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RSS2011 Vol. 35, No. 1
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2011, 35(1): 1-3.
doi: 10.3969/j.issn.1001-3806.2011.01.001
[Abstract]
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Abstract:
In order to investigate the performance of all-optical clock extraction using an amplified feedback laser, the method of single sideband phase noise intensity integration was adopted. The clock extraction from not-degraded and noise-degraded 40Gbit/s signals was experimentally demonstrated and timing jitter of the extracted clock was calculated. Besides, the locking range of amplified feedback laser was measured. As a result, the clock extracted from the not-degraded and noise-degraded signal with timing jitter of 130fs and 150fs were obtained respectively. The measured locking range of amplified feedback laser was 234MHz. The experimental results show that the amplified feedback laser-based all-optical clock extraction has a high tolerance to the noise degradation and a wide locking range. The results are important for the further development of all-optical clock extraction technology.
In order to investigate the performance of all-optical clock extraction using an amplified feedback laser, the method of single sideband phase noise intensity integration was adopted. The clock extraction from not-degraded and noise-degraded 40Gbit/s signals was experimentally demonstrated and timing jitter of the extracted clock was calculated. Besides, the locking range of amplified feedback laser was measured. As a result, the clock extracted from the not-degraded and noise-degraded signal with timing jitter of 130fs and 150fs were obtained respectively. The measured locking range of amplified feedback laser was 234MHz. The experimental results show that the amplified feedback laser-based all-optical clock extraction has a high tolerance to the noise degradation and a wide locking range. The results are important for the further development of all-optical clock extraction technology.
2011, 35(1): 4-6,93.
doi: 10.3969/j.issn.1001-3806.2011.01.002
Abstract:
Mo+Y2O3 alloy powders were used to coat uniformly on the surface of 40Cr steel roller substrates by adhesive for the laser surface alloying treatment by a continuous wave CO2 laser in order to improve the organizational performance of the metal rollers. The effect of the rare earth oxide to the alloy layer on the hardness, wearing resistance, microstructure, and formation mechanism was studied with a scanning electron microscope, X-ray diffractometer, micro-hardness tester, and a wearing tester. Many good consequences were obtained after adding the rare earth oxide Y2O3. The crystal grains of the alloy layer were significantly refined. The boundary of crystal grains was strengthened. The uniformity and density of the microstructure were increased. The hardness and wearing resistance the alloy layer were considerably improved. The results show that it helps to improve the surface hardness and wear resistance of metal rollers
Mo+Y2O3 alloy powders were used to coat uniformly on the surface of 40Cr steel roller substrates by adhesive for the laser surface alloying treatment by a continuous wave CO2 laser in order to improve the organizational performance of the metal rollers. The effect of the rare earth oxide to the alloy layer on the hardness, wearing resistance, microstructure, and formation mechanism was studied with a scanning electron microscope, X-ray diffractometer, micro-hardness tester, and a wearing tester. Many good consequences were obtained after adding the rare earth oxide Y2O3. The crystal grains of the alloy layer were significantly refined. The boundary of crystal grains was strengthened. The uniformity and density of the microstructure were increased. The hardness and wearing resistance the alloy layer were considerably improved. The results show that it helps to improve the surface hardness and wear resistance of metal rollers
2011, 35(1): 7-10.
doi: 10.3969/j.issn.1001-3806.2011.01.003
Abstract:
In order to adopt laser-welding technology in automotive body in white(BIW) welding production line, combining automatic control technology, communication technology with laser-welding technology, an automotive BIM laser welding production line was designed with programmable logic controller and industrial computer as the control core and assisted control core respectively, which could communicate with the fiber laser and the welding robot in real-time. By changing the welding parameters，the laser-welding results of left front door parts of a vehicle were compared with those of spot welding. The results show that: laser welding has several advantages of obviously improved welding speed, flexible control and higher welding strength increased by 70%. This provides a new welding production line technology for the development of miniaturization, lightweight Chinese automobiles with stronger comprehensive mechanical property in their bodies
In order to adopt laser-welding technology in automotive body in white(BIW) welding production line, combining automatic control technology, communication technology with laser-welding technology, an automotive BIM laser welding production line was designed with programmable logic controller and industrial computer as the control core and assisted control core respectively, which could communicate with the fiber laser and the welding robot in real-time. By changing the welding parameters，the laser-welding results of left front door parts of a vehicle were compared with those of spot welding. The results show that: laser welding has several advantages of obviously improved welding speed, flexible control and higher welding strength increased by 70%. This provides a new welding production line technology for the development of miniaturization, lightweight Chinese automobiles with stronger comprehensive mechanical property in their bodies
2011, 35(1): 11-14.
doi: 10.3969/j.issn.1001-3806.2011.01.004
Abstract:
In order to explore the detection of obscure targets by means of lidar, the effects of obscure targets on returned lidar waveforms were studied. By using the method of mathematical modeling, the model of lidar waveforms returned from obscure targets was constructed, in which the effects of pulse stretch, spectrum reflectivity and depolarization on return waveforms were considered. The simulation data of the waveforms returned from obscure targets were obtained based on this model. The simulation data indicate that the reflectivity and depolarization of different targets has the prominent effect on return lidar waveforms, provide a foundation for future study on the detection of the obscure target based on return lidar waveforms.
In order to explore the detection of obscure targets by means of lidar, the effects of obscure targets on returned lidar waveforms were studied. By using the method of mathematical modeling, the model of lidar waveforms returned from obscure targets was constructed, in which the effects of pulse stretch, spectrum reflectivity and depolarization on return waveforms were considered. The simulation data of the waveforms returned from obscure targets were obtained based on this model. The simulation data indicate that the reflectivity and depolarization of different targets has the prominent effect on return lidar waveforms, provide a foundation for future study on the detection of the obscure target based on return lidar waveforms.
2011, 35(1): 15-18.
doi: 10.3969/j.issn.1001-3806.2011.01.005
Abstract:
In order to study the property of Eu3+ and Li+ co-doped ZnO thin film, it was deposited on the P-type Si (111) substrate by means of pulsed laser deposition(PLD)method with Eu3+ as luminous center and Li+ as the low charged compensated ions and the sensitizer. The photoluminescent(PL) spectra and the X-ray diffraction(XRD) spectra of the film were measured to analyze the crystal structure and photoluminescent property. Through XRD, it can be seen that the ZnO:Eu3+，Li+ film was highly c-axis oriented. In the XRD spectrum, no other crystal orientations were observed except the ZnO crystal orientation. The doping of Eu3+ into ZnO lattice introduced tensile stress, making ZnO crystal lattice spacing larger; but as the oxygen pressure increased, the crystal lattice spacing and lattice constant both had a smaller trend. The PL spectra of the Eu3+, Li+ co-doped ZnO thin film was similar with that of pure ZnO films, but the UV emission peak showed a red-shift phenomenon at about 382nm, and the emission peak was not sharp. When irradiated under the wavelength of 395nm, obvious emission at the wavelength of about 594nm，613nm from the rare-earth element of Eu3+ was observed in the photoluminescence spectra. All the results indicate that the doping elements of Eu3+ and Li+ have incorporated into the crystal lattice of ZnO, and conform the wurtzite structure with Eu3+ as its luminescent centre.
