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RSS2019 Vol. 43, No. 2
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2019, 43(2): 147-153.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.001
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Abstract:
In order to study high efficiency welding of carbon fiber reinforced thermo-plastic (CFRTP) and metal, the experiment on the connection of CFRTP and Al was carried out by laser-induced Al-Ti-C powder interlayer self-propagating reaction.Reaction mechanism of weld formation in the interlayer self-propagating reaction, microscopic interface and the formation mechanism of CFRTP/Al joint were analyzed.The results show that, the self-propagating reaction starts when the temperature of the interlayer increases to approximately 933K by laser irradiation.The aluminum element melts and entraps the solid Ti to react to form a Ti-Al compound.At high temperatures, the compound continues to react with Ti to form TiC.It also releases heat.At the same time, elemental Ti and C react to generate TiC and release heat.The heat generated by the reaction continues to maintain the reaction of the next layer until the entire interlayer reaction ends to form a good "weld".These heat makes that the left and right sides of the interlayer of the base material are slightly melted and re-extruded to form a good quality joint.Laser-induced Al-Ti-C interlayer self-propagating high-temperature synthesis connection can realize the high quality connection of CFRTP/Al, which is helpful to realize the lightweight of the vehicle structure.
In order to study high efficiency welding of carbon fiber reinforced thermo-plastic (CFRTP) and metal, the experiment on the connection of CFRTP and Al was carried out by laser-induced Al-Ti-C powder interlayer self-propagating reaction.Reaction mechanism of weld formation in the interlayer self-propagating reaction, microscopic interface and the formation mechanism of CFRTP/Al joint were analyzed.The results show that, the self-propagating reaction starts when the temperature of the interlayer increases to approximately 933K by laser irradiation.The aluminum element melts and entraps the solid Ti to react to form a Ti-Al compound.At high temperatures, the compound continues to react with Ti to form TiC.It also releases heat.At the same time, elemental Ti and C react to generate TiC and release heat.The heat generated by the reaction continues to maintain the reaction of the next layer until the entire interlayer reaction ends to form a good "weld".These heat makes that the left and right sides of the interlayer of the base material are slightly melted and re-extruded to form a good quality joint.Laser-induced Al-Ti-C interlayer self-propagating high-temperature synthesis connection can realize the high quality connection of CFRTP/Al, which is helpful to realize the lightweight of the vehicle structure.
2019, 43(2): 154-160.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.002
Abstract:
In order to improve coating defects such as porosity, crack and poor bonding with substrate during laser deposition, Fe106+nickel-coated tungsten carbide (mass fraction of 0.05) composite coating was prepared on 304 austenitic stainless steel by the method of laser deposition assisted by rotating magnetic field.The microstructures and phase composition of the coating were analyzed by means of scanning electron microscope, X-ray diffraction and confocal laser scanning microscope.The wear resistance of the coating was studied by means of hardness tester and friction wear tester.The results indicate that the rotating magnetic field can inhibit the flow of molten pool and promote the fine grain strengthening and homogenization of the coating microstructure.The microhardness of the coating with magnetic field strength of 70mT is 1.16 times that without magnetic field strength.Under the same wear condition, the weight loss of the coating with magnetic field strength of 70mT is 64.2% lower than that of the coating without magnetic field.The wear resistance is obviously improved.laser deposition assisted by magnetic field is helpful to improve laser deposition defects.
In order to improve coating defects such as porosity, crack and poor bonding with substrate during laser deposition, Fe106+nickel-coated tungsten carbide (mass fraction of 0.05) composite coating was prepared on 304 austenitic stainless steel by the method of laser deposition assisted by rotating magnetic field.The microstructures and phase composition of the coating were analyzed by means of scanning electron microscope, X-ray diffraction and confocal laser scanning microscope.The wear resistance of the coating was studied by means of hardness tester and friction wear tester.The results indicate that the rotating magnetic field can inhibit the flow of molten pool and promote the fine grain strengthening and homogenization of the coating microstructure.The microhardness of the coating with magnetic field strength of 70mT is 1.16 times that without magnetic field strength.Under the same wear condition, the weight loss of the coating with magnetic field strength of 70mT is 64.2% lower than that of the coating without magnetic field.The wear resistance is obviously improved.laser deposition assisted by magnetic field is helpful to improve laser deposition defects.
2019, 43(2): 161-167.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.003
Abstract:
In order to study residual stress distribution characteristics of TC17 dual phase titanium alloy by one-side and two-side laser shock peening (LSP), numerical simulation was taken to analyze the residual stress distribution rules under one-side and two-side LSP.The results show that after the stabilization of one-side impact, tensile stress is generated on the opposite surface of the impact and compressive stress is generated on the impact surface.For two-side simultaneous LSP, part of the residual compressive stress is used to offset the tensile stress, and the superposition and weakening of the stress wave leads to the reduction of the residual stress level at the same time.The maximum residual stress in the x direction and y direction obtained by one-side LSP is 336.709MPa and 337.011MPa, while it is 326.401MPa for two-side simultaneous LSP in both directions.One-side LSP is unfavorable for suppressing the crack due to the caused tensile stress.The residual stress distribution on both sides of the specimen is almost the same for two-side simultaneous LSP.The residual stress of the first impact surface is higher than that of the second impact surface after two-side successive LSP.The influence of transverse propagation of shock wave on residual stress should be considered for finite specimens.The result would be a certain guidance for study on residual stress distribution rules by one-side and two-side LSP.
In order to study residual stress distribution characteristics of TC17 dual phase titanium alloy by one-side and two-side laser shock peening (LSP), numerical simulation was taken to analyze the residual stress distribution rules under one-side and two-side LSP.The results show that after the stabilization of one-side impact, tensile stress is generated on the opposite surface of the impact and compressive stress is generated on the impact surface.For two-side simultaneous LSP, part of the residual compressive stress is used to offset the tensile stress, and the superposition and weakening of the stress wave leads to the reduction of the residual stress level at the same time.The maximum residual stress in the x direction and y direction obtained by one-side LSP is 336.709MPa and 337.011MPa, while it is 326.401MPa for two-side simultaneous LSP in both directions.One-side LSP is unfavorable for suppressing the crack due to the caused tensile stress.The residual stress distribution on both sides of the specimen is almost the same for two-side simultaneous LSP.The residual stress of the first impact surface is higher than that of the second impact surface after two-side successive LSP.The influence of transverse propagation of shock wave on residual stress should be considered for finite specimens.The result would be a certain guidance for study on residual stress distribution rules by one-side and two-side LSP.
