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RSS2007 Vol. 31, No. 5
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2007, 31(5): 449-451.
[Abstract]
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Abstract:
Thermal induced distortion in the gain element is the main obstacle to be overcome in the scaling of solid-state lasers to very high output powers.In order to compensate the aberration,the method of using an intra-cavity deformable mirror was carried out.The intra-cavity configuration was change when the deformable mirror was input the voltage.A referenced light from out-cavity was used to get across the intra-cavity.The effect of the intra-cavity aberration to the referenced light could be detected with a wavefront detector and was compensated by using the deformable mirror.The experimental results indicate the intra-cavity aberration was effectively compensated and the output power and beam quality were improved.
Thermal induced distortion in the gain element is the main obstacle to be overcome in the scaling of solid-state lasers to very high output powers.In order to compensate the aberration,the method of using an intra-cavity deformable mirror was carried out.The intra-cavity configuration was change when the deformable mirror was input the voltage.A referenced light from out-cavity was used to get across the intra-cavity.The effect of the intra-cavity aberration to the referenced light could be detected with a wavefront detector and was compensated by using the deformable mirror.The experimental results indicate the intra-cavity aberration was effectively compensated and the output power and beam quality were improved.
2007, 31(5): 452-455,554.
Abstract:
A novel photonics detector arrays consisted of Geiger-mode avalanche photodiodes(G-APD) was introduced.The key techniques,device developments and system integration of this new image detector were emphasized.A G-APD array detector has two outstanding characters:single photon sensitivity and pico-second resolving power,which makes the detector very suitable for the weak optical signal 3-D imaging.On the other hand,the G-APD array detector is all-solid state photonics detection device.It has small size,light weight and high reliability,and it can be mass manufactured with nowadays matured micro photonics device process.Therefore,G-APD array is a great advantage at the array photonics detector development,and it will be applied widely in the advanced photonics imaging area.
A novel photonics detector arrays consisted of Geiger-mode avalanche photodiodes(G-APD) was introduced.The key techniques,device developments and system integration of this new image detector were emphasized.A G-APD array detector has two outstanding characters:single photon sensitivity and pico-second resolving power,which makes the detector very suitable for the weak optical signal 3-D imaging.On the other hand,the G-APD array detector is all-solid state photonics detection device.It has small size,light weight and high reliability,and it can be mass manufactured with nowadays matured micro photonics device process.Therefore,G-APD array is a great advantage at the array photonics detector development,and it will be applied widely in the advanced photonics imaging area.
2007, 31(5): 456-458.
Abstract:
End-cap is effective for avoiding the fiber facet damage of pulsed double-clad fiber lasers under high peak power.In order to achieve end-cap assembling of large diameter double-clad fibers with low cost,a fiber end-cap splicing system based on a CO2 laser was designed and built.The method and process of fiber end-cap assembling was studied.The quality of the end-cap was evaluated by testing a high-peak-power pulsed fiber laser,which was assembled with end-caps using our method.The experimental results show that high-quality low-cost splicing of end-caps on double-clad fibers can be achieved by our splicing system.The end-cap spliced by our method can evidently increase the damage threshold of the fiber.Meanwhile,the influence of the end-cap on the efficiency and beam quality of the laser output is not obvious.
End-cap is effective for avoiding the fiber facet damage of pulsed double-clad fiber lasers under high peak power.In order to achieve end-cap assembling of large diameter double-clad fibers with low cost,a fiber end-cap splicing system based on a CO2 laser was designed and built.The method and process of fiber end-cap assembling was studied.The quality of the end-cap was evaluated by testing a high-peak-power pulsed fiber laser,which was assembled with end-caps using our method.The experimental results show that high-quality low-cost splicing of end-caps on double-clad fibers can be achieved by our splicing system.The end-cap spliced by our method can evidently increase the damage threshold of the fiber.Meanwhile,the influence of the end-cap on the efficiency and beam quality of the laser output is not obvious.
2007, 31(5): 462-464,468.
Abstract:
In order to study the geometric characteristics of laser remelting zone was additional chemical reaction heat,the experiments of laser cladding with a CO2 laser were conducted by prefabricated coating of Al or Mg and Fe3O4 on the surface of low alloy steel,the effects of chemical reaction heat on morphology of laser remelting zone were obtained.The results show that the chemical reaction heat makes the increase of the width of laser remelting zone and heat-affected zone,and the decrease of the depth-to-width ratio of laser remelting zone.The melting depth adding Al and Fe3O4 coating is larger than that of blackened surface,and the melting depth adding Mg and Fe3O4 coating is lower than that of blackened surface.The multi-component alloy permeating layer may be formed quickly in laser remelting zone by means of multi-component reducing reaction of alloying oxidate.
In order to study the geometric characteristics of laser remelting zone was additional chemical reaction heat,the experiments of laser cladding with a CO2 laser were conducted by prefabricated coating of Al or Mg and Fe3O4 on the surface of low alloy steel,the effects of chemical reaction heat on morphology of laser remelting zone were obtained.The results show that the chemical reaction heat makes the increase of the width of laser remelting zone and heat-affected zone,and the decrease of the depth-to-width ratio of laser remelting zone.The melting depth adding Al and Fe3O4 coating is larger than that of blackened surface,and the melting depth adding Mg and Fe3O4 coating is lower than that of blackened surface.The multi-component alloy permeating layer may be formed quickly in laser remelting zone by means of multi-component reducing reaction of alloying oxidate.