In order to study the property of Eu3+ and Li+ co-doped ZnO thin film, it was deposited on the P-type Si (111) substrate by means of pulsed laser deposition(PLD)method with Eu3+ as luminous center and Li+ as the low charged compensated ions and the sensitizer. The photoluminescent(PL) spectra and the X-ray diffraction(XRD) spectra of the film were measured to analyze the crystal structure and photoluminescent property. Through XRD, it can be seen that the ZnO:Eu3+，Li+ film was highly c-axis oriented. In the XRD spectrum, no other crystal orientations were observed except the ZnO crystal orientation. The doping of Eu3+ into ZnO lattice introduced tensile stress, making ZnO crystal lattice spacing larger; but as the oxygen pressure increased, the crystal lattice spacing and lattice constant both had a smaller trend. The PL spectra of the Eu3+, Li+ co-doped ZnO thin film was similar with that of pure ZnO films, but the UV emission peak showed a red-shift phenomenon at about 382nm, and the emission peak was not sharp. When irradiated under the wavelength of 395nm, obvious emission at the wavelength of about 594nm，613nm from the rare-earth element of Eu3+ was observed in the photoluminescence spectra. All the results indicate that the doping elements of Eu3+ and Li+ have incorporated into the crystal lattice of ZnO, and conform the wurtzite structure with Eu3+ as its luminescent centre.
2011, 35(1): 19-21,125.
doi: 10.3969/j.issn.1001-3806.2011.01.006
Abstract:
In order to measure dynamic characteristics of a specimen in the laser shock forming laser shock forming accurately, a new experimental device was designed to detect the dynamic change of the loaded material based on shading principle. The experimental results indicate that elastic deformation and plastic deformation of 1060 thin aluminum coexist during the process of laser shock forming, and the existence of plastic deformation period is far longer than the elastic deformation. Based on the experiment, it can be calculated that the average speed of elastic deformation and average strain rate of the sample in central area are 3.2103m/s and 8.9104s-1 respectively. The results provide the experimental evidence for the development of relevant laser shock forming technology.
In order to measure dynamic characteristics of a specimen in the laser shock forming laser shock forming accurately, a new experimental device was designed to detect the dynamic change of the loaded material based on shading principle. The experimental results indicate that elastic deformation and plastic deformation of 1060 thin aluminum coexist during the process of laser shock forming, and the existence of plastic deformation period is far longer than the elastic deformation. Based on the experiment, it can be calculated that the average speed of elastic deformation and average strain rate of the sample in central area are 3.2103m/s and 8.9104s-1 respectively. The results provide the experimental evidence for the development of relevant laser shock forming technology.
2011, 35(1): 22-24.
doi: 10.3969/j.issn.1001-3806.2011.01.007
Abstract:
In order to shied the ultraviolet, sunshade on photonic band gap was proposed, the transmissivity of the ultraviolet radiation in 1-D and 2-D sunshade on photonic band gap was calculated by means of transfer matrix and the finite difference time domain method. The result shows that 1-D and 2-D sunshade on photonic band gap can be designed if appropriate parameter were selected. Incident angles have a greater impact on low limit of forbidden band.
In order to shied the ultraviolet, sunshade on photonic band gap was proposed, the transmissivity of the ultraviolet radiation in 1-D and 2-D sunshade on photonic band gap was calculated by means of transfer matrix and the finite difference time domain method. The result shows that 1-D and 2-D sunshade on photonic band gap can be designed if appropriate parameter were selected. Incident angles have a greater impact on low limit of forbidden band.
2011, 35(1): 25-28,78.
doi: 10.3969/j.issn.1001-3806.2011.01.008
Abstract:
In order to study the power distribution and output characteristics of gain guided index antiguided (GG-IAG) fiber lasers, rate equations of basic model light of double-clad GG-IAG fiber lasers with end-pumping were established, based on the principle and structure characteristics of GG-IAG fibers. After solving the rate equations with tangential method and Runge-Kutta method, power distribution and output characteristics of basic model light were gained. The results show that parameters of fiber and laser cavity, such as fiber length, output lens reflectivity, have significant influence on gain distribution and output power of basic model light. When using a GG-IAG fiber with a radius of 100m, index step -0.00094 and concentration of ions 51026/m3 to construct a GG-IAG fiber laser, fiber length needs to be 3cm and output lens reflectivity is 0.98 and 0.3 respectively, in order to restrain LP11 model, and while inputing a 30W pump-light, 2.42W single-mode laser with large-mode-area can be obtained. The analysis shows that by optimally designing cavity mirror reflectivity and fiber length, fundamental mode output with certain efficiency can be obtained in a short length large-mode-area highly doped GG-IAG fiber.
In order to study the power distribution and output characteristics of gain guided index antiguided (GG-IAG) fiber lasers, rate equations of basic model light of double-clad GG-IAG fiber lasers with end-pumping were established, based on the principle and structure characteristics of GG-IAG fibers. After solving the rate equations with tangential method and Runge-Kutta method, power distribution and output characteristics of basic model light were gained. The results show that parameters of fiber and laser cavity, such as fiber length, output lens reflectivity, have significant influence on gain distribution and output power of basic model light. When using a GG-IAG fiber with a radius of 100m, index step -0.00094 and concentration of ions 51026/m3 to construct a GG-IAG fiber laser, fiber length needs to be 3cm and output lens reflectivity is 0.98 and 0.3 respectively, in order to restrain LP11 model, and while inputing a 30W pump-light, 2.42W single-mode laser with large-mode-area can be obtained. The analysis shows that by optimally designing cavity mirror reflectivity and fiber length, fundamental mode output with certain efficiency can be obtained in a short length large-mode-area highly doped GG-IAG fiber.
2011, 35(1): 29-30.
doi: 10.3969/j.issn.1001-3806.2011.01.009
Abstract:
In order to improve the filtering effect of median filtering, a new method was put forward taking the local variation and local median value into account. The corrupted pixels were detected at first based on the discretion of the data and then filtered based on statistic characteristics. After computing the speckle indexes, peak signal-to-noise ratio and normalized mean square error of the processed images, their ability of suppressing speckle noise was compared. The results indicate that the new filtering method does have advantages.
