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RSS2002 Vol. 26, No. 2
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2002, 26(2): 81-83,93.
[Abstract]
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Abstract:
During high power CO2 laser beam welding,the plasma above the keyhole will influence the absorption ratio of the laser energy absorbed by the workpiece.In the paper,the feasibility to use assisting electric and magnetic(EM) field as a measure for plasma control is discussed in theory.Experimental results indicate that applicable assisting EM field can reduce the shielding effect of the plasma and increase the penetration depth.
During high power CO2 laser beam welding,the plasma above the keyhole will influence the absorption ratio of the laser energy absorbed by the workpiece.In the paper,the feasibility to use assisting electric and magnetic(EM) field as a measure for plasma control is discussed in theory.Experimental results indicate that applicable assisting EM field can reduce the shielding effect of the plasma and increase the penetration depth.
2002, 26(2): 84-85,96.
Abstract:
A new method is presented to detect the wavelength shift on in fiber Bragg gratings.The system employs a series of in fiber Bragg gratings,having the same parameters as the sensing in fiber Bragg gratings,as filter elements.Furthermore,the system tracks the maximum wavelength of the reflected spectrum of in fiber Bragg gratings through dithering and doubling the frequency.A grating with high sensitivity is used to read the output of the system.The non linearity and hysteresis of PZT have been erased thoroughly,so the accuracy of the system is improved a lot.
A new method is presented to detect the wavelength shift on in fiber Bragg gratings.The system employs a series of in fiber Bragg gratings,having the same parameters as the sensing in fiber Bragg gratings,as filter elements.Furthermore,the system tracks the maximum wavelength of the reflected spectrum of in fiber Bragg gratings through dithering and doubling the frequency.A grating with high sensitivity is used to read the output of the system.The non linearity and hysteresis of PZT have been erased thoroughly,so the accuracy of the system is improved a lot.
2002, 26(2): 86-89.
Abstract:
A 3D transient thermal model with inhomogeneous heat generation is presented to predicate the thermal response in high power/pulse face pumped slab amplifiers.Based on finite element(FE) analysis,the temperature and thermal stress distribution in Nd:YAG slab amplifiers for four different cooling schemes is derived and compared.According to the simulation results,an effective cooling method is put forward.
A 3D transient thermal model with inhomogeneous heat generation is presented to predicate the thermal response in high power/pulse face pumped slab amplifiers.Based on finite element(FE) analysis,the temperature and thermal stress distribution in Nd:YAG slab amplifiers for four different cooling schemes is derived and compared.According to the simulation results,an effective cooling method is put forward.
2002, 26(2): 90-93.
Abstract:
A real time temperature measurement system with InGaAs/I is introduced at first.Then measures to improve the accuracy are discussed.The first is to select the detector,optimize modulation disk and amplify the signal with selective frequency.The second is to place a narrow band filter between modulation disk and the detector.The third is to use water cooling shelter and take electrical compensation.The fourth is to improve the sampling accuracy of the system.At last some relative analyses and discussion are put forward.
A real time temperature measurement system with InGaAs/I is introduced at first.Then measures to improve the accuracy are discussed.The first is to select the detector,optimize modulation disk and amplify the signal with selective frequency.The second is to place a narrow band filter between modulation disk and the detector.The third is to use water cooling shelter and take electrical compensation.The fourth is to improve the sampling accuracy of the system.At last some relative analyses and discussion are put forward.
2002, 26(2): 94-96.
Abstract:
In the paper,the experiment with UV excimer laser etching PI for micropatterns is described in detail.With this method,micropatterns with micron scale line width and sub micron depth have been successfully fabricated on PI.
In the paper,the experiment with UV excimer laser etching PI for micropatterns is described in detail.With this method,micropatterns with micron scale line width and sub micron depth have been successfully fabricated on PI.
2002, 26(2): 97-101.
Abstract:
The recent developments on phase dislocation and branch point in optics are reviewed.It includes the conception,law and study method of wave front dislocation in scalar waves scattered by rough surface and propagate through random media and phenomena of the branch point in a daptive optics.
