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RSS2018 Vol. 42, No. 2
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2018, 42(2): 145-150.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.001
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Abstract:
In order to understand H2+ harmonic emission process, by using numerical solution of non-Bohn-Oppenheimer time-dependent Schrödinger equation, high-order harmonic generation (HHG) from H2+ driven by 10fs/800nm infrared (IR) field and 6fs/30nm extreme ultraviolet (XUV) pulse was theoretically investigated. The results show that, the contributions of HHG are mainly from Rabi-type oscillation, multi-photon resonance ionization, charge-resonance-enhanced ionization and dissociative ionization. With the introduction of XUV pulse, multi-harmonic cutoff extension separated by XUV photon energy can be found on HHG spectra. When the delay time between IR field and XUV pulse is larger than zero or smaller than zero, the red-shift and blue-shift of harmonics spectra can be obtained. The investigation is helpful to understand the molecular high-order harmonic generation.
In order to understand H2+ harmonic emission process, by using numerical solution of non-Bohn-Oppenheimer time-dependent Schrödinger equation, high-order harmonic generation (HHG) from H2+ driven by 10fs/800nm infrared (IR) field and 6fs/30nm extreme ultraviolet (XUV) pulse was theoretically investigated. The results show that, the contributions of HHG are mainly from Rabi-type oscillation, multi-photon resonance ionization, charge-resonance-enhanced ionization and dissociative ionization. With the introduction of XUV pulse, multi-harmonic cutoff extension separated by XUV photon energy can be found on HHG spectra. When the delay time between IR field and XUV pulse is larger than zero or smaller than zero, the red-shift and blue-shift of harmonics spectra can be obtained. The investigation is helpful to understand the molecular high-order harmonic generation.
2018, 42(2): 151-155.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.002
Abstract:
High-performance mid-infrared laser has important application value in the field of military confrontation, biological safety and environmental sciences. Fe:ZnS/ZnSe is considered to be the most effective laser medium to obtain 3μm~5μm mid-infrared lasers with high performance and wide tuning range because of long output wavelength, wide absorption band and emission band. The spectral and thermodynamic characteristics of Fe:ZnS/ZnSe are introduced. The latest development of Fe:ZnS/ZnSe at low temperature and room temperature is reviewed. Scientific challenges of Fe:ZnS/ZnSe laser in power, energy enhancement and room temperature operation are also analyzed.
High-performance mid-infrared laser has important application value in the field of military confrontation, biological safety and environmental sciences. Fe:ZnS/ZnSe is considered to be the most effective laser medium to obtain 3μm~5μm mid-infrared lasers with high performance and wide tuning range because of long output wavelength, wide absorption band and emission band. The spectral and thermodynamic characteristics of Fe:ZnS/ZnSe are introduced. The latest development of Fe:ZnS/ZnSe at low temperature and room temperature is reviewed. Scientific challenges of Fe:ZnS/ZnSe laser in power, energy enhancement and room temperature operation are also analyzed.
2018, 42(2): 156-160.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.003
Abstract:
In order to measure curvature radius of laser wavefront accurately, one method based on Talbot-Moire fringe technique was proposed. The theoretical model of measuring wavefront curvature radius was established. The relationship between wavefront curvature radius and angle of Moire fringe, and the measurement uncertainty of the system were analyzed. The measurement system was designed and constructed. Wavefront curvature radius of laser system with the diameter of 200mm was measured. The results show that, the repeatability of measurement is 0.2% when the measured result is 498m. The relative deviation between the waist position and the actual position of the beam is 0.4%. According to the measured results of 500m~3000m, the parameters such as wavefront curvature radius, the focal length of object and the position of eyepiece are calibrated. After calibration, the maximum deviation from the theoretical value is 2%. The method can achieve high precision measurement of wavefront curvature radius of laser launching system with large aperture.
In order to measure curvature radius of laser wavefront accurately, one method based on Talbot-Moire fringe technique was proposed. The theoretical model of measuring wavefront curvature radius was established. The relationship between wavefront curvature radius and angle of Moire fringe, and the measurement uncertainty of the system were analyzed. The measurement system was designed and constructed. Wavefront curvature radius of laser system with the diameter of 200mm was measured. The results show that, the repeatability of measurement is 0.2% when the measured result is 498m. The relative deviation between the waist position and the actual position of the beam is 0.4%. According to the measured results of 500m~3000m, the parameters such as wavefront curvature radius, the focal length of object and the position of eyepiece are calibrated. After calibration, the maximum deviation from the theoretical value is 2%. The method can achieve high precision measurement of wavefront curvature radius of laser launching system with large aperture.
2018, 42(2): 161-165.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.004
Abstract:
In order to study the attenuation of near infrared radiation by rainfall and quantitatively estimate the effects of rainfall on near infrared devices, on the basis of the establishment of two-element function model of raindrop distribution, a method for establishing the database of raindrop distribution was proposed. After the fitting of raindrop distribution data measured by LAWS and PARSONS in Washington region of the United States, raindrop distribution database was established. And then, combining with Mie scattering theory and attenuation coefficient formula, the relationship curves between extinction efficiency factor and raindrop diameter under 1μm, 2μm and 3μm wavelength near infrared radiation were obtained. Under the condition that rainfall was respectively 0.25mm/h, 1.25mm/h, 2.5mm/h, 12.5mm/h, 25mm/h and 50mm/h, the attenuation coefficients of near infrared radiation were calculated. The results show that, under different rainfall conditions, normal distribution has better fitting effect on function relation of raindrop spectral distribution. The envelope of extinction efficiency curve increases with the increasing of wavelength. After the fitting of function relation between attenuation coefficient and rainfall intensity, it is found that, the exponential function has the good fitting effect. The calculated results are important for studying the attenuation of near infrared radiation by rainfall.
