monochromator. The intensity of the incident light was modulated using a mechanical chopper to allow lock-in detection, and a beam splitter redirected a small fraction of the incident light onto a second detector, allowing for source intensity fluctua

Communication transceiver architecture

Abstract: A free-space communication transceiver includes a telescope for transmitting and receiving laser beams, a tunable laser transmitter for generating a transmit laser beam modulated with data, a tunable optical receiver for processing a receive laser beam received from the telescope to recover data, and a tunable beamsplitter that directs the transmit laser beam to the telescope and directs the receive laser beam from the telescope to the optical receiver. Between the telescope and beamsplitter, the transmit and receive laser beams travel along a common optical axis as collinear collimated free-space beams. The transmit and receive laser beams operate at different wavelengths that can be interchanged, thereby support full-duplex operation. The beamsplitter employs a tunable etalon filter whose wavelength-dependent transmission characteristics are adjusted according to the transmit and receive wavelengths. Optionally, RF signals can additionally be couple to the common optical axis and transmitted and received by the telescope.

Focusing optics of a parallel beam CCD optical tomography apparatus for 3D radiation gel dosimetry

Abstract: Optical tomography of gel dosimeters is a promising and cost-effective avenue for quality control of radiotherapy treatments such as intensity-modulated radiotherapy (IMRT). Systems based on a laser coupled to a photodiode have so far shown the best results within the context of optical scanning of radiosensitive gels, but are very slow ( approximately 9 min per slice) and poorly suited to measurements that require many slices. Here, we describe a fast, three-dimensional (3D) optical computed tomography (optical-CT) apparatus, based on a broad, collimated beam, obtained from a high power LED and detected by a charged coupled detector (CCD). The main advantages of such a system are (i) an acquisition speed approximately two orders of magnitude higher than a laser-based system when 3D data are required, and (ii) a greater simplicity of design. This paper advances our previous work by introducing a new design of focusing optics, which take information from a suitably positioned focal plane and project an image onto the CCD. An analysis of the ray optics is presented, which explains the roles of telecentricity, focusing, acceptance angle and depth-of-field (DOF) in the formation of projections. A discussion of the approximation involved in measuring the line integrals required for filtered backprojection reconstruction is given. Experimental results demonstrate (i) the effect on projections of changing the position of the focal plane of the apparatus, (ii) how to measure the acceptance angle of the optics, and (iii) the ability of the new scanner to image both absorbing and scattering gel phantoms. The quality of reconstructed images is very promising and suggests that the new apparatus may be useful in a clinical setting for fast and accurate 3D dosimetry.

Optimizing and calibrating a mode-mismatched thermal lens experiment for low absorption measurement

Abstract: We describe a calibrated two-beam mode-mismatched thermal lens experiment aimed at determination of the absorption coefficient and the photothermal parameters of a nearly transparent material. The use of a collimated probe beam in the presence of a focused excitation beam optimizes the thermal lens experiment. The signal becomes independent from the Rayleigh parameters and waist positions of the beams. We apply this method to determine the absolute value of the thermal diffusivity and absorption coefficient of distilled water at 533 nm.

Electrically tunable two-dimensional holographic photonic crystal fabricated by a single diffractive element

Abstract: An electrically tunable two-dimensional holographic photonic crystal was fabricated in polymer-dispersed liquid crystal using a single diffraction element, which was a specially designed photomask consisting of three diffraction gratings, which had a period of 4μm, oriented 120° relative to one another. With the photomask subjected to a collimated Ar+ laser beam operating at 514.5nm, a two-dimensional spatial light intensity pattern was created by interference of the three first order diffracted beams produced by the mask. The spatial light intensity pattern was then recorded inside a cell filled with the liquid crystal/prepolymer mixture to create a photonic crystal. The photonic crystal structures were observed under an optical microscope. It showed triangular structures with a lattice constant of about 2.50μm. The diffraction properties and electro-optic tunability were also presented.