2007, 31(5): 465-468.
Abstract:
The investigation on the interaction of laser induced plasma and arc plasma in the laser-arc hybrid welding process benefits the understanding of complicate physical phenomenon and the optimization of welding parameters.So far,the research materials about this are few.A detail experiment of laser-arc hybrid welding was carried out on 3mm thickness 316L stainless steel by a 5kW CO2 laser together with a TIG(tungsten inert gas) welder.A dimensionless parameter,the increment of melting efficiency of hybrid welding δ,is defined to indicate the heat sources interaction of laser and arc.With the bead shape,plasma shape and δ,the effect of heat sources distance and energy ratio of laser and arc was semi-quantitative analyzed.The results show that with the optimized combination of welding parameters,δ can reach 83.6%.Moreover,the preheating of arc on the work-piece can improve the efficiency of laser power and enhance the heat sources interaction,but the laser-arc interaction is the key mechanism to improve the heat sources interaction.
The investigation on the interaction of laser induced plasma and arc plasma in the laser-arc hybrid welding process benefits the understanding of complicate physical phenomenon and the optimization of welding parameters.So far,the research materials about this are few.A detail experiment of laser-arc hybrid welding was carried out on 3mm thickness 316L stainless steel by a 5kW CO2 laser together with a TIG(tungsten inert gas) welder.A dimensionless parameter,the increment of melting efficiency of hybrid welding δ,is defined to indicate the heat sources interaction of laser and arc.With the bead shape,plasma shape and δ,the effect of heat sources distance and energy ratio of laser and arc was semi-quantitative analyzed.The results show that with the optimized combination of welding parameters,δ can reach 83.6%.Moreover,the preheating of arc on the work-piece can improve the efficiency of laser power and enhance the heat sources interaction,but the laser-arc interaction is the key mechanism to improve the heat sources interaction.
2007, 31(5): 469-472.
Abstract:
In the application of the lidar system based on edge detecting technology,the laser's central frequency will drift.If the excursion of the central frequency is too big,it will influence the measuring precision of edge detecting system.Through simulation and calculation,the absorption spectrum of molecule iodine absorption filter from 470nm~550nm was obtained.Taking the atmospheric parameters and the underwater parameters as an example,based on the lidar system using edge detecting technology,the absorption spectrum of molecule iodine absorption filter,meeting the requirement of the detecting system' was obtained and the center emission frequency of laser emitter was determined.Based on the above results,the proper monochromatic and stable frequency,meeting the detecting system's demand,was determined and the results can be used as the guideline of laser emitter's choice in the practical systems.
In the application of the lidar system based on edge detecting technology,the laser's central frequency will drift.If the excursion of the central frequency is too big,it will influence the measuring precision of edge detecting system.Through simulation and calculation,the absorption spectrum of molecule iodine absorption filter from 470nm~550nm was obtained.Taking the atmospheric parameters and the underwater parameters as an example,based on the lidar system using edge detecting technology,the absorption spectrum of molecule iodine absorption filter,meeting the requirement of the detecting system' was obtained and the center emission frequency of laser emitter was determined.Based on the above results,the proper monochromatic and stable frequency,meeting the detecting system's demand,was determined and the results can be used as the guideline of laser emitter's choice in the practical systems.
2007, 31(5): 473-475.
Abstract:
In order to improve wear resistance of titanium alloy,a CO2 laser was used to clad coating onto TC4 alloy substrate with pre-placed nickel-coated graphite powder.An MXP-2000 type pin-on-disc wear tester was used to test the dry sliding friction behavior of titanium alloy and laser cladding coating.The morphology of worn surface was examined using a scanning electron microscope.The results of experiments indicate that the friction coefficient of laser cladding coating is 0.56,which is close to that of titanium alloy.Worn loss of the coating is one tenth of that of titanium alloy.It means that laser cladding coating can greatly improve wear resistance of titanium alloy.The wear mechanism of titanium alloy is adherence wear and the wear mechanism of laser cladding coating is particle wear.High hardness with TiC strengthen phase in it make the coating possess high wear resistance.
In order to improve wear resistance of titanium alloy,a CO2 laser was used to clad coating onto TC4 alloy substrate with pre-placed nickel-coated graphite powder.An MXP-2000 type pin-on-disc wear tester was used to test the dry sliding friction behavior of titanium alloy and laser cladding coating.The morphology of worn surface was examined using a scanning electron microscope.The results of experiments indicate that the friction coefficient of laser cladding coating is 0.56,which is close to that of titanium alloy.Worn loss of the coating is one tenth of that of titanium alloy.It means that laser cladding coating can greatly improve wear resistance of titanium alloy.The wear mechanism of titanium alloy is adherence wear and the wear mechanism of laser cladding coating is particle wear.High hardness with TiC strengthen phase in it make the coating possess high wear resistance.