In order to study the attenuation of near infrared radiation by rainfall and quantitatively estimate the effects of rainfall on near infrared devices, on the basis of the establishment of two-element function model of raindrop distribution, a method for establishing the database of raindrop distribution was proposed. After the fitting of raindrop distribution data measured by LAWS and PARSONS in Washington region of the United States, raindrop distribution database was established. And then, combining with Mie scattering theory and attenuation coefficient formula, the relationship curves between extinction efficiency factor and raindrop diameter under 1μm, 2μm and 3μm wavelength near infrared radiation were obtained. Under the condition that rainfall was respectively 0.25mm/h, 1.25mm/h, 2.5mm/h, 12.5mm/h, 25mm/h and 50mm/h, the attenuation coefficients of near infrared radiation were calculated. The results show that, under different rainfall conditions, normal distribution has better fitting effect on function relation of raindrop spectral distribution. The envelope of extinction efficiency curve increases with the increasing of wavelength. After the fitting of function relation between attenuation coefficient and rainfall intensity, it is found that, the exponential function has the good fitting effect. The calculated results are important for studying the attenuation of near infrared radiation by rainfall.
2018, 42(2): 166-171.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.005
Abstract:
In order to improve the difficulty and low efficiency of precision machining of KDP crystal, picosecond ultrafast laser was used in KDP crystal polishing. The influence of the factors of laser wavelength, pulse energy density, laser beam incident angle, overlapping rate, scan mode and laser focal depth on laser polishing quality of KDP crystal was studied. The interaction mechanism of laser and KDP crystal was analyzed. The experimental results show that, with the optimal parameters, such as, picosecond laser wavelength λ of 355nm, focal length f of 56mm, laser beam incident angle α of 84°, laser repetition frequency F of 800kHz, pulse energy density Q of 2.4J/cm2, overlapping rate O of 60%, 45° multi direction cross scanning and processing times T of 10, root mean square of surface roughness of KDP crystal can reach 76nm. The results add the supplements for the research of laser polishing technology.
In order to improve the difficulty and low efficiency of precision machining of KDP crystal, picosecond ultrafast laser was used in KDP crystal polishing. The influence of the factors of laser wavelength, pulse energy density, laser beam incident angle, overlapping rate, scan mode and laser focal depth on laser polishing quality of KDP crystal was studied. The interaction mechanism of laser and KDP crystal was analyzed. The experimental results show that, with the optimal parameters, such as, picosecond laser wavelength λ of 355nm, focal length f of 56mm, laser beam incident angle α of 84°, laser repetition frequency F of 800kHz, pulse energy density Q of 2.4J/cm2, overlapping rate O of 60%, 45° multi direction cross scanning and processing times T of 10, root mean square of surface roughness of KDP crystal can reach 76nm. The results add the supplements for the research of laser polishing technology.
2018, 42(2): 172-175.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.006
Abstract:
Frequency-shifted feedback laser based on acousto-optic modulation was one research hotspot in the current, and it can produce a string of harmonic wave with same interval frequency. In order to generate multi-frequency laser, the frequency-shifted feedback laser method was adopted to design an all-fiber frequency-shifted amplified feedback loop. A theoretical model of laser heterodyne correlation was established and the numerical simulation was carried out. At the same time, a fiber amplifier was introduced into the loop, and the influence of gain coefficient on the corresponding intensity of each harmonic was studied. The selection of different gain parameters for each order frequency was verified. The results show that, frequency-shifted feedback loop could be used to achieve the high-frequency modulation, several times of the fundamental frequency modulation. The highest modulation frequency is up to 4GHz. The study lays the theoretical and experimental foundation for the research of the new system of high-frequency modulation laser.
Frequency-shifted feedback laser based on acousto-optic modulation was one research hotspot in the current, and it can produce a string of harmonic wave with same interval frequency. In order to generate multi-frequency laser, the frequency-shifted feedback laser method was adopted to design an all-fiber frequency-shifted amplified feedback loop. A theoretical model of laser heterodyne correlation was established and the numerical simulation was carried out. At the same time, a fiber amplifier was introduced into the loop, and the influence of gain coefficient on the corresponding intensity of each harmonic was studied. The selection of different gain parameters for each order frequency was verified. The results show that, frequency-shifted feedback loop could be used to achieve the high-frequency modulation, several times of the fundamental frequency modulation. The highest modulation frequency is up to 4GHz. The study lays the theoretical and experimental foundation for the research of the new system of high-frequency modulation laser.
2018, 42(2): 176-180.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.007
Abstract:
In order to realize the metallization of ordinary silicate glass surface, roughness and activation were carried out by pulse ultraviolet (355nm wavelength) laser etching. The conductive copper layer was locally fabricated on the surface with the combination of chemical plating. The influence of laser processing parameters on micro topography, roughness and etching depth of glass surface was investigated. Palladium was successfully introduced into glass surface. The results show that, at the first scanning (UV laser scanning rate of 200mm/s, pulse frequency of 100kHz, energy density of 27J/cm2~37J/cm2 and filling interval of about 10μm), the etched depth of glass surface is between 25μm~35μm and roughness Ra of the etching region is between 6μm~7μm. Glass won't crack at this time. At the second scanning (energy density between 9J/cm2~11J/cm2 and the remaining unchanged parameters), chemical copper plating was realized by the introduction of palladium. At this point, the average bonding strength between copper layer and glass can be above 10MPa and volume resistivity of copper layer can reach 10-6Ω·cm orders of magnitude. The glass surface metallization process is with local selectivity, no needed mask, low cost, high bonding strength and good electrical conductivity.
