Spatial Distribution Of Light Intensity Research Articles

Testing and Analysis on the Spatial and Temporal Distribution of Light Intensity and CO2 Concentration in Solar Greenhouse

Greenhouses, as important parts of facility agriculture, can reduce the restrictions on agricultural production imposed by the natural environment and make rational and efficient use of production resources. We conducted long-term, continuous testing of temperature, humidity, light intensity, and CO2 concentration parameters in a heliostat greenhouse in the central and western parts of the Inner Mongolia Autonomous Region, a cold and arid region of northern China. A large amount of data was processed by statistical observation, simulation analysis, and 3D reconstruction to obtain the overall distribution, variation pattern, and mathematical model of the regional greenhouse environment in time and space. The results show that the temperature, humidity, light intensity, and CO2 concentration in the greenhouse have significant daily variation patterns, that there are strong coupling relationships between light intensity–CO2 concentration–time and indoor temperature–light intensity–CO2 concentration, that the coefficients of determination (R2) of the mathematical models are 0.88 and 0.89, and that the standard errors (RMSE) are 49.67 ppm and 45.30 ppm, respectively. The environmental parameters were fitted with high accuracy in order to provide scientific data for the cultivation of heliostats in the region.

Optical Logic Gate Operations With Single-Pixel Imaging

Optical computing has potential advantages of light-speed parallel processing and low power consumption over electronic computing. Logic gates are fundamental building blocks of modern computing systems. In this work, two types of single-pixel imaging systems are investigated for performing a non-imaging task of optical logic gate operations for the first time. In the first scheme, the spatial light intensity distribution of object image and illumination pattern is encoded based on the input binary values. Then the logic gate output result is indicated by the maximum single-pixel intensity when the encoded object image is incoherently illuminated by a most matched pattern. In the second scheme, the light amplitudes in corresponding sub-regions are directly proportional to the binary input values. A universal linear approximation model in the complex-amplitude domain allows the detected light intensity of a single-pixel holography system representing the logic gate output result. Various logic gate operations such as AND, OR and XOR can be implemented by these two systems in an individual or compound manner.

Impact of spatial distribution of light intensity on disinfection kinetics of Mycobacterium smegmatis and E. coli using TiO2-based photocatalyst

Impact of spatial distribution of light intensity on disinfection kinetics of Mycobacterium smegmatis and E. coli using TiO2-based photocatalyst

Flexible Short-Wave Infrared Image Sensors Enabled by High-Performance Polymeric Photodetectors

High-performance short-wave infrared (SWIR) photodetectors (PDs) possess great potential in health monitoring, remote control, telecommunication, and medical diagnostics. In comparison with inorganic PDs, organic PDs (OPDs) stand out as good candidates for next-generation photodetection devices because of their ease of processing, tunable optoelectronic properties, lightweight, easy portability, and low-manufacturing cost. Herein, we reported two conjugated polymers with ultranarrow band gaps (0.6 eV) for photoconductor-mode SWIR OPDs, which exhibited broad and excellent photoresponse across the visible and IR regions as long as 1450 nm. Specifically, one of the polymers possessing longer exciton lifetimes and favorable morphology and molecular orientation was further applied for flexible OPDs, demonstrating excellent performance with the responsivity (R) and external quantum efficiency as high as 0.96 A/W and 106% at 1122 nm, respectively, comparable to those of 2D nanomaterial-based IR PDs. In addition, an image sensor composed of 16 × 16 flexible OPDs was constructed, which can detect spatial light intensity distribution (1342 nm) clearly. This contribution shed light on designing excellent conjugated polymers for high-performance photoconductor-mode OPDs, which can be employed for SWIR light image sensors.

Monte-Carlo-based optical wireless underwater channel modeling with oceanic turbulence

Underwater optical wireless communication has attracted widespread attention due to its high bandwidth. The complex compositions of seawater affect the transmission of underwater optical signals. However, for underwater optical wireless channel modeling, the turbulence effect cannot be integrated into the Monte Carlo simulation framework for absorption and scattering. Based on the generalized Snell’s Law, we extend the multiple phase screen model to unify turbulence effects, absorption and scattering effects into the Monte Carlo simulation framework, which allows us to study the integration of absorption, scattering and turbulence effects on underwater channels simultaneously. The received intensity probability density distribution, spatial light intensity distribution and power loss are investigated. To the best of our knowledge, this is the first time to explore the integration of absorption, scattering and turbulence effects on underwater optical wireless channel.

