Large Deflection Angles Research Articles

High-Speed Time-Domain En Face Optical Coherence Tomography System Using KTN Optical Beam Deflector

We developed high-speed time-domain (TD) en face optical coherence tomography (OCT) system using KTN optical beam deflector. The KTN optical beam deflector operates at a high repetition rate of 200 kHz with a fairly large beam deflection angle. We proposed a high-speed en face OCT system that used a KTN optical deflector as the sample beam scanning. In the experiment, we obtained en face OCT images of human fingerprint with a frame rate of 800 fps, which is the fastest speed obtained by a TD-OCT imaging. Furthermore, a 3D-OCT image was also obtained at 0.2 s (=5 volumes/s) by our imaging system.

Yaw-control efficiency analysis for a diamond wing configuration with outboard split flaps

The yaw-control device of a low-aspect ratio flying wing with diamond-shaped wing planform is investigated. Extensive low-speed wind tunnel experiments have been carried out to obtain surface pressure data and the aerodynamic forces and moments of the configuration for six different flap deflection angles at varying angles of attack and sideslip. Complementary unsteady Reynolds-averaged Navier–Stokes simulations are performed for selected configurations. The experimental data is used to examine the validity of the numerical results. The analysis is focused on the aerodynamic coefficients and derivatives. Yaw-control effectiveness, yaw-control efficiency, crosswind landing capabilities and coupling effects are discussed. The results show sufficient yaw-control effectiveness and efficiency for a wide range of considered freestream conditions. The outboard flap exhibits a non-linear characteristic with respect to the flap deflection angle and freestream conditions. The efficiency is considerably reduced at high angles of attack due to large-scale flow separation in the wing outboard section. Non-linear coupling effects with the rolling moment become obvious for moderate to large flap deflections over the whole angle of attack polar. The numerical results show good agreement with the experimental data in the surface pressure distributions and longitudinal aerodynamic coefficients. The yawing moment is overpredicted by numerical simulations for large flap deflection angles.

Electro-optic deflection in a lithium niobate quasi-single mode waveguide with microstructured electrodes.

We propose an electro-optic mode deflection device based on an annealed proton exchange (APE) waveguide in lithium niobate, associated with isosceles-triangle-shaped array electrodes and a horn-shaped input waveguide. The input waveguide is tapered down to ensure that the output of the device has a good beam quality, i.e., a quasi-single mode in this case. This new device allows beam deflection at a relative low voltage and large deflection angle. At an APE-waveguide width of 80 μm, mode deflections of 0.265 and 0.240 μm/V are obtained for 1064 and 980 nm, respectively. This beam deflection device can be applied in high-speed optical switch, and beam smoothing of a high-power laser, etc.

High-Efficiency Beam Steering LCOS for Wavelength Selective Switch

A liquid crystal on silicon (LCOS) device exhibiting high diffraction efficiency at a large deflection angle is demonstrated. An LC mixture with a large birefringence ( $\Delta \text{n}\,\,=0.25$ at $\lambda =1550$ nm) and a large dielectric constant ( $\Delta \varepsilon = 10.4$ ) is developed to obtain the high-phase retardation, more than $4\pi $ , at 1550 nm within a relatively low operation voltage of 5.5 V on LCOS. When compared with the conventional modulation method of $2\pi $ phase retardation, both grating period and phase retardation are doubled in $4\pi $ modulo modulation. Using the high-phase retardation modulation method, the LCOS may achieve high diffraction efficiency more than 56.6% at 4.5° deflection angle of C-band wavelength with an optimized phase retardation profile. The high diffraction efficiency phase modulator shows the great potential application of beam steering for the wavelength selective switch and the holographic display.

A Novel Design of Serial Variable Stiffness Actuator Based on an Archimedean Spiral Relocation Mechanism

This paper presents a novel rotational serial variable stiffness actuator (SVSA) based on an Archimedean spiral relocation mechanism (ASRM), which is applied to linearly change the position of the pivot point of a lever as well as obtain a large range of motion and adjustable stiffness. Consequently, the ASRM introduced in this work contributes to a compact structure of the mechanical design without sacrificing the continuity of adjustable stiffness. In terms of the variable stiffness mechanism, two linear springs are assembled antagonistically on a spring shaft and rotate simultaneously with the output link. To improve the spring force transmission efficiency, these displacements of the springs are set to be perpendicular to the output link. A large deflection angle can therefore be achieved to obtain high passive energy storage ability. Moreover, the SVSA is also modeled to investigate the theoretical capabilities of the output stiffness and passive energy capability. Further control experiments are performed to quantitatively evaluate the physical performance of the SVSA. Our results demonstrate that the SVSA with a proportional-derivative feedback plus feedforward controller exhibits a fast response and high accuracy for both position and stiffness regulation and tracking tasks. In addition, the real output torque measurement verifies the fidelity of the SVSA for torque generation.

