Reference Light Source Research Articles

A non-contact solid particle moisture sensor based on near-infrared spectroscopy technology

The detection of moisture content in solid particles has important applications in fields such as biological research, coal mine production, and medicine. This article develops a non-contact solid particle moisture sensor (NcSPMS). NcSPMS uses the multi-light source detection method based on the principle of diffuse reflection absorption to detect the moisture content of solid particles with different particle sizes, distributions and colors. Firstly, the stacked LED light source structure (SLED-LSS) was designed to achieve illumination of LED light source for measurement (M-LED) and the LED light source for reference (R-LED) at the same position and exit angle, eliminating the influence of irregular particle size and distribution on diffuse reflected light intensity. Secondly, the stacked LED array light source structure (SLEDA-LSS) was designed to improve the detection light intensity and enable NcSPMS to detect the moisture content of solid particles of different colors. Thirdly, modulated light technology is used for the transmission of moisture content information. Two modulation frequencies were set to modulate the measurement light source and reference light source, and different intensities of square wave currents were determined to drive the M-LED and R-LED to improve detection accuracy. Fourthly, the FFT-KF data processing method was designed to effectively extract the information of diffuse reflection measurement light intensity. Finally, the function expression of moisture content was obtained through cubic fitting, and the detection of moisture content by NcSPMS was achieved. In order to verify the effectiveness of NcSPMS, the NcSPMS control system was designed. The experimental results show that compared with SLED-LSS, SLEDA-LSS improves measurement accuracy; the different current pairs driving M-LED and R-LED affect the measurement accuracy of NcSPMS; NcSPMS can detect the moisture content of white, yellow, green, red, and black sand particles, with the detection range of 0.10–11.00 %. The relative uncertainty obtained by applying NcSPMS to the detection of nickel ore particles is 4.37 %.

Изучение температуры гетерогенного пламени

Flames of heterogeneous condensed systems have sharp brightness inhomogeneities and their radiation is described using a multizone flame model. Each flame zone, which has its own level of brightness and, accordingly, temperature, makes a certain contribution to the total radiation of the flame. A wide-spectrum video camera with a large volume of CCD matrix served as a radiation receiver. A set of optical filters allows to register radiation in a narrower spectral range. The digitized flame image was processed by developed software in order to highlight zones with certain optical characteristics in a flame image. By comparing the brightness of flame zones with the brightness of reference light sources, the temperature of the flame zones and the radiation intensity of in different spectral ranges were determined. Single receivers register radiation from all flame zones and produce an average signal. Using flame radiation modeling methods, it has been shown that the single receiver signal, the level of which determines the flame temperature, depends on the number of zones.

О ВЫХОДАХ ВОЗБУЖДЕНИЯ И ЛЮМИНЕСЦЕНЦИИ ТРЕХВАЛЕНТНЫХ ИОНОВ ЛАНТАНИДОВ ПРИ ОДНОПУЗЫРЬКОВОМ СОНОЛИЗЕ РАСТВОРОВ В СЕРНОЙ КИСЛОТЕ

The light yields of luminescence (Glum) and the yields of excited ion production (yields of excitation, Gext) were measured for the first time for a number of trivalent lanthanide ions (Ln3+) during moving single-bubble sonoluminescence in solutions of 10-2 M Ln3+ in 70% H2SO4. The luminescence yields were determined by comparing the integrated sonoluminescence intensity of the test solution with the radioluminescence intensity of the reference light source, and the excitation yields were found from the relation Gext = Glum/φ, where φ are the photoluminescence quantum yields of Ln3+ ions in the solution, which were also measured experimentally in the work. Determined yields Glum = (0.63, 0.96, 1.8, 5.1, 0.49)´107 photon/100 eV and Gext = (0.066, 1.6, 0.7, 1.5, 0.7)´108 excited ions/100 eV for Ce3+, Eu3+, Gd3+, Tb3+ ions, Dy3+, respectively. It was confirmed that, as previously shown in the case of radiation-excited luminescence of lanthanide ions (Kazakov V.P., Sharipov G.L. Radioluminescence of aqueous solutions. M.: Nauka, 1986. p. 116), transition with a change in the principal quantum number (4f→5d, Ce3+ ion) is an order of magnitude or less lower than the excitation yield in a transition without its change (4f→4f, Eu3+, Tb3+ , and others ions).

