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RSS2018 Vol. 42, No. 4
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2018, 42(4): 433-439.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.001
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Abstract:
To develop an atmospheric NO2 differential absorption lidar (DIAL) with detection range of 3km and resolution of 10μg/m3, based on NO2 absorption spectrum and lidar equation, the relationships among echo signal-to-noise ratio (SNR), aerosol of the horizontal and vertical direction, NO2 concentration, detection distance and geometric factor were analyzed and simulated. The atmospheric NO2 experiment system was built, and the atmospheric NO2 concentration experiment was carried out. The NO2 concentration in horizontal and vertical height of 0.4km~3.0km was obtained in real time, and the resolution was up to 4.717μg/m3. The system was stable and reliable. The results show that, with two Nd:YAG lasers with wavelength of 354.7nm and laser energy not less than 100mJ to pump two dye lasers with C450 as the dye, two output light beams for differential absorption detection can be obtained with λon of 448.10nm, λoff of 446.80nm, and energy of 8mJ. This method provides theoretical basis and technical support for the design and application of practical NO2 differential absorption lidar light sources.
To develop an atmospheric NO2 differential absorption lidar (DIAL) with detection range of 3km and resolution of 10μg/m3, based on NO2 absorption spectrum and lidar equation, the relationships among echo signal-to-noise ratio (SNR), aerosol of the horizontal and vertical direction, NO2 concentration, detection distance and geometric factor were analyzed and simulated. The atmospheric NO2 experiment system was built, and the atmospheric NO2 concentration experiment was carried out. The NO2 concentration in horizontal and vertical height of 0.4km~3.0km was obtained in real time, and the resolution was up to 4.717μg/m3. The system was stable and reliable. The results show that, with two Nd:YAG lasers with wavelength of 354.7nm and laser energy not less than 100mJ to pump two dye lasers with C450 as the dye, two output light beams for differential absorption detection can be obtained with λon of 448.10nm, λoff of 446.80nm, and energy of 8mJ. This method provides theoretical basis and technical support for the design and application of practical NO2 differential absorption lidar light sources.
2018, 42(4): 440-445.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.002
Abstract:
Flexible electronic is an important research direction for the development of wearable equipment, internet of things and other applications. Laser lift-off technique is a technology to separate glass substrates from flexible substrates, and one of the important technologies to realize flexible electronic devices at present with advantages of optional light wavelength, short action time, and small heat effect areas.In this paper, the main technical characteristics of laser lift-off were introduced, its application in different flexible electronic fields was analyzed, the main processes and functions in the application process were discussed. Finally, the future development trend of laser lift-off technology was summarized.The rapid development of laser lift-off technologywill form a strong support for the research and development of flexible electronics industry.
Flexible electronic is an important research direction for the development of wearable equipment, internet of things and other applications. Laser lift-off technique is a technology to separate glass substrates from flexible substrates, and one of the important technologies to realize flexible electronic devices at present with advantages of optional light wavelength, short action time, and small heat effect areas.In this paper, the main technical characteristics of laser lift-off were introduced, its application in different flexible electronic fields was analyzed, the main processes and functions in the application process were discussed. Finally, the future development trend of laser lift-off technology was summarized.The rapid development of laser lift-off technologywill form a strong support for the research and development of flexible electronics industry.
2018, 42(4): 446-450.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.003
Abstract:
In order to study molten liquid ejection mechanism induced by interaction between millisecond laser and silicon targets, based on the so-called shadow method, the process of molten liquid ejection was studied after the sequence shading pictures of the interaction between the millisecond laser and the solid targets (silicon and aluminum) were recorded by high speed CCD. The difference between melting and splashing process of silicon and aluminum targets caused by millisecond laser was compared. The mechanism of solid melting splashing formed by millisecond laser was also discussed. According to the different melting and splashing mechanism of the two targets, the reasons of splashing angle, splash distribution and splash brightness of two targets were explained. The results show that, millisecond laser can produce gasification and melting spatter process for both targets, but gasification intensity, shape and brightness of the melted splash are different. When interacting with silicon targets, the gasification phenomenon is not obvious in the action area. The molten splash is liquid drop. Its brightness is stronger than the background. The maximum angle between the splashing direction and the normal line of the front target surface is 45°, and the molten spatter is distributed within the angle. When interacting with aluminum targets, gasification phenomenon is more obvious in the action area. The molten splash is linear opaque fluid. Its brightness is lower than the background light. The angle between the splashing direction and the normal line of the front target surface is 20°. The molten spatter is distributed along the line of splashing direction. The study is helpful for laser processing technology.
In order to study molten liquid ejection mechanism induced by interaction between millisecond laser and silicon targets, based on the so-called shadow method, the process of molten liquid ejection was studied after the sequence shading pictures of the interaction between the millisecond laser and the solid targets (silicon and aluminum) were recorded by high speed CCD. The difference between melting and splashing process of silicon and aluminum targets caused by millisecond laser was compared. The mechanism of solid melting splashing formed by millisecond laser was also discussed. According to the different melting and splashing mechanism of the two targets, the reasons of splashing angle, splash distribution and splash brightness of two targets were explained. The results show that, millisecond laser can produce gasification and melting spatter process for both targets, but gasification intensity, shape and brightness of the melted splash are different. When interacting with silicon targets, the gasification phenomenon is not obvious in the action area. The molten splash is liquid drop. Its brightness is stronger than the background. The maximum angle between the splashing direction and the normal line of the front target surface is 45°, and the molten spatter is distributed within the angle. When interacting with aluminum targets, gasification phenomenon is more obvious in the action area. The molten splash is linear opaque fluid. Its brightness is lower than the background light. The angle between the splashing direction and the normal line of the front target surface is 20°. The molten spatter is distributed along the line of splashing direction. The study is helpful for laser processing technology.
High intensity attosecond pulse generated by the improved multi-cycle polarization gating technology
2018, 42(4): 451-456.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.004
Abstract:
In order to produce high-intensity single attosecond pulse (SAP), an improved multi-cycle polarization gating (PG) technology was proposed and the inhomogeneous PG scheme was used to control harmonic emission and to produce the SAP in the bowtie-shaped nanostructure. After theoretical analysis and experimental verification, it is found that, due to the enhancement of plasma resonance on the surface of nanostructures, not only the extension of the harmonic cutoff can be found, but also the contribution of the harmonics from the long quantum path can be reduced. Further, with the control of PG technology, the contribution of supercontinuum is only from single harmonic emission peak, forming the platform area with the bandwidth of 140eV. By properly adding an ultrashort ultraviolet pulse, the harmonic yield can be enhanced by 2 orders of magnitude. By superposing this supercontinuum, a SAP with the full width at half maximum of 27as can be obtained. Moreover, the intensity of this SAP is 2 orders of magnitude higher than that produced from single PG scheme. The investigation is helpful to produce the high-intensity SAP and to advance the development of the attosecond science.
