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RSS2012 Vol. 36, No. 6
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2012, 36(6): 713-718.
doi: 10.3969/j.issn.1001-3806.2012.06.001
[Abstract]
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Abstract:
In order to study the burning loss of magnesium element in laser welding aluminum alloy,a specially-designed device was first used to collect the spectral signals emitted from the keyhole plasma in deep penetration laser welding aluminum alloy 5052.Then,the content of magnesium element in the welds was tested by an electron probe micro analyzer.Under the experimental conditions,the welding parameters heavily affect the spectral intensity of magnesium element plasma.The spectral intensity is not uniformly distributed in the keyhole region.In the radial direction,the spectral intensity of MgⅠ decreases from the center to the edge of the keyhole;in the depth direction,from the top to the bottom of the keyhole,the spectral intensity of MgⅠ increases first and then decreases.The Mg content changes inversely with the spectral intensity in the keyhole region.Therefore,spectral analysis technology can be used to monitor the burning loss of magnesium element in laser welding aluminum.It can be concluded that Mg loss in the keyhole region is determined by laser intensity absorbed there.The higher the absorbed laser intensity,the bigger the Mg loss.
In order to study the burning loss of magnesium element in laser welding aluminum alloy,a specially-designed device was first used to collect the spectral signals emitted from the keyhole plasma in deep penetration laser welding aluminum alloy 5052.Then,the content of magnesium element in the welds was tested by an electron probe micro analyzer.Under the experimental conditions,the welding parameters heavily affect the spectral intensity of magnesium element plasma.The spectral intensity is not uniformly distributed in the keyhole region.In the radial direction,the spectral intensity of MgⅠ decreases from the center to the edge of the keyhole;in the depth direction,from the top to the bottom of the keyhole,the spectral intensity of MgⅠ increases first and then decreases.The Mg content changes inversely with the spectral intensity in the keyhole region.Therefore,spectral analysis technology can be used to monitor the burning loss of magnesium element in laser welding aluminum.It can be concluded that Mg loss in the keyhole region is determined by laser intensity absorbed there.The higher the absorbed laser intensity,the bigger the Mg loss.
2012, 36(6): 719-723.
doi: 10.3969/j.issn.1001-3806.2012.06.002
Abstract:
In order to improve the properties of fluidized bed based powder feeder for laser cladding,3-D unsteady gas-solid two-phase flow during the powder feeding process was simulated with FLUENT software.The simulation results of Ni-based alloy powder feeding process in Syamlal-O'Brien,Gidaspow,Mckeen and modified Syamlal-O'Brien drag law model were compared,which show that the mass flow rate obtained from Mckeen drag model is consistent well with the experimental results.And the simulation results of different fluidizing gas flow rate also agree well with the experimental results,which indicate that Mckeen model is suitable to simulate this kind of powder feeder.Fluidizing characteristics of gas-solid flow rate in 2.6L/min were analyzed,which shows that fluidizing gas flow inlet 2 has little effect on powder feeding.Thus fine powder delivering characteristics can also be achieved without fluidizing gas flow inlet 2.Therefore,the numerical simulation in Mckeen model can provide a theoretical basis for optimization of powder feeder for laser cladding.
In order to improve the properties of fluidized bed based powder feeder for laser cladding,3-D unsteady gas-solid two-phase flow during the powder feeding process was simulated with FLUENT software.The simulation results of Ni-based alloy powder feeding process in Syamlal-O'Brien,Gidaspow,Mckeen and modified Syamlal-O'Brien drag law model were compared,which show that the mass flow rate obtained from Mckeen drag model is consistent well with the experimental results.And the simulation results of different fluidizing gas flow rate also agree well with the experimental results,which indicate that Mckeen model is suitable to simulate this kind of powder feeder.Fluidizing characteristics of gas-solid flow rate in 2.6L/min were analyzed,which shows that fluidizing gas flow inlet 2 has little effect on powder feeding.Thus fine powder delivering characteristics can also be achieved without fluidizing gas flow inlet 2.Therefore,the numerical simulation in Mckeen model can provide a theoretical basis for optimization of powder feeder for laser cladding.
2012, 36(6): 724-726.
doi: 10.3969/j.issn.1001-3806.2012.06.003
Abstract:
In order to design a laser marking digital galvanometer control system,taking a digital signal processor(DSP) chip as the main processor of the digital control board,taking universal serial bus for the communication of the host computer and digital control board because of its high-speed transfer rate and hot-plug support,mark graphic data processing algorithms was completed by the high-speed DSP chip,and a complex programmable logic device(CPLD)was used to control the signal timing.For RS-485 bus can transfer differential signal,it was used to communicate between the digital galvanometer and laser.According to theoretical analysis and simulation,the rotation of digital galvanometer and laser power can be controlled with high-precision.The results show that this system can be applied for real-time,high-speed,high-precision laser marking.
In order to design a laser marking digital galvanometer control system,taking a digital signal processor(DSP) chip as the main processor of the digital control board,taking universal serial bus for the communication of the host computer and digital control board because of its high-speed transfer rate and hot-plug support,mark graphic data processing algorithms was completed by the high-speed DSP chip,and a complex programmable logic device(CPLD)was used to control the signal timing.For RS-485 bus can transfer differential signal,it was used to communicate between the digital galvanometer and laser.According to theoretical analysis and simulation,the rotation of digital galvanometer and laser power can be controlled with high-precision.The results show that this system can be applied for real-time,high-speed,high-precision laser marking.
2012, 36(6): 727-730.
doi: 10.3969/j.issn.1001-3806.2012.06.004
Abstract:
In order to study the effects of hollow laser parameters on the sheet metal deformation,the dynamic response process and the deformation law of sheet metal deformation were analyzed with 3003 aluminum alloy sheet shocked under different laser parameters.The results show that,the sheet metal obtain initial velocity by hollow laser shock,the velocity of sheet metal in the spot region gradually reduces and the velocity of sheet metal outside the spot region increases,the movement of the entire plate is driven;compared with the deformation of sheet metal by solid laser shock,the deformation zone is relatively flat and well,the forming performance and the forming limit of sheet metal are improved.The forming law of sheet metal can be obtained by selecting different hollow laser parameters,providing a basis for the study about hollow laser shock forming technique.
