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RSS2010 Vol. 34, No. 5
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2010, 34(5): 577-580.
doi: 10.3969/j.issn.1001-3806.2010.O5.001
[Abstract]
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Abstract:
The method of the laser guiding combined-pulse discharge was studied to increase the phase-change layer depth of the laser guiding discharge pit, and avoid the energy loss induced by serious material surface vaporization. This method includes two schemes. One is increasing laser pulse numbers in the process of discharge to enhance the ability of the laser guiding. The other is increasing discharge pulses,in which the input of discharge energy is controlled by the temperature of the machining point so that the energy concentration is reduced and the depth of the strengthening pit is increased. The results showed that the diameter of the discharge pit reduced from 690μm to 652μm and 653μm, and the depth increased from 85μm to 100μm and 92μm, if increasing laser pulse numbers in the late discharge pulse and combining laser and discharge pulses respectively.These methods are applicable for the surface strengthening process of mechanical components.
The method of the laser guiding combined-pulse discharge was studied to increase the phase-change layer depth of the laser guiding discharge pit, and avoid the energy loss induced by serious material surface vaporization. This method includes two schemes. One is increasing laser pulse numbers in the process of discharge to enhance the ability of the laser guiding. The other is increasing discharge pulses,in which the input of discharge energy is controlled by the temperature of the machining point so that the energy concentration is reduced and the depth of the strengthening pit is increased. The results showed that the diameter of the discharge pit reduced from 690μm to 652μm and 653μm, and the depth increased from 85μm to 100μm and 92μm, if increasing laser pulse numbers in the late discharge pulse and combining laser and discharge pulses respectively.These methods are applicable for the surface strengthening process of mechanical components.
2010, 34(5): 581-583.
doi: 10.3969/j.issn.1001-3806.2010.O5.002
Abstract:
Ocean temperature and depth are important parameters. At present ocean temperature and depth measurement almost depend on electric signal inspection, so the sensor is not safety in the water.In order to overcome this shortage and improve measurement veracity and safety, a new ocean temperature and depth inspection system was presented based on fiber Bragg grating sensor with its advantages of all optic sensors, underwater safety and feasibility of sensor network, etc.Its measurement principle was described; its system and sensor structure was designed and manufactured.The experiments proved that sensor's linearity was very good and its value was up to 0.9999.It provides a new way to detect ocean temperature and depth.
Ocean temperature and depth are important parameters. At present ocean temperature and depth measurement almost depend on electric signal inspection, so the sensor is not safety in the water.In order to overcome this shortage and improve measurement veracity and safety, a new ocean temperature and depth inspection system was presented based on fiber Bragg grating sensor with its advantages of all optic sensors, underwater safety and feasibility of sensor network, etc.Its measurement principle was described; its system and sensor structure was designed and manufactured.The experiments proved that sensor's linearity was very good and its value was up to 0.9999.It provides a new way to detect ocean temperature and depth.
2010, 34(5): 584-586,623.
doi: 10.3969/j.issn.1001-3806.2010.O5.003
Abstract:
In order to improve the shielding effect of gas flow field in laser direct manufacturing, the shielding gas flow field of coaxial powder feeder nozzles was studied by means of smoke flow visualization technology.The influence of gas velocity from nozzle, distance between parts and nozzle exit,moving velocity of nozzle and crosswind velocity on shielding gas field was investigated systematically. The results show that with the increase of gas velocity from nozzle,shielding effect increases at first and then gets worse; with the increase of velocity of crosswind and nozzle,the axis of shielding field and nozzle get apart; when the velocity of crosswind surpasses 50% of velocity of gas from nozzle, shielding field fails to protect molten pool totally at the place 10mm below the nozzle.The information can be used to select appropriate nozzle flow parameters.
In order to improve the shielding effect of gas flow field in laser direct manufacturing, the shielding gas flow field of coaxial powder feeder nozzles was studied by means of smoke flow visualization technology.The influence of gas velocity from nozzle, distance between parts and nozzle exit,moving velocity of nozzle and crosswind velocity on shielding gas field was investigated systematically. The results show that with the increase of gas velocity from nozzle,shielding effect increases at first and then gets worse; with the increase of velocity of crosswind and nozzle,the axis of shielding field and nozzle get apart; when the velocity of crosswind surpasses 50% of velocity of gas from nozzle, shielding field fails to protect molten pool totally at the place 10mm below the nozzle.The information can be used to select appropriate nozzle flow parameters.
2010, 34(5): 587-590,595.
doi: 10.3969/j.issn.1001-3806.2010.O5.004
Abstract:
In order to realize 3-D joint seam tracking accurately in the process of non-ferrous metal complicated curve surface laser welding, the 3-D joint seam real-time measurement was adopted to compensate for the joint seam deformation dynamically. The control arithmetic and key technologies for 3-D seam welding-measuring integration control system were studied,including the mathematics model of motion control, the scheme of welding path and measuring path,the real time inspection and dynamic compensation in welding, etc.The proposed arithmetic was testified by the experiment in which the non-ferrous metal with less than 3mm thickness was welded by 4kW fiber laser. The test indicates that the 3-D joint seam welding-measuring integration control system can achieve the 3-D joint seam's online inspection, real time welding and dynamic compensation quickly and precisely, which satisfies the measuring system's precision requirement.
In order to realize 3-D joint seam tracking accurately in the process of non-ferrous metal complicated curve surface laser welding, the 3-D joint seam real-time measurement was adopted to compensate for the joint seam deformation dynamically. The control arithmetic and key technologies for 3-D seam welding-measuring integration control system were studied,including the mathematics model of motion control, the scheme of welding path and measuring path,the real time inspection and dynamic compensation in welding, etc.The proposed arithmetic was testified by the experiment in which the non-ferrous metal with less than 3mm thickness was welded by 4kW fiber laser. The test indicates that the 3-D joint seam welding-measuring integration control system can achieve the 3-D joint seam's online inspection, real time welding and dynamic compensation quickly and precisely, which satisfies the measuring system's precision requirement.
2010, 34(5): 591-595.
doi: 10.3969/j.issn.1001-3806.2010.O5.005
Abstract:
In order to study microstructure,high temperature oxidation resistance of Fe-based, Cr3C2/Fe composite coating, as well as phase structure evolution of Cr3C2/Fe composite coating, Fe-based alloy and Cr3C2/Fe-based alloy composite coatings were obtained on Q235 whose composition is similar with Fe-based alloy with a SkW CO2 laser.Then relevant test data were obtained and theoretical analysis was conducted.Results show that; the Fe-based alloy coating is mainly composed of phase α-Fe, Cr23C6,as well as the body-centered cubic α-Fe solid solution, etc.;the cladding layer mainly crystallizes in sub-eutectic crystallization way, there exists lamellar eutectic crystal organization between the primary solid solution.The main composition of Cr3C2/Fe-based alloy composite coating are γ-Fe,α-Fe, Cr23C6,Cr3C2,Cr7C3 and so on. The Fe-based alloy coating is composed of well-developed c}-Fe dendrites and the eutectic structure during the composition, Cr3C2/Fe-based alloy coating typical organizations are equiaxed grains, as well as small eutectic. Cr3C2 pairs play a major role in promoting the organization from dendrite to equiaxed transformation; Cr3C2 can significantly increase the micro-hardness, high temperature oxidation resistance and other physical properties of Fe-based alloy coating. The results have certain assistance for subsequent Fe-based alloy laser claddinc and laser surface modiCcation.