In order to produce high-intensity single attosecond pulse (SAP), an improved multi-cycle polarization gating (PG) technology was proposed and the inhomogeneous PG scheme was used to control harmonic emission and to produce the SAP in the bowtie-shaped nanostructure. After theoretical analysis and experimental verification, it is found that, due to the enhancement of plasma resonance on the surface of nanostructures, not only the extension of the harmonic cutoff can be found, but also the contribution of the harmonics from the long quantum path can be reduced. Further, with the control of PG technology, the contribution of supercontinuum is only from single harmonic emission peak, forming the platform area with the bandwidth of 140eV. By properly adding an ultrashort ultraviolet pulse, the harmonic yield can be enhanced by 2 orders of magnitude. By superposing this supercontinuum, a SAP with the full width at half maximum of 27as can be obtained. Moreover, the intensity of this SAP is 2 orders of magnitude higher than that produced from single PG scheme. The investigation is helpful to produce the high-intensity SAP and to advance the development of the attosecond science.
2018, 42(4): 457-461.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.005
Abstract:
In order to study relationship between output power and device temperature of a vertical cavity surface emitting laser (VCSEL)and determine the temperature range at which the user can use the network normally, the relationshipmodel between output power and working current (P-I) was used to do theoretical analysis and experimental verification. Then the model was optimized by simplifying the parameters and introducing voltage-current (U-I) relationship curve. The model parameters were obtained by means of Levenberg-Marquardt (LM) algorithm. The P-I characteristic curve data at different temperatures were predicted by comparing the similarity between measured data and fitting data at 20℃.The results show that, at a fixed temperature, optical output power increasesat first and then decreaseswith the increaseof driving current. At the fixed driving current, optical output power decreaseswith the increaseof temperature. To ensure the normal Internet using, room temperature of VCSEL laserscan notbe higher than 31℃.
In order to study relationship between output power and device temperature of a vertical cavity surface emitting laser (VCSEL)and determine the temperature range at which the user can use the network normally, the relationshipmodel between output power and working current (P-I) was used to do theoretical analysis and experimental verification. Then the model was optimized by simplifying the parameters and introducing voltage-current (U-I) relationship curve. The model parameters were obtained by means of Levenberg-Marquardt (LM) algorithm. The P-I characteristic curve data at different temperatures were predicted by comparing the similarity between measured data and fitting data at 20℃.The results show that, at a fixed temperature, optical output power increasesat first and then decreaseswith the increaseof driving current. At the fixed driving current, optical output power decreaseswith the increaseof temperature. To ensure the normal Internet using, room temperature of VCSEL laserscan notbe higher than 31℃.
2018, 42(4): 462-465.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.006
Abstract:
In order to study micronano fiber couplers, numerical simulation of the melting and drawing process of micronano fiber couplers was carried out by using beam propagation method. The curves of output light power with the change of tensile length and the distribution diagram of light field were obtained. The change of mode field and the characteristics of light field of three phases of the coupler were analyzed through software simulation. The results show that output light power of two fibers tends to be equal and no longer varies with the change of tensile length when a micronano fiber coupler is in the phase of losing the effective coupling. The characteristics of light field distribution of the fused taper coupler at various stages are different. The loss of effective coupling of taper-type micronano fiber coupler is directly related to fiber diameter of the melting zone. And the fiber diameter is related to the input light wavelength. The smaller the wavelength is, the smaller the fiber diameter that should be reached by the melt zone is. It is helpful for the study of the conditions for the loss of effective coupling of micronano fiber coupler.
In order to study micronano fiber couplers, numerical simulation of the melting and drawing process of micronano fiber couplers was carried out by using beam propagation method. The curves of output light power with the change of tensile length and the distribution diagram of light field were obtained. The change of mode field and the characteristics of light field of three phases of the coupler were analyzed through software simulation. The results show that output light power of two fibers tends to be equal and no longer varies with the change of tensile length when a micronano fiber coupler is in the phase of losing the effective coupling. The characteristics of light field distribution of the fused taper coupler at various stages are different. The loss of effective coupling of taper-type micronano fiber coupler is directly related to fiber diameter of the melting zone. And the fiber diameter is related to the input light wavelength. The smaller the wavelength is, the smaller the fiber diameter that should be reached by the melt zone is. It is helpful for the study of the conditions for the loss of effective coupling of micronano fiber coupler.
2018, 42(4): 466-469.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.007
Abstract:
The measurement and monitoring of the vibration of the rotating shaft are the main means of the fault analysis and diagnosis of the rotating machinery. In order to realize the portable and high precision field measurement, the technique of rotating shaft vibration measurement based on direct electron-modulation laser Doppler coherent was proposed. Through analysis of the measurement system, the mathematical model was derived.The results show that, direct modulation of the frequency of laser beam simplifies the measurement of optical path, reduces the volume and cost. The laser Doppler coherent measurement meets the high resolution requirements.The design of the second frequency-mixing solves the problem of direct processing of weak signals under electromagnetic interference. The application of sampling integration technique improves the signal to noise ratio and makes the system more accurate. The measurement uncertainty of the system is less than 0.1%.This study is of certain guiding significance for the intelligent field measurement.
The measurement and monitoring of the vibration of the rotating shaft are the main means of the fault analysis and diagnosis of the rotating machinery. In order to realize the portable and high precision field measurement, the technique of rotating shaft vibration measurement based on direct electron-modulation laser Doppler coherent was proposed. Through analysis of the measurement system, the mathematical model was derived.The results show that, direct modulation of the frequency of laser beam simplifies the measurement of optical path, reduces the volume and cost. The laser Doppler coherent measurement meets the high resolution requirements.The design of the second frequency-mixing solves the problem of direct processing of weak signals under electromagnetic interference. The application of sampling integration technique improves the signal to noise ratio and makes the system more accurate. The measurement uncertainty of the system is less than 0.1%.This study is of certain guiding significance for the intelligent field measurement.