Monte Carlo simulation and experimental evaluation of the quantum efficiency of Eu3+-doped glass at different temperatures.

The quantum efficiency (QE) is a key parameter to evaluate the optical properties of fluorescent glass. However, it is very difficult to measure the QE at high temperatures by the integrating sphere test system. In this paper, we report a new method to calculate the QE of five kinds of Eu3+-doped glasses at different temperatures based on experimental absorption and excitation spectra of Eu3+-doped glasses. The simulated QE values agree well with the experimental values of QE. Furthermore, the influence of the shape, refractive index and temperature on the QE and the spatial light intensity distribution of the Eu3+-doped glass is studied based on the Monte Carlo method. This work presents a simple method to calculate the QE and the spatial light intensity distribution at different temperatures.

Visualising Spatial Light Intensity Distribution on Optical Fibre Core with Spreadsheet

Abstract Spreadsheet software is a practical and powerful computing and graphical tool. This study presents a simple way to build a physics simulation in spreadsheet software. The simulation aims to visualise spatial light intensity distribution on an optical fibre core. The simulation can visualise various modes. The mathematical equation in optical fibre is quite complicated. The visualisation may help students in interpreting the mathematical equation and making a connection between theoretical modelling and experiment.

Optical System for Led Luminaire

Lighting devices are an important element of a large number of technical systems, including road, living, industrial lighting, lighting systems of vehicles. It is known that the light instrument must fulfill two basic lighting tasks: to redistribute the light source of light source in the right way and to limit its dazzling effect. The introduction of light-emitting diodes (LEDs) for lighting necessitated a completely new quality in the construction of luminaires. The different production technology required new methods and designing tools. It also challenged designers with new problems to solve. LEDs are light sources emitting in one hemisphere, which requires a special approach to designing an LED lighting unit. However, for the illumination of premises with high spans or streets, roads such a light distribution is not suitable. For luminaires with solid-state light sources, other materials and new technology must be used; moreover, light distribution needs to be formed using different methods.
 This paper presents the design process of a LED luminaire from concept to implementation, exemplified by road lighting, and describes the methods and procedures used by the designer. Also, technological problems influencing the quality of the above lighting are addressed. Optical systems for LEDs are considered. The peculiarities of the use of secondary optical elements in the form of lenses for purpose of obtaining different diagrams of the spatial distribution of light intensity of light-emitting diodes are analyzed. Features and problems of calculation of secondary optical systems are considered. Massive collimators do not have to be elements that focus a narrow beam of light. They are able to form a beam in accordance with any accepted distribution that is appropriate for a given application. They are also able to form a beam in a specific way that is required for outdoor lighting luminaires. The stages of a project for designing a road luminaire require the application of the knowledge and experience gained in various research projects. The design methods described in this paper have been developed designing activity and are also to be used successfully in lighting production.

The concept for realization of quantum-cascade lasers emitting at 7.5 μm wavelength

We consider the advantages and disadvantages of various designs of waveguide for heterostructures of quantum cascade lasers (QCL) in a spectral region of 7.5 μm. Based on a numerical calculation we make a comparison of light wave distribution in QCL waveguides with different designs. We demonstrate the benefits of practical QCL realization with an extended five-layered waveguide formed by introducing extra layers of InGaAs, which allows to modify the spatial distribution of the light wave and get the rectangular shape of the spatial distribution of light wave intensity in the laser active area.

