Showing papers on "Collimated light published in 2017"

Cooperative Resonances in Light Scattering from Two-Dimensional Atomic Arrays

Abstract: We consider light scattering off a two-dimensional (2D) dipolar array and show how it can be tailored by properly choosing the lattice constant of the order of the incident wavelength. In particular, we demonstrate that such arrays can operate as a nearly perfect mirror for a wide range of incident angles and frequencies, and shape the emission pattern from an individual quantum emitter into a well-defined, collimated beam. These results can be understood in terms of the cooperative resonances of the surface modes supported by the 2D array. Experimental realizations are discussed, using ultracold arrays of trapped atoms and excitons in 2D semiconductor materials, as well as potential applications ranging from atomically thin metasurfaces to single photon nonlinear optics and nanomechanics.

Cooperative resonances in light scattering from two-dimensional atomic arrays

Abstract: We consider light scattering off a two-dimensional (2D) dipolar array and show how it can be tailored by properly choosing the lattice constant of the order of the incident wavelength. In particular, we demonstrate that such arrays can operate as a nearly perfect mirror for a wide range of incident angles and frequencies, and shape the emission pattern from an individual quantum emitter into a well-defined, collimated beam. These results can be understood in terms of the cooperative resonances of the surface modes supported by the 2D array. Experimental realizations are discussed, using ultracold arrays of trapped atoms and excitons in 2D semiconductor materials, as well as potential applications ranging from atomically thin metasurfaces to single photon nonlinear optics and nanomechanics.

Transversely Divergent Second Harmonic Generation by Surface Plasmon Polaritons on Single Metallic Nanowires

Abstract: Coherently adding up signal wave from different locations are a prerequisite for realizing efficient nonlinear optical processes in traditional optical configurations. While nonlinear optical processes in plasmonic waveguides with subwavelength light confinement are in principle desirable for enhancing nonlinear effects, so far it has been difficult to improve the efficiency due to the large momentum mismatch. Here we demonstrate, using remotely excited surface plasmon polaritons (SPPs), axial collimated but transversely divergent second harmonic (SH) generation in a single silver nanowire–monolayer molybdenum disulfide hybrid system. Fourier imaging of the generated SH signal confirms the momentum conservation conditions between the incident and reflected SPPs and reveals distinct features inherent to the 1D plasmonic waveguides: (i) the SH photons are collimated perpendicular to the nanowire axis but are divergent within the perpendicular plane; (ii) the collimation (divergence) is inversely proportiona...

Waveguide illumination system

Abstract: An illumination system employing a waveguide that receives and propagates light in response to transmission and total internal reflection. Light deflecting elements distributed along the propagation path incrementally change the out-of-plane angles of light rays and cause decoupling of portions of light from the waveguide at different distances from the light input edge or end. Light may escape from the waveguide into an intermediate layer at low out-of-plane angles and can be further redirected by light extraction features out of the system. In one embodiment, the illumination system is configured to emit collimated light. In one embodiment, the illumination system includes shallow surface relief features. In one embodiment, the light deflecting elements include forward-scattering particles distributed throughout the volume of the waveguide.

Controlling light with freeform multifocal lens designed with supporting quadric method(SQM).

Abstract: The SQM is a versatile methodology for designing freeform optics for irradiance redistribution. Recently it has often been applied in design of freeform lenses, mirrors and diffractive optical elements. Still, many questions regarding theory and performance of optics designed with the SQM are open. Here we investigate theoretically plano-freeform refractive lenses designed with the SQM when an incident collimated beam must be transformed into a beam illuminating with prescribed irradiances a large number of pixels on a flat screen. It is shown that a lens designed for such task with the SQM operates as a multifocal lens segmented into subapertures with focal lengths providing accurate control of the irradiance distribution between pixels. These subapertures are patches of hyperboloids of revolution. Two different designs are possible, one of which defines a concave lens. Eikonal function for such lenses is also derived. As a proof of concept, we numerically analyze performance of a plano-freeform lens designed with the SQM for transforming a uniform circular parallel light into an image of A. Einstein represented by gray values at ≈ 38K pixels.