2019, 43(2): 168-173.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.004
Abstract:
In order to study the feasibility of applying laser technology to remove rust from collector rings of high-speed train, according to the effect of laser rust removal and cleaning efficiency, the optimal laser cleaning parameters of collector ring were determined.Overlap ratio of laser spot on the whole surface is 29.3%, laser power was 16W, laser repetition frequency was 70kHz and laser scanning speed was 1.0m/s.The optimal process parameters were used to remove rust from the collector ring samples.The surface microstructure of the original sample and the sample after laser rust removal were observed by scanning electron microscope and metallographic microscope.The surface hardness and surface mechanical properties of the original sample and the sample after laser rust removal were analyzed and compared by a new experimental analysis method.The resistivity of samples before and after laser cleaning was measured by LINSES resistivity tester at room temperature.The results show that there is no remelting and phase transformation on the surface of samples after laser derusting.The surface hardness and surface mechanical properties of the original sample and the laser rust removal sample don't change significantly.Due to the increase of surface roughness and lattice distortion of some crystal lattice, the probability of electron scattering increases and resistivity increases by 8.3%.But they still conform to the specifications.Laser derusting technology has no significant effect on the surface performance of collector ring substrate.The technology is suitable for surface rust removal on the collector rings of high-speed trains.
In order to study the feasibility of applying laser technology to remove rust from collector rings of high-speed train, according to the effect of laser rust removal and cleaning efficiency, the optimal laser cleaning parameters of collector ring were determined.Overlap ratio of laser spot on the whole surface is 29.3%, laser power was 16W, laser repetition frequency was 70kHz and laser scanning speed was 1.0m/s.The optimal process parameters were used to remove rust from the collector ring samples.The surface microstructure of the original sample and the sample after laser rust removal were observed by scanning electron microscope and metallographic microscope.The surface hardness and surface mechanical properties of the original sample and the sample after laser rust removal were analyzed and compared by a new experimental analysis method.The resistivity of samples before and after laser cleaning was measured by LINSES resistivity tester at room temperature.The results show that there is no remelting and phase transformation on the surface of samples after laser derusting.The surface hardness and surface mechanical properties of the original sample and the laser rust removal sample don't change significantly.Due to the increase of surface roughness and lattice distortion of some crystal lattice, the probability of electron scattering increases and resistivity increases by 8.3%.But they still conform to the specifications.Laser derusting technology has no significant effect on the surface performance of collector ring substrate.The technology is suitable for surface rust removal on the collector rings of high-speed trains.
2019, 43(2): 174-178.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.005
Abstract:
In order to optimize the performance of vertical cavity semiconductor optical amplifiers (VCSOA) in different applications and obtain accurate reflectivity with the general calculation method, considering the characteristics of light field distribution inside the device, the equivalent reflectivity of the distributed Bragg reflector (DBR) and the full width at half maximum of the beam in the device were obtained by using angular spectrum theory and transmission matrix method.The theoretical analysis and experimental verification were carried out.The results show that the equivalent reflectivity increases with the increase of structure period.However, when the period is greater than 25, it will not change any more.Compared with the case of normal incidence only, the revised equivalent reflectivity of DBR is less 2%~4%.Equivalent reflectance decreases with the increase of full width at half maximum θFWHM.The study provides theoretical guidance for accurately calculating the effect of stack number on equivalent reflectivity of DBR and optimizing the performance of VCSOA.
In order to optimize the performance of vertical cavity semiconductor optical amplifiers (VCSOA) in different applications and obtain accurate reflectivity with the general calculation method, considering the characteristics of light field distribution inside the device, the equivalent reflectivity of the distributed Bragg reflector (DBR) and the full width at half maximum of the beam in the device were obtained by using angular spectrum theory and transmission matrix method.The theoretical analysis and experimental verification were carried out.The results show that the equivalent reflectivity increases with the increase of structure period.However, when the period is greater than 25, it will not change any more.Compared with the case of normal incidence only, the revised equivalent reflectivity of DBR is less 2%~4%.Equivalent reflectance decreases with the increase of full width at half maximum θFWHM.The study provides theoretical guidance for accurately calculating the effect of stack number on equivalent reflectivity of DBR and optimizing the performance of VCSOA.
2019, 43(2): 179-183.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.006
Abstract:
In order to explore a controllable, stable and efficient method for preparing carbon nanohorns, Nd:YAG laser with high power and short pulse was used to irradiate natural flake graphite particles suspended in liquid medium.The experimental products were characterized by high resolution transmission electron microscopy and laser Raman spectroscopy.The experimental results were analyzed theoretically and experimentally.The results show that, when laser energy is 150mJ, 300mJ, 450mJ and 600mJ, the corresponding products are carbon nanohorns of seed type, bud type, dahlia type and petal-dahlia type respectively.The particle sizes of the four kinds of carbon nanohorns are all distributed in the range of 10nm to 80nm with average sizes of 29nm, 33nm, 36nm and 38nm, respectively.This study is helpful to prepare different forms of carbon nanohorn materials.
In order to explore a controllable, stable and efficient method for preparing carbon nanohorns, Nd:YAG laser with high power and short pulse was used to irradiate natural flake graphite particles suspended in liquid medium.The experimental products were characterized by high resolution transmission electron microscopy and laser Raman spectroscopy.The experimental results were analyzed theoretically and experimentally.The results show that, when laser energy is 150mJ, 300mJ, 450mJ and 600mJ, the corresponding products are carbon nanohorns of seed type, bud type, dahlia type and petal-dahlia type respectively.The particle sizes of the four kinds of carbon nanohorns are all distributed in the range of 10nm to 80nm with average sizes of 29nm, 33nm, 36nm and 38nm, respectively.This study is helpful to prepare different forms of carbon nanohorn materials.