In order to improve the filtering effect of median filtering, a new method was put forward taking the local variation and local median value into account. The corrupted pixels were detected at first based on the discretion of the data and then filtered based on statistic characteristics. After computing the speckle indexes, peak signal-to-noise ratio and normalized mean square error of the processed images, their ability of suppressing speckle noise was compared. The results indicate that the new filtering method does have advantages.
2011, 35(1): 31-35.
doi: 10.3969/j.issn.1001-3806.2011.01.010
Abstract:
In order to simulate accurate change of free surface of keyhole and the corresponding temperature distribution in laser deep penetration welding, heat source model conformed to laser penetration welding physical process was inferred using ray tracing method. Using the heat source model, a three-phase unified control equation of vapor phase, liquid phase and solid phase was established during laser deep penetration welding. The dynamic change process and its corresponding temperature distribution of keyhole can be calculated by tracing free surface of keyhole using the volume of fluid method. A conclusion is drawn that the computational results agree well with experimental results.
In order to simulate accurate change of free surface of keyhole and the corresponding temperature distribution in laser deep penetration welding, heat source model conformed to laser penetration welding physical process was inferred using ray tracing method. Using the heat source model, a three-phase unified control equation of vapor phase, liquid phase and solid phase was established during laser deep penetration welding. The dynamic change process and its corresponding temperature distribution of keyhole can be calculated by tracing free surface of keyhole using the volume of fluid method. A conclusion is drawn that the computational results agree well with experimental results.
2011, 35(1): 36-38,85.
doi: 10.3969/j.issn.1001-3806.2011.01.011
Abstract:
To investigate the effect of 157nm laser parameters on the ablation performance, two wide band-gap materials (fused silica and sapphire) were employed in 157nm laser micromachining experiments, and ideal parameter range of laser process was obtained. The ablation rate of sapphire is approximately half of that of fused silica, and the ablated surface of sapphire is much rougher than that of fused silica. With the increase of etching depth, the generated particles are difficult to escape from micro-structures so that the ablation rate decreases. For laser scanning, higher velocity and lower pulse repetition rate are favorable for reducing the surface roughness. Experimental results show that, for the etching of nonmetal materials, the laser fluence should be controlled 2.5 times~4 times of energy threshold of the ablated material, so as to get better etching effect.
To investigate the effect of 157nm laser parameters on the ablation performance, two wide band-gap materials (fused silica and sapphire) were employed in 157nm laser micromachining experiments, and ideal parameter range of laser process was obtained. The ablation rate of sapphire is approximately half of that of fused silica, and the ablated surface of sapphire is much rougher than that of fused silica. With the increase of etching depth, the generated particles are difficult to escape from micro-structures so that the ablation rate decreases. For laser scanning, higher velocity and lower pulse repetition rate are favorable for reducing the surface roughness. Experimental results show that, for the etching of nonmetal materials, the laser fluence should be controlled 2.5 times~4 times of energy threshold of the ablated material, so as to get better etching effect.
2011, 35(1): 39-42.
doi: 10.3969/j.issn.1001-3806.2011.01.012
Abstract:
The working principle of laser shot peening was introduced. The change of microstructure, the forming mechanism and distribution of compressive residual stress in the surface modification layer were described. The effect and mechanism of laser shot peening on resistance of stress corrosion cracking were analyzed in detail. On the base of comparing with shot peening, the superiorities of laser shot peening in improving metal resistance of stress corrosion cracking were summarized. Finally its potential application was also presented.
The working principle of laser shot peening was introduced. The change of microstructure, the forming mechanism and distribution of compressive residual stress in the surface modification layer were described. The effect and mechanism of laser shot peening on resistance of stress corrosion cracking were analyzed in detail. On the base of comparing with shot peening, the superiorities of laser shot peening in improving metal resistance of stress corrosion cracking were summarized. Finally its potential application was also presented.
2011, 35(1): 43-46.
doi: 10.3969/j.issn.1001-3806.2011.01.013
Abstract:
The modulation instability of self-generated magnetic field in the super strong relativistic laser-plasma interactions was investigated from a set of nonlinear kinetic governing equations taking into account of the wave-wave, wave-particle interactions and the relativistic effect of electrons. On the basis of the nonlinear kinetic governing equations, the dispersion equation of transverse perturbation was obtained through linear analysis. Theoretical analysis and numerical calculation indicate the spontaneous magnetic field will collapse and form a localized structure. Choosing appropriate parameters, the characteristic scale of magnetic field obtained from numerical calculation is consistent with the existing theoretical model.
The modulation instability of self-generated magnetic field in the super strong relativistic laser-plasma interactions was investigated from a set of nonlinear kinetic governing equations taking into account of the wave-wave, wave-particle interactions and the relativistic effect of electrons. On the basis of the nonlinear kinetic governing equations, the dispersion equation of transverse perturbation was obtained through linear analysis. Theoretical analysis and numerical calculation indicate the spontaneous magnetic field will collapse and form a localized structure. Choosing appropriate parameters, the characteristic scale of magnetic field obtained from numerical calculation is consistent with the existing theoretical model.
2011, 35(1): 47-50.
doi: 10.3969/j.issn.1001-3806.2011.01.014
Abstract:
Low-pulse position modulation(L-PPM) modulation technique is widely used in atmospheric laser communication. In order to correspond to L-PPM modulation technique better and improve correction ability, channel coding employs error correcting code over finite field GF(q). After discussing RS encoding and decoding algorithms over GF(17), and studying the RS(16，10) encoding and decoding algorithms and its realization process, results show that RS(16,10) code over GF(17) can correct 2-bit random errors after channel interference when transmitter employs 16-PPM modulation mode.
Low-pulse position modulation(L-PPM) modulation technique is widely used in atmospheric laser communication. In order to correspond to L-PPM modulation technique better and improve correction ability, channel coding employs error correcting code over finite field GF(q). After discussing RS encoding and decoding algorithms over GF(17), and studying the RS(16，10) encoding and decoding algorithms and its realization process, results show that RS(16,10) code over GF(17) can correct 2-bit random errors after channel interference when transmitter employs 16-PPM modulation mode.
2011, 35(1): 51-53.
doi: 10.3969/j.issn.1001-3806.2011.01.015
Abstract:
A theoretical model of high power and high efficiency picosecond laser oscillator pumped by 888nm LD was fabricated. Based on simulation calculation, resonance theory, ABCD law, self-consistent condition and continuous passive mode locking condition, absorption property of crystal Nd:YVO4 at 888nm wavelength, appropriate element parameters and mode parameters, and mode locking parameters were analyzed and calculated. Parameters of a model of picosecond laser oscillator were obtained based on the above calculated results. The results indicate that 61.5W high average power can be generated with 120W pump power and optical to optical conversion efficiency is 51.3％. The model helps for experiment on picosecond laser oscillator with high average power.