2018, 42(4): 470-475.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.008
Abstract:
In order to meet application requirements of optical axis stabilization on a vehicle platform, compositions of the optical axis stabilization system were introduced and selection requirements of the driver of a fast steering mirror (FSM) were analyzed. With piezoelectric ceramics actuators as the drivers for the FSM, modal analysis and mechanical simulation of the FSM were carried out and the structure design was optimized. Using the position of centroid detected by high frequency camera as feedback signal, high speed image processing was made with field-programmable gate array, and a FSM for optical axis stabilization based on vehicle platform was developed. Performance parameters of the FSM were tested. After integration test, it is found that the resolution is about 0.4μrad and the bandwidth of the closed loop is more than 100Hz. With the car running at 40km/h on a three-level road, with the FSM controlled by the central computer in unattended mode, the root-mean-square jitters on x and y axes of the closed loop decreases 3.6 and 2.1 times of that of the open loop respectively. The suppression effect of optical axis jitter within 20Hz is obvious and preferable test result is obtained. The system has characteristics of high bandwidth, high accuracy and high stability, and plays an important role in the optical axis stabilization on a vehicle platform.
In order to meet application requirements of optical axis stabilization on a vehicle platform, compositions of the optical axis stabilization system were introduced and selection requirements of the driver of a fast steering mirror (FSM) were analyzed. With piezoelectric ceramics actuators as the drivers for the FSM, modal analysis and mechanical simulation of the FSM were carried out and the structure design was optimized. Using the position of centroid detected by high frequency camera as feedback signal, high speed image processing was made with field-programmable gate array, and a FSM for optical axis stabilization based on vehicle platform was developed. Performance parameters of the FSM were tested. After integration test, it is found that the resolution is about 0.4μrad and the bandwidth of the closed loop is more than 100Hz. With the car running at 40km/h on a three-level road, with the FSM controlled by the central computer in unattended mode, the root-mean-square jitters on x and y axes of the closed loop decreases 3.6 and 2.1 times of that of the open loop respectively. The suppression effect of optical axis jitter within 20Hz is obvious and preferable test result is obtained. The system has characteristics of high bandwidth, high accuracy and high stability, and plays an important role in the optical axis stabilization on a vehicle platform.
2018, 42(4): 476-481.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.009
Abstract:
In order to study the microstructure and mechanical properties of welded joints of high nitrogen steel, high nitrogen steel plate with 8mm thickness was used as test material and Nd:YAG solid state laser with the rated power of 4kW was used to do laser-arc composite welding. The microstructure and fracture morphology of the welded joint were photographed and analyzed by a metallographic microscope and a scanning electron microscope. The microstructures of the base material, the heat affected zone and the welded zone were further analyzed in terms of element composition, content and phase composition by energy a spectrum analyzer and a X-ray diffractometer. The results show that the microstructure of the welded zone is typical dendrite and a small amount of equiaxial morphology. Both the base material and the heat affected zone are austenitic tissues.The welded zone is accompanied by a small amount of delta ferrite in addition to austenite tissues. The second phase particles in weld seam are mainly produced by metallurgical reaction in the form of TiO2, spinel (MnAl2O4) and silicate. It has obvious refinement to the grain and can increase the strength of weld seam. Tensile fracture occurs in the welded zone.Fracture morphology is typical of dimple fracture. The morphology of the cavity and the second phase particles can be found at the fracture. It is indicated that weld defects may lead to weak mechanical properties. The study lays a foundation for the application of laser-arc composite welding in the field of high nitrogen steel welding.
In order to study the microstructure and mechanical properties of welded joints of high nitrogen steel, high nitrogen steel plate with 8mm thickness was used as test material and Nd:YAG solid state laser with the rated power of 4kW was used to do laser-arc composite welding. The microstructure and fracture morphology of the welded joint were photographed and analyzed by a metallographic microscope and a scanning electron microscope. The microstructures of the base material, the heat affected zone and the welded zone were further analyzed in terms of element composition, content and phase composition by energy a spectrum analyzer and a X-ray diffractometer. The results show that the microstructure of the welded zone is typical dendrite and a small amount of equiaxial morphology. Both the base material and the heat affected zone are austenitic tissues.The welded zone is accompanied by a small amount of delta ferrite in addition to austenite tissues. The second phase particles in weld seam are mainly produced by metallurgical reaction in the form of TiO2, spinel (MnAl2O4) and silicate. It has obvious refinement to the grain and can increase the strength of weld seam. Tensile fracture occurs in the welded zone.Fracture morphology is typical of dimple fracture. The morphology of the cavity and the second phase particles can be found at the fracture. It is indicated that weld defects may lead to weak mechanical properties. The study lays a foundation for the application of laser-arc composite welding in the field of high nitrogen steel welding.
2018, 42(4): 482-486.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.010
Abstract:
In order to improve the sensitivity and stability of concentration and temperature measurement, the optical loss in the optical fiber system was monitored by means of time-domain analysis. A sensing system based on fiber loop ring-down spectroscopy (FLRDS) was proposed. Based on the measurement results of concentration and temperature, parameter selection of the core-offset sensing structure was analyzed experimentally. The effect of intra-cavity signal amplification on pulse intensity and pulse number was studied. The results show that, when the interference length L and offset D are 4cm and 3.75μm respectively, interference effect is optimal. Pulse peak intensity is 4 times that without intra-cavity amplification and pulse number is bigger. When the sucrose and glucose concentration is 0.100g/mL~0.400g/mL, concentration sensitivities are 756.51μs/(g/mL) and 909.07μs/(g/mL), and the detection limit is 0.0014g/mL. The temperature sensitivity is 1.83μs/℃ in the range of 30℃~200℃. The design and research of this system provide valuable guidance for sensing application of concentration and temperature.
In order to improve the sensitivity and stability of concentration and temperature measurement, the optical loss in the optical fiber system was monitored by means of time-domain analysis. A sensing system based on fiber loop ring-down spectroscopy (FLRDS) was proposed. Based on the measurement results of concentration and temperature, parameter selection of the core-offset sensing structure was analyzed experimentally. The effect of intra-cavity signal amplification on pulse intensity and pulse number was studied. The results show that, when the interference length L and offset D are 4cm and 3.75μm respectively, interference effect is optimal. Pulse peak intensity is 4 times that without intra-cavity amplification and pulse number is bigger. When the sucrose and glucose concentration is 0.100g/mL~0.400g/mL, concentration sensitivities are 756.51μs/(g/mL) and 909.07μs/(g/mL), and the detection limit is 0.0014g/mL. The temperature sensitivity is 1.83μs/℃ in the range of 30℃~200℃. The design and research of this system provide valuable guidance for sensing application of concentration and temperature.