2007, 31(5): 476-478.
Abstract:
A new bonding technique to alleviate the high temperature adverse effect in silicon-glass bonding process was presented which combines the advantages of surface activated direct bonding and local laser bonding techniques.RCA solution was used to make the bonding surfaces hydrophilic and the silicon-glass prebonding was accomplished at room temperature.The laser with a wavelength of 1064nm was used and its spot diameter was 500μm and the power was 70W.Without any external pressure,the prebonded pairs were bonded locally and the bonding strength reaches 6.3MPa~6.8Mpa.The experimental results of show that this bonding technique,which employs surface activated prebonding to substitute pressure to maintain the intimate contact of bonding chips,has overcome the disadvantages that focusing is difficult and bonding chips and glass cover are easy to broken in normal local laser bonding processing.This technique also improves the efficiency of surface activated direct bonding by shortening the annealing time.
A new bonding technique to alleviate the high temperature adverse effect in silicon-glass bonding process was presented which combines the advantages of surface activated direct bonding and local laser bonding techniques.RCA solution was used to make the bonding surfaces hydrophilic and the silicon-glass prebonding was accomplished at room temperature.The laser with a wavelength of 1064nm was used and its spot diameter was 500μm and the power was 70W.Without any external pressure,the prebonded pairs were bonded locally and the bonding strength reaches 6.3MPa~6.8Mpa.The experimental results of show that this bonding technique,which employs surface activated prebonding to substitute pressure to maintain the intimate contact of bonding chips,has overcome the disadvantages that focusing is difficult and bonding chips and glass cover are easy to broken in normal local laser bonding processing.This technique also improves the efficiency of surface activated direct bonding by shortening the annealing time.
2007, 31(5): 479-482.
Abstract:
The technique of gifferential absorption lidar(DIAL) is applicable for probing chemical polluted gas.The basic principle of DIAL was introduced.The main parts of our specially designed DIAL as well as its working flows were also described.The emulation and simulation results of the lidar system were obtained.These results indicate that the performance of TEA CO2 laser source has much influence on the capabilities of the DIAL.
The technique of gifferential absorption lidar(DIAL) is applicable for probing chemical polluted gas.The basic principle of DIAL was introduced.The main parts of our specially designed DIAL as well as its working flows were also described.The emulation and simulation results of the lidar system were obtained.These results indicate that the performance of TEA CO2 laser source has much influence on the capabilities of the DIAL.
2007, 31(5): 483-485,539.
Abstract:
In order to investigate the temperature distribution of the soda-lime glass irradiated by laser beam,experimental and numerical computing method was used.The temperature distribution of the soda-lime glass on the surface of the heated region under CO2 laser irradiation was measured with the thermovision infrared system.The thermocouple device was used to correct the thermovision infrared system,so the real temperature distribution was obtained.The result showed that the experimental temperature transformation was in accordance with the numerical computing.
In order to investigate the temperature distribution of the soda-lime glass irradiated by laser beam,experimental and numerical computing method was used.The temperature distribution of the soda-lime glass on the surface of the heated region under CO2 laser irradiation was measured with the thermovision infrared system.The thermocouple device was used to correct the thermovision infrared system,so the real temperature distribution was obtained.The result showed that the experimental temperature transformation was in accordance with the numerical computing.
2007, 31(5): 486-488,492.
Abstract:
The mechanism of nonlinear optical loop mirror(NOLM) based on all-optical demultiplexing of hyperbolic secant pulse for both signal and clock was theoretically analyzed.The expression of minimum initial peak power of clock pulses,with which the switching efficiency of pulses peak up to 100% can be obtained,was demonstrated.The influence of walk-off time,initial time delay and initial peak power of clock pulses on the shape of output signal were numerically analyzed.The results show that the walk-off between clock pulses and signal pulses plays an important role in all-optical demultiplexing based on NOLM,the lager the walk-off time is,the smaller the peak power of converted signal is,and the more asymmetric the waveform is.Also,it's found that proper initial peak power of clock pulses can compensate the walk-off induced degradation,and initial time delay between clock pulses and signal pulses can balance the waveform asymmetric of converted signal induced by walk-off.
The mechanism of nonlinear optical loop mirror(NOLM) based on all-optical demultiplexing of hyperbolic secant pulse for both signal and clock was theoretically analyzed.The expression of minimum initial peak power of clock pulses,with which the switching efficiency of pulses peak up to 100% can be obtained,was demonstrated.The influence of walk-off time,initial time delay and initial peak power of clock pulses on the shape of output signal were numerically analyzed.The results show that the walk-off between clock pulses and signal pulses plays an important role in all-optical demultiplexing based on NOLM,the lager the walk-off time is,the smaller the peak power of converted signal is,and the more asymmetric the waveform is.Also,it's found that proper initial peak power of clock pulses can compensate the walk-off induced degradation,and initial time delay between clock pulses and signal pulses can balance the waveform asymmetric of converted signal induced by walk-off.
2007, 31(5): 493-495,521.
