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RSS2009 Vol. 33, No. 1
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2009, 33(1): 1-4.
[Abstract]
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Abstract:
In order to analyze the feasibility of corner-pumped method in medium and small power lasers design,ray-tracing algorithm was used to simulate the pumping efficiency and absorbed energy distribution of diode corner-pumped lasers for different laser medium parameters and different diode temperatures.It is concluded that high pumping efficiency and good pump uniformity can be obtained for corner-pumped composite slab lasers with appropriate choice of laser medium parameters.A diode cornerpumped composite Nd:YAG slab laser was designed, whose output power was up to 12W under the pump power 45W at opticaloptical efficiency of about 26.7%,and whose M2 factors of beam quality at width and thickness direction were 1.47 and 1.36 respectively at 40W pumping energy.Theoretic; analysis and experimental design show that corner-pumped method is useful in medium and small power lasers design.
In order to analyze the feasibility of corner-pumped method in medium and small power lasers design,ray-tracing algorithm was used to simulate the pumping efficiency and absorbed energy distribution of diode corner-pumped lasers for different laser medium parameters and different diode temperatures.It is concluded that high pumping efficiency and good pump uniformity can be obtained for corner-pumped composite slab lasers with appropriate choice of laser medium parameters.A diode cornerpumped composite Nd:YAG slab laser was designed, whose output power was up to 12W under the pump power 45W at opticaloptical efficiency of about 26.7%,and whose M2 factors of beam quality at width and thickness direction were 1.47 and 1.36 respectively at 40W pumping energy.Theoretic; analysis and experimental design show that corner-pumped method is useful in medium and small power lasers design.
2009, 33(1): 5-7,31.
Abstract:
The impact of four-wave mixing(FWM) crosstalk on wavelength division multiplexing systems in high nonlinear fiber was studied experimentally.Results showed that the generated wave efficiency decreased with increasing channel spacing and input signal power.The influence of FWM on signal was compared when the channels were arranged equal and unequal.It was shown that 1.5dB larger penalty was introduced in the case of equal channel spacing than in the case of unequal channel spacing.
The impact of four-wave mixing(FWM) crosstalk on wavelength division multiplexing systems in high nonlinear fiber was studied experimentally.Results showed that the generated wave efficiency decreased with increasing channel spacing and input signal power.The influence of FWM on signal was compared when the channels were arranged equal and unequal.It was shown that 1.5dB larger penalty was introduced in the case of equal channel spacing than in the case of unequal channel spacing.
2009, 33(1): 8-11,41.
Abstract:
In order to realize 3-D object rotation-invariant recognition, with help of high relevancy of perspective array of 3-D objects, the depth information of 3-D objects was converted to 2-D elemental images by means of microlens array.Theoretical analysis showed that both 3-D object rotation-invariant recognition and exact orientation of rotation direction could be obtained.Taking a dice,a 3-D object as an example, it was recognized in real time by means of match filtering and the proposed method.The latter performed better, and the exact orientation of rotation direction and rotational angle size discrimination were recognized.The results showed that the real-time 3-D object rotation-invariant recognition can be accomplished with microlens array.
In order to realize 3-D object rotation-invariant recognition, with help of high relevancy of perspective array of 3-D objects, the depth information of 3-D objects was converted to 2-D elemental images by means of microlens array.Theoretical analysis showed that both 3-D object rotation-invariant recognition and exact orientation of rotation direction could be obtained.Taking a dice,a 3-D object as an example, it was recognized in real time by means of match filtering and the proposed method.The latter performed better, and the exact orientation of rotation direction and rotational angle size discrimination were recognized.The results showed that the real-time 3-D object rotation-invariant recognition can be accomplished with microlens array.
Measurement of high-birefringent polarization-maintaining fiber and its analysis with Mueller matrix
2009, 33(1): 15-17,56.
Abstract:
In order to measure the beat length of high-birefringent polarization-maintaining fibers,an all-fiber optic system,comprised of broadband light source, in-line polarizer with polarization-maintaining pigtail and optical spectrum analysis, was be constructed based on conoscopic interference effect.The expression of optical intensity arrived at the optical spectrum analyzer was derived with Mueller transfer matrix.The measured data of the beat length of a kind of panda high-birefringent polarizationmaintaining fiber was acquired in experiments.It is found that the intensity fluctuation due to conoscopic interference effect makes the spectrum variance in a certain period.The relative amplitude of the spectrum variance is decided by the angles between the chief axes of the polarization-maintaining fiber and the pigtail of in-line polarizer.When the angle is ±45°,the relative amplitude is maximal.Hence,the beat length of the panda high-birefringent polarization-maintaining fiber can be calculated as long as the spectrum fluctuation period is measured in experiments.
