Map
WeChat
Email alert
RSS2009 Vol. 33, No. 2
Display Method:
2009, 33(2): 113-116.
[Abstract]
[PDF 306KB]
Abstract:
In order to obtain good quality and high-dense wavelength division multiplexing (DWDM) devices,the diffraction property of volume holographic gratings, produced in an iron and indium co-doped LiNbO3 crystal by means of the transmission writing and orthogonal readout (TWOR) scheme,was analyzed theoretically and verified experimentally.The volume holographic grating with a grating size ratio of 1:1 was recorded at the laser wavelength of 532nm, and was successfully read out by using a tunable laser at the central wavelength around 1550nm.Correspondingly, the wavelength selectivity of 0.5nm was achieved, which was measured as the 3dB bandwidth of the diffraction efficiency curve.Meanwhile, the relationship of diffraction efficiency versus reading wavelength for such a volume holographic grating was obtained with the corrected solution to the 2-D coupled-wave equation in closed mathematical form.The experimental results agreed with the theoretical prediction well,and they show that the presented method is helpful for making a practical holographic grating DWDM device.
In order to obtain good quality and high-dense wavelength division multiplexing (DWDM) devices,the diffraction property of volume holographic gratings, produced in an iron and indium co-doped LiNbO3 crystal by means of the transmission writing and orthogonal readout (TWOR) scheme,was analyzed theoretically and verified experimentally.The volume holographic grating with a grating size ratio of 1:1 was recorded at the laser wavelength of 532nm, and was successfully read out by using a tunable laser at the central wavelength around 1550nm.Correspondingly, the wavelength selectivity of 0.5nm was achieved, which was measured as the 3dB bandwidth of the diffraction efficiency curve.Meanwhile, the relationship of diffraction efficiency versus reading wavelength for such a volume holographic grating was obtained with the corrected solution to the 2-D coupled-wave equation in closed mathematical form.The experimental results agreed with the theoretical prediction well,and they show that the presented method is helpful for making a practical holographic grating DWDM device.
2009, 33(2): 117-120.
Abstract:
To prepare the high properties Al-Y coating, laser cladding was carried out with a CO2 laser by melting the preplaced Al+Y powder on the surface of 2034 Al-based alloy.SEM, XRD, EMS and micro-hardmeter were used to analyze the microstructure, components, element distribution and micro-hardness of the cladding layer.The Al-Y coating mainly consisted of Al, Y5Al3, YAl3 and YAl phases, and Y was mostly found on the grain boundary and at the interspaces of the grains.The micro-hardness measurement of the coating was in the range of 70HV0.2～95HV0.2, which was lower than 100HV0.2～120HV0.2 of the base material for decreasing the effect of solid solution strengthening of Cu element.The results show that the clad layer and the base metal are joined by the metallurgical bonding,and it has obvious finer microstructure.
To prepare the high properties Al-Y coating, laser cladding was carried out with a CO2 laser by melting the preplaced Al+Y powder on the surface of 2034 Al-based alloy.SEM, XRD, EMS and micro-hardmeter were used to analyze the microstructure, components, element distribution and micro-hardness of the cladding layer.The Al-Y coating mainly consisted of Al, Y5Al3, YAl3 and YAl phases, and Y was mostly found on the grain boundary and at the interspaces of the grains.The micro-hardness measurement of the coating was in the range of 70HV0.2～95HV0.2, which was lower than 100HV0.2～120HV0.2 of the base material for decreasing the effect of solid solution strengthening of Cu element.The results show that the clad layer and the base metal are joined by the metallurgical bonding,and it has obvious finer microstructure.
2009, 33(2): 121-123.
Abstract:
High reflective metal materials have some disadvantages on laser heat treatment.In order to increase the laser absorption of metal materials, the effect of external applied electric field on the laser absorption was studied.A so-called saturated temperature technique was put forward to measure the laser absorptivity of 2Cr13 stainless steel with external applied electric field applied.The test results indicated the external electric field could increase the laser absoptivity of metal materials.