On Typhoon Track Deflections near the East Coast of Taiwan

Typhoons with “deflection tracks” (DTs) within a 200-km distance of the mountainous island of Taiwan are examined. We analyze 84 landfalling typhoons that compose 49 DT cases turning to the left-hand side, including 18 with very large deflection angles (DA > 20°) and another 7 having looped tracks (LTs). Most of the large DA and LT cases are “northern landfall” type, reaching Taiwan’s east coast poleward of 24°N and originally possessing relatively slow translation speeds (~4 m s−1). Their average translation speeds, however, increase by 50% in the 3 h prior to landfall. The WRF Model is used to simulate DT cases, and potential vorticity (PV) tendency diagnosis is used to interpret the contributions of the horizontal advection (HA), vertical advection (VA), and diabatic heating (DH) terms. The northern landfall tropical cyclones (TCs) possess significant cross-mountain flow to the south of the storm near the coast, resulting in vorticity stretching (the VA effect) and subsidence warming. The subsidence suppresses storm convection and produces heating asymmetries (the DH effect) that can induce significant southwestward deflections. The cross-mountain VA and DH effects are weaker for the “southern landfall” storms. The results explain well the observed increase of translation speed prior to landfall in DT cases and show that the HA effect, in general, does not contribute to the track deflection. Our results highlight the impact of topography on TC track by the vorticity stretching effect and by asymmetric diabatic heating.

Deflection angle detecting system for the large-angle and high-linearity fast steering mirror using quadrant detector

A deflection angle detecting system (DADS) using a quadrant detector (QD) is developed to achieve the large deflection angle and high linearity for the fast steering mirror (FSM). The mathematical model of the DADS is established by analyzing the principle of position detecting and error characteristics of the QD. Based on this mathematical model, the method of optimizing deflection angle and linearity of FSM is demonstrated, which is proved feasible by simulation and experimental results. Finally, a QD-based FSM is designed and tested. The results show that it achieves 0.72% nonlinearity, ±2.0 deg deflection angle, and 1.11-μrad resolution. Therefore, the application of this method will be beneficial to design the FSM.

Numerical investigation of slot variations on the efficiency of tangential blowing at a vertical tailplane with infinite span

On a swept vertical tailplane with infinite span tangential blowing over the shoulder of a deflected rudder is applied. For large rudder deflection angles the flow on the rudder is separated without blowing. A numerical study is conducted with the aim to increase the side force coefficient. This could, for example, be required during take-off if the engine on one side fails, necessitating the compensation of a large yawing moment. If this criterion is critical for the sizing of the vertical tailplane, active flow control like tangential blowing could help to reduce the size of the vertical tailplane and thus save weight and fuel. With a continuous slot it is demonstrated that the separation on the rudder can be reduced or avoided. It is shown that using discrete slots this can be achieved with a smaller momentum coefficient. To analyze the effects of the discrete slots and their jets on each other and their effectivity with regard to the gain in side force coefficient a parameter study is conducted. The number of slots as well as the size of the slots in spanwise direction is varied and the impact of jet velocity changes is also studied. In comparing the results for a constant increase in side force and constant slot size in spanwise direction the configuration with the smaller number of slots but a higher jet velocity proved to be the most effective one.