Laser radar and laser radar control method

Abstract: The embodiment of the invention discloses a laser radar and a laser radar control method. The laser radar comprises two or more than two detection units, each detection unit comprises: one emitter configured to emit an emergent laser; one emitting terminal collimation unit configured to perform collimation of the emergent laser emitted by the emitter; one polarizing beam-splitting unit configuredto allow the emergent laser after collimation to enter from a first light port of the polarizing beam-splitting unit to allow the P polarized light in the emergent laser after collimation to be emergent from the emitting terminal collimation unit; a quarter-wave plate configured to allow the P polarized light emergent from the second light port of the emitting terminal collimation unit to become circular polarized light; and a galvanometric scanner configured to change the emergent direction of the circular polarized light to become the emergent laser. The laser radar and the laser radar control method can enhance the scanning range of the laser radar and improve the resolution and precision of the laser radar.

An image-guided precision proton radiation platform for preclinical in vivo research.

Abstract: There are many unknowns in the radiobiology of proton beams and other particle beams. We describe the development and testing of an image-guided low-energy proton system optimized for radiobiological research applications. A 50 MeV proton beam from an existing cyclotron was modified to produce collimated beams (as small as 2 mm in diameter). Ionization chamber and radiochromic film measurements were performed and benchmarked with Monte Carlo simulations (TOPAS). The proton beam was aligned with a commercially-available CT image-guided x-ray irradiator device (SARRP, Xstrahl Inc.). To examine the alternative possibility of adapting a clinical proton therapy system, we performed Monte Carlo simulations of a range-shifted 100 MeV clinical beam. The proton beam exhibits a pristine Bragg Peak at a depth of 21 mm in water with a dose rate of 8.4 Gy min-1 (3 mm depth). The energy of the incident beam can be modulated to lower energies while preserving the Bragg peak. The LET was: 2.0 keV µm-1 (water surface), 16 keV µm-1 (Bragg peak), 27 keV µm-1 (10% peak dose). Alignment of the proton beam with the SARRP system isocenter was measured at 0.24 mm agreement. The width of the beam changes very little with depth. Monte Carlo-based calculations of dose using the CT image data set as input demonstrate in vivo use. Monte Carlo simulations of the modulated 100 MeV clinical proton beam show a significantly reduced Bragg peak. We demonstrate the feasibility of a proton beam integrated with a commercial x-ray image-guidance system for preclinical in vivo studies. To our knowledge this is the first description of an experimental image-guided proton beam for preclinical radiobiology research. It will enable in vivo investigations of radiobiological effects in proton beams.

Systems, devices, and methods for focusing laser projectors

Abstract: Systems, devices, and methods for focusing laser projectors are described. A laser projector includes N≥1 laser diodes, each of which emits laser light having a divergence. Each laser diode is paired with a respective primary or collimation lens to at least reduce a divergence of the laser light that the laser diode produces. Downstream from the primary lens(es) in the optical path(s) of the laser light, a single dedicated secondary or convergence lens converges the laser light to a focus. By initiating the convergence of the laser light at the secondary or convergence lens as opposed to at the primary or collimation lens(es), numerous benefits that are particularly advantageous in laser projection-based wearable heads-up displays are realized.

Laser projector and depth camera thereof

Abstract: The invention discloses a laser projector and a depth camera thereof The laser projector comprises a foundation, at least two light emitting elements, a controller, at least two lenses and a diffraction optical element, wherein the at least two light emitting elements are fixed at one side of the foundation facing towards the diffraction optical element and emit laser under the control of the controller, the diffraction optical element is arranged at a position spaced from the foundation a first distance and is used for emitting laser patterns after laser beam expansion, and the at least two lenses are arranged between the foundation and the diffraction optical element and/or at one side of the diffraction optical element opposite to the foundation, are used for carrying out focusing and/or collimation of the laser and are set to have at least two types of different focal lengths and/or at least two different second distances spaced from the at least two light emitting elements The laser projector is advantaged in that laser pattern irrelevance is improved on the condition that output power and volume requirements can be satisfied, and thereby a depth image acquisition speed and acquisition precision of the depth camera are improved

Three-dimensional display with directional beam splitter array.