High reflective metal materials have some disadvantages on laser heat treatment.In order to increase the laser absorption of metal materials, the effect of external applied electric field on the laser absorption was studied.A so-called saturated temperature technique was put forward to measure the laser absorptivity of 2Cr13 stainless steel with external applied electric field applied.The test results indicated the external electric field could increase the laser absoptivity of metal materials.
2009, 33(2): 124-126,137.
Abstract:
To increase the cladding efficiency and eliminate the cracks in the cladding layer,laser-induction hybrid cladding was adopted to obtain Ni-based WC composite coatings without porosities and cracks.The influence of processing parameters on the composite coatings by means of laser-induction hybrid cladding was investigated.The results showed that the area density of deposition powder had an increase with increasing laser specific energy.At the same laser specific energy, the cladding height increased and the dilution decreased with increasing area density of deposition powder.When the area density of deposition powder kept constant, the cladding width slightly increased and the contact angle decreased with increasing laser specific energy.Moreover,due to introduction of induction heater,the efficiency of laser-induction hybrid cladding was increased about five times higher than that of the individual laser cladding.As a result,the temperature gradient during laser-induction hybrid cladding was much lower than that during the general laser cladding, which was the main reason that no cracks appeared in Ni-based WC composite coatings.
To increase the cladding efficiency and eliminate the cracks in the cladding layer,laser-induction hybrid cladding was adopted to obtain Ni-based WC composite coatings without porosities and cracks.The influence of processing parameters on the composite coatings by means of laser-induction hybrid cladding was investigated.The results showed that the area density of deposition powder had an increase with increasing laser specific energy.At the same laser specific energy, the cladding height increased and the dilution decreased with increasing area density of deposition powder.When the area density of deposition powder kept constant, the cladding width slightly increased and the contact angle decreased with increasing laser specific energy.Moreover,due to introduction of induction heater,the efficiency of laser-induction hybrid cladding was increased about five times higher than that of the individual laser cladding.As a result,the temperature gradient during laser-induction hybrid cladding was much lower than that during the general laser cladding, which was the main reason that no cracks appeared in Ni-based WC composite coatings.
2009, 33(2): 127-129,133.
Abstract:
In order to study the photon localization property of photonic crystal, the localized field distribution of defect modes was computed by means of the optical transmission matrix method.The concept of relative localization length was introduced, which represents the degree of the localization of photons.The shorter the length, the more stronger the degree, and vice versa.The results show that the localization of photons in the structure with a defect layer bordering on high refractive index layers is stronger than that bordering on low refractive index layers.For the former structure, if the condition of resonance Bragg scattering or Mie scattering was satisfied, the relative localization length become smaller.
In order to study the photon localization property of photonic crystal, the localized field distribution of defect modes was computed by means of the optical transmission matrix method.The concept of relative localization length was introduced, which represents the degree of the localization of photons.The shorter the length, the more stronger the degree, and vice versa.The results show that the localization of photons in the structure with a defect layer bordering on high refractive index layers is stronger than that bordering on low refractive index layers.For the former structure, if the condition of resonance Bragg scattering or Mie scattering was satisfied, the relative localization length become smaller.
2009, 33(2): 130-133.
Abstract:
In order to retrive the particles emitted by vehicles with lidar.Firstly, the relation between backscattering coefficient and mass concentration was studied in theory.Then based on the baekscattering coefficient measured with lidar and aerosol mass concentration measured with aethalometer, the correlation between them and the correlation between the backscattering coefficient and vehicle flow are analyzed.Conclusions are drawn; it's possible to inverse the backscattering coefficient into the mass concentration because of their linear relation.The horizontal distribution and scattering characteristics of the particles emitted by vehicles can be studied because the aerosol mass concentration is consistent with the vehicle flow.The results are useful for vehicles management and air pollution control.