Optical system for 3 dimensional display

Abstract: An optical system that can add an optical depth information to a two- dimensional image (72) represented by substantially collimated light, e.g. by using a collimated light source in front of a LCD display. The optical system includes a first array of optical lenses (70) arranged at a first distance in front of the two-dimensional image (72), and a second array of optical lenses (71) arranged at a second distance in front of the two- dimensional image (72), the second distance being larger than the first distance. Optical properties, e.g. focal length, can be adjusted for the optical lenses of the first and second array of optical lenses (70, 71) in response to the optical depth information. The optical system can serve as an optical front for 3D multiview displays. Depending on embodiment, both horizontal and vertical angular resolution can be obtained, and the front end exhibits only a small brightness loss. Preferably one lens per pixel is used in case of a pixelized image. In one embodiment, a stack of several arrays of on/off switchab Ie optical lenses are arranged at different distances in front of the two-dimensional image, wherein a depth is applied by turning on one lens corresponding to the desired depth distance. In another preferred embodiment two arrays of continuously adjustable lenses are used to generate a depth by adjusting the lenses so as to provide an apparent position in between the two arrays. Preferably, a diffusor is positioned in front of the second array of lenses. Different shapes of lenses may be used such as spherical lenses, lenticular lenses, Fresnel type lenses or 'horse- saddle' shaped lenses. The arrays of lenses may be implemented using GRIN lenses or fluid- focus lenses. Preferably, the lenses of each array of lenses are individually adjustable.

Fourier-domain angle-resolved low coherence interferometry through an endoscopic fiber bundle for light-scattering spectroscopy

Abstract: We present a novel endoscopic fiber bundle probe incorporated in a Fourier-domain angle-resolved low coherence interferometry system for the measurement of depth-resolved angular scattering distributions to permit the determination of scatterer size via elastic scattering properties Depth resolution is achieved with a superluminescent diode via a Mach-Zehnder interferometer The sample is illuminated with a collimated beam, and a Fourier plane image of the backscattered light is collected by a coherent fiber bundle The angular scattering distribution relayed by the fiber bundle is mixed with the reference field and made to coincide with the input slit of an imaging spectrograph The data collected are processed in real time, producing a depth-resolved angular scattering distribution in 037 s The data are used to determine the sizes of polystyrene microspheres with subwavelength precision and accuracy

Light assembly for remote visual inspection apparatus

Abstract: An apparatus for use as a light assembly in remote visual inspection devices is provided. The light assembly may consist of a laser diode coupled to a fiber optic bundle that transmits collimated laser light onto a wavelength converter located in the distal end of the remote video inspection system. Wavelength converters consisting of phosphorescent materials can be used to convert collimated laser light into white light for inspection illumination purposes.

On-line measurement of surface roughness by laser light scattering

Abstract: On-line roughness measurement of a surface with one-dimensional manufacturing marks is difficult to implement. For example, a contact stylus-type inspection method often does not perform very well or fails without any prior knowledge of the mark distribution on the surface. In this paper, we propose an on-line surface roughness measurement method based on laser light scattering, which is very effective for roughness measurement of one-dimensional manufacturing surfaces. The surface roughness is obtained from the spatial distribution of the scattered light intensity. The measurement setup has a very simple configuration, which consists of a CCD sensor, a collimated diode laser and an expander. The orientation of the spatial distribution of the scattered light intensity from the surface, which depends on the surface orientation, is detected by the CCD sensor, and then the mark direction can be readily determined from image processing. After that the root-mean-square (RMS) height of the surface roughness is extracted by means of image processing of the scattered light distribution in the direction parallel to the manufacturing mark, rather than in the direction perpendicular to the mark which is often followed by other measurement probes. The experimental tests show that the non-contact method has great potential for on-line surface roughness measurement.

Characteristic analysis of a refractive axicon system for optical trepanning

Abstract: An annular beam provides a new laser drilling mechanism, which we refer to as optical trepanning. A refractive axicon system has been designed to transform an input Gaussian laser beam into a collimated annular beam. The diffractive effects of the axicon system and a convex lens focusing the collimated annular beam have been studied using the Fresnel diffraction integral. The theoretical diffraction patterns are compared with the patterns measured with a laser-beam analyzer. The results show that the refractive axicon system can produce Gaussian-like annular beams with the capability of easily adjusting the size of the annular beam.

X-ray Bragg diffraction in asymmetric backscattering geometry.

Abstract: We observe three effects in the Bragg diffraction of x rays in backscattering geometry from asymmetrically cut crystals. First, exact Bragg backscattering takes place not at normal incidence to the reflecting atomic planes. Second, a well-collimated () beam is transformed after the Bragg reflection into a strongly divergent beam () with reflection angle dependent on x-ray wavelength---an effect of angular dispersion. The asymmetrically cut crystal thus behaves like an optical prism, dispersing an incident collimated polychromatic beam. The dispersion rate is . Third, parasitic Bragg reflections accompanying Bragg backreflection are suppressed. These effects offer a radically new means for monochromatization of x rays not limited by the intrinsic width of the Bragg reflection.

Etendue-conserving illumination-optics for backlights and frontlights

Abstract: A luminance-preserving non-imaging backlight (20) that includes a luminous source emitting light (10), an injector (21), an ejector (23), a CPC profile(21) and microstructured facets (d,dd) that refract upwardly reflected light into a collimated direction common to the facets.