Abstract: Multi-view three-dimensional (3-D) displays using directional beam splitter array were proposed to achieve a perfect 3-D perception with low cross-talk. The multi-direction collimated light may project different images to different viewing zones to form the multi-view autostereoscopic display. Furthermore, a high resolution 3-D display can be realized with a sequential beam splitter array and a sequential liquid crystal display. By optimization, the cross-talk of the directional beam splitter backlight system was lowered to 5% to improve the perception of the 3-D displays.

Methods and systems for optical beam steering

Abstract: An integrated optical beam steering device includes a planar dielectric lens that collimates beams from different inputs in different directions within the lens plane. It also includes an output coupler, such as a grating or photonic crystal, that guides the collimated beams in different directions out of the lens plane. A switch matrix controls which input port is illuminated and hence the in-plane propagation direction of the collimated beam. And a tunable light source changes the wavelength to control the angle at which the collimated beam leaves the plane of the substrate. The device is very efficient, in part because the input port (and thus in-plane propagation direction) can be changed by actuating only log 2 N of the N switches in the switch matrix. It can also be much simpler, smaller, and cheaper because it needs fewer control lines than a conventional optical phased array with the same resolution.

Focused, evanescent, hollow, and collimated beams formed by microaxicons with different conical angles.

Abstract: Diffraction patterns formed by axicons with different tip (vertex) angles are analytically and numerically investigated. Results show that the axicon (or tapered dielectric probe) can form an extended axial light beam, a compact evanescent field, a hollow beam, and a collimated beam, depending on the vertex angle. Two-dimensional and three-dimensional models of a tapered dielectric probe show that, with small changes to the vertex angle, light transmitted by the probe is scattered rather than focused, and vice versa. Angle meanings corresponded to boundary transitions have a quantum character and densify as the angle approaches zero. These features should be taken into consideration when manufacturing microaxicons intended for various applications.

All-Dielectric Meta-lens Designed for Photoconductive Terahertz Antennas

Abstract: We present an all-dielectric meta-lens designed to collimate terahertz waves emitted from a terahertz antenna. The meta-lens is not only thinner than a conventional bulk silicon lens, but also promises to eliminate the use of parabolic mirrors in a terahertz time-domain spectroscopy system. A systematic numerical study reveals that the meta-lens exhibits excellent performance in both the emitter and detector modules, converting between the spherical wave of the antennas and the collimated beam. The frequency and alignment dependences of the meta-lens are also investigated to comprehensively map its response characteristics. The all-dielectric meta-lens presented here may pave a way in developing high-performance integrated photoconductive terahertz antenna components.

Ray-mapping approach in double freeform surface design for collimated beam shaping beyond the paraxial approximation.

Abstract: Numerous applications require the simultaneous redistribution of the irradiance and phase of a laser beam. The beam shape is thereby determined by the respective application. An elegant way to control the irradiance and phase at the same time is from double freeform surfaces. In this work, the numerical design of continuous double freeform surfaces from ray-mapping methods for collimated beam shaping with arbitrary irradiances is considered. These methods consist of the calculation of a proper ray mapping between the source and the target irradiance and the subsequent construction of the freeform surfaces. By combining the law of refraction, the constant optical path length, and the surface continuity condition, a partial differential equation (PDE) for the ray mapping is derived. It is shown that the PDE can be fulfilled in a small-angle approximation by a mapping derived from optimal mass transport with a quadratic cost function. To overcome the restriction to the paraxial regime, we use this mapping as an initial iterate for the simultaneous solution of the Jacobian equation and the ray mapping PDE by a root-finding algorithm. The presented approach enables the efficient calculation of double freeform lenses with small distances between the freeform surfaces for complex target irradiances. This is demonstrated by applying it to the design of a single-lens and a two-lens system.

