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RSS2014 Vol. 38, No. 3
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2014, 38(3): 289-292.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.001
[Abstract]
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Abstract:
Cylindrical dielectric-loaded quadrifilar helix antenna is an ideal choice for small satellite antenna owing to its advantages of wide beam, circular polarization and small volume. In order to solve the difficulty of the manufacture of dielectric-loaded quadrifilar helix antenna, a novel manufacture method combing magnetron sputtering metallization and laser etching was introduced. Computer control system with laser etching technology was used to produce three-dimensional quadrifilar helix structure, which is suitable for small satellite systems. The novel process can greatly improve the machining accuracy and shorten the processing cycle compared with traditional process. The results show that the manufactured antenna has good electrical performance, which meets the design requirements of a small satellite system, as well as good mechanical properties. It offers a method of manufacture of the cylindrical conformal antenna.
Cylindrical dielectric-loaded quadrifilar helix antenna is an ideal choice for small satellite antenna owing to its advantages of wide beam, circular polarization and small volume. In order to solve the difficulty of the manufacture of dielectric-loaded quadrifilar helix antenna, a novel manufacture method combing magnetron sputtering metallization and laser etching was introduced. Computer control system with laser etching technology was used to produce three-dimensional quadrifilar helix structure, which is suitable for small satellite systems. The novel process can greatly improve the machining accuracy and shorten the processing cycle compared with traditional process. The results show that the manufactured antenna has good electrical performance, which meets the design requirements of a small satellite system, as well as good mechanical properties. It offers a method of manufacture of the cylindrical conformal antenna.
2014, 38(3): 293-296.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.002
Abstract:
To verify the vernier effect of fiber ring resonators, fiber ring resonators in different length were studied. The relationship between the transmission spectrum and the fiber ring resonator with the length of 2.24m, 2.52m was analyzed and compared, one resonant spectrum could be used as the ruler and the other as the vernier, when the resonant frequency was the same and the number difference of free spectral range (FSR) was only one. Based on the difference aliquot measuring principle and by dividing FSR of the ruler into nine parts,the minimum measurement accuracy of the vernier was 0.01GHz which was consistent with MATLAB theoretical simulation result. Theory and experiments show that the accuracy can be improved by changing the size of the resonant cavity to increase the aliquot number of FSR difference. The vernier effect of resonator is expected to be potentially applied in the field of high-sensitivity sensor because of the sensitivity of the micro-cavity to the change of external environment.
To verify the vernier effect of fiber ring resonators, fiber ring resonators in different length were studied. The relationship between the transmission spectrum and the fiber ring resonator with the length of 2.24m, 2.52m was analyzed and compared, one resonant spectrum could be used as the ruler and the other as the vernier, when the resonant frequency was the same and the number difference of free spectral range (FSR) was only one. Based on the difference aliquot measuring principle and by dividing FSR of the ruler into nine parts,the minimum measurement accuracy of the vernier was 0.01GHz which was consistent with MATLAB theoretical simulation result. Theory and experiments show that the accuracy can be improved by changing the size of the resonant cavity to increase the aliquot number of FSR difference. The vernier effect of resonator is expected to be potentially applied in the field of high-sensitivity sensor because of the sensitivity of the micro-cavity to the change of external environment.
2014, 38(3): 297-301.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.003
Abstract:
When 3-D shapes of dynamic objects, especially with isolated area and discontinuous distribution, are measured with the traditional fringe projection and phase analysis method, it is difficult to get reliable expansion phase. A technique based on color-encoded sinusoidal fringe projection was proposed to solve the problem. The projected sinusoidal fringes were marked with two-level encoded color. After capturing the deformed fringe pattern, the fringe order was determined according to the color sequence based on the coded characteristics, and the cut-off phase was unwrapped. Finally, the 3-D shape of the dynamic object with isolate area was reconstructed. The results show the decoding method is stable and reliable. 3-D shape of the spatially isolated dynamic objects can be exactly reconstructed with only one shot.
When 3-D shapes of dynamic objects, especially with isolated area and discontinuous distribution, are measured with the traditional fringe projection and phase analysis method, it is difficult to get reliable expansion phase. A technique based on color-encoded sinusoidal fringe projection was proposed to solve the problem. The projected sinusoidal fringes were marked with two-level encoded color. After capturing the deformed fringe pattern, the fringe order was determined according to the color sequence based on the coded characteristics, and the cut-off phase was unwrapped. Finally, the 3-D shape of the dynamic object with isolate area was reconstructed. The results show the decoding method is stable and reliable. 3-D shape of the spatially isolated dynamic objects can be exactly reconstructed with only one shot.
2014, 38(3): 302-306.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.004
Abstract:
In order to study the damage mechanism of high reflective fluoride film under a certain condition, the damaged areas of the films made with the different processing techniques were analyzed by means of differential interference contrast microscopy, atomic force microscopy and optical profiler. With the increase of the film deposition temperature and the packing density of the film in vivo, laser induced damage threshold of film is improved. For the regular film series, a standing wave electric field intensity distribution of the standing wave in vivo has the greater impact on the film damage. The results show that the damage of high-reflection film is jointly caused by packing density of the film in vivo and electric field intensity distribution based on the damage morphology and damage depth of the film. The results provide the foundation for further research of high quality of laser reflective coatings.
