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[Laser Institute of America ICALEO? 2017: 36th International Congress on Applications of Lasers & Electro-Optics - Atlanta, Georgia, USA (October 22–26, 2017)] International Congress on Applications of Lasers & Electro-Optics - Study on laser multi-focus separation technology for thick KDP crystal
摘要： Potassium dihydrogen phosphate (KDP) crystal is an important electro-optic material in various laser system, and belongs to very difficult-to-cut material, especially for thick crystals. In this study, a laser multi-focus separation technology (LMFS) of thick KDP crystal has been developed by skillfully combining femtosecond laser and LMFS optical system. In this way, the uniformity of temperature and thermal stress distributions along crystal thickness and the utilization efficiency of the laser energy are greatly improved. A penetration crack along crystal thickness could be formed and its propagation direction could be controlled to achieve safe and high-quality separation. The separating thickness of LMFS (50 mm) is at least 4 times thicker than that of existing laser separating technology, and the separating efficiency of LMFS (200 mm/s) is at least 20 times faster than that of traditional mechanical method. The generation mechanism of multi-focus was expounded by optical analysis and design, and verified by an established LMFS optical system. A thick KDP crystal with the thickness of 50 mm was separated successfully by LMFS. The quality of the separated sidewall surface was clean and flat (roughness of 10.857 nm, flatness of 3.5389 mm) without any contamination, underground damage and edge fragmentation. The experimental results proved the feasibility of LMFS, and are in good agreement with the theoretical analysis.
关键词： femtosecond laser,KDP crystal,optical system,laser multi-focus separation technology,thermal stress
更新于2025-09-16 10:30:52
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[IEEE 2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO) - Manama, Bahrain (2019.4.15-2019.4.17)] 2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO) - Thermal Analysis in Laser Surface Alloying of Ti6Al4V with TiC
摘要： Laser Surface Alloying employs high laser power density to melt alloying material and a portion of the underlying substrate to form an alloyed layer over substrate. As melting temperature of Ti alloys is very high, it poses difficulty in alloying using conventional methods. Titanium alloys are vulnerable to induced thermal stresses at high temperature. In this study thermal analysis of laser surface alloyed Ti6Al4V with TiC at different laser power and laser spot diameter is modelled. Melt pool depth and developed thermal stresses at different process parameters are predicted. Subsequently, model is verified with published experimental results. It is observed that developed model is adequate in predicting pool depth with 6.43% error. The von-Mises stress is observed to be lower than the yield strength of the material, indicating less possibility of thermally induced cracks.
关键词： Thermal stress,Numerical modelling,Pool depth,Laser surface alloying,Thermal analysis
更新于2025-09-12 10:27:22
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Numerical Analyses of High Concentrator Triple-Junction Solar Cell under Jet Impingement Cooling
摘要： The triple junction III-V(TJ) solar cells are commonly used for the high concentrator photovoltaic (HCPV) arrangements as they have high efficiency and have a good response to high concentration. Nevertheless, the efficiency of solar cells decreases with an increase of temperature especially under high solar irradiance concentration ratios where the temperature of solar cells reaches to very high levels. Consequently, heat dissipation by cooling is crucial for a concentrator photovoltaic solar cell at high concentration. Moreover, significant temperature difference possibly will exist within the cell body, so it is vital to identify the presence of thermal stresses that can cause failure and deformation of the cell body. This work investigated the capability of impinging jet cooling technique to maintain a triple junction solar cell temperature under recommended operating conditions. Furthermore, thermal stress analyses were performed. The results showed that employing jet impingements cooling improved both of thermal energy and electrical generation. In addition, the thermal stress is considerably decreased with increasing the cooling inlet mass flow rate.