Realization of single polarization output and high light extraction efficiency of GaN based blue LED
2019, 43(2): 184-188.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.007
Abstract:
In order to improve light extraction efficiency of a flip-chip light-emitting diode (LED) and realize single polarization light output, three models of normal, flip-chip and integrated metal sub-wavelength grating flip-chip LED were established.RSOFT software was used to simulate and optimize the device, and theoretical analysis and simulation verification were carried out.The results show that, flip-chip LED can improve the light extraction efficiency, but it is very sensitive to the thickness of P-GaN layer and can not output single polarized light.Flip-chip LED integrated with metal sub-wavelength grating can achieve single polarized light output without the influence of P-GaN layer thickness; this kind of LED can output stable polarized light, but it is heavily affected by grating parameters and thickness of transition layer.The thickness of transition layer and parameters are very significant.By optimizing the structure, the extraction efficiency can reach 57.63% and the polarization extinction ratio can reach 25.8dB.The research has some guidance for manufacturing blue ray LED with high performance.
In order to improve light extraction efficiency of a flip-chip light-emitting diode (LED) and realize single polarization light output, three models of normal, flip-chip and integrated metal sub-wavelength grating flip-chip LED were established.RSOFT software was used to simulate and optimize the device, and theoretical analysis and simulation verification were carried out.The results show that, flip-chip LED can improve the light extraction efficiency, but it is very sensitive to the thickness of P-GaN layer and can not output single polarized light.Flip-chip LED integrated with metal sub-wavelength grating can achieve single polarized light output without the influence of P-GaN layer thickness; this kind of LED can output stable polarized light, but it is heavily affected by grating parameters and thickness of transition layer.The thickness of transition layer and parameters are very significant.By optimizing the structure, the extraction efficiency can reach 57.63% and the polarization extinction ratio can reach 25.8dB.The research has some guidance for manufacturing blue ray LED with high performance.
2019, 43(2): 189-194.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.008
Abstract:
In order to ensure the enough welding strength and durability of the ship in seawater environment, 5083-O aluminum alloy was used to simulate the corrosion resistance of welded joints in seawater.The effects of laser power, welding current and wire spacing on the corrosion resistance of aluminum alloy welded joints were studied by using the highly adaptable laser-melting inert gas (MIG) shielded welding hybrid welding system.The results show that, the self-corrosion current density increases first, then decreases and then increases with the increase of laser power, and varies in the V-shape with the increase of welding current and wire spacing, that is, it decreases first and then increases.When laser power is 3.0kW, welding current is 200A and wire spacing is 3mm, the microstructures of the joint are mainly equiaxed grains, and the defects such as pores are few.At the same time, the micro-blocking galvanic cell effect of the joint is weak, the self-corrosion current density is minimum, and the corrosion resistance of the joint is relatively good.This study is helpful to understand the defect formation mechanism and improve the corrosion resistance of aluminum alloy welded joints.
In order to ensure the enough welding strength and durability of the ship in seawater environment, 5083-O aluminum alloy was used to simulate the corrosion resistance of welded joints in seawater.The effects of laser power, welding current and wire spacing on the corrosion resistance of aluminum alloy welded joints were studied by using the highly adaptable laser-melting inert gas (MIG) shielded welding hybrid welding system.The results show that, the self-corrosion current density increases first, then decreases and then increases with the increase of laser power, and varies in the V-shape with the increase of welding current and wire spacing, that is, it decreases first and then increases.When laser power is 3.0kW, welding current is 200A and wire spacing is 3mm, the microstructures of the joint are mainly equiaxed grains, and the defects such as pores are few.At the same time, the micro-blocking galvanic cell effect of the joint is weak, the self-corrosion current density is minimum, and the corrosion resistance of the joint is relatively good.This study is helpful to understand the defect formation mechanism and improve the corrosion resistance of aluminum alloy welded joints.
2019, 43(2): 195-200.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.009
Abstract:
In order to study effect of laser sources with different linewidthes on positioning accuracy of Mach-Zehnder fiber interferometers, a set of disturbance location system was built using the principle of mutual-correlation positioning algorithm.3kHz and 1MHz semiconductor lasers were used as system output light sources respectively, and were subjected to multiple fixed-point disturbances.The experimental data were calculated according to the principle of mutual correlation, and the results were compared and analyzed.The results show that, in the case of time domain sampling rate of 100MHz, average positioning error of 3kHz laser is 34.4m, far less than positioning error of 225.4m for 1MHz light source.The method of using 3m single-mode fiber in the signal arm of the interferometer to make the signal arm and the reference arm basically the same length, largely suppresses the common-mode noise of the system.Narrow linewidth laser can improve the positioning accuracy of the system.The study has positive significance for the selection of interferometer lasers and the evaluation of system performance parameters.
In order to study effect of laser sources with different linewidthes on positioning accuracy of Mach-Zehnder fiber interferometers, a set of disturbance location system was built using the principle of mutual-correlation positioning algorithm.3kHz and 1MHz semiconductor lasers were used as system output light sources respectively, and were subjected to multiple fixed-point disturbances.The experimental data were calculated according to the principle of mutual correlation, and the results were compared and analyzed.The results show that, in the case of time domain sampling rate of 100MHz, average positioning error of 3kHz laser is 34.4m, far less than positioning error of 225.4m for 1MHz light source.The method of using 3m single-mode fiber in the signal arm of the interferometer to make the signal arm and the reference arm basically the same length, largely suppresses the common-mode noise of the system.Narrow linewidth laser can improve the positioning accuracy of the system.The study has positive significance for the selection of interferometer lasers and the evaluation of system performance parameters.
2019, 43(2): 201-204.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.010
Abstract:
In order to study effect of laser scanning speed on the properties of final cladding layer in laser cladding repair process, Ni-based alloy cladding samples were prepared on QT500 nodular cast iron by laser cladding at different scanning speeds under the condition of synchronous powder feeding.The metallographic microscope of the cladding layer was observed by metallographic microscope, and the microhardness of the cladding layer was measured and analyzed by means of microhardness tester.The hardness, microstructure and sample dilution ratio of the cladding samples were obtained.The results show that the microstructure and properties of the cladding layer would be better with the increase of the laser scanning speed.The microstructure of the cladding layer is more compact and the average microhardness of the uniform cladding layer is improved significantly with the increase of the laser scanning speed.The optimal parameters are laser power of 1.9kW, scanning speed of 5mm/s, and the diameter of the spot of 4mm.The study provides the theoretical basis for reasonable selection of process parameters in laser cladding surface strengthening process.
