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RSS2019 Vol. 43, No. 3
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2019, 43(3): 291-294.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.001
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Abstract:
In order to develop a single-frequency pumping source for an optical parametric oscillator, a seed-injected, single-end pumped, Q-switched, bonded Nd:YAG single-frequency laser with 500Hz pulse repetition rate was designed by using the ramp-fire resonance detection technique with bias feedback, and a single longitudinal mode oscillation was established. The technology was analyzed theoretically. The results show that, when pump energy is 36.8mJ, output single pulse energy is 8.4mJ and optical efficiency is 23%, pulse width is 6.8ns, beam quality factor M2 is about 1.3, and peak power is 1.2MW. The interference pattern of output laser is obtained by using a F-P etalon. After one hour observation, single longitudinal mode probability of laser output is 100%. The result is helpful for the pump design of optical parametric oscillators.
In order to develop a single-frequency pumping source for an optical parametric oscillator, a seed-injected, single-end pumped, Q-switched, bonded Nd:YAG single-frequency laser with 500Hz pulse repetition rate was designed by using the ramp-fire resonance detection technique with bias feedback, and a single longitudinal mode oscillation was established. The technology was analyzed theoretically. The results show that, when pump energy is 36.8mJ, output single pulse energy is 8.4mJ and optical efficiency is 23%, pulse width is 6.8ns, beam quality factor M2 is about 1.3, and peak power is 1.2MW. The interference pattern of output laser is obtained by using a F-P etalon. After one hour observation, single longitudinal mode probability of laser output is 100%. The result is helpful for the pump design of optical parametric oscillators.
2019, 43(3): 295-300.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.002
Abstract:
In order to improve the surface polishing quality of SUS 304, a laser chemical composite polishing method was proposed based on chemical polishing and laser polishing. SUS 304 was adopted as workpiece being polished by 1064nm laser in purified water and polishing solution, respectively. The influence of laser processing power and scanning times on the surface topography and quality of machined area was analyzed. The bubbles have a damaging effect on the passivation film formed on the surface of stainless steel, resulting in uneven polishing effect and increasing surface roughness. The results show that, laser polishing in polishing solution can significantly improve surface topography while suppressing surface oxidation blackening, and the surface roughness decreases from 0.845μm to 0.181μm. Laser chemical composite polishing can improve the polishing quality of stainless steel and reduce environmental pollution. This study has a great application prospect.
In order to improve the surface polishing quality of SUS 304, a laser chemical composite polishing method was proposed based on chemical polishing and laser polishing. SUS 304 was adopted as workpiece being polished by 1064nm laser in purified water and polishing solution, respectively. The influence of laser processing power and scanning times on the surface topography and quality of machined area was analyzed. The bubbles have a damaging effect on the passivation film formed on the surface of stainless steel, resulting in uneven polishing effect and increasing surface roughness. The results show that, laser polishing in polishing solution can significantly improve surface topography while suppressing surface oxidation blackening, and the surface roughness decreases from 0.845μm to 0.181μm. Laser chemical composite polishing can improve the polishing quality of stainless steel and reduce environmental pollution. This study has a great application prospect.
2019, 43(3): 301-306.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.003
Abstract:
In order to solve the problems of large number of gas holes, coarse grain size and poor mechanical properties of traditional aluminum alloy welded joints, laser-arc hybrid welding experiment assisted by ultrasonic vibration was carried out by taking 5083-O aluminium alloy as the research object. The effect of ultrasonic vibration on the number of pore, microstructure and tensile strength of aluminium alloy weld was studied. The mechanism of the effect of ultrasonic wave on pore discharge and microstructure refinement in welding pool was also discussed. The results show that, the number of gas holes in the weld seam of ultrasonic assisted welding decreases significantly. It is mainly attributed to the reduction of hydrogen concentration in aluminium alloy melt by ultrasonic cavitation. It also promotes the rapid escape of bubbles. The cavitation effect and acoustic flow effect of ultrasound change the pressure, temperature and flow state of melt. The crystallization condition of the molten pool is changed. The grain structure of the weld is refined by increasing the nucleation rate and breaking dendrite. The average tensile strength of weld increased from 242.9MPa to 270MPa after ultrasonic vibration is applied. The fracture location occurs in the heat-affected zone. It is mainly due to the decrease of porosity and the refinement of structure in the weld zone. This study is helpful to understand the forming mechanism of defects and improve the strength of joints in the welding process of aluminium alloys.
In order to solve the problems of large number of gas holes, coarse grain size and poor mechanical properties of traditional aluminum alloy welded joints, laser-arc hybrid welding experiment assisted by ultrasonic vibration was carried out by taking 5083-O aluminium alloy as the research object. The effect of ultrasonic vibration on the number of pore, microstructure and tensile strength of aluminium alloy weld was studied. The mechanism of the effect of ultrasonic wave on pore discharge and microstructure refinement in welding pool was also discussed. The results show that, the number of gas holes in the weld seam of ultrasonic assisted welding decreases significantly. It is mainly attributed to the reduction of hydrogen concentration in aluminium alloy melt by ultrasonic cavitation. It also promotes the rapid escape of bubbles. The cavitation effect and acoustic flow effect of ultrasound change the pressure, temperature and flow state of melt. The crystallization condition of the molten pool is changed. The grain structure of the weld is refined by increasing the nucleation rate and breaking dendrite. The average tensile strength of weld increased from 242.9MPa to 270MPa after ultrasonic vibration is applied. The fracture location occurs in the heat-affected zone. It is mainly due to the decrease of porosity and the refinement of structure in the weld zone. This study is helpful to understand the forming mechanism of defects and improve the strength of joints in the welding process of aluminium alloys.
2019, 43(3): 307-313.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.004
Abstract:
The welding effect of heterogeneous compatible polymers was poor due to the difference of temperature properties. In order to improve the laser transmission welding strength, laser transmission welding assisted by infrared heating lamp to heate superstructure material with high melting temperature was used. The welding ability was analyzed theoretically and experimentally from four aspects:optical property, temperature property, compatibility and heat absorption test of upper layer material. Response surface methodology was used to optimize process parameters and the optimum combination of process parameters was obtained. A 3-D microscope was used to study the fracture morphology and failure modes of weldments. The effect of air bubbles on the welding ability was also analyzed. The results show that the maximum shear force of the welding with infrared heating lamp can reach about 1.5 times of that without infrared heating lamp. The assistance of infrared heating lamp can effectively solve the problem that the welding effect of heterogeneous polymers is not ideal because ofgreat difference of temperature attributes.