In order to study microstructure,high temperature oxidation resistance of Fe-based, Cr3C2/Fe composite coating, as well as phase structure evolution of Cr3C2/Fe composite coating, Fe-based alloy and Cr3C2/Fe-based alloy composite coatings were obtained on Q235 whose composition is similar with Fe-based alloy with a SkW CO2 laser.Then relevant test data were obtained and theoretical analysis was conducted.Results show that; the Fe-based alloy coating is mainly composed of phase α-Fe, Cr23C6,as well as the body-centered cubic α-Fe solid solution, etc.;the cladding layer mainly crystallizes in sub-eutectic crystallization way, there exists lamellar eutectic crystal organization between the primary solid solution.The main composition of Cr3C2/Fe-based alloy composite coating are γ-Fe,α-Fe, Cr23C6,Cr3C2,Cr7C3 and so on. The Fe-based alloy coating is composed of well-developed c}-Fe dendrites and the eutectic structure during the composition, Cr3C2/Fe-based alloy coating typical organizations are equiaxed grains, as well as small eutectic. Cr3C2 pairs play a major role in promoting the organization from dendrite to equiaxed transformation; Cr3C2 can significantly increase the micro-hardness, high temperature oxidation resistance and other physical properties of Fe-based alloy coating. The results have certain assistance for subsequent Fe-based alloy laser claddinc and laser surface modiCcation.
2010, 34(5): 596-599.
doi: 10.3969/j.issn.1001-3806.2010.O5.006
Abstract:
In order to investigate the effect of laser shock processing on residual stress of crankshaft-connecting rod journal chamfer, the surface of crankshaft-connecting rod journal chamfer was processed by laser shock. Then, the residual stress distribution of the chamfer was measured with X-ray diffraction method, and the production mechanism of residual stress was analyzed. Finally, the effects of laser shock processing on resistance fatigue and resistance wear were investigated. The results show that micro-hardness of crankshaft-connecting rod journal chamfer processed by laser shock is above 600HV, and compressive residual stress in the shocked zone is attained 320MPa, which is benefit to increase its resistance wear and fatigue life.
In order to investigate the effect of laser shock processing on residual stress of crankshaft-connecting rod journal chamfer, the surface of crankshaft-connecting rod journal chamfer was processed by laser shock. Then, the residual stress distribution of the chamfer was measured with X-ray diffraction method, and the production mechanism of residual stress was analyzed. Finally, the effects of laser shock processing on resistance fatigue and resistance wear were investigated. The results show that micro-hardness of crankshaft-connecting rod journal chamfer processed by laser shock is above 600HV, and compressive residual stress in the shocked zone is attained 320MPa, which is benefit to increase its resistance wear and fatigue life.
2010, 34(5): 600-602,618.
doi: 10.3969/j.issn.1001-3806.2010.O5.007
Abstract:
In order to calibrate the coefficients of phase-height mapping equation in phase measuring profilometry (PMP) systems,virtual planes were introduced. Firstly,the intrinsic and extrinsic parameter, of camera and projector were calibrated with uniforni mathematics model and processing method,as a projector could be considered as a camera working in reverse.Secondly,geometric construction of the measurement system was calibrated by means of stereovisiou method.Thirdly, a reference plane was defined in the measuring volume.Phase distribution of reference plan and parallel standard planes at different distances from the reference plan was worked out according to the calibrated parameters.Finally, the coefficients of phase-height mapping equation were obtained with least square method.The standard deviation of measurement reached 0.046mm.A model consists of four steps with space of 1.00mm was also measured. The measured average height between neighbor steps was 0.99mm.The experiment results reveal that the method is feasible.The procedure of system calibration is simplified.
In order to calibrate the coefficients of phase-height mapping equation in phase measuring profilometry (PMP) systems,virtual planes were introduced. Firstly,the intrinsic and extrinsic parameter, of camera and projector were calibrated with uniforni mathematics model and processing method,as a projector could be considered as a camera working in reverse.Secondly,geometric construction of the measurement system was calibrated by means of stereovisiou method.Thirdly, a reference plane was defined in the measuring volume.Phase distribution of reference plan and parallel standard planes at different distances from the reference plan was worked out according to the calibrated parameters.Finally, the coefficients of phase-height mapping equation were obtained with least square method.The standard deviation of measurement reached 0.046mm.A model consists of four steps with space of 1.00mm was also measured. The measured average height between neighbor steps was 0.99mm.The experiment results reveal that the method is feasible.The procedure of system calibration is simplified.
2010, 34(5): 603-606.
doi: 10.3969/j.issn.1001-3806.2010.O5.008
Abstract:
In order to study pulsed electro-optic Q-switched Nd:YAG laser at 1319nm, the transition radiation energy level of Nd:YAG crystal was analyzed.A single pulsed laser at 1319nm was acquired after restraining laser oscillator of wavelength at 1064nm through coating chosen film on the mirror. In a configuration of lamp pumped, water-cooled Nd:YAG with KD*P as eleciro-optic Q-switched, pulsed output static energy of 340.9mJ at 1319nm, Q-switched output energy of 768mJ with pulsed-width of 17ns and divergence of 2.7mrad were acquired.Experimental results show that coating chosen-film can be used to obtain laser at 1319nm.
In order to study pulsed electro-optic Q-switched Nd:YAG laser at 1319nm, the transition radiation energy level of Nd:YAG crystal was analyzed.A single pulsed laser at 1319nm was acquired after restraining laser oscillator of wavelength at 1064nm through coating chosen film on the mirror. In a configuration of lamp pumped, water-cooled Nd:YAG with KD*P as eleciro-optic Q-switched, pulsed output static energy of 340.9mJ at 1319nm, Q-switched output energy of 768mJ with pulsed-width of 17ns and divergence of 2.7mrad were acquired.Experimental results show that coating chosen-film can be used to obtain laser at 1319nm.
2010, 34(5): 607-610.
doi: 10.3969/j.issn.1001-3806.2010.O5.009
Abstract:
In order to provide more position information of the accessed nodes to media access layer and routing layer in a wireless "solar-blind" ultraviolet mesh network,trilateration position algorithm was employed to locate the nodes in the wireless network and function for the ultraviolet channel was found. Finally, this algorithm was simulated. The simulation showed that when appropriate transmitting angle and receiving angle are selected and the position error could be less than 0.01 km. This algorithm is feasible for the ultraviolet communication which does not need rigorous pointing accuracy.