A collisional-radiative model for lithium impurity in plasma boundary region of Experimental Advanced Superconducting Tokamak

A green emission layer caused by lithium impurity is universally observed in plasma boundary region of Experimental Advanced Superconducting Tokamak (EAST) via a visible-light camera, where lithium coating is normally adopted as a routine technique of wall conditioning. In this article, in order to estimate the spatial distribution of green light intensity of this emission layer according to the given real parameter distributions of edge plasmas, a practicable method is proposed based on a collisional-radiative model. In this model, a finite number of energy levels of lithium are taken into account, and proper simplifications of convection-diffusion equations are made according to the order-of-magnitude analysis. We process the atomic data collected from the OPEN-ADAS database, and develop a corresponding program in Mathematica 10.4.1 to solve the simplified one-dimensional problem numerically. Estimation results are obtained respectively for the two sets of edge plasma profiles of EAST in L-mode and H-mode regimes, and both clearly show a good unimodal structure of the spatial distribution of green light intensity of this emission layer. These analyses actually provide the spatial distributions of lithium impurities at different energy levels, not only indicating the spatial distribution of the intensity of this emission layer induced by lithium impurity but also revealing the physical processes that lithium experiences in edge plasma. There are some different and common characteristics in the spatial distribution of the intensity of this emission layer in these two important cases. This emission layer is kept outside the last closed magnetic surface in both cases while it becomes thinner with a higher intensity peak in H-mode case. Besides, the sensitivity of this algorithm to the measurement error of edge plasma profile is also explored in this work. It is found that the relative errors of the numerical results obtained by our proposed method are comparable to those of edge plasma profiles. This work provides important theoretical references for developing a new practical technique of fast reconstructing edge plasma configurations in EAST based on the emission of lithium impurity, and may further contribute a lot to the studies of edge plasma behaviors when three-dimensional perturbation fields are adopted.

Light Extraction Enhancement in GaN-Based Light-Emitting Diodes with Patterned Micro-Pillars

A nitride-based light-emitting diode (LED) is a key device for the next-generation solid-state lighting due to its high efficiency, high reliability, and potential to offer new functionalities. However, the large contrast in the refractive index between the LED semiconductor and ambient air (i) limits the light extraction efficiency (LEE) of LEDs by means of total internal reflection, and (ii) distorts the spatial distribution of light intensity emitted from the LED. As a result, planar-surface LEDs normally have a very low LEE and an emission pattern with the peak emission intensity along the LED surface-normal. Such a pointed emission pattern is not appropriate for uniform illumination, e.g. an interior and a street lighting. These two problems have been solved separately. First, the low LEE of GaN-based LEDs has been improved by means of surface/interface roughening and chip shaping. Second, the emission pattern of LEDs has been controlled by the help of secondly optics and external cavities such as photonic crystals. However, a combined solution for both problems requires advanced manipulation capabilities for the surface of LEDs, which is not fully developed yet. Here, we present a technique that provides full control of surface properties (esp. refractive index) in the LED structure: the LEDs having patterned micro-pillars. The effect of the patterned micro-pillars is investigated and the structure of micro-pillars is optimized in order to obtain maximum LEE and also emission-pattern control.

Combining near-field hyperspectral imaging and far-field spectral-angular distribution to develop mid-field white LED optical models with spatial color deviation.

The integration of spatial distribution of light intensity and color in the midfield is instrumental for LED optical design. On the basis of this rationale, we proposed an accurate and convenient method for developing white LED optical models. Near-field hyperspectral images and far-field spectral-angular distributions were integrated to illustrate changes in spatial light intensity and color distribution in the mid-field, to the exclusion of the absorption, conversion, and scattering of phosphors. The corresponding optical models were developed for three LED samples under different packaging conditions. Their normalized cross-correlation values for spatial light intensity and correlated-color-temperature distribution between simulation and measurement averaged as high as 0.995 and 0.99 respectively, which validated the accuracy and feasibility of the proposed method.

Flexible and Semitransparent Organolead Triiodide Perovskite Network Photodetector Arrays with High Stability.