The welding effect of heterogeneous compatible polymers was poor due to the difference of temperature properties. In order to improve the laser transmission welding strength, laser transmission welding assisted by infrared heating lamp to heate superstructure material with high melting temperature was used. The welding ability was analyzed theoretically and experimentally from four aspects:optical property, temperature property, compatibility and heat absorption test of upper layer material. Response surface methodology was used to optimize process parameters and the optimum combination of process parameters was obtained. A 3-D microscope was used to study the fracture morphology and failure modes of weldments. The effect of air bubbles on the welding ability was also analyzed. The results show that the maximum shear force of the welding with infrared heating lamp can reach about 1.5 times of that without infrared heating lamp. The assistance of infrared heating lamp can effectively solve the problem that the welding effect of heterogeneous polymers is not ideal because ofgreat difference of temperature attributes.
2019, 43(3): 314-317.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.005
Abstract:
In order to obtain high power, high beam quality and high efficiency of solid-state lasers, by means of theoretical analysis, the models of temperature distribution and cooling rate of slab laser mediums were established. A lamp-pumped Nd:glass slab solid-state laser was taken as an example for numerical calculation. The results show that, the temperature distribution and cooling rate of slab solid-state lasers can be more accurately described by the 2-D model. This research has certain guiding significance for the design of high power slab laser mediums.
In order to obtain high power, high beam quality and high efficiency of solid-state lasers, by means of theoretical analysis, the models of temperature distribution and cooling rate of slab laser mediums were established. A lamp-pumped Nd:glass slab solid-state laser was taken as an example for numerical calculation. The results show that, the temperature distribution and cooling rate of slab solid-state lasers can be more accurately described by the 2-D model. This research has certain guiding significance for the design of high power slab laser mediums.
2019, 43(3): 318-323.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.006
Abstract:
In order to improve the processing speed and display efficiency of laser scanning data, octree structure was constructed by parallel threshold segmentation and massive point clouds were processed in blocks. The data in octree leaf nodes was simplified by data thinning method based on height difference layer by layer and was stored in octree external memory structure. The multi-resolution level of detail model of point cloud was constructed. The internal and external memory scheduling strategy based on view change and paging database was adopted. The laser scanning point cloud data acquired by a group of power line patrol helicopters were experimentally validated. The results show that this method has advantages of octree construction speed and display efficiency of large amount of point cloud data. It can satisfy the timeliness requirement of power line patrol very well.
In order to improve the processing speed and display efficiency of laser scanning data, octree structure was constructed by parallel threshold segmentation and massive point clouds were processed in blocks. The data in octree leaf nodes was simplified by data thinning method based on height difference layer by layer and was stored in octree external memory structure. The multi-resolution level of detail model of point cloud was constructed. The internal and external memory scheduling strategy based on view change and paging database was adopted. The laser scanning point cloud data acquired by a group of power line patrol helicopters were experimentally validated. The results show that this method has advantages of octree construction speed and display efficiency of large amount of point cloud data. It can satisfy the timeliness requirement of power line patrol very well.
2019, 43(3): 324-328.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.007
Abstract:
In order to verify the feasibility of the mathematical model of two-circle coaxial optical fiber sensors for measuring the surface topography of objects, the parameters of the novel structure optical fiber sensor were optimized to improve the linear measurement range and sensitivity of the optical fiber sensors. The mirror paper, which does not affect the front slope data of the modulation characteristic curve, was used as the reflector for experimental verification. The theoretical analysis and mathematical modeling of the new structure of optical fiber sensor were also carried out. Then, the tilt angle of the novel structure was optimized by using particle swarm optimization. The results show that the experimental curve obtained by using mirror paper as reflector coincides with the simulation modulation characteristic curve. The feasibility of the mathematical model of the two-circle coaxial optical fiber sensor used to measure the surface topography of the object is proved. The slope angle optimized by particle swarm optimization is 2.33°. At this time, the linear measurement range and sensitivity of the front slope are 1.14 times and 1.89 times respectively when the inclination angle is zero. The novel structure of two-circle coaxial optical fiber sensor shows good measurement performance and application prospects.
In order to verify the feasibility of the mathematical model of two-circle coaxial optical fiber sensors for measuring the surface topography of objects, the parameters of the novel structure optical fiber sensor were optimized to improve the linear measurement range and sensitivity of the optical fiber sensors. The mirror paper, which does not affect the front slope data of the modulation characteristic curve, was used as the reflector for experimental verification. The theoretical analysis and mathematical modeling of the new structure of optical fiber sensor were also carried out. Then, the tilt angle of the novel structure was optimized by using particle swarm optimization. The results show that the experimental curve obtained by using mirror paper as reflector coincides with the simulation modulation characteristic curve. The feasibility of the mathematical model of the two-circle coaxial optical fiber sensor used to measure the surface topography of the object is proved. The slope angle optimized by particle swarm optimization is 2.33°. At this time, the linear measurement range and sensitivity of the front slope are 1.14 times and 1.89 times respectively when the inclination angle is zero. The novel structure of two-circle coaxial optical fiber sensor shows good measurement performance and application prospects.
2019, 43(3): 329-334.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.008
Abstract:
In order to improve the performance of free space optical/radio frequency(FSO/RF) hybrid communication links, one modulation method combining hybrid low density parity check (LDPC) coding with subcarrier phase shift keying/quadrature amplitude modulation(PSK/QAM) was adopted. Bit error ratio(BER) performance of hybrid systems with different transmission ratios was simulated and analyzed. BER data of single link and mixed link transmission schemes under different channel conditions were obtained. The results show that subcarrier binary phase shift keying (BPSK) modulation used in weak, moderate and strong turbulence can obtain gain about 4.4dB to 5.2dB compared with on-off keying (OOK) modulation. One soft-switching modulation scheme of hybrid LDPC coding and subcarrier BPSK/16QAM is adopted. When the ratio is adjusted to 1:1 and 3:1 according to link state, performance gains about 0.3dB to 7.4dB can be obtained under different turbulence intensities. This research result has important reference value for improving all-weather efficient and reliable transmission performance of FSO/RF hybrid communication systems.
