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RSS2007 Vol. 31, No. 2
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2007, 31(2): 113-116,140.
[Abstract]
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Abstract:
Based on the phenomena of laser supported combustion or detonation wave induced by the interaction between the high-intensity laser and material,a new method is present for diagnosing the ignition threshold of laser supported detonation wave by measuring the jump of the sound peak pressure of laser-target plasma.The ignition threshold can be obtained by analyzing the jump stage between laser power density and the sound peak pressure of laser-target plasma,which generates on the surface of target due to interaction between Nd:YAG laser whose wavelength is 1064nm and aluminum target.The test results are largely in accord with those form other methods.The experiment result is helpful to understand the mechanism and process of the interaction between the laser and the matter.
Based on the phenomena of laser supported combustion or detonation wave induced by the interaction between the high-intensity laser and material,a new method is present for diagnosing the ignition threshold of laser supported detonation wave by measuring the jump of the sound peak pressure of laser-target plasma.The ignition threshold can be obtained by analyzing the jump stage between laser power density and the sound peak pressure of laser-target plasma,which generates on the surface of target due to interaction between Nd:YAG laser whose wavelength is 1064nm and aluminum target.The test results are largely in accord with those form other methods.The experiment result is helpful to understand the mechanism and process of the interaction between the laser and the matter.
2007, 31(2): 117-119,146.
Abstract:
In order to study the questions of micro-Doppler effect detection in a laser radar and the extraction of micro-Doppler features indicating target characteristics from radar returned signal,a physical model for micro-Doppler effect in laser radar was built up,then the simulation of the micro-Doppler effect in the laser radar induced by vibration of the target was conducted.Because of the signal is time-varying,joint time-frequency analysis method was introduced.Short time Fourier transform was used to analyze the simulated signal in the time-frequency domain,a micro-Doppler image that can demonstrate the target characteristics was generated.Results show that a laser radar is fit for the detection of low amplitude micro-Doppler effect,and micro-Doppler features can be extracted from radar returned signal effectively by means of timefrequency analysis method.
In order to study the questions of micro-Doppler effect detection in a laser radar and the extraction of micro-Doppler features indicating target characteristics from radar returned signal,a physical model for micro-Doppler effect in laser radar was built up,then the simulation of the micro-Doppler effect in the laser radar induced by vibration of the target was conducted.Because of the signal is time-varying,joint time-frequency analysis method was introduced.Short time Fourier transform was used to analyze the simulated signal in the time-frequency domain,a micro-Doppler image that can demonstrate the target characteristics was generated.Results show that a laser radar is fit for the detection of low amplitude micro-Doppler effect,and micro-Doppler features can be extracted from radar returned signal effectively by means of timefrequency analysis method.
2007, 31(2): 120-122.
Abstract:
By using short-pulse field,the periodically poled grating(Λ=29μm) was successfully fabricated in 1.0mm thick MgO:LiNbO3(mole fraction of doped MgO is 0.05).A high-repetition-rate optical parametric generation(OPG) based on PPMgLN pumped by a 1.064μm acousto-optically Q-switched Nd:YVO4 laser.Under the condition of 3W of input pump power,44mW of output signal power was obtained,and the conversion efficiency was 1.5%.Furthermore a tunable infrared(IR) output from 1.4538μm~1.4750μm was obtained by tuning the temperature of PPMgLN(45℃~160℃).
By using short-pulse field,the periodically poled grating(Λ=29μm) was successfully fabricated in 1.0mm thick MgO:LiNbO3(mole fraction of doped MgO is 0.05).A high-repetition-rate optical parametric generation(OPG) based on PPMgLN pumped by a 1.064μm acousto-optically Q-switched Nd:YVO4 laser.Under the condition of 3W of input pump power,44mW of output signal power was obtained,and the conversion efficiency was 1.5%.Furthermore a tunable infrared(IR) output from 1.4538μm~1.4750μm was obtained by tuning the temperature of PPMgLN(45℃~160℃).
2007, 31(2): 123-126.
Abstract:
The holographic characteristics of the photopolymer dry film,which is based on acrylic acid and N,N'-methylenebisacrylamide as monomers,was studied by recording the transmission diffraction gratings and carrying out the digital holographic storage.Diffraction efficiency of above 40% and energetic sensitivities of 0.01cm2/mJ was obtained in photosensitive films of 180 μm thickness.The recorded gratings are homogenous without overmodulation and noise gratings.In the terms of the Bragg-mismatch,the thickness shrinkage of 1.7% was obtained with a bit-error rate of about 5.3×10-4.These results show the photopolymer is adaptive to the holographic storage.
The holographic characteristics of the photopolymer dry film,which is based on acrylic acid and N,N'-methylenebisacrylamide as monomers,was studied by recording the transmission diffraction gratings and carrying out the digital holographic storage.Diffraction efficiency of above 40% and energetic sensitivities of 0.01cm2/mJ was obtained in photosensitive films of 180 μm thickness.The recorded gratings are homogenous without overmodulation and noise gratings.In the terms of the Bragg-mismatch,the thickness shrinkage of 1.7% was obtained with a bit-error rate of about 5.3×10-4.These results show the photopolymer is adaptive to the holographic storage.