In order to study the effects of hollow laser parameters on the sheet metal deformation,the dynamic response process and the deformation law of sheet metal deformation were analyzed with 3003 aluminum alloy sheet shocked under different laser parameters.The results show that,the sheet metal obtain initial velocity by hollow laser shock,the velocity of sheet metal in the spot region gradually reduces and the velocity of sheet metal outside the spot region increases,the movement of the entire plate is driven;compared with the deformation of sheet metal by solid laser shock,the deformation zone is relatively flat and well,the forming performance and the forming limit of sheet metal are improved.The forming law of sheet metal can be obtained by selecting different hollow laser parameters,providing a basis for the study about hollow laser shock forming technique.
2012, 36(6): 731-734.
doi: 10.3969/j.issn.1001-3806.2012.06.005
Abstract:
In order to obtain high power and high pulse-repetition-frequency(PRF) laser pulse,a nanosecond nanosecond-level laser diode driver with advantages of small size,light weight and low cost was designed.The narrow pulse,which was generated by an improved mono-stable circuit,was amplified to high current narrow pulse to drive metal-oixde-semiconducor field-effect-transistor(MOSFET)switch for narrow pulse of high current.The output current of the driver was 0A~80A;the rise time of the pulse was 2.8ns;the fall time was 3.8ns;the pulse width can could be adjusted between 5ns and 500ns;the narrowest with the minimal pulse width can be of 5.2ns;and the PRF pulse repetition frequency was up to 200kHz.When this power supply was used for a 905nm laser diode,its peak laser power was up to 70W at PRF of 10kHz.The results show that the narrow pulse can be used to drive MOSFET to obtain 10ns or narrower pulse with high PRF and current,and this driver can completely meet the demand for driving high power laser diode.Further research is necessary for 100A or higher drive current.
In order to obtain high power and high pulse-repetition-frequency(PRF) laser pulse,a nanosecond nanosecond-level laser diode driver with advantages of small size,light weight and low cost was designed.The narrow pulse,which was generated by an improved mono-stable circuit,was amplified to high current narrow pulse to drive metal-oixde-semiconducor field-effect-transistor(MOSFET)switch for narrow pulse of high current.The output current of the driver was 0A~80A;the rise time of the pulse was 2.8ns;the fall time was 3.8ns;the pulse width can could be adjusted between 5ns and 500ns;the narrowest with the minimal pulse width can be of 5.2ns;and the PRF pulse repetition frequency was up to 200kHz.When this power supply was used for a 905nm laser diode,its peak laser power was up to 70W at PRF of 10kHz.The results show that the narrow pulse can be used to drive MOSFET to obtain 10ns or narrower pulse with high PRF and current,and this driver can completely meet the demand for driving high power laser diode.Further research is necessary for 100A or higher drive current.
2012, 36(6): 735-737.
doi: 10.3969/j.issn.1001-3806.2012.06.006
Abstract:
In order to measure the vertical target coordinates of the large target surface,a coordinate measurement method with laser screen target was presented with four 90° fan-shaped lasers as light sources,and a high-sensitivity photodiode array as the receiver.When bullets fly through the rectangular laser screen,formed by the intersected light from the four lasers,they will block part of the laser in the x and y directions respectively,and thus corresponding signal produces from the photodiodes.The impact coordinates can be obtained by acquiring and processing the signal.Finally the coordinates of the bullet were tested in active experiments.The results show that this vertical target system has the characteristics of high precision and high sensitivity.
In order to measure the vertical target coordinates of the large target surface,a coordinate measurement method with laser screen target was presented with four 90° fan-shaped lasers as light sources,and a high-sensitivity photodiode array as the receiver.When bullets fly through the rectangular laser screen,formed by the intersected light from the four lasers,they will block part of the laser in the x and y directions respectively,and thus corresponding signal produces from the photodiodes.The impact coordinates can be obtained by acquiring and processing the signal.Finally the coordinates of the bullet were tested in active experiments.The results show that this vertical target system has the characteristics of high precision and high sensitivity.
2012, 36(6): 738-741.
doi: 10.3969/j.issn.1001-3806.2012.06.007
Abstract:
In order to make the displacement measuring system achieve the large-range and high-resolution,theoretical analysis and experimental verification were conducted with the multiplexed fiber interferometer.Two fiber Michelson interferometers sharing common-interferometric-optical path were configured by employing fiber Bragg gratings as in-fiber reflective mirrors.One of the interferometer was used to stabilize the measurement system with a feedback loop compensating the influence induced by the environmental disturbance so that the measurement system was kept stable enough for on-line measurement,while the other one was for performing the measurement task.Two different wavelengths are working simultaneously in the measurement interferometer.The measurement range determined by the synthetic-wavelength interferometric signal of the two wavelengths was expanded to be larger than 1mm,while the measurement resolution determined by one of the single-wavelength interferometric signals was maintained less than 1nm.The displacement measurement system achieved the large-range and high-resolution purpose based on multiplexed fiber interferometry.
In order to make the displacement measuring system achieve the large-range and high-resolution,theoretical analysis and experimental verification were conducted with the multiplexed fiber interferometer.Two fiber Michelson interferometers sharing common-interferometric-optical path were configured by employing fiber Bragg gratings as in-fiber reflective mirrors.One of the interferometer was used to stabilize the measurement system with a feedback loop compensating the influence induced by the environmental disturbance so that the measurement system was kept stable enough for on-line measurement,while the other one was for performing the measurement task.Two different wavelengths are working simultaneously in the measurement interferometer.The measurement range determined by the synthetic-wavelength interferometric signal of the two wavelengths was expanded to be larger than 1mm,while the measurement resolution determined by one of the single-wavelength interferometric signals was maintained less than 1nm.The displacement measurement system achieved the large-range and high-resolution purpose based on multiplexed fiber interferometry.