In order to realize the metallization of ordinary silicate glass surface, roughness and activation were carried out by pulse ultraviolet (355nm wavelength) laser etching. The conductive copper layer was locally fabricated on the surface with the combination of chemical plating. The influence of laser processing parameters on micro topography, roughness and etching depth of glass surface was investigated. Palladium was successfully introduced into glass surface. The results show that, at the first scanning (UV laser scanning rate of 200mm/s, pulse frequency of 100kHz, energy density of 27J/cm2~37J/cm2 and filling interval of about 10μm), the etched depth of glass surface is between 25μm~35μm and roughness Ra of the etching region is between 6μm~7μm. Glass won't crack at this time. At the second scanning (energy density between 9J/cm2~11J/cm2 and the remaining unchanged parameters), chemical copper plating was realized by the introduction of palladium. At this point, the average bonding strength between copper layer and glass can be above 10MPa and volume resistivity of copper layer can reach 10-6Ω·cm orders of magnitude. The glass surface metallization process is with local selectivity, no needed mask, low cost, high bonding strength and good electrical conductivity.
2018, 42(2): 181-186.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.008
Abstract:
In order to improve the precision of laser triangulation sensor and optimize the optical parameters of design process, through mathematical modeling and computer-aided analysis method, the relationship between key parameters of laser triangulation sensor and each index of measurement system was analyzed. A method of parameter optimization based on particle swarm algorithm was adopted. After theoretical analysis and experimental verification, the parameters to meet the requirements of optical system optimization were gotten. The results show that, the parameter is controlled by each other during designing. Search spaces and constraints of particle swarm are determined. When sensitivity Smin reaches 2.2386mm, the resolution of system can reach 2.8μm. Other parameters meet the system requirements, and the optimization efficiency is greatly improved. The optimization method is simple and convenient to operate.
In order to improve the precision of laser triangulation sensor and optimize the optical parameters of design process, through mathematical modeling and computer-aided analysis method, the relationship between key parameters of laser triangulation sensor and each index of measurement system was analyzed. A method of parameter optimization based on particle swarm algorithm was adopted. After theoretical analysis and experimental verification, the parameters to meet the requirements of optical system optimization were gotten. The results show that, the parameter is controlled by each other during designing. Search spaces and constraints of particle swarm are determined. When sensitivity Smin reaches 2.2386mm, the resolution of system can reach 2.8μm. Other parameters meet the system requirements, and the optimization efficiency is greatly improved. The optimization method is simple and convenient to operate.
2018, 42(2): 187-191.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.009
Abstract:
To enhance the tunability of subwavelength grating/waveguide structure for Fano resonance, the embedded graphene monolayer was replaced by graphene-dielectric stack as a buffer layer. The improved structure was simulated by using the method of rigorous coupled-wave analysis. Nanoscale dielectric thickness in each stack cell can strengthen the effects of the alteration of graphene's conductivity on the equivalent permittivity of stack structure. The results show that, if the system is exploited as an efficient photoswitch, the demanded change of chemical potential of grapheme decreases from original 0.06eV down to 0.02eV and the modulation depth of the switch is up to 94%. If the system is employed as a tunable absorber, the frequency modulation depth of absorption spectrum is raised from 0.14THz to 0.36THz and the tuning range is extended greatly. The improved structure strengthens the tunability of system for Fano resonance.
To enhance the tunability of subwavelength grating/waveguide structure for Fano resonance, the embedded graphene monolayer was replaced by graphene-dielectric stack as a buffer layer. The improved structure was simulated by using the method of rigorous coupled-wave analysis. Nanoscale dielectric thickness in each stack cell can strengthen the effects of the alteration of graphene's conductivity on the equivalent permittivity of stack structure. The results show that, if the system is exploited as an efficient photoswitch, the demanded change of chemical potential of grapheme decreases from original 0.06eV down to 0.02eV and the modulation depth of the switch is up to 94%. If the system is employed as a tunable absorber, the frequency modulation depth of absorption spectrum is raised from 0.14THz to 0.36THz and the tuning range is extended greatly. The improved structure strengthens the tunability of system for Fano resonance.
2018, 42(2): 192-195.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.010
Abstract:
In order to accurately test the thermocouple time constant, a high power semiconductor laser with rise time of 5μs and power of 500W was used as excitation source to heat the thermocouple. Theoretical analysis and experimental verification were carries out about time constant. Because of continuous output of semiconductor laser and stable uniformity of spot energy, the restriction of traditional excitation source mechanism of the formal test system was solved. The results show that, as the output power of semiconductor laser is constant, by closed-loop feedback control of laser power, laser step temperature rise signal is generated to ensure the uniform heating of thermocouple and obtain expected equilibrium temperature. Time constants of four different thermocouples were 2.806s, 3.094s, 2.229s and 2.457s. The feedback controller has strong robustness. The test system can stimulate the ideal step temperature rise signal to provide high quality excitation source for thermocouple time constant test.
In order to accurately test the thermocouple time constant, a high power semiconductor laser with rise time of 5μs and power of 500W was used as excitation source to heat the thermocouple. Theoretical analysis and experimental verification were carries out about time constant. Because of continuous output of semiconductor laser and stable uniformity of spot energy, the restriction of traditional excitation source mechanism of the formal test system was solved. The results show that, as the output power of semiconductor laser is constant, by closed-loop feedback control of laser power, laser step temperature rise signal is generated to ensure the uniform heating of thermocouple and obtain expected equilibrium temperature. Time constants of four different thermocouples were 2.806s, 3.094s, 2.229s and 2.457s. The feedback controller has strong robustness. The test system can stimulate the ideal step temperature rise signal to provide high quality excitation source for thermocouple time constant test.
2018, 42(2): 196-200.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.011
Abstract:
In order to improve spectral resolution of an imaging spectrometer without changing its hardware structure, a novel method of spectral refinement was adopted. An imaging spectrometer with liquid crystal tunable filter was used to obtain the approximate spectral data of the incident light for theoretical analysis and experimental verification. In three sets of numerical simulation data, the standard deviations of the spectral intensity difference between the approximate spectra and the true spectral were reduced by 79.3%, 68.3% and 58.8%, compared with the spectra measured with an imaging spectrometer. In two sets of experiment data, the standard deviations were decreased by 84.4% and 60.7%. The results show that the approximation degree between the approximate spectrum and the real spectrum of the incident light is improved and the spectral peaks are separated very well. It is helpful to improve the spectral detection capability of imaging spectrometers.