2007, 31(2): 127-130.
Abstract:
The two-dimensional(2-D) photonic crystal with layered composite medium cylinder was proposed,and effect of the refraction indexes,thicknesses,layers and composition sequences on the transmittance of the 2-D photonic crystal composed of multilayered composite medium was studied by means of the finite-difference time-domain method.The numerical results show that the forbidden band width and the position of central frequency in 2-D photonic crystal with multilayered medium are different from those composed of single medium.Therefore,the adjustable factors for 2-D photonic crystal with multilayered medium are more than those with single medium in application and the above theory can be as a theoretical basis on 2-D photonic crystal design.
The two-dimensional(2-D) photonic crystal with layered composite medium cylinder was proposed,and effect of the refraction indexes,thicknesses,layers and composition sequences on the transmittance of the 2-D photonic crystal composed of multilayered composite medium was studied by means of the finite-difference time-domain method.The numerical results show that the forbidden band width and the position of central frequency in 2-D photonic crystal with multilayered medium are different from those composed of single medium.Therefore,the adjustable factors for 2-D photonic crystal with multilayered medium are more than those with single medium in application and the above theory can be as a theoretical basis on 2-D photonic crystal design.
2007, 31(2): 131-133,136.
Abstract:
The correct recognition of film damage plays an important role in the experiment of measuring laser damage threshold.In ISO11254,film damage is recongnized through observation under a microscope.In order to realize on-line and automatic damage recognition,adopting the method of digital image processing,combining wavelet transform with pattern correlation recognition technology,how to carry out film laser damage recognition with wavelet transform is realized.The result illustrates this method not only has highest precision but also avoids heavy labor manipulation and play an important role in automatic damage threshold measurement.
The correct recognition of film damage plays an important role in the experiment of measuring laser damage threshold.In ISO11254,film damage is recongnized through observation under a microscope.In order to realize on-line and automatic damage recognition,adopting the method of digital image processing,combining wavelet transform with pattern correlation recognition technology,how to carry out film laser damage recognition with wavelet transform is realized.The result illustrates this method not only has highest precision but also avoids heavy labor manipulation and play an important role in automatic damage threshold measurement.
2007, 31(2): 134-136.
Abstract:
To improve the technology of modifying material properties by using laser induced shock waves,the properties of laser shock waves were studied.The piezoelectric waves were measured using a polyvinylidene fluoride(PVDF) piezoelectric gauge of a short rise time and a wide linear response range,together with an oscilloscope.Depending on the piezoelectric waves,laser-induced shock waves were measured.The laser-induced shock waves in the confinement geometry were analyzed and compared to that in the direct ablation regime.In the confined condition,the FWHM of laser-induced shock wave was three times that of laser and the peak pressure was much higher than that in the direct ablation regime.The average propagation velocity of the laser-induced shock wave in stainless steel was 5.72×103m/s.
To improve the technology of modifying material properties by using laser induced shock waves,the properties of laser shock waves were studied.The piezoelectric waves were measured using a polyvinylidene fluoride(PVDF) piezoelectric gauge of a short rise time and a wide linear response range,together with an oscilloscope.Depending on the piezoelectric waves,laser-induced shock waves were measured.The laser-induced shock waves in the confinement geometry were analyzed and compared to that in the direct ablation regime.In the confined condition,the FWHM of laser-induced shock wave was three times that of laser and the peak pressure was much higher than that in the direct ablation regime.The average propagation velocity of the laser-induced shock wave in stainless steel was 5.72×103m/s.
2007, 31(2): 137-140.
Abstract:
Based on the transfer matrix method,the effects of the pump optical power,the distributed Bragger reflector(DBR) periods and the intensity of the input optical signal on the optical bandwidth characteristics of vertical cavity semiconductor optical amplifiers(VCSOAs) are simulated numerically.The computer model includes the longitudinal distribution of carrier and optical intensity and the influence of the ununiformity of the refractive index of the material inside the cavity on the propagation of the optical signal.The obtained results agree well with the conclusion of previous literatures.The results show that the enhancement of the pump level will increase the peak gain of VCSOAs and decrease the optical bandwidth simultaneously;reducing the DBR periods will induce larger optical gain bandwidth product.In addition,the intensity of input optical signal will obviously affect the range of the optical bandwidth of VCSOAs.
Based on the transfer matrix method,the effects of the pump optical power,the distributed Bragger reflector(DBR) periods and the intensity of the input optical signal on the optical bandwidth characteristics of vertical cavity semiconductor optical amplifiers(VCSOAs) are simulated numerically.The computer model includes the longitudinal distribution of carrier and optical intensity and the influence of the ununiformity of the refractive index of the material inside the cavity on the propagation of the optical signal.The obtained results agree well with the conclusion of previous literatures.The results show that the enhancement of the pump level will increase the peak gain of VCSOAs and decrease the optical bandwidth simultaneously;reducing the DBR periods will induce larger optical gain bandwidth product.In addition,the intensity of input optical signal will obviously affect the range of the optical bandwidth of VCSOAs.
2007, 31(2): 141-143.