2018, 42(4): 487-493.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.011
Abstract:
In order to study mode conversion of laser-excited shear waves interaction with the side of vertical cracks, the laser-generated ultrasound propagating along the horizontal surface and received on the vertical surface was simulated by means of finite element method. After experiments, the change of displacement signals received by side receiving point at different depths was analyzed when laser-excited ultrasonic was transmitted to the vertical side. The results show that, when the side receiving point is within the corresponding depth of the critical angle, the surface wave signal generated by laser-excited surface wave at the secondary source of the corner appears. When the side receiving point is outside the critical angle, there is a mode transformation generated by laser-induced shear wave acting on the side of the vertical crack, and a new surface wave is formed. Furthermore, when the excitation position is fixed, time difference of arrival between both signals increases gradually with the downward receiving position. The results can promote the detection of vertical cracks by laser ultrasound.
In order to study mode conversion of laser-excited shear waves interaction with the side of vertical cracks, the laser-generated ultrasound propagating along the horizontal surface and received on the vertical surface was simulated by means of finite element method. After experiments, the change of displacement signals received by side receiving point at different depths was analyzed when laser-excited ultrasonic was transmitted to the vertical side. The results show that, when the side receiving point is within the corresponding depth of the critical angle, the surface wave signal generated by laser-excited surface wave at the secondary source of the corner appears. When the side receiving point is outside the critical angle, there is a mode transformation generated by laser-induced shear wave acting on the side of the vertical crack, and a new surface wave is formed. Furthermore, when the excitation position is fixed, time difference of arrival between both signals increases gradually with the downward receiving position. The results can promote the detection of vertical cracks by laser ultrasound.
2018, 42(4): 494-499.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.012
Abstract:
In order to analyze effect of laser power on microstructure and properties of Co-based gradient wear-resistant coatings, alloy powders of St6, St12B and Co47+WC (mass fraction of 0.05) were claded on the surface of 20CrMnMo steel. Co-based gradient wear-resistant coatings with the thickness of about 2.4mm were prepared to do microstructure analysis, microhardness test, friction and wear test. The results show that there is no crack on the surface of the coatings under different laser powers. The morphology of the crystals in each coating is similar:dense equiaxed grains in the surface layer, large columnar crystals in the transition layer, and plane and dendrites in the bottom layer. The unmelted WC particles are found in the wear-resistant layer at 600W. The hard phase of CoW2B2 is found in the wear-resistant layer at 800W. From the study about the properties of the coatings, the higher the laser power, the better the microhardness and wear resistance of the coatings in the range of 600W to 800W. When laser power is 800W, microhardness of the wear-resistant layer is 730HV0.1, and wear resistance of the coating is 300% higher than that of the matrix. The results of this study provide a reference for the preparation of Co-based gradient wear-resistant coatings by laser cladding.
In order to analyze effect of laser power on microstructure and properties of Co-based gradient wear-resistant coatings, alloy powders of St6, St12B and Co47+WC (mass fraction of 0.05) were claded on the surface of 20CrMnMo steel. Co-based gradient wear-resistant coatings with the thickness of about 2.4mm were prepared to do microstructure analysis, microhardness test, friction and wear test. The results show that there is no crack on the surface of the coatings under different laser powers. The morphology of the crystals in each coating is similar:dense equiaxed grains in the surface layer, large columnar crystals in the transition layer, and plane and dendrites in the bottom layer. The unmelted WC particles are found in the wear-resistant layer at 600W. The hard phase of CoW2B2 is found in the wear-resistant layer at 800W. From the study about the properties of the coatings, the higher the laser power, the better the microhardness and wear resistance of the coatings in the range of 600W to 800W. When laser power is 800W, microhardness of the wear-resistant layer is 730HV0.1, and wear resistance of the coating is 300% higher than that of the matrix. The results of this study provide a reference for the preparation of Co-based gradient wear-resistant coatings by laser cladding.
2018, 42(4): 500-504.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.013
Abstract:
In order to study the effect of two kinds of heat sources (laser and arc) in laser-metal inert gas (MIG) hybrid welding and obtain the best coupling effect of both the heat sources, the microstructure of the joint and the cross section of the weld were observed. The effects of laser and arc on the weld were analyzed. On the basis, the parameters such as porosity and mechanical property of the weld were further measured. The influence of the proportion of energy distribution on the performance of welded joint was analyzed. The results show that, in laser-MIG hybrid welding of 6061 aluminum alloy, when the energy ratio of arc and laser is controlled near 0.9, assisted by the suitable process, the porosity of the welded joint is only 1.5%, and tensile strength is 291MPa, up to 82.9% of the base material. The parameters meet the needs of the project. This study is of general guiding significance for hybrid welding of aluminum alloy with different thickness.
In order to study the effect of two kinds of heat sources (laser and arc) in laser-metal inert gas (MIG) hybrid welding and obtain the best coupling effect of both the heat sources, the microstructure of the joint and the cross section of the weld were observed. The effects of laser and arc on the weld were analyzed. On the basis, the parameters such as porosity and mechanical property of the weld were further measured. The influence of the proportion of energy distribution on the performance of welded joint was analyzed. The results show that, in laser-MIG hybrid welding of 6061 aluminum alloy, when the energy ratio of arc and laser is controlled near 0.9, assisted by the suitable process, the porosity of the welded joint is only 1.5%, and tensile strength is 291MPa, up to 82.9% of the base material. The parameters meet the needs of the project. This study is of general guiding significance for hybrid welding of aluminum alloy with different thickness.
2018, 42(4): 505-510.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.014
Abstract:
Wear elements in engine oil play important roles in the normal operation of engines. Real-time detection of wear elements in engine oil can prevent engine from wearing and predict accidents. Therefore, the detection of wear elements in oil has important application value. The key problems of atomic spectroscopy in oil detection are summarized. The research advances of laser induced breakdown spectroscopy (LIBS) and other techniquesof atomic emission spectroscopy in oil sample detection are pointed out.The advantages and disadvantages of various techniques are analyzed. The advantages of LIBS technology in oil detection are introduced, and then indirect ablative LIBS technology is introduced. The technology of indirect ablative LIBS not only preserves the advantages of LIBS technology itself, but also improves detection sensitivity greatly. The use of indirect ablative LIBS technology to detect wear elements in oil has a great application prospect. The application of this technology in field detection is prospected.