In order to study effect of laser scanning speed on the properties of final cladding layer in laser cladding repair process, Ni-based alloy cladding samples were prepared on QT500 nodular cast iron by laser cladding at different scanning speeds under the condition of synchronous powder feeding.The metallographic microscope of the cladding layer was observed by metallographic microscope, and the microhardness of the cladding layer was measured and analyzed by means of microhardness tester.The hardness, microstructure and sample dilution ratio of the cladding samples were obtained.The results show that the microstructure and properties of the cladding layer would be better with the increase of the laser scanning speed.The microstructure of the cladding layer is more compact and the average microhardness of the uniform cladding layer is improved significantly with the increase of the laser scanning speed.The optimal parameters are laser power of 1.9kW, scanning speed of 5mm/s, and the diameter of the spot of 4mm.The study provides the theoretical basis for reasonable selection of process parameters in laser cladding surface strengthening process.
2019, 43(2): 205-211.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.011
Abstract:
Compared with femtosecond laser pulses in the near-infrared region, femtosecond pulses in the ultraviolet region have the advantages of high single-photon energy, good focusing property, high ionization rate and low filament threshold value.It has broad application prospects in the production of high power density optical field and the field of plasma photophysics.Femtosecond pulses in the ultraviolet region have become a hot spot of laser technology.With the development of ultraviolet femtosecond laser technology, the traditional pulse width measurement method cannot meet the demand.The main advances in the study on pulse width measurement of ultraviolet femtosecond lasers are pointed out.The measurement methods currently available for ultraviolet (UV) femtosecond laser pulse width are discussed, mainly including two-photon fluorescence measurement, cross-correlation method, degenerate four-wave mixing method, multiphoton ionization method.The relevant easurement principles and characteristics are introduced.Based on the research, the research prospects of the ultraviolet femtosecond laser pulse width measurement technology are prospected.
Compared with femtosecond laser pulses in the near-infrared region, femtosecond pulses in the ultraviolet region have the advantages of high single-photon energy, good focusing property, high ionization rate and low filament threshold value.It has broad application prospects in the production of high power density optical field and the field of plasma photophysics.Femtosecond pulses in the ultraviolet region have become a hot spot of laser technology.With the development of ultraviolet femtosecond laser technology, the traditional pulse width measurement method cannot meet the demand.The main advances in the study on pulse width measurement of ultraviolet femtosecond lasers are pointed out.The measurement methods currently available for ultraviolet (UV) femtosecond laser pulse width are discussed, mainly including two-photon fluorescence measurement, cross-correlation method, degenerate four-wave mixing method, multiphoton ionization method.The relevant easurement principles and characteristics are introduced.Based on the research, the research prospects of the ultraviolet femtosecond laser pulse width measurement technology are prospected.
2019, 43(2): 212-216.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.012
Abstract:
In order to study effect of defocus amount on the weld formation, the microstructure characteristics and properties of 5mm thick laser welding copper, metallographic microscope was used to analyze the microstructure and morphology of the weld.The tensile strength and electrical conductivity of the joint were tested.The results show that, when the absolute value of defocus is high, it is easy to spatter and cause holes on the weld surface.A well-formed weld can be obtained within the defocus range of 0mm~-2mm.The angle between the columnar crystal and the welding direction of the longitudinal section of the weld is gradually reduced from 90°on the sides to 0°in the middle.The columnar crystal near the upper surface of the weld is about 2.96 times the length of the columnar crystal near the bottom surface.The grain size of heat affected zone coarsen.And the width of heat affected zone corresponding to defocus+1mm is the largest.Under the penetration condition, the tensile strength of the joints corresponding to the different defocus amounts is equal, up to 77.3% of base metal.The joint elongation with defocus 0mm~-1mm is slightly higher than that with defocus-1mm~-4mm, up to 54.9% of base metal.The electrical conductivity of the weld is almost the same as that of the base metal.The study is beneficial to obtain good shaped laser welded joints of copper.
In order to study effect of defocus amount on the weld formation, the microstructure characteristics and properties of 5mm thick laser welding copper, metallographic microscope was used to analyze the microstructure and morphology of the weld.The tensile strength and electrical conductivity of the joint were tested.The results show that, when the absolute value of defocus is high, it is easy to spatter and cause holes on the weld surface.A well-formed weld can be obtained within the defocus range of 0mm~-2mm.The angle between the columnar crystal and the welding direction of the longitudinal section of the weld is gradually reduced from 90°on the sides to 0°in the middle.The columnar crystal near the upper surface of the weld is about 2.96 times the length of the columnar crystal near the bottom surface.The grain size of heat affected zone coarsen.And the width of heat affected zone corresponding to defocus+1mm is the largest.Under the penetration condition, the tensile strength of the joints corresponding to the different defocus amounts is equal, up to 77.3% of base metal.The joint elongation with defocus 0mm~-1mm is slightly higher than that with defocus-1mm~-4mm, up to 54.9% of base metal.The electrical conductivity of the weld is almost the same as that of the base metal.The study is beneficial to obtain good shaped laser welded joints of copper.
2019, 43(2): 217-221.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.013
Abstract:
In order to solve the problem of complex structure, time-consuming and unstable state in the process of adjusting optical elements in a traditional birefringence measurement system, the duty cycles of o light and e light at low levels in polarization flipping curves were calculated.The function of automatic rotating wave-plate was added in a birefringence measurement system optimized with high efficiency.The system can automatically adjust the direction of fast axis of the wave-plate aligned with the intrinsic polarization direction of laser and reduce the measurement error that may be introduced when judging the fast axis of wave-plate artificially.After many measurements, the results show that the maximum deviation of wave-plate phase delay is 0.65°, and the standard deviation is reduced by 28%.The measurement accuracy and stability of birefringence measurement systems have met the requirements of industrial production.