In order to improve spectral resolution of an imaging spectrometer without changing its hardware structure, a novel method of spectral refinement was adopted. An imaging spectrometer with liquid crystal tunable filter was used to obtain the approximate spectral data of the incident light for theoretical analysis and experimental verification. In three sets of numerical simulation data, the standard deviations of the spectral intensity difference between the approximate spectra and the true spectral were reduced by 79.3%, 68.3% and 58.8%, compared with the spectra measured with an imaging spectrometer. In two sets of experiment data, the standard deviations were decreased by 84.4% and 60.7%. The results show that the approximation degree between the approximate spectrum and the real spectrum of the incident light is improved and the spectral peaks are separated very well. It is helpful to improve the spectral detection capability of imaging spectrometers.
2018, 42(2): 201-205.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.012
Abstract:
In order to measure thermal effect parameters of high-energy laser material on-line, a testing device with aperture of 50mm was specially designed. Collimating He-Ne laser was used as light source. The optical-path difference of testing beam after passing the material was measured by Hartmann-Shack wavefront sensor. According to wavefront aberration decomposition theory and wavefront transformation relationship, thermal effect parameters of high-energy laser material were gotten. Measurement uncertainty of the device was analyzed and evaluated. The system parameters which affected measurement uncertainty were calibrated. Finally, a comparative experiment of measurement uncertainty was designed and completed. The result shows that, the measurement uncertainty of system wavefront aberration is 0.06λ. The measurement uncertainty is 8.4% with thermal focal length of 30m~120m. The system can be applied to measure thermal effect parameters of high-energy laser material online.
In order to measure thermal effect parameters of high-energy laser material on-line, a testing device with aperture of 50mm was specially designed. Collimating He-Ne laser was used as light source. The optical-path difference of testing beam after passing the material was measured by Hartmann-Shack wavefront sensor. According to wavefront aberration decomposition theory and wavefront transformation relationship, thermal effect parameters of high-energy laser material were gotten. Measurement uncertainty of the device was analyzed and evaluated. The system parameters which affected measurement uncertainty were calibrated. Finally, a comparative experiment of measurement uncertainty was designed and completed. The result shows that, the measurement uncertainty of system wavefront aberration is 0.06λ. The measurement uncertainty is 8.4% with thermal focal length of 30m~120m. The system can be applied to measure thermal effect parameters of high-energy laser material online.
2018, 42(2): 206-211.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.013
Abstract:
In order to improve the thermal stability of V-type resonant cavity, based on graphic analysis, a simple V-type folded cavity was transformed into a coaxial spherical cavity with a thin lens. At the same time, considering the thermal effect of lens and combining with equivalent cavity analysis method of multi element optical resonator, the V-type folded cavity with lens group was transformed into a coaxial spherical cavity with no lens in the cavity. And the thermal stability of coaxial spherical cavity with no lens was calculated and analyzed. The results show that, the cavity has the widest range of thermal stability when the total cavity is 75mm and the fold angle is 0.15π. When the interval between the gain medium and folding mirror is 28mm, the focal length of the minimum thermal lens being suitable for the cavity can reach 12mm. The study shows that the key parameters of the cavity are important to thermal stability, and it has guiding significance for the optimization design of laser cavity stability.
In order to improve the thermal stability of V-type resonant cavity, based on graphic analysis, a simple V-type folded cavity was transformed into a coaxial spherical cavity with a thin lens. At the same time, considering the thermal effect of lens and combining with equivalent cavity analysis method of multi element optical resonator, the V-type folded cavity with lens group was transformed into a coaxial spherical cavity with no lens in the cavity. And the thermal stability of coaxial spherical cavity with no lens was calculated and analyzed. The results show that, the cavity has the widest range of thermal stability when the total cavity is 75mm and the fold angle is 0.15π. When the interval between the gain medium and folding mirror is 28mm, the focal length of the minimum thermal lens being suitable for the cavity can reach 12mm. The study shows that the key parameters of the cavity are important to thermal stability, and it has guiding significance for the optimization design of laser cavity stability.
2018, 42(2): 212-216.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.014
Abstract:
In order to design optical filter with high quality, dual-channel optical filter in quaternary-heterostructure photonic crystal (ABC)7D (CBA)7 was constructed by using transfer matrix method and the characteristics were studied. The results show that, with the increasing of DA(or DC), the filtering quality factor of short wave channel decreases and quality factor of long wave channel increases. With the increasing of DB, both the filtering quality factors of short and long wave channels decrease. With the increasing of DD, quality factor of short wave channel increases and quality factor of long wave channel decreases. With the increasing of optical thickness, both channels of the filter are red shifted toward long wave. Optical transmittances of each filter channel remain constant perfectly. The study can provide the reference for the design of new optical filters and optical switches of photonic crystals.
In order to design optical filter with high quality, dual-channel optical filter in quaternary-heterostructure photonic crystal (ABC)7D (CBA)7 was constructed by using transfer matrix method and the characteristics were studied. The results show that, with the increasing of DA(or DC), the filtering quality factor of short wave channel decreases and quality factor of long wave channel increases. With the increasing of DB, both the filtering quality factors of short and long wave channels decrease. With the increasing of DD, quality factor of short wave channel increases and quality factor of long wave channel decreases. With the increasing of optical thickness, both channels of the filter are red shifted toward long wave. Optical transmittances of each filter channel remain constant perfectly. The study can provide the reference for the design of new optical filters and optical switches of photonic crystals.