In order to study the damage mechanism of high reflective fluoride film under a certain condition, the damaged areas of the films made with the different processing techniques were analyzed by means of differential interference contrast microscopy, atomic force microscopy and optical profiler. With the increase of the film deposition temperature and the packing density of the film in vivo, laser induced damage threshold of film is improved. For the regular film series, a standing wave electric field intensity distribution of the standing wave in vivo has the greater impact on the film damage. The results show that the damage of high-reflection film is jointly caused by packing density of the film in vivo and electric field intensity distribution based on the damage morphology and damage depth of the film. The results provide the foundation for further research of high quality of laser reflective coatings.
2014, 38(3): 307-310.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.005
Abstract:
In order to improve the plane fitting precision of point cloud data, the intensity weighted total least square method was proposed. The method, based on the ordinary weighted total least square method, determined the weight value of plant fitting using the intensity information of each point in point cloud data. The application of the method was analyzed with three different homogenous data. Experimental results show that the method is effective for plane fitting of point clouds with good homogeneity, and more accurate solution can be obtained compared with total least squares method and least squares method. As for plane fitting of inhomogeneous point clouds, the total least squares method is superior to the proposed method.
In order to improve the plane fitting precision of point cloud data, the intensity weighted total least square method was proposed. The method, based on the ordinary weighted total least square method, determined the weight value of plant fitting using the intensity information of each point in point cloud data. The application of the method was analyzed with three different homogenous data. Experimental results show that the method is effective for plane fitting of point clouds with good homogeneity, and more accurate solution can be obtained compared with total least squares method and least squares method. As for plane fitting of inhomogeneous point clouds, the total least squares method is superior to the proposed method.
2014, 38(3): 311-315.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.006
Abstract:
In order to detect the Brillouin optical time domain reflectometry signal (BOTDR) of photoelectric composite submarine cable from the noise background effectively, wavelet threshold method was proposed to denoise the real-time monitoring signal according to the characteristics of signal. Optimal parameters of wavelet threshold denoising suitable for Brillouin optical time domain reflectometer signal of the cable were determined through theoretical analysis and experimental comparison. The effect of wavelet threshold denoising was compared with the effects of median filtering method and mean filtering method. The results show that compared with both the traditional filtering methods, wavelet threshold method with optimal parameters can effectively denoise the signal. It not only can improve signal noise ratio to 14.1dB, but also can detect strain change of 100με. The study has important reference for efficient processing of BOTDR of submarine cables.
In order to detect the Brillouin optical time domain reflectometry signal (BOTDR) of photoelectric composite submarine cable from the noise background effectively, wavelet threshold method was proposed to denoise the real-time monitoring signal according to the characteristics of signal. Optimal parameters of wavelet threshold denoising suitable for Brillouin optical time domain reflectometer signal of the cable were determined through theoretical analysis and experimental comparison. The effect of wavelet threshold denoising was compared with the effects of median filtering method and mean filtering method. The results show that compared with both the traditional filtering methods, wavelet threshold method with optimal parameters can effectively denoise the signal. It not only can improve signal noise ratio to 14.1dB, but also can detect strain change of 100με. The study has important reference for efficient processing of BOTDR of submarine cables.
2014, 38(3): 316-320.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.007
Abstract:
In order to monitor the density and distribution of water-drop at the end stage of the steam turbine, the off-axis angular scattering method was proposed to measure the parameters of wet steam. In this way, it not only guides economic operation of the turbine but also guarantee water allowance of the boiler. At the same time, it can reduce the influence of wet steam on the turbine. Based on the structure and parameters of mock cylinder, a mathematic model was built. This mathematic model can find whether the middle radius of quantity, the density of number and the distribution of magnitude in water-drop have impact on the scattering ratio. The wet steam was measured under different conditions. The analysis result was similar to the experimental result. The experimental results proved the off-axis angular scattering method is feasible for measuring wet steam parameters. This research is helpful for monitoring the parameters of wet steam and other particles.
In order to monitor the density and distribution of water-drop at the end stage of the steam turbine, the off-axis angular scattering method was proposed to measure the parameters of wet steam. In this way, it not only guides economic operation of the turbine but also guarantee water allowance of the boiler. At the same time, it can reduce the influence of wet steam on the turbine. Based on the structure and parameters of mock cylinder, a mathematic model was built. This mathematic model can find whether the middle radius of quantity, the density of number and the distribution of magnitude in water-drop have impact on the scattering ratio. The wet steam was measured under different conditions. The analysis result was similar to the experimental result. The experimental results proved the off-axis angular scattering method is feasible for measuring wet steam parameters. This research is helpful for monitoring the parameters of wet steam and other particles.
2014, 38(3): 321-324.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.008
Abstract:
In order to make laser etching on the semicircle accurately, engrave the hemispherical platinum resistance of heat flux sensor and meet the precise positioning of the heat flow measurement points, the method of positioning processing point based on the vision imaging system was used. After theoretical analysis and experimental verification, the positioning data of high platinum resistance was gotten. Firstly, the edge contour was illuminated by the backlight and was visible clearly. Then, after extracting four coordinates on the edges, the hemisphere vertex was calculated. After rotating the platform and compensating the deviation value, the precise processing position was found. Finally, the resistance position of the heat hemispherical sensor was measured and verified. The experimental results show that the method has good positioning effect, the relative error of sphere radius by corrosion is about 0.39%, the relative error of rotation angle of loading platform is controlled in 3.9%. The problem of positioning hemisphere vertex is solved and the precision of laser corrosion is raised. This study is helpful to make platinum resistance on curve surface model by laser.
