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Investigation of the multi-elemental self-absorption mechanism and experimental optimization in laser-induced breakdown spectroscopy
摘要： The self-absorption effect reduces the accuracy of elements measurement in laser-induced breakdown spectroscopy (LIBS) experiments. In this paper, the mechanism of the self-absorption effect was studied. First, we established a plasma concentration distribution model and plasma dynamics model of the plasma expansion in three directions during LIBS based on physical laws. By coupling a plasma concentration distribution model with a self-absorption model, the LIBS self-absorption effect value model was obtained. Second, the models were applied in a numerical simulation to determine plasma spatial distribution characteristics during LIBS. The self-absorption effect values of spectral lines were calculated. Finally, experiments were conducted with an optical spectrometer to obtain the Na, K, and Al atomic emission spectra. On the theoretical plane, the Boltzmann plot method and the Stark broadening method were used to obtain the plasma characteristic parameters. The spectral line intensities of the Na, K and Al atom lines were obtained without and with microwave-assisted LIBS experiments for comparison. The experimental analysis showed that during the LIBS process, microwave assistance can enhance the emission spectroscopy intensity and inhibit or reduce the LIBS self-absorption effect. The experimental samples were in good agreement with those of theoretical simulation, indicating the effectiveness and practicability of the created LIBS self-absorption effect value model, which can improve the optimization of the LIBS process.
关键词： Self-absorption,LIBS,Numerical simulation,Spectral analysis,Material surface
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - CAOL 2019 Contents
摘要： Manifold learning, especially spectral embedding, is known as one of the most effective learning approaches on high dimensional data, but for real-world applications it raises a serious computational burden in constructing spectral embeddings for large datasets. To overcome this computational complexity, we propose a novel efficient embedding construction, Diverse Power Iteration Embedding (DPIE). DPIE shows almost the same effectiveness of spectral embeddings and yet is three order of magnitude faster than spectral embeddings computed from eigen-decomposition. Our DPIE is unique in that 1) it finds linearly independent embeddings and thus shows diverse aspects of dataset; 2) the proposed regularized DPIE is effective if we need many embeddings; 3) we show how to efficiently orthogonalize DPIE if one needs; and 4) Diverse Power Iteration Value (DPIV) provides the importance of each DPIE like an eigen value. Such various aspects of DPIE and DPIV ensure that our algorithm is easy to apply to various applications, and we also show the effectiveness and efficiency of DPIE on clustering, anomaly detection, and feature selection as our case studies.
关键词： Approximated spectral analysis,power iteration
更新于2025-09-23 15:19:57
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Study on the reflection characteristics of the composite structure coupled with periodic plasma and frequency selective surface
摘要： Modified Legendre rational spectral methods for solving second-order differential equations on the half line are proposed. Some Sobolev orthogonal Legendre rational basis functions are constructed, which lead to the diagonalization of discrete systems. Accordingly, both the exact solutions and the approximate solutions can be represented as infinite and truncated Fourier series. Numerical results demonstrate the effectiveness and the spectral accuracy of this approach.
关键词： Sobolev orthogonal functions,elliptic boundary value problems,numerical results,modified Legendre rational spectral methods
更新于2025-09-23 15:19:57
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Spectral filtering of photovoltaic cells using novel bio-filter: Silver coated Hibiscus extract using methanol solution
摘要： Spectra filtering is a fairly new concept to control the damaging contributions of solar IR radiations to photovoltaic (PV) cells or panel. In this research, the bio-filter was synthesized and tested. The bio-filter was proposed as the panacea to filtering the solar IR radiations. The bio-filter performance was adjudged to show little success, as it was 3% lower than the normal performance in the monocrystalline solar PV panel and 50% higher than the normal performance in the polycrystalline solar PV panel. The varying results in the polycrystalline and monocrystalline PV panels may arise as a result of unequal coating of the panel. Hence, the coating technique is recommended to be uniform and precise in further research work.
关键词： bio-filter,Hibiscus extract,photovoltaic cells,methanol solution,spectral filtering
更新于2025-09-23 15:19:57
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Spectral splitting and phase matching of the macroscopic high-order harmonic generation in intense laser fields
摘要： We theoretically investigate the macroscopic high-order harmonic generation in argon gaseous medium by numerically solving the three-dimensional macroscopic propagation equation, and the results show that the harmonic spectral and spatial profiles of harmonics are gradually splitting with the increasing of the driving laser intensity. This splitting is mainly due to the distortions which the driving field suffers during propagation and the consequence is also on phase matching. To illustrate the physical mechanisms of harmonic splitting, a theoretical analysis of the phase matching is presented. The harmonic spectra from different focus positions reveal that the split is dependent on the focus-gas-jet relative position. Moreover, we demonstrate that the spectral splitting of high harmonics can hardly be observed for neon gas jet due to the high ionization energy.
关键词： phase matching,high-order harmonic generation,intense laser fields,macroscopic propagation,spectral splitting
更新于2025-09-23 15:19:57
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Efficiency and spectral performance of narrowband organic and perovskite photodetectors: a cross-sectional review
摘要： The capability of detecting visible and near infrared light within a narrow wavelength range is in high demand for numerous emerging application areas, including wearable electronics, the Internet of Things, computer vision, artificial vision and biosensing. Organic and perovskite semiconductors possess a set of properties that make them particularly suitable for narrowband photodetection. This has led to rising interest in their use towards such functionality, and has driven remarkable progress in recent years. Through a comparative analysis across an extensive body of literature, this review provides an up-to-date assessment of this rapidly growing research area. The transversal approach adopted here focuses on the identification of: (a) the unifying aspects underlying organic and perovskite narrowband photodetection in the visible and in the near infrared range; and (b) the trends relevant to photoconversion efficiency and spectral width in relation to material, device and processing strategies. A cross-sectional view of organic and perovskite narrowband photodetection is thus delineated, giving fresh insight into the status and prospects of this research area.
关键词： narrowband organic photodetectors,narrowband perovskite photodetectors,NIR photodetectors,colour sensors,spectral selectivity
更新于2025-09-23 15:19:57
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Reconstructing ultrafast energy-time-entangled two-photon pulses
摘要： The generation of ultrafast laser pulses and the reconstruction of their electric fields is essential for many applications in modern optics. Quantum optical fields can also be generated on ultrafast timescales; however, the tools and methods available for strong laser pulses are not appropriate for measuring the properties of weak, possibly entangled pulses. Here, we demonstrate a method to reconstruct the joint-spectral amplitude of a two-photon energy-time entangled state from joint measurements of the frequencies and arrival times of the photons, and the correlations between them. Our reconstruction method is based on a modified Gerchberg-Saxton algorithm. Such techniques are essential to measure and control the shape of ultrafast entangled photon pulses.
关键词： joint-spectral amplitude,quantum optical fields,energy-time entangled state,ultrafast laser pulses,Gerchberg-Saxton algorithm
更新于2025-09-23 15:19:57
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Tunability of the Freea??Spectral Range by Microwave Injection into a Mida??Infrared Quantum Cascade Laser
摘要： The free-spectral range (FSR) of quantum cascade lasers (QCLs) emitting at 4.7 μm can be tuned through direct microwave modulation. The intrinsic short carrier lifetime of inter-subband transitions, along with impedance matched electrical packaging, allows a high-speed modulation up to more than 30 GHz. A signi?cant broadening and ?attening of the lasing spectrum is observed under radio frequency (RF) injection with frequencies close to the round-trip cavity. An accurate analysis of the high resolution spectra of the laser shows a comb-like regime for both free-running and RF modulated QCLs, if the modulation frequency is within the locking-range of the device. One of the main advantages of collecting high-resolution mid-infrared spectra, over the plain investigation of the beatnote in the microwave region, is the access to all the longitudinal modes and thus the accurate measure of the FSR over the whole optical spectrum. The use of high-resolution spectroscopy provides an in-depth and comprehensive analysis of lasing spectra under microwave modulations.
关键词： quantum devices,mid-infrared region,injection locking,tunability of the free-spectral-range,ultrafast devices
更新于2025-09-23 15:19:57
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Modifying twisted nematic LCD screens to create dichromatic visual stimuli with LEDs
摘要： 1. The use of computers to create and display animations/videos in the study of visually-guided behaviors has been instrumental in understanding sensory mechanisms underlying complex traits. Using computer displays scientists are able to create a wide array of colors using three differently colored lights (Red, Green, Blue: RGB). While it is possible to generate scenes with RGB displays that mimic animals’ color perceptual experience, this can be problematic because it requires knowledge of the spectral absorbance of the animals’ photoreceptor classes, which are often unknown and are difficult to obtain. Even then, stimuli are limited to the central part of the visible spectrum (e.g., ultraviolet (UV) stimuli are not possible). 2. We present a cost-effective way of modifying a twisted nematic LCD screen that utilizes colored LEDs, that allows measuring animals’ sensitivity to, and discrimination between, wavelengths of light. It has the benefit of not requiring a-priori knowledge of animals’ photoreceptor classes. An LCD screen can be modified by removing the screen’s back polarizer (behind the liquid crystal layer) and backlighting the screen with LEDs of two different colors. One of the LED colors transmits through a polarizer with a transmission axis parallel to the screen’s front polarizer, and other LED color transmits through a polarizer orthogonal to the first. 3. To test color discrimination one can create a dichromatic stimulus in which both LED colors are ‘ON’ and the current fithrough one LED color is decreased, while the other is constant, which generated a maximum intensity contrast of 1.84 log units in our setup. To test color sensitivity one can create a monochromatic stimulus in which only one LED color is ‘ON’, which generates a contrast similar to the dichromatic stimulus. This technique overcomes many of the limitations of RGB-based LCD screens in a cost-effective way, and allows more accurate testing of the role of color in visually-guided behaviors. Besides the questions in vision research this setup can answer, it can also be used as an outreach tool in classrooms where children can learn about light, color, polarization, and technology.
关键词： twisted nematic LCD screen,spectral sensitivity,polarization,visually-guided behavior,color vision,spectrometer,LED
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Performance and Techno-Economic Evaluation of a Three-Phase, 50-kW SiC-Based PV Inverter
摘要： We address the problem of detecting a stealth aircraft flying far away from an observer with limited visibility conditions using their multispectral signature. In such environment, the aircraft is a very low-contrast target, i.e., the target spectral signature may have a similar magnitude to the background clutter. Therefore, methods accounting only for the spectral features of the target, while leaving aside its spatial pattern, may either lead to poor detection statistics or high false alarm rate. We propose a new detection method which accounts for both spectral and spatial dispersions, by inferring level sets of the Mahalanobis transform of the multispectral image. This combines the approach of the well-known Reed Xiaoli (RX) detector with some elements of the level set methods for shapes analysis. This algorithm is in turn used to specify the wavelength bands which maximize an aircraft detection probability, for a given false alarm rate. This methodology is illustrated in a typical scenario, consisting of a daylight air-to-ground full-frontal attack by a generic combat aircraft flying at low altitude, over a database of 30 000 simulated multispectral infrared signature (IRS). The results emphasize that, in the context of aircraft detection, there is great interest in using multispectral IRS rather than integrated IRS, as long as the IR bands are well chosen.
关键词： Aircraft detection,multispectral infrared signature (IRS),spectral band selection,anomaly detection
更新于2025-09-23 15:19:57