A theoretical model of high power and high efficiency picosecond laser oscillator pumped by 888nm LD was fabricated. Based on simulation calculation, resonance theory, ABCD law, self-consistent condition and continuous passive mode locking condition, absorption property of crystal Nd:YVO4 at 888nm wavelength, appropriate element parameters and mode parameters, and mode locking parameters were analyzed and calculated. Parameters of a model of picosecond laser oscillator were obtained based on the above calculated results. The results indicate that 61.5W high average power can be generated with 120W pump power and optical to optical conversion efficiency is 51.3％. The model helps for experiment on picosecond laser oscillator with high average power.
2011, 35(1): 54-57.
doi: 10.3969/j.issn.1001-3806.2011.01.016
Abstract:
In order to study the effects of the laser polarized direction and the incident angle on the laser reflectivity, transmissivity and absorptivity, the sapphire reflectivity, transmissivity and absorptivity at linearly-polarized 532nm laser beam were obtained by means of calorimetry. The obtained absorptivity was in good agreement with the one calculated with Fresnel formula. Experiment also examined the law of the sapphire reflectivity, transmissivity and absorptivity at different incident angle and polarization state. The experimental results have indicated that the reflectivity of linearly-polarized laser beam perpendicular to the incident plane increases with the incident angle. On the other hand the one parallel to the incident plane decreases gradually to the minimum till the incident angle close to 60, and then sharply increases. Under the radiation of parallel and perpendicular linearly-polarized laser beam the transmissivity decreases with the incident angle, while the absorptivity increases. It provides some references for the selection and optimization of technological parameters during the laser material processing.
In order to study the effects of the laser polarized direction and the incident angle on the laser reflectivity, transmissivity and absorptivity, the sapphire reflectivity, transmissivity and absorptivity at linearly-polarized 532nm laser beam were obtained by means of calorimetry. The obtained absorptivity was in good agreement with the one calculated with Fresnel formula. Experiment also examined the law of the sapphire reflectivity, transmissivity and absorptivity at different incident angle and polarization state. The experimental results have indicated that the reflectivity of linearly-polarized laser beam perpendicular to the incident plane increases with the incident angle. On the other hand the one parallel to the incident plane decreases gradually to the minimum till the incident angle close to 60, and then sharply increases. Under the radiation of parallel and perpendicular linearly-polarized laser beam the transmissivity decreases with the incident angle, while the absorptivity increases. It provides some references for the selection and optimization of technological parameters during the laser material processing.
2011, 35(1): 58-60.
doi: 10.3969/j.issn.1001-3806.2011.01.017
Abstract:
The output characteristics of a passively mode-locked erbium-doped ring fiber laser with a semiconductor saturable absorber mirror were studied. This ring fiber laser was constructed with a 1480nm laser diode as pump source, erbium-doped fiber as gain medium, as well as circular, polarization controller, wavelength division multiplexier and coupler. In experiments, the fiber laser operated stably with mode-locked pulse laser output, whose peak wavelength of 1586nm, spectrum width of 4.8nm, repetition frequency of 11.2MHz and maximum mean optical power of 8.4mW. It was found that the characteristics of the output laser pulse in time domain would change a little while adjusting the polarization controller in experiments. Hence, the effect of the polarization change in the fiber laser on characteristics of the output laser pulse should be paid attention to in practical utilization. The experimental results are helpful to the use of semiconductor saturable absorber mirror in passively mode-locked fiber lasers.
The output characteristics of a passively mode-locked erbium-doped ring fiber laser with a semiconductor saturable absorber mirror were studied. This ring fiber laser was constructed with a 1480nm laser diode as pump source, erbium-doped fiber as gain medium, as well as circular, polarization controller, wavelength division multiplexier and coupler. In experiments, the fiber laser operated stably with mode-locked pulse laser output, whose peak wavelength of 1586nm, spectrum width of 4.8nm, repetition frequency of 11.2MHz and maximum mean optical power of 8.4mW. It was found that the characteristics of the output laser pulse in time domain would change a little while adjusting the polarization controller in experiments. Hence, the effect of the polarization change in the fiber laser on characteristics of the output laser pulse should be paid attention to in practical utilization. The experimental results are helpful to the use of semiconductor saturable absorber mirror in passively mode-locked fiber lasers.
2011, 35(1): 61-64.
doi: 10.3969/j.issn.1001-3806.2011.01.018
Abstract:
In order to obtain a new flat dispersion photonic crystal fiber with low confinement loss, six octagonal rings of air holes in different diameters of d1, d2 and d3 were designed in the cladding of the fiber. Effect of the structure parameters on the dispersion and confinement loss was simulated by means of multi-pole method. The results show that the dispersion is among -0.1ps/(kmnm)~ 0.58 ps/(kmnm) in the wavelength range of 1.3m to 1.72m.The confinement loss is 0.16dB/km at 1.55m. So the special octagonal structure is more suitable for photonic crystal fibers with flat dispersion and low confinement loss. The results are useful for application of photonic crystal fibers in the optical communication.
In order to obtain a new flat dispersion photonic crystal fiber with low confinement loss, six octagonal rings of air holes in different diameters of d1, d2 and d3 were designed in the cladding of the fiber. Effect of the structure parameters on the dispersion and confinement loss was simulated by means of multi-pole method. The results show that the dispersion is among -0.1ps/(kmnm)~ 0.58 ps/(kmnm) in the wavelength range of 1.3m to 1.72m.The confinement loss is 0.16dB/km at 1.55m. So the special octagonal structure is more suitable for photonic crystal fibers with flat dispersion and low confinement loss. The results are useful for application of photonic crystal fibers in the optical communication.
2011, 35(1): 65-69.
doi: 10.3969/j.issn.1001-3806.2011.01.019
Abstract:
Laser-arc hybrid welding, as an innovative fusion welding technology, has attracted tremendous attention recently and has already been investigated for applications in many fields. However, laser-arc hybrid welding, as the combination of laser welding and arc welding process, involves a large number of parameters. These parameters and identified settings have important influence on the welding stability and weld quality. The effects of process parameters such as laser types assistant power supply, welding direction, focal point position, laser-arc distance, ratio of laser to arc power, shielding gas on the weld shape were reviewed. The future work should be made in this area was presented at last.
Laser-arc hybrid welding, as an innovative fusion welding technology, has attracted tremendous attention recently and has already been investigated for applications in many fields. However, laser-arc hybrid welding, as the combination of laser welding and arc welding process, involves a large number of parameters. These parameters and identified settings have important influence on the welding stability and weld quality. The effects of process parameters such as laser types assistant power supply, welding direction, focal point position, laser-arc distance, ratio of laser to arc power, shielding gas on the weld shape were reviewed. The future work should be made in this area was presented at last.