In order to make laser etching on the semicircle accurately, engrave the hemispherical platinum resistance of heat flux sensor and meet the precise positioning of the heat flow measurement points, the method of positioning processing point based on the vision imaging system was used. After theoretical analysis and experimental verification, the positioning data of high platinum resistance was gotten. Firstly, the edge contour was illuminated by the backlight and was visible clearly. Then, after extracting four coordinates on the edges, the hemisphere vertex was calculated. After rotating the platform and compensating the deviation value, the precise processing position was found. Finally, the resistance position of the heat hemispherical sensor was measured and verified. The experimental results show that the method has good positioning effect, the relative error of sphere radius by corrosion is about 0.39%, the relative error of rotation angle of loading platform is controlled in 3.9%. The problem of positioning hemisphere vertex is solved and the precision of laser corrosion is raised. This study is helpful to make platinum resistance on curve surface model by laser.
2014, 38(3): 325-329.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.009
Abstract:
In order to obtain transmission formula of TM wave in 1-D photonic crystal,the characteristic matrix and the reflection and transmission coefficients of TM wave in dielectric layer were deduced based on the transfer matrix method and the boundary conditions of electromagnetic wave. The results show that the reflection and transmission coefficients of TM wave converted from the reflection and transmission coefficients of TE wave were not correct. And then, the deduced reflection and transmission coefficients of TM wave were analyzed. The transmittance and reflectance of TM wave intensity satisfies the law of energy conservation. Reflection coefficient formula of TM wave can not only reflect the relationship between the number of reflection wave and incident wave, but also reflect the phase relationship between the reflection wave and incident wave TM wave reflection coefficient formula can reflect the reflection wave and incident wave number and the phase relation. These results are helpful for study of transmission properties of TM wave in 1-D photonic crystal.
In order to obtain transmission formula of TM wave in 1-D photonic crystal,the characteristic matrix and the reflection and transmission coefficients of TM wave in dielectric layer were deduced based on the transfer matrix method and the boundary conditions of electromagnetic wave. The results show that the reflection and transmission coefficients of TM wave converted from the reflection and transmission coefficients of TE wave were not correct. And then, the deduced reflection and transmission coefficients of TM wave were analyzed. The transmittance and reflectance of TM wave intensity satisfies the law of energy conservation. Reflection coefficient formula of TM wave can not only reflect the relationship between the number of reflection wave and incident wave, but also reflect the phase relationship between the reflection wave and incident wave TM wave reflection coefficient formula can reflect the reflection wave and incident wave number and the phase relation. These results are helpful for study of transmission properties of TM wave in 1-D photonic crystal.
2014, 38(3): 330-334.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.010
Abstract:
To obtain better result of laser etching, micro-machining of alumina ceramics with ultraviolet(UV) laser (355nm) was conducted in air and water respectively. The impact of laser parameters, such as laser fluence, scan speed, and laser frequency on the etching depth was investigated. The mechanism of laser etching and the physical process of water-assisted etching were studied. Etching morphology in air and water with UV laser and etching depth with different laser parameters were obtained. The results show that water-assisted laser etching can improve the etching efficiency and etching surface quality. The etching depth has close relationship with laser fluence, scan speed, laser frequency and water depth. The water cooling effect and vacuum occurring during water-assisted etching could prevent the secondary adhesion to the eclipse material effectively and the formation of metamorphic layer.
To obtain better result of laser etching, micro-machining of alumina ceramics with ultraviolet(UV) laser (355nm) was conducted in air and water respectively. The impact of laser parameters, such as laser fluence, scan speed, and laser frequency on the etching depth was investigated. The mechanism of laser etching and the physical process of water-assisted etching were studied. Etching morphology in air and water with UV laser and etching depth with different laser parameters were obtained. The results show that water-assisted laser etching can improve the etching efficiency and etching surface quality. The etching depth has close relationship with laser fluence, scan speed, laser frequency and water depth. The water cooling effect and vacuum occurring during water-assisted etching could prevent the secondary adhesion to the eclipse material effectively and the formation of metamorphic layer.
2014, 38(3): 335-341.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.011
Abstract:
The Goldstein branch-cut method is a traditional method for phase unwrapping. Its phase unwrapping result is easily affected by phase residues caused by noise and discontinuous phase flaws in practice. To characterize effect of discontinuous phase on unwrapping algorithm, after simulating a data base for discontinuous phase, unwrapping was studied with Goldstein branch-cut phase unwrapping method. The effect of the residual phase on the size of the searching window radius was focused on specifically. The unwrapped phase was compared with the actual phase. The results show that accurate unwrapped phases can be obtained in situations with one and two disjointed discontinuity flaws. Accurate unwrapping phase results cannot be obtained in situations with two crossing phase discontinuous flaws. Good results can not be obtained for two crossing phase discontinuous flaws. Different discontinuous phase flaws have different effective branch cut searching window radius. There is an effective searching window radius for the Goldstein branch-cut approach. Those results can provide reference to research of the phase unwrapping only and jointly with Goldstein branch-cut.