The recent developments on phase dislocation and branch point in optics are reviewed.It includes the conception,law and study method of wave front dislocation in scalar waves scattered by rough surface and propagate through random media and phenomena of the branch point in a daptive optics.
Numerical simulation for the process of 3D transient convection and heat transfer in the molten pool
2002, 26(2): 102-105.
Abstract:
A 3D model for fluid flow and heat transfer process has been developed to predict the transient distribution of temperature and velocity of a thick solid irradiated by a moving laser.The governing equations are solved by means of a finite difference on the self adaptive grids.The results show that the unsteady state process of fluid flow and heat transfer in laser molten pool is a preheating process as the highest surface temperature,depth and radius of the molten pool increase with the scanning time.According to the sequence of time,the unsteady state process can be divided into three stages:the initial stage,the quasi state stage and the rapidly rising temperature stage.At quasi state stage,there is a little increase in the dimension and the highest surface temperature of the molten pool,the staying time is much longer than those of the other stages,which show that 3D quasi state is a good approximation to 3D unsteady state model.The calculated results are consistent with those obtained by Wang.
A 3D model for fluid flow and heat transfer process has been developed to predict the transient distribution of temperature and velocity of a thick solid irradiated by a moving laser.The governing equations are solved by means of a finite difference on the self adaptive grids.The results show that the unsteady state process of fluid flow and heat transfer in laser molten pool is a preheating process as the highest surface temperature,depth and radius of the molten pool increase with the scanning time.According to the sequence of time,the unsteady state process can be divided into three stages:the initial stage,the quasi state stage and the rapidly rising temperature stage.At quasi state stage,there is a little increase in the dimension and the highest surface temperature of the molten pool,the staying time is much longer than those of the other stages,which show that 3D quasi state is a good approximation to 3D unsteady state model.The calculated results are consistent with those obtained by Wang.
2002, 26(2): 106-107.
Abstract:
Based on the coupled mode theory,the effect of the fiber grating length on its peak reflectivity has been studied for a uniform grating and a DC apodized Gaussian grating.The obtained results are important for a fiber grating external cavity semiconductor laser.
Based on the coupled mode theory,the effect of the fiber grating length on its peak reflectivity has been studied for a uniform grating and a DC apodized Gaussian grating.The obtained results are important for a fiber grating external cavity semiconductor laser.
2002, 26(2): 108-110113.
Abstract:
In the paper,the power in the bucket(PIB), β and η parameters are chosen as criteria to characterize the laser beam quality in the far field,then the beam quality of super Gaussian beams passing through a spherically aberrated lens with an annular rectangular aperture is studied.It is shown by a great number of numerical calculation results and physical analyses that the beam quality depends on the obscure ratio of the rectangular aperture,spherical aberration of the lens and the order of the super Gaussian beam.If a suitable lens with negative spherical coefficient is selected,a better beam quality at the real focal plane can be obtained.Namely,larger PIB and η,smaller β,even β smaller than 1.
In the paper,the power in the bucket(PIB), β and η parameters are chosen as criteria to characterize the laser beam quality in the far field,then the beam quality of super Gaussian beams passing through a spherically aberrated lens with an annular rectangular aperture is studied.It is shown by a great number of numerical calculation results and physical analyses that the beam quality depends on the obscure ratio of the rectangular aperture,spherical aberration of the lens and the order of the super Gaussian beam.If a suitable lens with negative spherical coefficient is selected,a better beam quality at the real focal plane can be obtained.Namely,larger PIB and η,smaller β,even β smaller than 1.
2002, 26(2): 111-113.