In order to provide more position information of the accessed nodes to media access layer and routing layer in a wireless "solar-blind" ultraviolet mesh network,trilateration position algorithm was employed to locate the nodes in the wireless network and function for the ultraviolet channel was found. Finally, this algorithm was simulated. The simulation showed that when appropriate transmitting angle and receiving angle are selected and the position error could be less than 0.01 km. This algorithm is feasible for the ultraviolet communication which does not need rigorous pointing accuracy.
2010, 34(5): 611-613,627.
doi: 10.3969/j.issn.1001-3806.2010.O5.010
Abstract:
In order to study the effect of incident angles on the characteristics of symmetric periodic multilayer polarizing beam sputter (PBS),based on equivalent layers concept and stop-hand theory, the bandwidth of spectrum and transmittance change with incident angles were analyzed with the graphical method. The transmittance spectrum of(LHL)^N PBS was measured with a UV3101-PC spectrometer.The experimental results show that the bandwidth spectrum becomes wider and then narrower with incident angles increase, so there is a maximum bandwidth. Taking the point corresponding to the maximum bandwidth as a reference point, the transmittance spectrum moves to longer-wave band and appears hollow aperture with the incident angle decreases;on the other hand,the transmittance spectrum moves to shorter-wave band with the incident angle increases.The experimental results are consistent with theoretical ones.The results provide an important reference for design and optimization of the symmetric periodic multilayer PBS.
In order to study the effect of incident angles on the characteristics of symmetric periodic multilayer polarizing beam sputter (PBS),based on equivalent layers concept and stop-hand theory, the bandwidth of spectrum and transmittance change with incident angles were analyzed with the graphical method. The transmittance spectrum of(LHL)^N PBS was measured with a UV3101-PC spectrometer.The experimental results show that the bandwidth spectrum becomes wider and then narrower with incident angles increase, so there is a maximum bandwidth. Taking the point corresponding to the maximum bandwidth as a reference point, the transmittance spectrum moves to longer-wave band and appears hollow aperture with the incident angle decreases;on the other hand,the transmittance spectrum moves to shorter-wave band with the incident angle increases.The experimental results are consistent with theoretical ones.The results provide an important reference for design and optimization of the symmetric periodic multilayer PBS.
2010, 34(5): 614-618.
doi: 10.3969/j.issn.1001-3806.2010.O5.011
Abstract:
A new ray tracing method based on Level Set method and finite difference model was proposed to calculate the laser density distribution of the keyhole wall during the transient keyhole evolution process of deep penetration laser welding.The multiple reflections Fresnel absorption of the keyhole wall and the inverse bremsstrahlung absorption of the vapor plume/plasma were simultaneously considered in this new method. The results demonstrate that the presented method can be used to calculate the laser density distribution of arbitrarily shaped keyhole accurately.
A new ray tracing method based on Level Set method and finite difference model was proposed to calculate the laser density distribution of the keyhole wall during the transient keyhole evolution process of deep penetration laser welding.The multiple reflections Fresnel absorption of the keyhole wall and the inverse bremsstrahlung absorption of the vapor plume/plasma were simultaneously considered in this new method. The results demonstrate that the presented method can be used to calculate the laser density distribution of arbitrarily shaped keyhole accurately.
2010, 34(5): 619-623.
doi: 10.3969/j.issn.1001-3806.2010.O5.012
Abstract:
In order to obtain results of the two-photon incoherently coupled bright-dark hybrid screening-photovoltaic spatial soliton families, the propagation of multiple mutually incoherent optical beams in biased two-photon photovoltaic-photorefractive crystal were numerically studied under steady-state conditions. It is shown that two-photon incoherently coupled bright-dark hybrid screening-photovoltaic soliton families can be established in the crystals with mutually incoherent incident beams at the same wavelength and polarization incident in the crystal. The screening-photovoltaic soliton families can be considered as the united form of screening soliton families and photovoltaic soliton families. When the photovoltaic effect is negligible,the screening-photovoltaic soliton families are the screening one. If the external field is absent, the screening-photovoltaic soliton families are photovoltaic ones under the open-and closed-circuit condition.Such soliton families reduce to screening-photovoltaic soliton pairs when they contain only two components.It turned out that this research provides theoretic basis for development of the spatial solitons theory.
In order to obtain results of the two-photon incoherently coupled bright-dark hybrid screening-photovoltaic spatial soliton families, the propagation of multiple mutually incoherent optical beams in biased two-photon photovoltaic-photorefractive crystal were numerically studied under steady-state conditions. It is shown that two-photon incoherently coupled bright-dark hybrid screening-photovoltaic soliton families can be established in the crystals with mutually incoherent incident beams at the same wavelength and polarization incident in the crystal. The screening-photovoltaic soliton families can be considered as the united form of screening soliton families and photovoltaic soliton families. When the photovoltaic effect is negligible,the screening-photovoltaic soliton families are the screening one. If the external field is absent, the screening-photovoltaic soliton families are photovoltaic ones under the open-and closed-circuit condition.Such soliton families reduce to screening-photovoltaic soliton pairs when they contain only two components.It turned out that this research provides theoretic basis for development of the spatial solitons theory.
2010, 34(5): 624-627.
doi: 10.3969/j.issn.1001-3806.2010.O5.013
Abstract:
In order to study the image analysis method suitable for the sectional detection system based on high power semiconductor line-laser, several threshold algorithms were proposed to process and analyze the light-stripe images. An outdoor platform was built to simulate large-visual-angle laser projection, then images were collected by CMOS camera. Three threshold algorithms were introduced to analyze the images,and the center position of the light stripe was extracted by barycenter method, then advantages and disadvantages of the algorithms were compared. Results showed that the improved Otsu method could obtain a good performance. Besides,after considering signal-to-noise ratio, the character of objects and line-laser itself, the common applicable conditions of the algorithm were proposed under the line-laser system.
In order to study the image analysis method suitable for the sectional detection system based on high power semiconductor line-laser, several threshold algorithms were proposed to process and analyze the light-stripe images. An outdoor platform was built to simulate large-visual-angle laser projection, then images were collected by CMOS camera. Three threshold algorithms were introduced to analyze the images,and the center position of the light stripe was extracted by barycenter method, then advantages and disadvantages of the algorithms were compared. Results showed that the improved Otsu method could obtain a good performance. Besides,after considering signal-to-noise ratio, the character of objects and line-laser itself, the common applicable conditions of the algorithm were proposed under the line-laser system.
2010, 34(5): 628-631.
doi: 10.3969/j.issn.1001-3806.2010.O5.014
Abstract:
The reflection characteristics of the measured objects and the obtrusive light of the environment will have strong impacts on the accuracy of laser triangulation displacement measurement. In order to reduce the impact, a new imaging parameters adaptive control methods was proposed. The imaging parameters of an image sensor were described and the effect of these parameters on the accuracy of measurement was analyzed. Then an idea of improving the accuracy was put forward by parameters adjustment. The experimental results show that this method can adaptively adjust the parameters based on the environment, effectively reduce the environment inteuerence and ultimately improve the displacement measurement accuracy.