2011, 35(1): 70-73.
doi: 10.3969/j.issn.1001-3806.2011.01.020
Abstract:
In order to obtain results of incoherently coupled spatial soliton pairs in biased centrosymmetric photorefractive crystal circuit with a divider resistance, the characteristics of these soliton pairs were numerically investigated. The result shows that these soliton pairs are established by the mutually incoherent solitary beams with the same polarization and wavelength. The incoherently coupled screening spatial soliton pairs in biased centrosymmetric photorefractive crystal with a divider resistance or not can be obtained from this theory by adjusting the value of the divider resistance. Incoherently coupled dark-dark, bright-bright and bright-dark screening soliton pairs in centrosymmetric photorefractive crystals are possible due to photorefractive effect.
In order to obtain results of incoherently coupled spatial soliton pairs in biased centrosymmetric photorefractive crystal circuit with a divider resistance, the characteristics of these soliton pairs were numerically investigated. The result shows that these soliton pairs are established by the mutually incoherent solitary beams with the same polarization and wavelength. The incoherently coupled screening spatial soliton pairs in biased centrosymmetric photorefractive crystal with a divider resistance or not can be obtained from this theory by adjusting the value of the divider resistance. Incoherently coupled dark-dark, bright-bright and bright-dark screening soliton pairs in centrosymmetric photorefractive crystals are possible due to photorefractive effect.
2011, 35(1): 79-81.
doi: 10.3969/j.issn.1001-3806.2011.01.022
Abstract:
To explore the influence of molecular structures on the nonlinear optical property, the third-order nonlinear optical property of three organometallic complexes with different central metallic atoms (Ni, Cu, and Pd) was investigated by means of z-scan technique. After comparing the nonlinear refractive indexes and the excited state absorption cross-sections of the complexes, it was found that the heavy central metallic atom enhanced the third-order optical property obviously, but the resonant absorption did not have much effect on the nonlinear optical property. The experiment results show that all the three complexes have self focusing and reverse saturation absorption characteristics.
To explore the influence of molecular structures on the nonlinear optical property, the third-order nonlinear optical property of three organometallic complexes with different central metallic atoms (Ni, Cu, and Pd) was investigated by means of z-scan technique. After comparing the nonlinear refractive indexes and the excited state absorption cross-sections of the complexes, it was found that the heavy central metallic atom enhanced the third-order optical property obviously, but the resonant absorption did not have much effect on the nonlinear optical property. The experiment results show that all the three complexes have self focusing and reverse saturation absorption characteristics.
2011, 35(1): 82-85.
doi: 10.3969/j.issn.1001-3806.2011.01.023
Abstract:
In order to study the performance of an Yb:YAG thin disk laser, a 16-pass pumped micro-channel cooled scheme was adopted. The optimum thickness of the Yb:YAG disk, the thermo-mechanical effect in the disk and the laser performance are analyzed. The 16-pass pumping coupling is achieved in preliminary experiment using an Yb:YAG disk (250m in thickness and 10mm in diameter) with atomic fractional 0.1 doping concentration. The output power of 24.4W was obtained from the laser oscillator when the total pump power was 81.9W. The optical-to-optical conversion efficiency was up to 29.8%. The result shows that the higher conversion efficiency can be achieved in the 16-pass pumped micro-channel cooled Yb:YAG thin disk laser.
In order to study the performance of an Yb:YAG thin disk laser, a 16-pass pumped micro-channel cooled scheme was adopted. The optimum thickness of the Yb:YAG disk, the thermo-mechanical effect in the disk and the laser performance are analyzed. The 16-pass pumping coupling is achieved in preliminary experiment using an Yb:YAG disk (250m in thickness and 10mm in diameter) with atomic fractional 0.1 doping concentration. The output power of 24.4W was obtained from the laser oscillator when the total pump power was 81.9W. The optical-to-optical conversion efficiency was up to 29.8%. The result shows that the higher conversion efficiency can be achieved in the 16-pass pumped micro-channel cooled Yb:YAG thin disk laser.
2011, 35(1): 86-88.
doi: 10.3969/j.issn.1001-3806.2011.01.024
Abstract:
In order to reveal the physical mechanism of broadband modulated hypocrellin A(HA), the effect of high power laser excitation was studied. The existence of excited-state intramolecular proton transfer(ESIPT)in HA molecules was proved in theory and experiments. The energy level model of HA molecules was presented. The results show that ESIPT process in HA molecules can be achieved only under the condition of two-photon absorption. This result is helpful for a better understanding of the photophysical mechanism of HA.
In order to reveal the physical mechanism of broadband modulated hypocrellin A(HA), the effect of high power laser excitation was studied. The existence of excited-state intramolecular proton transfer(ESIPT)in HA molecules was proved in theory and experiments. The energy level model of HA molecules was presented. The results show that ESIPT process in HA molecules can be achieved only under the condition of two-photon absorption. This result is helpful for a better understanding of the photophysical mechanism of HA.
2011, 35(1): 89-93.
doi: 10.3969/j.issn.1001-3806.2011.01.025
Abstract:
In order to analyze diffraction fields of combined cosine-gratings, considering the influence of the limited aperture of the gratings, the elements of the diffraction fields of the combined cosine-gratings were obtained and the corresponding integral expressions of the diffraction fields were derived based on the method of wavefront phase-factors. Then the formulae of the amplitude distribution of diffraction fields were deduced. Finally the amplitude and intensity distribution along the axis, the transverse line-width and axial line-width of that real focal-spot were obtained. This study may further provide a theoretical foundation for the application of combined cosine-gratings in filtering and optical signal processing.
In order to analyze diffraction fields of combined cosine-gratings, considering the influence of the limited aperture of the gratings, the elements of the diffraction fields of the combined cosine-gratings were obtained and the corresponding integral expressions of the diffraction fields were derived based on the method of wavefront phase-factors. Then the formulae of the amplitude distribution of diffraction fields were deduced. Finally the amplitude and intensity distribution along the axis, the transverse line-width and axial line-width of that real focal-spot were obtained. This study may further provide a theoretical foundation for the application of combined cosine-gratings in filtering and optical signal processing.