Abstract:
A long period fiber grating(LPFG) is a wavelength seletive filter developed in recent years.According to its behavior of wavelength dependent loss,a LPFG is used as wavelength division demultiplexer for 1310nm/1550nm wavelength division multiplexing(WDM) system.By means of groove curving with electric arc discharge,several LPFGs are fabricated.Ideal spectra of LPFGs are obtained by controlling the process of electric arc discharge and the period and the length of LPFGs.The results show that insertion loss of pass channel is able to be less than 0.5dB,20dB loss bandwidth of rejection band is nearly 15nm,and that isolation of neighboring channel is about 25dB.
A long period fiber grating(LPFG) is a wavelength seletive filter developed in recent years.According to its behavior of wavelength dependent loss,a LPFG is used as wavelength division demultiplexer for 1310nm/1550nm wavelength division multiplexing(WDM) system.By means of groove curving with electric arc discharge,several LPFGs are fabricated.Ideal spectra of LPFGs are obtained by controlling the process of electric arc discharge and the period and the length of LPFGs.The results show that insertion loss of pass channel is able to be less than 0.5dB,20dB loss bandwidth of rejection band is nearly 15nm,and that isolation of neighboring channel is about 25dB.
2002, 26(2): 114-116.
Abstract:
A proposal is introduced in the paper that the control method of multiple axis pointing can be used to improve the tracking and pointing system in intersatellite optical communication.The models of coarse pointing and fine pointing are set up,and then a controlller is designed.Based on the above conditions,a simulation cocntrol system in the laboratory has been built.It shows that the maximal angular error of the system is 14μrad while the tracked target moving at an even angular speed.
A proposal is introduced in the paper that the control method of multiple axis pointing can be used to improve the tracking and pointing system in intersatellite optical communication.The models of coarse pointing and fine pointing are set up,and then a controlller is designed.Based on the above conditions,a simulation cocntrol system in the laboratory has been built.It shows that the maximal angular error of the system is 14μrad while the tracked target moving at an even angular speed.
2002, 26(2): 117-119122.
Abstract:
A coherent flattened Gaussian beam has been obtained in the XeCl excimer laser with directional prism.The beam is well distributed in the near field and highly focused in the far field.Immunity to misalignment of excimer laser increases.
A coherent flattened Gaussian beam has been obtained in the XeCl excimer laser with directional prism.The beam is well distributed in the near field and highly focused in the far field.Immunity to misalignment of excimer laser increases.
2002, 26(2): 119-122.
Abstract:
A new laser blood therapy with a laser diode(LD) put close to the skin and radiating the subcutaneous vein is introduced.The subcutaneous vein at the back of the hand is suggested as the target of laser irradiation.The experimental foundation is explained.A set of design program of the laser radiation instrument corresponding to the new method and the manner of irradiation for this instrument are presented.The aim of the study is to look for a new path for laser blood therapy.
A new laser blood therapy with a laser diode(LD) put close to the skin and radiating the subcutaneous vein is introduced.The subcutaneous vein at the back of the hand is suggested as the target of laser irradiation.The experimental foundation is explained.A set of design program of the laser radiation instrument corresponding to the new method and the manner of irradiation for this instrument are presented.The aim of the study is to look for a new path for laser blood therapy.
2002, 26(2): 123-125128.
Abstract:
The development of laser cladding ceramic and its composite coatings in home and aboard is analyzed.The material system,properties and application prospect of laser clad corrosion resistant,wear resistant,oxidation resistant coatings are reviewed.
The development of laser cladding ceramic and its composite coatings in home and aboard is analyzed.The material system,properties and application prospect of laser clad corrosion resistant,wear resistant,oxidation resistant coatings are reviewed.
2002, 26(2): 126-128.
Abstract:
Some key techniques of Raman shifted laser with high repetitive frequency and twin wavelength outputs have been studied experimentally.Operating at 15Hz,output laser energy of more than 20mJ with twin wavelengths of 1.54μm and 1.06μm has achieved.
Some key techniques of Raman shifted laser with high repetitive frequency and twin wavelength outputs have been studied experimentally.Operating at 15Hz,output laser energy of more than 20mJ with twin wavelengths of 1.54μm and 1.06μm has achieved.
2002, 26(2): 129-131137.