The reflection characteristics of the measured objects and the obtrusive light of the environment will have strong impacts on the accuracy of laser triangulation displacement measurement. In order to reduce the impact, a new imaging parameters adaptive control methods was proposed. The imaging parameters of an image sensor were described and the effect of these parameters on the accuracy of measurement was analyzed. Then an idea of improving the accuracy was put forward by parameters adjustment. The experimental results show that this method can adaptively adjust the parameters based on the environment, effectively reduce the environment inteuerence and ultimately improve the displacement measurement accuracy.
2010, 34(5): 632-635,639.
doi: 10.3969/j.issn.1001-3806.2010.O5.015
Abstract:
In order to study the characteristics of the residual stress field, the effect of laser shock parameters on residual stress field in overlapping area, overlapping laser shock of TC4 Titanium alloy was carried out with high-power Q-switched, pulsed neodymium-glass laser.Then the process of overlapping laser shock was simulated with ANSYS. The numerical results showed good agreement with the experimental data. Without considering the interaction between the shock parameters, increasing the overlapping rate,the laser power density and the laser pulse duration, the surface residual compressive stress and the depth of residual compressive stress field in overlapping zone can be increased. However, if the overlapping rate and laser pulse duration exceeds a threshold value, the depth of residual compressive stress field and the value of surface residual compressive stress in overlapping zone decline respectively with the increase of the overlapping rate and the laser pulse duration.
In order to study the characteristics of the residual stress field, the effect of laser shock parameters on residual stress field in overlapping area, overlapping laser shock of TC4 Titanium alloy was carried out with high-power Q-switched, pulsed neodymium-glass laser.Then the process of overlapping laser shock was simulated with ANSYS. The numerical results showed good agreement with the experimental data. Without considering the interaction between the shock parameters, increasing the overlapping rate,the laser power density and the laser pulse duration, the surface residual compressive stress and the depth of residual compressive stress field in overlapping zone can be increased. However, if the overlapping rate and laser pulse duration exceeds a threshold value, the depth of residual compressive stress field and the value of surface residual compressive stress in overlapping zone decline respectively with the increase of the overlapping rate and the laser pulse duration.
2010, 34(5): 636-639.
doi: 10.3969/j.issn.1001-3806.2010.O5.016
Abstract:
In order to probe micromachining technology of sapphire material,the ablation characteristics of 157nm deep ultraviolet laser were studied. The effect of laser process parameters on etching efficiency and surface quality was studied by scanning ablation and drilling on sapphire substrate. Moreover, the etching mechanism of 157nm laser on sapphire was analyzed.And then,a 2-D pattern was ablated onto the sapphire substrate by scanning approach. Both analysis and experimental results indicate that micromachining process that 157nm deep ultraviolet laser reacts on sapphire includes photochemical reactions and photothermolysis,and that a set of proper parameters about scanning etching were obtained,i.e.,scanning velocity at 0.15 mm/min with flnence of 3.2J/cm2,repetition frequency at 10Hz-20Hz; etching rate of drilling at 0.039μm/pulse with fluence of 2.5J/cm2. Precise micromachining could be realized under control of laser repetition rate and scanning velocity.
In order to probe micromachining technology of sapphire material,the ablation characteristics of 157nm deep ultraviolet laser were studied. The effect of laser process parameters on etching efficiency and surface quality was studied by scanning ablation and drilling on sapphire substrate. Moreover, the etching mechanism of 157nm laser on sapphire was analyzed.And then,a 2-D pattern was ablated onto the sapphire substrate by scanning approach. Both analysis and experimental results indicate that micromachining process that 157nm deep ultraviolet laser reacts on sapphire includes photochemical reactions and photothermolysis,and that a set of proper parameters about scanning etching were obtained,i.e.,scanning velocity at 0.15 mm/min with flnence of 3.2J/cm2,repetition frequency at 10Hz-20Hz; etching rate of drilling at 0.039μm/pulse with fluence of 2.5J/cm2. Precise micromachining could be realized under control of laser repetition rate and scanning velocity.
2010, 34(5): 640-642,646.
doi: 10.3969/j.issn.1001-3806.2010.O5.017
Abstract:
In order to study the molecular structure of acetic acid-water solution,the fluorescence spectra of acetic acid-water solution excited by ultraviolet light at 284nm and the excitation spectrum with 17uorescence peak of 334nm were obtained based on steady state fluorescence spectroscopy. The fluorescence spectra of acetic acid-water solution with 10 various volume percentages induced by the same wavelength exciting light were detected.After studying the excitation spectral characteristics and the relationship between fluorescence peak intensity and acetic acid volume percentage,the total absorbance and fluorescence emission of the mixture were discussed theoretically. The fluorescence quantum yield at the emission wavelength of 334nm was calculated and the fluoresoenoe spectra intrinsic peak of acetic acid-water mixture was explained. The results show that when the volume ratios of acetic acid and water mixture are 1:1 and 4:1,the bonding numbers of acetic acid and water molecular association are n=3 and n=1,respectively. The result can contribute to the further study of acetic acid and water molecular association.
In order to study the molecular structure of acetic acid-water solution,the fluorescence spectra of acetic acid-water solution excited by ultraviolet light at 284nm and the excitation spectrum with 17uorescence peak of 334nm were obtained based on steady state fluorescence spectroscopy. The fluorescence spectra of acetic acid-water solution with 10 various volume percentages induced by the same wavelength exciting light were detected.After studying the excitation spectral characteristics and the relationship between fluorescence peak intensity and acetic acid volume percentage,the total absorbance and fluorescence emission of the mixture were discussed theoretically. The fluorescence quantum yield at the emission wavelength of 334nm was calculated and the fluoresoenoe spectra intrinsic peak of acetic acid-water mixture was explained. The results show that when the volume ratios of acetic acid and water mixture are 1:1 and 4:1,the bonding numbers of acetic acid and water molecular association are n=3 and n=1,respectively. The result can contribute to the further study of acetic acid and water molecular association.
2010, 34(5): 643-646.
doi: 10.3969/j.issn.1001-3806.2010.O5.018
Abstract:
The mechanism of damage on the linear CCD and array CCD was analyzed. Under the irradiation of 532nm laser, the crosstalk threshold, all-pixel crosstalk threshold and totally damaged threshold of both the types of CCDs were measured. Experimental results show that the crosstalk threshold and permanent damage threshold of array CCD are higher than those of linear CCD,while the all-pixel crosstalk threshold of array CCD is lower.This reflects the linear CCD is more resistant to laser interference and sabotage due to its one-dimension structure, while the array CCD is better at resisting the spread of crosstalk between pixels.