Vehicle trajectory at curved sections of two-lane mountain roads: a field study under natural driving conditions

PurposeThe trajectory of a vehicle is comprehensively affected by the interactions between the vehicle, the driving behavior, and the road environment. High-risk driving behaviors and accident-prone road sections can be identified based on the relationship between the trajectory and road geometry. Previous related studies mostly focused on the trajectory deviation at a few points on the road, which cannot capture the continuous variation of the trajectory in an entire curve, and seldom considered the trajectory characteristics along curves with large deflection angles. The aim of this study is to investigate the trajectories passenger cars take on two-lane mountain roads and thus to determine the track patterns and its relevant risks.MethodsField driving experiments were performed on four two-lane mountain highways, and vehicle trajectories under natural driving conditions were acquired. The continuous change in the lateral deviation rate of the trajectory was also determined by putting the measured trajectories into the coordinate frame together with the edge line of roadway. Further, the morphological features of the vehicle trajectory and how it is affected by the highway geometry were analyzed.Results and conclusionsThe following were observed: i) Typical track patterns were determined according to features of LDRT profiles, four patterns for left-hand bends and five patterns for right-hand bends, which can be used to identify crash prone position and reveal the mechanism of crash. ii) Inertia may cause the vehicle to move too close to the outer side of the curve after a cut, for which reason the driver has to correct the trajectory, although overcorrection may move the vehicle into the oncoming lane. iii) A higher speed at curve entry adopt by the driver could result in a larger encroachment into opposite lane or shoulder. iv) The smaller the radius of the horizontal curve, the more frequently the trajectory entered the oncoming lane. These findings could provide a better understanding of the track behavior of passenger cars, judge the safety implications of driver behavior, and thus identify crash prone positioning and the potential mechanisms of head-on crashes, run-off-road and guardrail collisions.

High-performance axicon lenses based on high-contrast, multilayer gratings

Axicon lenses are versatile optical elements that can convert Gaussian beams to Bessel-like beams. In this letter, we demonstrate that axicons operating with high efficiencies and at large angles can be produced using high-contrast, multilayer gratings made from silicon. Efficient beam deflection of incident monochromatic light is enabled by higher-order optical modes in the silicon structure. Compared to diffractive devices made from low-contrast materials such as silicon dioxide, our multilayer devices have a relatively low spatial profile, reducing shadowing effects and enabling high efficiencies at large deflection angles. In addition, the feature sizes of these structures are relatively large, making the fabrication of near-infrared devices accessible with conventional optical lithography. Experimental lenses with deflection angles as large as 40° display field profiles that agree well with theory. Our concept can be used to design optical elements that produce higher-order Bessel-like beams, and the combination of high-contrast materials with multilayer architectures will more generally enable new classes of diffractive photonic structures.

Optimization design of the angle detecting system used in the fast steering mirror

In this paper, in order to design a fast steering mirror (FSM) with large deflection angle and high linearity, a deflection angle detecting system (DADS) using quadrant detector (QD) is developed. And the mathematical model describing DADS is established by analyzing the principle of position detecting and error characteristics of QD. Based on this mathematical model, the variation tendencies of deflection angle and linearity of FSM are simulated. Then, by changing the parameters of the DADS, the optimization of deflection angle and linearity of FSM is demonstrated. Finally, a QD-based FSM is designed based on this method, which achieves ±2° deflection angle and 0.72% and 0.68% linearity along x and y axis, respectively. Moreover, this method will be beneficial to the design of large deflection angle and high linearity FSM.

Hysteresis of magnetization reversal loops in films with perpendicular anisotropy in an inclined magnetic field

Numerical calculations of magnetization reversal loops of nanogranular films having perpendicular anisotropy in an inclined magnetic field at finite temperature, for film “quality parameters” both less than, and greater than, one. The calculations are performed with consideration of the film's demagnetizing field in the two-level approximation for the energy of the granule. It is found that the hysteresis of the transition fields between states with uniformly directed and non-uniformly directed magnetic moments for all granules narrows with increasing temperature and field deviation angle from the normal to the film. As the field deviation increases this hysteresis vanishes, and there is a transition from the uniformly magnetized state of the granules to the equilibrium non-homogeneous state without hysteresis. In the case of large field deflection angles, at finite temperature the magnetization consists of three regions. At the center of the magnetization curve there is a hysteresis region in which the m...

Design and measurement of an acoustic bi-anisotropic metasurface for scattering-free manipulation of the refracted wavefront

Relying on the generalized Snell's law which defines a phase gradient to the surface, extraordinary control of the reflected and transmitted wavefronts can be achieved by metasurfaces with subwavelength thickness. However, a fundamental limitation for such metasurfaces is their power transmission efficiency, especially at large deflection angles. Building on the theoretical requirements for the boundary conditions at an ideal metasurface, we designed and fabricated the necessary bi-anisotropic cells for a wave-front transformation acoustic metasurface that overcomes the fundamental limits of conventional designs, allowing us to steer the energy flow in an arbitrary manner without parasitic scattering. The design with a discretized structure is verified both numerically and experimentally and an energy conversion efficiency of 93% is observed for the transmitted wave into the desired direction of 60 degrees, higher than the corresponding theoretical upper limit in generalized Snell’s law based designs (89%). Our experimental demonstration confirms the theoretical results and opens a new way of designing practical and highly efficient metasurfaces for different functionalities, allowing nearly ideal control over the energy flow through metasurfaces.