Abstract:
Based on Cowan program,atom parameters have been computed.Cowan program,based on Maxwell has been extended to be applicable for any electron distribution with the help of an additional program written by the authors.The computed parameters comprise the levels,oscillator strength,spontaneous decay rate coefficient and level lifetime.
Based on Cowan program,atom parameters have been computed.Cowan program,based on Maxwell has been extended to be applicable for any electron distribution with the help of an additional program written by the authors.The computed parameters comprise the levels,oscillator strength,spontaneous decay rate coefficient and level lifetime.
2002, 26(2): 132-134.
Abstract:
With power in the bucket(PIB) and β parameter to characterize beam quality,the effect of some parameters,such as spherical aberration coefficient C 4 and obscure ratio ε,on the beam quality of Gaussian beams is analyzed.It is worthwhile to note that PIB is larger at the actual focal plane than that at the geometrical plane due to focal shift,and that β can become less than 1 when a negative spherically aberrated annular lens is properly selected,hence a higher energy density beam can be achieved compared with the case of the annular lens without spherical aberration.
With power in the bucket(PIB) and β parameter to characterize beam quality,the effect of some parameters,such as spherical aberration coefficient C 4 and obscure ratio ε,on the beam quality of Gaussian beams is analyzed.It is worthwhile to note that PIB is larger at the actual focal plane than that at the geometrical plane due to focal shift,and that β can become less than 1 when a negative spherically aberrated annular lens is properly selected,hence a higher energy density beam can be achieved compared with the case of the annular lens without spherical aberration.
2002, 26(2): 135-137.
Abstract:
The fast flow axial CO2 laser is usually used for laser cutting because of its good laser beam quality.To ensure the stability of the output laser power,the working gas should be stabilized at an optimal pressure.Based on exact study on the working theory and effect factors,PID with intelligent integral separation is applied to adjust the pressure of the working gas.The gas pressure control precision is improved with this simple and practical algorithm.Finally,the precision and stability of the output laser power can be ensured.All the above are testified by experiments.
The fast flow axial CO2 laser is usually used for laser cutting because of its good laser beam quality.To ensure the stability of the output laser power,the working gas should be stabilized at an optimal pressure.Based on exact study on the working theory and effect factors,PID with intelligent integral separation is applied to adjust the pressure of the working gas.The gas pressure control precision is improved with this simple and practical algorithm.Finally,the precision and stability of the output laser power can be ensured.All the above are testified by experiments.
2002, 26(2): 138-140.
Abstract:
Speed,accuracy and stability are often required in the response of a system,but they are hardly obtained using traditional methods,such as PID.In the paper,an intelligent control method based on pattern recognition is presented,which can achieve better results by identifying the output of the system on line with different control strategies.It is proved that the method is feasible through the debug of a camera servo device.
Speed,accuracy and stability are often required in the response of a system,but they are hardly obtained using traditional methods,such as PID.In the paper,an intelligent control method based on pattern recognition is presented,which can achieve better results by identifying the output of the system on line with different control strategies.It is proved that the method is feasible through the debug of a camera servo device.
2002, 26(2): 141-143.
Abstract:
The characteristics of back reflected laser from an infrared system are investigated in theory and through experiment.The mechanism of back reflection,reflected laser signal characteristics,direction of reflected laser and the application of the reflected laser are discussed.An experiment set up is designed to test the theoretical analysis.
The characteristics of back reflected laser from an infrared system are investigated in theory and through experiment.The mechanism of back reflection,reflected laser signal characteristics,direction of reflected laser and the application of the reflected laser are discussed.An experiment set up is designed to test the theoretical analysis.
2002, 26(2): 144-146.
Abstract:
A Cr4+:YAG Q-switched SBS laser has been studied experimentally and calculated numerically.The results prove that appropriate combination of two passive Q switched can enhance the laser's stability.
A Cr4+:YAG Q-switched SBS laser has been studied experimentally and calculated numerically.The results prove that appropriate combination of two passive Q switched can enhance the laser's stability.