Wear elements in engine oil play important roles in the normal operation of engines. Real-time detection of wear elements in engine oil can prevent engine from wearing and predict accidents. Therefore, the detection of wear elements in oil has important application value. The key problems of atomic spectroscopy in oil detection are summarized. The research advances of laser induced breakdown spectroscopy (LIBS) and other techniquesof atomic emission spectroscopy in oil sample detection are pointed out.The advantages and disadvantages of various techniques are analyzed. The advantages of LIBS technology in oil detection are introduced, and then indirect ablative LIBS technology is introduced. The technology of indirect ablative LIBS not only preserves the advantages of LIBS technology itself, but also improves detection sensitivity greatly. The use of indirect ablative LIBS technology to detect wear elements in oil has a great application prospect. The application of this technology in field detection is prospected.
2018, 42(4): 511-520.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.015
Abstract:
Under the excitation of the external light field, the collective electron oscillation mode formed on the surface of the metal nanostructure can effectively modulate the local electromagnetic field distribution, and control the fluorescence radiation of fluorescent molecules near the substrate. The affecting factors mainly depend on electromagnetic oscillation mode and electromagnetic field distribution formed on the surface of the substrate. The key problems in the study on surface enhanced fluorescence effect in spectroscopy are summarized. The main progress of the research of periodically ordered substrate metal enhanced fluorescence and metal nanoparticle enhanced fluorescence is performed. Based on local electromagnetic field enhancement mechanism model, the mechanism and affecting factors of fluorescence regulation of fluorescent molecules on different substrates are discussed. The research prospect of surface enhanced fluorescence effect is prospected.
Under the excitation of the external light field, the collective electron oscillation mode formed on the surface of the metal nanostructure can effectively modulate the local electromagnetic field distribution, and control the fluorescence radiation of fluorescent molecules near the substrate. The affecting factors mainly depend on electromagnetic oscillation mode and electromagnetic field distribution formed on the surface of the substrate. The key problems in the study on surface enhanced fluorescence effect in spectroscopy are summarized. The main progress of the research of periodically ordered substrate metal enhanced fluorescence and metal nanoparticle enhanced fluorescence is performed. Based on local electromagnetic field enhancement mechanism model, the mechanism and affecting factors of fluorescence regulation of fluorescent molecules on different substrates are discussed. The research prospect of surface enhanced fluorescence effect is prospected.
2018, 42(4): 521-524.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.016
Abstract:
In order to explore a flexible and efficient multiband frequency conversion scheme based on optical frequency comb, a system consisting of one dual-drive Mach-Zehnder modulator (D-MZM) and two double-parallel Mach-Zehnder modulators (DP-MZM) was used. D-MZM was drived by the received radio frequency signal, single side band modulation was carried out and then one carrier and +1 order side band were obtained. Two DP-MZMs were used as two optical comb generators, and two optical frequency combs with different phase coherence and different center frequencies were produced. The influence of DC bias point drift on frequency conversion efficiency of the system was also studied. After theoretical analysis and experimental verification, the results show that the proposed frequency conversion system can convert 15GHz microwave signals in Ku band into 3GHz, 7GHz, 11GHz, 19GHz, 23GHz and 27GHz. The signal-to-noise ratio of output microwave signal can reach 28.82dB~29.99dB. The drift of DC bias point is within the range of -10% to 50%. The influence is obvious. This method can provide multiband frequency conversion for a satellite communication system to meet requirements of multiband communication.
In order to explore a flexible and efficient multiband frequency conversion scheme based on optical frequency comb, a system consisting of one dual-drive Mach-Zehnder modulator (D-MZM) and two double-parallel Mach-Zehnder modulators (DP-MZM) was used. D-MZM was drived by the received radio frequency signal, single side band modulation was carried out and then one carrier and +1 order side band were obtained. Two DP-MZMs were used as two optical comb generators, and two optical frequency combs with different phase coherence and different center frequencies were produced. The influence of DC bias point drift on frequency conversion efficiency of the system was also studied. After theoretical analysis and experimental verification, the results show that the proposed frequency conversion system can convert 15GHz microwave signals in Ku band into 3GHz, 7GHz, 11GHz, 19GHz, 23GHz and 27GHz. The signal-to-noise ratio of output microwave signal can reach 28.82dB~29.99dB. The drift of DC bias point is within the range of -10% to 50%. The influence is obvious. This method can provide multiband frequency conversion for a satellite communication system to meet requirements of multiband communication.
2018, 42(4): 525-530.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.017
Abstract:
In order to study the characteristics of magnetic-optical images of weld defects excited by magnetic field, low carbon steel of laser welding was used as test object and the welding defects were excited by constant magnetic field and 50Hz alternating magnetic field. Real-time magnetic field distribution of welding defect area was obtained by magnetic-optical imaging sensor. Through theoretical analysis and experimental verification, the magneto-optic images of welding defects of low carbon steel (Q235) of thickness of 1mm, 2mm and 3mm with constant magnetic field and alternating magnetic field were obtained, and then, were compared with COMSOL simulation results. The weighted average image fusion technique was used to fuse the magnetic-optical images of welding defects in the alternating magnetic field. The results show that, compared with the excitation of constant magnetic field, the welding defect information obtained by the alternating excitation is more accurate, fast and complete, and avoids the omission of welding defect information effectively. This study provides the basis for improving the detection efficiency of welding defects.
In order to study the characteristics of magnetic-optical images of weld defects excited by magnetic field, low carbon steel of laser welding was used as test object and the welding defects were excited by constant magnetic field and 50Hz alternating magnetic field. Real-time magnetic field distribution of welding defect area was obtained by magnetic-optical imaging sensor. Through theoretical analysis and experimental verification, the magneto-optic images of welding defects of low carbon steel (Q235) of thickness of 1mm, 2mm and 3mm with constant magnetic field and alternating magnetic field were obtained, and then, were compared with COMSOL simulation results. The weighted average image fusion technique was used to fuse the magnetic-optical images of welding defects in the alternating magnetic field. The results show that, compared with the excitation of constant magnetic field, the welding defect information obtained by the alternating excitation is more accurate, fast and complete, and avoids the omission of welding defect information effectively. This study provides the basis for improving the detection efficiency of welding defects.