2012, 36(6): 742-744.
doi: 10.3969/j.issn.1001-3806.2012.06.008
Abstract:
In order to study stress distribution in Zr films prepared by magnetron sputtering,after measuring the profile of the substrate before and after the coating,the stress distribution in the Zr film was calculated and the relationship between the work pressure,Zr film thickness and residual stress was studied.The results show that it is mainly uneven compressive stress in the Zr thin films.Work pressure has little effect on the residual stress of Zr thin films.Thickness of Zr thin films has greater influence on the residual stress,with increase of thickness,film stress decreases.
In order to study stress distribution in Zr films prepared by magnetron sputtering,after measuring the profile of the substrate before and after the coating,the stress distribution in the Zr film was calculated and the relationship between the work pressure,Zr film thickness and residual stress was studied.The results show that it is mainly uneven compressive stress in the Zr thin films.Work pressure has little effect on the residual stress of Zr thin films.Thickness of Zr thin films has greater influence on the residual stress,with increase of thickness,film stress decreases.
2012, 36(6): 745-748.
doi: 10.3969/j.issn.1001-3806.2012.06.009
Abstract:
In order to study SiC crystal application in optics,the grating structures on the surface and inside of SiC crystals were fabricated using femtosecond laser cold processing method,respectively.The effect of femtosecond laser power density and scanning speeds was studied in detail.Finally,the gratings were fabricated under appropriate processing conditions.After that the gratings period was verified in the diffraction experiments and the diffraction angles at different orders were calculated,the gratings were annealed at 1300℃,the grating parameters had no obvious change after annealing.It indicates that the fabricated gratings in SiC can be applied in high temperature environment.
In order to study SiC crystal application in optics,the grating structures on the surface and inside of SiC crystals were fabricated using femtosecond laser cold processing method,respectively.The effect of femtosecond laser power density and scanning speeds was studied in detail.Finally,the gratings were fabricated under appropriate processing conditions.After that the gratings period was verified in the diffraction experiments and the diffraction angles at different orders were calculated,the gratings were annealed at 1300℃,the grating parameters had no obvious change after annealing.It indicates that the fabricated gratings in SiC can be applied in high temperature environment.
2012, 36(6): 749-753.
doi: 10.3969/j.issn.1001-3806.2012.06.010
Abstract:
In order to study effect of ambient pressure on the liquid jet of laser-induced bubbles,the collapse time and the water hammer pressure of the liquid jet were obtained after studying the collapse action of the bubbles by means of a fiber-optic diagnostic technique based on probe beam deflection(PBD) in experiments.The data indicate that the collapse time decreases nonlinearly with the ambient pressure increasing,and the water hammer pressure increases nonlinearly with the ambient pressure increasing.At the initial stage of the collapse stage,the acceleration of the bubble wall and the effect of the ambient pressure on the acceleration are very small;at the final stage of the collapse stage,the velocity of the center of the top bubble wall increases very quickly,and the acceleration increases with the ambient pressure increasing at the same stage.It's helpful to underwater laser processing and study about cavitation bubble dynamics.
In order to study effect of ambient pressure on the liquid jet of laser-induced bubbles,the collapse time and the water hammer pressure of the liquid jet were obtained after studying the collapse action of the bubbles by means of a fiber-optic diagnostic technique based on probe beam deflection(PBD) in experiments.The data indicate that the collapse time decreases nonlinearly with the ambient pressure increasing,and the water hammer pressure increases nonlinearly with the ambient pressure increasing.At the initial stage of the collapse stage,the acceleration of the bubble wall and the effect of the ambient pressure on the acceleration are very small;at the final stage of the collapse stage,the velocity of the center of the top bubble wall increases very quickly,and the acceleration increases with the ambient pressure increasing at the same stage.It's helpful to underwater laser processing and study about cavitation bubble dynamics.
2012, 36(6): 754-758.
doi: 10.3969/j.issn.1001-3806.2012.06.011
Abstract:
In order to study the thermal and stress field of metal plates irradiated moving pulsed laser beam,3-D simulation models for thermal and stress field were built by means of finite element analysis method based on the thermal elasto-plastic constitutive theory.The distribution and evolvement of temperature and stress with the space and time was obtained.The numerical results show that the surface of the metal is melt within the laser pulse existing time,solidified in the interval of the discontinuous pulses.The temperature variation curves are serrate with different peaks.The stress field varies tempestuously with the tensile stress and compressive stresses transformed reciprocally.After the remelting and cooling down,residual tensile stress retains in the remelting zone with the longitudinal tensile stress reaches 799MPa and the transverse stress reaches 700MPa.
In order to study the thermal and stress field of metal plates irradiated moving pulsed laser beam,3-D simulation models for thermal and stress field were built by means of finite element analysis method based on the thermal elasto-plastic constitutive theory.The distribution and evolvement of temperature and stress with the space and time was obtained.The numerical results show that the surface of the metal is melt within the laser pulse existing time,solidified in the interval of the discontinuous pulses.The temperature variation curves are serrate with different peaks.The stress field varies tempestuously with the tensile stress and compressive stresses transformed reciprocally.After the remelting and cooling down,residual tensile stress retains in the remelting zone with the longitudinal tensile stress reaches 799MPa and the transverse stress reaches 700MPa.
2012, 36(6): 759-762.
doi: 10.3969/j.issn.1001-3806.2012.06.012
Abstract:
In order to obtain the interference signal in a high-precision heterodyne interferometer,a new design of gain-controlled weak-signal detector was presented.In the detector circuit,a low noise photoelectric conversion pre-amplifier was designed based on AD645 to convert the weak interferometric beam effectively.A gain-controlled main amplifier was designed to guarantee the dynamic range for the signal and applicable for various processing circuit.A biquad band-pass filter was introduced to minimize the noise and the temperature drift.It is verified experimentally that the output signal of detector has high signal-to-noise ratio,large dynamic range and high gain.The detector with high performance can be used in high precision interferometers.