2011, 35(1): 94-98.
doi: 10.3969/j.issn.1001-3806.2011.01.026
Abstract:
In order to study thermal effect of laser crystal end-pumped by pulsed laser diode, transient temperature field and thermal deformation field on the laser crystal were analytically investigated and calculated. Taking into account the outgoing light pulse LD with the super-Gaussian distribution and the Nd:YAG crystal isotropic heat conduction characteristics, the general analytical expressions of the transient temperature field and thermal deformation field of Nd:YAG crystal end-pumped by super-Gaussian distribution were obtained based on Poission equation of thermal conduction. The effect of the super-Gaussian pump light spot radius and super-Gaussian order times, pulse width on the transient temperature field of Nd:YAG crystal during the single-pulse-pumped and the quasi-thermal equilibrium temperature field of time-varying characteristics were quantitatively analyzed. The results show that when the LD end-pumped pulsed light has a third-order super-Gaussian distribution, the pump power is 80W, pulse frequency is 100Hz, pulse width is 200s, the mass fraction of neodymium-doped 0.01 Nd:YAG crystal transient temperature field with the pump pulse showing a periodic distribution, the quasi-thermal equilibrium the temperature of 25.5℃ to 29.2℃ into a zigzag shape between the distribution of the period. Crystal surface heat pump shape variables between 0.13m and 0.19m showing cyclical changes. The results have the theoretical instruction for designing the heat insensitive resonant cavity for the pulsed LD end-pumped all solid-state lasers.
In order to study thermal effect of laser crystal end-pumped by pulsed laser diode, transient temperature field and thermal deformation field on the laser crystal were analytically investigated and calculated. Taking into account the outgoing light pulse LD with the super-Gaussian distribution and the Nd:YAG crystal isotropic heat conduction characteristics, the general analytical expressions of the transient temperature field and thermal deformation field of Nd:YAG crystal end-pumped by super-Gaussian distribution were obtained based on Poission equation of thermal conduction. The effect of the super-Gaussian pump light spot radius and super-Gaussian order times, pulse width on the transient temperature field of Nd:YAG crystal during the single-pulse-pumped and the quasi-thermal equilibrium temperature field of time-varying characteristics were quantitatively analyzed. The results show that when the LD end-pumped pulsed light has a third-order super-Gaussian distribution, the pump power is 80W, pulse frequency is 100Hz, pulse width is 200s, the mass fraction of neodymium-doped 0.01 Nd:YAG crystal transient temperature field with the pump pulse showing a periodic distribution, the quasi-thermal equilibrium the temperature of 25.5℃ to 29.2℃ into a zigzag shape between the distribution of the period. Crystal surface heat pump shape variables between 0.13m and 0.19m showing cyclical changes. The results have the theoretical instruction for designing the heat insensitive resonant cavity for the pulsed LD end-pumped all solid-state lasers.
2011, 35(1): 99-101.
doi: 10.3969/j.issn.1001-3806.2011.01.027
Abstract:
In order to study influence of multiple-beam interference on the transmittance of yttrium vanadate prisms, transmittance from 800nm to 2400nm was theoretically analyzed taking multiple-beam interference into consideration or not. Experiments were carried out with a UV-3101PC spectral photometer. It is found that transmittance of the prism increases and vibrates with wavelength. The result shows that multiple-beam interference makes a disturbance to the transmittance of the prism. It is a good reference to the application of yttrium vanadate prisms.
In order to study influence of multiple-beam interference on the transmittance of yttrium vanadate prisms, transmittance from 800nm to 2400nm was theoretically analyzed taking multiple-beam interference into consideration or not. Experiments were carried out with a UV-3101PC spectral photometer. It is found that transmittance of the prism increases and vibrates with wavelength. The result shows that multiple-beam interference makes a disturbance to the transmittance of the prism. It is a good reference to the application of yttrium vanadate prisms.
2011, 35(1): 102-105.
doi: 10.3969/j.issn.1001-3806.2011.01.028
Abstract:
To solve the problems of unsatisfied water-cooling and deposit deviation induced by gravity during laser cladding, a series of feeding nozzles distributed radially and symmetrically was designed to obtain satisfied powder stream and improve cladding quality (the main structure including laser beam routeway, shielding gas routeway, water-cooling routeway and gas feeding routeway). It was found that the powder pooling was satisfied during experiments conducted under conditions that the angles between the nozzle and horizontal plane were 90, 60, 30 and 0 respectively. Some experiments were also conducted adopting powders of Ti, Ni and tool steel respectively. Powders were fed stably and uniformly during experiments. The cladding samples with smooth surface and homogeneous microstructure were metallurgically bonded with the substrate. Experimental results show that the nozzles are satisfactory for powder feeding in laser cladding and can be used for material synthesis of powders. The system is suit for surface modification and 3-D solid fabrication.
To solve the problems of unsatisfied water-cooling and deposit deviation induced by gravity during laser cladding, a series of feeding nozzles distributed radially and symmetrically was designed to obtain satisfied powder stream and improve cladding quality (the main structure including laser beam routeway, shielding gas routeway, water-cooling routeway and gas feeding routeway). It was found that the powder pooling was satisfied during experiments conducted under conditions that the angles between the nozzle and horizontal plane were 90, 60, 30 and 0 respectively. Some experiments were also conducted adopting powders of Ti, Ni and tool steel respectively. Powders were fed stably and uniformly during experiments. The cladding samples with smooth surface and homogeneous microstructure were metallurgically bonded with the substrate. Experimental results show that the nozzles are satisfactory for powder feeding in laser cladding and can be used for material synthesis of powders. The system is suit for surface modification and 3-D solid fabrication.
2011, 35(1): 106-108.
doi: 10.3969/j.issn.1001-3806.2011.01.029
Abstract:
In order to study the transmission spectrum of rotary quartz at normal temperature, the spectrum within 300nm~1500nm was tested with a UV-3101PC spectrophotometer. Then the experimental result was compared with the theoretical one. The result shows that the peak transmittance is less than 50% among the range of 0nm~400nm, for the absorption of quartz crystal is obvious, and the spectrum cycle is small with the rotation rate changing with wavelength. The peak transmittance is 60% among the range of 400nm~800nm and the transmission spectrum cycle as well as the peak number is affected significantly by the crystal thickness. At wavelength larger than 1000nm, because rotation rate changes little with the wavelength, cycle of the spectrum becomes big and the spectrum is irregular due to selective absorption of the quartz material.
In order to study the transmission spectrum of rotary quartz at normal temperature, the spectrum within 300nm~1500nm was tested with a UV-3101PC spectrophotometer. Then the experimental result was compared with the theoretical one. The result shows that the peak transmittance is less than 50% among the range of 0nm~400nm, for the absorption of quartz crystal is obvious, and the spectrum cycle is small with the rotation rate changing with wavelength. The peak transmittance is 60% among the range of 400nm~800nm and the transmission spectrum cycle as well as the peak number is affected significantly by the crystal thickness. At wavelength larger than 1000nm, because rotation rate changes little with the wavelength, cycle of the spectrum becomes big and the spectrum is irregular due to selective absorption of the quartz material.