关键词： Triple-Junction Solar Cell,High Concentrator Photovoltaic,High Concentrations,Thermal Stress
更新于2025-09-12 10:27:22
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Analysis of Thermal Stress and Temperature Distribution of Laser Power 10.0w and 20.0w on Material Removal in Aluminium Oxide Ceramic
摘要： The momentum look into researches the thermal stress investigation and temperature distribution of laser power 10.0w and 20.0w in aluminum oxide ceramic. Additionally, this paper explores the impact of thermal stress analysis and temperature distribution on material removal prepare. At the point when laser is connected for machining process for making smaller scale groove, temperature distribution assumes an imperative part for that since large amount of heat release by the laser which is influenced the material and deliver a heat affected zone thus material gets melted and vaporize. Thermal Stress is likewise being done because of nearness of thermal impact in material at the time of heat generation and it additionally assumes a decent part to achieve the great material removal handle. Accomplishing a fancied score of particular measurements is conceivable by having control over process parameters of a laser grooving machine which thus represents the measure of material removed. To handle with this, and concentrating on current trend where laser machining is exceptionally Demanded and connected in industry like like bio medical engineering, aerospace, automobile etc., and so on., it is particularly fundamental to concentrate the temperature distribution in the heat affected zone of the material where heat is created (due to heat energy released by laser beam) and equivalent thermal stress in the material body that is in charge of material removal, Achieving a desired groove with great precision. Limited component examination technique utilizing ANSYS is utilized to to simulate and analyze this temperature distribution and equivalent thermal stress of different laser power. In this paper temperature distribution FEM chart with diagrams for 10.0W and 20.0W, Material removal for 10.0W, 20.0W, Equivalent stress FEM diagram with graph for 100W, 200W are appeared furthermore the correlation of laser power in the vicinity of 10.0w and 20.0w are available.
关键词： Temperature Distribution,ANSYS,Laser Power,Material Removal,Thermal Stress
更新于2025-09-12 10:27:22
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Thermal-stress distribution and damage characteristics of three-junction GaAs solar cell irradiated by continuous laser beam
摘要： According to the theory of Fourier heat transfer and thermal stress field, a model on thermal damage of three-junction GaAs solar cell is established. The temperature and thermal-stress distribution inside the solar cell, which irradiated by continuous laser, are calculated. Results show that the temperature and thermal-stress distribution are corresponded to the intensity distribution of the incident laser beam. The maximum values of the compressive and tensile stress increase with the increasing of the power density and waist radius of the incident laser. When the waist radius is 0.5 cm, the melting damage is the main damage pattern as the power density is below about 40 W/cm2. However, when the laser power density is higher the stress damage will change to the main damage form. As the waist radius increases, the change in damage processes will also occur at lower laser power density.
关键词： Three-junction GaAs solar cell,Thermal-stress,Continuous laser beam,Damage
更新于2025-09-12 10:27:22
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Stress-induced refractive index changes in laser fibers and preforms
摘要： Refractive index profile of the core is a key design parameter in fiber lasers and amplifiers. During manufacturing, the initial information of the index profile is obtained from the preform, while ultimately the performance is defined by the index profile of the fiber. Depending on stresses and diffusion, the two profiles may be different. It is possible to predict more accurately the laser fiber refractive index when we apply a stress-induced index change model to the measured preform index profile data. The improved capability to predict the fiber index from preform increases the confidence in achieving the designed index profile in fiber, which enables faster process feedback and higher fiber yields.
关键词： laser fiber,tension,optical fiber,modelling,thermal stress,preform,Refractive index change,DND,stress
更新于2025-09-11 14:15:04
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On Time Domain Analysis of Photoplethysmogram Signals for Monitoring Heat Stress
摘要： There are a limited number of studies on heat stress dynamics during exercise using the photoplethysmogram (PPG) and its second derivative (APG). However, we investigate the most suitable index from short PPG signal recordings for heat stress assessment. The APG waveform consists of a, b, c and d waves in systole and an e wave in diastole. Our preliminary results indicate that the use of the energy of aa area, derived from PPG signals measured from emergency responders in tropical conditions, is promising in determining the heat stress level using 20-s recordings. After examining 14 time domain features using leave-one-out cross-validation, we found that the aa energy extracted from PPG signals is the most informative feature for classifying heat-stressed subjects, with an overall accuracy of 79%. Moreover, the combination of the aa energy with the traditional heart rate variability index of heat stress (i.e., the square root of the mean of the squares of the successive aa intervals) improved the heat stress detection to an overall accuracy of 83%.