Intercrystal Scatter Rejection for Pixelated PET Detectors

Abstract: High-resolution positron emission tomography (PET) scanners often use pixelated scintillator arrays with lightsharing for the detection of gamma rays. The aim of this paper is to enhance the spatial resolution of such a pixelated scintillator detector by filtering out events with multiple interactions of gamma rays in the scintillator based on the measured light distributions. To develop and evaluate such enhancements in spatial resolution, we measure the point spread function (PSF) of our detector directly using a thinly collimated gamma ray beam setup, and then later verify their benefits on a full preclinical PET system with a hotrod phantom. The scintillator detector comprises a $30\times 30\times 12$ mm3 lutetium–yttrium oxyorthosilicate array with a pitch of 1 mm coupled to a digital silicon photomultiplier array via a 2-mm lightguide. We use a center of gravity algorithm for the crystal identification; however, the proposed filters are independent of the crystal identification algorithm. Investigating a single detector with our collimated gamma beam, we reject 15% of the events as multiple interaction while improving the crystal identification efficiency from 60.0% to 68.3% and the 90th-percentile diameter of the PSF from 7.88 to 3.98 mm. On system level, we analyze a line profile through two different rod sizes in a hotrod phantom. The filters reject 32% of the coincidences and increase the peak-to-valley ratio by 8% (0.9-mm rods) and by 18% (1.2-mm rods).

Refractive Index Imaging of Cells with Variable-Angle Near-Total Internal Reflection (TIR) Microscopy

Abstract: The refractive index in the interior of single cells affects the evanescent field depth in quantitative studies using total internal reflection (TIR) fluorescence, but often that index is not well known. We here present method to measure and spatially map the absolute index of refraction in a microscopic sample, by imaging a collimated light beam reflected from the substrate/buffer/cell interference at variable angles of incidence. Above the TIR critical angle (which is a strong function of refractive index), the reflection is 100%, but in the immediate sub-critical angle zone, the reflection intensity is a very strong ascending function of incidence angle. By analyzing the angular position of that edge at each location in the field of view, the local refractive index can be estimated. In addition, by analyzing the steepness of the edge, the distance-to-substrate can be determined. We apply the technique to liquid calibration samples, silica beads, cultured Chinese hamster ovary cells, and primary culture chromaffin cells. The optical technique suffers from decremented lateral resolution, scattering, and interference artifacts. However, it still provides reasonable results for both refractive index (~1.38) and for distance-to-substrate (~150 nm) for the cells, as well as a lateral resolution to about 1 µm.

Deviation correction method for close-range photometric stereo with nonuniform illumination

Abstract: Classical photometric stereo requires uniform collimated light, but point light sources are usually employed in practical setups. This introduces errors to the recovered surface shape. We found that when the light sources are evenly placed around the object with the same slant angle, the main component of the errors is the low-frequency deformation, which can be approximately described by a quadratic function. We proposed a postprocessing method to correct the deviation caused by the nonuniform illumination. The method refines the surface shape with prior information from calibration using a flat plane or the object itself. And we further introduce an optimization scheme to improve the reconstruction accuracy when the three-dimensional information of some locations is available. Experiments were conducted using surfaces captured with our device and those from a public dataset. The results demonstrate the effectiveness of the proposed approach.

A fingerprint identification apparatus, a display panel and a fingerprint identification method

Abstract: The invention provides a fingerprint identification apparatus, a display panel and a fingerprint identification method belonging to the technical field of displaying, and can solve the problem that the fingerprint identification apparatuses of the existing organic light emitting diode display products occupy the frame areas and are not conducive to the narrow bezel design. In the fingerprint identification apparatus of the invention, a collimator transmits the collimated light reflected through a fingerprint and blocks the scattered light, which is equivalent to that the light emitted by a light-emitting layer is reflected by a finger and the approximately collimated reflected light can pass through the collimator area, and the tilted light will be blocked by the collimator. A sensor identifies the wave crest and the wave ridge according to the light transmission area of the collimator. The fingerprint identification apparatus is simple in making process, high in practicality, and is suitable for fingerprint acquisition and identification in an organic light-emitting diode display area.

On the internal structure of relativistic jets collimated by ambient gas pressure

Abstract: Recent progress in very long baseline interferometry (VLBI) observations of relativistic jets outflowing from active galactic nuclei gives us direct information about jet width rjet(l) dependence on the distance l from the ‘central engine’. Being the missing link in previous works, this relation opens the possibility of determining the internal structure of a jet. In this article, we consider a relativistic jet submerged in an external medium with finite gas pressure Pext. Neither an external magnetic field nor an infinitely thin current sheet will be assumed. This approach allows us to construct a reasonable solution in which both the magnetic field and the flow velocity vanish at the jet boundary r = rjet. In particular, the connection between external gas pressure and internal structure of a relativistic jet is determined.