Study on the calibration of full polarization imager

Polarization is one of the fundamental properties of light, which has a wide range of applications and is developing rapidly. To meet the needs of polarization detection, different types of polarization instruments came into being. The precision of the polarization detection instruments is vital to the result analysis. In this paper, a full polarization imager is designed, and the radiometric calibration and polarization calibration of this instrument are studied. In radiometric calibration, the different numbers lights are set to verify the light intensity response of the imager. The mathematical model was constructed for numerical fitting, and the correlation between the fitted values and the measured values in the 490 nm, 550 nm, and 670 nm bands was above 0.99. Fixed the radiance of the integrating sphere, and adjusted exposure times. The correlation of the three bands is above 0.99, which verifies that the radiative stability of the imager is good. The polarimetric calibration system adopts the adjustable degree of polarization reference light source (APOL). The theoretical and measured values of the degree of polarization of reference light sources in three different bands are analyzed. The results show that the measurement accuracy of the 490 nm band is less than 2%. The precision of polarization measurement in the 550 nm band is less than 1.5%, and the precision of polarization calibration in the 670 nm band is less than 1%. The imager is verified to have high polarization calibration accuracy and meets the requirements of high-precision polarization detection.

Assessment of the Performance of a Portable, Low-Cost and Open-Source Device for Luminance Mapping through a DIY Approach for Massive Application from a Human-Centred Perspective.

Ubiquitous computing has enabled the proliferation of low-cost solutions for capturing information about the user’s environment or biometric parameters. In this sense, the do-it-yourself (DIY) approach to build new low-cost systems or verify the correspondence of low-cost systems compared to professional devices allows the spread of application possibilities. Following this trend, the authors aim to present a complete DIY and replicable procedure to evaluate the performance of a low-cost video luminance meter consisting of a Raspberry Pi and a camera module. The method initially consists of designing and developing a LED panel and a light cube that serves as reference illuminance sources. The luminance distribution along the two reference light sources is determined using a Konica Minolta luminance meter. With this approach, it is possible to identify an area for each light source with an almost equal luminance value. By applying a frame that covers part of the panel and shows only the area with nearly homogeneous luminance values and applying the two systems in a dark space in front of the low-cost video luminance meter mounted on a professional reference camera photometer LMK mobile air, it is possible to check the discrepancy in luminance values between the low-cost and professional systems when pointing different homogeneous light sources. In doing so, we primarily consider the peripheral shading effect, better known as the vignetting effect. We then differentiate the correction factor S of the Radiance Pcomb function to better match the luminance values of the low-cost system to the professional device. We also introduce an algorithm to differentiate the S factor depending on the light source. In general, the DIY calibration process described in the paper is time-consuming. However, the subsequent applications in various real-life scenarios allow us to verify the satisfactory performance of the low-cost system in terms of luminance mapping and glare evaluation compared to a professional device.