In order to obtain the interference signal in a high-precision heterodyne interferometer,a new design of gain-controlled weak-signal detector was presented.In the detector circuit,a low noise photoelectric conversion pre-amplifier was designed based on AD645 to convert the weak interferometric beam effectively.A gain-controlled main amplifier was designed to guarantee the dynamic range for the signal and applicable for various processing circuit.A biquad band-pass filter was introduced to minimize the noise and the temperature drift.It is verified experimentally that the output signal of detector has high signal-to-noise ratio,large dynamic range and high gain.The detector with high performance can be used in high precision interferometers.
2012, 36(6): 763-766.
doi: 10.3969/j.issn.1001-3806.2012.06.013
Abstract:
In order to achieve the pulse energy stability of high-repetition-rate ArF excimer lasers,the technology of pulse energy control was studied from the perspective of power supply adjustment.The closed-loop control principle for pulse energy stability of high-repetition-rate ArF excimer lasers was introduced.The function model between the output energy of excimer laser and the discharge voltage was established with approximation method,and the proportion-integration(PI) algorithm for real-time adjustment of discharge voltage based on the real-time detection of pulse energy was proposed.combined with the function model and the control algorithm,simulation was carried out with MATLAB software.The simulation results indicate that the pulse energy model is reasonable and the PI algorithm is feasible for improving the laser pulse energy stability.
In order to achieve the pulse energy stability of high-repetition-rate ArF excimer lasers,the technology of pulse energy control was studied from the perspective of power supply adjustment.The closed-loop control principle for pulse energy stability of high-repetition-rate ArF excimer lasers was introduced.The function model between the output energy of excimer laser and the discharge voltage was established with approximation method,and the proportion-integration(PI) algorithm for real-time adjustment of discharge voltage based on the real-time detection of pulse energy was proposed.combined with the function model and the control algorithm,simulation was carried out with MATLAB software.The simulation results indicate that the pulse energy model is reasonable and the PI algorithm is feasible for improving the laser pulse energy stability.
2012, 36(6): 767-770.
doi: 10.3969/j.issn.1001-3806.2012.06.014
Abstract:
In order to increase the hardness,strength and wear resistance of the compound material,based on the in-situ synthesis self-propagation reaction induced by high energy laser,the NiAl composite material was prepared by synthesizing the reinforced metal-ceramic hard particles.Added 0.01,0.015 and 0.02(mass fraction w) of tungsten concentrate powder respectively,combined hypereutectic Ni85Al15 powder was pressed into three kinds of billets.After sintering,the results of the the X-ray diffraction(XRD),secanning electron microscope(SEM),hardness and wear resistance of the sintering alloy were obtained.The results show that when the tungsten concentrate powder is not added,the main product phase of the sintering alloy are NiAl,Ni3Al and Al2O3;while if the tungsten concentrate powder is added,the sintering alloy products will produce Ni4W and WO3 phase on the side.When the mass fraction of tungsten is 0.01,the relative density of the sintering alloy is the biggest,which is 5.84g/cm3;the porosity rate is the lowest,which is 0.13%;the hardness rate of the sintering alloy is the highest,which is 325.2HK;the wear rate is the lowest,which is 0.27mg/mm2.The results show that the powder of tungsten concentrate can increase the hardness and wear resistance of the material,the material has the best hardness and wear resistance when its mass fraction is 0.01.
In order to increase the hardness,strength and wear resistance of the compound material,based on the in-situ synthesis self-propagation reaction induced by high energy laser,the NiAl composite material was prepared by synthesizing the reinforced metal-ceramic hard particles.Added 0.01,0.015 and 0.02(mass fraction w) of tungsten concentrate powder respectively,combined hypereutectic Ni85Al15 powder was pressed into three kinds of billets.After sintering,the results of the the X-ray diffraction(XRD),secanning electron microscope(SEM),hardness and wear resistance of the sintering alloy were obtained.The results show that when the tungsten concentrate powder is not added,the main product phase of the sintering alloy are NiAl,Ni3Al and Al2O3;while if the tungsten concentrate powder is added,the sintering alloy products will produce Ni4W and WO3 phase on the side.When the mass fraction of tungsten is 0.01,the relative density of the sintering alloy is the biggest,which is 5.84g/cm3;the porosity rate is the lowest,which is 0.13%;the hardness rate of the sintering alloy is the highest,which is 325.2HK;the wear rate is the lowest,which is 0.27mg/mm2.The results show that the powder of tungsten concentrate can increase the hardness and wear resistance of the material,the material has the best hardness and wear resistance when its mass fraction is 0.01.
2012, 36(6): 771-775.
doi: 10.3969/j.issn.1001-3806.2012.06.015
Abstract:
In order to obtain stable output power and wavelength from a semiconductor laser in a large range of temperature,according to the characteristics of small volume,light weight and the high requirement of temperature stability of a semiconductor laser,with a negative-coefficient heat-sensitive resistance as a temperature sensor,a temperature control system was designed based on a micro control unit(MCU)and direct proportion-integration-differentiation(PID)algorithm.Changing the width and amplitude of the pulse width modulation signal output from the MCU to adjust the driving current and direction of the thermoelectric cooler,the temperature of the semiconductor laser was controlled at about 25℃±0.1℃.Experimental results show that the temperature control system is with high precision and fast responsibility in a large range of temperature,it is better than other similar products.