The Goldstein branch-cut method is a traditional method for phase unwrapping. Its phase unwrapping result is easily affected by phase residues caused by noise and discontinuous phase flaws in practice. To characterize effect of discontinuous phase on unwrapping algorithm, after simulating a data base for discontinuous phase, unwrapping was studied with Goldstein branch-cut phase unwrapping method. The effect of the residual phase on the size of the searching window radius was focused on specifically. The unwrapped phase was compared with the actual phase. The results show that accurate unwrapped phases can be obtained in situations with one and two disjointed discontinuity flaws. Accurate unwrapping phase results cannot be obtained in situations with two crossing phase discontinuous flaws. Good results can not be obtained for two crossing phase discontinuous flaws. Different discontinuous phase flaws have different effective branch cut searching window radius. There is an effective searching window radius for the Goldstein branch-cut approach. Those results can provide reference to research of the phase unwrapping only and jointly with Goldstein branch-cut.
2014, 38(3): 342-346.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.012
Abstract:
In order to achieve good automotive joining of aluminum/steel dissimilar metals, the experiments of butt joining aluminum alloy to galvanized steel were carried out by laser deep penetration welding-brazing with a fiber laser. The seam appearance, the intermetallic composition layer as well as the mechanical properties of the joints were analyzed. The results show that a typical deep penetration welding seam is formed on the aluminum alloy side, while a brazed seam is generated on the solid galvanized steel side. There is a thin layer of the intermetallic composition on the interface between the galvanized steel and the brazed seam, which is less than 10μm. The main intermetallic compositions were Al7.2Fe2Si and (Al,Si)13Fe4. The tensile samples were fractured at the heat affected zone of the aluminum alloy. The average tensile strength of the joint is 145MPa. The fracture mode of the joint is ductile fracture.
In order to achieve good automotive joining of aluminum/steel dissimilar metals, the experiments of butt joining aluminum alloy to galvanized steel were carried out by laser deep penetration welding-brazing with a fiber laser. The seam appearance, the intermetallic composition layer as well as the mechanical properties of the joints were analyzed. The results show that a typical deep penetration welding seam is formed on the aluminum alloy side, while a brazed seam is generated on the solid galvanized steel side. There is a thin layer of the intermetallic composition on the interface between the galvanized steel and the brazed seam, which is less than 10μm. The main intermetallic compositions were Al7.2Fe2Si and (Al,Si)13Fe4. The tensile samples were fractured at the heat affected zone of the aluminum alloy. The average tensile strength of the joint is 145MPa. The fracture mode of the joint is ductile fracture.
2014, 38(3): 347-351.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.013
Abstract:
To achieve 2μm laser output, 793nm LD face-pumping Tm3+-doped fiber laser was adopted. Double lens coupling system was designed. Cross relaxation of Tm3+-doped fiber laser and thermal effect were analyzed, and then the related experiments were carried out. The results show that coupling efficiency of coupling system is 84%. When the pump power is 70W, the output power is 34W with slop efficiency of 59%, central wavelength of 2001.2nm and M2 of less than 1.2. The results are helpful to design Tm3+-doped fiber lasers.
To achieve 2μm laser output, 793nm LD face-pumping Tm3+-doped fiber laser was adopted. Double lens coupling system was designed. Cross relaxation of Tm3+-doped fiber laser and thermal effect were analyzed, and then the related experiments were carried out. The results show that coupling efficiency of coupling system is 84%. When the pump power is 70W, the output power is 34W with slop efficiency of 59%, central wavelength of 2001.2nm and M2 of less than 1.2. The results are helpful to design Tm3+-doped fiber lasers.
2014, 38(3): 352-356.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.014
Abstract:
In order to study the mode distribution in a laser resonator, a circular mirror resonator was analyzed based on finite element matrix and the feasibility and effectiveness of this method was verified. On the basis of the study, the rational division of the cavity mirror was studied. After fitting the relationship between the relative error and the fine extent of division elements, the reasonable number of elements was obtained. The results conformed with the actual calculation and analysis well. The results show that this method makes the mode analysis of a laser resonator more accurately and conveniently.
In order to study the mode distribution in a laser resonator, a circular mirror resonator was analyzed based on finite element matrix and the feasibility and effectiveness of this method was verified. On the basis of the study, the rational division of the cavity mirror was studied. After fitting the relationship between the relative error and the fine extent of division elements, the reasonable number of elements was obtained. The results conformed with the actual calculation and analysis well. The results show that this method makes the mode analysis of a laser resonator more accurately and conveniently.
2014, 38(3): 357-359.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.015
Abstract:
In order to study inverse bremsstrahlung (IB) effect in process of laser-induced copper plasma, copper plasma was induced by Nd：YAG laser at 1064nm. The electron temperature 6902K of the copper plasma was calculated with the Boltzmann plot of 3 Cu Ⅰ lines. By measuring the Stark broadening of Cu Ⅰ at 324.75nm, its electron density of 3.6×1017cm-3 was obtained. Based on these characteristic parameters of copper plasma, the inverse bremsstrahlung coefficient of 0.021cm-1 was obtained. Experimental results show that the plasma parameters can be obtained without any disturbance with the spectral analysis method.
In order to study inverse bremsstrahlung (IB) effect in process of laser-induced copper plasma, copper plasma was induced by Nd：YAG laser at 1064nm. The electron temperature 6902K of the copper plasma was calculated with the Boltzmann plot of 3 Cu Ⅰ lines. By measuring the Stark broadening of Cu Ⅰ at 324.75nm, its electron density of 3.6×1017cm-3 was obtained. Based on these characteristic parameters of copper plasma, the inverse bremsstrahlung coefficient of 0.021cm-1 was obtained. Experimental results show that the plasma parameters can be obtained without any disturbance with the spectral analysis method.