In order to measure the beat length of high-birefringent polarization-maintaining fibers,an all-fiber optic system,comprised of broadband light source, in-line polarizer with polarization-maintaining pigtail and optical spectrum analysis, was be constructed based on conoscopic interference effect.The expression of optical intensity arrived at the optical spectrum analyzer was derived with Mueller transfer matrix.The measured data of the beat length of a kind of panda high-birefringent polarizationmaintaining fiber was acquired in experiments.It is found that the intensity fluctuation due to conoscopic interference effect makes the spectrum variance in a certain period.The relative amplitude of the spectrum variance is decided by the angles between the chief axes of the polarization-maintaining fiber and the pigtail of in-line polarizer.When the angle is ±45°,the relative amplitude is maximal.Hence,the beat length of the panda high-birefringent polarization-maintaining fiber can be calculated as long as the spectrum fluctuation period is measured in experiments.
2009, 33(1): 18-20.
Abstract:
In order to study the transmission properties of laser in bubble films, the extinction section and the extinction efficiency of bubbles were calculated by means of Mie scattering theory.The light extinction properties of underwater bubble films were analyzed theoretically and validated in laboratory based on the Lambert-Beer law.The laser power transmitted through bubble film of different density, thickness, and distances was measured with a power meter.The results indicated that the power decayed exponentially with the density and the thickness, but had no relation to the distance between the film and the detector.The conclusions are helpful for optical detection of bubble wakes of ships.
In order to study the transmission properties of laser in bubble films, the extinction section and the extinction efficiency of bubbles were calculated by means of Mie scattering theory.The light extinction properties of underwater bubble films were analyzed theoretically and validated in laboratory based on the Lambert-Beer law.The laser power transmitted through bubble film of different density, thickness, and distances was measured with a power meter.The results indicated that the power decayed exponentially with the density and the thickness, but had no relation to the distance between the film and the detector.The conclusions are helpful for optical detection of bubble wakes of ships.
2009, 33(1): 21-23.
Abstract:
In order to improve the pumping efficiency and make the temperature distribution more uniformity, a V-shape active mirror heat capacity laser was set up.Heat distribution of the laser medium was studied with numerical simulation and experimental methods.In numerical simulation, asymmetry of inner heat source was sufficiently considered, and in three-dimension heat distribution was analysed.In experiment, the temperature on the surface of the laser medium was measured by a thermal imaging system.The result of numerical simulation and experimental measurement were quite identical.It is demonstrated that the shape of the heat capacity has great advantage on improving thermal distribution.
In order to improve the pumping efficiency and make the temperature distribution more uniformity, a V-shape active mirror heat capacity laser was set up.Heat distribution of the laser medium was studied with numerical simulation and experimental methods.In numerical simulation, asymmetry of inner heat source was sufficiently considered, and in three-dimension heat distribution was analysed.In experiment, the temperature on the surface of the laser medium was measured by a thermal imaging system.The result of numerical simulation and experimental measurement were quite identical.It is demonstrated that the shape of the heat capacity has great advantage on improving thermal distribution.
2009, 33(1): 24-26.
Abstract:
The dispersion properties of photonic crystal fibers were studied with finite element method (FEM)by changing the diameter of the air-holes belonging to the first three rings.It was found that zero dispersion wavelength could be shifted in the range of 1100nm～1800nm by adjusting the air-hole diameter of the first, the second or the third ring.Photonic crystal fibers with nearly zero flattened dispersion over a very broad spectral range can be designed through choosing the suitable air-hole diameter of the first,the second or the third ring.The results is useful for photonic crystal fibers design.
The dispersion properties of photonic crystal fibers were studied with finite element method (FEM)by changing the diameter of the air-holes belonging to the first three rings.It was found that zero dispersion wavelength could be shifted in the range of 1100nm～1800nm by adjusting the air-hole diameter of the first, the second or the third ring.Photonic crystal fibers with nearly zero flattened dispersion over a very broad spectral range can be designed through choosing the suitable air-hole diameter of the first,the second or the third ring.The results is useful for photonic crystal fibers design.
2009, 33(1): 27-31.
Abstract:
In order to use plasma electro-optic switch in repetition frequency lasers, the effect of crystal absorption coefficient,the crystal thickness, the distance between focula boundary and crystal boundary, power-intensity distribution, on temperature and strain distribution was analyzed by means of finite element method.The simulation results indicate that the heat deposit depends on absorption coefficient and crystal thickness, the temperature distribution is not only related with power intensity distribution of incident laser but also the distance between focula boundary and crystal boundary.The temperature distribution as well as the thermodynamic parameter determinates the strain field.
In order to use plasma electro-optic switch in repetition frequency lasers, the effect of crystal absorption coefficient,the crystal thickness, the distance between focula boundary and crystal boundary, power-intensity distribution, on temperature and strain distribution was analyzed by means of finite element method.The simulation results indicate that the heat deposit depends on absorption coefficient and crystal thickness, the temperature distribution is not only related with power intensity distribution of incident laser but also the distance between focula boundary and crystal boundary.The temperature distribution as well as the thermodynamic parameter determinates the strain field.