The mechanism of damage on the linear CCD and array CCD was analyzed. Under the irradiation of 532nm laser, the crosstalk threshold, all-pixel crosstalk threshold and totally damaged threshold of both the types of CCDs were measured. Experimental results show that the crosstalk threshold and permanent damage threshold of array CCD are higher than those of linear CCD,while the all-pixel crosstalk threshold of array CCD is lower.This reflects the linear CCD is more resistant to laser interference and sabotage due to its one-dimension structure, while the array CCD is better at resisting the spread of crosstalk between pixels.
2010, 34(5): 647-649.
doi: 10.3969/j.issn.1001-3806.2010.O5.019
Abstract:
In order to study microstructure of single crystal silicon wafers under laser irradiation in different ambient atmosphere, the microstructure of silicon surface irradiated by infrared(IR, fundamental wavelength 1064nm) and ultraviolet (UV, third harmonic wavelength 355nm) Nd:YAG nanosecond laser in SF6,air, N2 and vacuum was experimentally studied respectively. It is seen that the microstructure formed in SF6 or air atmosphere by IR nanosecond laser irradiation has higher aspect ratio than that formed in vacuum or N2 atmosphere, and the microstructure formed in SF6 or vacuum atmosphere by UV nanosecond laser irradiation is more outstanding than that formed in air or N2 atmosphere, however the microstructure created in SF6 atmosphere have some flocculation material. The results show that formation of microstructure depends on laser wavelength and ambient atmosphere, and the efficiency of laser-induced chemical etching is different.The results are helpful to further study about nanosecond laser induced microstructure on silicon surface.
In order to study microstructure of single crystal silicon wafers under laser irradiation in different ambient atmosphere, the microstructure of silicon surface irradiated by infrared(IR, fundamental wavelength 1064nm) and ultraviolet (UV, third harmonic wavelength 355nm) Nd:YAG nanosecond laser in SF6,air, N2 and vacuum was experimentally studied respectively. It is seen that the microstructure formed in SF6 or air atmosphere by IR nanosecond laser irradiation has higher aspect ratio than that formed in vacuum or N2 atmosphere, and the microstructure formed in SF6 or vacuum atmosphere by UV nanosecond laser irradiation is more outstanding than that formed in air or N2 atmosphere, however the microstructure created in SF6 atmosphere have some flocculation material. The results show that formation of microstructure depends on laser wavelength and ambient atmosphere, and the efficiency of laser-induced chemical etching is different.The results are helpful to further study about nanosecond laser induced microstructure on silicon surface.
2010, 34(5): 650-652,693.
doi: 10.3969/j.issn.1001-3806.2010.O5.020
Abstract:
In order to solve the problem of declining performance caused by intersymhol interference and the interchannel interferencein orthogonal frequency division multiplexing systems,a new method, residual elimination algorithm based on transform-domain processing channel estimation, was used in analysis and experimental dada processing. The scientific and accurate data were obtained. The simulation results with MATLAB show that in a broadband wireless localareahet, when the cyclic prefix length is insufficient to protect the algorithm, the performance of the orthogonal frequency division multiplexing system is significantly improved after finite iterations, and the difficult in the calculation is reduced.The result is helpful for the study of optical communication technology.
In order to solve the problem of declining performance caused by intersymhol interference and the interchannel interferencein orthogonal frequency division multiplexing systems,a new method, residual elimination algorithm based on transform-domain processing channel estimation, was used in analysis and experimental dada processing. The scientific and accurate data were obtained. The simulation results with MATLAB show that in a broadband wireless localareahet, when the cyclic prefix length is insufficient to protect the algorithm, the performance of the orthogonal frequency division multiplexing system is significantly improved after finite iterations, and the difficult in the calculation is reduced.The result is helpful for the study of optical communication technology.
2010, 34(5): 653-656.
doi: 10.3969/j.issn.1001-3806.2010.O5.021
Abstract:
Wiih the method of plane wave expansion, the band gap structures of 2-D photonic crystal were calculated.Connecting square dielectric cylinder of silicon with the grid structure,the band gap structure of square lattice was optimized to gain bigger full band gap. After adjusting the media at the appropriate width of dielectric cylinder of silicon and the width of grid, a larger complete band gap was obtained in the compound structure of square lattice. The results show that in case of square lattice structure, only the TE mode band gap is found in the square dielectric cylinder in 0.5a width(a is the lattice constant), only the band gap of TM mode is formed in the structure of the same periodic grid in 0.22a width. In the case of compound structure,adjusting the width of w and d appropriately, when media column width is 0.5a and the grid width is 0.05a,a larger complete band gap in 0.0417ωe could be obtained(ωe is center frequency).In the case of w constant, full band gap can be formed with the grid width of 0.04a-0.11a;in the case of the grid width d unchanged, full band gap can be found with the dielectric pillar width of 0.42a-0.76a; adjusting the dielectric constant within 4-36,it can find different full band gaps are found with the dielectric constant of 8.41-36. The results are very useful to the production and application of two-dimension photonic crystal.
Wiih the method of plane wave expansion, the band gap structures of 2-D photonic crystal were calculated.Connecting square dielectric cylinder of silicon with the grid structure,the band gap structure of square lattice was optimized to gain bigger full band gap. After adjusting the media at the appropriate width of dielectric cylinder of silicon and the width of grid, a larger complete band gap was obtained in the compound structure of square lattice. The results show that in case of square lattice structure, only the TE mode band gap is found in the square dielectric cylinder in 0.5a width(a is the lattice constant), only the band gap of TM mode is formed in the structure of the same periodic grid in 0.22a width. In the case of compound structure,adjusting the width of w and d appropriately, when media column width is 0.5a and the grid width is 0.05a,a larger complete band gap in 0.0417ωe could be obtained(ωe is center frequency).In the case of w constant, full band gap can be formed with the grid width of 0.04a-0.11a;in the case of the grid width d unchanged, full band gap can be found with the dielectric pillar width of 0.42a-0.76a; adjusting the dielectric constant within 4-36,it can find different full band gaps are found with the dielectric constant of 8.41-36. The results are very useful to the production and application of two-dimension photonic crystal.
2010, 34(5): 657-660.
doi: 10.3969/j.issn.1001-3806.2010.O5.022
Abstract:
In order to design excellent interference filters, based on photonic crystals, narrow-band filters,band stop and band pass filters were designed by means of genetic algorithm. Some uncompleted issues were introduced. According to the cting index of the given filter material, its optimal delivery rate can be calculated.
In order to design excellent interference filters, based on photonic crystals, narrow-band filters,band stop and band pass filters were designed by means of genetic algorithm. Some uncompleted issues were introduced. According to the cting index of the given filter material, its optimal delivery rate can be calculated.
