Direction Of Light Beam Research Articles

Chloroplast photoprotection: face the light or run and hide?

Chloroplast photoprotection: face the light or run and hide?

Adaptive museum lighting using CNN-based image segmentation

Modern smart lighting systems have the potential to improve lighting conditions by employing adaptive dimming. However, the light intensity pattern of the individual luminaires is often not optimally matching with the region(s) of interest. By using adaptive lighting fixtures with a tunable radiation pattern, much more targeted illumination can be enabled. The already demonstrated adaptive lighting fixtures are typically quite bulky, and require user input to optimize the emitted light. In this paper, a compact lighting fixture is proposed that consists of a high-power LED, a sequence of lenses, an adjustable mirror and tunable diffuser, to achieve an adaptive lighting functionality. This adaptive luminaire is integrated with an embedded system and camera, to realize autonomous beam adjustment based on computer vision in a museum setting. The embedded system performs semantic segmentation to detect painting masks, and adapts the light beam direction and spot size to the detected painting frame via a feedback loop. The system can be considered as a first demonstration of the integration between state-of-the-art computer vision and adaptive light fixtures for indoor lighting.

Broadband multifunctional plasmonic polarization converter based on multimode interference coupler

We propose a multifunctional integrated plasmonic–photonic polarization converter for polarization demultiplexing in an indium-phosphide membrane on silicon platform. By using a compact 1 × 4 multimode interference coupler, this device can provide simultaneous half-wave plate (HWP) and quarter-wave plate (QWP) functionalities. Our device employs a two-section HWP to obtain a very large conversion efficiency of ≥ 91% over the entire C to U telecom bands, while it offers a conversion efficiency of ≥ 95% over ∼ 86% of the C to U bands. Our device also illustrates QWP functionality, where the transmission contrast between the transverse electric and transverse magnetic modes is ≈ 0 dB over the whole C band and 55% of the C to U bands. Using this functionality, our device generates two quasi-circular polarized beams with opposite spins and topological charges of l=±1, based on only one input polarization, and one incoming light beam direction. We expect that this device can be a promising building block for the realization of ultracompact on-chip polarization demultiplexing and lab-on-a-chip biosensing platforms. Finally, our proposed device allows the use of the polarization and angular momentum degrees of freedom, which makes it attractive for quantum information processing.

The interaction in nonlocal nonlinearity media under fractional effects

The propagation properties of the interaction of Airy Gaussian beams and solitons modeled by the fractional Schrödinger equation in nonlocal nonlinear media are demonstrated numerically. The transmission direction of beams is deflected in the nonlocal nonlinear media and the direction of deflection is related to the symbol of nonlocal nonlinear parameter. The interval parameter and Lévy index determine whether the beams form bound state or soliton in the transmission process. When the absolute value of the interval parameter and Lévy index are large, the beams cannot form solitons, but only a bound state beam. The transmission dynamics of the double Airy Gaussian beams and single soliton interaction are also discussed in this paper, as well as the numerical simulation results obtained for the double Airy Gaussian beams and double solitons interaction. These properties have potential application value for controlling the propagation and direction of light beams and have certain significance in the field of optical switches.

Numerical analysis of power generation characteristics in beam irradiation control of indoor OWPT system

Optical wireless power transmission (OWPT), a new WPT alternative, is a promising solution to tackle the challenges like providing over watt-level power over meter-level distance that conventional WPT technologies face, to provide convenient and perpetual energy supply to the internet of things (IoT), mobile devices, and other various electrical equipments. In the OWPT system, in a room which has a light source at the ceiling, the beam deformation caused by changing the light beam direction affects the power generation efficiency reduction. Investigating and improving the performance of the power generation efficiency of OWPT system is necessary. In this paper, numerical analysis of the power generation efficiency of the solar cell module in a room was investigated. In the case of fixed light divergence angle, the efficiency reduced rapidly when the solar cell is located within a few meters from the room center. Therefore, continuous change of the divergence angle is required. In addition, we proposed a new configuration of the OWPT system with mirrors and clarified that using mirror to transmit light to the solar cell is useful in a wide range of indoor OWPT systems.

Fatigue life evaluation and failure analysis of light beam direction adjusting mechanism of an automobile headlight exposed to random loading

Failure of the light beam direction adjusting mechanism (LDAM) of an automotive headlight might occur after hundreds of driving hours, though the strength of components conforms to the requirement specified in the random vibration bench test standard. In order to determine the causes of the failure, fatigue life prediction and failure analysis based on numerical method of the LDAM exposed to random loading both in bench test and field experiment were carried out. In the bench test analysis, the Dirlik method was utilized to calculate the lifetime by taking the power spectrum density in the frequency domain. In the fatigue analysis for the field experimental loading, to consider the effect of nonuniform temperature distribution, a numerical process in time domain is developed to calculate the lifetime of the LDAM subjected to the random vibration caused by road surface roughness. As a result, the predicted life and failure locations are in good agreement with real life and actual failure regions, respectively.