Abstract:
For the sake of studying thermal conduction characteristic of different doped YAG and GGG laser crystals,the thermal conductivities of different doped YAG and GGG laser crystal generated from 273K to 393K were measured by making use of instantaneous measuring method,and the temperature field model of the experimental sample was established,the function of thermal conductivity to the temperature was educed.The obtained conductivity/temperature curves almost conformed with the experimental results.The experimental results make clear that the thermal conductivity of the laser crystal decline to the temperature,the thermal conductivity of YAG laser crystal declines after doped with Yb ions,the thermal conductivity of the GGG laser crystal declines with the rising of the doped Nd ions concentration.Finally,the experimental results were theoretically explained.
For the sake of studying thermal conduction characteristic of different doped YAG and GGG laser crystals,the thermal conductivities of different doped YAG and GGG laser crystal generated from 273K to 393K were measured by making use of instantaneous measuring method,and the temperature field model of the experimental sample was established,the function of thermal conductivity to the temperature was educed.The obtained conductivity/temperature curves almost conformed with the experimental results.The experimental results make clear that the thermal conductivity of the laser crystal decline to the temperature,the thermal conductivity of YAG laser crystal declines after doped with Yb ions,the thermal conductivity of the GGG laser crystal declines with the rising of the doped Nd ions concentration.Finally,the experimental results were theoretically explained.
2007, 31(2): 144-146.
Abstract:
A simple cavity design for a pulsed Nd:YAG laser employed a 1mm-diameter laser rod pumped by a single laser diode module was reported.An experiment was performed to optimize the cavity design to obtain a laser output of 10W average power and a nearly diffraction-limited TEM00 mode.In this design,the small-diameter laser rod was used to eliminate the oscillation of high-order transverse modes,and a combination of a curved rear mirror and a negative lens placed inside the cavity was employed to compensate the thermal lens effect inside the laser rod.By experimentally optimizing the values of curvature of the rear mirror,the focal length of the negative lens,and the cavity spacing to maximize simultaneously the output power and the beam circularity,the pulsed Nd:YAG laser reached an average power of 10.8W,a beam circularity of 98.8%±0.8%,and M2 value of 1.1.The experimental results showed that in laser engineering the small-diameter laser rod could be used to improve the beam quality of high-power lasers.
A simple cavity design for a pulsed Nd:YAG laser employed a 1mm-diameter laser rod pumped by a single laser diode module was reported.An experiment was performed to optimize the cavity design to obtain a laser output of 10W average power and a nearly diffraction-limited TEM00 mode.In this design,the small-diameter laser rod was used to eliminate the oscillation of high-order transverse modes,and a combination of a curved rear mirror and a negative lens placed inside the cavity was employed to compensate the thermal lens effect inside the laser rod.By experimentally optimizing the values of curvature of the rear mirror,the focal length of the negative lens,and the cavity spacing to maximize simultaneously the output power and the beam circularity,the pulsed Nd:YAG laser reached an average power of 10.8W,a beam circularity of 98.8%±0.8%,and M2 value of 1.1.The experimental results showed that in laser engineering the small-diameter laser rod could be used to improve the beam quality of high-power lasers.
2007, 31(2): 147-149.
Abstract:
The silica glass doped with Er3+ and Al3+ iones were synthesized through sol-gel process.The effect of Al3+ on luminescence properties of Er3+ was studied.The results show that the concentration of Er3+ in co-doped silica glass can be improved one time than Erdoped glass,and the intensity is 20 times than that of Al non-doped glass.We concluded that the relation between Al3+ and Er3+ is just not energy transfer,but is that Al3+ not only change the configuration of sample,but also disperse the Er3+,as a result,the odds of cross-relaxation is depressed.And find that Er3+ iones have only an up-conversion emission at 654nm using 980nm excitation.
The silica glass doped with Er3+ and Al3+ iones were synthesized through sol-gel process.The effect of Al3+ on luminescence properties of Er3+ was studied.The results show that the concentration of Er3+ in co-doped silica glass can be improved one time than Erdoped glass,and the intensity is 20 times than that of Al non-doped glass.We concluded that the relation between Al3+ and Er3+ is just not energy transfer,but is that Al3+ not only change the configuration of sample,but also disperse the Er3+,as a result,the odds of cross-relaxation is depressed.And find that Er3+ iones have only an up-conversion emission at 654nm using 980nm excitation.
2007, 31(2): 150-152,178.
Abstract:
In order to theoretically study high-power multi-position-pumped double-clad fiber lasers intensively,the numerical analysis methods for this kind of fiber lasers were studied,based on the rate equations and boundary conditions of Yb-doped double-clad fiber lasers.By coordinate scale transform and continuum boundary transform of pumping powers and laser powers,the multi-position-pumped double-clad fiber lasers were transformed into two-boundary value problems and could be numerically analyzed effectively.And the power distributions of pumping lights and lasers along the double-clad fiber laser could be obtained.With numerical analysis,output powers,lost pumping powers and lost laser powers of the multi-position-pumped double-clad fiber lasers could be obtained also,which is very helpful for the optimal analysis and design of this kind of fiber lasers.The research shows that the numerical analysis methods are valuable for advanced study of multi-position-pumped double-clad fiber lasers.
