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Standards, Methods and Solutions of Metrology || Third-Order Nonlinear Optical Properties of Quantum Dots
摘要： Quantum dots (QDs) are semiconducting nanocrystalline particles. QDs are attractive photonic media. In this chapter, we introduce third-order nonlinear optical properties and a brief idea about the physics of QDs. Z-scan technique and theoretical analysis adopted to obtain nonlinear parameters will be discussed. Analysis of third-order nonlinear optical parameters for PbS QDs suspended in toluene with radii 2.4 and 5.0 nm under different excitation beam power level and three different wavelengths (488, 514, and 633 nm) will be detailed. Third-order optical susceptibility χ(3) and optical-limiting behavior of PbS QD suspended in toluene are presented. Irrespective of their size, QDs are a good example of optical limiters with low threshold.
关键词： Z-scan technique,semiconductor,nonlinear absorption coefficient,third-order optical susceptibility,quantum dot,optical limiting,nonlinear optics,optical switching,nonlinear index of refraction
更新于2025-09-16 10:30:52
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[IEEE 2019 Workshop on Recent Advances in Photonics (WRAP) - Guwahati, India (2019.12.13-2019.12.14)] 2019 Workshop on Recent Advances in Photonics (WRAP) - Stand-off Femtosecond Laser Induced Breakdown Spectroscopy of Metals, Soil, Plastics and Classification Studies
摘要： This paper presents one of the first studies of the harmonic impact of a significantly large photovoltaic (PV) solar farm of 20 MW in a utility distribution system. This solar farm is a constituent of the 80-MW PV solar farm in Sarnia, Ontario, which is so far the largest solar farm in Canada. The utility network is modeled in detail using the commercial grade PSCAD/EMTDC software, which is validated through load flow studies conducted by CYME software and correlated with SCADA measurements. The validated network model is used for network resonance study and harmonics impact analysis of the solar farms under different network conditions. The harmonics data instrumented for several months were provided by the transmission utility at the two solar farm units and at the main feeder substation. These data were utilized for extensive harmonic impact studies with widely different short-circuit levels and network resonance conditions. This paper presents the detailed procedure adopted for performing such harmonic impact studies. It is concluded that this large solar farm may not cause any substantial voltage distortion on the distribution network during steady-state operating conditions. However, recommendations are made for utilities to perform such studies to ensure the safe operation of critical loads.
关键词： network resonance,total harmonic distortion,solar energy,harmonics,Distribution systems,total demand distortion,photovoltaic (PV) solar system,frequency scan
更新于2025-09-16 10:30:52
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The Extrinsic Calibration of Area-Scan Camera and 2D Laser Rangefinder (LRF) Using Checkerboard Trihedron
摘要： The combination of area-scan camera and 2D laser range?nder (LRF) can capture both textural and geometrical information from a scene at the same time, and has been widely used in various ?elds. Due to the differences of the installation position and acquisition mode, calibrating the extrinsic parameters, including the rotation and translation, of two sensors is necessary for fusing the camera image and LRF data. In this paper, a simple and ?exible extrinsic calibration method is proposed by only acquiring a checkerboard trihedron once. Using checkerboard trihedron as a mobile referenced control ?eld, the proposed method includes three steps to calibrate the extrinsic parameters. First, the rotation and translation between the trihedron and LRF are solved with a simpli?ed perspective-three-point (P3P) solution; Second, using the collinear equation of checkerboard corners and their pixels in the image, the camera is calibrated with respect to the trihedron; Third, combining the last two steps, the rotation and translation parameters between the camera and LRF are ?nally calibrated with the intermediate referenced trihedron. After a lot of simulation and real experiments, the proposed method has been demonstrated to have the advantages of simple operation, strong robustness and high accuracy in real experiment.