Abstract:
The coupling loss between photonic crystal fiber(PCF),single mode fiber(SMF),and other PCF with different structure is an urgent problem to be solved today.The local orthogonal functions model of PCF was applied to theoretical analysis of the coupling loss between PCF,SMF and PCF with different structures.The relation between coupling loss and the structural parameter of PCF and mode wavelength was obtained,and the optimal structural parameter was given.The result shows that(1) the main factor that affects the coupling loss between PCF and SMF is the hole space Λ of PCF.When the hole space is fixed to a certain value and the mode radii of PCF and SMF are the same,the coupling loss reaches its minimum value,i.e.,any deviation from this value will increase the coupling loss;(2) The coupling loss between PCFs is determined by the difference of their hole spaces.As the mode radius depends on mode wavelength,the coupling loss will also be in its minimum value when wavelength keeps constant and the mode radii of PCF and SMF are the same.Therefore,the factors should be comprehensively considered in the design process of PCF.
The coupling loss between photonic crystal fiber(PCF),single mode fiber(SMF),and other PCF with different structure is an urgent problem to be solved today.The local orthogonal functions model of PCF was applied to theoretical analysis of the coupling loss between PCF,SMF and PCF with different structures.The relation between coupling loss and the structural parameter of PCF and mode wavelength was obtained,and the optimal structural parameter was given.The result shows that(1) the main factor that affects the coupling loss between PCF and SMF is the hole space Λ of PCF.When the hole space is fixed to a certain value and the mode radii of PCF and SMF are the same,the coupling loss reaches its minimum value,i.e.,any deviation from this value will increase the coupling loss;(2) The coupling loss between PCFs is determined by the difference of their hole spaces.As the mode radius depends on mode wavelength,the coupling loss will also be in its minimum value when wavelength keeps constant and the mode radii of PCF and SMF are the same.Therefore,the factors should be comprehensively considered in the design process of PCF.
2007, 31(5): 503-506.
Abstract:
To improve the reliability of the real-time monitoring for laser welding,a multi-sensor signal sampling and processing system was built based on LabVIEW,a virtual instrument development tool.Three signals of audible sound(20Hz~20kHz),plasma optical emission(400nm~500nm),and infrared emission(1200nm~1600nm) during the laser welding process,were picked up and analyzed.Correlation analysis of the three signals shows that the two optic signals are synchronous and the audible sound signal is hysteresis to the optic signal.The hysteresis time is just equal to the sound transferring from welding point to senor,which proved the validity of the three detecting signals.Two examples show that the reliability of multi-sensor monitoring is higher than single sensor monitoring.So,the multi-sensor detecting and signal fusion is the developing direction for the laser welding monitoring in the future.
To improve the reliability of the real-time monitoring for laser welding,a multi-sensor signal sampling and processing system was built based on LabVIEW,a virtual instrument development tool.Three signals of audible sound(20Hz~20kHz),plasma optical emission(400nm~500nm),and infrared emission(1200nm~1600nm) during the laser welding process,were picked up and analyzed.Correlation analysis of the three signals shows that the two optic signals are synchronous and the audible sound signal is hysteresis to the optic signal.The hysteresis time is just equal to the sound transferring from welding point to senor,which proved the validity of the three detecting signals.Two examples show that the reliability of multi-sensor monitoring is higher than single sensor monitoring.So,the multi-sensor detecting and signal fusion is the developing direction for the laser welding monitoring in the future.
2007, 31(5): 507-510,529.
Abstract:
For simplifying the diode pumped solid-state laser pump beam collimation system,a simple model was developed to the laser pumping waist design,in which the cylindrical lens was used as the fast axis beam collimator.The system design clue and the key parameters were listed.The feasibility of the cylindrical lens as the fast axis beam collimator was prooved through simulation analysis.The pumping beam waist could be controlled through elaborate selection of parameter R,L1,L0 and f.The experiment showed that the optical to optical efficiency could get larger than 47% when the radius of the cylindrical lens was 3mm,the range between the laser source and the lens was 0.7mm and both the range between the cylindrical lens and the focusing lens and the focal length of the focusing lens are 5mm.
For simplifying the diode pumped solid-state laser pump beam collimation system,a simple model was developed to the laser pumping waist design,in which the cylindrical lens was used as the fast axis beam collimator.The system design clue and the key parameters were listed.The feasibility of the cylindrical lens as the fast axis beam collimator was prooved through simulation analysis.The pumping beam waist could be controlled through elaborate selection of parameter R,L1,L0 and f.The experiment showed that the optical to optical efficiency could get larger than 47% when the radius of the cylindrical lens was 3mm,the range between the laser source and the lens was 0.7mm and both the range between the cylindrical lens and the focusing lens and the focal length of the focusing lens are 5mm.
2007, 31(5): 511-514.
Abstract:
Artificial neural networks were introduced in the area of laser cladding forming.The prediction model of surface quality in laser cladding parts,including the width,depth of cladding layer and dilution,was proposed based on the improved learned arithmetic.The model combined the global optimization searching performance of the genetic algorithm and the localization of the back propagation(BP) neural networks.Five technical parameters were selected to test the reliability of the model.The simulation and experimental results show that the evolutionary neural network based on genetic algorithm can effectively overcome the problem of falling into local minimum point.This method can get higher accuracy of prediction.It improves the measurement precision with the maximum relative error 2.14% between the predicted content and the real value.