In order to improve the performance of free space optical/radio frequency(FSO/RF) hybrid communication links, one modulation method combining hybrid low density parity check (LDPC) coding with subcarrier phase shift keying/quadrature amplitude modulation(PSK/QAM) was adopted. Bit error ratio(BER) performance of hybrid systems with different transmission ratios was simulated and analyzed. BER data of single link and mixed link transmission schemes under different channel conditions were obtained. The results show that subcarrier binary phase shift keying (BPSK) modulation used in weak, moderate and strong turbulence can obtain gain about 4.4dB to 5.2dB compared with on-off keying (OOK) modulation. One soft-switching modulation scheme of hybrid LDPC coding and subcarrier BPSK/16QAM is adopted. When the ratio is adjusted to 1:1 and 3:1 according to link state, performance gains about 0.3dB to 7.4dB can be obtained under different turbulence intensities. This research result has important reference value for improving all-weather efficient and reliable transmission performance of FSO/RF hybrid communication systems.
2019, 43(3): 335-340.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.009
Abstract:
In order to reduce the guidance error of a satellite/inertial integrated navigation system and improve its navigation and positioning accuracy, a new navigation system scheme combining position sensitive detector (PSD) laser guidance with airborne satellite/inertial integrated navigation system was proposed. In this system, 1064nm infrared pulse laser was used as the guiding light source, and the combination of satellite/inertial navigation in the middle flight segment and laser guidance in the terminal flight segment was adopted. Through theoretical analysis and comparative experiments, the results show that the system always maintains high positioning accuracy and consistent results in the outdoor flight environment and the indoor strong, weak and normal lighting flight environment. Compared with the other existing guidance methods, the detection frequency of the system always remains 5kHz, and the positioning accuracy always keeps its circular error probable at the order of 0.10m. Good positioning experimental results are obtained. The system has the characteristics of strong robustness, simple circuit, flexible detection, high speed and precision. It is of great importance to the terminal guidance of unmanned aerial vehicle.
In order to reduce the guidance error of a satellite/inertial integrated navigation system and improve its navigation and positioning accuracy, a new navigation system scheme combining position sensitive detector (PSD) laser guidance with airborne satellite/inertial integrated navigation system was proposed. In this system, 1064nm infrared pulse laser was used as the guiding light source, and the combination of satellite/inertial navigation in the middle flight segment and laser guidance in the terminal flight segment was adopted. Through theoretical analysis and comparative experiments, the results show that the system always maintains high positioning accuracy and consistent results in the outdoor flight environment and the indoor strong, weak and normal lighting flight environment. Compared with the other existing guidance methods, the detection frequency of the system always remains 5kHz, and the positioning accuracy always keeps its circular error probable at the order of 0.10m. Good positioning experimental results are obtained. The system has the characteristics of strong robustness, simple circuit, flexible detection, high speed and precision. It is of great importance to the terminal guidance of unmanned aerial vehicle.
2019, 43(3): 341-346.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.010
Abstract:
In order to detect and analyze the safety of high voltage transmission lines, based on airborne light detection and rangring(LiDAR) power corridor data, a segmentation and extraction algorithm of power line laser point cloud was proposed based on density-based spatial clustering of applications with noise (DBSCAN). This method can realize fast segmentation and extraction of single power line in transmission corridor. Firstly, the point cloud of power line was projected on the x-O-y plane. The projected laser points were fitted linearly by the least square method. Secondly, after calculating the length of transmission corridor, empirical parameters were used to segment power line point clouds. Then, DBSCAN was applied to segment point clouds in the projection plane. Finally, the classification of segmentation clustering results was normalized and the laser point cloud data of a single power line was obtained. The results show that, with this method, fast and accurate segmentation and extraction of power line laser point cloud can be obtained when the piecewise width of the empirical parameter is only needed. According to the segmentation results, the distance between the power line and the objects in the power corridor is calculated and the type and distance of dangerous points can be judged. By comparing and verifying the experiment with the field measurement results, the proposed method has high extraction and measurement accuracy. It can be effectively applied to power line safety detection and analysis.
In order to detect and analyze the safety of high voltage transmission lines, based on airborne light detection and rangring(LiDAR) power corridor data, a segmentation and extraction algorithm of power line laser point cloud was proposed based on density-based spatial clustering of applications with noise (DBSCAN). This method can realize fast segmentation and extraction of single power line in transmission corridor. Firstly, the point cloud of power line was projected on the x-O-y plane. The projected laser points were fitted linearly by the least square method. Secondly, after calculating the length of transmission corridor, empirical parameters were used to segment power line point clouds. Then, DBSCAN was applied to segment point clouds in the projection plane. Finally, the classification of segmentation clustering results was normalized and the laser point cloud data of a single power line was obtained. The results show that, with this method, fast and accurate segmentation and extraction of power line laser point cloud can be obtained when the piecewise width of the empirical parameter is only needed. According to the segmentation results, the distance between the power line and the objects in the power corridor is calculated and the type and distance of dangerous points can be judged. By comparing and verifying the experiment with the field measurement results, the proposed method has high extraction and measurement accuracy. It can be effectively applied to power line safety detection and analysis.
2019, 43(3): 347-352.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.011
Abstract:
In order to realize a novel microwave photon phase shifter with 360° phase shift, the phase of radio frequency signal was controlled by using a phase modulator, delay line and optical filter to control the phase of carrier and sideband. The phase modulator only needs to control a voltage to adjust the phase shift angle. The effect of drift caused by the use of complex dual-parallel Mach-Zehnder modulator (DPMZM) was reduced. The system had the advantages of simple structure and low cost. The results show that, the microwave photonic phase shifter can achieve full phase shifting from 0°~360° in the frequency range of 0GHz~40GHz. And at the same output phase and under the frequency ranges from 0GHz to 40GHz, the power is basically unchanged. This research has certain reference significance for microwave photonic phase shifter technology.