关键词： affordable healthcare,thermal stress,global warming
更新于2025-09-10 09:29:36
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(111)Si thin layers detachment by stress-induced spallation
摘要： In this work, results of controlled detachment of (111) silicon by stress induced spalling (SIS) process, which is based on a gluing on a metallic stressor layer by an epoxy adhesive on top of a silicon substrate, are presented. It is shown that silicon foils mainly (1x1) cm2 with different thicknesses (~50-170 μm) can be successfully detached using different materials (steel, copper, aluminum, nickel and titanium) as stressor layers with thicknesses ~50-500 μm. Such detachment can be realized by dipping of a stressor/glue/silicon wafer based structure into liquid nitrogen. As a result, Si foils with different thicknesses from ~50 μm to ~170 μm can be detached. An analytical and numerical approaches based on principles of linear elastic fracture mechanics is developed and they are shown that such approaches can predict general trends and conditions for the detachment of silicon foils with desired thicknesses using a stressor layer. Raman spectroscopy analysis of the residual stresses in detached silicon foils shows, that tensile stresses (up to - 36MPa) as well as higher value compressive stresses (up to ~444 MPa) are present in such foils. Moreover, optical and scanning electron microscopy (SEM) measurements show that surface of the detached foils exhibits some periodic lines originated by stresses.
关键词： Exfoliation of silicon,Thermal stress,Raman spectroscopy,Kerf-free,photovoltaics (PV)
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE Industry Applications Society Annual Meeting (IAS) - Portland, OR, USA (2018.9.23-2018.9.27)] 2018 IEEE Industry Applications Society Annual Meeting (IAS) - Effect of thermal and electrical stress on photometric, radiometric, and colorimetric characteristics of large area white organic light emitting diodes
摘要： The aim of this paper is to identify the photometric, radiometric, and colorimetric signatures of degradations of large area white organic light emitting diodes (Philips GL55, 41cm2 active area), subjected to various stress conditions. Nine devices have been stressed at a constant current density of 11.25mA/cm2, 13mA/cm2 and 15mA/cm2 at 23°C (room temperature), 40°C and 60°C. We have also stocked three devices under purely thermal stress at the same temperatures. Thus, we can make comparison between electrical-thermal stress and purely thermal stress. Over aging time, an increase of both the correlated color temperature and the general rendering index was observed. The degradation rate of the blue emitter is more significant than the other emitters, which induced a color shift toward a green-yellow.
关键词： OLED,thermal stress,colorimetric characterization,electrical stress,degradation signature,aging
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Thermally Triggered SiC MOSFET Aging Effect on Conducted EMI
摘要： In this paper, thermally triggered SiC MOSFET aging effect on SiC based boost PFC converter’s conducted EMI is investigated. Existing EMI evaluation and suppression studies are mostly based on power devices at healthy state. This study provides a comprehensive EMI evaluation at different state of health of SiC MOSFET used in continuous conduction mode (CCM) Boost PFC converter. For this purpose, SiC MOSFET samples are exposed to accelerated aging and the corresponding device degradations are triggered by thermal stresses. To study device characteristics at different state of health, devices under test (DUT) electrical parameters and switching transients are evaluated over aging to support SiC based AC/DC converter’s conducted EMI discussion. Respectively, device aging effect on differential mode (DM) noise and common mode (CM) noise changes are discussed in detail. An 800W single phase CCM Boost PFC prototype is built to evaluate both DM and CM noise in band B frequency range (150kHz~30MHz) with experimental testing results. According to the study, high frequency noise decrement is observed after SiC MOSFET is thermally aged.
关键词： thermal stress,power factor correction (PFC),Accelerated aging,SiC power MOSFET,EMI/EMC
更新于2025-09-04 15:30:14