Artificial neural networks were introduced in the area of laser cladding forming.The prediction model of surface quality in laser cladding parts,including the width,depth of cladding layer and dilution,was proposed based on the improved learned arithmetic.The model combined the global optimization searching performance of the genetic algorithm and the localization of the back propagation(BP) neural networks.Five technical parameters were selected to test the reliability of the model.The simulation and experimental results show that the evolutionary neural network based on genetic algorithm can effectively overcome the problem of falling into local minimum point.This method can get higher accuracy of prediction.It improves the measurement precision with the maximum relative error 2.14% between the predicted content and the real value.
2007, 31(5): 515-517.
Abstract:
In order to study the efficiency of detecting thickness of CO2 in low space by differential absorption lidar(DIAL),the detection principle and the SNR(signal to noise ratio) of the system were analyzed.With the simulation experiments of a kind of near-infrared micro pulse lidar with energy of 20μJ and repetition rate of 10kHz,the relation among the SNR,the needed accumulation time and detection distance was calculated.The results show that without regard to the background noise(working at night),the thickness of CO2 can be detected below 4.5km.Whereas,with regard to the background noise(working in daylight),the thickness of CO2 can only be detected below 2.4km.The conclusion is drawn that working at night and with other better performance instruments can increase the detection distance.
In order to study the efficiency of detecting thickness of CO2 in low space by differential absorption lidar(DIAL),the detection principle and the SNR(signal to noise ratio) of the system were analyzed.With the simulation experiments of a kind of near-infrared micro pulse lidar with energy of 20μJ and repetition rate of 10kHz,the relation among the SNR,the needed accumulation time and detection distance was calculated.The results show that without regard to the background noise(working at night),the thickness of CO2 can be detected below 4.5km.Whereas,with regard to the background noise(working in daylight),the thickness of CO2 can only be detected below 2.4km.The conclusion is drawn that working at night and with other better performance instruments can increase the detection distance.
2007, 31(5): 518-521.
Abstract:
Collapsing of the edges is one of the most important problems in laser-cladding process.The objective is to find the reason and how to solve it.At first,an analytical model was established and the temperature field in the laser-cladding was calculated.After analyzing the calculation results,it was found that the centralization of heat energy at edges was the main reason of edge collapse.Based on experiments,how to solve the edge collapse was found.Finally,this method was applied to laser-cladding on tooth surface and amelioration was achieved on the tooth surface.The results of the experiments prove that this method is valuable and reliable.
Collapsing of the edges is one of the most important problems in laser-cladding process.The objective is to find the reason and how to solve it.At first,an analytical model was established and the temperature field in the laser-cladding was calculated.After analyzing the calculation results,it was found that the centralization of heat energy at edges was the main reason of edge collapse.Based on experiments,how to solve the edge collapse was found.Finally,this method was applied to laser-cladding on tooth surface and amelioration was achieved on the tooth surface.The results of the experiments prove that this method is valuable and reliable.
2007, 31(5): 522-525.
Abstract:
Fully digital control implemented by DSP for the capacitor charging power supply of TEA CO2 laser was studied in order to improve its applicability and reliability.A real-time resonant period tracking scheme of "comparing-capture" was proposed,based on which comparing studies was conducted with the scheme of "sampling-calculation".Both of them can complete the tracking in 3 switching periods when the resonant current is strong and the signal noise ratio(SNR) is high,but the "sampling-calculation" scheme can not realize tracking when the resonant current is weak or the SNR is low.These experimental results and its insensibility to the waveform distortion of resonance current show that the "comparing-capture" scheme is a better tracking scheme to ensure the zero-current-switching of serial resonant circuit.
Fully digital control implemented by DSP for the capacitor charging power supply of TEA CO2 laser was studied in order to improve its applicability and reliability.A real-time resonant period tracking scheme of "comparing-capture" was proposed,based on which comparing studies was conducted with the scheme of "sampling-calculation".Both of them can complete the tracking in 3 switching periods when the resonant current is strong and the signal noise ratio(SNR) is high,but the "sampling-calculation" scheme can not realize tracking when the resonant current is weak or the SNR is low.These experimental results and its insensibility to the waveform distortion of resonance current show that the "comparing-capture" scheme is a better tracking scheme to ensure the zero-current-switching of serial resonant circuit.
2007, 31(5): 526-529.
Abstract:
In order to analyze the characteristics of multi-position pumped fiber laser expediently,the predominant part of the re-emission was adopted to improve the solutions precise,and the rate equations describing the Yb-doped multi-position pumped fiber lasers were solved analytically.The solutions of the output power of the fiber lasers were got approximately.Comparing the analytical solutions and the numerical solutions,the result shows the difference between them is small than 5%.Based on the relationship between the position of the pump point and the utilization efficiency of pump light,the conclusion was drawn that pump sources should be set near the fiber ends.Simulating the distribution of pump light along the fiber of the two schemes(one-position-pump and multi-position-pump),the results show that for the multi-position-pump scheme,the distribution of pump power is relatively uniform along the fiber compared to that of the one-position-pump scheme.In other words,extra local temperature rise arising from the absorption of the external cald can be reduced in the multi-position-pump scheme,rendering it a better choice for the high power fiber lasers.