In order to realize a novel microwave photon phase shifter with 360° phase shift, the phase of radio frequency signal was controlled by using a phase modulator, delay line and optical filter to control the phase of carrier and sideband. The phase modulator only needs to control a voltage to adjust the phase shift angle. The effect of drift caused by the use of complex dual-parallel Mach-Zehnder modulator (DPMZM) was reduced. The system had the advantages of simple structure and low cost. The results show that, the microwave photonic phase shifter can achieve full phase shifting from 0°~360° in the frequency range of 0GHz~40GHz. And at the same output phase and under the frequency ranges from 0GHz to 40GHz, the power is basically unchanged. This research has certain reference significance for microwave photonic phase shifter technology.
2019, 43(3): 353-358.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.012
Abstract:
In order to preliminarily explore the spatial and temporal distribution characteristics of SO2 and NO2 in the atmosphere of Huainan area, one self-developed differential absorption lidar system was used to measure the distribution profiles of SO2 and NO2 concentrations in the atmosphere of a certain Huainan area in some months. The typical examples were selected and the distribution characteristics of SO2 and NO2 were analyzed from three aspects of diurnal variation of horizontal concentration, variation of vertical concentration and monthly variation of horizontal concentration of gases. The results show that, the concentration of SO2 and NO2 at night on the same day was higher than that at afternoon. The vertical concentration of SO2 and NO2 decreased with the increase of altitude. The monthly variation of horizontal concentration of SO2 and NO2 gas is the highest in winter and the lowest in summer, the second in spring and autumn months. The variation of SO2 and NO2 concentration is the result of the interaction of population activities and meteorological conditions.
In order to preliminarily explore the spatial and temporal distribution characteristics of SO2 and NO2 in the atmosphere of Huainan area, one self-developed differential absorption lidar system was used to measure the distribution profiles of SO2 and NO2 concentrations in the atmosphere of a certain Huainan area in some months. The typical examples were selected and the distribution characteristics of SO2 and NO2 were analyzed from three aspects of diurnal variation of horizontal concentration, variation of vertical concentration and monthly variation of horizontal concentration of gases. The results show that, the concentration of SO2 and NO2 at night on the same day was higher than that at afternoon. The vertical concentration of SO2 and NO2 decreased with the increase of altitude. The monthly variation of horizontal concentration of SO2 and NO2 gas is the highest in winter and the lowest in summer, the second in spring and autumn months. The variation of SO2 and NO2 concentration is the result of the interaction of population activities and meteorological conditions.
2019, 43(3): 359-362.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.013
Abstract:
In the traditional Raman spectrum detection process, the effective signal of Raman spectrum is sometimes submerged by the fluorescent background and is difficult to be recognized. In order to separate differential signals and baseline deviations accurately and effectively, combining differential Raman technique with error back propagation algorithm neural network, a differential Raman demodulation and denoising algorithm was proposed. The theoretical and experimental validation was carried out. The fluorescent substances such as paraquat, kidney-tonifying pills, engine oil and heroin were detected and analyzed. The results show that Raman characteristic spectra can be obtained effectively. The study solves the difficult problem of detection in industry application.
In the traditional Raman spectrum detection process, the effective signal of Raman spectrum is sometimes submerged by the fluorescent background and is difficult to be recognized. In order to separate differential signals and baseline deviations accurately and effectively, combining differential Raman technique with error back propagation algorithm neural network, a differential Raman demodulation and denoising algorithm was proposed. The theoretical and experimental validation was carried out. The fluorescent substances such as paraquat, kidney-tonifying pills, engine oil and heroin were detected and analyzed. The results show that Raman characteristic spectra can be obtained effectively. The study solves the difficult problem of detection in industry application.
2019, 43(3): 363-368.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.014
Abstract:
In order to establish a general model for qualitative and quantitative analysis of alcohol gasoline, mid-infrared spectra of methanol gasoline and ethanol gasoline were obtained by using WQF-510A Fourier transform infrared spectrometer and OPUS spectral acquisition software. Principal component (PC) analysis and partial least square (PLS) discrimination were used to identify the alcohol gasoline samples. Band screening was conducted by uninformation variable elimination(UVE). The general model of alcohol gasoline was established based on UVE-PLS and UVE-LSSVM (least square support vector machine) and the data were evaluated. The results show that, the accuracy rate of qualitative discrimination of alcohol gasoline by PC analysis and PLS discrimination is 100%.The general model based on UVE-LSSVM method has the best effect, with root mean square error prediction of 2.187 and decision coefficient of 0.945 respectively. The general model is feasible to identify alcohol gasoline by qualitative and quantitative analysis, which can be used as technical reference and theoretical basis for alcohol gasoline alcohol content detection.
In order to establish a general model for qualitative and quantitative analysis of alcohol gasoline, mid-infrared spectra of methanol gasoline and ethanol gasoline were obtained by using WQF-510A Fourier transform infrared spectrometer and OPUS spectral acquisition software. Principal component (PC) analysis and partial least square (PLS) discrimination were used to identify the alcohol gasoline samples. Band screening was conducted by uninformation variable elimination(UVE). The general model of alcohol gasoline was established based on UVE-PLS and UVE-LSSVM (least square support vector machine) and the data were evaluated. The results show that, the accuracy rate of qualitative discrimination of alcohol gasoline by PC analysis and PLS discrimination is 100%.The general model based on UVE-LSSVM method has the best effect, with root mean square error prediction of 2.187 and decision coefficient of 0.945 respectively. The general model is feasible to identify alcohol gasoline by qualitative and quantitative analysis, which can be used as technical reference and theoretical basis for alcohol gasoline alcohol content detection.