2009, 33(1): 32-35.
Abstract:
In order to study iteration searching properties of genetic simulated annealing algorithm (GSAA) parameters in bidirectional reflectance distribution, function (BRDF) model, GSAA and genetic algorithm(GA) were employed, respectively, to search iteratively parameters of BRDF model for several media.The retrieved results of the two algorithms were compared with the BRDF experimental data at a certain laser wavelength.By theoretically analyzing and experimentally demonstrating, fitting values for both the algorithms were obtained, which were consistent with experimental values very well.Meanwhile, the difference of iteration number,computation time and mean square error in both the algorithms was compared.The results show that, the BRDF experimental data can be retrieved satisfactorily using both GSAA and GA, and the former is better than the latter.The aforementioned results are of help to the study of iteration searching properties of algorithms.
In order to study iteration searching properties of genetic simulated annealing algorithm (GSAA) parameters in bidirectional reflectance distribution, function (BRDF) model, GSAA and genetic algorithm(GA) were employed, respectively, to search iteratively parameters of BRDF model for several media.The retrieved results of the two algorithms were compared with the BRDF experimental data at a certain laser wavelength.By theoretically analyzing and experimentally demonstrating, fitting values for both the algorithms were obtained, which were consistent with experimental values very well.Meanwhile, the difference of iteration number,computation time and mean square error in both the algorithms was compared.The results show that, the BRDF experimental data can be retrieved satisfactorily using both GSAA and GA, and the former is better than the latter.The aforementioned results are of help to the study of iteration searching properties of algorithms.
2009, 33(1): 36-38.
Abstract:
In order to study the propagation characteristics of two-dimension square lattice photonic crystal in THz rang, the band gap structure and density of photon states were calculated by plane-wave expansion method.It was found that the maximum photonic band gap generated when the f was 0.6362 and 0.7854 in the E and H polarization, and the maximum absolute photonic band gap generated when the f=0.7791;and large photonic band gap would generate by increasing difference inralue of dielectric constant;the photonic band structure was also shown by the photonic density of states.It turned out that this research provides theoretic basis for the development of THz devices.
In order to study the propagation characteristics of two-dimension square lattice photonic crystal in THz rang, the band gap structure and density of photon states were calculated by plane-wave expansion method.It was found that the maximum photonic band gap generated when the f was 0.6362 and 0.7854 in the E and H polarization, and the maximum absolute photonic band gap generated when the f=0.7791;and large photonic band gap would generate by increasing difference inralue of dielectric constant;the photonic band structure was also shown by the photonic density of states.It turned out that this research provides theoretic basis for the development of THz devices.
2009, 33(1): 42-45,49.
Abstract:
Study on diode-pumped all-solid-state 447nm lasers is hot for the wide applications of 447nm blue laser sources.Based on lots of references at home and abroad, the development situation of all-solid-state blue lasers was introduced and summarized focusing on their technical routes.And then according to our study,21mW 447nm CW laser was gotten.Finally, the likely realization approaches of the 447nm lasers and the present feasibility was analyzed.
Study on diode-pumped all-solid-state 447nm lasers is hot for the wide applications of 447nm blue laser sources.Based on lots of references at home and abroad, the development situation of all-solid-state blue lasers was introduced and summarized focusing on their technical routes.And then according to our study,21mW 447nm CW laser was gotten.Finally, the likely realization approaches of the 447nm lasers and the present feasibility was analyzed.
2009, 33(1): 46-49.
Abstract:
In order to deduce that the bending loss was a function of curvature radius and temperature,WKB method was used to solve the number of modes of non-uniform straight fibers, the effective refractive index, the cut-off of propagation constant of bending fibers and thermo-optic effect of fibers were introduced to the number of modes of non-uniform straight fiber also.Choosing multimode graded-index optical fibers to get a temperature sensor, the sensitivity of the sensor was 0.1/℃ and the temperature sensing range was 10℃～70℃.The results indicate that the smaller the curvature radius and the temperature, the bigger the bending loss.Bending loss can be used to measure the temperature.
In order to deduce that the bending loss was a function of curvature radius and temperature,WKB method was used to solve the number of modes of non-uniform straight fibers, the effective refractive index, the cut-off of propagation constant of bending fibers and thermo-optic effect of fibers were introduced to the number of modes of non-uniform straight fiber also.Choosing multimode graded-index optical fibers to get a temperature sensor, the sensitivity of the sensor was 0.1/℃ and the temperature sensing range was 10℃～70℃.The results indicate that the smaller the curvature radius and the temperature, the bigger the bending loss.Bending loss can be used to measure the temperature.
2009, 33(1): 50-52,70.