In order to theoretically study high-power multi-position-pumped double-clad fiber lasers intensively,the numerical analysis methods for this kind of fiber lasers were studied,based on the rate equations and boundary conditions of Yb-doped double-clad fiber lasers.By coordinate scale transform and continuum boundary transform of pumping powers and laser powers,the multi-position-pumped double-clad fiber lasers were transformed into two-boundary value problems and could be numerically analyzed effectively.And the power distributions of pumping lights and lasers along the double-clad fiber laser could be obtained.With numerical analysis,output powers,lost pumping powers and lost laser powers of the multi-position-pumped double-clad fiber lasers could be obtained also,which is very helpful for the optimal analysis and design of this kind of fiber lasers.The research shows that the numerical analysis methods are valuable for advanced study of multi-position-pumped double-clad fiber lasers.
2007, 31(2): 153-155,159.
Abstract:
For the propose of incomplete data reconstruction caused by opaque objects in a complex flow field,a novel iterative algorithm based on series expansion methods by Moiré tomography is developed from the essence of Moiré deflection,the property matrix of a priori knowledge is introduced into the iterative process.The algorithm is studied by using it to reconstruct three-hump simulated temperature fields with opaque objects,so an ideal reconstruction results are achieved.Results are also compared with results from the traditional filtered back-projection algorithm under same conditions.Results show that having been combined with the property matrix of a priori information,new algorithm is more efficient to handle incomplete data reconstructive problems than the filtered back-projection algorithm.So the foundation of taking Moiré tomography into practice is established.
For the propose of incomplete data reconstruction caused by opaque objects in a complex flow field,a novel iterative algorithm based on series expansion methods by Moiré tomography is developed from the essence of Moiré deflection,the property matrix of a priori knowledge is introduced into the iterative process.The algorithm is studied by using it to reconstruct three-hump simulated temperature fields with opaque objects,so an ideal reconstruction results are achieved.Results are also compared with results from the traditional filtered back-projection algorithm under same conditions.Results show that having been combined with the property matrix of a priori information,new algorithm is more efficient to handle incomplete data reconstructive problems than the filtered back-projection algorithm.So the foundation of taking Moiré tomography into practice is established.
2007, 31(2): 156-159.
Abstract:
Considering the difference between the real blood cells and their spheroid model for the scattering detection of cells,a model was presented to calculate the light scattering properties of nucleated cells which were mimicked by flat ellipsoid.The light-scattering characteristics were derived from the Rayleigh-Debye-Gans approximation and the volume polarizability.Results show that the model is superior to ball model.The model can reflect the true configuration of the blood cells more accurately.In addition,the simultaneous detection of the light-scatter intensities in the forward-scatter,lateral-scatter,and back-scatter directions can help us to distinguish the different cell types from heterogeneous population of blood cells.It can be well used in cell classification and research of cell transfiguration.
Considering the difference between the real blood cells and their spheroid model for the scattering detection of cells,a model was presented to calculate the light scattering properties of nucleated cells which were mimicked by flat ellipsoid.The light-scattering characteristics were derived from the Rayleigh-Debye-Gans approximation and the volume polarizability.Results show that the model is superior to ball model.The model can reflect the true configuration of the blood cells more accurately.In addition,the simultaneous detection of the light-scatter intensities in the forward-scatter,lateral-scatter,and back-scatter directions can help us to distinguish the different cell types from heterogeneous population of blood cells.It can be well used in cell classification and research of cell transfiguration.
2007, 31(2): 160-162.
Abstract:
In order to improve the performance of lithium niobate acousto-electro-optic(AEO) modulator,the acousto-optic operating modes were systematically studied according to tangent condition after the determination of electro-optic operating mode.Acousto-optic merit for sheared ultrasonic wave in x-O-z plane and y-O-z plane were calculated respectively and the optimum operating mode for lithium niobate AEO modulator was determined.Furthermore,the design parameters for central frequency in range of 50MHz～300MHz were also given.By this optimum operating mode,the AEO device can gain a higher acousto-optic merit and achieve a higher diffractive efficiency.
In order to improve the performance of lithium niobate acousto-electro-optic(AEO) modulator,the acousto-optic operating modes were systematically studied according to tangent condition after the determination of electro-optic operating mode.Acousto-optic merit for sheared ultrasonic wave in x-O-z plane and y-O-z plane were calculated respectively and the optimum operating mode for lithium niobate AEO modulator was determined.Furthermore,the design parameters for central frequency in range of 50MHz～300MHz were also given.By this optimum operating mode,the AEO device can gain a higher acousto-optic merit and achieve a higher diffractive efficiency.
2007, 31(2): 163-165,174.
Abstract:
Both from experiments and theoretical analysis,the influenceof laser processing parameters on the case-depth and the hardness in laser quenching was studied.Under the condition of equal input laser energyand different laser power and scanning velocity,the variation of the case-depth and the hardness was measured.Measurement results show that the change of both the laser power and the scanning velocity can affect the case-depth and the hardness obviously and the change of laser power affects the case-depth more significantly.On the other hand,the change of either the laser power or the scanning velocity has a little influence on the hardness.Correspondingly,the change of the scanning velocity has a little more influence on the hardness.By means of analytical simulation of the temperature distribution and the heating/cooling rates under the laser scanning,reasonable explanation for the results was put forward.