In order to retrive the particles emitted by vehicles with lidar.Firstly, the relation between backscattering coefficient and mass concentration was studied in theory.Then based on the baekscattering coefficient measured with lidar and aerosol mass concentration measured with aethalometer, the correlation between them and the correlation between the backscattering coefficient and vehicle flow are analyzed.Conclusions are drawn; it's possible to inverse the backscattering coefficient into the mass concentration because of their linear relation.The horizontal distribution and scattering characteristics of the particles emitted by vehicles can be studied because the aerosol mass concentration is consistent with the vehicle flow.The results are useful for vehicles management and air pollution control.
2009, 33(2): 134-137.
Abstract:
In order to measure the optical trap force, how two beams with optical off-axes in one plane generate an interference field was introduced, based on which a so-called interferometric optical tweezers was built up.Firstly how two coplanar laser beams at a certain angle interfered was analyzed,i.e.,the principle of two-dimension optical tweezers,then the principle of the three-dimension optical tweezers was presented.After analyzing the force acting on the polystyrene beads, the analytical and experimental data of the optical trap force were obtained.The result showed that interferometric optical tweezers could provide cross trap force about pico-Newton level and achieve optical trapping,the experiment data accorded with the theoretic results very well when only the optical power and the full width half maximum of the beam were considered.The result is very helpful to optical tweezers' application in biology, biomedicine and nano-technology.
In order to measure the optical trap force, how two beams with optical off-axes in one plane generate an interference field was introduced, based on which a so-called interferometric optical tweezers was built up.Firstly how two coplanar laser beams at a certain angle interfered was analyzed,i.e.,the principle of two-dimension optical tweezers,then the principle of the three-dimension optical tweezers was presented.After analyzing the force acting on the polystyrene beads, the analytical and experimental data of the optical trap force were obtained.The result showed that interferometric optical tweezers could provide cross trap force about pico-Newton level and achieve optical trapping,the experiment data accorded with the theoretic results very well when only the optical power and the full width half maximum of the beam were considered.The result is very helpful to optical tweezers' application in biology, biomedicine and nano-technology.
2009, 33(2): 138-140.
Abstract:
In order to study the principle of laser-induced discharge breakdown and reduce the breakdown voltage (U50) to overcome the processing risk, the relationships between U50 and some factors were carried out, including the single pulse energy, the distance between the electrodes and the cathode materials.It was confirmed that the channel could be broken down effectively only when the surface of the workpiece was vaporized by the laser with the single pulse energy W≤0.15mJ.The breakdown voltage would decrease with the increasing of the single pulse energy.When the cathode material was made of 45 steel, U50 rose with the increase of the distance between the electrodes.And when increasing the single pulse energy,the rising trend would be slowed down obviously.Altering the cathode material with other conditions kept unchanged, it was found that the copper could reduce the U50, compared to graphite.So the effective measure of reducing the U50 is increasing the single pulse energy, decreasing the distance between the electrodes, and using smaller work function and lower melting point material as the cathode materials.
In order to study the principle of laser-induced discharge breakdown and reduce the breakdown voltage (U50) to overcome the processing risk, the relationships between U50 and some factors were carried out, including the single pulse energy, the distance between the electrodes and the cathode materials.It was confirmed that the channel could be broken down effectively only when the surface of the workpiece was vaporized by the laser with the single pulse energy W≤0.15mJ.The breakdown voltage would decrease with the increasing of the single pulse energy.When the cathode material was made of 45 steel, U50 rose with the increase of the distance between the electrodes.And when increasing the single pulse energy,the rising trend would be slowed down obviously.Altering the cathode material with other conditions kept unchanged, it was found that the copper could reduce the U50, compared to graphite.So the effective measure of reducing the U50 is increasing the single pulse energy, decreasing the distance between the electrodes, and using smaller work function and lower melting point material as the cathode materials.
2009, 33(2): 141-144.