In order to analyze the characteristics of multi-position pumped fiber laser expediently,the predominant part of the re-emission was adopted to improve the solutions precise,and the rate equations describing the Yb-doped multi-position pumped fiber lasers were solved analytically.The solutions of the output power of the fiber lasers were got approximately.Comparing the analytical solutions and the numerical solutions,the result shows the difference between them is small than 5%.Based on the relationship between the position of the pump point and the utilization efficiency of pump light,the conclusion was drawn that pump sources should be set near the fiber ends.Simulating the distribution of pump light along the fiber of the two schemes(one-position-pump and multi-position-pump),the results show that for the multi-position-pump scheme,the distribution of pump power is relatively uniform along the fiber compared to that of the one-position-pump scheme.In other words,extra local temperature rise arising from the absorption of the external cald can be reduced in the multi-position-pump scheme,rendering it a better choice for the high power fiber lasers.
2007, 31(5): 530-533,536.
Abstract:
The mechanism of photoacoustic was briefly introduced,the development of photoacoustic imaging technology and algorithm of reconstructed images,which has instructional effect on development of photoacoustic imaging technology,were reported.
The mechanism of photoacoustic was briefly introduced,the development of photoacoustic imaging technology and algorithm of reconstructed images,which has instructional effect on development of photoacoustic imaging technology,were reported.
2007, 31(5): 534-536.
Abstract:
In order to compare the irradiation damage difference of three polymer optical fiber(POF),by analyzing the physical and chemical changes of polymethylmethacrylate(PMMA),polystyrene(PS) and polycarbonate(PC) optical fiber under γ-ray irradiation and measuring the transmission rate of three POFs under different dose γ-ray irradiation,the quantitative irradiation damage results is given.Under lower dose 0.1kGy and 1kGy,the transmission curves of three kinds of POF are flat in the whole visible light range.When the irradiation dose is 5kGy and 10kGy,the three transmission rates have evident peak value in the different wavelength range.The high the dose is,the more evident the peak effect is,and transmission curves become fluctuating,moreover,the peak value wavelength move to longer wavelength.The results indicated that the radiaton damage of three kinds of POF was wavelength-dependent,which is good reference to applying POF in nuclear radiation environment.
In order to compare the irradiation damage difference of three polymer optical fiber(POF),by analyzing the physical and chemical changes of polymethylmethacrylate(PMMA),polystyrene(PS) and polycarbonate(PC) optical fiber under γ-ray irradiation and measuring the transmission rate of three POFs under different dose γ-ray irradiation,the quantitative irradiation damage results is given.Under lower dose 0.1kGy and 1kGy,the transmission curves of three kinds of POF are flat in the whole visible light range.When the irradiation dose is 5kGy and 10kGy,the three transmission rates have evident peak value in the different wavelength range.The high the dose is,the more evident the peak effect is,and transmission curves become fluctuating,moreover,the peak value wavelength move to longer wavelength.The results indicated that the radiaton damage of three kinds of POF was wavelength-dependent,which is good reference to applying POF in nuclear radiation environment.
2007, 31(5): 537-539.
Abstract:
An experimental setup was constructed to measure the thickness less than 0.5mm of the indissoluble liquid film.When the laser falls on the liquid film surface waves,steady and visible diffraction patterns were obtained.Based on laser diffration,the theory of dispersion relations for waves on liquid film surfaces was testified.Subsequently,the thickness of the liquid film was measured carefully.The result shows that the measured thickness corresponded with the actual thickness very wel1.Based on the principle of this experiment,a new method for thickness measurement of indissoluble liquid film is built in a real time and non-contact way.
An experimental setup was constructed to measure the thickness less than 0.5mm of the indissoluble liquid film.When the laser falls on the liquid film surface waves,steady and visible diffraction patterns were obtained.Based on laser diffration,the theory of dispersion relations for waves on liquid film surfaces was testified.Subsequently,the thickness of the liquid film was measured carefully.The result shows that the measured thickness corresponded with the actual thickness very wel1.Based on the principle of this experiment,a new method for thickness measurement of indissoluble liquid film is built in a real time and non-contact way.
2007, 31(5): 540-543.
Abstract:
The basic configuration and principle of Tm3+-doped fiber laser were introduced.The latest reseach progresses of Tm3+-doped fiber lasers pumped by various pump sources,such as LD,Nd:YAG laser,Yb3+-doped fiber lasers and Er3+-doped fiber lasers,were reviewed and analysed in detail.Output characteristics of lasers could be improved through improving cross relaxation rate,minimising energy transfer upconversion and addressing thermal management issues.Some potential applications in the biomedical field was also presented.
The basic configuration and principle of Tm3+-doped fiber laser were introduced.The latest reseach progresses of Tm3+-doped fiber lasers pumped by various pump sources,such as LD,Nd:YAG laser,Yb3+-doped fiber lasers and Er3+-doped fiber lasers,were reviewed and analysed in detail.Output characteristics of lasers could be improved through improving cross relaxation rate,minimising energy transfer upconversion and addressing thermal management issues.Some potential applications in the biomedical field was also presented.