In order to solve the problem of complex structure, time-consuming and unstable state in the process of adjusting optical elements in a traditional birefringence measurement system, the duty cycles of o light and e light at low levels in polarization flipping curves were calculated.The function of automatic rotating wave-plate was added in a birefringence measurement system optimized with high efficiency.The system can automatically adjust the direction of fast axis of the wave-plate aligned with the intrinsic polarization direction of laser and reduce the measurement error that may be introduced when judging the fast axis of wave-plate artificially.After many measurements, the results show that the maximum deviation of wave-plate phase delay is 0.65°, and the standard deviation is reduced by 28%.The measurement accuracy and stability of birefringence measurement systems have met the requirements of industrial production.
2019, 43(2): 222-226.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.014
Abstract:
In order to improve the response speed of broadband wavelength conversion technology, a tunable all-optical broadband wavelength converter based on stimulated Raman scattering (SRS) using highly nonlinear photonic crystal fiber (PCF) was designed.Based on Raman effect in optical fiber, Raman gain spectrum of photonic crystal fiber was fitted by Gaussian curve.The theoretical model of a Raman wavelength converter was established, and the effect of fiber length on conversion efficiency was discussed.The results show that 100nm conversion bandwidth is achieved under the condition of the communication system.The bandwidth is 1487nm~1587nm.Q factor changes with the wavelength of probe light and the trend of Raman gain spectrum is the same.The best wavelength conversion quality is at the maximum Raman gain coefficient.The study is of great significance to the wavelength assignment of wavelength converters and the configuration of fiber length in future optical networks.
In order to improve the response speed of broadband wavelength conversion technology, a tunable all-optical broadband wavelength converter based on stimulated Raman scattering (SRS) using highly nonlinear photonic crystal fiber (PCF) was designed.Based on Raman effect in optical fiber, Raman gain spectrum of photonic crystal fiber was fitted by Gaussian curve.The theoretical model of a Raman wavelength converter was established, and the effect of fiber length on conversion efficiency was discussed.The results show that 100nm conversion bandwidth is achieved under the condition of the communication system.The bandwidth is 1487nm~1587nm.Q factor changes with the wavelength of probe light and the trend of Raman gain spectrum is the same.The best wavelength conversion quality is at the maximum Raman gain coefficient.The study is of great significance to the wavelength assignment of wavelength converters and the configuration of fiber length in future optical networks.
Research of effect of guide-mode resonance grating parameters on resonance wavelength and line width
2019, 43(2): 227-232.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.015
Abstract:
In order to design guided mode resonance gratings with reflection function, based on equivalent medium theory, planar waveguide theory and rigorous coupled wave analysis, theoretical analysis and experimental verification were carried out, guide-mode resonance gratings were designed to realize reflection resonance on 850nm (TE).The effects of grating parameters, incident angle and thickness of waveguide layer on resonance wavelength and linewidth were calculated by rigorous coupled wave method.The results show that, with the increase of duty cycle, resonance wavelength will shift red and resonance linewidth increases first and then decreases with the increase of duty cycle.When duty cycle is 0.5, line width can reach the widest.Resonant wavelength increases with the increase of grating period and waveguide layer thickness.But the line width is almost unchanged.When the period increases from 490nm to 520nm, resonance wavelength is red-shifted by nearly 50nm.When the thickness of waveguide layer increases from 217nm to 251nm, resonance wavelength is red-shifted by nearly 25nm.The influence of grating thickness on resonance wavelength and resonance linewidth is very weak.When the incident angle is perpendicular, there is only one resonance peak.But when the incident angle is not 0°, there will be two resonance peaks.And with the increase of incident angle, one resonance wavelength will be blue-shifted while the other will be red-shifted.This study provides theoretical guidance for practical preparation of reflective guided mode resonance gratings.
In order to design guided mode resonance gratings with reflection function, based on equivalent medium theory, planar waveguide theory and rigorous coupled wave analysis, theoretical analysis and experimental verification were carried out, guide-mode resonance gratings were designed to realize reflection resonance on 850nm (TE).The effects of grating parameters, incident angle and thickness of waveguide layer on resonance wavelength and linewidth were calculated by rigorous coupled wave method.The results show that, with the increase of duty cycle, resonance wavelength will shift red and resonance linewidth increases first and then decreases with the increase of duty cycle.When duty cycle is 0.5, line width can reach the widest.Resonant wavelength increases with the increase of grating period and waveguide layer thickness.But the line width is almost unchanged.When the period increases from 490nm to 520nm, resonance wavelength is red-shifted by nearly 50nm.When the thickness of waveguide layer increases from 217nm to 251nm, resonance wavelength is red-shifted by nearly 25nm.The influence of grating thickness on resonance wavelength and resonance linewidth is very weak.When the incident angle is perpendicular, there is only one resonance peak.But when the incident angle is not 0°, there will be two resonance peaks.And with the increase of incident angle, one resonance wavelength will be blue-shifted while the other will be red-shifted.This study provides theoretical guidance for practical preparation of reflective guided mode resonance gratings.
2019, 43(2): 233-237.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.016
Abstract:
In order to improve civil aviation safety and flight efficiency and realize accurate identification of wake vortex, aerodynamic theory of aircraft tail vortex, especially the classical Halock-Burnham wake velocity mathematical model was analyzed and studied.One standard radial velocity model for radar aircraft wake detection was established by using the principle of Doppler lidar to detect the radial velocity of vortex wind field.The idea of sliding window was introduced.A method based on waveform similarity matching was proposed to identify the wake vortex automatically.The detailed algorithm flow was also given.The recognition method is theoretically analyzed and experimentally verified by using the measured data of lidar wind field and the hypothesis testing method.The results show that the effective recognition rate of this algorithm for aircraft wake vortex is 90%.The results of the study have some reference value for further wake monitoring.