In order to obtain stable output power and wavelength from a semiconductor laser in a large range of temperature,according to the characteristics of small volume,light weight and the high requirement of temperature stability of a semiconductor laser,with a negative-coefficient heat-sensitive resistance as a temperature sensor,a temperature control system was designed based on a micro control unit(MCU)and direct proportion-integration-differentiation(PID)algorithm.Changing the width and amplitude of the pulse width modulation signal output from the MCU to adjust the driving current and direction of the thermoelectric cooler,the temperature of the semiconductor laser was controlled at about 25℃±0.1℃.Experimental results show that the temperature control system is with high precision and fast responsibility in a large range of temperature,it is better than other similar products.
2012, 36(6): 776-779.
doi: 10.3969/j.issn.1001-3806.2012.06.016
Abstract:
In order to prepare high-quality,high-orientation,high-density,well-aligned ZnO nanorods,firstly,ZnO seed layers were prepared on glass substrates by means of pulsed laser deposition(PLD),then ZnO nanorods were prepared on the glass substrates with hydrothermal method.The role of the seed layer was explored and effects of different solution concentration on structure and photoluminescence(PL)properties of ZnO nanorods were investigated.The morphology and structure of the samples were measured by scanning electron microscope(SEM) and X-ray diffraction(XRD).The PL spectra of the workpieces were measured with an established photoluminescence test system.SEM and XRD results show that ZnO nanorods have highly orientation,distribution compact uniform.The excitons emission is slightly lower than the deep level luminescence.As the solution concentration increasing,the ratio of exciton and deep level luminescence relative intensity decreases in order.
In order to prepare high-quality,high-orientation,high-density,well-aligned ZnO nanorods,firstly,ZnO seed layers were prepared on glass substrates by means of pulsed laser deposition(PLD),then ZnO nanorods were prepared on the glass substrates with hydrothermal method.The role of the seed layer was explored and effects of different solution concentration on structure and photoluminescence(PL)properties of ZnO nanorods were investigated.The morphology and structure of the samples were measured by scanning electron microscope(SEM) and X-ray diffraction(XRD).The PL spectra of the workpieces were measured with an established photoluminescence test system.SEM and XRD results show that ZnO nanorods have highly orientation,distribution compact uniform.The excitons emission is slightly lower than the deep level luminescence.As the solution concentration increasing,the ratio of exciton and deep level luminescence relative intensity decreases in order.
2012, 36(6): 780-782.
doi: 10.3969/j.issn.1001-3806.2012.06.017
Abstract:
Hybrid CO2 laser-metal inertia gas(MIG) welding is an efficient and fast welding method,however,porosity is prone to produce when welding aluminum alloy.In order to analyze the porosity characteristics of aluminum alloy in medium thickness by means of hybrid CO2 laser-MIG welding,10mm thick 5052 aluminum alloy was welded by means of bead weld.Theoretical analysis and experimental verification was carried out.The results show that the heat source space and the back protection cushion block influence the porosity obviously.The porosity rate is minimum when the heat source spacing is 2mm~3mm.Porosity can be effectively suppressed by the back protection of cushion block.
Hybrid CO2 laser-metal inertia gas(MIG) welding is an efficient and fast welding method,however,porosity is prone to produce when welding aluminum alloy.In order to analyze the porosity characteristics of aluminum alloy in medium thickness by means of hybrid CO2 laser-MIG welding,10mm thick 5052 aluminum alloy was welded by means of bead weld.Theoretical analysis and experimental verification was carried out.The results show that the heat source space and the back protection cushion block influence the porosity obviously.The porosity rate is minimum when the heat source spacing is 2mm~3mm.Porosity can be effectively suppressed by the back protection of cushion block.
2012, 36(6): 783-787.
doi: 10.3969/j.issn.1001-3806.2012.06.018
Abstract:
The fabrication process,investigation of femtosecond laser direct writing optical waveguides,different transparent materials for direct writing optical waveguides,and the applications of direct writing optical waveguides were reviewed.As is summarized,the induced refractive index changes are materials related,and also dependent on laser energy,pulse duration repetition rate,polarization,and the scan velocity,etc.The femtosecond laser micromachining technique has extensive application prospects in the field of photonic devices.
The fabrication process,investigation of femtosecond laser direct writing optical waveguides,different transparent materials for direct writing optical waveguides,and the applications of direct writing optical waveguides were reviewed.As is summarized,the induced refractive index changes are materials related,and also dependent on laser energy,pulse duration repetition rate,polarization,and the scan velocity,etc.The femtosecond laser micromachining technique has extensive application prospects in the field of photonic devices.
2012, 36(6): 788-792.
doi: 10.3969/j.issn.1001-3806.2012.06.019
Abstract:
In order to study the 3-D features of Cr atoms in laser cooling field,the interaction process of Cr atom and laser cooling field was analyzed.Based on the semi-classical theory of Doppler and polarization gradient force,the fourth-order Runge-Kutta algorithm was adopted to simulate 3-D trajectory of Cr atoms,at the same time,three-dimension distribution of them was also obtained.After passing through laser cooling field,the divergence angle of Cr atomic beam becomes smaller,and the corresponding velocity also decreases.The results show that the three-dimension features of Cr atoms agree with the two-dimension cases,and can provide more comprehensive,richer cooling information.
In order to study the 3-D features of Cr atoms in laser cooling field,the interaction process of Cr atom and laser cooling field was analyzed.Based on the semi-classical theory of Doppler and polarization gradient force,the fourth-order Runge-Kutta algorithm was adopted to simulate 3-D trajectory of Cr atoms,at the same time,three-dimension distribution of them was also obtained.After passing through laser cooling field,the divergence angle of Cr atomic beam becomes smaller,and the corresponding velocity also decreases.The results show that the three-dimension features of Cr atoms agree with the two-dimension cases,and can provide more comprehensive,richer cooling information.