2002, 26(2): 147-149.
Abstract:
In the paper,the principle of laser tracking is described and the important factors affecting the echo probability of a laser tracking system are analyzed.The basic method and rules to choose circuit loop parameters to ensure a certain echo probability is introduced.The analytical results have been proved with a laser tracking system tested in room and outdoors and an army's ground.
In the paper,the principle of laser tracking is described and the important factors affecting the echo probability of a laser tracking system are analyzed.The basic method and rules to choose circuit loop parameters to ensure a certain echo probability is introduced.The analytical results have been proved with a laser tracking system tested in room and outdoors and an army's ground.
2002, 26(2): 150-152.
Abstract:
A new broadband coherent anti Stoke Raman spectral(CARS) thermoscope,consisting of a frequency double Nd:YAG laser and an optical parametric oscillator(OPO) instead of the dye laser,is introduced.In order to increase the precision of CARS temperature measurement,the slit function of the detection system is studied and determined.The precision of the system is evaluated based on the difference between the best fitting temperature of CARS spectrum and temperature of thermocouple reading.The uncertainty of the temperature measurement is less than 2% in the range of 300K～1200K.
A new broadband coherent anti Stoke Raman spectral(CARS) thermoscope,consisting of a frequency double Nd:YAG laser and an optical parametric oscillator(OPO) instead of the dye laser,is introduced.In order to increase the precision of CARS temperature measurement,the slit function of the detection system is studied and determined.The precision of the system is evaluated based on the difference between the best fitting temperature of CARS spectrum and temperature of thermocouple reading.The uncertainty of the temperature measurement is less than 2% in the range of 300K～1200K.
2002, 26(2): 153-155149.
Abstract:
Based on the second-order moment method,the closed form expression of the waist width of Hermite-cosh-Gaussian beams is derived.For example,the closed form expressions of the waist width for Hermite-cosine-Gaussian,cosh-Gaussian,cosine-Gaussian and Hermite-Gaussian beams are also provided.Numerical calculations are performed and theresults are analyzed.
Based on the second-order moment method,the closed form expression of the waist width of Hermite-cosh-Gaussian beams is derived.For example,the closed form expressions of the waist width for Hermite-cosine-Gaussian,cosh-Gaussian,cosine-Gaussian and Hermite-Gaussian beams are also provided.Numerical calculations are performed and theresults are analyzed.
2002, 26(2): 156-158143.
Abstract:
The mathematical model of general Fourier heat conduction law is discussed in the paper.Based on the hyperbolic heat conduction equation of non Fourier heat conduction law,an analytical solution of a semi infinite body has been derived under the first boundary condition.With the temperature distribution analyzed,the transient criterion and the applicable scope of non Fourier heat conduction law has been proposed,which is important for the study on special area of transient heat conduction problem in engineering,such as laser process and electron beams process.
The mathematical model of general Fourier heat conduction law is discussed in the paper.Based on the hyperbolic heat conduction equation of non Fourier heat conduction law,an analytical solution of a semi infinite body has been derived under the first boundary condition.With the temperature distribution analyzed,the transient criterion and the applicable scope of non Fourier heat conduction law has been proposed,which is important for the study on special area of transient heat conduction problem in engineering,such as laser process and electron beams process.
2002, 26(2): 159-160.
Abstract:
It is still an important subject in hematology how to effectively purge leukemia cell in hematopoietic stem cell transplantation.The up to date failure of all pharmacological purging attempts has been promoting the development of alternative strategies.A new clinical method to purge leukemia cell through photodunamic therapy with anti sense oligonucleotides modified by photosensitizer is provided in the paper.
It is still an important subject in hematology how to effectively purge leukemia cell in hematopoietic stem cell transplantation.The up to date failure of all pharmacological purging attempts has been promoting the development of alternative strategies.A new clinical method to purge leukemia cell through photodunamic therapy with anti sense oligonucleotides modified by photosensitizer is provided in the paper.