Collimated gamma photon emission driven by PW laser pulse in a plasma density channel

Abstract: We use three-dimensional particle-in-cell simulations to demonstrate that a plasma density channel can stably guide the petawatt laser pulse in near critical plasmas. In this regime, a directed, collimated, and micro-sized gamma photon beam is emitted by the direct-laser accelerated electrons along the channel axis. While in the case without the plasma density channel, the laser tilting behavior leads to the generation of randomly deflected gamma photon beams with a large divergence angle and transverse source size. In addition, in the plasma density channels, the divergence angle of the gamma photon beams can be much reduced by using a smaller value of n0/a0nc. The energy conversion efficiency can also be improved by increasing the laser power or the plasma density. This regime provides an efficient and compact approach for the production of high quality gamma photon beams.

An optical lever by using a mode-locked laser for angle measurement

Abstract: A new concept of optical lever for angle measurement having an extended angular measurement range with a mode-locked laser as the light source, which is significantly extended from the conventional photodiode (PD)-type optical levers with a single frequency laser, is proposed. In the proposed concept, a collimated laser beam of the mode-locked laser is made incident to a grating reflector to generate a group of first-order diffracted beams from the grating reflector. Differing from a conventional PD-type optical lever employing a laser beam with a single frequency as the light source, the angle measurement range can be significantly expanded for the sake of the group of widely-spread first-order diffracted beams. In addition, the proposed optical lever has a potential of assuring the traceability of angle measurement by linking it to the optical frequency comb based on the mode-locked laser, which is employed as the national standard of time and frequency. In this paper, as a first step of this research, a mode-locked femtosecond laser is employed as the light source of the proposed optical lever. To distinguish each of the first-order diffracted beams generated with the combination of the mode-locked femtosecond laser and the diffraction grating having a grating period of 1.67 μm, a Fabry-Perot etalon is employed in the setup of the optical lever to modulate the distance between two neighboring beams in the group of first-order diffracted beams. Experimental setups are developed, and basic experiments are carried out to verify the feasibility of the proposed optical lever.

Optimization of the mechanical collimation for minibeam generation in proton minibeam radiation therapy.

Abstract: Purpose The dose tolerances of normal tissues continue to be the main barrier in radiation therapy. To lower it, a novel concept based on a combination of proton therapy and the use of arrays of parallel and thin beams has been recently proposed: proton minibeam radiation therapy (pMBRT). It allies the inherent advantages of protons with the remarkable normal tissue preservation observed when irradiated with submillimetric spatially fractionated beams. Due to multiple Coulomb scattering, the tumor receives a homogeneous dose distribution, while normal tissues in the beam path benefit from the spatial fractionation of the dose. This promising technique has already been implemented at a clinical center (Proton therapy Center of Orsay) by means of a first prototype of a multislit collimator. The main goal of this work was to optimize the minibeam generation by means of a mechanical collimation. Methods Monte Carlo simulations (GATE V7.1) were used to evaluate the influence of the collimator material (brass, nickel, iron, tungsten), thickness, phantom-to-collimator distance (PCD), among other parameters, on the dose distributions. Maximization of the peak-to-valley dose ratios (PVDR) in normal tissues along with minimization of full width at half maximum, penumbras and neutron contamination were used as figures of merit. As a starting point for the optimization, the collimator employed in our previous works was used. It consisted in 400 μm × 2 cm slits with a center-to-center distance (c-t-c) of 3200 μm. As the main targets of pMBRT will be neurological cases, 100 MeV energy proton minibeams were considered. This energy range would allow treating tumors located at the center of the brain (the worst scenario). Results Tungsten and brass are the most advantageous materials among those considered. A tungsten collimator provides the highest PVDR and lowest penumbra. Although the neutron yield generated in the tungsten collimator is 3 times higher than that of the other materials, the biologic neutron doses at the patient position amount to less than 0.05% and 0.7% of the peak and valley doses, respectively. In addition, shorter PCD than the one currently used (7 cm) leads to thinner beams (enhancing the dose-volume effects), accompanied, however, by an increase of neutron dose at the phantom surface. Finally, no gain in dose distributions is obtained by using nonparallel slits. Conclusions The collimator design and irradiation configuration have been optimized to minimize the angular spread, deliver the highest PVDR and the lowest valley possible in the normal tissues in pMBRT. We have also confirmed that even though the neutron yield generated in the multislit collimator is higher with respect to the one produced by the collimators used in conventional proton therapy, the increase of biological neutron dose in the patient will remain low (less than 1%).