2011, 35(1): 109-111.
doi: 10.3969/j.issn.1001-3806.2011.01.030
Abstract:
An optical system of a laser Doppler velocimeter based on dual-beam mode was designed for flow velocity measurement in field, and error analysis was discussed with experimental results performed. In order to create interference fringe, the beam of a fiber-coupled laser diode was split by a polarization maintaining fiber coupler, then both the beams behind the fiber coupler were collimated by fiber collimator and focused by an aspheric lens. In order to detect Doppler signal, a collecting lens and pinhole was used to project the useful scattering light onto an avalanche photo diode. Resolution of the built optical system was 0.046mm3, and measurement error was less than 0.59% in theory. Because of its advantages such as small size, integration and convenience, the system is suitable for field measurement.
An optical system of a laser Doppler velocimeter based on dual-beam mode was designed for flow velocity measurement in field, and error analysis was discussed with experimental results performed. In order to create interference fringe, the beam of a fiber-coupled laser diode was split by a polarization maintaining fiber coupler, then both the beams behind the fiber coupler were collimated by fiber collimator and focused by an aspheric lens. In order to detect Doppler signal, a collecting lens and pinhole was used to project the useful scattering light onto an avalanche photo diode. Resolution of the built optical system was 0.046mm3, and measurement error was less than 0.59% in theory. Because of its advantages such as small size, integration and convenience, the system is suitable for field measurement.
2011, 35(1): 112-116.
doi: 10.3969/j.issn.1001-3806.2011.01.031
Abstract:
In order to reduce the impact of fiber chromatic dispersion on the transmission performance of an orthogonal frequency division multiplexing (OFDM) system, a channel estimator was introduced into the system. The influence of fiber chromatic dispersion on OFDM signals transmission in optical fiber was theoretically investigated. And the performance of an OFDM system with a channel estimator based on combined pilots and the least square estimation was demonstrated in the experiment. The amplitude response and phase response for the OFDM system showed that the optical OFDM signal modulated by a direct modulator can transmit 200km in the single-mode dispersion fiber. The bit error rate was less than 10-6 and the power penalty was smaller than 2dB.The results show that fiber chromatic dispersion plays a stronger impact on high frequency subcarrier than low frequency subcarrier. The proposed method can effectively compensate the phase shift and amplitude attenuation caused by fiber chromatic dispersion.
In order to reduce the impact of fiber chromatic dispersion on the transmission performance of an orthogonal frequency division multiplexing (OFDM) system, a channel estimator was introduced into the system. The influence of fiber chromatic dispersion on OFDM signals transmission in optical fiber was theoretically investigated. And the performance of an OFDM system with a channel estimator based on combined pilots and the least square estimation was demonstrated in the experiment. The amplitude response and phase response for the OFDM system showed that the optical OFDM signal modulated by a direct modulator can transmit 200km in the single-mode dispersion fiber. The bit error rate was less than 10-6 and the power penalty was smaller than 2dB.The results show that fiber chromatic dispersion plays a stronger impact on high frequency subcarrier than low frequency subcarrier. The proposed method can effectively compensate the phase shift and amplitude attenuation caused by fiber chromatic dispersion.
2011, 35(1): 117-121.
doi: 10.3969/j.issn.1001-3806.2011.01.032
Abstract:
In order to study stimulated Brillouin scattering（SBS） in Yb3+-doped double clad single-frequency fiber amplifiers, numerical simulation was carried out based on the rate equations. The results show that fiber length, pump schemes, pump power, heat transfer coefficient make great impact on SBS effect. On the other hand the impact of the signal power is small. The results of simulation provide a theoretical guide to optimum design of high power single-frequency fiber amplifiers.
In order to study stimulated Brillouin scattering（SBS） in Yb3+-doped double clad single-frequency fiber amplifiers, numerical simulation was carried out based on the rate equations. The results show that fiber length, pump schemes, pump power, heat transfer coefficient make great impact on SBS effect. On the other hand the impact of the signal power is small. The results of simulation provide a theoretical guide to optimum design of high power single-frequency fiber amplifiers.
2011, 35(1): 122-125.
doi: 10.3969/j.issn.1001-3806.2011.01.033
Abstract:
In order to measure the concentration of carbon monoxide gas in a smelting furnace in real time and with high precision, an 1.58m distributed feedback(DFB) laser was used to measure the absorption harmonics of different concentrations by means of laser frequency scanning. The hybrid algebra calculation of the maximum values of its first harmonic and second harmonics can effectively overcome the influence of laser aging, disperse and modulation change in the laser system on the measurement results. It is shown that the relative measurement error increases with the modulation linearly in the small-signal modulation and exponentially in the large-signal modulation. With the increase of transfer factor of laser driver current and laser frequency, the relative error will increase. The conclusion show that the CO gas concentration can be calculated efficiently, fast, in real-time and with high-precision by means of the hybrid calculation method of absorption lines at special frequencies of the first harmonic and second harmonic intensity.
In order to measure the concentration of carbon monoxide gas in a smelting furnace in real time and with high precision, an 1.58m distributed feedback(DFB) laser was used to measure the absorption harmonics of different concentrations by means of laser frequency scanning. The hybrid algebra calculation of the maximum values of its first harmonic and second harmonics can effectively overcome the influence of laser aging, disperse and modulation change in the laser system on the measurement results. It is shown that the relative measurement error increases with the modulation linearly in the small-signal modulation and exponentially in the large-signal modulation. With the increase of transfer factor of laser driver current and laser frequency, the relative error will increase. The conclusion show that the CO gas concentration can be calculated efficiently, fast, in real-time and with high-precision by means of the hybrid calculation method of absorption lines at special frequencies of the first harmonic and second harmonic intensity.
2011, 35(1): 126-129,136.
doi: 10.3969/j.issn.1001-3806.2011.01.034
Abstract:
In order to study the effect of the radio of micro plasma layer width to dielectric width, dielectric constant of the dielectric material, the plasma frequency and the incident angle on the cut-off frequency, the dispersion relation of one-dimension plasma photonic crystals was analyzed by means of transfer matrix method and the change rule of the cut-off frequency was put forward. The results show that plasma photonic crystals can't completely cut off the electromagnetic wave, whose frequency is less than the plasma frequency. The cutoff frequency comes close to the frequency of plasma when the incident angle of electromagnetic wave increases. The function of modulation for plasma photonic crystals can be realized by adjusting the index mentioned above.
In order to study the effect of the radio of micro plasma layer width to dielectric width, dielectric constant of the dielectric material, the plasma frequency and the incident angle on the cut-off frequency, the dispersion relation of one-dimension plasma photonic crystals was analyzed by means of transfer matrix method and the change rule of the cut-off frequency was put forward. The results show that plasma photonic crystals can't completely cut off the electromagnetic wave, whose frequency is less than the plasma frequency. The cutoff frequency comes close to the frequency of plasma when the incident angle of electromagnetic wave increases. The function of modulation for plasma photonic crystals can be realized by adjusting the index mentioned above.