Abstract:
The finite difference time domain method was used to simulate the transmission characteristics of 2-D triangular lattices SiO2/Si photonic crystal.Furthermore,it was also studied how the change of the shape of SiO2 and the mode of incident wave affect transmission properties of photonic crystal.The curves of transmissivity versus frequency of the incident wave in the different conditions were obtained.The calculated results obviously show that the band gap width and position are related to the shape of SiO2 in photonic crystal.With the increase of the radius of SiO2 cylinder, the band gap is widened and the central frequency is enhanced,but the largest band gap appears when R=0.4α.Compared with TM wave, the band gap appears more easily under the TE wave.The study provides the theory basis of the manufacture and application of photonic crystal.
The finite difference time domain method was used to simulate the transmission characteristics of 2-D triangular lattices SiO2/Si photonic crystal.Furthermore,it was also studied how the change of the shape of SiO2 and the mode of incident wave affect transmission properties of photonic crystal.The curves of transmissivity versus frequency of the incident wave in the different conditions were obtained.The calculated results obviously show that the band gap width and position are related to the shape of SiO2 in photonic crystal.With the increase of the radius of SiO2 cylinder, the band gap is widened and the central frequency is enhanced,but the largest band gap appears when R=0.4α.Compared with TM wave, the band gap appears more easily under the TE wave.The study provides the theory basis of the manufacture and application of photonic crystal.
2009, 33(1): 53-56.
Abstract:
In order to achieve real-time temperature reconstruction,high-end digital signal processor(DSP) was used as the computing core of simultaneous iterative reconstruction technique reconstruction algorithm.Emission spectral tomography (EST) real-time reconstruction of the temperature field was achieved.Through the experiment, the data was obtained that reconstruction algorithm needs different time under DSP system and PC system.The results indicate that using DSP as computing core,real-time EST reconstruction of temperature field can be achieved.DSP-based temperature reconstruction algorithm combined with a generic PC's control and display function is a good method for EST temperature field reconstruction.
In order to achieve real-time temperature reconstruction,high-end digital signal processor(DSP) was used as the computing core of simultaneous iterative reconstruction technique reconstruction algorithm.Emission spectral tomography (EST) real-time reconstruction of the temperature field was achieved.Through the experiment, the data was obtained that reconstruction algorithm needs different time under DSP system and PC system.The results indicate that using DSP as computing core,real-time EST reconstruction of temperature field can be achieved.DSP-based temperature reconstruction algorithm combined with a generic PC's control and display function is a good method for EST temperature field reconstruction.
2009, 33(1): 57-59,66.
Abstract:
In order to study the relationship between the bubbles' backscattering signal intensity and the position of bubble film and receiver angle, based on Monte Carlo method, the backscattering signal was simulated under the boundary condition of the flume.Experimental results of backscattering signal were also obtained in different bubble film positions and receiver angles.It is turned out that there is a peak in backscattering signal,which is corresponding to a certain receiver angle for different bubble film positions.The conclusions are helpful for optical detection of bubble wakes of ships on the sea.
In order to study the relationship between the bubbles' backscattering signal intensity and the position of bubble film and receiver angle, based on Monte Carlo method, the backscattering signal was simulated under the boundary condition of the flume.Experimental results of backscattering signal were also obtained in different bubble film positions and receiver angles.It is turned out that there is a peak in backscattering signal,which is corresponding to a certain receiver angle for different bubble film positions.The conclusions are helpful for optical detection of bubble wakes of ships on the sea.
2009, 33(1): 60-62.
Abstract:
In order to reduce distortion of remote signal induced by wide dynamic range of lidar signal,a voltage controlled transmission modulation was used to suppress the dynamic range of lidar signal.The result of simulation indicates that the minimum transmissivity of the system is 4.05×10-5 and the dynamic range can be reduced to 4 orders of magnitude.The system receives both ordinary light and extraordinary light, so it can avoid the disadvantage of the time-dependent attenuator in whieh only polarizing light in one direction can be received.It provides new valuable approach to suppress lidar dynamic range.
In order to reduce distortion of remote signal induced by wide dynamic range of lidar signal,a voltage controlled transmission modulation was used to suppress the dynamic range of lidar signal.The result of simulation indicates that the minimum transmissivity of the system is 4.05×10-5 and the dynamic range can be reduced to 4 orders of magnitude.The system receives both ordinary light and extraordinary light, so it can avoid the disadvantage of the time-dependent attenuator in whieh only polarizing light in one direction can be received.It provides new valuable approach to suppress lidar dynamic range.
2009, 33(1): 63-66.