DRONE POSITIONING SYSTEMS THAT USE DIGITAL CAMERAS

Unmanned aerial vehicles are very important in everyday life. Their number is increasing every day, as well as the scope of their use. Therefore, it becomes necessary to automate their flight from departure to kindergarten. During automatic flight, drones have certain problems during takeoff, landing and positioning. The problem is that when landing and taking off, it is necessary to ensure high positioning accuracy, which is impossible when using GPS, as it can provide accuracy of only a few meters, which is not enough, and the use of operators is accurate, but this method requires the use of quality cameras with stabilization. These stabilization cameras are very heavy, so the payload of drones is reduced, and they are very expensive (usually more expensive than the drone itself). Also, the use of operators during landing and departure can lead to a catastrophe due to human factors. The task of this article is to create a classification table, analyze landing methods, assess their advantages and disadvantages, give recommendations for the use of the most effective positioning system, as well as the development of new positioning methods.
 In the course of work modern, and also the most widespread methods of positioning were considered, the critical analysis of robots is made. As a result, it was proposed to classify drone positioning systems that provide reliable takeoff, landing and delivery of goods using digital cameras. This classification includes all combinations of digital cameras and radiation sources that can be located both on the drone and on the landing or cargo delivery area. Examples are given for each combination proposed in the classification. A thorough analysis of the advantages and disadvantages of each configuration of digital cameras and radiation sources is given. Recommendations for choosing the best drone positioning system are provided. The main disadvantages of these systems are the complexity of algorithms, which makes systems more expensive, as well as complicates the creation of the system, which does not preclude the possibility of making a mistake when creating a system. And this can lead to an accident. All DPSs can be classified on group depending on the number of digital cameras, number and shape of reference light sources, locations of digital cameras and location of the light sources. From the point of reliability and economy the best DPS should include one camera on a drone and a minimal set of reference light sources on the ground. The authors suppose that three reference light sources that specify a triangle is the best choice because it makes possible estimation of the distance and angular coordinates of the landing pad.

Developing test color samples to compute color fidelity of light sources for printing matter

Based on the clustering optimization of test color samples and a psychophysical experiment, the objective and subjective color fidelity of light sources for printing matter is evaluated, and an improved evaluation method thus has been proposed. Firstly, for representing the output characteristics of printing press, the International Color Consortium standard color target samples (ICC SCTS), which is measured in the process of color management, is used as a large color sample set. In a 6D spectral color space proposed in this paper, the optimized color sample set (OCSS) is obtained by Self Organizing Maps Neural Networks (SOMNN) clustering algorithm from ICC SCTS. Taking OCSS, ICC SCTS, and standard color sample set (SCSS) as the test color sample set, three objective color fidelity indexes (CFIs) CIE-Ra, Ra,2012, and CIE-Rf of 1202 light sources are calculated. The correlation metrics of the CFIs show that the OCSS highly improved the objective accuracy of color fidelity evaluation for printing matters. Secondly, in the psychophysical experiment, 20 observers have evaluated the visual color difference of the OCSS under the illumination of nine pairs of test and reference light sources. The subjective CFIs are calculated by using the visual color difference of OCSS obtained from the psychophysical experiment. In order to improve the subjective and objective consistency of CFIs, a polynomial modified model for objective color difference of OCSS is proposed. By the optimization of test color samples and the modification of color difference calculation, the method developed in this paper can be effectively and conveniently applied to the subjective and objective evaluation of light source for printing matters.

Field Quality Control of Spectral Solar Irradiance Measurements by Comparison with Broadband Measurements

Measurement of solar spectral irradiance is required in an increasingly wide variety of technical applications, such as atmospheric studies, health, and solar energy, among others. The solar spectral irradiance at ground level has a strong dependence on many atmospheric parameters. In addition, spectroradiometer optics and detectors have high sensitivity. Because of this, it is necessary to compare with a reference instrumentation or light source to verify the quality of measurements. A simple and realistic test for validating solar spectral irradiance measurements is presented in this study. This methodology is applicable for a specific spectral range inside the broadband range from 280 to 4000 nm under cloudless sky conditions. The method compares solar spectral irradiance measurements with both predictions of clear-sky solar spectral irradiance and measurements of broadband instruments such as pyrheliometers. For the spectral estimation, a free atmospheric transmittance simulation code with the air mass calculation as the mean parameter was used. The spectral direct normal irradiance (Gbλ) measurements of two different spectroradiometers were tested at Plataforma Solar de Almería, Spain. The results are presented in this article. Although only Gbλ measurements were considered in this study, the same methodology can be applied to the other solar irradiance components.

Continuous Hue-Based Self-Calibration of a Smartphone Spectrometer Applied to Optical Fiber Fabry-Perot Sensor Interrogation.