2011, 35(1): 130-132,140.
doi: 10.3969/j.issn.1001-3806.2011.01.035
Abstract:
In order to study the influence of annealing oxygen pressure on crystalline and laser-induced voltages (LIV) of Al-doped ZnO thin film, it was prepared on sapphire(0001) single crystal substrates by means of pulsed laser deposition technology. Then the micro-structure of the thin film was determined by means of X-ray diffraction (XRD). The corresponding LIV signals were detected with these thin film illuminated by ultraviolet pulsed laser. The results were theoretically analyzed and experimentally validated. The results indicated that c-axis oriented thin film was produced and the optimal generation conditions were determined. Meanwhile, the results showed that the both ends of the film would induce LIV and its maximal value was 0.532V when the film was irradiated by laser with wavelength of 248nm, pulse bandwidth of 20ns. With the annealing oxygen pressure increasing, the peak LIV increases at first and then decreases. It is helpful to in the application of the film in ultraviolet detectors
In order to study the influence of annealing oxygen pressure on crystalline and laser-induced voltages (LIV) of Al-doped ZnO thin film, it was prepared on sapphire(0001) single crystal substrates by means of pulsed laser deposition technology. Then the micro-structure of the thin film was determined by means of X-ray diffraction (XRD). The corresponding LIV signals were detected with these thin film illuminated by ultraviolet pulsed laser. The results were theoretically analyzed and experimentally validated. The results indicated that c-axis oriented thin film was produced and the optimal generation conditions were determined. Meanwhile, the results showed that the both ends of the film would induce LIV and its maximal value was 0.532V when the film was irradiated by laser with wavelength of 248nm, pulse bandwidth of 20ns. With the annealing oxygen pressure increasing, the peak LIV increases at first and then decreases. It is helpful to in the application of the film in ultraviolet detectors
2011, 35(1): 133-136.
doi: 10.3969/j.issn.1001-3806.2011.01.036
Abstract:
In order to study the influence of laser shock on the electrical property of ZnO varistor ceramics, ZnO varistor ceramics was shocked by an Nd:YAG laser. Electrical parameters of ZnO varistor ceramics were measured with a CJ1001 varistor tester and morphology and microstructure of ZnO varistor ceramics was characterized by X-ray diffraction and scanning electron microscope. The experimental data of electrical property of ZnO varistor ceramics was obtained by laser shock process. The results indicate that after laser shock processing, the voltage gradient of ZnO varistor ceramics was reduced by 15.6%; its nonlinear coefficient substantially increased by 43.4% and leakage current reduced by 50%. Phase composition of ZnO varistor ceramics includes mainly ZnO main phase, Zn2.33Sb0.67O4 phase and -Bi2O3 phase in high-temperature sintering. However, it include not only the former three phases, but also the new phase -Bi2O3 phase after laser shock process. The emergence of the new phase is the main cause for change of the electrical property of ZnO varistor ceramics.
In order to study the influence of laser shock on the electrical property of ZnO varistor ceramics, ZnO varistor ceramics was shocked by an Nd:YAG laser. Electrical parameters of ZnO varistor ceramics were measured with a CJ1001 varistor tester and morphology and microstructure of ZnO varistor ceramics was characterized by X-ray diffraction and scanning electron microscope. The experimental data of electrical property of ZnO varistor ceramics was obtained by laser shock process. The results indicate that after laser shock processing, the voltage gradient of ZnO varistor ceramics was reduced by 15.6%; its nonlinear coefficient substantially increased by 43.4% and leakage current reduced by 50%. Phase composition of ZnO varistor ceramics includes mainly ZnO main phase, Zn2.33Sb0.67O4 phase and -Bi2O3 phase in high-temperature sintering. However, it include not only the former three phases, but also the new phase -Bi2O3 phase after laser shock process. The emergence of the new phase is the main cause for change of the electrical property of ZnO varistor ceramics.
2011, 35(1): 137-140.
doi: 10.3969/j.issn.1001-3806.2011.01.037
Abstract:
In order to study the kinetic energy of accelerated positrons in the laser-driven wakefield, the positron kinetic energy in the wakefield driven by symmetric and asymmetric Gaussian laser pulse was simulated. Numerical result shows that the positron kinetic energy driven by asymmetric Gaussian laser pulses is higher than that driven by quasi-Gaussian laser pulses.
In order to study the kinetic energy of accelerated positrons in the laser-driven wakefield, the positron kinetic energy in the wakefield driven by symmetric and asymmetric Gaussian laser pulse was simulated. Numerical result shows that the positron kinetic energy driven by asymmetric Gaussian laser pulses is higher than that driven by quasi-Gaussian laser pulses.
2011, 35(1): 141-144.
doi: 10.3969/j.issn.1001-3806.2011.01.038
Abstract:
In order to overcome the particle depletion phenomenon in the particle filter algorithm and the problem of heavy large amount of calculation, a fission bootstrap particle filtering method was used at the moment of measurement. At first, fissile breeding was carried out on the particles with big weights. The particles after fissile breeding are proportional to those before fissile breeding. Then the particles with small weights in the particle group were covered. The particle pre-smoothing was carried out with the characteristics of the particle group maintained. After sampling once again, the function of particle anti-depletion was compensated. An appropriate sampling threshold was set to eliminate the sampling points with smaller weights. Multiple sampling points were derived from the sampling points with bigger weights in the premise of maintaining the total number of sampling points. The root mean square (RMS) error and calculation steps were shown in the model and best tracking effect was obtained. Simulation was carried out with MATLAB. The results show that the RMS error of the algorithm is 0.36445, better than that of the basic particle filtering algorithm.
In order to overcome the particle depletion phenomenon in the particle filter algorithm and the problem of heavy large amount of calculation, a fission bootstrap particle filtering method was used at the moment of measurement. At first, fissile breeding was carried out on the particles with big weights. The particles after fissile breeding are proportional to those before fissile breeding. Then the particles with small weights in the particle group were covered. The particle pre-smoothing was carried out with the characteristics of the particle group maintained. After sampling once again, the function of particle anti-depletion was compensated. An appropriate sampling threshold was set to eliminate the sampling points with smaller weights. Multiple sampling points were derived from the sampling points with bigger weights in the premise of maintaining the total number of sampling points. The root mean square (RMS) error and calculation steps were shown in the model and best tracking effect was obtained. Simulation was carried out with MATLAB. The results show that the RMS error of the algorithm is 0.36445, better than that of the basic particle filtering algorithm.