2012, 36(6): 793-797.
doi: 10.3969/j.issn.1001-3806.2012.06.020
Abstract:
In order to measure male thread efficiently,vertical projection measurement method was studied in theory and experiment.The reason and conditions for the distortion of thread profiles in process of measuring profile angles was explained taking tri-angular thread and acme thread as examples.It is proved in principle that thread profile distortion cannot occur in measuring tri-angular thread profiles with vertical projection measuring method,while it does for acme thread.After comparing the measurement data of tri-angular thread and acme thread that measured with tool microscope and image instrument respectively,it shows that tri-angular and pipe thread can be measured properly with vertical projection measurement,and it can bring about big error for acme thread measurement.The result is helpful to measure male thread efficiently with vertical projection measurement.
In order to measure male thread efficiently,vertical projection measurement method was studied in theory and experiment.The reason and conditions for the distortion of thread profiles in process of measuring profile angles was explained taking tri-angular thread and acme thread as examples.It is proved in principle that thread profile distortion cannot occur in measuring tri-angular thread profiles with vertical projection measuring method,while it does for acme thread.After comparing the measurement data of tri-angular thread and acme thread that measured with tool microscope and image instrument respectively,it shows that tri-angular and pipe thread can be measured properly with vertical projection measurement,and it can bring about big error for acme thread measurement.The result is helpful to measure male thread efficiently with vertical projection measurement.
2012, 36(6): 798-801.
doi: 10.3969/j.issn.1001-3806.2012.06.021
Abstract:
Precision measurement of mini-rotating-angle is of significance in practice engineering applications.In order to measure mini-rotating-angles with much higher precision,a new method was presented combining the digital holographic,double-exposure of interferometry with image processing.Through detailed theoretical analysis and experimental verification,the Young's modulus of steel wires was measured with this method,and its error was only 1.1%.Results indicate that the method can be widely used in practical application because of its high accuracy,strong feasibility.The results are helpful for the future design of more perfect goniometers.
Precision measurement of mini-rotating-angle is of significance in practice engineering applications.In order to measure mini-rotating-angles with much higher precision,a new method was presented combining the digital holographic,double-exposure of interferometry with image processing.Through detailed theoretical analysis and experimental verification,the Young's modulus of steel wires was measured with this method,and its error was only 1.1%.Results indicate that the method can be widely used in practical application because of its high accuracy,strong feasibility.The results are helpful for the future design of more perfect goniometers.
2012, 36(6): 802-805.
doi: 10.3969/j.issn.1001-3806.2012.06.022
Abstract:
In order to study effect of two pieces of potassium titanyl phosphate(KTiOPO4,KTP) crystal in tandem to improve the conversion efficiency of the frequency doubling green lasers,three pieces of KTP crystal in 6mm,8mm,15mm long separately were used in experiments with two of them in tandem.The conversion efficiency curves of monolithic crystal and two tandem crystals were drawn.The results of scheme of two-piece KTP crystal orthogonal or parallel tandem were compared with that of a single monolithic KTP.The result shows that two-piece KTP orthogonal tandem has nearly 10% higher conversion efficiency than two-piece KTP parallel tandem,and two-piece KTP orthogonal tandem has nearly 30% higher conversion efficiency than a monolithic one in the same length with power density at fundamental frequency from 520MW/cm2 to 750MW/cm2.The experimental results have a certain significance in improving the conversion efficiency of frequency doubling green lasers.
In order to study effect of two pieces of potassium titanyl phosphate(KTiOPO4,KTP) crystal in tandem to improve the conversion efficiency of the frequency doubling green lasers,three pieces of KTP crystal in 6mm,8mm,15mm long separately were used in experiments with two of them in tandem.The conversion efficiency curves of monolithic crystal and two tandem crystals were drawn.The results of scheme of two-piece KTP crystal orthogonal or parallel tandem were compared with that of a single monolithic KTP.The result shows that two-piece KTP orthogonal tandem has nearly 10% higher conversion efficiency than two-piece KTP parallel tandem,and two-piece KTP orthogonal tandem has nearly 30% higher conversion efficiency than a monolithic one in the same length with power density at fundamental frequency from 520MW/cm2 to 750MW/cm2.The experimental results have a certain significance in improving the conversion efficiency of frequency doubling green lasers.
2012, 36(6): 806-809.
doi: 10.3969/j.issn.1001-3806.2012.06.023
Abstract:
In order to obtain higher measurement resolution,an analogical differential-phase low homological optical reflecting system was developed with a differential amplifier combined with a high magnification microscope objective lens based on a low homological light source and a Michelson interferometer.High signal-to-noise ratio and high sensitivity can be obtained by means of the balanced detecting structure.The high time-frequency width product can be acquired by using the differential amplifier with frequency width of 100MHz.Thus a higher sensitivity can be achieved for measuring the surface morphology and moving rate.The result indicates that the local measurement by use of a super luminiferous diode(SLD) with narrow frequency width and a microscope objective with large number aperture has the same effect on local location.
In order to obtain higher measurement resolution,an analogical differential-phase low homological optical reflecting system was developed with a differential amplifier combined with a high magnification microscope objective lens based on a low homological light source and a Michelson interferometer.High signal-to-noise ratio and high sensitivity can be obtained by means of the balanced detecting structure.The high time-frequency width product can be acquired by using the differential amplifier with frequency width of 100MHz.Thus a higher sensitivity can be achieved for measuring the surface morphology and moving rate.The result indicates that the local measurement by use of a super luminiferous diode(SLD) with narrow frequency width and a microscope objective with large number aperture has the same effect on local location.
2012, 36(6): 810-813.
doi: 10.3969/j.issn.1001-3806.2012.06.024
Abstract:
In order to study effect of substrates on the focusing laser beam in atom lithograph,the characteristics of Gaussian laser standing wave affected by diffraction of straight edge were simulated based on the scalar optical theory.The results indicate that diffracted by the straight edge,Gaussian laser will show the similar oscillation of intensity to plane wave and the Gaussian incident wave has 1.18 times of the intensity of the central axis at the first mutation of intensity,while the plane is 1.37 times.The diffraction of the Gaussian laser by straight edge trends to that of plane wave when the waist becomes larger;the distance between laser axis and substrate will affect the illumination area of the laser outside the straight edge.The optical field superimposed by the diffracted Gaussian laser and its retro-reflective wave is the standing wave with oscillation of intensity outside the shaded area.All the results can make us well understand the essence of the Gaussian laser standing wave with diffraction by straight edge.