In order to improve civil aviation safety and flight efficiency and realize accurate identification of wake vortex, aerodynamic theory of aircraft tail vortex, especially the classical Halock-Burnham wake velocity mathematical model was analyzed and studied.One standard radial velocity model for radar aircraft wake detection was established by using the principle of Doppler lidar to detect the radial velocity of vortex wind field.The idea of sliding window was introduced.A method based on waveform similarity matching was proposed to identify the wake vortex automatically.The detailed algorithm flow was also given.The recognition method is theoretically analyzed and experimentally verified by using the measured data of lidar wind field and the hypothesis testing method.The results show that the effective recognition rate of this algorithm for aircraft wake vortex is 90%.The results of the study have some reference value for further wake monitoring.
2019, 43(2): 238-245.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.017
Abstract:
In order to effectively suppress the strong turbulence effect caused by the wake of helicopter during landing, diversity reception technology was used for suppression.According to the characteristics of wireless ultraviolet slant communication and approximate-line-of-sight (ALOS) communication, the probability density function of edge distribution of the received signal strength was given.The correction model of UV ALOS communication system based on gamma-gamma distribution was established.The diversity reception technology was introduced into the model.The influence of turbulence effect on the edge probability density distribution of optical signal intensity was analyzed theoretically.Bit error performances of maximal ratio combining (MRC), equal gain combining (EGC) and selective combining (SC) were analyzed.The results show that, the stronger the turbulence intensity is, the worse the bit error rate performance of UV ALOS system is.With two diversities, the signal-to-noise rates of MRC, EGC and SC have increased 22dB, 18dB and 16dB respectively.The diversity reception technology can effectively suppress the strong turbulence effect in helicopter assisted landing and improve the stability and anti-fading performance of communication system.
In order to effectively suppress the strong turbulence effect caused by the wake of helicopter during landing, diversity reception technology was used for suppression.According to the characteristics of wireless ultraviolet slant communication and approximate-line-of-sight (ALOS) communication, the probability density function of edge distribution of the received signal strength was given.The correction model of UV ALOS communication system based on gamma-gamma distribution was established.The diversity reception technology was introduced into the model.The influence of turbulence effect on the edge probability density distribution of optical signal intensity was analyzed theoretically.Bit error performances of maximal ratio combining (MRC), equal gain combining (EGC) and selective combining (SC) were analyzed.The results show that, the stronger the turbulence intensity is, the worse the bit error rate performance of UV ALOS system is.With two diversities, the signal-to-noise rates of MRC, EGC and SC have increased 22dB, 18dB and 16dB respectively.The diversity reception technology can effectively suppress the strong turbulence effect in helicopter assisted landing and improve the stability and anti-fading performance of communication system.
2019, 43(2): 246-250.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.018
Abstract:
In order to achieve surface metallization on glass substrates, metallic copper was directly deposited on the surface of conventional transparent silicate glass by means of laser-induced plasma deposition technology with a T2 copper target and a cheap and easily-maintained 1064nm wavelength infrared nanosecond fiber laser.Micro-morphology of the copper deposition layer was observed by an optical microscope and a scanning electron microscope.The results show that, in the range of laser energy density from 12.50J/cm2(deposition threshold) to 27.13J/cm2(the maximal fluence of the laser), the deposition amount of copper particles on the glass surface increases with the increase of laser fluence.Under the condition of constant laser fluence (e.g., 27.13J/cm2) and the same horizontal and vertical spot overlaps, copper deposition process fails if the spot overlap percentage is equal to or large than 50% bcause of the strong absorption of laser by glass.And if the overlap percentage ranges from-20% to 50%, deposition amount of copper particles has a tendency of increase firstly and then decrease.Laser-induced plasma deposition technology is a facile process to realize surface metallization on transparent substrate material.
In order to achieve surface metallization on glass substrates, metallic copper was directly deposited on the surface of conventional transparent silicate glass by means of laser-induced plasma deposition technology with a T2 copper target and a cheap and easily-maintained 1064nm wavelength infrared nanosecond fiber laser.Micro-morphology of the copper deposition layer was observed by an optical microscope and a scanning electron microscope.The results show that, in the range of laser energy density from 12.50J/cm2(deposition threshold) to 27.13J/cm2(the maximal fluence of the laser), the deposition amount of copper particles on the glass surface increases with the increase of laser fluence.Under the condition of constant laser fluence (e.g., 27.13J/cm2) and the same horizontal and vertical spot overlaps, copper deposition process fails if the spot overlap percentage is equal to or large than 50% bcause of the strong absorption of laser by glass.And if the overlap percentage ranges from-20% to 50%, deposition amount of copper particles has a tendency of increase firstly and then decrease.Laser-induced plasma deposition technology is a facile process to realize surface metallization on transparent substrate material.
2019, 43(2): 251-255.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.019
Abstract:
In order to provide the reliable step temperature signal in thermocouple time constant test, optimize the feedback control effect, further shorten the rising delay time of step temperature-rising signal and ensure the accuracy of thermocouple time constant measurement, the static temperature-voltage calibration was carried out for the high-speed radiation temperature measurement module by using medium-temperature blackbody furnace.The relationship between pulse width and temperature of single pulse width modulation (PWM) was obtained by heating the thermocouple with a laser.The nonlinear relationship between the voltage of infrared radiation thermometer module and the blackbody temperature, pulse width of PWM wave and temperature was analyzed theoretically.Experimental verification was provided for the further optimization of control effect and the establishment of system mathematical model.The results show that output voltage of infrared radiation thermometer module is quadratic to blackbody temperature and pulse width of single PWM wave is cubic to temperature.The experimental results can provide a theoretical basis for the controller to adjust PWM pulse width (duty cycle) by feedback control.
In order to provide the reliable step temperature signal in thermocouple time constant test, optimize the feedback control effect, further shorten the rising delay time of step temperature-rising signal and ensure the accuracy of thermocouple time constant measurement, the static temperature-voltage calibration was carried out for the high-speed radiation temperature measurement module by using medium-temperature blackbody furnace.The relationship between pulse width and temperature of single pulse width modulation (PWM) was obtained by heating the thermocouple with a laser.The nonlinear relationship between the voltage of infrared radiation thermometer module and the blackbody temperature, pulse width of PWM wave and temperature was analyzed theoretically.Experimental verification was provided for the further optimization of control effect and the establishment of system mathematical model.The results show that output voltage of infrared radiation thermometer module is quadratic to blackbody temperature and pulse width of single PWM wave is cubic to temperature.The experimental results can provide a theoretical basis for the controller to adjust PWM pulse width (duty cycle) by feedback control.