2014, 38(3): 360-363.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.016
Abstract:
In order to study the thermal effect of LD end-pumped Nd:GGG laser, the thermal focal length, intrinsic loss and thermal loss were measured with the laser operating continuously. The results show the maximal output power of 13.2W, the maximal slope efficiency of 51.5% and the optical conversion efficiency of 49.5% were obtained in a plano-concave cavity when the pump power was 28.8W. The intrinsic loss of Nd:GGG crystal was 0.86%/cm. The result was in good agreement with the theoretically calculation. The results can offer experimental and theoretical basis for the further optimizaiton of LD pumped Nd:GGG laser.
In order to study the thermal effect of LD end-pumped Nd:GGG laser, the thermal focal length, intrinsic loss and thermal loss were measured with the laser operating continuously. The results show the maximal output power of 13.2W, the maximal slope efficiency of 51.5% and the optical conversion efficiency of 49.5% were obtained in a plano-concave cavity when the pump power was 28.8W. The intrinsic loss of Nd:GGG crystal was 0.86%/cm. The result was in good agreement with the theoretically calculation. The results can offer experimental and theoretical basis for the further optimizaiton of LD pumped Nd:GGG laser.
2014, 38(3): 364-367.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.017
Abstract:
Maximum between-class variance (Otsu) image segmentation method is a common image threshold segmentation method based on statistical theory, but Otsu image segmentation method has some disadvantages, such as more time-consuming, low segmentation accuracy and false image segmentation. Combining the principles of monkey king genetic algorithms, with Otsu algorithm, image gray, just as optimal threshold, was found. The results show that combined method not only improves the quality of image segmentation but also reduce the computation time. It is very suitable for real-time image processing.
Maximum between-class variance (Otsu) image segmentation method is a common image threshold segmentation method based on statistical theory, but Otsu image segmentation method has some disadvantages, such as more time-consuming, low segmentation accuracy and false image segmentation. Combining the principles of monkey king genetic algorithms, with Otsu algorithm, image gray, just as optimal threshold, was found. The results show that combined method not only improves the quality of image segmentation but also reduce the computation time. It is very suitable for real-time image processing.
2014, 38(3): 368-371.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.018
Abstract:
In order to obtain 3.8μm laser output, it was demonstrated in optical parametric oscillator(OPO)with periodically poled lithium niobate crystals doped with magnesium oxide (mole fraction of MgO-doping is 0.05) pumped by 1.064μm laser. The relationship curve between output wavelength and polarization period and the temperature was calculated. When polarization period is 29.2μm and the temperature is 400K, 3.8μm laser output is achieved. When pump power is 35W at repetition rate of 8kHz, an average output power of 3.9W at 3.84μm is obtained with slope efficiency of 11.14%, and the M2 factor is 6.46. The results show that 3.8μm laser output can be obtained with high conversion efficiency, and it can be used as laser sources of infrared laser interference.
In order to obtain 3.8μm laser output, it was demonstrated in optical parametric oscillator(OPO)with periodically poled lithium niobate crystals doped with magnesium oxide (mole fraction of MgO-doping is 0.05) pumped by 1.064μm laser. The relationship curve between output wavelength and polarization period and the temperature was calculated. When polarization period is 29.2μm and the temperature is 400K, 3.8μm laser output is achieved. When pump power is 35W at repetition rate of 8kHz, an average output power of 3.9W at 3.84μm is obtained with slope efficiency of 11.14%, and the M2 factor is 6.46. The results show that 3.8μm laser output can be obtained with high conversion efficiency, and it can be used as laser sources of infrared laser interference.
2014, 38(3): 372-374.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.019
Abstract:
In order to improve image acquisition rate and axial resolution of optical coherence tomography at lower cost, spectral-domain optical coherence tomography (SD-OCT) was studied both theoretically and experimentally. Some basic data and images were obtained based on the measurement of film workpieces. The results show that the images of their internal structure are visible clearly and SD-OCT under white light illumination is feasible and enables to realize the real-time 3-D imaging reconstructions of internal structure of engineering and biological materials.
In order to improve image acquisition rate and axial resolution of optical coherence tomography at lower cost, spectral-domain optical coherence tomography (SD-OCT) was studied both theoretically and experimentally. Some basic data and images were obtained based on the measurement of film workpieces. The results show that the images of their internal structure are visible clearly and SD-OCT under white light illumination is feasible and enables to realize the real-time 3-D imaging reconstructions of internal structure of engineering and biological materials.
2014, 38(3): 375-379.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.020
Abstract:
In order to reduce thermal deformation of high reflectance sapphire mirrors under high power laser irradiation and improve the beam quality, effect of the diameter and thickness on thermal deformation of the high reflectance mirror was studied. The heat conduction equation expressed in polar coordinate and the thermal deformation formula were used to describe the distribution of the temperature field and the displacement field of the sapphire mirror. Then, the numerical calculation model was built with the finite element analysis software and the temperature field and displacement field in different thickness and diameter was calculated. The thermal deformation with respect to the thickness and diameter was obtained. The results indicate that the main factors affecting the PV value of the sapphire mirror surface is the temperature variation and the change of the size has effect on both temperature and stiffness. Appropriate size and thickness effectively reduce the rise of mirror's temperature and keep suitable axial structural stiffness, and thus the thermal deformation of the reflective mirror is decreased. The study results are useful for the size determination and selection of high reflectance sapphire mirrors under high power laser irradiation.