Abstract:
For the sake of directly fabricating metal parts by means of selective laser melting, experimental study about rapid manufacturing metal parts from CuP powder with average particle size of 75μm were carried out on Dimetal 240 equipped with a 200W CW Nd:YAG laser, laser power 103W～117W, scanning speed 0.25m/s～0.41 m/s (inner),0.15m/s (frame), powder thickness 0.2mm.The scanning electron microscope (SEM) and the metalloscope were used to analyze the microstructure of the sample.The results show that a complete metallurgical bonding is obtained after selective laser mehing process and the density reaches 90%.The intra-layer microstructure is slender arborescent crystalwhile microstructure between layers is small isometric crystal.Therefore, it is feasible to directly manufacture metal parts by means of selective laser mehing under appropriate parameters.
For the sake of directly fabricating metal parts by means of selective laser melting, experimental study about rapid manufacturing metal parts from CuP powder with average particle size of 75μm were carried out on Dimetal 240 equipped with a 200W CW Nd:YAG laser, laser power 103W～117W, scanning speed 0.25m/s～0.41 m/s (inner),0.15m/s (frame), powder thickness 0.2mm.The scanning electron microscope (SEM) and the metalloscope were used to analyze the microstructure of the sample.The results show that a complete metallurgical bonding is obtained after selective laser mehing process and the density reaches 90%.The intra-layer microstructure is slender arborescent crystalwhile microstructure between layers is small isometric crystal.Therefore, it is feasible to directly manufacture metal parts by means of selective laser mehing under appropriate parameters.
2009, 33(1): 67-70.
Abstract:
For typical high order modes of Hermite-Gaussian beam,the effect of frequency doubling on beam quality factor and the space distribution was studied by means of calculation and experiments.The beam quality of the frequency doubled beam was deteriorated seriously with the beam quality of basic frequency reducing.The beam quality of the frequency doubled beam was invariant when the radius of the basic beam with the same beam quality was variant in the crystal surface.Green power of 49.5W was generated with a 15kHz repetition rate by intracavity frequency doubling of a diode-pumped Nd:YAG laser.The beam quality factor of the frequency doubled beam was 10.2 with the basic beam quality factor of M2=4.93.The result of experiment was the same with the theoretical calculation.
For typical high order modes of Hermite-Gaussian beam,the effect of frequency doubling on beam quality factor and the space distribution was studied by means of calculation and experiments.The beam quality of the frequency doubled beam was deteriorated seriously with the beam quality of basic frequency reducing.The beam quality of the frequency doubled beam was invariant when the radius of the basic beam with the same beam quality was variant in the crystal surface.Green power of 49.5W was generated with a 15kHz repetition rate by intracavity frequency doubling of a diode-pumped Nd:YAG laser.The beam quality factor of the frequency doubled beam was 10.2 with the basic beam quality factor of M2=4.93.The result of experiment was the same with the theoretical calculation.
2009, 33(1): 71-73.
Abstract:
In order to evaluate the surface quality of a laser cutting die-board,the relationship between carbon layer attacked to die-hoard surface and laser cutting parameters were analyzed through three methods,i, e.macroscopic observation,microcosmic observation and carbon content measurement.Results indicate that carbon area will extend with the decreasing of cutting speed.The surface striation becomes prominent with the increasing of cutting speed at the same laser power,while diminishes or vanishes with reducing the speed.In the case of lower speed, carbon attacked to surface will decrease with increasing of laser power.In the case of higher speed,carbon attacked to surface is almost the same with increasing of laser power and surface striation is not so prominent.Carbon layer is distributed along the wood grain, while honeycomb distributed perpendicular to the wood grain.Both cases exist holes and the hole diameter reduces with the decreasing of speed.
In order to evaluate the surface quality of a laser cutting die-board,the relationship between carbon layer attacked to die-hoard surface and laser cutting parameters were analyzed through three methods,i, e.macroscopic observation,microcosmic observation and carbon content measurement.Results indicate that carbon area will extend with the decreasing of cutting speed.The surface striation becomes prominent with the increasing of cutting speed at the same laser power,while diminishes or vanishes with reducing the speed.In the case of lower speed, carbon attacked to surface will decrease with increasing of laser power.In the case of higher speed,carbon attacked to surface is almost the same with increasing of laser power and surface striation is not so prominent.Carbon layer is distributed along the wood grain, while honeycomb distributed perpendicular to the wood grain.Both cases exist holes and the hole diameter reduces with the decreasing of speed.
2009, 33(1): 74-76,86.
Abstract:
A variable constant-current driver was proposed for a super luminescent diode (SLED) to meet the constanttemperature working requirement.This method was carried out by a microcomputer, MSP430, combining with proportional-integraldifferential(PID) algorithm and a semiconductor cooler.Driven by this controller,the SLED generated a stable output power and central wavelength.Experimental results demonstrated that the temperature accuracy of 0.1℃ was achieved when the environmental temperature changed from 10℃ to 40℃.The constant-driving current was stabilized at 0.1mA in the range from 0mA to 200mA.Thus,the driver can meet the demand of SLED application.