2018, 42(2): 217-221.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.015
Abstract:
In order to solve the problem that metallic powder active fillers were easily dispersed nonuniformly while preparing ceramic coatings by polymer derived ceramics method, the ceramic coating was prepared by laser pyrolysis of polydimethylsiloxane modified by butyl titanate. The composition and structure of products were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that, while the mass fraction of the addition of butyl titanate is 0.05, the relative content of Ti element in different areas of coatings is about 3% and Ti element disperses uniformly in ceramic coating. Under the action of high energy laser, the ceramic coating generated from the polydimethylsiloxane modified by butyl titanate is composed of crystalline SiC and TiO2, as long as amorphous SiO2, (TiO2)56(SiO2)44 and C6H18OSi2. The formation of new ceramic phase such as TiO2 and (TiO2)56(SiO2)44 can fill the pores and lead to the less porosity of the ceramic coating, and make the coating surface uniform and densified. The study solves the dispersion of active filler of metal powder.
In order to solve the problem that metallic powder active fillers were easily dispersed nonuniformly while preparing ceramic coatings by polymer derived ceramics method, the ceramic coating was prepared by laser pyrolysis of polydimethylsiloxane modified by butyl titanate. The composition and structure of products were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that, while the mass fraction of the addition of butyl titanate is 0.05, the relative content of Ti element in different areas of coatings is about 3% and Ti element disperses uniformly in ceramic coating. Under the action of high energy laser, the ceramic coating generated from the polydimethylsiloxane modified by butyl titanate is composed of crystalline SiC and TiO2, as long as amorphous SiO2, (TiO2)56(SiO2)44 and C6H18OSi2. The formation of new ceramic phase such as TiO2 and (TiO2)56(SiO2)44 can fill the pores and lead to the less porosity of the ceramic coating, and make the coating surface uniform and densified. The study solves the dispersion of active filler of metal powder.
2018, 42(2): 222-228.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.016
Abstract:
In order to research the effect of different nozzle shapes on the quality of weld forming joint, numerical simulation of flow field of different shape nozzles were established by FLUENT software. The testing of bead-on-plate welding to 5083 aluminum alloy plate with 10mm thickness was carried out under the same processing parameters by using Nd:YAG-MIG hybrid welding. After experimental verification, the results show that, the welding stability of multi-row round nozzle is the best, and weld penetration and weld width are the largest, 9.41mm and 4.45mm respectively, but the porosity is up to 7.34%. The protective effect of single side square nozzle is the best, but its welding stability, weld penetration and weld width are between multi row round nozzle and single side round nozzle. Protection effect of single side round nozzle is between multi row round nozzle and single side square nozzle, and then, welding stability and characteristic value of welding appearance have the worst results. Protection effect of square nozzle is the best. The research illustrates numerical simulation of protection effective range and airflow stiffness of different nozzle shapes.
In order to research the effect of different nozzle shapes on the quality of weld forming joint, numerical simulation of flow field of different shape nozzles were established by FLUENT software. The testing of bead-on-plate welding to 5083 aluminum alloy plate with 10mm thickness was carried out under the same processing parameters by using Nd:YAG-MIG hybrid welding. After experimental verification, the results show that, the welding stability of multi-row round nozzle is the best, and weld penetration and weld width are the largest, 9.41mm and 4.45mm respectively, but the porosity is up to 7.34%. The protective effect of single side square nozzle is the best, but its welding stability, weld penetration and weld width are between multi row round nozzle and single side round nozzle. Protection effect of single side round nozzle is between multi row round nozzle and single side square nozzle, and then, welding stability and characteristic value of welding appearance have the worst results. Protection effect of square nozzle is the best. The research illustrates numerical simulation of protection effective range and airflow stiffness of different nozzle shapes.
2018, 42(2): 229-233.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.017
Abstract:
In order to study effect of laser welding on the properties of dissimilar metal welding joints of K418 and 0Cr18Ni9, microstructure and morphology of the weld were analyzed by using a metallographic microscope. The hardness and strength of weld seams and their surrounding area were evaluated. The results show that when laser welding of K418 superalloy and 0Cr18Ni9, there are great differences in thermal parameters of the base metal. In order to guarantee weld quality, laser spot should be biased on the side of 0Cr18Ni9 alloy. In order to prevent thermal cracks and liquation cracks, coagulation time of the melted pool should be prolonged as far as possible and heat input with heat effect should be reduced simultaneously. The protection of weld seam is the best when protection gas flow rate is 12L/min. Compared with Ar2, N2 can effectively reduce the porosity in weld seams, and it also reduces the weld performance. The hardness of the weld is between the hardness of two base materials. The strength of the weld joint is about 89% of that of the base metal. Good welding quality of K418 alloy and 0Cr18Ni9 can be achieved by adopting suitable laser welding process.
In order to study effect of laser welding on the properties of dissimilar metal welding joints of K418 and 0Cr18Ni9, microstructure and morphology of the weld were analyzed by using a metallographic microscope. The hardness and strength of weld seams and their surrounding area were evaluated. The results show that when laser welding of K418 superalloy and 0Cr18Ni9, there are great differences in thermal parameters of the base metal. In order to guarantee weld quality, laser spot should be biased on the side of 0Cr18Ni9 alloy. In order to prevent thermal cracks and liquation cracks, coagulation time of the melted pool should be prolonged as far as possible and heat input with heat effect should be reduced simultaneously. The protection of weld seam is the best when protection gas flow rate is 12L/min. Compared with Ar2, N2 can effectively reduce the porosity in weld seams, and it also reduces the weld performance. The hardness of the weld is between the hardness of two base materials. The strength of the weld joint is about 89% of that of the base metal. Good welding quality of K418 alloy and 0Cr18Ni9 can be achieved by adopting suitable laser welding process.