Both from experiments and theoretical analysis,the influenceof laser processing parameters on the case-depth and the hardness in laser quenching was studied.Under the condition of equal input laser energyand different laser power and scanning velocity,the variation of the case-depth and the hardness was measured.Measurement results show that the change of both the laser power and the scanning velocity can affect the case-depth and the hardness obviously and the change of laser power affects the case-depth more significantly.On the other hand,the change of either the laser power or the scanning velocity has a little influence on the hardness.Correspondingly,the change of the scanning velocity has a little more influence on the hardness.By means of analytical simulation of the temperature distribution and the heating/cooling rates under the laser scanning,reasonable explanation for the results was put forward.
2007, 31(2): 166-168.
Abstract:
Study on electroluminescence from porous silicon(PS) has important application value in silicon-based photoelectron integration.Electrically induced visible light-emitting PS device with structure of ITO/PS/p-Si/Al were fabricated by means of evaporation-anodic oxidation method.The light emission of the device lasted for a few hours under 7.5V forward bias conditions.Luminescent and electronic properties were investigated.Results suggest that ITO thin films should have both high electrical conductivity and optical transmittance in order to achieve light-emitting PS device with fine luminescent and current-voltage properties.
Study on electroluminescence from porous silicon(PS) has important application value in silicon-based photoelectron integration.Electrically induced visible light-emitting PS device with structure of ITO/PS/p-Si/Al were fabricated by means of evaporation-anodic oxidation method.The light emission of the device lasted for a few hours under 7.5V forward bias conditions.Luminescent and electronic properties were investigated.Results suggest that ITO thin films should have both high electrical conductivity and optical transmittance in order to achieve light-emitting PS device with fine luminescent and current-voltage properties.
2007, 31(2): 169-171.
Abstract:
Atmospheric propagation delay is one of the main error sources for geodetic measurement.Its correction is necessary for accurate measurements.Atmospheric delay depends on many atmosphere parameters,especially atmosphere density,pressure,temperature,etc.Atmosphere parameter distribution changes with elevation angles,and so does the atmospheric delay.The total delay can be calculated from the zenith delay.The theoretic formula of the zenith delay is deduced,and a simplified mapping function for large elevation angles is proposed and compared with Mendes' new continued fraction form.The difference is less than 0.1mm for the total delay.Lastely,the system's mean total delay and its error is solved on the basis of geoscience laser altimeter system(GLAS) observation data in Antarctica,the results are 2.35m and 12mm respectively.
Atmospheric propagation delay is one of the main error sources for geodetic measurement.Its correction is necessary for accurate measurements.Atmospheric delay depends on many atmosphere parameters,especially atmosphere density,pressure,temperature,etc.Atmosphere parameter distribution changes with elevation angles,and so does the atmospheric delay.The total delay can be calculated from the zenith delay.The theoretic formula of the zenith delay is deduced,and a simplified mapping function for large elevation angles is proposed and compared with Mendes' new continued fraction form.The difference is less than 0.1mm for the total delay.Lastely,the system's mean total delay and its error is solved on the basis of geoscience laser altimeter system(GLAS) observation data in Antarctica,the results are 2.35m and 12mm respectively.
2007, 31(2): 172-174.
Abstract:
In order to measure the velocity history of the reflected surface or the internal particles velocity history of the materials under shock wave conditions,on the basis of the frequency-selecting principle of F-P optical resonator,a new type of velocity interferometer is developed,which makes use of the absolute magnitude of Doppler shift to continuously measure the moving of a flyer speed.The flyer is driven by a electric exploding foil,the magnitude of its speed can reach up to 3km/s within 60ns.Preliminary results show that the uncertainty in data is less than 5%.Compared with other laser interferometers,the lately developed thin cavity interferometer is compact,simple and low cost.So it can be widely used in the detonation and shock wave physics experimental research.
In order to measure the velocity history of the reflected surface or the internal particles velocity history of the materials under shock wave conditions,on the basis of the frequency-selecting principle of F-P optical resonator,a new type of velocity interferometer is developed,which makes use of the absolute magnitude of Doppler shift to continuously measure the moving of a flyer speed.The flyer is driven by a electric exploding foil,the magnitude of its speed can reach up to 3km/s within 60ns.Preliminary results show that the uncertainty in data is less than 5%.Compared with other laser interferometers,the lately developed thin cavity interferometer is compact,simple and low cost.So it can be widely used in the detonation and shock wave physics experimental research.
2007, 31(2): 175-178.
Abstract:
The holograhic transmission grating is recorded in the photopolymer,which is composed of the acrylamide radical monomers and sensitized by yellowish erosion.The effect of such factors as spatial frequency,exposure intensity and time on gratings' diffraction efficiency is studied with experimental method.The experimental results show that the grating spatial frequency,the exposure intensity and time have a preferable and related range where the diffraction efficiency could arrive at the maximum.When the grating's spatial frequency is near 2751line/mm,the exposure intensity is between 12mW and 15mW and the exposure energy is 770mJ/cm2,the diffraction efficiency arrives at the maximum.The maximun diffaction efficiency is about 75%,higher than some other holograhic gratings.