A variable constant-current driver was proposed for a super luminescent diode (SLED) to meet the constanttemperature working requirement.This method was carried out by a microcomputer, MSP430, combining with proportional-integraldifferential(PID) algorithm and a semiconductor cooler.Driven by this controller,the SLED generated a stable output power and central wavelength.Experimental results demonstrated that the temperature accuracy of 0.1℃ was achieved when the environmental temperature changed from 10℃ to 40℃.The constant-driving current was stabilized at 0.1mA in the range from 0mA to 200mA.Thus,the driver can meet the demand of SLED application.
2009, 33(1): 77-79.
Abstract:
The nonlinear dispersion relation of an elliptically polarized laser pulse in plasmas was derived by means of Lorentz technique.The modulation instability with finite amplitude in plasmas was analyzed on the basis of the nonlinear controlling equation for transverse wave.The temporal growth rate as a function of perturbed wave number for laser beam propagating through plasmas was found analytically and the modulation instability growth rates in the different regions of plasmas were compared, It is shown that the temporal growth rate of modulation instability is increased significantly in the corona region near the critical surface in laser-produced plasmas.
The nonlinear dispersion relation of an elliptically polarized laser pulse in plasmas was derived by means of Lorentz technique.The modulation instability with finite amplitude in plasmas was analyzed on the basis of the nonlinear controlling equation for transverse wave.The temporal growth rate as a function of perturbed wave number for laser beam propagating through plasmas was found analytically and the modulation instability growth rates in the different regions of plasmas were compared, It is shown that the temporal growth rate of modulation instability is increased significantly in the corona region near the critical surface in laser-produced plasmas.
2009, 33(1): 80-82.
Abstract:
Based on semi-analytical theory,thermal effect of rectangle YVO4-Nd: YVO4 composite crystal end-pumped by the diode laser with super-Gaussian mode was studied through academic analysis and experimental validation.When the output power of diode laser was 15W and the order of the super-Gaussian beam was 2, in the center of the pump-lace of neodymium-doped YVO4-Nd: YVO4 composite crystal, the maximum temperature rise and thermal distortion got up to 175.4℃, 1.97μm respectively.The results show that super-Gaussian model is widely applieable and composite crystals can reduce the top temperature but can't reduce thermal distortion obviously.The result can offer theoretical basis for efficiently resolving the thermal problems in laser systems.
Based on semi-analytical theory,thermal effect of rectangle YVO4-Nd: YVO4 composite crystal end-pumped by the diode laser with super-Gaussian mode was studied through academic analysis and experimental validation.When the output power of diode laser was 15W and the order of the super-Gaussian beam was 2, in the center of the pump-lace of neodymium-doped YVO4-Nd: YVO4 composite crystal, the maximum temperature rise and thermal distortion got up to 175.4℃, 1.97μm respectively.The results show that super-Gaussian model is widely applieable and composite crystals can reduce the top temperature but can't reduce thermal distortion obviously.The result can offer theoretical basis for efficiently resolving the thermal problems in laser systems.
2009, 33(1): 83-86.
Abstract:
In order to investigate interaction between Rayleigh waves and the notches on the surface of a cylinder, an experiment setup was designed.By changing the relative position between generation source and the notch, Rayleigh waves were detected by a laser interferometer with applying a pulse laser to generate the signal.Experimental results demonstrated that different Rayleigh waves were obtained at different positions, that peak-to-peak value of reflective Rayleigh waves increased with the decrease of laser source-notch distance, and that the waves'polarity transformed.Therefore, detecting the maximum of peakpeak value can be utilized to judge the position of the notch by rotating the sample while keeping the position of generation source unchanged; the polarity can also be used in further judgments.
In order to investigate interaction between Rayleigh waves and the notches on the surface of a cylinder, an experiment setup was designed.By changing the relative position between generation source and the notch, Rayleigh waves were detected by a laser interferometer with applying a pulse laser to generate the signal.Experimental results demonstrated that different Rayleigh waves were obtained at different positions, that peak-to-peak value of reflective Rayleigh waves increased with the decrease of laser source-notch distance, and that the waves'polarity transformed.Therefore, detecting the maximum of peakpeak value can be utilized to judge the position of the notch by rotating the sample while keeping the position of generation source unchanged; the polarity can also be used in further judgments.
2009, 33(1): 87-90.
Abstract:
In order to study the possibility of laser welding bulk metallic glass, two pieces of bulk metallic glass based on Zr45Cu48Al7 without crystallization were successfully welded laser welding.No crystallization was observed and no visible defect of crack was recognized in the bead and heated-affected zone (HAZ) under the condition of welding scanning speed of 8m/min with output laser power of 1.2kW.The temperature profile of the thermal cycle (temperature history) in the bead and HAZ indicates that the reason of non-crystallization of the sample is that the temperature in the bead and HAZ rapidly decreased to below 430℃ in glass formation from the melt.The laser welding method can be used to weld the bulk metallic glass successfully.