In order to reduce thermal deformation of high reflectance sapphire mirrors under high power laser irradiation and improve the beam quality, effect of the diameter and thickness on thermal deformation of the high reflectance mirror was studied. The heat conduction equation expressed in polar coordinate and the thermal deformation formula were used to describe the distribution of the temperature field and the displacement field of the sapphire mirror. Then, the numerical calculation model was built with the finite element analysis software and the temperature field and displacement field in different thickness and diameter was calculated. The thermal deformation with respect to the thickness and diameter was obtained. The results indicate that the main factors affecting the PV value of the sapphire mirror surface is the temperature variation and the change of the size has effect on both temperature and stiffness. Appropriate size and thickness effectively reduce the rise of mirror's temperature and keep suitable axial structural stiffness, and thus the thermal deformation of the reflective mirror is decreased. The study results are useful for the size determination and selection of high reflectance sapphire mirrors under high power laser irradiation.
2014, 38(3): 380-383.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.021
Abstract:
In order to study effect of substrate on the focusing laser field in atom lithograph, based on geometrical optics and numerical simulation, effects of substrate surface slope on optical potential were studied. The results indicate that when the substrate surface has positive slope related to the laser standing wave axis, there is an area without light illumination on the surface whose optical potential is zero, and the curve of optical potential in z direction will suddenly vanish; when the substrate surface has negative slope related to the laser standing wave axis, all the surface will be illuminated by the laser and the curve of optical potential in z direction will vary smoothly to zero, and the optical potential will be symmetric related to z=0. The results are useful for the experiment of laser-focusing atom deposition.
In order to study effect of substrate on the focusing laser field in atom lithograph, based on geometrical optics and numerical simulation, effects of substrate surface slope on optical potential were studied. The results indicate that when the substrate surface has positive slope related to the laser standing wave axis, there is an area without light illumination on the surface whose optical potential is zero, and the curve of optical potential in z direction will suddenly vanish; when the substrate surface has negative slope related to the laser standing wave axis, all the surface will be illuminated by the laser and the curve of optical potential in z direction will vary smoothly to zero, and the optical potential will be symmetric related to z=0. The results are useful for the experiment of laser-focusing atom deposition.
2014, 38(3): 384-388.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.022
Abstract:
In order to realize the efficient detection of remote multiple nodes and reduce the cost, a distributed feedback semiconductor laser working at special central wavelength was shared and placed at a local control node being connected to each remote detection node with bi-directional fiber links in series. Furthermore, a novel distributed optical fiber gas sensor system was designed by using the special structure of remote nodes and fiber segments. At each detection node, the gas cell was added between two Y-couplers. There were the upstream signal and the downstream signal in the system, which could avoid the influences of the signals from other nodes and implement time division multiplexing directly. The numerical calculation and experiments were carried out in a 3-node methane detection system. The results show that the proportion of the laser diode in the total cost drops from about 60% to about 38%. When the loop number is increased, the relative error of the measured gas density at each node can be reduced, and particularly the relative error at the first node can be reduced to below 0.2% or even lower. Distributed sensing with a shared light source can be achieved efficiently.
In order to realize the efficient detection of remote multiple nodes and reduce the cost, a distributed feedback semiconductor laser working at special central wavelength was shared and placed at a local control node being connected to each remote detection node with bi-directional fiber links in series. Furthermore, a novel distributed optical fiber gas sensor system was designed by using the special structure of remote nodes and fiber segments. At each detection node, the gas cell was added between two Y-couplers. There were the upstream signal and the downstream signal in the system, which could avoid the influences of the signals from other nodes and implement time division multiplexing directly. The numerical calculation and experiments were carried out in a 3-node methane detection system. The results show that the proportion of the laser diode in the total cost drops from about 60% to about 38%. When the loop number is increased, the relative error of the measured gas density at each node can be reduced, and particularly the relative error at the first node can be reduced to below 0.2% or even lower. Distributed sensing with a shared light source can be achieved efficiently.
2014, 38(3): 389-393.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.023
Abstract:
In order to solve the problem confronted with the online steam humidity measurement of turbine flow pass, a semi-empirical formula of phase function computing method was proposed to improve the inversion algorithm on scattering light distribution. Phase function of double Gaussian fitting by using MATLAB with cftool was adopted in this algorithm. The fitting result shows that the relative error is in small, and the approximate analytic solution of the Mie scattering theory could be got by the fitting function, which means that a rapid inversion from the scattering light intensity distribution to water quality radius. According to the results, with the restriction of the range of the droplet size, the approximation of the theory between the droplet size and scattering ratio was got. Contrast experiment showed the measured scattering ratio was similar with the simulated scattering ratio. Based on the semi-empirical model, the water quality of middle radius was 1.1μm.The fast inversion algorithm can well resolve the online measurement of steam humidity.
In order to solve the problem confronted with the online steam humidity measurement of turbine flow pass, a semi-empirical formula of phase function computing method was proposed to improve the inversion algorithm on scattering light distribution. Phase function of double Gaussian fitting by using MATLAB with cftool was adopted in this algorithm. The fitting result shows that the relative error is in small, and the approximate analytic solution of the Mie scattering theory could be got by the fitting function, which means that a rapid inversion from the scattering light intensity distribution to water quality radius. According to the results, with the restriction of the range of the droplet size, the approximation of the theory between the droplet size and scattering ratio was got. Contrast experiment showed the measured scattering ratio was similar with the simulated scattering ratio. Based on the semi-empirical model, the water quality of middle radius was 1.1μm.The fast inversion algorithm can well resolve the online measurement of steam humidity.