Abstract:
In order to study the effect of the surface temperature of reflector under the laser irradiation during laser propulsion,a self-designed temperature measurement system was adopted to measure the surface temperature of the rotating parabolic aluminum target under the irradiation of different laser power,the temperature vs.time curves in different conditions was obtained.The results show that the laser absorptivity increases with the incidence angle; the surface temperature depends on the radial distance from irradiating position according to the Gaussian distribution function.The inadiation position has different rising and lowering temperature features compared with other positions.The temperatures on the surface tend to be the same and follow the same thermal diffusion and temperature lowing curve since several seconds after switching off the laser irradiation.
In order to study the effect of the surface temperature of reflector under the laser irradiation during laser propulsion,a self-designed temperature measurement system was adopted to measure the surface temperature of the rotating parabolic aluminum target under the irradiation of different laser power,the temperature vs.time curves in different conditions was obtained.The results show that the laser absorptivity increases with the incidence angle; the surface temperature depends on the radial distance from irradiating position according to the Gaussian distribution function.The inadiation position has different rising and lowering temperature features compared with other positions.The temperatures on the surface tend to be the same and follow the same thermal diffusion and temperature lowing curve since several seconds after switching off the laser irradiation.
2009, 33(2): 145-146,150.
Abstract:
Laser power has important influence on the cutting quality,and the burning defect is easy to happen if the laser power is too high.In order to guarantee the cutting quality,a real-time power control method based on programmable multiple axes controller was presented to study the relationship between laser power and cutting speed.The analysis of laser cutting test shows that burning defect can be avoided when laser power can change with the cutting speed, the cutting quality can be improved effectively by this method,and efficiency of laser cutting is guaranteed.
Laser power has important influence on the cutting quality,and the burning defect is easy to happen if the laser power is too high.In order to guarantee the cutting quality,a real-time power control method based on programmable multiple axes controller was presented to study the relationship between laser power and cutting speed.The analysis of laser cutting test shows that burning defect can be avoided when laser power can change with the cutting speed, the cutting quality can be improved effectively by this method,and efficiency of laser cutting is guaranteed.
2009, 33(2): 147-150.
Abstract:
In order to solve the forming difficulty occurring in the microforming microparts made of hard-to-deform materials, the experimental study on laser-assisted heating of the micropart of aluminum alloy was performed by means of pulsed laser.With the help of ABAQUS finite element software, the coupled thermomechanical finite element model of microupset was built up based on laser-assisted heating method.Then the temperature distribution of the workpiece and microforming process were simulated and analyzed.The results show that the temperature field distributions are oval and flatting with the certain laser parameters (laser power is 800mW,heating time is 0.08s and spot radius is 0.1mm), and that the temperature distribution is uniform after a very short time.The microforming stress using laser-heating method decreased about 30% compared with that of room temperature.The obtained results are helpful to improve the microforming properties of plastic materials and perfect micro-hot and microwarm forming process.
In order to solve the forming difficulty occurring in the microforming microparts made of hard-to-deform materials, the experimental study on laser-assisted heating of the micropart of aluminum alloy was performed by means of pulsed laser.With the help of ABAQUS finite element software, the coupled thermomechanical finite element model of microupset was built up based on laser-assisted heating method.Then the temperature distribution of the workpiece and microforming process were simulated and analyzed.The results show that the temperature field distributions are oval and flatting with the certain laser parameters (laser power is 800mW,heating time is 0.08s and spot radius is 0.1mm), and that the temperature distribution is uniform after a very short time.The microforming stress using laser-heating method decreased about 30% compared with that of room temperature.The obtained results are helpful to improve the microforming properties of plastic materials and perfect micro-hot and microwarm forming process.
2009, 33(2): 151-155,158.