Smartphone-based optical spectrometers allow the development of a new generation of portable and cost-effective optical sensing solutions that can be easily integrated into sensor networks. However, most commonly the spectral calibration relies on the external reference light sources which have known narrow spectral lines. Such calibration must be repeated each time the fiber and diffraction grating holders are removed from the smartphone and reattached. Moreover, the spectrometer wavelength scale can drift during the measurement because of the smartphone temperature fluctuations. The present work reports on a novel spectral self-calibration approach, based on the correspondence between the light wavelength and the hue features of the spectrum measured using a color RGB camera. These features are caused by the nonuniformity of camera RGB filters’ responses and their finite overlap, which is a typical situation for RGB cameras. Thus, the wavelength scale should be externally calibrated only once for each smartphone spectrometer and can further be continuously verified and corrected using the proposed self-calibration approach. An ability of the plug-and play operation and the temperature drift elimination of the smartphone spectrometer was experimentally demonstrated. Conducted experiments involved interrogation of optical fiber Fabry-Perot interferometric sensor and demonstrated a nanometer-level optical path difference resolution.

便携式多通道辐射参考光源的设计与测试

便携式多通道辐射参考光源的设计与测试

Tri-chromatic quantum-dot synthesized sun-like white light-emitting diodes reaching maximum spectral similarity of 0.98

In this work, we synthesized a sun-like light source with tri-chromatic broad spectra, composed of light source units with single-peak 435-nm carbon quantum dots (QDs) and 695-nm perovskite QDs, and dual-peak 510- and 590-nm Ag-doped InP QDs, referencing CIE standard illuminants D50 and D65. Based on a spectral angle measure approach, we adopt the spectral similarity index (SSI) to measure the similarity between the synthesized light source and reference light source. We quantify the colour rendering and SSI of the tri-chromatic light source units and obtain the colour rendering and SSI as a function of chromaticity coordinate. The synthesized light source reaches an ideal performance with a maximum spectral similarity of 0.98 and colour rendering of about 93. This work is the first to synthesize a full-spectrum sun-like source with three QD light units, including a dual-peak QD unit, and proves QD LEDs as promising light sources for synthesizing full-spectrum light sources. In the future, improving the long wavelength part (>700 nm) of the broad-spectrum QD LED unit may significantly improve the colour rendering property.

Low-Attenuation Variable Mode Control Using Twist Processing for Step-Index Optical Fiber Loops

We propose a method of variable mode control that generates an equilibrium modal distribution (EMD) in step-index multimode fibers. The proposed method can control the modal power distribution variably from a low-order mode distribution to a high-order mode distribution (including EMD) by twisting fiber loops. The attenuation of the controller for EMD generation is five times smaller than those of conventional EMD generation methods. As a reference light source with high measurement reproducibility, the EMD light source obtained by the variable mode control method can be used to evaluate hard polymer cladding fiber link systems. The proposed method is applicable to all types of step-index multimode optical fibers, including all-glass fibers, hard polymer cladding fibers, and plastic optical fibers.

The SI Unit Candela

AbstractThe history of photometry, the measurement of light—and thus also the root of the basic unit for the luminous intensity, goes back to the seventeenth century. The theoretical foundations are provided by Johann H. Lambert in his treatise on photometry around 1760. With industrialization in the nineteenth century, there is an increasing demand for stable reference light sources for the measurement of light and for an reliable definition of the unit for light. But it is not until the middle of the twentieth century that the basic prerequisites had been created to use a common, internationally recognized unit, the Candela, as a measure of the visible light. The following article describes the basics and the boundary conditions that arise for the unit candela from the revision of the SI.

Appearance of Achromatic Colors Under Optimized Light Source Spectrum

Light source spectrum can be optimized for object reflectance to reduce the energy consumption by reducing the amount of light absorbed by surfaces. While the feasibility of this approach to architectural lighting has been demonstrated, this concept has only been tested with objects of highly saturated colors. Here, the color appearance of 24 Macbeth ColorChecker test samples, which includes achromatic surfaces (i.e., gray, black, and white), illuminated by optimized theoretical test spectra and reference light sources (incandescent, equal-energy radiator, and phosphor-coated white LED) were calculated using a color space based on the International Commission on Illumination's (CIE) color appearance model, CIECAM02-UCS. Results show that energy consumption could be reduced to between 39% and 90%, with small shifts in color appearance, when considering all object colors. When lighting is optimized for achromatic test samples, energy consumption and light absorption were reduced more than when optimized for colorful surfaces, with imperceptible shifts in color appearance.