The holograhic transmission grating is recorded in the photopolymer,which is composed of the acrylamide radical monomers and sensitized by yellowish erosion.The effect of such factors as spatial frequency,exposure intensity and time on gratings' diffraction efficiency is studied with experimental method.The experimental results show that the grating spatial frequency,the exposure intensity and time have a preferable and related range where the diffraction efficiency could arrive at the maximum.When the grating's spatial frequency is near 2751line/mm,the exposure intensity is between 12mW and 15mW and the exposure energy is 770mJ/cm2,the diffraction efficiency arrives at the maximum.The maximun diffaction efficiency is about 75%,higher than some other holograhic gratings.
2007, 31(2): 179-181,184.
Abstract:
To investigate the practicability of a solar-directpumped fiber laser by using a parabolic dish concentrator,the solar power absorbed by the fiber laser and its absorption efficiency were calculated with numerical method based on the characteristics of solar spectrum in outer space.Results showed that it was realizable by taking such measures as using high inner-clad numerical aperture,appropriate rare-earth doped double-clad fiber and decreasing transmission loss of sunlight.In this paper,a new structure of multi-mode fiber array or parabolic dish concentrator array combination with tapered fiber bundles was proposed to enhance the solar pump power.
To investigate the practicability of a solar-directpumped fiber laser by using a parabolic dish concentrator,the solar power absorbed by the fiber laser and its absorption efficiency were calculated with numerical method based on the characteristics of solar spectrum in outer space.Results showed that it was realizable by taking such measures as using high inner-clad numerical aperture,appropriate rare-earth doped double-clad fiber and decreasing transmission loss of sunlight.In this paper,a new structure of multi-mode fiber array or parabolic dish concentrator array combination with tapered fiber bundles was proposed to enhance the solar pump power.
2007, 31(2): 182-184.
Abstract:
When high power laser transmits in the atmosphere,thermal blooming will be generated.In order to study the phenomenon,the effect parameters to steady-state thermal blooming without wind are solved in detail by numerical simulation.It is studied that both epaxial light intensity and energy distribution at far field are affected by steady-state thermal blooming without wind.The study results indicate that as emission power increases,the peak power density on the section of a certain distance will increase firstly,then it will descend and that the peak light intensity on the section will increase with the increasing of spot radius of basic mode Gaussian beam.As the propagation distance increases,the peak light intensity on the section will descend gradually,and the laser energy will spread.The light intensity distribution exhibits straw hat shape on a certain conditions,in other word to say,the central light intensity is less than acroteric light intensity.The results is helpful to the research of high power laser's irradiation effect at far field.
When high power laser transmits in the atmosphere,thermal blooming will be generated.In order to study the phenomenon,the effect parameters to steady-state thermal blooming without wind are solved in detail by numerical simulation.It is studied that both epaxial light intensity and energy distribution at far field are affected by steady-state thermal blooming without wind.The study results indicate that as emission power increases,the peak power density on the section of a certain distance will increase firstly,then it will descend and that the peak light intensity on the section will increase with the increasing of spot radius of basic mode Gaussian beam.As the propagation distance increases,the peak light intensity on the section will descend gradually,and the laser energy will spread.The light intensity distribution exhibits straw hat shape on a certain conditions,in other word to say,the central light intensity is less than acroteric light intensity.The results is helpful to the research of high power laser's irradiation effect at far field.
2007, 31(2): 185-187,191.
Abstract:
Based on the characteristic of space circumstance and space debris,the lidar equation in the space is deduced,and the space radiation is analyzed at length.The formula of the minimal detectable laser power is deduced in detail,and the minimal emitting laser power and the signal-to-noise ratio of the system are given where-after.The results indicate that the large space debris within dozens of kilometers can be detected with lidar.
Based on the characteristic of space circumstance and space debris,the lidar equation in the space is deduced,and the space radiation is analyzed at length.The formula of the minimal detectable laser power is deduced in detail,and the minimal emitting laser power and the signal-to-noise ratio of the system are given where-after.The results indicate that the large space debris within dozens of kilometers can be detected with lidar.
2007, 31(2): 188-191.
Abstract:
The advancement and actuality of detecting technology of multi-spectrum was introduced,the key technology and its development of detecting system of laser multi-spectrum scanning imaging were chiefly discussed.Based on the advantage of laser multi-spectrum active detection technology,it can be used in broad field such as control and guide,target identifying,terrain matching and other field that laser active detection can be used.
The advancement and actuality of detecting technology of multi-spectrum was introduced,the key technology and its development of detecting system of laser multi-spectrum scanning imaging were chiefly discussed.Based on the advantage of laser multi-spectrum active detection technology,it can be used in broad field such as control and guide,target identifying,terrain matching and other field that laser active detection can be used.
2007, 31(2): 192-195.