In order to study the possibility of laser welding bulk metallic glass, two pieces of bulk metallic glass based on Zr45Cu48Al7 without crystallization were successfully welded laser welding.No crystallization was observed and no visible defect of crack was recognized in the bead and heated-affected zone (HAZ) under the condition of welding scanning speed of 8m/min with output laser power of 1.2kW.The temperature profile of the thermal cycle (temperature history) in the bead and HAZ indicates that the reason of non-crystallization of the sample is that the temperature in the bead and HAZ rapidly decreased to below 430℃ in glass formation from the melt.The laser welding method can be used to weld the bulk metallic glass successfully.
2009, 33(1): 91-93,96.
Abstract:
Aiming at the special requirements such as homogeneous intensity, high ratio of applied energy and small sidelobe for the focal spot of drive source in large-sized laser device, a hybrid method based on geometrical transformation and modified Gerchberg-Saxton (G-S) algorithm was proposed to design continuous phase plates(CPP).The performance of the CPP was verified by means of diffraction numerical integrating method and the result showed that the CPP obtained good 24th-order super-Gaussian fit with diffractive efficiency up to 99.79%, top mean square error of 0.35% and top modulation of 1.33%.This method is fast and avoiding the shortcoming that the G-S result is easy to trap in local optimum.Moreover, the designed plate is fully continuous, so the plate is easy to be fabricated and improves the smoothing performance of the plate.
Aiming at the special requirements such as homogeneous intensity, high ratio of applied energy and small sidelobe for the focal spot of drive source in large-sized laser device, a hybrid method based on geometrical transformation and modified Gerchberg-Saxton (G-S) algorithm was proposed to design continuous phase plates(CPP).The performance of the CPP was verified by means of diffraction numerical integrating method and the result showed that the CPP obtained good 24th-order super-Gaussian fit with diffractive efficiency up to 99.79%, top mean square error of 0.35% and top modulation of 1.33%.This method is fast and avoiding the shortcoming that the G-S result is easy to trap in local optimum.Moreover, the designed plate is fully continuous, so the plate is easy to be fabricated and improves the smoothing performance of the plate.
2009, 33(1): 94-96.
Abstract:
In order to analyze the error of the velocity of sound in atmosphere, based on Brillouin lidar, the measuring method of sound velocity in atmosphere was put forward for its high precision, high speed and real time. The concrete relation between the velocity of sound and other atmosphere parameters was analyzed. Then, the measurement error of the velocity of sound was calculated and the numerical analysis was fulfilled. The results show that, in the condition of standard atmosphere, the precision of the velocity of sound is less than 0.269m/s in the height of 0km～86km. The Brillouin frequency shift has a greater influence on the error of the velocity of sound than the refractive index and the laser wavelength in the atmosphere. This analysis is a significant guide for the lidar design.
In order to analyze the error of the velocity of sound in atmosphere, based on Brillouin lidar, the measuring method of sound velocity in atmosphere was put forward for its high precision, high speed and real time. The concrete relation between the velocity of sound and other atmosphere parameters was analyzed. Then, the measurement error of the velocity of sound was calculated and the numerical analysis was fulfilled. The results show that, in the condition of standard atmosphere, the precision of the velocity of sound is less than 0.269m/s in the height of 0km～86km. The Brillouin frequency shift has a greater influence on the error of the velocity of sound than the refractive index and the laser wavelength in the atmosphere. This analysis is a significant guide for the lidar design.
2009, 33(1): 97-99,103.
Abstract:
In order to obtain the effect of temperature on the dynamical evolution of Gaussian beam in biased photovoltaic-photorefractive crystal, the dynamical evolution of Gaussian beam in biased photovoltaic photorefractive crystal at different temperatures was investigated by taking into account the temperature dependence of dark irradiation. Taking the Gaussian beam as the input wave, the beam propagation equation was solved numerically. A matched Gaussian beam can evolve into a stable screening-photovoltaic bright soliton at temperature of 300K, whereas it will become unstable or diverge when the temperature change is large enough. Under mismatch conditions, an unstable Gaussian beam can evolve into stable screening-photovoltaic bright solitons by adjusting the crystal temperature. The result indicate that the change of the evolution of a Gaussian beam in photovoltaic-photorefractive crystal controlled by the increases or decreases of the temperature can be applied in thermo-control optical devices.
In order to obtain the effect of temperature on the dynamical evolution of Gaussian beam in biased photovoltaic-photorefractive crystal, the dynamical evolution of Gaussian beam in biased photovoltaic photorefractive crystal at different temperatures was investigated by taking into account the temperature dependence of dark irradiation. Taking the Gaussian beam as the input wave, the beam propagation equation was solved numerically. A matched Gaussian beam can evolve into a stable screening-photovoltaic bright soliton at temperature of 300K, whereas it will become unstable or diverge when the temperature change is large enough. Under mismatch conditions, an unstable Gaussian beam can evolve into stable screening-photovoltaic bright solitons by adjusting the crystal temperature. The result indicate that the change of the evolution of a Gaussian beam in photovoltaic-photorefractive crystal controlled by the increases or decreases of the temperature can be applied in thermo-control optical devices.