Abstract:
In order to study the characteristics and the future development direction of terahertz two-dimension imaging methods based on CO2 laser-pumped far-infrared laser source, the basic principle of CO2 laser-pumped far-infrared laser source and two typical lasers,SIFIR-50FPL and FIRL100 made in USA and England respectively, were introduced.Then the domestic and international research results of imaging in recent years and their imaging characteristics were discussed.Finally it was concluded that the long-distance three-dimension image THz radar, the real-time imaging focal plane array (FPA) detection and the real-time image processing and automatic target recognition system were the development trends of the research of CO2 laserpumped terahertz imaging.
In order to study the characteristics and the future development direction of terahertz two-dimension imaging methods based on CO2 laser-pumped far-infrared laser source, the basic principle of CO2 laser-pumped far-infrared laser source and two typical lasers,SIFIR-50FPL and FIRL100 made in USA and England respectively, were introduced.Then the domestic and international research results of imaging in recent years and their imaging characteristics were discussed.Finally it was concluded that the long-distance three-dimension image THz radar, the real-time imaging focal plane array (FPA) detection and the real-time image processing and automatic target recognition system were the development trends of the research of CO2 laserpumped terahertz imaging.
2009, 33(2): 156-158.
Abstract:
In order to use the wave-plate better within the band with crystal dichroism,the effect of the dichroism on the circular polarized light induced by a λ/4 wave-plate, the plane of polarization rotated by a λ/2 wave-plate and the output amplitude was analyzed respectively based on matrix optics.Because of dichroic absorption of the crystal, the transmitted ray becomes elliptical polarized light instead of circular polarized light when the optical vector of the linear polarized light inputs at 45° with respect to the fast axis of the λ/4 wave-plate.For a λ/4 wave-plate,only when tan θ=exp(-△ad), the transmitted ray is circular polarized light with lower amplitude.As to a λ/2 wave-plate,with dichroism taken into account,the rotation angle of the optical vector of the linear polarized light is not twice as the angle between the optical vector of the incident light and the fast axis of the wave-plate.The rotation angle and amplitude are the function of the dichroic absorption coefficient and the angle between the vector of the incident light and the optical axis of the crystal.The results show that the crystal dichroism of the wave-plate cannot be ignored,it should be paid more attention.
In order to use the wave-plate better within the band with crystal dichroism,the effect of the dichroism on the circular polarized light induced by a λ/4 wave-plate, the plane of polarization rotated by a λ/2 wave-plate and the output amplitude was analyzed respectively based on matrix optics.Because of dichroic absorption of the crystal, the transmitted ray becomes elliptical polarized light instead of circular polarized light when the optical vector of the linear polarized light inputs at 45° with respect to the fast axis of the λ/4 wave-plate.For a λ/4 wave-plate,only when tan θ=exp(-△ad), the transmitted ray is circular polarized light with lower amplitude.As to a λ/2 wave-plate,with dichroism taken into account,the rotation angle of the optical vector of the linear polarized light is not twice as the angle between the optical vector of the incident light and the fast axis of the wave-plate.The rotation angle and amplitude are the function of the dichroic absorption coefficient and the angle between the vector of the incident light and the optical axis of the crystal.The results show that the crystal dichroism of the wave-plate cannot be ignored,it should be paid more attention.
2009, 33(2): 159-161,216.
Abstract:
In order to study the photoresponse properties of photodetectors with different configuration, the ultraviolet photodetectors were prepared on ZnO substrate by means of pulsed laser deposition (PLD) method.It could be seen that the ZnO film was heteromorphic and had good stoichiometric composition and uniform crystal size of 60nm, under the X-ray diffraction (XRD) pattern, the photoluminescence (PL) spectrum and the scanning electron microscopy (SEM), respectively.After comparing the photoresponse characteristics of the photodetectors with planar electrode configuration and sandwiched electrode configuration,a conclusion can be drawn that the photodetector configuration has a great effect on the response time.Considering the competition between response time and responsivity in planar electrode configuration photodetectors, the sandwiched electrode configuration photodetectors with transparent electrode are preferable.