Abstract:
In order to study the mode and the phase characteristic of laser in an unstable resonator with Gaussian reflectivity mirrors,a finite element method is presented to numerically calculate mode-fields of the spherical plano-convex unstable resonator with Gaussian reflectivity mirrors,which is based on the canonical formulation of SIEGMAN's theory for analyzing multi-element unstable resonators.The round-trip cylindrical Huygen's integral is expressed for the resonator in terms of spherical resonator analysis and ABCDM matrix.The Huygen's integral is transformed to a finite sum format by dividing the output mirror into several width-equal circles.The eigenmode and phase result of self-reproduce field of perfect empty resonator and misalignment empty resonator are obtained via numerical calculation.The calculation result indicates that when the radius and Gaussian reflectivity of output mirror are appropriately selected,the fundamental mode distribution of Gaussian beam which has a spot radius of 0.3cm can be obtained.The calculation result accords with the experiment result.Simultaneously the influence of the output mirror on the beam quality is also discussed.
In order to study the mode and the phase characteristic of laser in an unstable resonator with Gaussian reflectivity mirrors,a finite element method is presented to numerically calculate mode-fields of the spherical plano-convex unstable resonator with Gaussian reflectivity mirrors,which is based on the canonical formulation of SIEGMAN's theory for analyzing multi-element unstable resonators.The round-trip cylindrical Huygen's integral is expressed for the resonator in terms of spherical resonator analysis and ABCDM matrix.The Huygen's integral is transformed to a finite sum format by dividing the output mirror into several width-equal circles.The eigenmode and phase result of self-reproduce field of perfect empty resonator and misalignment empty resonator are obtained via numerical calculation.The calculation result indicates that when the radius and Gaussian reflectivity of output mirror are appropriately selected,the fundamental mode distribution of Gaussian beam which has a spot radius of 0.3cm can be obtained.The calculation result accords with the experiment result.Simultaneously the influence of the output mirror on the beam quality is also discussed.
2007, 31(2): 196-199.
Abstract:
Based on a 3-D transient thermal model with inhomogeneous heat generation,the temperature and thermal stress distribution in the disk of heat capacity laser pumped by high power laser diode array(LDA) are simulated and analyzed by means of finite element methods.The results indicate that for the same pump intensity,the temperature and thermal stress distribution in the disk are not only related with the medium's geometry and the special distribution of pump intensity but also related with the fill factor of pump area.When the fill factor is less than 1,the concentrated tensile stress appeares near edge of disk surface,while the fill factor reaches up to 1,the surface exhibites compressive stress,and the center is less tensile stress.
Based on a 3-D transient thermal model with inhomogeneous heat generation,the temperature and thermal stress distribution in the disk of heat capacity laser pumped by high power laser diode array(LDA) are simulated and analyzed by means of finite element methods.The results indicate that for the same pump intensity,the temperature and thermal stress distribution in the disk are not only related with the medium's geometry and the special distribution of pump intensity but also related with the fill factor of pump area.When the fill factor is less than 1,the concentrated tensile stress appeares near edge of disk surface,while the fill factor reaches up to 1,the surface exhibites compressive stress,and the center is less tensile stress.
2007, 31(2): 200-202.
Abstract:
In order to improve the technology in atmosphere detection and explore new,faster,and more accurate methods to retrieve atmosphere visibility,the atmosphere visibility was simultaneously measured in Qingdao with a micro-pulsed lidar,designed by Ocean Remote Sensing Laboratory,Ocean University of China,and a NQ-1 commercial visibility meter respectively.The results indicate both has a high correlation coefficient up to 0.88 when the visibility is poor or moderate and the their correlation coefficients are above 0.73 in good visibility conditions,which indicates it is feasible for micro-pulsed lidars to measure the visibility.
In order to improve the technology in atmosphere detection and explore new,faster,and more accurate methods to retrieve atmosphere visibility,the atmosphere visibility was simultaneously measured in Qingdao with a micro-pulsed lidar,designed by Ocean Remote Sensing Laboratory,Ocean University of China,and a NQ-1 commercial visibility meter respectively.The results indicate both has a high correlation coefficient up to 0.88 when the visibility is poor or moderate and the their correlation coefficients are above 0.73 in good visibility conditions,which indicates it is feasible for micro-pulsed lidars to measure the visibility.
Propagation properties of hollow Gaussian beams through an optical system with a hard-edged aperture
2007, 31(2): 203-205,208.
Abstract:
In order to study propagation properties of hollow beams through a paraxial optical ABCD system with a hard-edged circle aperture and a lens,the expressions for the propagation of hollow Gaussian beams through such a system are derived based on the Collins diffraction integral.The effects of an aperture,a lens and an aperture-lens system on the propagation properties of hollow Gaussian beams are studied and illustrated with numerical examples,which shows that both aperture and lens can shift the field of hollow Gaussian beams towards the source plane.It is also found that hollowness of the beam will be destroyed by the aperture,but not by the lens.The results of this study play a guiding role in the generation and application of hollow beams.
