A visual sensing system was established to monitor the weld pool in laser spot welding. The top-hat and bottom-hat transformation algorithms based on mathematical morphology were used to compensate for non-uniform con...A visual sensing system was established to monitor the weld pool in laser spot welding. The top-hat and bottom-hat transformation algorithms based on mathematical morphology were used to compensate for non-uniform contrast of weld pool edge. Moreover, the canny edge detector was applied to extract the weld paol profile. The edge detected results show that the morphological operation is obviously superior to the traditional contrast enhancement method. In addition, the combination of dilation and erosion was applied to eliminate the irrelevant edge details, and the smooth weld pool edge was acquired. Based on the image processing technology described above, the dynamic process of weld pool diameter during laser spot welding was obtained.展开更多
Laser spot thermography is a novel technique for the detection of surface cracks with a laser to heat sample locally and with an IR camera to record the surface temperature distribution. Common methods to characterize...Laser spot thermography is a novel technique for the detection of surface cracks with a laser to heat sample locally and with an IR camera to record the surface temperature distribution. Common methods to characterize cracks are only suitable for the situation that the laser scanning path is vertical to the crack. But due to the randomness of cracks,when the scanning path is parallel to the crack,surface cracks cannot be detected by these methods. To tackle this problem,a method is presented which is suitable for the situation that the scanning path is parallel to crack. The main idea is to evaluate the crack-caused asymmetries of the surface temperature distribution. The effect of temperature gradient and the maximum scanning interval are analyzed by a 2D simulation. A new crack imaging technique is presented that is based on delayed temperature difference at symmetric points to characterize the crack in the thermal image. Compared well with those obtained by the spatial first derivative method,experimental results are shown to efficiently prove this method.展开更多
Laser shock peening（LSP） is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy...Laser shock peening（LSP） is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot.Nd：glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied.The surface morphology and surface residual stress of the TC17 titanium alloy,treated with varying peening parameters such as laser power density and overlapping ratio,have been studied in detail.The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas,and compressive residual stresses are saturated as laser pulse energy is over 55 J.There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios.A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8 %.The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz.The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.展开更多
Phosphor-in-glass(PiG)film is a promising luminescent material in high-brightness laser lighting for its advantages of high efficiency,outstanding color quality,and low-cost preparation,which must bear high laser powe...Phosphor-in-glass(PiG)film is a promising luminescent material in high-brightness laser lighting for its advantages of high efficiency,outstanding color quality,and low-cost preparation,which must bear high laser power(LP)and laser power density(LPD)simultaneously to enable high-luminance light.Herein,laser spot associated high-saturation PiG film was proposed for transmissive and reflective high-brightness laser lighting.Two types of PiG films were prepared by printing and sintering La_(3)Si_(6)N_(11):Ce^(3+)(LSN)phosphor-borosilicate glass pastes on a sapphire substrate(PiG-S)and an AlN substrate(PiG-A),respectively.The PiG films with perfect crystal structure of phosphor were reliably bonded on the substrates.The effects of laser spot areas on the luminescence saturation of LP and LPD were investigated in the PiG films.With the increase of laser spot area from 0.5 to 2.5 mm^(2),the LP threshold of PiG films is gradually raised,while the LPD threshold of PiG films is decreased.The PiG-S withstands a high LP of 23.46 W and a high LPD of 20.64 W/mm^(2),enabling white light with a luminous flux of 3677 lm.The PiG-A withstands a high LP of 41.12 W and a high LPD of 35.56 W/mm^(2),enabling white light with a luminous flux of 2882 lm.Moreover,the PiG-A maintains lower working temperature compared with the PiG-S,and the temperatures reduce with the increasing laser spot area.The results demonstrate that the laser spot associated PiG films realize high saturation thresholds of LP and LPD simultaneously,and enable high luminance for laser lighting.展开更多