2018, 42(4): 531-535.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.018
Abstract:
In order to quickly determine the volume fraction of acetic acid in Chinese aged liquor, 3-D fluorescence spectroscopy and alternate fitting residual algorithm were used. Firstly, 3-D fluorescence spectra of different volume fraction of acetic acid of ethanol aqueous solution was used as the calibration set. 3-D fluorescence spectrum of liquor was used as the predicted set. Alternate fitting residual algorithm was used to analyze. Standard addition method was used to verify the accuracy of the results. Through theoretical analysis and experimental verification, the results show that, correlation coefficient between the predicted volume fraction and the experimental volume fraction is 0.9926. Average recovery percentage is 101.97%. 3-D fluorescence spectrometry combined with alternate fitting residual algorithm can quickly and effectively determine the volume fraction of acetic acid in Chinese aged liquor. This result is helpful for the detection of monomer volume fraction in Chinese aged liquor.
In order to quickly determine the volume fraction of acetic acid in Chinese aged liquor, 3-D fluorescence spectroscopy and alternate fitting residual algorithm were used. Firstly, 3-D fluorescence spectra of different volume fraction of acetic acid of ethanol aqueous solution was used as the calibration set. 3-D fluorescence spectrum of liquor was used as the predicted set. Alternate fitting residual algorithm was used to analyze. Standard addition method was used to verify the accuracy of the results. Through theoretical analysis and experimental verification, the results show that, correlation coefficient between the predicted volume fraction and the experimental volume fraction is 0.9926. Average recovery percentage is 101.97%. 3-D fluorescence spectrometry combined with alternate fitting residual algorithm can quickly and effectively determine the volume fraction of acetic acid in Chinese aged liquor. This result is helpful for the detection of monomer volume fraction in Chinese aged liquor.
2018, 42(4): 536-540.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.019
Abstract:
In order to study cooling characteristics of neutral Sr of alkaline-earth metal in a Doppler cooling laser field, the relationship between the cooling results of strontium atomic in 1-D laser standing wave light field with energy level transition (5s2)1S0~(5s5p)1P1 and 3-D magneto-optical trap and laser parameters, including laser intensity and frequency detuning, was obtained by using the theory of laser cooling based on Heisenberg equations. The results show that, when the strontium atoms are in 1-D standing wave laser field and under the condition of weak laser field and frequency detuning, the dissipation force of strontium atoms is linearly related to the two parameters. But when the two parameters increase to a certain degree, the dissipative force is saturated. When strontium atoms are in 3-D magneto-optical trap and frequency detuning of laser light field in the traps is -16MHz, alkaline-earth metal strontium atoms have the lowest cooling temperature of 0.76mK. The characteristics analysis of neutral strontium atoms in Doppler cooling field provides some theoretical guidance for cooling study on other alkaline-earth metal atoms.
In order to study cooling characteristics of neutral Sr of alkaline-earth metal in a Doppler cooling laser field, the relationship between the cooling results of strontium atomic in 1-D laser standing wave light field with energy level transition (5s2)1S0~(5s5p)1P1 and 3-D magneto-optical trap and laser parameters, including laser intensity and frequency detuning, was obtained by using the theory of laser cooling based on Heisenberg equations. The results show that, when the strontium atoms are in 1-D standing wave laser field and under the condition of weak laser field and frequency detuning, the dissipation force of strontium atoms is linearly related to the two parameters. But when the two parameters increase to a certain degree, the dissipative force is saturated. When strontium atoms are in 3-D magneto-optical trap and frequency detuning of laser light field in the traps is -16MHz, alkaline-earth metal strontium atoms have the lowest cooling temperature of 0.76mK. The characteristics analysis of neutral strontium atoms in Doppler cooling field provides some theoretical guidance for cooling study on other alkaline-earth metal atoms.
2018, 42(4): 541-544.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.020
Abstract:
In order to develop a lidar to measure temperature profiles in the planetary boundary layer, the vertical distribution of atmospheric temperature was retrieved based on the ratio of the rotational Raman spectrum intensity of nitrogen and oxygen. After theoretical analysis and experimental research of rotational Raman lidar system, the atmospheric temperature data in the boundary layer were obtained.The results show that, the atmospheric temperature measured by the lidar is in good agreement with atmospheric model in the range of 0km to 2.5km. The statistical error caused by random fluctuation of signal at 2.5km reaches 1K under the conditions of laser energy of 100mJ, measurement time of about 17min and vertical resolution of 7.5m. The atmospheric temperature below 2.5km within the boundary layer can be measured with high accuracy. The increase of laser pulse energy or the select of the telescope with large caliber would improve the height of the measurement further. The study provides the favorable guidance for development of rotational Raman lidar systems for detecting atmosphere temperature in boundary layer.
In order to develop a lidar to measure temperature profiles in the planetary boundary layer, the vertical distribution of atmospheric temperature was retrieved based on the ratio of the rotational Raman spectrum intensity of nitrogen and oxygen. After theoretical analysis and experimental research of rotational Raman lidar system, the atmospheric temperature data in the boundary layer were obtained.The results show that, the atmospheric temperature measured by the lidar is in good agreement with atmospheric model in the range of 0km to 2.5km. The statistical error caused by random fluctuation of signal at 2.5km reaches 1K under the conditions of laser energy of 100mJ, measurement time of about 17min and vertical resolution of 7.5m. The atmospheric temperature below 2.5km within the boundary layer can be measured with high accuracy. The increase of laser pulse energy or the select of the telescope with large caliber would improve the height of the measurement further. The study provides the favorable guidance for development of rotational Raman lidar systems for detecting atmosphere temperature in boundary layer.
2018, 42(4): 545-549.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.021
Abstract:
In order to achieve rapid prototyping of fine electronic circuits at low cost, an activation layer was formed on the surface of the matrix by using the mixed solution of CuSO4 and NaH2PO2 as the activator. 450nm blue laser was used to scan the activation layer on the surface of the matrix and the matrix was activated. Combined with electroless copper plating, the conductive metal copper layer was prepared in the laser scanning region. The influence of mass concentration of CuSO4 and NaH2PO2, scanning rate and the number of coating on forming effect of the coating was studied. Energy spectrum analysis of the activated matrix was carried out. The appearance of the coating was characterized by scanning electron microscope. The bonding characteristics and the electrical conductivity of the coating were detected. The results show that coating coverage rate is 100% when mass concentration of CuSO4 and NaH2PO2 is 10g/L and 30g/L, the scanning speed is 320mm/s and coating number is 3. After laser scanning, Cu2+ in the activation layer is reduced to Cu particles. The microstructure of the coating line is uniform and compact with clear contour, neat boundary and strong adhesion. Surface resistance is close to 0Ω, and electrical conductivity is good. This process solves the problem of poor operability of laser induced technology and high cost of precious metal coating to a certain extent. The study has high practical value and has a certain application prospect in electronic circuit forming.