Analysis of material selection on dielectric metasurface performance.

Dielectric metasurfaces are ultra-thin devices that can shape optical wavefronts with extreme control. While an assortment of materials possessing a wide range of dielectric constants have been proposed and implemented, the minimum dielectric contrast required for metasurfaces to achieve high-efficiency performance, for a given device function and feature size constraint, is unclear. In this Article, we examine the impact of dielectric material selection on metasurface efficiency at optical frequencies. As a model system, we design transmissive, single-layer periodic metasurfaces (i.e., metagratings) using topology optimization, and we sweep device thickness and light deflection angle for differing material types. We find that for modest deflection angles below 40 degrees, materials with relatively low dielectric constants near 4 can be used to produce metagratings with efficiencies over 80%. However, ultra-high-efficiency devices designed for large deflection angles and multiple functions require materials with high dielectric constants comparable to silicon. We also identify, for all materials, a minimum device thickness required for optimal metagrating performance that scales inversely with dielectric constant. Our work presents materials selection guidelines for high-performance metasurfaces operating at visible and infrared wavelengths.

Measurements of jet quenching with semi-inclusive hadron+jet distributions in Au+Au collisions at sNN=200 GeV

The STAR Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum hadron trigger, in central and peripheral Au+Au collisions at sNN=200 GeV. Charged jets are reconstructed with the anti-kT algorithm for jet radii R between 0.2 and 0.5 and with low infrared cutoff of track constituents (pT>0.2 GeV/c). A novel mixed-event technique is used to correct the large uncorrelated background present in heavy ion collisions. Corrected recoil jet distributions are reported at midrapidity, for charged-jet transverse momentum pT,jetch<30 GeV/c. Comparison is made to similar measurements for Pb+Pb collisions at s=2.76 TeV, to calculations for p+p collisions at s=200 GeV based on the pythia Monte Carlo generator and on a next-to-leading order perturbative QCD approach, and to theoretical calculations incorporating jet quenching. The recoil jet yield is suppressed in central relative to peripheral collisions, with the magnitude of the suppression corresponding to medium-induced charged energy transport out of the jet cone of 2.8±0.2(stat)±1.5(sys) GeV/c, for 10<pT,jetch<20 GeV/c and R=0.5. No medium-induced change in jet shape is observed for R<0.5. The azimuthal distribution of low-pT,jetch recoil jets may be enhanced at large azimuthal angles to the trigger axis, due to scattering off quasiparticles in the hot QCD medium. Measurement of this distribution gives a 90% statistical confidence upper limit to the yield enhancement at large deflection angles in central Au+Au collisions of 50±30(sys)% of the large-angle yield in p+p collisions predicted by pythia.14 MoreReceived 4 February 2017DOI:https://doi.org/10.1103/PhysRevC.96.024905©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHard scatteringJets & heavy flavor physicsQuark-gluon plasmaRelativistic heavy-ion collisionsNuclear Physics

Gaussian beam diffraction by two-dimensional refractive index modulation for high diffraction efficiency and large deflection angle.

The propagation of Gaussian beams is analyzed for an acousto-optic deflector by varying the refractive index in two-dimensions with a row of phased array piezoelectric transducers. Inhomogeneous domains of phase grating are produced by operating the transducers at different phase shifts, resulting in two-dimensional index modulation of periodic and sinc function profiles. Also different phase shifts provide a mechanism to steer the grating lobe in various directions and, therefore, the incident angle of the laser beam on the grating plane is automatically modified without moving the beam. Additionally, the acoustic frequency can be varied to achieve the Bragg condition for the new incident angle of the laser beam so that the diffraction efficiency of the deflector is maximized. The Gaussian beam is expressed in terms of planes and the second order coupled mode theory is implemented to analyze the diffraction of the beam. The diffraction efficiency is found to be nearly unity for optimal operating parameters of the acousto-optic device.