Background Idiopathic choroidal neovascularization （ICNV） affects young patients and thus may have a significant impact on vision and life quality over a patient＇s lifespan. This study was designed to compare the v...Background Idiopathic choroidal neovascularization （ICNV） affects young patients and thus may have a significant impact on vision and life quality over a patient＇s lifespan. This study was designed to compare the visual outcome and retinal pigment epithelium （RPE） damage after photodynamic therapy （PDT） with small laser spot and PDT with standard laser spot for idiopathic choroidal neovascularization （ICNV）. Methods This was a randomized controlled study. Fifty-two patients with ICNV were enrolled and randomly divided into a study group （small laser spot PDT, n=27） and a control group （standard laser spot PDT, n=25）. Best corrected visual acuity （BCVA）, optic coherence tomography （OCT） and fluorescein angiography （FA） findings were the main measurements. The patients were followed up 1 week, 1, 3, 6, 9 months and 1 year after PDT. Results BCVA improvement was statistically significantly higher in the study group than the control group at 6-month （（25.53±15.01） letters vs. （14.71±11.66） letters, P=-0.025） and 9-month follow-ups （（27.53±17.78） letters vs. （15.59±12.21） letters, P=0.039）. At 3- and 6-month follow-ups, the quadrants of RPE damage between the two groups varied significantly （P 〈0.001 and P=0.023, respectively）. In each follow-up, the number of cases with decreased or unchanged leakage of choroidal neovascularization by FA and reduced subretinal fluid by OCT did not vary significantly between the two groups. Ten cases （37.0%） in the study group and eight cases （32.0%） in the control group suffered from recurrent CNV （P=-0.703）. Conclusions Better visual improvements, less RPE damage, a similar recurrent rate of CNV and change of subretinal fluid were observed in the small laser spot PDT group than in the standard laser spot PDT group for ICNV.展开更多
An automatic monitoring method of the 3-D deformation is presented for crustal fault based on laser and machine vision. The laser source and screen are independently set up in the headwall and footwall, the collimated...An automatic monitoring method of the 3-D deformation is presented for crustal fault based on laser and machine vision. The laser source and screen are independently set up in the headwall and footwall, the collimated laser beam creates a circular spot on the screen, meanwhile, the industrial camera captures the tiny deformation of the crustal fault by monitoring the change of the spot position. This method significantly reduces the cost of equipment and labor, provides daily sampling to ensure high continuity of data. A prototype of the automatic monitoring system is developed, and a repeatability test indicates that the error of spot jitter can be minimized by consecutive samples. Meanwhile, the environmental correction model is determined to ensure that environmental changes do not disturb the system. Furthermore, the automatic monitoring system has been applied at the deformation monitoring station(KJX02) of China Beishan underground research laboratory, where continuous deformation monitoring is underway.展开更多
In indirect drive, reducing peak intensity of a single beam and controlling overlap of multi-beams are two opposite requirements for laser focal spot design. In this paper, an improved laser spot design technique for ...In indirect drive, reducing peak intensity of a single beam and controlling overlap of multi-beams are two opposite requirements for laser focal spot design. In this paper, an improved laser spot design technique for indirect drive built upon the geometric structures of laser propagation into hohlraum has been introduced. The proposed technique is able to generate appropriate continuous phase plate(CPP) producing a special shaped spot that can balance the opposite requirements. The corresponding CPP does not bring difficulties to the design and fabrication. Phase aberrations are more sensitive to the special shaped spot; however, it can be tolerable for the current beam control level.展开更多
Laser shock processing（LSP）,also known as laser peening,is a novel surface treatment technique in the past few years.Compressive residual stresses which imparted by LSP are very important for improving fatigue,corro...Laser shock processing（LSP）,also known as laser peening,is a novel surface treatment technique in the past few years.Compressive residual stresses which imparted by LSP are very important for improving fatigue,corrosion and wea rresistance of metals.Finite element analysis（FEA） simulation using ABAQUS software has been applied to predict residualstresses induced by LSP on Ti-6Al-4V titanium alloy with laser pulse duration 30 ns and water confined ablation mode.The residual stress field generated by different shape laser spots was studied,and the square laser spot is shown the most suitability for avoiding stress lack phenomenon and overlapping LSP.Surface residual stresses and plastically affected depth within single square spot both increased with the increase of laser intensity and laser shock times.Furthermore,compared with circle and ellipse spot,the residual stress distribution in overlapping square spots is very uniform only with small overlapping ratio.LSP with square spot can process advantageous residual stress field,and this technique will be used widely.展开更多