In order to achieve rapid prototyping of fine electronic circuits at low cost, an activation layer was formed on the surface of the matrix by using the mixed solution of CuSO4 and NaH2PO2 as the activator. 450nm blue laser was used to scan the activation layer on the surface of the matrix and the matrix was activated. Combined with electroless copper plating, the conductive metal copper layer was prepared in the laser scanning region. The influence of mass concentration of CuSO4 and NaH2PO2, scanning rate and the number of coating on forming effect of the coating was studied. Energy spectrum analysis of the activated matrix was carried out. The appearance of the coating was characterized by scanning electron microscope. The bonding characteristics and the electrical conductivity of the coating were detected. The results show that coating coverage rate is 100% when mass concentration of CuSO4 and NaH2PO2 is 10g/L and 30g/L, the scanning speed is 320mm/s and coating number is 3. After laser scanning, Cu2+ in the activation layer is reduced to Cu particles. The microstructure of the coating line is uniform and compact with clear contour, neat boundary and strong adhesion. Surface resistance is close to 0Ω, and electrical conductivity is good. This process solves the problem of poor operability of laser induced technology and high cost of precious metal coating to a certain extent. The study has high practical value and has a certain application prospect in electronic circuit forming.
2018, 42(4): 550-555.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.022
Abstract:
In order to design optical filter components with high-quality and high-performance, transfer matrix method was used to study the narrowband and broadband dual channel optical filtering function of photonic crystal (HL)mDl (LH)m. Computer simulation was performed. The simulation results show that, whether the dielectric layer H is left hand material(LHM) or right hand material(RHM), with the increasing of cycle number m, a single narrow transmission peak always appears at odd times of ω/ω0. With irregular variations of m, the transmission rate of transmission peak at odd times of ω/ω0 will decrease at the same speed and the transmission rate of pass band at even times of ω/ω0 will unchanged. When H is LHM, more narrow transmission peaks appear at odd times of ω/ω0 and pass band appears at even times of ω/ω0。The bigger m is, the narrower the bandwidth of transmission peak or pass band is. The results show that photonic crystal made of LHM and RHM will provide better narrowband and broadband dual channel filtering effect and modulation. The study has the guiding role in the research and design of new optical filters.
In order to design optical filter components with high-quality and high-performance, transfer matrix method was used to study the narrowband and broadband dual channel optical filtering function of photonic crystal (HL)mDl (LH)m. Computer simulation was performed. The simulation results show that, whether the dielectric layer H is left hand material(LHM) or right hand material(RHM), with the increasing of cycle number m, a single narrow transmission peak always appears at odd times of ω/ω0. With irregular variations of m, the transmission rate of transmission peak at odd times of ω/ω0 will decrease at the same speed and the transmission rate of pass band at even times of ω/ω0 will unchanged. When H is LHM, more narrow transmission peaks appear at odd times of ω/ω0 and pass band appears at even times of ω/ω0。The bigger m is, the narrower the bandwidth of transmission peak or pass band is. The results show that photonic crystal made of LHM and RHM will provide better narrowband and broadband dual channel filtering effect and modulation. The study has the guiding role in the research and design of new optical filters.
2018, 42(4): 556-561.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.023
Abstract:
In recent years, great progress has been made in the field of tunable vertical cavity surface emitting lasers. The vertical cavity surface emitting laser is perpendicular to the substrate, and this novel structure has the advantages, such as small optical divergence angle, being suitable for integration with other optoelectronic devices, and testing in chip. Simulation method was used to simulate wavelength tunable vertical cavity surface-emitting lasers with micro-mechanical structure. The structure, principle and development history of tunable vertical cavity surface emitting lasers were described. The advantages and disadvantages of different structures were introduced. The development prospects of tunable lasers were also discussed. Wavelength tunable lasers of light source can make network construction cost lower. Large range tunable lasers without mode hop can be used for high-resolution laser spectroscopy and laser ranging. This kind of device has good application prospects in optical transmission, optical interconnection and optical parallel information processing.
In recent years, great progress has been made in the field of tunable vertical cavity surface emitting lasers. The vertical cavity surface emitting laser is perpendicular to the substrate, and this novel structure has the advantages, such as small optical divergence angle, being suitable for integration with other optoelectronic devices, and testing in chip. Simulation method was used to simulate wavelength tunable vertical cavity surface-emitting lasers with micro-mechanical structure. The structure, principle and development history of tunable vertical cavity surface emitting lasers were described. The advantages and disadvantages of different structures were introduced. The development prospects of tunable lasers were also discussed. Wavelength tunable lasers of light source can make network construction cost lower. Large range tunable lasers without mode hop can be used for high-resolution laser spectroscopy and laser ranging. This kind of device has good application prospects in optical transmission, optical interconnection and optical parallel information processing.
2018, 42(4): 562-566.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.024
Abstract:
In order to quickly and accurately measure the molten steel temperature on line, infrared CCD camera temperature measurement technology was used to measure the surface temperature of molten steel. The image of molten steel at different temperatures was collected by an infrared CCD camera to calculate the average of the grayscale values in the region of the image near the temperature measured by the thermocouple. The golden section optimization method was introduced to determine the expansion coefficient in the generalized regression neural network. The nonlinear curve fitting between gray scale and temperature was compared by using the traditional least square method and the modified generalized regression neural network. The results show that the temperature measurement model established by the improved generalized regression neural network can effectively improve the on-line temperature measurement accuracy and make the measurement error of molten steel temperature within 0.1%. It meets the requirements of industrial design. This study provides a reference for the application of generalized regression neural network in the field of molten steel temperature measurement.
In order to quickly and accurately measure the molten steel temperature on line, infrared CCD camera temperature measurement technology was used to measure the surface temperature of molten steel. The image of molten steel at different temperatures was collected by an infrared CCD camera to calculate the average of the grayscale values in the region of the image near the temperature measured by the thermocouple. The golden section optimization method was introduced to determine the expansion coefficient in the generalized regression neural network. The nonlinear curve fitting between gray scale and temperature was compared by using the traditional least square method and the modified generalized regression neural network. The results show that the temperature measurement model established by the improved generalized regression neural network can effectively improve the on-line temperature measurement accuracy and make the measurement error of molten steel temperature within 0.1%. It meets the requirements of industrial design. This study provides a reference for the application of generalized regression neural network in the field of molten steel temperature measurement.