2019, 43(3): 369-373.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.015
Abstract:
In order to improve the quality of glass cut by laser controlled fracture method, the temperature change of material after 6.45μm laser irradiation was studied. The temperature distribution of glass irradiated by 6.45μm laser was calculated by using the continuous laser output power, and the correctness of the model was verified by experiments. Temperature field of glass heated by 6.45μm laser and 10.6μm laser under the same laser parameters was simulated and compared. The smooth and crack-free cutting samples were obtained by experiment. The results show that, the surface temperature of 6.45μm laser is below than that of 10.6μm laser. 6.45μm laser can obtain high quality cutting face by hot cracking. The research is helpful for the modeling and the optimization of mid infrared laser glass cutting.
In order to improve the quality of glass cut by laser controlled fracture method, the temperature change of material after 6.45μm laser irradiation was studied. The temperature distribution of glass irradiated by 6.45μm laser was calculated by using the continuous laser output power, and the correctness of the model was verified by experiments. Temperature field of glass heated by 6.45μm laser and 10.6μm laser under the same laser parameters was simulated and compared. The smooth and crack-free cutting samples were obtained by experiment. The results show that, the surface temperature of 6.45μm laser is below than that of 10.6μm laser. 6.45μm laser can obtain high quality cutting face by hot cracking. The research is helpful for the modeling and the optimization of mid infrared laser glass cutting.
2019, 43(3): 374-379.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.016
Abstract:
When fused quartz substrates are irradiated by high energy laser, the thermal deformation caused by heating would deteriorate the beam quality emitted by the system. In order to study the deterioration of beam quality, COMSOL finite element analysis software was used. The thermal deformation analysis model of fused quartz substrates irradiated by continuous high energy laser was established. The thermal deformations of the substrates under different clamping modes were compared and analyzed. The temperature distribution and deformation distribution of the substrate after heating were obtained. The effect of thermal deformation of fused quartz substrates on beam quality was quantitatively analyzed by VirtualLab software. The results show that, the thermal deformation is the smallest in boundary fixation. The thermal deformation of the substrate will affect the beam quality. The longer the laser irradiation time, the greater the thermal deformation, the greater the impact on the beam quality. When the substrate is irradiated by laser for 20s, the maximum deformation of the substrate of splint fixation is 415.90nm. The beam quality factor is deteriorated from 1.0036 to 1.4571. The maximum deformation of the substrate of boundary fixation is 98.38nm. The beam quality factor is deteriorated from 1.0036 to 1.0064. This result has important guiding significance for the subsequent laser beam combining system construction and beam quality optimization.
When fused quartz substrates are irradiated by high energy laser, the thermal deformation caused by heating would deteriorate the beam quality emitted by the system. In order to study the deterioration of beam quality, COMSOL finite element analysis software was used. The thermal deformation analysis model of fused quartz substrates irradiated by continuous high energy laser was established. The thermal deformations of the substrates under different clamping modes were compared and analyzed. The temperature distribution and deformation distribution of the substrate after heating were obtained. The effect of thermal deformation of fused quartz substrates on beam quality was quantitatively analyzed by VirtualLab software. The results show that, the thermal deformation is the smallest in boundary fixation. The thermal deformation of the substrate will affect the beam quality. The longer the laser irradiation time, the greater the thermal deformation, the greater the impact on the beam quality. When the substrate is irradiated by laser for 20s, the maximum deformation of the substrate of splint fixation is 415.90nm. The beam quality factor is deteriorated from 1.0036 to 1.4571. The maximum deformation of the substrate of boundary fixation is 98.38nm. The beam quality factor is deteriorated from 1.0036 to 1.0064. This result has important guiding significance for the subsequent laser beam combining system construction and beam quality optimization.
2019, 43(3): 380-386.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.017
Abstract:
In order to study effect of defocus on droplet transfer and related characteristics of laser welding with filler wire, and achieve stable droplet transfer mode, a high speed camera system was used to observe droplet transfer under different defocus parameters. Droplet transfer was divided into three kinds:liquid bridge transfer, mixed transfer and drop transfer. The results show that, liquid bridge transfer mode with defocus of -1mm and +3mm could improve the stability of welding process with good quality, such as the weld cross section without porosity. For the drop transfer mode with defocus of +5mm, the welding stability is the worst. During the welding process, keyhole is completely closed, the surface of weld bead is formed irregularly, and the large pores appear at the bottom of the weld corrosion-face. The research results have guiding effect on actual production.
In order to study effect of defocus on droplet transfer and related characteristics of laser welding with filler wire, and achieve stable droplet transfer mode, a high speed camera system was used to observe droplet transfer under different defocus parameters. Droplet transfer was divided into three kinds:liquid bridge transfer, mixed transfer and drop transfer. The results show that, liquid bridge transfer mode with defocus of -1mm and +3mm could improve the stability of welding process with good quality, such as the weld cross section without porosity. For the drop transfer mode with defocus of +5mm, the welding stability is the worst. During the welding process, keyhole is completely closed, the surface of weld bead is formed irregularly, and the large pores appear at the bottom of the weld corrosion-face. The research results have guiding effect on actual production.
2019, 43(3): 387-391.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.018
Abstract:
Resonant frequency of a photoacoustic cell is one of its key parameters. In order to measure resonant frequency of a resonant photoacoustic cell quickly and accurately, a resonant frequency measurement method based on resonant acoustic spectroscopy was used to built a photoacoustic spectroscopy detection system and a resonant acoustic spectroscopy measurement system. The factors affecting the accuracy of measurement results were analyzed. Resonant frequency of the resonant photoacoustic cell was measured by the resonant acoustic spectroscopy method and photoacoustic signal intensity method respectively in the case of different gas concentrations. The experimental results indicate that the resonance frequency measured by the resonant acoustic spectroscopy method is independent of excitation voltage of the sound signal, distance and angle of sound source. Under the conditions of 5 different concentrations of acetylene(C2H2) gas, the maximum deviation of the resonant frequency between the resonance acoustic spectroscopy and photoacoustic signal intensity method is 1.1Hz. It is considered that the measured results of both the methods are consistent. The resonant acoustic spectroscopy method is simple, fast, reliable and accurate. It can be used to determine the resonant frequency of a photoacoustic cell.