In order to study propagation properties of hollow beams through a paraxial optical ABCD system with a hard-edged circle aperture and a lens,the expressions for the propagation of hollow Gaussian beams through such a system are derived based on the Collins diffraction integral.The effects of an aperture,a lens and an aperture-lens system on the propagation properties of hollow Gaussian beams are studied and illustrated with numerical examples,which shows that both aperture and lens can shift the field of hollow Gaussian beams towards the source plane.It is also found that hollowness of the beam will be destroyed by the aperture,but not by the lens.The results of this study play a guiding role in the generation and application of hollow beams.
2007, 31(2): 206-208.
Abstract:
In order to break through the choke point of the traditional design of a telephoto lens,how to eliminate aberrance by means of hybrid refraction-diffraction was studied from the view of the phase polynomial of diffractive surface and phase transformation polynomial of general lens.The telephoto lens system consisted of only two pieces of optical elements made of FK1 glass has an equivalent optical performance to the traditional telephoto lens system made of five pieces of optical elements made of defferent kinds of glass.Which shows that the hybrid refractive-diffractive lens can effectively eliminate the aberrance of a telephoto lens with lower weight and simple structure.
In order to break through the choke point of the traditional design of a telephoto lens,how to eliminate aberrance by means of hybrid refraction-diffraction was studied from the view of the phase polynomial of diffractive surface and phase transformation polynomial of general lens.The telephoto lens system consisted of only two pieces of optical elements made of FK1 glass has an equivalent optical performance to the traditional telephoto lens system made of five pieces of optical elements made of defferent kinds of glass.Which shows that the hybrid refractive-diffractive lens can effectively eliminate the aberrance of a telephoto lens with lower weight and simple structure.
2007, 31(2): 209-212,216.
Abstract:
In order to get the depolarization performance of a dualistic birefringent crystal,the performance of white light through it with different optical axis angles and thicknesses was dicussed.A the performance of the single crystal depolarizer and the Lyot depolarizer was proved through experiments.Some conclusions are drawn as follows:there are some indirect impacts on polarization with different optical axis angles;the thickness has a vital impact on polarization;the ratio of the thickness has a direct impact on polarization.These conclusions can give theoretic analysis and reference to the design and application of the depolarizers.
In order to get the depolarization performance of a dualistic birefringent crystal,the performance of white light through it with different optical axis angles and thicknesses was dicussed.A the performance of the single crystal depolarizer and the Lyot depolarizer was proved through experiments.Some conclusions are drawn as follows:there are some indirect impacts on polarization with different optical axis angles;the thickness has a vital impact on polarization;the ratio of the thickness has a direct impact on polarization.These conclusions can give theoretic analysis and reference to the design and application of the depolarizers.
2007, 31(2): 213-216.
Abstract:
The collapse behavior of Langmuir waves excited by laser near critical surface is numerically studied.On the basis of Zakharov equations in frame of strong turbulence,it is shown that Langmuir waves excited by transverse pumping plasmons near critical surface may collapse,leading to the formation of density cavity due to ponderomotive force.The interaction will lead to tendency of an equilibration of energy over both of transverse and Langmuir plasmons with the same frequencies near ωp,which is agreement with our numerical analysis.The value of width of the density cavity estimated is similar to the experimental result.
The collapse behavior of Langmuir waves excited by laser near critical surface is numerically studied.On the basis of Zakharov equations in frame of strong turbulence,it is shown that Langmuir waves excited by transverse pumping plasmons near critical surface may collapse,leading to the formation of density cavity due to ponderomotive force.The interaction will lead to tendency of an equilibration of energy over both of transverse and Langmuir plasmons with the same frequencies near ωp,which is agreement with our numerical analysis.The value of width of the density cavity estimated is similar to the experimental result.
2007, 31(2): 217-219.
Abstract:
In order to meet the needs of variable pulse width,frequency and power for laser fuze,a model of the LD driver circuit is built up based on its principle.By using monostable multivibrators to provide the trigger signal,and using the double MOS driver to drive the LD,a variable high power LD driver circuit,which can meet the requirement of pulse width,frequency and power of laser fuze,is designed through a lot of experiments,emulation and comparison.
In order to meet the needs of variable pulse width,frequency and power for laser fuze,a model of the LD driver circuit is built up based on its principle.By using monostable multivibrators to provide the trigger signal,and using the double MOS driver to drive the LD,a variable high power LD driver circuit,which can meet the requirement of pulse width,frequency and power of laser fuze,is designed through a lot of experiments,emulation and comparison.
2007, 31(2): 220-224.
Abstract:
The characteristics of laser cladding and its application status quo in surface modification of metallic alloys is introduced,and then the research status quo of fabrication of functionally gradient coating using laser cladding is reviewed.After analysis,it can be found that the different thermophysical parameters between the reinforced particle and matrix are the main reason to cause crack and failure of coating.Fabrication of in-situ synthesized and functionally gradient composite coating or components using laser direct fabrication technique is the future development direction.
The characteristics of laser cladding and its application status quo in surface modification of metallic alloys is introduced,and then the research status quo of fabrication of functionally gradient coating using laser cladding is reviewed.After analysis,it can be found that the different thermophysical parameters between the reinforced particle and matrix are the main reason to cause crack and failure of coating.Fabrication of in-situ synthesized and functionally gradient composite coating or components using laser direct fabrication technique is the future development direction.