The surface profile of laser peened stainless steel was researched in this paper,a special lens was used to convert circle laser spot to square spot,the difference of surface profile obtained by laser peening with cir...The surface profile of laser peened stainless steel was researched in this paper,a special lens was used to convert circle laser spot to square spot,the difference of surface profile obtained by laser peening with circle laser spot was compared with that with square laser spot.Laser peened zone showed steep depression at the edge with square spot,but the surface in the shocked zone was very smooth.With suitable overlapped rate,square spot can produce smoother surface profile than circle spot,and laser peening with square spot is more effective than circle spot.展开更多
Microscale laser shock processing （μLSP）, also known as laser shock processing in microscale, is a technique that uses microscale focused laser beam to induce high pressure plasma and generates plastic deformation ...Microscale laser shock processing （μLSP）, also known as laser shock processing in microscale, is a technique that uses microscale focused laser beam to induce high pressure plasma and generates plastic deformation and compressive residual stress in target materials, thus improves fatigue or stress corrosion cracking resistance of MEMS （Micro Electromechanical Systems） devices made of such a material. Many works have been reported about the research and experiment for μLSP. But the diameters of 50-200 μm were used at the first time for this field, which was useful for treating micro-device components with larger area and curved surface. The excimer laser was used firstly on μLSP for shorter wavelength than that of used in previous researches. The determination method of laser spot size at micro-level spatial resolution was presented. Under these conditions, plastic deformation, the stress analysis and microhardness with different pulse number, pulse energy and pulse spacing were investigated. Especially the residual stress distribution with depth treated by #LSP, was first investigated. Experiment results showed that the material performance was improved remarkably after μLSP.展开更多
文摘A visual sensing system was established to monitor the weld pool in laser spot welding. The top-hat and bottom-hat transformation algorithms based on mathematical morphology were used to compensate for non-uniform contrast of weld pool edge. Moreover, the canny edge detector was applied to extract the weld paol profile. The edge detected results show that the morphological operation is obviously superior to the traditional contrast enhancement method. In addition, the combination of dilation and erosion was applied to eliminate the irrelevant edge details, and the smooth weld pool edge was acquired. Based on the image processing technology described above, the dynamic process of weld pool diameter during laser spot welding was obtained.
基金supported by the National Key Scientific Instrument and Equipment Development Projects,China(Grant No.2013YQ470767)。
文摘Laser spot thermography is a novel technique for the detection of surface cracks with a laser to heat sample locally and with an IR camera to record the surface temperature distribution. Common methods to characterize cracks are only suitable for the situation that the laser scanning path is vertical to the crack. But due to the randomness of cracks,when the scanning path is parallel to the crack,surface cracks cannot be detected by these methods. To tackle this problem,a method is presented which is suitable for the situation that the scanning path is parallel to crack. The main idea is to evaluate the crack-caused asymmetries of the surface temperature distribution. The effect of temperature gradient and the maximum scanning interval are analyzed by a 2D simulation. A new crack imaging technique is presented that is based on delayed temperature difference at symmetric points to characterize the crack in the thermal image. Compared well with those obtained by the spatial first derivative method,experimental results are shown to efficiently prove this method.
基金Subject in Advance of General Armament Department(813040405-1)
文摘Laser shock peening（LSP） is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot.Nd：glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied.The surface morphology and surface residual stress of the TC17 titanium alloy,treated with varying peening parameters such as laser power density and overlapping ratio,have been studied in detail.The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas,and compressive residual stresses are saturated as laser pulse energy is over 55 J.There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios.A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8 %.The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz.The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.