2018, 42(4): 567-571.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.025
Abstract:
Laser-induced plasma has shown increasing potential in removing micro-/nano-particles stuck onto the surface of precise components in nano-science and nano-technology. In order to study the removal mechanism of the micro-/nano-particles, silicon surfaces were cleaned by means of nanosecond laser plasma, during which the removal results was observed and then the optimized conditions for laser plasma to flush the silicon surface was recommended. The results show that plasma radiates out wide-spectrum light, whose ultraviolet short wave accelerates the ionization of surrounding air, increases the volume of plasma and increase the temperature of base and particle effectively. Because of thermal expansion difference between the base and particles, the particles are peeled from the base easily. At the same time, the high pressure shock waves up to GPa are formed resulting from the expansion and diffusion of plasma to the surrounding area. It can overcome van Edward force between the particles and the substrate and remove the micro-/nano-particles. Especially, the removal effect of the particle size larger than 0.5μm is more obvious. During the actual removal process, the distance from the plasma to the base should be between 0.2mm and 2mm. The distance can ensure the effective removal of the particles and cause no damage to the base. The effect of laser plasma on the removal of particles is obvious and it is the combined effect of the radiation effect and the shock wave effect of the plasma.
Laser-induced plasma has shown increasing potential in removing micro-/nano-particles stuck onto the surface of precise components in nano-science and nano-technology. In order to study the removal mechanism of the micro-/nano-particles, silicon surfaces were cleaned by means of nanosecond laser plasma, during which the removal results was observed and then the optimized conditions for laser plasma to flush the silicon surface was recommended. The results show that plasma radiates out wide-spectrum light, whose ultraviolet short wave accelerates the ionization of surrounding air, increases the volume of plasma and increase the temperature of base and particle effectively. Because of thermal expansion difference between the base and particles, the particles are peeled from the base easily. At the same time, the high pressure shock waves up to GPa are formed resulting from the expansion and diffusion of plasma to the surrounding area. It can overcome van Edward force between the particles and the substrate and remove the micro-/nano-particles. Especially, the removal effect of the particle size larger than 0.5μm is more obvious. During the actual removal process, the distance from the plasma to the base should be between 0.2mm and 2mm. The distance can ensure the effective removal of the particles and cause no damage to the base. The effect of laser plasma on the removal of particles is obvious and it is the combined effect of the radiation effect and the shock wave effect of the plasma.
2018, 42(4): 572-576.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.026
Abstract:
To further improve combining efficiency of polarized beam combination, effect of polarization error and systematical extensibility were analyzed byusing numerical simulation method. The influence of polarization error on combining efficiency of coherent polarization beams was calculated under three kinds of different expanded structures. The overall combining efficiency of 16 path beamswith Y structure decreases 0.33% when the transmittance of polarization beam combiner(PBC) and the reflectance of PBC are 96% and 99.5% respectively, the transmittance of the half wave-plate is 99.7% and polarization error is 0.03rad. The combining efficiency declines gradually with the increase of beam number.The combining efficiency of 128 beams with Y structure drops to 83%. The results show that, Y structure with the relative balance of light power has the highest combining efficiency, and has the least influence by the polarization error.This study determines the optimal combining scheme of the system and provides a reference for the efficiency analysis based on coherent polarization combination.
To further improve combining efficiency of polarized beam combination, effect of polarization error and systematical extensibility were analyzed byusing numerical simulation method. The influence of polarization error on combining efficiency of coherent polarization beams was calculated under three kinds of different expanded structures. The overall combining efficiency of 16 path beamswith Y structure decreases 0.33% when the transmittance of polarization beam combiner(PBC) and the reflectance of PBC are 96% and 99.5% respectively, the transmittance of the half wave-plate is 99.7% and polarization error is 0.03rad. The combining efficiency declines gradually with the increase of beam number.The combining efficiency of 128 beams with Y structure drops to 83%. The results show that, Y structure with the relative balance of light power has the highest combining efficiency, and has the least influence by the polarization error.This study determines the optimal combining scheme of the system and provides a reference for the efficiency analysis based on coherent polarization combination.
2018, 42(4): 577-582.
doi: 10.7510/jgjs.issn.1001-3806.2018.04.027
Abstract:
In order to realize 2-D distribution reconstruction of methane volume fraction field, based on tunable diode laser absorption spectroscopy (TDLAS) detection technology, methane was used as the target gas and the absorption spectrum signal of methane and nitrogen mixture was detected by direct absorption method. Volume fraction of methane was simulated and reconstructed by algebraic reconstruction algorithm. During simulation reconstruction, square reconstruction area with total 36 squares of 6×6 was used. By assuming volume fraction of a hole in a square area and simulating 24 beams through the reconstruction region from 4 directions, the projection values under the simulated ray were obtained. The results show that root mean square error of the repeated experiment is 2.58%. After adding Gaussian white noise with different signal-to-noise ratio (5%, 10%, 20%) to the simulated projection signal, root mean square error is between 4.17%~9.30%. Surface source leakage diffusion was adopted in the experiments. Artificial volume fraction hole was created and inhomogeneous volume fraction field was formed after quartz a column was placed near the center. By comparing the reconstruction results before and after the placement of quartz column, it can be seen that there is significant decrease of volume fraction in hole position. It is feasible to detect local distribution of gas volume fraction by TDLAS technology and computer tomography, and has the potential to detect volume fraction of toxic and harmful gas clouds.
In order to realize 2-D distribution reconstruction of methane volume fraction field, based on tunable diode laser absorption spectroscopy (TDLAS) detection technology, methane was used as the target gas and the absorption spectrum signal of methane and nitrogen mixture was detected by direct absorption method. Volume fraction of methane was simulated and reconstructed by algebraic reconstruction algorithm. During simulation reconstruction, square reconstruction area with total 36 squares of 6×6 was used. By assuming volume fraction of a hole in a square area and simulating 24 beams through the reconstruction region from 4 directions, the projection values under the simulated ray were obtained. The results show that root mean square error of the repeated experiment is 2.58%. After adding Gaussian white noise with different signal-to-noise ratio (5%, 10%, 20%) to the simulated projection signal, root mean square error is between 4.17%~9.30%. Surface source leakage diffusion was adopted in the experiments. Artificial volume fraction hole was created and inhomogeneous volume fraction field was formed after quartz a column was placed near the center. By comparing the reconstruction results before and after the placement of quartz column, it can be seen that there is significant decrease of volume fraction in hole position. It is feasible to detect local distribution of gas volume fraction by TDLAS technology and computer tomography, and has the potential to detect volume fraction of toxic and harmful gas clouds.