2014, 38(3): 394-397.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.024
Abstract:
Adopting the means of light vector superimposition, the polarization states of linearly polarized light transmitting through several wave-plates with arbitrary thickness were analyzed. Taking two wave plates whose optical axes are oriented at 45° as example, the polarization states and intensity of transmitted light were calculated. It is found that the polarization states are dependent on retardation of the back wave-plate, and the intensity is dependent on retardation of the front wave-plate and vibration azimuth angle of incident light. It also indicates that the characteristics are not the same when the two wave plates are used in forward and reverse directions. The theoretical results can be applied to the analysis of depolarizer, such as Lyot depolarizer.
Adopting the means of light vector superimposition, the polarization states of linearly polarized light transmitting through several wave-plates with arbitrary thickness were analyzed. Taking two wave plates whose optical axes are oriented at 45° as example, the polarization states and intensity of transmitted light were calculated. It is found that the polarization states are dependent on retardation of the back wave-plate, and the intensity is dependent on retardation of the front wave-plate and vibration azimuth angle of incident light. It also indicates that the characteristics are not the same when the two wave plates are used in forward and reverse directions. The theoretical results can be applied to the analysis of depolarizer, such as Lyot depolarizer.
2014, 38(3): 398-401.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.025
Abstract:
In order to study the characteristics of the wet steam in steam turbine unit, the new measurement method based on laser backscattering method was proposed to get the data of scattering light intensity of the wet steam at different angles and at different locations. And then, the parameters of the wet steam were gotten and the middle radius of the wet steam droplets quality was about 1μm. The results show that the blank data of none wet steam also has the impact on the wet steam method, so the formula should be corrected. And no matter there is the wet steam or not, the scattered light intensity at 30° is about 1.5 times of the scattering light intensity at 60°, so the scattered light at 30° is more suitable for measurement. The results show that the backscattering theory is feasible for wet steam measurement.
In order to study the characteristics of the wet steam in steam turbine unit, the new measurement method based on laser backscattering method was proposed to get the data of scattering light intensity of the wet steam at different angles and at different locations. And then, the parameters of the wet steam were gotten and the middle radius of the wet steam droplets quality was about 1μm. The results show that the blank data of none wet steam also has the impact on the wet steam method, so the formula should be corrected. And no matter there is the wet steam or not, the scattered light intensity at 30° is about 1.5 times of the scattering light intensity at 60°, so the scattered light at 30° is more suitable for measurement. The results show that the backscattering theory is feasible for wet steam measurement.
2014, 38(3): 402-405.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.026
Abstract:
To measure the radial distortion in optical imaging systems, adopting the straight sinusoidal carrier-fringe pattern, the radial modulated phase resulting from radial distortion was extracted by means of instantaneous frequency integration. The formula between the instantaneous frequency and the radial modulated phase was deduced, and the conversion formula between the radial modulated phase and the radial distortion displacement was obtained. The instantaneous frequency of the distorted fringe pattern in the radial direction was calculated by using frequency estimation of Gabor wavelet transform, and integrated to obtain the radial modulated phase. The radial modulated phase and the cubic convolution interpolation algorithm were used to calibrate the distorted image. Experimental results demonstrate that the method is available.
To measure the radial distortion in optical imaging systems, adopting the straight sinusoidal carrier-fringe pattern, the radial modulated phase resulting from radial distortion was extracted by means of instantaneous frequency integration. The formula between the instantaneous frequency and the radial modulated phase was deduced, and the conversion formula between the radial modulated phase and the radial distortion displacement was obtained. The instantaneous frequency of the distorted fringe pattern in the radial direction was calculated by using frequency estimation of Gabor wavelet transform, and integrated to obtain the radial modulated phase. The radial modulated phase and the cubic convolution interpolation algorithm were used to calibrate the distorted image. Experimental results demonstrate that the method is available.
2014, 38(3): 406-410.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.027
Abstract:
In order to improve the property and the efficiency of traditional removal function of small tool polish, ellipse motion method was achieved through three-rotor movement on the basis of planet motion. Then, a new removal function was investigated and deduced based on the assumption of Preston. At last, the surface matrix of removal function was calculated by computer and after optimization. The final parameters and the removal function which was close to the ideal Gaussian function were obtained. The results show the removal efficiency of ellipse motion is better than planetary removal's. Removal function based on ellipse motion can avoid the defect of previous function of planet motion and increase the removal efficiency during polishing process.
In order to improve the property and the efficiency of traditional removal function of small tool polish, ellipse motion method was achieved through three-rotor movement on the basis of planet motion. Then, a new removal function was investigated and deduced based on the assumption of Preston. At last, the surface matrix of removal function was calculated by computer and after optimization. The final parameters and the removal function which was close to the ideal Gaussian function were obtained. The results show the removal efficiency of ellipse motion is better than planetary removal's. Removal function based on ellipse motion can avoid the defect of previous function of planet motion and increase the removal efficiency during polishing process.