基金supported by the National Natural Science Foundation of China(51805196 and 51775219)National Key R&D Program of China(2022YFB3604803)Key Research and Development Program of Hubei Province(2021BAA213 and 2020BAB068).
文摘Phosphor-in-glass(PiG)film is a promising luminescent material in high-brightness laser lighting for its advantages of high efficiency,outstanding color quality,and low-cost preparation,which must bear high laser power(LP)and laser power density(LPD)simultaneously to enable high-luminance light.Herein,laser spot associated high-saturation PiG film was proposed for transmissive and reflective high-brightness laser lighting.Two types of PiG films were prepared by printing and sintering La_(3)Si_(6)N_(11):Ce^(3+)(LSN)phosphor-borosilicate glass pastes on a sapphire substrate(PiG-S)and an AlN substrate(PiG-A),respectively.The PiG films with perfect crystal structure of phosphor were reliably bonded on the substrates.The effects of laser spot areas on the luminescence saturation of LP and LPD were investigated in the PiG films.With the increase of laser spot area from 0.5 to 2.5 mm^(2),the LP threshold of PiG films is gradually raised,while the LPD threshold of PiG films is decreased.The PiG-S withstands a high LP of 23.46 W and a high LPD of 20.64 W/mm^(2),enabling white light with a luminous flux of 3677 lm.The PiG-A withstands a high LP of 41.12 W and a high LPD of 35.56 W/mm^(2),enabling white light with a luminous flux of 2882 lm.Moreover,the PiG-A maintains lower working temperature compared with the PiG-S,and the temperatures reduce with the increasing laser spot area.The results demonstrate that the laser spot associated PiG films realize high saturation thresholds of LP and LPD simultaneously,and enable high luminance for laser lighting.
基金This study was supported by grants from National Basic Research Program of China （973 Program, No. 2011CB510200）, an education grant from Novartis China, Beijing Novel Program （No. 2009B04） and National Natural Science Foundation of China （No. 30901639）.
文摘Background Idiopathic choroidal neovascularization （ICNV） affects young patients and thus may have a significant impact on vision and life quality over a patient＇s lifespan. This study was designed to compare the visual outcome and retinal pigment epithelium （RPE） damage after photodynamic therapy （PDT） with small laser spot and PDT with standard laser spot for idiopathic choroidal neovascularization （ICNV）. Methods This was a randomized controlled study. Fifty-two patients with ICNV were enrolled and randomly divided into a study group （small laser spot PDT, n=27） and a control group （standard laser spot PDT, n=25）. Best corrected visual acuity （BCVA）, optic coherence tomography （OCT） and fluorescein angiography （FA） findings were the main measurements. The patients were followed up 1 week, 1, 3, 6, 9 months and 1 year after PDT. Results BCVA improvement was statistically significantly higher in the study group than the control group at 6-month （（25.53±15.01） letters vs. （14.71±11.66） letters, P=-0.025） and 9-month follow-ups （（27.53±17.78） letters vs. （15.59±12.21） letters, P=0.039）. At 3- and 6-month follow-ups, the quadrants of RPE damage between the two groups varied significantly （P 〈0.001 and P=0.023, respectively）. In each follow-up, the number of cases with decreased or unchanged leakage of choroidal neovascularization by FA and reduced subretinal fluid by OCT did not vary significantly between the two groups. Ten cases （37.0%） in the study group and eight cases （32.0%） in the control group suffered from recurrent CNV （P=-0.703）. Conclusions Better visual improvements, less RPE damage, a similar recurrent rate of CNV and change of subretinal fluid were observed in the small laser spot PDT group than in the standard laser spot PDT group for ICNV.
基金supported by Earthquake Sciences Spark Programs of China Earthquake Administration(No.XH22020YA)Science Innovation Fund granted by the First Monitoring and Application Center of China Earthquake Administration(No.FMC202309).