关键词： checkerboard trihedron,Area-scan camera,2D laser range?nder,P3P,extrinsic calibration,collinear equation
更新于2025-09-16 10:30:52
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Third-order nonlinear optical response of Yb:YAG ceramics under femtosecond laser irradiation
摘要： Transparent ceramic laser materials, as an important alternate of traditional laser gain medium materials, have aroused much attention for their excellent performance. Here, we investigated the third-order nonlinear susceptibility of high quality transparent Ytterbium-doped Yttrium Aluminium Garnet (Yb:YAG) ceramics. Under an ultrafast femtosecond laser irradiation, we experimentally demonstrated the nonlinear optical limiting and self-focusing behaviors of Yb:YAG ceramic by Z-scan method at 800 nm. It was found that Yb:YAG ceramics exhibit a relatively small nonlinear refractive index (~3.8 × 10?20 m2/W) which exerts little dependence on the Yb3+ doping concentration and laser intensity. This work could illustrate the application potential of transparent ceramic under high-power condition and can also provide useful design guidelines for high power ceramic laser system.
关键词： Third-order optical nonlinearity,Z-scan,Nonlinear refractive index,Yb:YAG ceramics
更新于2025-09-16 10:30:52
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[IEEE 2019 Far East NDT New Technology & Application Forum (FENDT) - Qingdao, Shandong province, China (2019.6.24-2019.6.27)] 2019 Far East NDT New Technology & Application Forum (FENDT) - Visual Detection of AM Surface Defects Based on Laser Ultrasound Technology
摘要： Selective Laser Melting (SLM) process is a kind of Additive Manufacturing (AM) method, which can process parts with arbitrary complex geometry. However, macro-defects will destroy the mechanical properties of metal materials manufactured by SLM. Laser ultrasound can excite broadband surface waves and realize non-contact nondestructive testing of surface defects. In this paper, 316L stainless steel samples are prepared by SLM process are used for laser ultrasonic detection. According to the diffraction phenomenon of surface wave at the defect, a laser ultrasonic B-scan detection platform is built. The B-scan images of different length defects on the sample surface are obtained, and the quantitative detection of surface defects is realized quickly. In order to further improve the signal-to-noise ratio and the accuracy of imaging detection, EEMD (Ensemble Empirical Mode Decomposition) denoising is applied to the collected ultrasonic signal, which improves the accuracy of imaging, makes the signal more stable and realizes the visual detection of surface length defects clearly and intuitively.
关键词： b-scan,additive manufacturing,laser ultrasound technology,EEMD
更新于2025-09-16 10:30:52
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Nonlinear Optical Properties of Zinc Oxide Thin Films Produced by Pulsed Laser Deposition
摘要： In this work, the nonlinear optical properties of Zinc Oxide (ZnO) thin films produced on microscope slide glass substrates at room temperature (RT) using Pulsed Laser Deposition (PLD) method has been presented. PLD system consists of a vacuum chamber (pumped by a turbo molecular pump, backed with a rotary pump), rotating sample and substrate holders, optical thickness measurement system, infrared temperature measurement system and a nanosecond laser system. Previously deposition vacuum chamber evacuated down to ~10-8 mbar and deposition was taken place about 1.3×10-1 mbar oxygen background gas pressure value. Morphological properties of thin films were obtained by Atomic Force Microscopy (AFM) that shows homogenous and smooth film structure. Thin films crystallinity were investigated by using X-Ray Diffraction (XRD) method and showed that polycrystalline ZnO structure with the largest peak corresponding to (002) orientation but some films contain Zn with (101) orientation . The thicknesses of the films were deduced from reflectance measurement using a fitting software and crosschecked with profilometer and AFM measurements. The thickness of the films ranged between 10 nm and 220 nm. Linear optical properties were obtained by using UV-VIS Spectrometer. Furthermore, we presented the nonlinear optical properties of the ZnO thin films that were obtained by the z-scan method.
关键词： Z-scan system,Zinc Oxide Thin Film,Nonlinear Optical Properties,Pulsed Laser Deposition
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - St. Petersburg, Russia (2019.10.17-2019.10.18)] 2019 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Radiomics: Extracting more Features using Endoscopic Imaging
摘要： Cancer is the leading cause of death in the world and delayed detection being the cause of the most significant factor for its high mortality rate. Computers can help radiologists in analyzing medical images and detection of cancer. Radiomics refers to the computerized extraction of information from medical images and provides the potential for making cancer screening with high rapid and more accurate using machine learning algorithms. Endoscopic imaging and X-ray imaging (Computed tomography) are two common methods used in medical imaging. In this paper, the advantages and limitations of endoscopic and CT scan images discussed. Then the features that can be extracted from endoscopic and CT scans are discussed and finally these two imaging methods are considered and compared to use for computer-aided detection systems.
关键词： feature extraction,Computed tomography (CT) scan,Endoscopic image,Radiomics,texture features
更新于2025-09-12 10:27:22
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Laser scanned patterns of machined surfaces
摘要： In this contribution, machined surfaces are analyzed corresponding to the dynamic aspects of cutting operation. Productivity is limited due to harmful vibrations that deteriorate the quality of the machined surface. The related surface pattern carries the history of the resultant relative vibrations, thus the dynamical properties of the machining system could be extracted. To describe the surface of a machined workpiece, a laser displacement sensor is applied for scanning purposes. The measurement procedure of the surface scanning is described, its applicability and limitations are also discussed. In turning processes, the static displacement error and the arising chatter frequency are analyzed along a shaft by means of the measured diameter offset and gradient of the chatter marks, respectively.
关键词： Machining,Surface analysis,Chatter,Laser scan
更新于2025-09-12 10:27:22
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Implementation of Advanced Laser Control Strategies for Powder Bed Fusion Systems
摘要： Laser path, scan speed, and laser power are critical machine parameters for determining the quality of the output of laser-based powder bed fusion (LPBF) processes. A jerk-limited control strategy is implemented for laser path planning on a LPBF additive manufacturing (AM) testbed. The actual and commanded laser paths/velocities are found to be in better agreement with each other compared to conventional controls. The new controller enabled implementation of advanced laser power control strategies synchronized with laser position and velocity by embedding all into a modified G-code (referred as AM G-code). An interpreter is developed to utilize sophisticated LPBF laser control commands.
关键词： Jerk-limited Control,Scan Strategies,Laser Powder Bed Fusion Additive Manufacturing (LPBF AM),AM G-code
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Common Pulse Retrieval Algorithm: A Fast and Universal Method to Retrieve Ultrashort Pulses
摘要： Measuring the temporal shape of ultrashort laser pulses is an important standard task in ultrafast optics. A multitude of methods has been devised for that purpose [1]. However, in many cases a specific, iterative algorithm has to be applied to retrieve the pulse shape from the measurement. In this work we present a common pulse retrieval algorithm (COPRA) that can be universally applied to such pulse measurement methods and compares favorably in terms of speed and accuracy to existing approaches [2]. For example, COPRA can be applied to the well-established frequency-resolved optical gating (FROG) [3], as well as, more recent techniques, such as dispersion scan (d-scan) [4] or time-domain ptychography (TDP) [5] (see Fig. 1). Generally, it is designed for a broad class of measurements where sets of pulse spectra after a nonlinear process such as second-harmonic generation (SHG) or third-harmonic generation (THG) are measured. Specifically, the measurement process has to be tunable by some parameter δ that forms the second measurement dimension. We call this class of measurements parametrized nonlinear process spectra (PNPS). COPRA now finds the pulse spectrum ?E(ω) that matches best to a PNPS measurement T meas(ω, δ ) in the least-squares sense. It does so in two stages: first the local iteration subsequently optimizes ?E(ω) with respect to single spectra, then the global iteration optimizes ?E(ω) with respect to the entire measurement. COPRA usually finds a least-squares solution to the pulse retrieval problem within a few hundreds iterations, i.e., within few tens of seconds on a standard workstation for usual measurement dimensions. This compares very favorably to existing approaches. Additionally, the retrieved pulses are more robust in the presence of Gaussian measurement noise than those retrieved by generalized projections or ptychography. Many existing pulse measurement schemes can directly benefit from COPRA for more robust and faster retrieval. Also, the framework of PNPS measurements may allow to gain more insight on fundamental questions of pulse measurement, will make measurement schemes more comparable and may lead to new and improved methods.
关键词： time-domain ptychography,pulse retrieval,frequency-resolved optical gating,dispersion scan,ultrashort pulses
更新于2025-09-12 10:27:22