2018, 42(2): 234-238.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.018
Abstract:
In order to solve the problem of low quality of micro hole processed by micro/nanosecond laser, using pulse laser with pulse width of 200ps and high speed rotary cutting method, a micropore process test with a diameter of 200μm was conducted on SUS 304 stainless steel sheet with thickness of 0.2mm. The morphologies of the micro holes were observed by laser scanning confocal microscope. The effects of cutting speed, laser power and defocusing distance on machining quality of aperture, taper and heat affected zone were investigated. The results show that, the cutting speed has the direct influence on the quality of micro porous wall. By increasing the rotating speed, the overlap rate of laser pulse and the heat affected zone of the inner wall of micro hole can be reduced. At the same time, the machining quality of micro incision by rotary cutting method can be improved by increasing laser power. The taper of micro hole can be reduced to a certain extent by adopting positive defocusing machining. The study shows that, the optimized technological parameters can be used to process small taper pores with small heat affected zone and good edge quality.
In order to solve the problem of low quality of micro hole processed by micro/nanosecond laser, using pulse laser with pulse width of 200ps and high speed rotary cutting method, a micropore process test with a diameter of 200μm was conducted on SUS 304 stainless steel sheet with thickness of 0.2mm. The morphologies of the micro holes were observed by laser scanning confocal microscope. The effects of cutting speed, laser power and defocusing distance on machining quality of aperture, taper and heat affected zone were investigated. The results show that, the cutting speed has the direct influence on the quality of micro porous wall. By increasing the rotating speed, the overlap rate of laser pulse and the heat affected zone of the inner wall of micro hole can be reduced. At the same time, the machining quality of micro incision by rotary cutting method can be improved by increasing laser power. The taper of micro hole can be reduced to a certain extent by adopting positive defocusing machining. The study shows that, the optimized technological parameters can be used to process small taper pores with small heat affected zone and good edge quality.
2018, 42(2): 239-244.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.019
Abstract:
In order to study the effects of 1070nm continuous wave laser irradiation on output performance of three-junction GaAs solar cell, a physical model was established by software COMSOL. The influence of laser power density, spot radius, anti reflection film, thermal radiation and thermal convection on temperature field were studied by numerical simulation. The results show that, absorption coefficient, thermal conductivity and photoelectric conversion efficiency are three main factors of temperature evolution. The magnitude of temperature increases with the increasing of laser power density. The smaller the spot radius is, the greater the temperature difference of cell surface. The conversion efficiency of solar cells can be effectively improved by anti reflection film structure, but it also makes battery temperature higher. Thermal convection dominates under the lower temperature (300K~400K) of the battery. When the incident power density is 16.7W/cm2 and spot radius is the same as the cell radius, after 20s, the central temperature of battery can reach 501.521K and lead to photoelectric conversion efficiency of 0. The numerical simulation results are in good agreement with the experimental results. The study provides a theoretical basis for the research of the mechanism of laser damage solar cells.
In order to study the effects of 1070nm continuous wave laser irradiation on output performance of three-junction GaAs solar cell, a physical model was established by software COMSOL. The influence of laser power density, spot radius, anti reflection film, thermal radiation and thermal convection on temperature field were studied by numerical simulation. The results show that, absorption coefficient, thermal conductivity and photoelectric conversion efficiency are three main factors of temperature evolution. The magnitude of temperature increases with the increasing of laser power density. The smaller the spot radius is, the greater the temperature difference of cell surface. The conversion efficiency of solar cells can be effectively improved by anti reflection film structure, but it also makes battery temperature higher. Thermal convection dominates under the lower temperature (300K~400K) of the battery. When the incident power density is 16.7W/cm2 and spot radius is the same as the cell radius, after 20s, the central temperature of battery can reach 501.521K and lead to photoelectric conversion efficiency of 0. The numerical simulation results are in good agreement with the experimental results. The study provides a theoretical basis for the research of the mechanism of laser damage solar cells.
2018, 42(2): 245-248.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.020
Abstract:
In order to switch multiple semiconductor lasers, realize time-sharing work, and reduce the volume of driving circuit, multi-channel selection switch and multi-channel analog switch was used to switch laser diode and photodiode. Different working voltages were set by digital to analog conversion chip. A circuit that can drive multiple different types of laser diodes was achieved. After theoretical analysis and experimental verification, stability test data with long time were obtained. The results indicate that, the output precision of constant current circuit can reach 0.005%, the instability of output power of laser diode with 830nm is 0.048%, and the instability of output power of laser diode with 1550nm is 0.046%. A stable light source is achieved. This result is helpful for the design of small volume drive circuit of multi channel semiconductor lasers.
In order to switch multiple semiconductor lasers, realize time-sharing work, and reduce the volume of driving circuit, multi-channel selection switch and multi-channel analog switch was used to switch laser diode and photodiode. Different working voltages were set by digital to analog conversion chip. A circuit that can drive multiple different types of laser diodes was achieved. After theoretical analysis and experimental verification, stability test data with long time were obtained. The results indicate that, the output precision of constant current circuit can reach 0.005%, the instability of output power of laser diode with 830nm is 0.048%, and the instability of output power of laser diode with 1550nm is 0.046%. A stable light source is achieved. This result is helpful for the design of small volume drive circuit of multi channel semiconductor lasers.
2018, 42(2): 249-253.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.021
Abstract:
In order to analysis systematically the splitting characteristics of a Wollaston-type symmetric beam-splitting prism, by using refractive formula and Fresnel formula and taking 632.8nm for example, relationship curve among the angle of emergent light to the horizontal direction, deviation angle and structure angle, relationship curve between intensity splitting beam ratio and structure angle, relationship curve among incident angle, splitting beam angle of the prism and emerging light symmetry were gotten. The results show that, strict symmetric beam can be achieved through the correction of output face of Wollaston prism. Splitting angles of o light and e light mainly depend on the prism structure angle. The effect of deviation angle is smaller. The changing magnification of beam splitting ratio with the increase of structure angle is small. When the incident angle is small, it has main effect on the symmetry of prism splitting angle. When incident angle changes between-3ånd+3°, the asymmetry degree of two beam is less than 6°, which can guarantee good effect of symmetry beam splitting. The study provides a theoretical guidance for design and application of the prism.