Optical metasurfaces for high angle steering at visible wavelengths

Metasurfaces have facilitated the replacement of conventional optical elements with ultrathin and planar photonic structures. Previous designs of metasurfaces were limited to small deflection angles and small ranges of the angle of incidence. Here, we have created two types of Si-based metasurfaces to steer visible light to a large deflection angle. These structures exhibit high diffraction efficiencies over a broad range of angles of incidence. We have demonstrated metasurfaces working both in transmission and reflection modes based on conventional thin film silicon processes that are suitable for the large-scale fabrication of high-performance devices.

Light curves of light rays passing through a wormhole

Gravitational lensing is a good probe into the topological structure of dark gravitating celestial objects. In this paper, we investigate the light curve of a light ray that passes through the throat of an Ellis wormhole, the simplest example of traversable wormholes. The method developed here is also applicable to other traversable wormholes. To study whether the light curve of a light ray that passes through a wormhole throat is distinguishable from that which does not, we also calculate light curves without the passage of a throat for an Ellis wormhole, a Schwarzschild black hole, and an ultrastatic wormhole with the spatial geometry identical to that of the Schwarzschild black hole in the following two cases: (i) "microlensing," where the source, lens, and observer are almost aligned in this order and the light ray starts at the source, refracts in the weak gravitational field of the lens with a small deflection angle, and reaches the observer, and (ii) "retrolensing," where the source, observer, and lens are almost aligned in this order, and the light ray starts at the source, refracts in the vicinity of the light sphere of the lens with a deflection angle very close to $\pi$, and reaches the observer. We find that the light curve of the light ray that passes through the throat of the Ellis wormhole is clearly distinguishable from that by the microlensing but not from that by the retrolensing. This is because the light curve of a light ray that passes by a light sphere of a lens with a large deflection angle has common characters, irrespective of the details of the lens object. This implies that the light curves of the light rays that pass through the throat of more general traversable wormholes are qualitatively the same as that of the Ellis wormhole.

Two-dimensional refractive index modulation by phased array transducers in acousto-optic deflectors

Acousto-optic deflectors are photonic devices that are used for scanning high-power laser beams in advanced microprocessing applications such as marking and direct writing. The operation of conventional deflectors mostly relies on one-dimensional sinusoidal variation of the refractive index in an acousto-optic medium. Sometimes static phased array transducers, such as step configuration or planar configuration transducer architecture, are used to tilt the index modulation planes for achieving higher performance and higher resolution than a single transducer AO device. However, the index can be modulated in two dimensions, and the modulation plane can be tilted arbitrarily by creating dynamic phase gratings in the medium using phased array transducers. This type of dynamic two-dimensional acousto-optic deflector can provide better performance using, for example, a large deflection angle and high diffraction efficiency. This paper utilizes an ultrasonic beam steering approach to study the two-dimensional strain-induced index modulation due to the photoelastic effect. The modulation is numerically simulated, and the effects of various parameters, such as the operating radiofrequency of the transducers, the ultrasonic beam steering angle, and different combinations of pressure on each element of the transducer array, are demonstrated.

Athermal migration of vacancies in iron and copper induced by electron irradiation

Irradiation with high-energy particles induces athermal migration of point defects, which affects defect reactions at low temperatures where thermal migration is negligible. We conducted molecular dynamics simulations of vacancy migration in iron and copper driven by recoil energies under electron irradiation in a high-voltage electron microscope. Minimum kinetic energy required for migration was about 0.8 and 1.0 eV in iron and copper at 20 K, which was slightly higher than the activation energy for vacancy migration. Around the minimum energy, the migration succeeded only when a first nearest neighbour (1NN) atom received the kinetic energy towards the vacancy. The migration was induced by higher kinetic energies even with larger deflection angles. Above several electron-volts and a few 10s of electron-volts, vacancies migrated directly to 2NN and 3NN sites, respectively. Vacancy migration had complicated directional dependence at higher kinetic energies through multiple collisions and replacement of atoms. The probability of vacancy migration increased with the kinetic energy and remained around 0.3–0.5 jumps per recoil event for 20–100 eV. At higher temperatures, thermal energies slightly increased the probability for kinetic energies less than 1.5 eV. The cross section of vacancy migration was 3040 and 2940 barns for 1NN atoms in iron and copper under irradiation with 1.25 MV electrons at 20 K: the previous result was overestimated by about five times.