2019, 43(2): 256-262.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.020
Abstract:
In order to achieve the absorption curve with broadening (within 11GHz~14GHz band) and tunable bandwidth under TE wave, a new metamaterial absorber was proposed whose periodic structural unit adopted honeycomb-shaped hexagonal structure.The parametric analysis chart of the absorber was calculated.The effects of variables g and d on absorbing band and absorbing bandwidth were studied.The cause of bandwidth broadening of the etched cross-shaped absorber was also explained.The results show that, absorption rate of the absorber in the low frequency domain at 9.17GHz~9.5GHz is over 90%.When different plasma resonance regions are excited, the time-frequency domain absorption of the absorber can be realized.And the absorptive capacity of the absorber can be improved.By changing the variables g and d, the dynamic control of the absorption band can be realized.The absorption bandwidth in the high frequency domain can be widened by etching cross-shaped structure in a square structure.Its absorption rate in the frequency domain of 12.08GHz~13.91GHz is higher than 90%.By changing the variable s, the absorption band can be obviously widened.The absorber is insensitive to the angle of incident electromagnetic wave.The design idea provides an effective way to broaden the absorption bandwidth of absorbers.
In order to achieve the absorption curve with broadening (within 11GHz~14GHz band) and tunable bandwidth under TE wave, a new metamaterial absorber was proposed whose periodic structural unit adopted honeycomb-shaped hexagonal structure.The parametric analysis chart of the absorber was calculated.The effects of variables g and d on absorbing band and absorbing bandwidth were studied.The cause of bandwidth broadening of the etched cross-shaped absorber was also explained.The results show that, absorption rate of the absorber in the low frequency domain at 9.17GHz~9.5GHz is over 90%.When different plasma resonance regions are excited, the time-frequency domain absorption of the absorber can be realized.And the absorptive capacity of the absorber can be improved.By changing the variables g and d, the dynamic control of the absorption band can be realized.The absorption bandwidth in the high frequency domain can be widened by etching cross-shaped structure in a square structure.Its absorption rate in the frequency domain of 12.08GHz~13.91GHz is higher than 90%.By changing the variable s, the absorption band can be obviously widened.The absorber is insensitive to the angle of incident electromagnetic wave.The design idea provides an effective way to broaden the absorption bandwidth of absorbers.
2019, 43(2): 263-268.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.021
Abstract:
In order to study influence rules of process parameters on residual stress distribution of cladding layers, the numerical simulation and experiments test were adopted.The residual stress distribution rules in depth direction of cladding layer section along the scanning path direction (y-direction) and the vertical scanning path direction (x-direction) were obtained.At the same time, the stress field was also analyzed under different process parameters.The results show that the residual stress of y-direction is tensile stress, which is first increasing and then decreasing, and the maximum tensile stress is 262MPa at 0.2mm position from the top of cladding layer.The residual stress of x-direction is from compressive stress converted gradually to tensile stress, which is less than the value of the y-direction stress with the depth of the cladding layer increasing.The x-direction residual stress gradually increases and the y-direction residual stress gradually decreases with the increasing of laser power.The x-direction residual stress gradually decreases and the y-direction residual stress gradually increases with the increasing of scanning speed.The x-direction residual stress and the y-direction residual stress decreases with the increasing of powder mass flow rate.Meanwhile it can provide a method for decreasing residual stress and optimizing process parameters.
In order to study influence rules of process parameters on residual stress distribution of cladding layers, the numerical simulation and experiments test were adopted.The residual stress distribution rules in depth direction of cladding layer section along the scanning path direction (y-direction) and the vertical scanning path direction (x-direction) were obtained.At the same time, the stress field was also analyzed under different process parameters.The results show that the residual stress of y-direction is tensile stress, which is first increasing and then decreasing, and the maximum tensile stress is 262MPa at 0.2mm position from the top of cladding layer.The residual stress of x-direction is from compressive stress converted gradually to tensile stress, which is less than the value of the y-direction stress with the depth of the cladding layer increasing.The x-direction residual stress gradually increases and the y-direction residual stress gradually decreases with the increasing of laser power.The x-direction residual stress gradually decreases and the y-direction residual stress gradually increases with the increasing of scanning speed.The x-direction residual stress and the y-direction residual stress decreases with the increasing of powder mass flow rate.Meanwhile it can provide a method for decreasing residual stress and optimizing process parameters.
2019, 43(2): 269-274.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.022
Abstract:
In order to improve the denoising effect and the edge detail protection of traditional multi-scale transform filtering in the fringe pattern of electronic speckle pattern interferometry (ESPI), an improved nonsubsampling contourlet transform (NSCT) filtering algorithm was proposed.Discrete stationary wavelet transform and NSCT model were adopted with nonlinear diffusion and improved fast non local mean filtering algorithm.The algorithm was applied to the quantitative analysis of simulated and experimental ESPI fringe pattern filtering results.After theoretical analysis and experimental verification, the results show that, the minimum speckle index of the algorithm in this paper is 0.41121, 0.38043 and 0.35362 respectively in simulated and experimental ESPI fringe pattern.The peak signal-to-noise ratio is the largest.This algorithm improves the ability of denoising and recovers the details of stripes.The results lay the foundation for the application of multi-scale transform filtering in ESPI fringe pattern.
In order to improve the denoising effect and the edge detail protection of traditional multi-scale transform filtering in the fringe pattern of electronic speckle pattern interferometry (ESPI), an improved nonsubsampling contourlet transform (NSCT) filtering algorithm was proposed.Discrete stationary wavelet transform and NSCT model were adopted with nonlinear diffusion and improved fast non local mean filtering algorithm.The algorithm was applied to the quantitative analysis of simulated and experimental ESPI fringe pattern filtering results.After theoretical analysis and experimental verification, the results show that, the minimum speckle index of the algorithm in this paper is 0.41121, 0.38043 and 0.35362 respectively in simulated and experimental ESPI fringe pattern.The peak signal-to-noise ratio is the largest.This algorithm improves the ability of denoising and recovers the details of stripes.The results lay the foundation for the application of multi-scale transform filtering in ESPI fringe pattern.