In order to analysis systematically the splitting characteristics of a Wollaston-type symmetric beam-splitting prism, by using refractive formula and Fresnel formula and taking 632.8nm for example, relationship curve among the angle of emergent light to the horizontal direction, deviation angle and structure angle, relationship curve between intensity splitting beam ratio and structure angle, relationship curve among incident angle, splitting beam angle of the prism and emerging light symmetry were gotten. The results show that, strict symmetric beam can be achieved through the correction of output face of Wollaston prism. Splitting angles of o light and e light mainly depend on the prism structure angle. The effect of deviation angle is smaller. The changing magnification of beam splitting ratio with the increase of structure angle is small. When the incident angle is small, it has main effect on the symmetry of prism splitting angle. When incident angle changes between-3ånd+3°, the asymmetry degree of two beam is less than 6°, which can guarantee good effect of symmetry beam splitting. The study provides a theoretical guidance for design and application of the prism.
2018, 42(2): 254-258.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.022
Abstract:
In order to solve the problem of laser welding porosity of 5183 aluminum alloy with 6.0mm thickness, laser-weaving welding was carried out by using IPG laser-weaving welding head. The test was carried out by changing scanning mode, scanning frequency, scanning amplitude and so on. The influence of laser-weaving technology on the quality of thick aluminum alloy welding joint was studied, and the optimum process parameters were found and verified. The results show that the appearance of aluminum alloy welds under laser-weaving welding is significantly improved. In addition to the small number of air holes in the linear scanning mode, the porosity of other four scanning modes (clockwise, counter-clockwise, figure 8 and infinity) decreases significantly with the increase of scanning frequency and scanning amplitude. When the scanning frequency is more than 200Hz and scanning amplitude is more than 2.0mm, no porosity weld can be obtained. Aluminum alloy with 6.0mm thickness can be processed as the butt joint with no porosity, tensile strength of 271MPa and base metal strength of 88%, under the best process parameters of scanning mode infinity, scanning frequency of 300Hz, scanning amplitude of 3.0mm. The laser-weaving welding shows a good prospect.
In order to solve the problem of laser welding porosity of 5183 aluminum alloy with 6.0mm thickness, laser-weaving welding was carried out by using IPG laser-weaving welding head. The test was carried out by changing scanning mode, scanning frequency, scanning amplitude and so on. The influence of laser-weaving technology on the quality of thick aluminum alloy welding joint was studied, and the optimum process parameters were found and verified. The results show that the appearance of aluminum alloy welds under laser-weaving welding is significantly improved. In addition to the small number of air holes in the linear scanning mode, the porosity of other four scanning modes (clockwise, counter-clockwise, figure 8 and infinity) decreases significantly with the increase of scanning frequency and scanning amplitude. When the scanning frequency is more than 200Hz and scanning amplitude is more than 2.0mm, no porosity weld can be obtained. Aluminum alloy with 6.0mm thickness can be processed as the butt joint with no porosity, tensile strength of 271MPa and base metal strength of 88%, under the best process parameters of scanning mode infinity, scanning frequency of 300Hz, scanning amplitude of 3.0mm. The laser-weaving welding shows a good prospect.
2018, 42(2): 259-264.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.023
Abstract:
In order to achieve high absorption and conversion efficiency of thin disk lasers, the method of multiple pumping absorptions was adopted. Combining with the pumping structure of light spot asymmetric parabolic surface and light spot symmetrical aspheric surface, a new method of high pumping passing was proposed to improve the duty ratio of aspheric beam distribution. The multipass pumping structure was designed. The optical path distribution and spot position diagram of 24 passes pumping schemes were simulated by using ZEMAX. Absorption efficiency of thin disk crystal on pump light with different pumping passes was calculated theoretically according to Bill's absorption law. The results show that among the designed pump structures of 24 passes, 36 passes, 40 passes and 80 passes schemes, the absorption efficiency of 36 passes pumping scheme is the most cost-effective. The research has guiding function for the design of small multi-pass pumping structures with high power.
In order to achieve high absorption and conversion efficiency of thin disk lasers, the method of multiple pumping absorptions was adopted. Combining with the pumping structure of light spot asymmetric parabolic surface and light spot symmetrical aspheric surface, a new method of high pumping passing was proposed to improve the duty ratio of aspheric beam distribution. The multipass pumping structure was designed. The optical path distribution and spot position diagram of 24 passes pumping schemes were simulated by using ZEMAX. Absorption efficiency of thin disk crystal on pump light with different pumping passes was calculated theoretically according to Bill's absorption law. The results show that among the designed pump structures of 24 passes, 36 passes, 40 passes and 80 passes schemes, the absorption efficiency of 36 passes pumping scheme is the most cost-effective. The research has guiding function for the design of small multi-pass pumping structures with high power.
2018, 42(2): 265-270.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.024
Abstract:
In order to study the influence of pulse width and repetition frequency on the damage threshold of HgCdTe detector, finite element method was used to build 2-D model of HgCdTe infrared detector and the temperature field of laser irradiation detector was simulated. Damage threshold of single pulse laser of off-band and in-band was obtained from the range of 10ns to 1000ns. Measurement of damage threshold of all pulse width was hard. After simulation and calculation, the damage threshold formula from the range of 10ns to 1000ns was concluded. The results show that, single pulse laser damage threshold of off-band laser is 9MW/cm2~0.9MW/cm2, and 150MW/cm2~15MW/cm2 for in-band laser. And single pulse damage threshold has the negative exponential relationship with laser pulse width. And then, repetition frequency laser was used to irradiate detector with the same repetition frequency. The temperature accumulation effect and damages of large area are more likely to occur under long pulse laser irradiation, because pulse separation of long pulse laser is smaller than narrow pulse laser. The research is useful for studying stress field distribution、thermoplastic wave and laser protection.