Resonant frequency of a photoacoustic cell is one of its key parameters. In order to measure resonant frequency of a resonant photoacoustic cell quickly and accurately, a resonant frequency measurement method based on resonant acoustic spectroscopy was used to built a photoacoustic spectroscopy detection system and a resonant acoustic spectroscopy measurement system. The factors affecting the accuracy of measurement results were analyzed. Resonant frequency of the resonant photoacoustic cell was measured by the resonant acoustic spectroscopy method and photoacoustic signal intensity method respectively in the case of different gas concentrations. The experimental results indicate that the resonance frequency measured by the resonant acoustic spectroscopy method is independent of excitation voltage of the sound signal, distance and angle of sound source. Under the conditions of 5 different concentrations of acetylene(C2H2) gas, the maximum deviation of the resonant frequency between the resonance acoustic spectroscopy and photoacoustic signal intensity method is 1.1Hz. It is considered that the measured results of both the methods are consistent. The resonant acoustic spectroscopy method is simple, fast, reliable and accurate. It can be used to determine the resonant frequency of a photoacoustic cell.
2019, 43(3): 392-396.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.019
Abstract:
In order to reduce cracks in cladding layers caused by large temperature gradient in laser cladding technology, preheated matrix in laser cladding process was used to reduce temperature gradient. The finite element model of multi-lap temperature field of laser cladding nickel-based metal powder on 45# steel substrate was established by using ANSYS software. The reliability of the model was verified by thermocouple temperature measurement. Temperature gradient of cladding layer on the edge of cladding layer during the cladding process and the effect of the preheating temperature of the substrate on temperature gradient of cladding layer were analyzed by the finite element model. The results show that the maximum temperature gradient is located at the edge of the bonding interface between the cladding layer and the substrate. It is an extreme condition for the solidification of the metal molten pool and causes the crack to be easily produced here. With preheating temperature of 200℃, the substrate preheating can significantly reduce the temperature gradient during the solidification process of the cladding layer, and the decrease of the temperature gradient is more obvious, which can effectively inhibit the crack generation. The combination of simulation and experiment provides a practical reference for the actual laser cladding manufacturing.
In order to reduce cracks in cladding layers caused by large temperature gradient in laser cladding technology, preheated matrix in laser cladding process was used to reduce temperature gradient. The finite element model of multi-lap temperature field of laser cladding nickel-based metal powder on 45# steel substrate was established by using ANSYS software. The reliability of the model was verified by thermocouple temperature measurement. Temperature gradient of cladding layer on the edge of cladding layer during the cladding process and the effect of the preheating temperature of the substrate on temperature gradient of cladding layer were analyzed by the finite element model. The results show that the maximum temperature gradient is located at the edge of the bonding interface between the cladding layer and the substrate. It is an extreme condition for the solidification of the metal molten pool and causes the crack to be easily produced here. With preheating temperature of 200℃, the substrate preheating can significantly reduce the temperature gradient during the solidification process of the cladding layer, and the decrease of the temperature gradient is more obvious, which can effectively inhibit the crack generation. The combination of simulation and experiment provides a practical reference for the actual laser cladding manufacturing.
2019, 43(3): 397-400.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.020
Abstract:
In order to study the properties of laser butt welding joint of pure titanium sheet, a welding system consisting of fiber laser and robot was used to carry out the welding test. Effect of defocus on the properties of the joint was evaluated comprehensively by testing the tensile properties, porosity and cupping value of the joint. The microstructure of the joint was revealed. The results show that the tensile and forming properties of the joints are lower than those of the base metal. The defocus has no direct effect on the tensile properties. To a certain extent, the formability of the joint increases with the increase of defocus. When the defocus is +20mm, the joint has the best tensile and forming properties. The microstructures in the weld zone are coarse α grains + serrated α grains + a small amount of acicular α grains. The existence of acicular α grains is beneficial to improve the formability of the joints. The microstructure of heat affecting zone (HAZ) is composed of irregular coarse α grains + serrated α grains. The grain size of HAZ is lower than that of weld zone. This research has certain theoretical guiding significance for laser welding of pure titanium.
In order to study the properties of laser butt welding joint of pure titanium sheet, a welding system consisting of fiber laser and robot was used to carry out the welding test. Effect of defocus on the properties of the joint was evaluated comprehensively by testing the tensile properties, porosity and cupping value of the joint. The microstructure of the joint was revealed. The results show that the tensile and forming properties of the joints are lower than those of the base metal. The defocus has no direct effect on the tensile properties. To a certain extent, the formability of the joint increases with the increase of defocus. When the defocus is +20mm, the joint has the best tensile and forming properties. The microstructures in the weld zone are coarse α grains + serrated α grains + a small amount of acicular α grains. The existence of acicular α grains is beneficial to improve the formability of the joints. The microstructure of heat affecting zone (HAZ) is composed of irregular coarse α grains + serrated α grains. The grain size of HAZ is lower than that of weld zone. This research has certain theoretical guiding significance for laser welding of pure titanium.
2019, 43(3): 401-405.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.021
Abstract:
In order to measure the frequency of microwave signal better, an instantaneous frequency measurement method based on phase modulation and intensity modulation was adopted. A continuous wave light source was divided into two channels by a coupler. Unknown microwave signals passed through both phase modulator and intensity modulator respectively. Accordingly, the carrier was modulated. Then it entered into two long-distance single-mode fibers. Because of the characteristics of microwave power loss caused by dispersion in optical fibers, the mapping relation between frequency and amplitude of monotone change was obtained. Then the amplitude comparison function was obtained by output power ratio of microwave signal detected by photoelectric method. In addition, the range and accuracy of frequency measurement were optimized. The results show that, the structure of the scheme is simple. It can measure the frequency of unknown signal quickly and accurately. The measurement range can reach 0.5GHz~53GHz. The measurement error is less than ±200MHz. This method can effectively measure the frequency of microwave signal and has strong reliability and wide application range.