Beam focusing and unidirectional excitation from four nanoslits filled with air and non-linear material

We theoretically design a device composed of four nanoslits to dynamically modulate the propagation direction of light beam by embedding non-linear material and air, respectively. Directions of radiation fields are determined by the phase difference of the surface waves at the exit interface and distance of each slit. Numerical simulations using finite element method verify that the unidirectional excitation and beam focusing can be achieved easily by changing the intensity of incident light.

A method for eliminating Faraday rotation in cryostat windows in longitudinal magneto-optical Kerr effect measurements.

A solution to the problem of disturbing effect of the background Faraday rotation in the cryostat windows on longitudinal magneto-optical Kerr effect (LMOKE) measured under vacuum conditions and/or at low temperatures is proposed. The method for eliminating the influence of Faraday rotation in cryostat windows is based on special arrangement of additional mirrors placed on sample holder. In this arrangement, the orientation of the cryostat window is perpendicular to the light beam direction and parallel to an external magnetic field generated by the H-frame electromagnet. The operation of the LMOKE magnetometer with the special sample holder based on polarization modulation technique with a photo-elastic modulator is theoretically analyzed with the use of Jones matrices, and formulas for evaluating of the actual Kerr rotation and ellipticity of the sample are derived. The feasibility of the method and good performance of the magnetometer is experimentally demonstrated for the LMOKE effect measured in Fe/Au multilayer structures. The influence of imperfect alignment of the magnetometer setup on the Kerr angles, as derived theoretically through the analytic model and verified experimentally, is examined and discussed.

A new angle on imaging

Capturing the direction of light beams can make for after-the-fact focusing - All cameras capture the intensity of light as it strikes their imaging chips. Color filters provide a second set of data, sorting the rays into different wavelengths. But new devices–including one produced commercially and others still in the lab–are starting to capture a third piece of information: angle. This allows cameras to go beyond focusing on a single plane to taking images at many different depths of a scene at once. Cameras that capture both intensity and angle will allow for refocusing already-snapped pictures, lensless cameras, and the creation of 3-D images with a single camera, according to researchers in several competing groups.

Violation of axial symmetry of optical properties in the trigonal crystal Nd:GdFe 2.1Ga 0.9(BO 3) 4

Strong dependence of birefringence and absorption spectra of d– d, f– f and charge transfer transitions on the direction of light beam in the plane perpendicular to the threefold crystallographic axis has been found out in trigonal crystal Nd:GdFe 2.1Ga 0.9(BO 3) 4. X-ray measurements have shown that the crystal consists of inversion twins, whose formation is stimulated by the partial substitution of Fe by Ga. Observed violation of axial symmetry of the trigonal crystal optical properties is accounted for on the basis of assumption about stripe domain structure of the inversion twins.

Symmetry-induced singularities of the dispersion surface curvature and high sensitivities of a photonic crystal

We rigorously analyze the dispersion function and the curvature of the dispersion surface of a photonic crystal to explore the fundamental limit of its angular sensitivities. With insight gained from group theory, we find that symmetry induced degeneracy gives rise to a singular dispersion surface curvature and a nonvanishing group velocity simultaneously. Near such a singularity, high angular sensitivities can be achieved at low optical loss. This phenomenon exists generally in most common two-dimensional and three-dimensional photonic crystal lattices, although it occurs only for certain photonic bands as dictated by symmetry. This symmetryinduced effect is absent in one-dimensional crystals. Rigorous formulas of the sensitivities of the light beam directions to wavelength and refractive index changes are derived. Individual contributions of the dispersion surface curvature and group velocity to these sensitivities are separated. In the absence of the Van Hove singularity, a singular dispersion surface curvature gives rise to ultrahigh dispersion d d 10 3 deg/nm and refractive index sensitivity d dna 10 4 deg without compromising optical transmission. The angular dispersion value is significantly larger than those previously reported for the superprism effect and is not due to slow group velocity. We also discuss how various parameters intrinsic and extrinsic to a photonic crystal may suppress or enhance the angular sensitivities according to the rigorous formulas we obtain.