2010, 34(5): 661-664,716.
doi: 10.3969/j.issn.1001-3806.2010.O5.023
Abstract:
Methods of displacement measurement based on grating interFerometry, including classical dual-grating measurement systems,nonsymmetrical doubly blazed reference grating measurement systems,single grating measurement systems,grating measurement systems based on the 2nd harmonic Moiré fringes, concentric-circle grating two-dimension displacement measurement systems,and the two-dimension grating measurement systems, were introduced. The key problems and disadvantages of each system were presented as well. According to dual-frequency laser interferometer the dual-wavelength single grating nanometer displacement measurement was put forth based on the single grating measurement system.After analyzing its characteristics,it was pointed out that it could realize the measurement with a wide range,nanometer precision and nanometer resolution. After a general comparison among these methods,a conclusion of key technologies was drawn,and an outlook of displacement measurement based on grating interferometry was presented.
Methods of displacement measurement based on grating interFerometry, including classical dual-grating measurement systems,nonsymmetrical doubly blazed reference grating measurement systems,single grating measurement systems,grating measurement systems based on the 2nd harmonic Moiré fringes, concentric-circle grating two-dimension displacement measurement systems,and the two-dimension grating measurement systems, were introduced. The key problems and disadvantages of each system were presented as well. According to dual-frequency laser interferometer the dual-wavelength single grating nanometer displacement measurement was put forth based on the single grating measurement system.After analyzing its characteristics,it was pointed out that it could realize the measurement with a wide range,nanometer precision and nanometer resolution. After a general comparison among these methods,a conclusion of key technologies was drawn,and an outlook of displacement measurement based on grating interferometry was presented.
2010, 34(5): 665-669.
doi: 10.3969/j.issn.1001-3806.2010.O5.024
Abstract:
Laser shock peening suitable for metal micro components was introduced. The desirable compressive stress distribution might be induced by the control of process parameters and reasonable path,so the wear and fatigue resistance can be improved. The research status,mechanism, key technology and influence factors of microscale laser shock peening were summarized and the problems in microscale laser shock peening were analyzed, which provides guidance for further research.
Laser shock peening suitable for metal micro components was introduced. The desirable compressive stress distribution might be induced by the control of process parameters and reasonable path,so the wear and fatigue resistance can be improved. The research status,mechanism, key technology and influence factors of microscale laser shock peening were summarized and the problems in microscale laser shock peening were analyzed, which provides guidance for further research.
2010, 34(5): 670-672.
doi: 10.3969/j.issn.1001-3806.2010.O5.025
Abstract:
In order to investigate effect of the stress on the thin film polarizing beam sputters and seek the techniques to reduce stress.prior to the deposition polarizing splitter coatings,Al203 buffer layer was coated,the degree of vacuum was improved,the substrate temperature was increased, the film deposition rate was slowed down during deposition processes.During encapsulation process,optical photosensitive adhesive rapid solidification under UV irradiation was used. The spot images of reflected light and transmitted light of the thin film polarizing beam sputter were collected with CCD before and after process improvement respectively.The extinction ratios of reflected light and transmitted light of the thin film polarizing beam splitter were measured before and after process improvement respectively. The results indicate that after applying improved technologies, the spot energy of reflected and transmitted light is more concentrated, speckle phenomenon becomes smaller; the extinction ratios characteristic of reflected and transmission light dramatically are improved.Thus,thin film polarizing beam sputters can reach the application requirements by optimizing the process and packaging technology.
In order to investigate effect of the stress on the thin film polarizing beam sputters and seek the techniques to reduce stress.prior to the deposition polarizing splitter coatings,Al203 buffer layer was coated,the degree of vacuum was improved,the substrate temperature was increased, the film deposition rate was slowed down during deposition processes.During encapsulation process,optical photosensitive adhesive rapid solidification under UV irradiation was used. The spot images of reflected light and transmitted light of the thin film polarizing beam sputter were collected with CCD before and after process improvement respectively.The extinction ratios of reflected light and transmitted light of the thin film polarizing beam splitter were measured before and after process improvement respectively. The results indicate that after applying improved technologies, the spot energy of reflected and transmitted light is more concentrated, speckle phenomenon becomes smaller; the extinction ratios characteristic of reflected and transmission light dramatically are improved.Thus,thin film polarizing beam sputters can reach the application requirements by optimizing the process and packaging technology.
2010, 34(5): 673-675.
doi: 10.3969/j.issn.1001-3806.2010.O5.026
Abstract:
In order to reduce the data delay in the ring laser gyro (RLG) and adopt it in the fast tracking application, the small delay dither signal removal method was proposed based on recursive least-squares(RIS) adaptive filter. Firstly, the theory of RIS adaptive noise cancelling was described. Secondly, the hardware was designed through which the dither feedback signal after A/D transfer and RLG readout signal could be sent to computer via universal serial bus interface.Finally, the RIS adaptive software was programmed to remove the dither signal based on MATLAB.The residual count of deprived signal filtered by an 11-order finite impulse response(FIR) filter is corresponding with that of original ItLG readout signal filtered by a 31-order FIR filter, but the latency is smaller.Experiments show this algorithm has a faster convergence speed and the dither signal can be removed effectively.
In order to reduce the data delay in the ring laser gyro (RLG) and adopt it in the fast tracking application, the small delay dither signal removal method was proposed based on recursive least-squares(RIS) adaptive filter. Firstly, the theory of RIS adaptive noise cancelling was described. Secondly, the hardware was designed through which the dither feedback signal after A/D transfer and RLG readout signal could be sent to computer via universal serial bus interface.Finally, the RIS adaptive software was programmed to remove the dither signal based on MATLAB.The residual count of deprived signal filtered by an 11-order finite impulse response(FIR) filter is corresponding with that of original ItLG readout signal filtered by a 31-order FIR filter, but the latency is smaller.Experiments show this algorithm has a faster convergence speed and the dither signal can be removed effectively.
2010, 34(5): 676-678.
doi: 10.3969/j.issn.1001-3806.2010.O5.027
Abstract:
The transmission properties of evanescent wave in ordinary 1-D photonic crystal were simulated by means of the eigen matrix method.In wide gap, there are a series of transmission bands composed of some discrete peaks. The transmission mode comes from localized resonant modes through evanescent wave coupling.The results indicate that these discrete transmission peaks can be used as multi-channel filter with high Q value.
The transmission properties of evanescent wave in ordinary 1-D photonic crystal were simulated by means of the eigen matrix method.In wide gap, there are a series of transmission bands composed of some discrete peaks. The transmission mode comes from localized resonant modes through evanescent wave coupling.The results indicate that these discrete transmission peaks can be used as multi-channel filter with high Q value.
2010, 34(5): 679-681,720.
doi: 10.3969/j.issn.1001-3806.2010.O5.028
Abstract:
In order to develop a high-precision speedometer so that the mistake and missing punishment of the traffic administration can be avoided, a laser speedometer with a diode laser source was designed based on AT89S52 single-chip microcomputer.Comparing the field test results with the theoretical one, the relative error was 0.1% order of magnitude.It not only supplies a kind of new precise speedometer to measure the instant speed of vehicles on the road,but also supplies a new calibration instrument for radar speedometers and reflex laser velocimeters.
In order to develop a high-precision speedometer so that the mistake and missing punishment of the traffic administration can be avoided, a laser speedometer with a diode laser source was designed based on AT89S52 single-chip microcomputer.Comparing the field test results with the theoretical one, the relative error was 0.1% order of magnitude.It not only supplies a kind of new precise speedometer to measure the instant speed of vehicles on the road,but also supplies a new calibration instrument for radar speedometers and reflex laser velocimeters.
2010, 34(5): 682-685.
doi: 10.3969/j.issn.1001-3806.2010.O5.029
Abstract:
A synchronization controller based on field programmable gate array(FPGA) for an underwater laser imaging system was proposed to realize the synchronization of the pulsed laser and the intensified CCD (ICCD) and improve the image resolution.The controller, taking the advantages of FPGA's high compact and flexibility, uses the phase-locking-loop for the global clock frequency and the carry chain for delay cell so that the precision of pulse delay and pulse width gets up to a nanosecond level.Problems with the precision and stabilization induced by discrete components in conventional control circuits were solved. Experimental results indicate that synchronization controller is a feasible solution for gated imaging system working under tight time and visibility requirements of stability and real-time applications.
A synchronization controller based on field programmable gate array(FPGA) for an underwater laser imaging system was proposed to realize the synchronization of the pulsed laser and the intensified CCD (ICCD) and improve the image resolution.The controller, taking the advantages of FPGA's high compact and flexibility, uses the phase-locking-loop for the global clock frequency and the carry chain for delay cell so that the precision of pulse delay and pulse width gets up to a nanosecond level.Problems with the precision and stabilization induced by discrete components in conventional control circuits were solved. Experimental results indicate that synchronization controller is a feasible solution for gated imaging system working under tight time and visibility requirements of stability and real-time applications.
2010, 34(5): 686-689.
doi: 10.3969/j.issn.1001-3806.2010.O5.030
Abstract:
Analysis and experiments were conducted to study how to fabricate large-area polyimide multimode waveguide by means of CO2 laser direct writing. Firstly, the laser fabrication model was built. Secondly, the relationship between the temperature distribution in the material and the laser scanning parameters was simulated. Finally,a method was proposed to increase the verticality of the sidewall of the waveguide. The influence of the processing parameters on the property of the waveguide material, the structure of the waveguide and the roughness on the surface of the waveguide was also studied by experimental method.The results show that the width, verticality and roughness of the waveguide depend on the laser power density, direct writing speed and the position of the aperture.
Analysis and experiments were conducted to study how to fabricate large-area polyimide multimode waveguide by means of CO2 laser direct writing. Firstly, the laser fabrication model was built. Secondly, the relationship between the temperature distribution in the material and the laser scanning parameters was simulated. Finally,a method was proposed to increase the verticality of the sidewall of the waveguide. The influence of the processing parameters on the property of the waveguide material, the structure of the waveguide and the roughness on the surface of the waveguide was also studied by experimental method.The results show that the width, verticality and roughness of the waveguide depend on the laser power density, direct writing speed and the position of the aperture.
2010, 34(5): 690-693.
doi: 10.3969/j.issn.1001-3806.2010.O5.031
Abstract:
In order to reduce the bending loss of optical waveguide,the source of bending loss and transition loss of optical waveguide was analyzed. A series of curved line expression were obtained,i.e.,five-power function, six-power function, seven-power function,eight-power function and nine-power function expression. With the help of MATLAB and MAPLE, calculation results show that the curves of the nine-power function is the most smooth, when taking h=125μm, L=800μm(high branching ratio),the loss can be reduced to 4.57dB, which is much smaller than conventional sine function and cosine functions.At last, an optimum route composed of 1×4 optical splitters was designed and simulated in which the energy distribution was symmetric and uniform. This can offer some valuable guidance to the research of Y-type optical waveguide.
In order to reduce the bending loss of optical waveguide,the source of bending loss and transition loss of optical waveguide was analyzed. A series of curved line expression were obtained,i.e.,five-power function, six-power function, seven-power function,eight-power function and nine-power function expression. With the help of MATLAB and MAPLE, calculation results show that the curves of the nine-power function is the most smooth, when taking h=125μm, L=800μm(high branching ratio),the loss can be reduced to 4.57dB, which is much smaller than conventional sine function and cosine functions.At last, an optimum route composed of 1×4 optical splitters was designed and simulated in which the energy distribution was symmetric and uniform. This can offer some valuable guidance to the research of Y-type optical waveguide.
2010, 34(5): 694-696.
doi: 10.3969/j.issn.1001-3806.2010.O5.032
Abstract:
In order to study the relationship between the amplitude of the shock wave in air and the amplitude of the shock wave in the workpiece, and the relationship bettveen time-of-flight of the shock wave in air and the compressive residual stress in the workpiece respectively, the acoustic emission sensor and the polyvinylidene fluoride piezoelectricity gauge were used to detect laser induced plasma shock wave in air and the workpiece.In the experiment, the workpiece is 45# steel,the absorption layer is Al foil,and the confinement layer is fluid overlays. The results show that with laser intensities increases, time-of-flight of the shock wave in air decreases nonlinearly,and the amplitude of the shock wave in air and workpiece increases nonlinearly, and the compressive residual stress closes to saturation.Finally, the empirical formulas for the amplitude of the shock wave in air and the amplitude in the workpiece,and for time of flight of the shock wave in air and the compressive residual stress in the workpiece were established respectively, which could provide theoretical reference for quality assurance of laser shock processing.
In order to study the relationship between the amplitude of the shock wave in air and the amplitude of the shock wave in the workpiece, and the relationship bettveen time-of-flight of the shock wave in air and the compressive residual stress in the workpiece respectively, the acoustic emission sensor and the polyvinylidene fluoride piezoelectricity gauge were used to detect laser induced plasma shock wave in air and the workpiece.In the experiment, the workpiece is 45# steel,the absorption layer is Al foil,and the confinement layer is fluid overlays. The results show that with laser intensities increases, time-of-flight of the shock wave in air decreases nonlinearly,and the amplitude of the shock wave in air and workpiece increases nonlinearly, and the compressive residual stress closes to saturation.Finally, the empirical formulas for the amplitude of the shock wave in air and the amplitude in the workpiece,and for time of flight of the shock wave in air and the compressive residual stress in the workpiece were established respectively, which could provide theoretical reference for quality assurance of laser shock processing.
2010, 34(5): 697-700.
doi: 10.3969/j.issn.1001-3806.2010.O5.033
Abstract:
The research of the failure mechanism of load-carrying construction under high-power laser irradiation can expand the field of laser application.In order to investigate the influence of beam intensity distribution on the thermal-mechanical behavior of cylindrical shells under laser irradiation, firstly the thermal-mechanical model of the cylindrical shell was constructed by means of finite element method. Taking total laser power equal, several typical distributions were analyzed and compared. Then thermal-mechanical response of the internal pressured cylindrical shell under different laser irradiation was studied. Numerical results indicate that intensity distribution has a significant effect on temperature, stress and displacement fields of cylindrical shell. The cylindrical shells irradiated by laser beams with different intensity have different failure mode and failure time.