2014, 38(3): 411-416.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.028
Abstract:
In order to investigate the detection performance and range accuracy of a laser radar using Geiger mode avalanche photodiode (GM-APD) as detector, by using the method of mathematical modeling, based on the system working principle and detection time sequence, the target detection probability was analyzed under the condition that the GM-APD detector operated under long dead-time and the echo pulse width was larger than the resolving time of the time-to-digital converter (TDC). According to the statistical theory and centroid method, the theoretical model of range accuracy was established. Using the system design parameters, the influence of the echo intensity, pulse width, noise, and echo position on the range accuracy was discussed. The results show that the stronger echo intensity, the narrower echo pulse width, the lower noise and the more front echo position result in the higher target detection probability, the lower false alarm rate and the better detection performance. Echo intensity and pulse width are the main influence factors. The stronger echo intensity and the narrower pulse width result in the higher range accuracy.
In order to investigate the detection performance and range accuracy of a laser radar using Geiger mode avalanche photodiode (GM-APD) as detector, by using the method of mathematical modeling, based on the system working principle and detection time sequence, the target detection probability was analyzed under the condition that the GM-APD detector operated under long dead-time and the echo pulse width was larger than the resolving time of the time-to-digital converter (TDC). According to the statistical theory and centroid method, the theoretical model of range accuracy was established. Using the system design parameters, the influence of the echo intensity, pulse width, noise, and echo position on the range accuracy was discussed. The results show that the stronger echo intensity, the narrower echo pulse width, the lower noise and the more front echo position result in the higher target detection probability, the lower false alarm rate and the better detection performance. Echo intensity and pulse width are the main influence factors. The stronger echo intensity and the narrower pulse width result in the higher range accuracy.
2014, 38(3): 417-421.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.029
Abstract:
To calculate the optical properties of uniaxial crystal F-P filters, with theoretical analysis, the boundary condition of the electric field of the film at the interface of ordinary light and extraordinary light, vertically from the optical axial to the incident plane of single uniaxial crystal film, and the phase of the electric field of the film at the interface were analyzed. The calculating method of reflectivity and transmission of single crystal film was obtained. After the simulation of optical property of uniaxial crystal F-P filter, the data of the filter transmission changing with the optical axis direction was obtained. The results show that optical axis rotation angle has obvious effect on the transmission peak of F-P filter.
To calculate the optical properties of uniaxial crystal F-P filters, with theoretical analysis, the boundary condition of the electric field of the film at the interface of ordinary light and extraordinary light, vertically from the optical axial to the incident plane of single uniaxial crystal film, and the phase of the electric field of the film at the interface were analyzed. The calculating method of reflectivity and transmission of single crystal film was obtained. After the simulation of optical property of uniaxial crystal F-P filter, the data of the filter transmission changing with the optical axis direction was obtained. The results show that optical axis rotation angle has obvious effect on the transmission peak of F-P filter.
2014, 38(3): 422-424.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.030
Abstract:
In order to measure the liquid crystal birefringence,a simple and accurate method called polarization interferometry was used from the theoretical formula of polarized light interference and by making a certain approximation. More satisfactory data were achieved by theoretically analysis and experimental verification. The results show the use of polarized light interferometry to measure the liquid crystal material avoids the measurement of the absolute intensity of transmission spectrum, and has high accuracy. It is helpful for the design, manufacture and application of liquid crystal device.
In order to measure the liquid crystal birefringence,a simple and accurate method called polarization interferometry was used from the theoretical formula of polarized light interference and by making a certain approximation. More satisfactory data were achieved by theoretically analysis and experimental verification. The results show the use of polarized light interferometry to measure the liquid crystal material avoids the measurement of the absolute intensity of transmission spectrum, and has high accuracy. It is helpful for the design, manufacture and application of liquid crystal device.
2014, 38(3): 425-430.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.031
Abstract:
In order to fuse the information of multiple optical images in a certain area, an image fusion algorithm based on joint photographic experts group(JPEG) in wavelet domain was adopted. The main idea of the method was to regard the inverse wavelet transform as information fusion process. Each source image was compressed into a group of binary code flow according to JPEG standard. Then the group of binary code flow was taken as the wavelet coefficients and the fused image was obtained by taking inverse wavelet transform. The results show that the algorithm can realize the fusion of multiple gray-scale images and color images, improve the amount of information in a single space and be conducive to multiple images storage and transmission.
In order to fuse the information of multiple optical images in a certain area, an image fusion algorithm based on joint photographic experts group(JPEG) in wavelet domain was adopted. The main idea of the method was to regard the inverse wavelet transform as information fusion process. Each source image was compressed into a group of binary code flow according to JPEG standard. Then the group of binary code flow was taken as the wavelet coefficients and the fused image was obtained by taking inverse wavelet transform. The results show that the algorithm can realize the fusion of multiple gray-scale images and color images, improve the amount of information in a single space and be conducive to multiple images storage and transmission.
2014, 38(3): 431-434.
doi: 10.7510/jgjs.issn.1001-3806.2014.03.032
Abstract:
In order to study the best 3-D modeling method of the building point cloud data, the point cloud data of a building were acquired with a 3-D laser scanner and pretreated. Three methods were used for the modeling of the buildings. From the view of modeling effect and complexity, the model effect with the SketchUp software was the best. The results show that the modeling effect of the point cloud data of buildings with SketchUp software is better than those with the scanner system software CYCLONE and AutoCAD software.
In order to study the best 3-D modeling method of the building point cloud data, the point cloud data of a building were acquired with a 3-D laser scanner and pretreated. Three methods were used for the modeling of the buildings. From the view of modeling effect and complexity, the model effect with the SketchUp software was the best. The results show that the modeling effect of the point cloud data of buildings with SketchUp software is better than those with the scanner system software CYCLONE and AutoCAD software.