In order to study effect of substrates on the focusing laser beam in atom lithograph,the characteristics of Gaussian laser standing wave affected by diffraction of straight edge were simulated based on the scalar optical theory.The results indicate that diffracted by the straight edge,Gaussian laser will show the similar oscillation of intensity to plane wave and the Gaussian incident wave has 1.18 times of the intensity of the central axis at the first mutation of intensity,while the plane is 1.37 times.The diffraction of the Gaussian laser by straight edge trends to that of plane wave when the waist becomes larger;the distance between laser axis and substrate will affect the illumination area of the laser outside the straight edge.The optical field superimposed by the diffracted Gaussian laser and its retro-reflective wave is the standing wave with oscillation of intensity outside the shaded area.All the results can make us well understand the essence of the Gaussian laser standing wave with diffraction by straight edge.
2012, 36(6): 814-817.
doi: 10.3969/j.issn.1001-3806.2012.06.025
Abstract:
In order to study tribological behaviors of surface micro-forming 20CrNiMo steel under laser shock processing(LSP),the effects of LSP on the friction and wear behaviors of 20CrNiMo steel were investigated through observing micro-structure and measuring the macro-surface profile.Firstly,20CrNiMo was impacted by overlapping LSP in different overlap ratio,and then micro-structure of surface layer was observed through transmission electron microscope,finally,the pictures for surface layer grain state were obtained.Friction and wear test was conducted by CETR UMT Tribometer,surface friction coefficient and wear volume was obtained.The results indicate that grain refinement happens in the surface layer due to LSP impacting 20CrNiMo.Friction and wear behaviors can be improved obviously because fine grain in the grain refinement layer can restrain fatigue wear on lubricated sliding wear process effectively.
In order to study tribological behaviors of surface micro-forming 20CrNiMo steel under laser shock processing(LSP),the effects of LSP on the friction and wear behaviors of 20CrNiMo steel were investigated through observing micro-structure and measuring the macro-surface profile.Firstly,20CrNiMo was impacted by overlapping LSP in different overlap ratio,and then micro-structure of surface layer was observed through transmission electron microscope,finally,the pictures for surface layer grain state were obtained.Friction and wear test was conducted by CETR UMT Tribometer,surface friction coefficient and wear volume was obtained.The results indicate that grain refinement happens in the surface layer due to LSP impacting 20CrNiMo.Friction and wear behaviors can be improved obviously because fine grain in the grain refinement layer can restrain fatigue wear on lubricated sliding wear process effectively.
2012, 36(6): 818-821.
doi: 10.3969/j.issn.1001-3806.2012.06.026
Abstract:
In order to overcome the difficulties of transmission calculation of arbitrary polarized electrical-magnetic waves passing through anisotropic materials by means of the traditional transfer matrix,1-D photonic crystal with magnetic defect was designed.After incident elliptically polarization wave is decomposed into left-handed and right-handed circular polarized waves,a transfer matrix for dealing with anisotropic material and arbitrary elliptically polarization was deduced.The result indicates that the change of polarization states of reflected and transmitted waves from 1-D photonic crystal can be determined by means of this new method.
In order to overcome the difficulties of transmission calculation of arbitrary polarized electrical-magnetic waves passing through anisotropic materials by means of the traditional transfer matrix,1-D photonic crystal with magnetic defect was designed.After incident elliptically polarization wave is decomposed into left-handed and right-handed circular polarized waves,a transfer matrix for dealing with anisotropic material and arbitrary elliptically polarization was deduced.The result indicates that the change of polarization states of reflected and transmitted waves from 1-D photonic crystal can be determined by means of this new method.
2012, 36(6): 822-824.
doi: 10.3969/j.issn.1001-3806.2012.06.027
Abstract:
In order to obtain high performance S+C+L optical fiber light sources with ultra bandwidth and taking a new hybrid-doped optical fiber as transmission medium and taking laser diodes pumping thulium-doped and Er-doped optical fibers,with two 3dB wide band couplers as the optical fiber reflector,a new fiber laser was designed and its energy was controlled stable with the help of a power control circuit.Experiments and the theoretical analysis were carried out.The total output was 28mW with bandwidth from 1460nm to 1610nm in the S+C+L wave band.The experimental results indicate optical-fiber-loop mirrors not only improve the flatness of the light source but also enhance the light-to-light conversion efficiency greatly.
In order to obtain high performance S+C+L optical fiber light sources with ultra bandwidth and taking a new hybrid-doped optical fiber as transmission medium and taking laser diodes pumping thulium-doped and Er-doped optical fibers,with two 3dB wide band couplers as the optical fiber reflector,a new fiber laser was designed and its energy was controlled stable with the help of a power control circuit.Experiments and the theoretical analysis were carried out.The total output was 28mW with bandwidth from 1460nm to 1610nm in the S+C+L wave band.The experimental results indicate optical-fiber-loop mirrors not only improve the flatness of the light source but also enhance the light-to-light conversion efficiency greatly.
2012, 36(6): 825-827.
doi: 10.3969/j.issn.1001-3806.2012.06.028
Abstract:
In order to simulate all-optical logic operation,based on visualization characteristics of the Simulink module,according to the theory of cross-gain modulation(XGM)of linear optical amplifiers(LOA),the logic NOR gate operation was achieved by means of modular building method.Results show that the Simulink module can be used to simulate better output results;Proper input current groups have the advantages to achieve better logic operation effect.Because the modular structure can be modified and expanded easily,modular building can be used in more logical operations too.