2009, 33(1): 100-103.
Abstract:
To solve the problem of that the electromagnetic interference (EMI) induced by a working excimer laser, which might affect the signal of the laser control system, the analog and digital optical fiber models for signal transmission and embedded eximer laser control system were designed by transmitting the signals with optical fibers for their character of immunity to EMI. It was proved that the system's analog channel's-3dB bandwidth was DC-3MHz,its max nonlinearity was 1.2%, and the control system was stable and reliable while the excimer laser working. Experiment results indicate that this system have good character of immunity to EMI.
To solve the problem of that the electromagnetic interference (EMI) induced by a working excimer laser, which might affect the signal of the laser control system, the analog and digital optical fiber models for signal transmission and embedded eximer laser control system were designed by transmitting the signals with optical fibers for their character of immunity to EMI. It was proved that the system's analog channel's-3dB bandwidth was DC-3MHz,its max nonlinearity was 1.2%, and the control system was stable and reliable while the excimer laser working. Experiment results indicate that this system have good character of immunity to EMI.
2009, 33(1): 104-106.
Abstract:
In order to examine the variation of CO2 laser beam mode profile,and analyze the effect of different laser modes on the uniformity of quenching hardened layers,a pyroelectric camera-based industrial inline laser beam analyzer was installed to monitor the laser beam profiles in real-time during the laser quenching process. Results showed that due to the ununiformity of the laser power intensity in spatial distribution, the depth of the hardened layer at either side of the beam spot differed obviously. In addition,it was found the microstructures of laser quenching layers were dominated by laser beam modes and uniform power distribution resulted in uniform microstructures.
In order to examine the variation of CO2 laser beam mode profile,and analyze the effect of different laser modes on the uniformity of quenching hardened layers,a pyroelectric camera-based industrial inline laser beam analyzer was installed to monitor the laser beam profiles in real-time during the laser quenching process. Results showed that due to the ununiformity of the laser power intensity in spatial distribution, the depth of the hardened layer at either side of the beam spot differed obviously. In addition,it was found the microstructures of laser quenching layers were dominated by laser beam modes and uniform power distribution resulted in uniform microstructures.
2009, 33(1): 107-109.
Abstract:
A large aperture reflector is an important optical element in the inetrial confinement fusion driver with high-power solid laser and the quality of its surface has direct impact on the output characteristics of the whole equipment. In order to study the surface deformation of a large aperture reflector, after comprehensive investigation of the stress-controlling technique of large aperture reflectors, the research was carried out both theoretically and experimentally. Firstly, the model for a large aperture reflector was constructed by means of ANSYS. Then the DPV-S curve,indicating the relationship between deformation and change of pressed area under the effect of gravity, was obtained. Secondly, an interferometer was used to measure the upside and backside deformation of the large aperture reflector. The test result was consistent with that in theory and their difference was only 0.002μm～0.122μm. The results show that the study provides a good method for surface detection, surface control and alignment for large aperture reflectors.
A large aperture reflector is an important optical element in the inetrial confinement fusion driver with high-power solid laser and the quality of its surface has direct impact on the output characteristics of the whole equipment. In order to study the surface deformation of a large aperture reflector, after comprehensive investigation of the stress-controlling technique of large aperture reflectors, the research was carried out both theoretically and experimentally. Firstly, the model for a large aperture reflector was constructed by means of ANSYS. Then the DPV-S curve,indicating the relationship between deformation and change of pressed area under the effect of gravity, was obtained. Secondly, an interferometer was used to measure the upside and backside deformation of the large aperture reflector. The test result was consistent with that in theory and their difference was only 0.002μm～0.122μm. The results show that the study provides a good method for surface detection, surface control and alignment for large aperture reflectors.
2009, 33(1): 110-112.
Abstract:
In order to analyze the relationship between the laser propagation and atmospheric parameters like visibility and refractive index structure constant and laser beam parameters like the wave length and waist width, the propagating law and the influence on the laser intensity was studied based on the Gaussian beam. The results indicates that if the parameters of the laser source and atmosphere are confirmed, the effect of laser propagation is easy to know, which could provide a rule for the feasibility of laser engineering application, as well as conduct laser system design optimization.
In order to analyze the relationship between the laser propagation and atmospheric parameters like visibility and refractive index structure constant and laser beam parameters like the wave length and waist width, the propagating law and the influence on the laser intensity was studied based on the Gaussian beam. The results indicates that if the parameters of the laser source and atmosphere are confirmed, the effect of laser propagation is easy to know, which could provide a rule for the feasibility of laser engineering application, as well as conduct laser system design optimization.