Organolead triiodide perovskite (CH3NH3PbI3) as a light-sensitive material has attracted extensive attention in optoelectronics. The reported perovskite photodetectors (PDs) mainly focus on the individual, which limits their spatial imaging applications. Uniform perovskite networks combining transparency and device performance were synthesized on poly(ethylene terephthalate) (PET) by controlling perovskite crystallization. Photodetector arrays based on above network were fabricated to demonstrate the potential for image mapping. The trade-off between the PD performance and transparency was systematically investigated and the optimal device was obtained from 30 wt % precursor concentration. The switching ratio, normalized detectivity, and equivalent dark current derived shot noise as the critical parameters of PD arrays reached 300, 1.02 × 10(12) Jones, and 4.73 × 10(-15)A Hz(-1/2), respectively. Furthermore, the PD arrays could clearly detect spatial light intensity distribution, thus demonstrating its preliminary imaging function. The perovskite network PD arrays fabricated on PET substrates could also conduct superior flexibility under wide angle and large number of bending. For the common problem of perovskite optoelectronics in stability, the perovskite networks sheathed with hydrophobic polymers greatly enhanced the device stability due to the improved interface contacts, surface passivation, and moisture isolation. Taking into consideration transparency, flexibility, imaging and stability, the present PD arrays were expected to be widely applied in visualized portable optoelectronic system.

Accuracy improvement in laser stripe extraction for large-scale triangulation scanning measurement system

Large-scale triangulation scanning measurement systems are widely used to measure the three-dimensional profile of large-scale components and parts. The accuracy and speed of the laser stripe center extraction are essential for guaranteeing the accuracy and efficiency of the measuring system. However, in the process of large-scale measurement, multiple factors can cause deviation of the laser stripe center, including the spatial light intensity distribution, material reflectivity characteristics, and spatial transmission characteristics. A center extraction method is proposed for improving the accuracy of the laser stripe center extraction based on image evaluation of Gaussian fitting structural similarity and analysis of the multiple source factors. First, according to the features of the gray distribution of the laser stripe, evaluation of the Gaussian fitting structural similarity is estimated to provide a threshold value for center compensation. Then using the relationships between the gray distribution of the laser stripe and the multiple source factors, a compensation method of center extraction is presented. Finally, measurement experiments for a large-scale aviation composite component are carried out. The experimental results for this specific implementation verify the feasibility of the proposed center extraction method and the improved accuracy for large-scale triangulation scanning measurements.

Optimization of spatial light distribution through genetic algorithms for vision systems applied to quality control

The paper presents an adaptive illumination system for image quality enhancement in vision-based quality control systems. In particular, a spatial modulation of illumination intensity is proposed in order to improve image quality, thus compensating for different target scattering properties, local reflections and fluctuations of ambient light. The desired spatial modulation of illumination is obtained by a digital light projector, used to illuminate the scene with an arbitrary spatial distribution of light intensity, designed to improve feature extraction in the region of interest. The spatial distribution of illumination is optimized by running a genetic algorithm. An image quality estimator is used to close the feedback loop and to stop iterations once the desired image quality is reached. The technique proves particularly valuable for optimizing the spatial illumination distribution in the region of interest, with the remarkable capability of the genetic algorithm to adapt the light distribution to very different target reflectivity and ambient conditions. The final objective of the proposed technique is the improvement of the matching score in the recognition of parts through matching algorithms, hence of the diagnosis of machine vision-based quality inspections. The procedure has been validated both by a numerical model and by an experimental test, referring to a significant problem of quality control for the washing machine manufacturing industry: the recognition of a metallic clamp. Its applicability to other domains is also presented, specifically for the visual inspection of shoes with retro-reflective tape and T-shirts with paillettes.

Bloch oscillations in plasmonic waveguide arrays.

The combination of modern nanofabrication techniques and advanced computational tools has opened unprecedented opportunities to mold the flow of light. In particular, discrete photonic structures can be designed such that the resulting light dynamics mimics quantum mechanical condensed matter phenomena. By mapping the time-dependent probability distribution of an electronic wave packet to the spatial light intensity distribution in the corresponding photonic structure, the quantum mechanical evolution can be visualized directly in a coherent, yet classical wave environment. On the basis of this approach, several groups have recently observed discrete diffraction, Bloch oscillations and Zener tunnelling in different dielectric structures. Here we report the experimental observation of discrete diffraction and Bloch oscillations of surface plasmon polaritons in evanescently coupled plasmonic waveguide arrays. The effective external potential is tailored by introducing an appropriate transverse index gradient during nanofabrication of the arrays. Our experimental results are in excellent agreement with numerical calculations.