In order to simulate all-optical logic operation,based on visualization characteristics of the Simulink module,according to the theory of cross-gain modulation(XGM)of linear optical amplifiers(LOA),the logic NOR gate operation was achieved by means of modular building method.Results show that the Simulink module can be used to simulate better output results;Proper input current groups have the advantages to achieve better logic operation effect.Because the modular structure can be modified and expanded easily,modular building can be used in more logical operations too.
2012, 36(6): 828-831.
doi: 10.3969/j.issn.1001-3806.2012.06.029
Abstract:
In order to study the temperature field on metal material induced by pulse laser irradiation,the finite element simulation software was introduced to simulate the process of laser irradiation.The material surface and internal changes of the transient temperature field was obtained.The results show that the time of hot effect is very short in the laser irradiation process,and the heat affected zone is limited to material surface of laser irradiation area.
In order to study the temperature field on metal material induced by pulse laser irradiation,the finite element simulation software was introduced to simulate the process of laser irradiation.The material surface and internal changes of the transient temperature field was obtained.The results show that the time of hot effect is very short in the laser irradiation process,and the heat affected zone is limited to material surface of laser irradiation area.
2012, 36(6): 832-835.
doi: 10.3969/j.issn.1001-3806.2012.06.030
Abstract:
In order to analyze effect of atomic distribution on deposition preparation of nanometer gratings under the action of collimated laser,based on semi-classical theory and Runge-Kutta numerical integration algorithm,the characteristics of dissipative force and the distribution of chromium atoms in 1-D optical molasses was discussed.Then the distribution of chromium atoms was simulated under different laser parameters.The results show that the best distribution appears when the detuning of the laser frequency equals to half of line width of chromium atoms.After the atom beam passing through 1-D optical molasses,its spatial width was suppressed to 0.43 times of that before and the atomic density becomes 1.79 times larger than before,under the condition that laser power equals to 40mW and laser detuning is-2.5MHz.This results show that the atomic distribution can be improved under the action of collimated laser and it's helpful for the deposition preparation of nanometer gratings.
In order to analyze effect of atomic distribution on deposition preparation of nanometer gratings under the action of collimated laser,based on semi-classical theory and Runge-Kutta numerical integration algorithm,the characteristics of dissipative force and the distribution of chromium atoms in 1-D optical molasses was discussed.Then the distribution of chromium atoms was simulated under different laser parameters.The results show that the best distribution appears when the detuning of the laser frequency equals to half of line width of chromium atoms.After the atom beam passing through 1-D optical molasses,its spatial width was suppressed to 0.43 times of that before and the atomic density becomes 1.79 times larger than before,under the condition that laser power equals to 40mW and laser detuning is-2.5MHz.This results show that the atomic distribution can be improved under the action of collimated laser and it's helpful for the deposition preparation of nanometer gratings.
2012, 36(6): 836-839.
doi: 10.3969/j.issn.1001-3806.2012.06.031
Abstract:
It is always expected that the conversion efficiency is as high as possible for nonlinear interaction at any pump intensity.A method was presented to control the conversion efficiency of difference-frequency generation(DFG) in the periodic poled lithium niobate,by modulating the refractive index induced by electro-optic effect.The variation of DFG conversion effieciency with the external electric field was simulated.The calculated results indicate that this method is feasible and very efficient in attaining the high conversion efficiency at any given pump intensity.This result is very useful to get new lasers especially in mid-infrared region.
It is always expected that the conversion efficiency is as high as possible for nonlinear interaction at any pump intensity.A method was presented to control the conversion efficiency of difference-frequency generation(DFG) in the periodic poled lithium niobate,by modulating the refractive index induced by electro-optic effect.The variation of DFG conversion effieciency with the external electric field was simulated.The calculated results indicate that this method is feasible and very efficient in attaining the high conversion efficiency at any given pump intensity.This result is very useful to get new lasers especially in mid-infrared region.
2012, 36(6): 840-843.
doi: 10.3969/j.issn.1001-3806.2012.06.032
Abstract:
In order to study the dynamics of accelerated electrons in the plasma wakefield driven by asymmetric laser pulses,the phase space,electron density and potential energy of accelerated electrons were obtained by means of numerical simulation.The results show that the electrons have high energy in the wakefield of asymmetric laser pulses.In order to accelerate the electron effectively,it is necessary to chose appropriate rise length and fall length in the wakefield of asymmetric laser pulses.
In order to study the dynamics of accelerated electrons in the plasma wakefield driven by asymmetric laser pulses,the phase space,electron density and potential energy of accelerated electrons were obtained by means of numerical simulation.The results show that the electrons have high energy in the wakefield of asymmetric laser pulses.In order to accelerate the electron effectively,it is necessary to chose appropriate rise length and fall length in the wakefield of asymmetric laser pulses.
2012, 36(6): 844-848.
doi: 10.3969/j.issn.1001-3806.2012.06.033
Abstract:
为了实现对激光制导**半实物仿真系统中能量的精确控制,采用理论分析和工程实践相结合的方法,设计了能量仿真系统,对能量衰减模型及系统设计方案进行了研究,对其中激光生成子系统和能量衰减子系统进行了优化设计,并利用E1000激光能量计对设计的系统进行了标定。结果表明,该系统在不同频率下生成的能量稳定在40mJ左右,可变衰减比范围优于47dB。该系统的实时性和精度均满足半实物仿真中激光能量模拟的要求,且稳定可靠。
为了实现对激光制导**半实物仿真系统中能量的精确控制,采用理论分析和工程实践相结合的方法,设计了能量仿真系统,对能量衰减模型及系统设计方案进行了研究,对其中激光生成子系统和能量衰减子系统进行了优化设计,并利用E1000激光能量计对设计的系统进行了标定。结果表明,该系统在不同频率下生成的能量稳定在40mJ左右,可变衰减比范围优于47dB。该系统的实时性和精度均满足半实物仿真中激光能量模拟的要求,且稳定可靠。