Research on tunable distributed SPR sensor based on bimetal film.

In order to overcome the limitations in range of traditional prism structure surface plasmon resonance (SPR) single-point sensor measurement, a symmetric bimetallic film SPR multi-sensor structure is proposed. Based on this, the dual-channel sensing attenuation mechanism of SPR in gold and silver composite film and the improvement of sensing characteristics were studied. By optimizing the characteristics such as material and thickness, a wider range of dual-channel distributed sensing is realized. Using a He-Ne laser (632.8nm) as the reference light source, prism-excited symmetric SPR sensing was studied theoretically for a symmetrical metal-clad dielectric waveguide using thin-film optics theory. The influence of the angle of incidence of the light source and the thickness of the dielectric layer on the performance of SPR dual formant sensing is explained. The finite-difference time-domain method was used for the simulation calculation for various thicknesses and compositions of the symmetric combined layer, resulting in the choice of silver (30nm) and gold (10nm). When the incident angle was 78deg, the quality factor reached 5960, showing an excellent resonance sensing effect. The sensitivity reached a maximum of 5.25×10-5 RIU when testing the water content of an aqueous solution of honey, which proves the feasibility and practicality of the structure design. The structure improves the theoretical basis for designing an SPR multi-channel distributed sensing system, which can greatly reduce the cost of biochemical detection and significantly increase the detection efficiency.

Verification of Doppler coherence imaging for 2D ion velocity measurements on DIII-D.

Coherence Imaging Spectroscopy (CIS) has emerged as a powerful tool for investigating complex ion phenomena in the boundary of magnetically confined plasma devices. The combination of Fourier-transform interferometry and high-resolution fast-framing cameras has made it possible to make sensitive velocity measurements that are also spatially resolved. However, this sensitivity makes the diagnostic vulnerable to environmental effects including thermal drifts, vibration, and magnetic fields that can influence the velocity measurement. Additionally, the ability to provide an absolute calibration for these geometries can be impacted by differences in the light-collection geometry between the plasma and reference light source, spectral impurities, and the presence of thin-films on in-vessel optics. This paper discusses the mitigation of these effects and demonstration that environmental effects result in less than 0.5 km/s error on the DIII-D CIS systems. A diagnostic comparison is used to demonstrate agreement between CIS and traditional spectroscopy once tomographic artifacts are accounted for.

Calibration and cross-laboratory implementation of scintillating screens for electron bunch charge determination.

We revise the calibration of scintillating screens commonly used to detect relativistic electron beams with low average current, e.g., from laser-plasma accelerators, based on new and expanded measurements that include higher charge density and different types of screens than previous work [Buck et al., Rev. Sci. Instrum. 81, 033301 (2010)]. Electron peak charge densities up to 10 nC/mm2 were provided by focused picosecond-long electron beams delivered by the Electron Linac for beams with high Brilliance and low Emittance (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf. At low charge densities, a linear scintillation response was found, followed by the onset of saturation in the range of nC/mm2. The absolute calibration factor (photons/sr/pC) in this linear regime was measured to be almost a factor of 2 lower than that reported by Buck et al. retrospectively implying a higher charge in the charge measurements performed with the former calibration. A good agreement was found with the results provided by Glinec et al. [Rev. Sci. Instrum. 77, 103301 (2006)]. Furthermore long-term irradiation tests with an integrated dose of approximately 50 nC/mm2 indicate a significant decrease of the scintillation efficiency over time. Finally, in order to enable the transfer of the absolute calibration between laboratories, a new constant reference light source has been developed.