The research of the failure mechanism of load-carrying construction under high-power laser irradiation can expand the field of laser application.In order to investigate the influence of beam intensity distribution on the thermal-mechanical behavior of cylindrical shells under laser irradiation, firstly the thermal-mechanical model of the cylindrical shell was constructed by means of finite element method. Taking total laser power equal, several typical distributions were analyzed and compared. Then thermal-mechanical response of the internal pressured cylindrical shell under different laser irradiation was studied. Numerical results indicate that intensity distribution has a significant effect on temperature, stress and displacement fields of cylindrical shell. The cylindrical shells irradiated by laser beams with different intensity have different failure mode and failure time.
2010, 34(5): 701-703.
doi: 10.3969/j.issn.1001-3806.2010.O5.034
Abstract:
In order to study the phase shift of the carrier envelope of the linear chirped pulsed Gaussian beam in the propagation direction and the cross section, the phase shift was simulated. The results show the carrier envelope phase φCEP for beam with different pulse width undergoes a -π shift from negative infinity to positive infinity and gradually changes to -π/2.The farther from the original beam waist plane, the smaller the phase shift, and the smaller the radius to the axis.The phase shift of the carrier envelope is dependent on the relation between the phase front and the phase radius.
In order to study the phase shift of the carrier envelope of the linear chirped pulsed Gaussian beam in the propagation direction and the cross section, the phase shift was simulated. The results show the carrier envelope phase φCEP for beam with different pulse width undergoes a -π shift from negative infinity to positive infinity and gradually changes to -π/2.The farther from the original beam waist plane, the smaller the phase shift, and the smaller the radius to the axis.The phase shift of the carrier envelope is dependent on the relation between the phase front and the phase radius.
Transmission characteristics of flattened Gaussian beams passing through a misaligned optical system
2010, 34(5): 704-707.
doi: 10.3969/j.issn.1001-3806.2010.O5.035
Abstract:
In order to study the transmission characteristics of flattened Gaussian beams passing through a misaligned optical system with a narrow slot aperture,the approximate analytical transmission equations of output light field distributions was derived adopting generalized diffraction formula and the approximate expansion equations of the narrow slot aperture. Consequently, the analysis and simulation in accordance with the preset optical system and flattened Gaussian beams was made. The result shows that influence of misalignments of optical system on the characteristics of the output light is more notable than misalignments of diaphragm's when the ratio of half width of the aperture to half waist width of the flattened Gaussian beams is more than one.This method is helpful for the analysis of the transmission characteristic of flattened Gaussian beams.
In order to study the transmission characteristics of flattened Gaussian beams passing through a misaligned optical system with a narrow slot aperture,the approximate analytical transmission equations of output light field distributions was derived adopting generalized diffraction formula and the approximate expansion equations of the narrow slot aperture. Consequently, the analysis and simulation in accordance with the preset optical system and flattened Gaussian beams was made. The result shows that influence of misalignments of optical system on the characteristics of the output light is more notable than misalignments of diaphragm's when the ratio of half width of the aperture to half waist width of the flattened Gaussian beams is more than one.This method is helpful for the analysis of the transmission characteristic of flattened Gaussian beams.
2010, 34(5): 708-711.
doi: 10.3969/j.issn.1001-3806.2010.O5.036
Abstract:
To describe the non-equilibrium phenomenon in interaction between the metal thin film and femtosecond laser, the temperature field of metal film was simulated by means of finite-difference method. The effects of electron-lattice couple coefficient G,pulse width and electrical ballistic contribution on surface temperature of metal film were analyzed.The results show that G determines the surface temperature rising rate and electron-lattice couple time decreases exponentially with the increase of G.The result is helpful to improve the temperature rise of thin films in the semiconductor.
To describe the non-equilibrium phenomenon in interaction between the metal thin film and femtosecond laser, the temperature field of metal film was simulated by means of finite-difference method. The effects of electron-lattice couple coefficient G,pulse width and electrical ballistic contribution on surface temperature of metal film were analyzed.The results show that G determines the surface temperature rising rate and electron-lattice couple time decreases exponentially with the increase of G.The result is helpful to improve the temperature rise of thin films in the semiconductor.
2010, 34(5): 712-716.
doi: 10.3969/j.issn.1001-3806.2010.O5.037
Abstract:
In order to calculate the intensity of beams diffracted at an hard-edge aperture, by expanding a hard-edge aperture function into a finite sum of complex Gaussian functions, an approximate expression for the spectrum of polychromatic Gaussian-Schell model beams diffracted at the aperture was derived. Simulation results were compared with those obtained by means of the conventional method, i.e.,the direct integral of the cross-spectral density function.It is shown that the computing time is strongly reduced under the condition of satisfying calculation accuracy. Taking flattened Gaussian beams as an example, this method is applicable for calculation of the spectrum of other kinds of beams propagating through a hard-edge aperture.
In order to calculate the intensity of beams diffracted at an hard-edge aperture, by expanding a hard-edge aperture function into a finite sum of complex Gaussian functions, an approximate expression for the spectrum of polychromatic Gaussian-Schell model beams diffracted at the aperture was derived. Simulation results were compared with those obtained by means of the conventional method, i.e.,the direct integral of the cross-spectral density function.It is shown that the computing time is strongly reduced under the condition of satisfying calculation accuracy. Taking flattened Gaussian beams as an example, this method is applicable for calculation of the spectrum of other kinds of beams propagating through a hard-edge aperture.
2010, 34(5): 717-720.
doi: 10.3969/j.issn.1001-3806.2010.O5.038
Abstract:
Bidirectional reflectance distribution function(BRDF) can be used to study the laser scattering properties of target surface.A setup for the measurement of scattering characteristics of the sample's BRDF was designed in the laboratory.The powder pressboard of BaSO4 was used as the standard reflection board.The spatial distribution of reflected light intensity was obtained at different roughness and incident angles. The sample's BRDF at space was obtained. The results indicate that the lower the roughness of the surface plate, the larger the BRDF in the mirror direction; the larger the incident angle, the larger the BRDF in the mirror direction;tacertain degree of diffusive reflection characteristics appears; and vice versa. Different surface roughness determines corresponding different degrees of laser scattering.
Bidirectional reflectance distribution function(BRDF) can be used to study the laser scattering properties of target surface.A setup for the measurement of scattering characteristics of the sample's BRDF was designed in the laboratory.The powder pressboard of BaSO4 was used as the standard reflection board.The spatial distribution of reflected light intensity was obtained at different roughness and incident angles. The sample's BRDF at space was obtained. The results indicate that the lower the roughness of the surface plate, the larger the BRDF in the mirror direction; the larger the incident angle, the larger the BRDF in the mirror direction;tacertain degree of diffusive reflection characteristics appears; and vice versa. Different surface roughness determines corresponding different degrees of laser scattering.