Asymmetric nanofluidic grating detector for differential refractive index measurement and biosensing.

Abstract: Measuring small changes in refractive index can provide both sensitive and contactless information on molecule concentration or process conditions for a wide range of applications. However, refractive index measurements are easily perturbed by non-specific background signals, such as temperature changes or non-specific binding. Here, we present an optofluidic device for measuring refractive index with direct background subtraction within a single measurement. The device is comprised of two interdigitated arrays of nanofluidic channels designed to form an optical grating. Optical path differences between the two sets of channels can be measured directly via an intensity ratio within the diffraction pattern that forms when the grating is illuminated by a collimated laser beam. Our results show that no calibration or biasing is required if the unit cell of the grating is designed with an appropriate built-in asymmetry. In proof-of-concept experiments we attained a noise level equivalent to ∼10-5 refractive index units (30 Hz sampling rate, 4 min measurement interval). Furthermore, we show that the accumulation of biomolecules on the surface of the nanochannels can be measured in real-time. Because of its simplicity and robustness, we expect that this inherently differential measurement concept will find many applications in ultra-low volume analytical systems, biosensors, and portable devices.

Low-frequency ultrasonic Bessel-like collimated beam generation from radial modes of piezoelectric transducers

Abstract: We present a very simple approach to generate a collimated ultrasonic beam that exploits the natural Bessel-like vibration pattern of the radial modes of a piezoelectric disc with lateral clamping. This eliminates the need for the conventional annular Bessel pattern of the electrodes with individual electrode excitation on the piezo-disc, thus simplifying the transducer design. Numerical and experimental studies are carried out to investigate the Bessel-like vibration patterns of these radial modes showing an excellent agreement between these two studies. Measured ultrasonic beam-profiles in water from the radial modes confirm the profile to be a Bessel beam. Collimated beam generation from radial modes is investigated using a coupled electromechanical finite-element model. It is found that clamping the lateral edges of piezoelectric transducers results in a high-degree of collimation with practically no side-lobes similar to a parametric array beam. Ultrasonic beam-profile measurements in water with both...

Sidelobe Suppression and Beam Collimation in the Generation of Vortex Electromagnetic Waves for Radar Imaging

Abstract: For the electromagnetic (EM) vortex imaging purposes, the sidelobe suppression and the beam collimation method in the generation of orbital angular momentum (OAM) beams is proposed. Based on the concentric ring array, the objective function for the generic algorithm is defined to calculate the signal amplitude for each ring. Comprehensive simulations are conducted to validate the effectiveness of the proposed method. Results show that the main lobes of the radiation pattern of different OAM modes are collimated in the same direction and the sidelobes are all lower than –20 dB. Furthermore, the imaging model of the concentric-ring array is established, and the target image is obtained through numerical simulations. The work can advance the development of the EM vortex imaging technique and novel radar detection technology as well.

X-ray luminescence computed tomography using a focused x-ray beam.

Abstract: Due to the low x-ray photon utilization efficiency and low measurement sensitivity of the electron multiplying charge coupled device camera setup, the collimator-based narrow beam x-ray luminescence computed tomography (XLCT) usually requires a long measurement time We, for the first time, report a focused x-ray beam-based XLCT imaging system with measurements by a single optical fiber bundle and a photomultiplier tube (PMT) An x-ray tube with a polycapillary lens was used to generate a focused x-ray beam whose x-ray photon density is 1200 times larger than a collimated x-ray beam An optical fiber bundle was employed to collect and deliver the emitted photons on the phantom surface to the PMT The total measurement time was reduced to 125 min For numerical simulations of both single and six fiber bundle cases, we were able to reconstruct six targets successfully For the phantom experiment, two targets with an edge-to-edge distance of 04 mm and a center-to-center distance of 08 mm were successfully reconstructed by the measurement setup with a single fiber bundle and a PMT