Light scattering by dislocations in group‐III nitrides

AbstractLight scattering by dislocations in group‐III nitrides has been studied. The effects of dislocation strain field and hollow cores on light scattering have been investigated. It is found that the coreless edge dislocation and the edge dislocations with hollow cores both participate in light scattering. Screw dislocations contribute to light scattering only if they have hollow cores. Analytical expressions for differential cross sections of light scattering by edge and screw dislocations have been obtained. Transport cross sections for in‐plane and transversal light polarizations have been calculated. Calculated spectral dependencies of the scattering cross sections show significant resonant enhancement of the light scattering in the vicinity of the absorption edge. An angle diffusion coefficient of light beam directions has been obtained that can be used for experimental determination of density, Burgers vectors and core radii of threading dislocations in III‐nitride crystals by optical means. In crystal films with high dislocation density the exponential decay of laterally propagating light rays resulting from scattering by dislocations can exceed the decay related to light absorption. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Frequency-tunable high-power terahertz wave generation from GaP

A frequency-tunable terahertz wave was generated from GaP crystals using an optical parametric oscillator as the pump source and a YAG laser (1.064 μm) as the signal source. By tuning the very small angle, θin, between the pump and signal light beam directions, tunable terahertz waves over the frequency range from 0.5 to 3 THz were obtained. The THz frequency changed almost linearly with the angle θin. The precise noncollinear phase matching condition is discussed. The pulsed peak power of the THz wave was as high as 480 mW at 1.3 THz.

On the Accuracy of Beam-Averaged Interferometric Heat Transfer Measurements

Laser interferometry can be used in a three dimensional temperature field to measure the average fluid temperature and heat transfer rate, integrated over the length of an experimental model. However, such measurements are inherently approximate when the surface temperature varies in the direction of the test/object beam. In this study an analysis is performed to determine the accuracy of beam-averaged heat transfer rate measurements made in ideal gases. Two analysis methods are considered. The first method is based on extrapolation of the near-wall temperature field to obtain the surface gradient. In the second method, the temperature gradient at the surface is obtained directly from the gradient of the fringe field. The results show that the intrinsic error in the measurements depends strongly upon the form and magnitude of the temperature variation in the light beam direction. Although the error in the measured heat transfer rate is shown to be small for many commonly encountered conditions, it can be greater than ten percent in extreme cases.

THE ACCURACY OF BEAM-AVERAGED INTERFEROMETRIC TEMPERATURE MEASUREMENTS IN A THREE-DIMENSIONAL FIELD

A classical or holographic interferometer can be used to measure the average fluid temperature integrated in the direction of the test/object beam. However, such beam-averaged measurements are not exact for a three-dimensional temperature field, when a standard two-dimensional analysis technique is applied. In the current study, an analysis is performed to determine the error in the average fluid temperature measurement caused by temperature variations in the light beam direction. The error has been calculated for both an ideal gas and water as the test fluid. The results show that for typical experimental conditions, the measurement error introduced by this temperature variation is less than 2%, even for the most adverse temperature distribution in the light beam direction. For reasons discussed in this article, this result may promote the wider application of interferometry to three-dimensional heat transfer problems.

Directional light scattering by domain walls in uniaxial ferroelectrics

It was revealed that specific directional light scattering takes place in ferroelectric semiconductors in polydomain states. This scattering is observed at to the light beam direction. The behaviour of this effect suggests that it is caused by light reflection by layers formed by charge carriers which screen charged domain walls between opposing domains. The orientation of the reflecting layers was determined. This effect allows one to check easily the degree of unipolarity throughout the sample and refine optically the complete crystallographic orientation.

Angular dependence of X-ray absorption spectra

A detailed account of the dependence of X-ray absorption spectra (XAS) on polarisation and light beam directions is given. Anisotropic XAS measured on single crystals, layered compounds, polymers and oriented powders are tabulated. The X-ray absorption cross section by non-magnetic samples is derived, including electric dipole and quadrupole contributions. Orders of magnitude are found for magnetic dipole and electric dipole-octupole terms. Using a spherical tensor expansion of the absorption cross section, simple analytical formulae are given for the angular dependence of the electric dipole and quadrupole contributions to XAS for all crystal point groups. These formulae are valid down to the edge and include many-body effects. The are applied to two experimental examples, the iron K-edge in haematite and the copper K-edge in CuCl42-. For the latter case, spherical tensor components are interpreted in terms of molecular orbitals. The influence of unpolarised and circularly polarised X-rays is discussed, as well as various experimental problems met in angle-resolved XAS. In an appendix, the quadrupole contribution to angular XAS is derived within the multiple-scattering formalism, along with closed expressions for the dipole and quadrupole spherical tensor components.

Laser cathode ray tube with a semiconductor double-heterostructure screen

Room-temperature laser action has been achieved in a cathode ray tube (CRT) in which the target screen is a (GaAs) (GaAlAs) double-heterostructure (DH) single-crystal semiconductor. The light-beam direction is normal to the face of the tube, i.e., parallel to the pump-electron-beam direction and, hence, scannable in two dimensions. Electron-beam energy is 34 keV and threshold current is 700 µA, corresponding to a current density of about 5 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .