A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finit...A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finite impulse response （FIR） digital filter. The processing of backscatter signals using single-pulse and three-pulse cross-correlation detection methods is depicted in detail. From calculation results, the multi-pulse cross-correlation detection could effectively improve signal-to-noise ratio （SNR）. Finally, both wind velocity and direction are determined by the peak-delay method based on the correlation function which shows high measuring precision and high SNR of the MLBM system with the assistance of the digital cross- correlation detection.展开更多
A novel multi-laser beams measuring system （MLBM） for high precision detection on displacement of flow fields based on laser backscatter was designed and studied. MLBM has many advantages, such as simple structure, ...A novel multi-laser beams measuring system （MLBM） for high precision detection on displacement of flow fields based on laser backscatter was designed and studied. MLBM has many advantages, such as simple structure, high stability, and no limitation of the monochromaticity of laser. By circumventing the strong influence of atmospheric backscattering on the high sensitivity of target echo detection, high precision detection on backscatter density of laser by signal processing was achieved. Furthermore, the signal densities of various distances were extracted by time sampling and precise frequency control of digital circuit. Finally, the MLBM system including devices integrated of emitting and reviving equipments and program was obtained. Detection experiments showed that our system has high precision and the measurement error could be controlled within 5% to 10%.展开更多
Multi-lasers are proposed to enhance the proton acceleration in laser plasma interaction. A rear-holed target is illuminated by three lasers from different directions. The scheme is demonstrated by two-dimensional par...Multi-lasers are proposed to enhance the proton acceleration in laser plasma interaction. A rear-holed target is illuminated by three lasers from different directions. The scheme is demonstrated by two-dimensional particlein-cell simulations. The electron cloud shape is controlled well and the electron density is improved significantly. The electrons accelerated by the three lasers induce an enhanced target normal sheath acceleration(TNSA) which suppresses the proton beam divergence and improves the maximum proton energy. The maximum proton energy is 22.9 Me V, which increased significantly than that of a single-laser target interaction. Meanwhile, the average divergence angle(22.3?) is reduced. The dependence of the proton beam on the length of sidewall is investigated in detail and the optimal length is obtained.展开更多
Contactless measurement of wind flow has been utilized in many fields, such as weather forecasting, hurricane tracking, and aeronautic alarm. In this paper, a novel multi-laser beams measuring system （MLBM） for high...Contactless measurement of wind flow has been utilized in many fields, such as weather forecasting, hurricane tracking, and aeronautic alarm. In this paper, a novel multi-laser beams measuring system （MLBM） for high precision detection of wind field based on optical scintillations and small perturbation theory was proposed and verified. According to the fluctuation intensity of laser backscatter received by two detectors, peak delay technique was adopted to determine the velocity of wind flow. Detailed procedure to deal with backscatter signals was also presented. Then, practical experiments and measurement results showed high precision of the proposed system for wind measurement with a relative error as 3.21%. Consequently, the MLBM system possesses obvious potential application in engineering project.展开更多
Multi-laser-target tracking is an important subject in the field of signal processing of laser warners. A clustering method is applied to the measurement of laser warner, and the space-time fusion for measurements in ...Multi-laser-target tracking is an important subject in the field of signal processing of laser warners. A clustering method is applied to the measurement of laser warner, and the space-time fusion for measurements in the same cluster is accomplished. Real-time tracking of multi-laser-target and real-time picking of multi-laser-signal are introduced using data fusion of the measurements. A prototype device of the algorithm is built up. The results of experiments show that the algorithm is very effective.展开更多
Metal additive manufacturing,especially laser powder bed fusion(L-PBF),is increasingly being used to fabricate complex parts with fine features.Emerging L-PBF systems have large build volumes and several lasers that o...Metal additive manufacturing,especially laser powder bed fusion(L-PBF),is increasingly being used to fabricate complex parts with fine features.Emerging L-PBF systems have large build volumes and several lasers that op-erate simultaneously.Hence,they can produce large and complex parts at reduced costs and short build times.However,the thermal distortion remains a critical challenge.Hence,a thorough understanding of the impact of multiple lasers on part distortion in multi-laser PBF(ML-PBF)is imperative.Although experimental investigation is possible,a more conducive approach is to design and create suitable predictive models to understand the impact of multiple lasers consolidating a part into layers.To fulfill this goal,in this study,a commercially available and widely used thermo-mechanical model,Netfabb,was used to investigate the effects of multiple lasers for com-plex scan patterns such as raster,spiral,and Hilbert on the temperature distribution and thermal distortion.The results show that the thermal distortion is minimal for the spiral scan pattern.Additionally,multiple lasers were found to decrease the build time(as expected)while maintaining or reducing the thermal distortion compared with their single-laser counterparts for all scan patterns(except Hilbert).Therefore,the newly developed ML-PBF predictive model is capable of providing critical insights into the effects of using multiple lasers,thereby opening new possibilities for the faster production of complex parts.In the future,small-scale computational models will be expanded to include large-scale parts,and probabilistic models will be developed to establish correlations.展开更多
基金supported by National Natural Science Foundation of China under Grant No. 60425101-1Foundation for Innovative Research Groups of NSFC under Grant No. 60721001
文摘A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finite impulse response （FIR） digital filter. The processing of backscatter signals using single-pulse and three-pulse cross-correlation detection methods is depicted in detail. From calculation results, the multi-pulse cross-correlation detection could effectively improve signal-to-noise ratio （SNR）. Finally, both wind velocity and direction are determined by the peak-delay method based on the correlation function which shows high measuring precision and high SNR of the MLBM system with the assistance of the digital cross- correlation detection.