2019, 43(2): 275-279.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.023
Abstract:
In order to get higher frequency signal, a 24-tupling frequency microwave millimeter-wave signal generation scheme based on parallel Mach-Zehnder modulators (MZM) and semiconductor optical amplifier (SOA) four-wave mixing effect was presented and simulated.The local oscillator signal was modulated by parallel MZM to obtain high-purity ±4 sidebands.Under the four-wave mixing effect, the ±12 sidebands were generated.The ±4 sideband was filtered by cascaded Bragg grating filters.After the beat frequency of photoelectric detector, 24-tupling frequency signal was generated.The results show that, when input local oscillator signal is 5GHz, radio frequency spurious rejection ratio of the generated 120GHz high frequency microwave millimeter wave signal is 22dB.The spectrum purity is high, and the tunability is good.This study provides a high frequency doubling method for the generation of high frequency microwave and millimeter wave signal.
In order to get higher frequency signal, a 24-tupling frequency microwave millimeter-wave signal generation scheme based on parallel Mach-Zehnder modulators (MZM) and semiconductor optical amplifier (SOA) four-wave mixing effect was presented and simulated.The local oscillator signal was modulated by parallel MZM to obtain high-purity ±4 sidebands.Under the four-wave mixing effect, the ±12 sidebands were generated.The ±4 sideband was filtered by cascaded Bragg grating filters.After the beat frequency of photoelectric detector, 24-tupling frequency signal was generated.The results show that, when input local oscillator signal is 5GHz, radio frequency spurious rejection ratio of the generated 120GHz high frequency microwave millimeter wave signal is 22dB.The spectrum purity is high, and the tunability is good.This study provides a high frequency doubling method for the generation of high frequency microwave and millimeter wave signal.
2019, 43(2): 280-285.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.024
Abstract:
Under given illumination and observation conditions, in order to reconstruct the spectral reflectance of the object surface from the camera response signal to achieve high-precision color reproduction, multi-spectral imaging technology was used to acquire multi-spectral image response of an object.The principal component analysis, matrix R and the new regularization matrix R method were used to analyze the theoretical analysis of spectral reflectance reconstruction.The results of the research were verified experimentally in the color reproduction of mural color blocks.The reconstructed spectral reflectance and color reproduction data of mural color blocks were obtained.At the same time, the color reproduction results of mural color blocks based on regularization matrix R method were evaluated.The results show that the regularization matrix R method is superior to the principal component analysis and matrix R method in the spectral accuracy and reconstructed accuracy.Compared with the principal component analysis and the matrix R method, the color difference is reduced by 0.0732, the fitness coefficient is increased by 1.10%, the root mean square error is reduced by 0.0035, and the spectral matching partial index is reduced by 0.0225.This method can meet the needs of high-precision color reproduction, which is suitable for digital archiving of cultural relic artwork, restoration of cultural relics and other fields.
Under given illumination and observation conditions, in order to reconstruct the spectral reflectance of the object surface from the camera response signal to achieve high-precision color reproduction, multi-spectral imaging technology was used to acquire multi-spectral image response of an object.The principal component analysis, matrix R and the new regularization matrix R method were used to analyze the theoretical analysis of spectral reflectance reconstruction.The results of the research were verified experimentally in the color reproduction of mural color blocks.The reconstructed spectral reflectance and color reproduction data of mural color blocks were obtained.At the same time, the color reproduction results of mural color blocks based on regularization matrix R method were evaluated.The results show that the regularization matrix R method is superior to the principal component analysis and matrix R method in the spectral accuracy and reconstructed accuracy.Compared with the principal component analysis and the matrix R method, the color difference is reduced by 0.0732, the fitness coefficient is increased by 1.10%, the root mean square error is reduced by 0.0035, and the spectral matching partial index is reduced by 0.0225.This method can meet the needs of high-precision color reproduction, which is suitable for digital archiving of cultural relic artwork, restoration of cultural relics and other fields.
2019, 43(2): 286-290.
doi: 10.7510/jgjs.issn.1001-3806.2019.02.025
Abstract:
In the process of infrared and visible image fusion, the details of the fusion image are often missing.In order to solve this problem, an improved image fusion algorithm based on nonsubsampled contourlet transform (NSCT) was adopted, which integrated the dynamic weighted non-negative matrix factorization (WNMF) rule into the image fusion.The results show that, the low-frequency and high-frequency parts can be obtained by multi-scale and multi-directional decomposition of two source images by using NSCT algorithm.The dynamic WNMF fusion rule was used as the fusion rule of low frequency parts.The decomposition scale of the highest level in the high frequency part was based on the absolute value method.The matching threshold was set in the other parts of the high frequency part.When the threshold value was lower, the method of region variance based on region energy matching degree was used.When the threshold value is higher, the weighted average method was used.By processing the low frequency part and the high frequency part, the fused image was obtained by NSCT inverse transform.This method effectively improves the definition of the fused image, highlights its details and shortens the calculation time.
In the process of infrared and visible image fusion, the details of the fusion image are often missing.In order to solve this problem, an improved image fusion algorithm based on nonsubsampled contourlet transform (NSCT) was adopted, which integrated the dynamic weighted non-negative matrix factorization (WNMF) rule into the image fusion.The results show that, the low-frequency and high-frequency parts can be obtained by multi-scale and multi-directional decomposition of two source images by using NSCT algorithm.The dynamic WNMF fusion rule was used as the fusion rule of low frequency parts.The decomposition scale of the highest level in the high frequency part was based on the absolute value method.The matching threshold was set in the other parts of the high frequency part.When the threshold value was lower, the method of region variance based on region energy matching degree was used.When the threshold value is higher, the weighted average method was used.By processing the low frequency part and the high frequency part, the fused image was obtained by NSCT inverse transform.This method effectively improves the definition of the fused image, highlights its details and shortens the calculation time.