FDTD simulation of the electromagnetic field surface states in 2D photonic crystals

FDTD simulation was applied to study an optical field structure near the 2D photonic crystal surface. An effect of the optical field intensity redistribution was demonstrated for the first time. Spatial distribution of light intensity contains sharp peaks, focused in a certain parts of the crystal structure. The intensity peaks' magnitude could be very high. In case the incident light wavelength corresponds to the photonic crystal bandgap, the light could penetrate in a small depth into the crystal, but magnitude of the intensity peaks becomes several times higher in comparison to magnitude of the light intensity in the equal but homogeneous medium. Observed effect could be used for the enhancement of the light-matter interactions efficiency, for instance, for effective nonlinear conversion of light with photonic crystals, for Raman spectroscopy of small particles injected in crystals and etc.

Optimization Design of Cylinder Grating Used for Non-Contact Speed Measurement

In order to realize the detection of diffractive light after the image segmentation using cylinder grating, the parameters of a cylinder grating was optimized using the wave optics theory. By analyzing the relation of optical path length variation with the diffraction angle of single cylinder lens diffraction, and by Fraunhofer approximation, the analytical expressions of cylinder lens diffraction was given. By setting parameters to calculate and simulate, it was found that to increase the ratio of curvature radius and grating period could effectively reduce the spatial distribution of the diffraction light intensity. For the gratings that already exist, by reducing the ratio of refractive index of the gratings material and environment, the spatial light distribution of the grating could be reduced. If the cylinder grating period is too small, the overlap part of images segmentation light diffraction intensity will increase. But it occupies smaller proportion of the total light intensity. After the optimization design of cylinder grating, the results showed that it could be used for non-contact speed measurement in the range of some parameter.

Error Factors in Oxygenation Measurement Using Continuous Wave and Spatially Resolved Near-infrared Spectroscopy

Abstract: The main error factors on near-infrared spectroscopy (NIRS) measurements for deep tissue are (1) thickness of overlying tissues, (2) oxygenation of surface tissues, (3) difference between an assumed value and an actual value of scattering coefficient for tissues, and (4) concentrations of hemoglobin derivatives. These factors affect the accuracy on time-resolved NIRS, intensity-modulated NIRS, spatially resolved NIRS, and continuous wave NIRS. In this paper, we present the accurate oxygenation measurement in surface and deep tissues using continuous wave and spatially resolved NIRS. The relationship between spatial distribution of light intensity and absorption coefficient of the muscle was obtained from the Monte Carlo simulation. Fat thickness greatly affected the absolute value of hemoglobin concentration. The influence of skin oxygenation caused several percent error factor of muscle oxygenation. We obtained curves to correct the influences. To reduce the error due to assumed scattering coefficient, a simple method for determining optical properties with laser rangefinder was practical and useful. Moreover, the absolute values of hemoglobin derivative concentrations were successfully measured by spatially resolved NIRS. It was also helpful for accurate oxygenation measurement. The combination of these measurements and corrections would be essential for an accurate NIRS.

Recording of holographic gratings and their coherent self-enhancement in an a-As<sub>2</sub>S<sub>3</sub> film with a minimum light intensity modulation

The holographic grating recording efficiency and the coherent self-enhancement efficiency of gratings are experimentally studied depending on the recording light interference fringe visibility in an a-As2S3 chalcogenide film in order to find the minimum visibility. The minimum fringe visibility Mmin = 3.6×10–4 is found, which is determined by the scattered light background. In this case the maximal diffraction efficiency ηmax = 0.05% and the maximal self-enhancement factor ξmax = 5.0, compared to ηmax = 15% and ξmax = 12.3 in the optimal M = 1.0000 case. In the case of two-beam holographic grating recording the maximal diffraction efficiency increases when M is increased, whereas sensitivity decreases. A simple model, based on linear recording with the spatial light intensity distribution governed by M and including intensity-dependent material photosensitivity and grating relaxation, is proposed to explain these results. In the case of coherent self-enhancement both the maximal diffraction efficiency and sensitivity increase with fringe visibility M. This can be explained by the fact that mechanical stress modulation during the initial grating recording depending on M is followed by relaxational structural changes reinforcing the coherent self-enhancement effect. The developed approach may explain the absence of this effect in some azobenzene oligomer films.