基金supported by National Natural Science Foundation of China under Grant No.60425101-1Fund for Innovative Research Groups of NSFC under Grant No.60721001
文摘A novel multi-laser beams measuring system （MLBM） for high precision detection on displacement of flow fields based on laser backscatter was designed and studied. MLBM has many advantages, such as simple structure, high stability, and no limitation of the monochromaticity of laser. By circumventing the strong influence of atmospheric backscattering on the high sensitivity of target echo detection, high precision detection on backscatter density of laser by signal processing was achieved. Furthermore, the signal densities of various distances were extracted by time sampling and precise frequency control of digital circuit. Finally, the MLBM system including devices integrated of emitting and reviving equipments and program was obtained. Detection experiments showed that our system has high precision and the measurement error could be controlled within 5% to 10%.
文摘Multi-lasers are proposed to enhance the proton acceleration in laser plasma interaction. A rear-holed target is illuminated by three lasers from different directions. The scheme is demonstrated by two-dimensional particlein-cell simulations. The electron cloud shape is controlled well and the electron density is improved significantly. The electrons accelerated by the three lasers induce an enhanced target normal sheath acceleration(TNSA) which suppresses the proton beam divergence and improves the maximum proton energy. The maximum proton energy is 22.9 Me V, which increased significantly than that of a single-laser target interaction. Meanwhile, the average divergence angle(22.3?) is reduced. The dependence of the proton beam on the length of sidewall is investigated in detail and the optimal length is obtained.
基金supported by National Science Foundation of China (NSFC) under Grant No.60425101-1Foundation for Innovative Research Groups of NSFC under Grant No.60721001
文摘Contactless measurement of wind flow has been utilized in many fields, such as weather forecasting, hurricane tracking, and aeronautic alarm. In this paper, a novel multi-laser beams measuring system （MLBM） for high precision detection of wind field based on optical scintillations and small perturbation theory was proposed and verified. According to the fluctuation intensity of laser backscatter received by two detectors, peak delay technique was adopted to determine the velocity of wind flow. Detailed procedure to deal with backscatter signals was also presented. Then, practical experiments and measurement results showed high precision of the proposed system for wind measurement with a relative error as 3.21%. Consequently, the MLBM system possesses obvious potential application in engineering project.
基金University Doctor Subject Foundation of China (20060699024)
文摘Multi-laser-target tracking is an important subject in the field of signal processing of laser warners. A clustering method is applied to the measurement of laser warner, and the space-time fusion for measurements in the same cluster is accomplished. Real-time tracking of multi-laser-target and real-time picking of multi-laser-signal are introduced using data fusion of the measurements. A prototype device of the algorithm is built up. The results of experiments show that the algorithm is very effective.
基金supported by Defense Advanced Research Projects Agency of USA(Grant.No.D22AP00147-00).
文摘Metal additive manufacturing,especially laser powder bed fusion(L-PBF),is increasingly being used to fabricate complex parts with fine features.Emerging L-PBF systems have large build volumes and several lasers that op-erate simultaneously.Hence,they can produce large and complex parts at reduced costs and short build times.However,the thermal distortion remains a critical challenge.Hence,a thorough understanding of the impact of multiple lasers on part distortion in multi-laser PBF(ML-PBF)is imperative.Although experimental investigation is possible,a more conducive approach is to design and create suitable predictive models to understand the impact of multiple lasers consolidating a part into layers.To fulfill this goal,in this study,a commercially available and widely used thermo-mechanical model,Netfabb,was used to investigate the effects of multiple lasers for com-plex scan patterns such as raster,spiral,and Hilbert on the temperature distribution and thermal distortion.The results show that the thermal distortion is minimal for the spiral scan pattern.Additionally,multiple lasers were found to decrease the build time(as expected)while maintaining or reducing the thermal distortion compared with their single-laser counterparts for all scan patterns(except Hilbert).Therefore,the newly developed ML-PBF predictive model is capable of providing critical insights into the effects of using multiple lasers,thereby opening new possibilities for the faster production of complex parts.In the future,small-scale computational models will be expanded to include large-scale parts,and probabilistic models will be developed to establish correlations.