2007, 31(5): 548-550.
Abstract:
A new kind of insert loss and return loss measurement system was developed to improve the precision and speed of the measurement.The new system was made of optical unit and circuit unit.Optical couplers were used to get the loss power of optical connectors,and the power was transformed into electric current by detectors.The current was received and then amplified and transformed into digital signals by circuit unit.A single chip was used to calculate digital signals and output the result to the LCD.The experimental results show that the system is able to display the return loss and insert loss immediately with at the precision of 0.05dB.Further,the result indicates that the high precision measuring range can reach 70dB.
A new kind of insert loss and return loss measurement system was developed to improve the precision and speed of the measurement.The new system was made of optical unit and circuit unit.Optical couplers were used to get the loss power of optical connectors,and the power was transformed into electric current by detectors.The current was received and then amplified and transformed into digital signals by circuit unit.A single chip was used to calculate digital signals and output the result to the LCD.The experimental results show that the system is able to display the return loss and insert loss immediately with at the precision of 0.05dB.Further,the result indicates that the high precision measuring range can reach 70dB.
2007, 31(5): 551-554.
Abstract:
In order to find out temperature influence on 2m KTA OPO(KTA optical parametric oscillator) laser,the temperature effect on phase-matching angle and nonlinear coefficient was calculated,the graph of the relationship between the temperature and the tunable-angle was drawn and the walk-off angle and accept angle of the phase-matched crystal in different temperature were analyzed.It was found that the crystal was in the best condition when the temperature kept in 20℃.
In order to find out temperature influence on 2m KTA OPO(KTA optical parametric oscillator) laser,the temperature effect on phase-matching angle and nonlinear coefficient was calculated,the graph of the relationship between the temperature and the tunable-angle was drawn and the walk-off angle and accept angle of the phase-matched crystal in different temperature were analyzed.It was found that the crystal was in the best condition when the temperature kept in 20℃.
2007, 31(5): 555-557.
Abstract:
In order to study the dynamic response of sheet metal to the laser shockwave loading,the characteristics of laser shock forming,the effect of pulse energy on sheet metal deformation and the distribution of shockwave pressure in irradiated zone,single laser shock forming of LD31 aluminum alloy was carried out with high-power Q-switched,pulsed neodymium-glass laser.Then the process of laser shock forming was simulated with ABAQUS.The results reveal that viscoplastic deformation happens in sheet metal under laser shocking,the deformation of sheet metal increases with the increase of pulse energy in nonlinear way,and pressure in irradiated zone decreases along radius.
In order to study the dynamic response of sheet metal to the laser shockwave loading,the characteristics of laser shock forming,the effect of pulse energy on sheet metal deformation and the distribution of shockwave pressure in irradiated zone,single laser shock forming of LD31 aluminum alloy was carried out with high-power Q-switched,pulsed neodymium-glass laser.Then the process of laser shock forming was simulated with ABAQUS.The results reveal that viscoplastic deformation happens in sheet metal under laser shocking,the deformation of sheet metal increases with the increase of pulse energy in nonlinear way,and pressure in irradiated zone decreases along radius.
2007, 31(5): 558-560.
Abstract:
The methodology was proposed for image processing and interactive visualization of confocal microscopy images.Firstly,an intensity compensation algorithm was applied to reduce noises resulted from light absorption and scattering by objects and particles in the volume through which light passes.Secondly,a deconvolution algorithm based on maximum a posteriori was applied to improve the image stacks quality.At last,the ray-casting algorithm was used to reconstruct the fine details in the volume.Furthermore,virtual reality technique was integrated with volume rendering in order to provide users an intuitive interface to view the cells and its structures through translation,rotation and zoom operations.The speed and versatility of the program allows for convenient,fast,interactive examination of unknown cell structures even on common PC.The program can be applied for different types of confocal microscopy data sets with good results.
The methodology was proposed for image processing and interactive visualization of confocal microscopy images.Firstly,an intensity compensation algorithm was applied to reduce noises resulted from light absorption and scattering by objects and particles in the volume through which light passes.Secondly,a deconvolution algorithm based on maximum a posteriori was applied to improve the image stacks quality.At last,the ray-casting algorithm was used to reconstruct the fine details in the volume.Furthermore,virtual reality technique was integrated with volume rendering in order to provide users an intuitive interface to view the cells and its structures through translation,rotation and zoom operations.The speed and versatility of the program allows for convenient,fast,interactive examination of unknown cell structures even on common PC.The program can be applied for different types of confocal microscopy data sets with good results.
2007, 31(5): 459-461.
Abstract:
In order to study the optical feedback characteristics of the dual frequency laser,a birefringent external cavity was studied throughboth theoretical analysis and experiments.In the experiments,the phenomenon of the fringe frequency doubled was observed.It was found that the resolution of the optical feedback system was doubled and the sensitivity of the optical feedback system was also improved after the modes competition between both the polarized light beams.The work is useful for improving the resolution of the optical feedback systems.