In order to study the influence of pulse width and repetition frequency on the damage threshold of HgCdTe detector, finite element method was used to build 2-D model of HgCdTe infrared detector and the temperature field of laser irradiation detector was simulated. Damage threshold of single pulse laser of off-band and in-band was obtained from the range of 10ns to 1000ns. Measurement of damage threshold of all pulse width was hard. After simulation and calculation, the damage threshold formula from the range of 10ns to 1000ns was concluded. The results show that, single pulse laser damage threshold of off-band laser is 9MW/cm2~0.9MW/cm2, and 150MW/cm2~15MW/cm2 for in-band laser. And single pulse damage threshold has the negative exponential relationship with laser pulse width. And then, repetition frequency laser was used to irradiate detector with the same repetition frequency. The temperature accumulation effect and damages of large area are more likely to occur under long pulse laser irradiation, because pulse separation of long pulse laser is smaller than narrow pulse laser. The research is useful for studying stress field distribution、thermoplastic wave and laser protection.
2018, 42(2): 271-275.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.025
Abstract:
In order to solve the problem that recastation layer can not be eliminated in traditional process, ultrafoot picosecond laser was used to do the drilling experiment of Al2O3 ceramics in water medium. Compared with the drilling results in the air, the influences of main parameters such as single pulse energy and scanning frequency on pore size, taper and thickness of ceramic micro pores were analyzed. Interaction mechanism between picosecond laser and Al2O3 ceramics and material removal mechanism with different media were analyzed and discussed. The results show that, the diameter of laser drilling in water medium increases by about 35μm, micropore taper reduces to 1.04° and the effect of no reclamation layer drilling can be obtained. The presence of water in the process of laser drilling can cause vacuolization, absorption and transportation.It can effectively prevent the secondary adhesion of erosion material, eliminate re-cast layer and reduce micro-hole taper and improve the quality of micro-porous. The study describes the specific impact of water-assisted laser drilling and deepens the understanding of the mechanism of water-assisted effects.
In order to solve the problem that recastation layer can not be eliminated in traditional process, ultrafoot picosecond laser was used to do the drilling experiment of Al2O3 ceramics in water medium. Compared with the drilling results in the air, the influences of main parameters such as single pulse energy and scanning frequency on pore size, taper and thickness of ceramic micro pores were analyzed. Interaction mechanism between picosecond laser and Al2O3 ceramics and material removal mechanism with different media were analyzed and discussed. The results show that, the diameter of laser drilling in water medium increases by about 35μm, micropore taper reduces to 1.04° and the effect of no reclamation layer drilling can be obtained. The presence of water in the process of laser drilling can cause vacuolization, absorption and transportation.It can effectively prevent the secondary adhesion of erosion material, eliminate re-cast layer and reduce micro-hole taper and improve the quality of micro-porous. The study describes the specific impact of water-assisted laser drilling and deepens the understanding of the mechanism of water-assisted effects.
2018, 42(2): 276-281.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.026
Abstract:
In order to find the effects of different process parameters(laser repetition frequency, laser scanning velocity, laser scanning times) on the dimension and the morphology of composite grooves during laser etching of surface composite grooves on micro heat pipe, a series of experiments were carried out by single factor experimental method. The reasonable process parameters of 1064nm wavelength fiber laser were confirmed. The experimental results show that, under the conditions of 40kHz laser repetition frequency, 150mm/s laser scanning velocity and 25 laser scanning times, composite grooves can provide larger capillary pressure for liquid reflux in micro heat pipe. This study is of great significance to improve the heat transfer performance of grooved micro heat pipes.
In order to find the effects of different process parameters(laser repetition frequency, laser scanning velocity, laser scanning times) on the dimension and the morphology of composite grooves during laser etching of surface composite grooves on micro heat pipe, a series of experiments were carried out by single factor experimental method. The reasonable process parameters of 1064nm wavelength fiber laser were confirmed. The experimental results show that, under the conditions of 40kHz laser repetition frequency, 150mm/s laser scanning velocity and 25 laser scanning times, composite grooves can provide larger capillary pressure for liquid reflux in micro heat pipe. This study is of great significance to improve the heat transfer performance of grooved micro heat pipes.
2018, 42(2): 282-288.
doi: 10.7510/jgjs.issn.1001-3806.2018.02.027
Abstract:
In order to solve the connection problem of Al2O3 ceramic lined pipe in petroleum pipeline, a special semiconductor laser light source was developed for ceramic laser welding. The technological parameters and beam requirements for ceramic laser welding were investigated experimentally. By means of single tube space beam combination, polarization beam combination, wavelength combination and Fresnel focusing system, a semiconductor laser ceramic welding system with uniform light distribution field was developed. The results show that, the output power of the polarization combination module is 384W, the beam combination efficiency is up to 96.62%. After wavelength combination, the output power can exceed 800W, and the output spot uniformity of focusing system is 93.85%. The system can be applied to ceramic welding in different occasions, and meet the requirements of Al2O3 ceramic laser welding with 2mm thickness.
In order to solve the connection problem of Al2O3 ceramic lined pipe in petroleum pipeline, a special semiconductor laser light source was developed for ceramic laser welding. The technological parameters and beam requirements for ceramic laser welding were investigated experimentally. By means of single tube space beam combination, polarization beam combination, wavelength combination and Fresnel focusing system, a semiconductor laser ceramic welding system with uniform light distribution field was developed. The results show that, the output power of the polarization combination module is 384W, the beam combination efficiency is up to 96.62%. After wavelength combination, the output power can exceed 800W, and the output spot uniformity of focusing system is 93.85%. The system can be applied to ceramic welding in different occasions, and meet the requirements of Al2O3 ceramic laser welding with 2mm thickness.