In order to measure the frequency of microwave signal better, an instantaneous frequency measurement method based on phase modulation and intensity modulation was adopted. A continuous wave light source was divided into two channels by a coupler. Unknown microwave signals passed through both phase modulator and intensity modulator respectively. Accordingly, the carrier was modulated. Then it entered into two long-distance single-mode fibers. Because of the characteristics of microwave power loss caused by dispersion in optical fibers, the mapping relation between frequency and amplitude of monotone change was obtained. Then the amplitude comparison function was obtained by output power ratio of microwave signal detected by photoelectric method. In addition, the range and accuracy of frequency measurement were optimized. The results show that, the structure of the scheme is simple. It can measure the frequency of unknown signal quickly and accurately. The measurement range can reach 0.5GHz~53GHz. The measurement error is less than ±200MHz. This method can effectively measure the frequency of microwave signal and has strong reliability and wide application range.
2019, 43(3): 406-410.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.022
Abstract:
In order to know effect of bandwidth on the focused properties and focal shift of Hermite-Gaussian (H-G) beam, propagation formula of H-G beams passing through a dispersion lens system with polychromatic TEM11 mode and TEM22 mode was obtained by using diffraction integral. The focused intensity distribution was studied by numerical calculation. The effect of bandwidth on focal shift of both modes were analyzed. The results show that the focal shifts of H-G beams with TEM11 mode and TEM22 mode increase with the increase of the bandwidth and depend on the relative bandwidth. Focal shift of TEM22 mode is greater than that of TEM11 mode when relative bandwidth is smaller than 0.25 whereas the latter is somewhat greater than the former when relative bandwidth exceeds 0.25. The principle maximum intensity and the secondary maximum intensity of TEM22 mode on the axis compete each other with the vary of bandwidth and then the axial primary maximum intensity transits from one place to another. The results are helpful for further application of the polychromatic H-G beams.
In order to know effect of bandwidth on the focused properties and focal shift of Hermite-Gaussian (H-G) beam, propagation formula of H-G beams passing through a dispersion lens system with polychromatic TEM11 mode and TEM22 mode was obtained by using diffraction integral. The focused intensity distribution was studied by numerical calculation. The effect of bandwidth on focal shift of both modes were analyzed. The results show that the focal shifts of H-G beams with TEM11 mode and TEM22 mode increase with the increase of the bandwidth and depend on the relative bandwidth. Focal shift of TEM22 mode is greater than that of TEM11 mode when relative bandwidth is smaller than 0.25 whereas the latter is somewhat greater than the former when relative bandwidth exceeds 0.25. The principle maximum intensity and the secondary maximum intensity of TEM22 mode on the axis compete each other with the vary of bandwidth and then the axial primary maximum intensity transits from one place to another. The results are helpful for further application of the polychromatic H-G beams.
2019, 43(3): 411-416.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.023
Abstract:
Additive manufacturing (3-D printing) is a near-net forming technology. It provides a new way for manufacturing high quality blanks of thin-wall titanium alloy parts. However, in the forming process of thin-wall parts, deformation and residual stress will affect forming quality and subsequent processing of the specimens. In order to solve this problem, TC4 titanium alloy thin-wall parts were formed by selective laser melting. The effects of laser power, scanning speed, thickness of thin-wall and direction of scanning path on deformation and residual stress of specimens were studied. Surface residual stresses at different depths were measured. The results show that deformation occurs mainly on both sides of the top layer of thin-wall parts. The maximum residual stress is mainly distributed in the bottom and the middle of thin walls. With laser power of 180W and scanning speed of 1200mm/s, the deformation of specimen is the smallest. With wall thickness of 0.6mm and scanning path direction of 45°, residual stress of the specimen is the smallest. Residual stress of the untreated surface of thin-walled parts is larger than that of the inner surface. This research provides technical assistance for the manufacture of high quality thin-wall titanium alloy blanks.
Additive manufacturing (3-D printing) is a near-net forming technology. It provides a new way for manufacturing high quality blanks of thin-wall titanium alloy parts. However, in the forming process of thin-wall parts, deformation and residual stress will affect forming quality and subsequent processing of the specimens. In order to solve this problem, TC4 titanium alloy thin-wall parts were formed by selective laser melting. The effects of laser power, scanning speed, thickness of thin-wall and direction of scanning path on deformation and residual stress of specimens were studied. Surface residual stresses at different depths were measured. The results show that deformation occurs mainly on both sides of the top layer of thin-wall parts. The maximum residual stress is mainly distributed in the bottom and the middle of thin walls. With laser power of 180W and scanning speed of 1200mm/s, the deformation of specimen is the smallest. With wall thickness of 0.6mm and scanning path direction of 45°, residual stress of the specimen is the smallest. Residual stress of the untreated surface of thin-walled parts is larger than that of the inner surface. This research provides technical assistance for the manufacture of high quality thin-wall titanium alloy blanks.
2019, 43(3): 417-420.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.024
Abstract:
In order to analyze and study the influence of laser focusing position on photoasound signal of gold nanoparticles, ultrasound detectors were used to detect ultrasound and the state of solution was observed by CCD. The results show that, when the laser pulse is focused in the middle of the colorimeter, the photoacoustic signal is the ultrasonic signal of gold nanoparticles suspended in solution under the action of laser. When the laser is focused on the interface between the inner wall of the colorimetric dish and the solution, the photoacoustic signal duration of gold nanoparticles increases and becomes disordered. In this case, if the ultrasonic signal oscillates periodically, the solution of gold nanoparticles starts from the laser focus and flows at high speed along the laser direction. This research has certain reference significance for opening up a new research field of microfluidics.
In order to analyze and study the influence of laser focusing position on photoasound signal of gold nanoparticles, ultrasound detectors were used to detect ultrasound and the state of solution was observed by CCD. The results show that, when the laser pulse is focused in the middle of the colorimeter, the photoacoustic signal is the ultrasonic signal of gold nanoparticles suspended in solution under the action of laser. When the laser is focused on the interface between the inner wall of the colorimetric dish and the solution, the photoacoustic signal duration of gold nanoparticles increases and becomes disordered. In this case, if the ultrasonic signal oscillates periodically, the solution of gold nanoparticles starts from the laser focus and flows at high speed along the laser direction. This research has certain reference significance for opening up a new research field of microfluidics.