文摘An automatic monitoring method of the 3-D deformation is presented for crustal fault based on laser and machine vision. The laser source and screen are independently set up in the headwall and footwall, the collimated laser beam creates a circular spot on the screen, meanwhile, the industrial camera captures the tiny deformation of the crustal fault by monitoring the change of the spot position. This method significantly reduces the cost of equipment and labor, provides daily sampling to ensure high continuity of data. A prototype of the automatic monitoring system is developed, and a repeatability test indicates that the error of spot jitter can be minimized by consecutive samples. Meanwhile, the environmental correction model is determined to ensure that environmental changes do not disturb the system. Furthermore, the automatic monitoring system has been applied at the deformation monitoring station(KJX02) of China Beishan underground research laboratory, where continuous deformation monitoring is underway.
基金supported by the National Nature Science Foundation of China (No.11404306)the Presidential Foundation of the Chinese Academy of Engineering Physics (No.YZJJLX2016008)
文摘In indirect drive, reducing peak intensity of a single beam and controlling overlap of multi-beams are two opposite requirements for laser focal spot design. In this paper, an improved laser spot design technique for indirect drive built upon the geometric structures of laser propagation into hohlraum has been introduced. The proposed technique is able to generate appropriate continuous phase plate(CPP) producing a special shaped spot that can balance the opposite requirements. The corresponding CPP does not bring difficulties to the design and fabrication. Phase aberrations are more sensitive to the special shaped spot; however, it can be tolerable for the current beam control level.
基金Project supported by the Foundation of National Key Laboratory of Science and Technology on Power Beam Processing(Grant No.9140C4505020705)
文摘Laser shock processing（LSP）,also known as laser peening,is a novel surface treatment technique in the past few years.Compressive residual stresses which imparted by LSP are very important for improving fatigue,corrosion and wea rresistance of metals.Finite element analysis（FEA） simulation using ABAQUS software has been applied to predict residualstresses induced by LSP on Ti-6Al-4V titanium alloy with laser pulse duration 30 ns and water confined ablation mode.The residual stress field generated by different shape laser spots was studied,and the square laser spot is shown the most suitability for avoiding stress lack phenomenon and overlapping LSP.Surface residual stresses and plastically affected depth within single square spot both increased with the increase of laser intensity and laser shock times.Furthermore,compared with circle and ellipse spot,the residual stress distribution in overlapping square spots is very uniform only with small overlapping ratio.LSP with square spot can process advantageous residual stress field,and this technique will be used widely.
文摘The surface profile of laser peened stainless steel was researched in this paper,a special lens was used to convert circle laser spot to square spot,the difference of surface profile obtained by laser peening with circle laser spot was compared with that with square laser spot.Laser peened zone showed steep depression at the edge with square spot,but the surface in the shocked zone was very smooth.With suitable overlapped rate,square spot can produce smoother surface profile than circle spot,and laser peening with square spot is more effective than circle spot.
基金supported by the National Natural Sci-ence Foundation of China (Grant No 50575078)
文摘Microscale laser shock processing （μLSP）, also known as laser shock processing in microscale, is a technique that uses microscale focused laser beam to induce high pressure plasma and generates plastic deformation and compressive residual stress in target materials, thus improves fatigue or stress corrosion cracking resistance of MEMS （Micro Electromechanical Systems） devices made of such a material. Many works have been reported about the research and experiment for μLSP. But the diameters of 50-200 μm were used at the first time for this field, which was useful for treating micro-device components with larger area and curved surface. The excimer laser was used firstly on μLSP for shorter wavelength than that of used in previous researches. The determination method of laser spot size at micro-level spatial resolution was presented. Under these conditions, plastic deformation, the stress analysis and microhardness with different pulse number, pulse energy and pulse spacing were investigated. Especially the residual stress distribution with depth treated by #LSP, was first investigated. Experiment results showed that the material performance was improved remarkably after μLSP.