Effect of laser contrast ratio on electron beam stability in laser wakefield acceleration experiments

Abstract: Laser wakefield accelerators offer the possibility of compact electron acceleration. However one of the key outstanding issues with the results reported to date is the electron beam stability. Experiments on two laser systems reveal that the contrast ratio between the ASE pedestal and main pulse is an important factor in determining the quality of the electron beam. With a high contrast ratio (10^8) the electron beam profile is a well collimated single beam having a low pointing instability (<10 mrad rms). With a lower contrast (10^6) the beam profile contains multiple beamlets which exhibit a large pointing instability (~50 mrad rms). Ahigh contrast ratio not only improves the beam pointing stability (~6 mrad) but also stabilizes the electron beam energy reproducibility (5%). (Less)

Method and system for inspecting indirect bandgap semiconductor structure

Abstract: Methods (600) and systems (100) for inspecting an indirect bandgap semiconductor structure (140) are described A light source (110) generates light (612) suitable for inducing photoluminescence in the indirect bandgap semiconductor structure (140) A short-pass filter unit (114) reduces long-wavelength light of the generated light above a specified emission peak A collimator (112) collimates (616) the light A large area of the indirect bandgap semiconductor structure (140) is substantially uniformly and simultaneously illuminated (618) with the collimated, short-pass filtered light An image capture device (130) captures (620) images of photoluminescence simultaneously induced by the substantially uniform, simultaneous illumination incident across the large area of the indirect bandgap semiconductor structure The photoluminescence images are image processed (622) to quantify spatially resolved specified electronic properties of the indirect bandgap semiconductor structure (140) using the spatial variation of the photoluminescence induced in the large area

Light expanding system for producing a planar light beam from point light sources

Abstract: A light expanding system for converting light beams generated from point-like light sources into a collimated planar light beam is described herein. The light expanding system is especially suitable for backlighting a liquid crystal flat panel display or other such arrangement requiring backlighting with LEDs as the light source. According to an embodiment of the invention, a system for producing a planar light beam includes a light pipe with microprisms on one of its surfaces, and a beam collector which has microprisms in a plane perpendicular to the microprisms in the light guide. According to another embodiment, the light guide has microprisms on two opposite surfaces, and is capable of multiple mode operation. This multiple mode backlight is capable of illuminating a given active area uniformly with light of different spectrum.

Observation of nonlinear optical phenomena in air and fused silica using a 100 GW, 1.54 μm source

Abstract: A 100-GW optical parametric chirped-pulse amplifier system is used to study nonlinear effects in the 1.54 µm regime. When focusing this beam in air, strong third-harmonic generation (THG) is observed, and both the spectra and efficiency are measured. Broadening is observed on only the blue side of the third-harmonic signal and an energy conversion efficiency of 0.2% is achieved. When propagated through a 10-cm block of fused silica, a collimated beam is seen to collapse and form multiple filaments. The measured spectral features span 400–2100 nm. The spectrum is dominated by previously unobserved Stokes emissions and broad emissions in the visible.

Extended collimator model for pencil-beam dose calculation in proton radiotherapy.

Abstract: We have developed a simple collimator model to improve the accuracy of penumbra behaviour in pencil-beam dose calculation for proton radiotherapy. In this model, transmission of particles through a three-dimensionally extended opening of a collimator is calculated in conjunction with phase-space distribution of the particles. Comparison of the dose distributions calculated using the new three-dimensional collimator model and the conventional two-dimensional model to lateral dose profiles experimentally measured with collimated proton beams showed the superiority of the new model over the conventional one.

Solar concentrator system

Abstract: A means for concentrating direct solar radiation into controllable and directable beams that can optically transport the beam radiation to a central targeting area such as a steam turbine reactor 16 to generate electricity 21; and a method for concentrating solar radiation whereby the radiation is converted from a widely dispersed wave-front to concentrated and directable collimated light beams that provide the energy for steam turbine reactor 16 to generate electricity 21; and an apparatus comprising a fresnel lens 1 that focuses light in concave lenses 3 which convert the converging light into a beam of light, where the beam is targeted with a mirror 4; a plurality of said lens 1 /lens 3 /mirror 4 collectors which track the direct solar radiation by a solar tracker 12, the said plurality of lens 1 /lens 3 /mirror 4 collectors are targeted to a cone shaped mirror 7, where the cone shaped mirror directs the light into a targeting system 15 where multiple collectors concentrate their beams onto a steam turbine reactor 16 to generate electricity 21.