2019, 43(3): 421-426.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.025
Abstract:
In order to study the important relationship between combining efficiency and reflectivity of dichroic mirrors, rough surface reflection model of multilayer coatings was established. Reflective curves of high-steepness dichroic mirrors for spectral beam combining were calculated and analyzed. Simulation results of combining efficiency were obtained by combining the spectral curves of fiber lasers. The relationship between the surface shape of dichroic mirrors with different angles and reflectivity and combining efficiency were analyzed. The stability of the beam combining system based on dichroic mirrors was simulated and discussed. The results show that, output power of more than 10kW can be obtained by using a small angle dichroic mirror, and combining efficiency can reach 97%. This result is helpful for the improvement of the parameters of dichroic mirrors.
In order to study the important relationship between combining efficiency and reflectivity of dichroic mirrors, rough surface reflection model of multilayer coatings was established. Reflective curves of high-steepness dichroic mirrors for spectral beam combining were calculated and analyzed. Simulation results of combining efficiency were obtained by combining the spectral curves of fiber lasers. The relationship between the surface shape of dichroic mirrors with different angles and reflectivity and combining efficiency were analyzed. The stability of the beam combining system based on dichroic mirrors was simulated and discussed. The results show that, output power of more than 10kW can be obtained by using a small angle dichroic mirror, and combining efficiency can reach 97%. This result is helpful for the improvement of the parameters of dichroic mirrors.
2019, 43(3): 427-431.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.026
Abstract:
In order to compare and analyze the enhancement effect of surface-enhanced Raman spectroscopy (SERS) by two substrates of TiO2-AgNPs thin film and silver sol nanoparticles solution on the samples of traditional Chinese medicine solution, aconite solution was selected as the experimental sample and surface enhancement Raman spectra of two substrates were obtained after Raman scattering experiment. The analytical comparison was made. The results show that, Raman scattering spectra of aconite solution are enhanced by two SERS substrates of TiO2-AgNPs film and silver sol nanoparticle solution. The enhancement effect 1398cm-1 of TiO2-AgNPs thin film is more sensitive than that of silver sol nanoparticles. For example, relative peak-to-intensity ratio at Raman shift of TiO2-AgNPs thin film is 27.85% and that of silver sol nanoparticle solution is 11.97%. However, TiO2-AgNPs thin film has disadvantages of easy oxidation, short usage time, difficult preparation and low repeatability. Therefore, it is more suitable for the accurate identification of sample components. Silver sol nanoparticle solution has advantages of simpler preparation, longer use time, good stability and repeatability. It is suitable for the determination and comparison of a large number of samples. The results can be used as the reference for the selection of substrate for analysis of active ingredients in traditional Chinese medicine by SERS technology at home and abroad.
In order to compare and analyze the enhancement effect of surface-enhanced Raman spectroscopy (SERS) by two substrates of TiO2-AgNPs thin film and silver sol nanoparticles solution on the samples of traditional Chinese medicine solution, aconite solution was selected as the experimental sample and surface enhancement Raman spectra of two substrates were obtained after Raman scattering experiment. The analytical comparison was made. The results show that, Raman scattering spectra of aconite solution are enhanced by two SERS substrates of TiO2-AgNPs film and silver sol nanoparticle solution. The enhancement effect 1398cm-1 of TiO2-AgNPs thin film is more sensitive than that of silver sol nanoparticles. For example, relative peak-to-intensity ratio at Raman shift of TiO2-AgNPs thin film is 27.85% and that of silver sol nanoparticle solution is 11.97%. However, TiO2-AgNPs thin film has disadvantages of easy oxidation, short usage time, difficult preparation and low repeatability. Therefore, it is more suitable for the accurate identification of sample components. Silver sol nanoparticle solution has advantages of simpler preparation, longer use time, good stability and repeatability. It is suitable for the determination and comparison of a large number of samples. The results can be used as the reference for the selection of substrate for analysis of active ingredients in traditional Chinese medicine by SERS technology at home and abroad.
2019, 43(3): 432-436.
doi: 10.7510/jgjs.issn.1001-3806.2019.03.027
Abstract:
In order to study the propagation characteristics of non-diffracting light waves in special materials and achieve better optical communication, one periodic circular dielectric structure with axial step change was proposed by combining traditional right-handed materials with bi-negative refractive index materials. Based on the generalized Huygens-Fresnel optical integral formula, the distribution characteristics of the emitted surface light intensity and the profile of the side light intensity of the Airy beam in this transmission medium were analyzed by using optical transmission matrix. The influence of negative refractive index parameters on the evolution of such light waves and its compensation mechanism were analyzed. The quantitative relationship between the negative refractive index and the length of the dielectric unit was analyzed when the output light wave was perfectly restored. The results show that, when the pore size of the medium decreases gradually, the diffraction effect of finite Airy beam is getting worse and worse. The profile of the emitted light intensity gradually transits from the Airy beam to the Gaussian beam. When the absolute value of nl is greater than nr, the bi-negative refractive index material layer is longer when the perfect light wave reduction is achieved on the exit surface. Conversely, the shorter. The study is helpful for analyzing optical wave communication in circular flat dielectrics with periodic or quasi-periodic axial step changes.
In order to study the propagation characteristics of non-diffracting light waves in special materials and achieve better optical communication, one periodic circular dielectric structure with axial step change was proposed by combining traditional right-handed materials with bi-negative refractive index materials. Based on the generalized Huygens-Fresnel optical integral formula, the distribution characteristics of the emitted surface light intensity and the profile of the side light intensity of the Airy beam in this transmission medium were analyzed by using optical transmission matrix. The influence of negative refractive index parameters on the evolution of such light waves and its compensation mechanism were analyzed. The quantitative relationship between the negative refractive index and the length of the dielectric unit was analyzed when the output light wave was perfectly restored. The results show that, when the pore size of the medium decreases gradually, the diffraction effect of finite Airy beam is getting worse and worse. The profile of the emitted light intensity gradually transits from the Airy beam to the Gaussian beam. When the absolute value of nl is greater than nr, the bi-negative refractive index material layer is longer when the perfect light wave reduction is achieved on the exit surface. Conversely, the shorter. The study is helpful for analyzing optical wave communication in circular flat dielectrics with periodic or quasi-periodic axial step changes.