A Novel Method for 3-D Millimeter-Wave Holographic Reconstruction Based on Frequency Interferometry Techniques

A novel interferometry technique is proposed and introduced into active millimeter-wave (MMW) holography. Different from optical holographic interferometry, which relies on a reference light source or the interferometric synthetic aperture radar where data from apertures of different elevations are interfered, data are interfered between different frequencies in the proposed method. Higher ranging accuracy is achieved, since the residual phase information which is always neglected is utilized by the interferometry manner. The proposed method also avoids interpolations in the traditional MMW holographic imaging algorithms, by which the computational complexity can be reduced. First, theoretical derivation of the 3-D reconstruction method based on frequency interferometry is presented, and detailed algorithms considering noise resistance and phase unwrapping are designed. Then, numerical simulations are conducted to validate our methods. Different aspects of the proposed algorithms’ performance are analyzed and compared with previous methods. Finally, laboratory experiments are carried out. Both the simulation and experimental results validate the superiority of our method on reconstruction accuracy and computational efficiency.

Development of a new linearly variable edge filter (LVEF)-based compact slit-less mini-spectrometer

This paper presents the development of a compact charge-coupled detector (CCD) spectrometer. We describe the design, concept and characterization of VNIR linear variable edge filter (LVEF)- based mini-spectrometer. The new instrument has been realized for operation in the 300 nm to 850 nm wavelength range. The instrument consists of a linear variable edge filter in front of CCD array. Low-size, light-weight and low-cost could be achieved using the linearly variable filters with no need to use any moving parts for wavelength selection as in the case of commercial spectrometers available in the market. This overview discusses the main components characteristics, the main concept with the main advantages and limitations reported. Experimental characteristics of the LVEFs are described. The mathematical approach to get the position-dependent slit function of the presented prototype spectrometer and its numerical de-convolution solution for a spectrum reconstruction is described. The performance of our prototype instrument is demonstrated by measuring the spectrum of a reference light source.

LED lighting, ultra-low-power lighting schemes for new lighting applications

In 2018, Solid-State Lighting (SSL) can totally outperform, if properly designed, most of other lighting products used for general lighting applications. This concerns various attributes such as luminous efficacy, life, spectral qualities, dimming potential, and more and more total cost of ownership. SSL can also mimic a large variety of reference light sources from candlelight to sunlight. The absence of international standards concerning LED modules remains the major difficulty for luminaire manufacturers and their clients, since perfectly matching replacement of ever-changing LED modules is not guaranteed over time. But extraordinarily innovative lighting schemes can be developed, bridging the gap between the world of entertainment and the world of general lighting, and leading to new lighting schemes with more powerful emotional content. LED sources, mostly DC driven, also can benefit from progress in photovoltaics and batteries, as well as wireless control to offer integrated solutions. This could radically change the operation of lighting in the next 10 years. En 2018, les dispositifs luminescents solides (SSL) peuvent surpasser, s'ils sont correctement conçus, la plupart des autres systèmes d'éclairage couramment utilisés. Ceci concerne différentes caractéristiques telles que l'efficacité lumineuse, la durée de vie, les qualités spectrales, le potentiel de gradation et, de plus en plus, le coût total de possession. Les SSL peuvent aussi imiter une large variété de sources lumineuses de référence, de la chandelle au soleil. L'absence de standards internationaux concernant les modules LED reste la difficulté majeure pour les fabricants de luminaires et leurs clients, puisque la possibilité de remplacement à l'identique de modules LED qui changent régulièrement n'est pas garantie dans le temps. Mais des schémas d'éclairage extraordinairement innovants peuvent être développés, jetant une passerelle entre le monde des loisirs et celui de l'éclairage généraliste, conduisant à de nouveaux modes d'éclairage avec un contenu émotionnel encore plus puissant. Les sources LED, pour la plupart alimentées en courant continu, peuvent aussi tirer bénéfice des progrès dans les domaines de l'énergie photovoltaïque et des batteries, aussi bien que dans celui du contrôle sans fil pour offrir des solutions intégrées. Cela pourrait changer radicalement la mise en œuvre de l'éclairage dans les dix prochaines années.