In order to study the optical feedback characteristics of the dual frequency laser,a birefringent external cavity was studied throughboth theoretical analysis and experiments.In the experiments,the phenomenon of the fringe frequency doubled was observed.It was found that the resolution of the optical feedback system was doubled and the sensitivity of the optical feedback system was also improved after the modes competition between both the polarized light beams.The work is useful for improving the resolution of the optical feedback systems.
2007, 31(5): 489-492.
Abstract:
A serious experiment of CO2 laser-tungsten inert gas(TIG) arc hybrid welding was used to weld the 316L stainless steel with Rofin Sinar 5kW CO2 laser and Miller TIG welding machine.The effect of various parameters such as laser power,arc current and the laser-arc distance on the welding shape was studied in detail.The result showed that there was a "key hole" when the laser power was above 2.5kW,which dominantly affected the weld penetration;the weld width was relative to the power of the laser and energy of the arc when the arc current was less than 150A,but the weld width was determined by the energy of the arc only when the arc current was larger than 150A.There was an optimal laser-arc distance(2mm~3mm),with which the weld penetration can be improved to 1.46 times~2.54 times.The research shows that the hybrid welding can improve the weld ability of 316L stainless steel.
A serious experiment of CO2 laser-tungsten inert gas(TIG) arc hybrid welding was used to weld the 316L stainless steel with Rofin Sinar 5kW CO2 laser and Miller TIG welding machine.The effect of various parameters such as laser power,arc current and the laser-arc distance on the welding shape was studied in detail.The result showed that there was a "key hole" when the laser power was above 2.5kW,which dominantly affected the weld penetration;the weld width was relative to the power of the laser and energy of the arc when the arc current was less than 150A,but the weld width was determined by the energy of the arc only when the arc current was larger than 150A.There was an optimal laser-arc distance(2mm~3mm),with which the weld penetration can be improved to 1.46 times~2.54 times.The research shows that the hybrid welding can improve the weld ability of 316L stainless steel.
2007, 31(5): 496-499,502.
Abstract:
In order to improve the gain saturation property of vertical-cavity semiconductor optical amplifiers(VCSOAs),based on the structure character,applying gain enhancement factor and modifying the boundary condition,the relation between input signal power and photon density was derived to study the gain saturation property.The calculation result was agreement with the experiment.Four factors affecting property of gain saturation were obtained.The results showed that the active region area,top mirror reflectivity,pump power,spontaneous emission factor affected the property of gain saturation.After optimizing the parameter,the input saturation power could arrive-2dBm.It is useful to improve the gain saturation property of VCSOAs.
In order to improve the gain saturation property of vertical-cavity semiconductor optical amplifiers(VCSOAs),based on the structure character,applying gain enhancement factor and modifying the boundary condition,the relation between input signal power and photon density was derived to study the gain saturation property.The calculation result was agreement with the experiment.Four factors affecting property of gain saturation were obtained.The results showed that the active region area,top mirror reflectivity,pump power,spontaneous emission factor affected the property of gain saturation.After optimizing the parameter,the input saturation power could arrive-2dBm.It is useful to improve the gain saturation property of VCSOAs.
2007, 31(5): 500-502.
Abstract:
In order to understand how the multiple scattering affecting the atmosphere laser communication in haze weather,the multiple scattering model was set up.After analysis,a conclusion was drawn that in light haze weather,the effect of forward scattering on laser communication could be ignored.The theory can be used in atmosphere laser communication system design.
In order to understand how the multiple scattering affecting the atmosphere laser communication in haze weather,the multiple scattering model was set up.After analysis,a conclusion was drawn that in light haze weather,the effect of forward scattering on laser communication could be ignored.The theory can be used in atmosphere laser communication system design.
2007, 31(5): 544-547,550.
Abstract:
Thermal effect of high power fiber laser severely limits the output power and beam quality.Temperature distribution in a double-clad high power fiber laser was analyzed based on thermal conductive equation and boundary condition,and thermal stress distribution was presented by temperature distribution,the change of index refraction induced by temperature and stress was analyzed separately,optic path difference in double-clad high power fiber laser induced by thermal effect was presented.Results indicate that all stresses are compressive,in the fiber core region,however,in the cladding region,the stress is partly compressive and tensile;at the fiber outer boundary,the radial stress is zero while the tangential and longitudinal stress are equal and tensile;the change of index refraction induced by temperature is larger than by stress;optic path difference was caused mostly by the change of temperature,very small by thermal expand and thermal stress.
Thermal effect of high power fiber laser severely limits the output power and beam quality.Temperature distribution in a double-clad high power fiber laser was analyzed based on thermal conductive equation and boundary condition,and thermal stress distribution was presented by temperature distribution,the change of index refraction induced by temperature and stress was analyzed separately,optic path difference in double-clad high power fiber laser induced by thermal effect was presented.Results indicate that all stresses are compressive,in the fiber core region,however,in the cladding region,the stress is partly compressive and tensile;at the fiber outer boundary,the radial stress is zero while the tangential and longitudinal stress are equal and tensile;the change of index refraction induced by temperature is larger than by stress;optic path difference was caused mostly by the change of temperature,very small by thermal expand and thermal stress.