In order to study the photoresponse properties of photodetectors with different configuration, the ultraviolet photodetectors were prepared on ZnO substrate by means of pulsed laser deposition (PLD) method.It could be seen that the ZnO film was heteromorphic and had good stoichiometric composition and uniform crystal size of 60nm, under the X-ray diffraction (XRD) pattern, the photoluminescence (PL) spectrum and the scanning electron microscopy (SEM), respectively.After comparing the photoresponse characteristics of the photodetectors with planar electrode configuration and sandwiched electrode configuration,a conclusion can be drawn that the photodetector configuration has a great effect on the response time.Considering the competition between response time and responsivity in planar electrode configuration photodetectors, the sandwiched electrode configuration photodetectors with transparent electrode are preferable.
2009, 33(2): 162-165.
Abstract:
Because ultra short optical pulses can be obtained from a mode-locked fiber laser, it can be applied in many fields.The principle, structure and new evolution of mode-locked fiber lasers were summarized in this paper.The advantage, disadvantages of active,passive and mixed mode-locked technology were analyzed.The new evolution of multi-wavelength mode-lock, stretched pulse mode-lock and photonic crystal based mode-locked techniques were introduced.Finally the latest evolution of mode-locked fiber lasers was discussed and the key issues were pointed out.
Because ultra short optical pulses can be obtained from a mode-locked fiber laser, it can be applied in many fields.The principle, structure and new evolution of mode-locked fiber lasers were summarized in this paper.The advantage, disadvantages of active,passive and mixed mode-locked technology were analyzed.The new evolution of multi-wavelength mode-lock, stretched pulse mode-lock and photonic crystal based mode-locked techniques were introduced.Finally the latest evolution of mode-locked fiber lasers was discussed and the key issues were pointed out.
2009, 33(2): 166-168.
Abstract:
In order to study the output characteristics of diode-end-pumped Nd: YAP laser operating at 1341.4nm,the thermal focal lengths of end-pumped Nd:YAP laser were calculated and measured, and the output results of lasers with plane-plane and plano-concave resonators were compared respectively.Making use of plane-concave resonator with the coupler transmission of 2.4% and plane-plane cavity with the coupler transmission of 2.6%,3.15W and 2.86W linearly polarized laser radiation at 1341.4 nm were obtained,respectively,corresponding optical slope efficiency of 18.4% and 17.5%.The results show that Nd:YAP laser crystal owns the potential advantages on 1.3μm laser.
In order to study the output characteristics of diode-end-pumped Nd: YAP laser operating at 1341.4nm,the thermal focal lengths of end-pumped Nd:YAP laser were calculated and measured, and the output results of lasers with plane-plane and plano-concave resonators were compared respectively.Making use of plane-concave resonator with the coupler transmission of 2.4% and plane-plane cavity with the coupler transmission of 2.6%,3.15W and 2.86W linearly polarized laser radiation at 1341.4 nm were obtained,respectively,corresponding optical slope efficiency of 18.4% and 17.5%.The results show that Nd:YAP laser crystal owns the potential advantages on 1.3μm laser.
2009, 33(2): 169-171,190.
Abstract:
The modulating characteristics of Mach-Zehnder modulator and pulse-amplitude equalization condition were demonstrated in detail.By adjusting the direct-current bias voltage and modulation depth,the shape of transmission curve can be controlled.Mode locking pulse train and the modulator transmission curve were numerically studied in time domain at 5GHz of modulation frequency.The pulse train and modulation curves for mode-locking pulse in the second to seventh order were simulated and analyzed with MATLAB software.The numerical result shows that: equalization of pulse-amplitude occurs only when the transmission coefficient in the modulator is uniform; amplitude-equalized pulses can be obtained both in the linear region and the nonlinear region; when the rational harmonic mode-locking order p is larger than 4, the value of modulation depth affects the pulse-amplitude equalization severely.The figure in the paper is laconic and the result is helpful to get amplitude equalized mode-locked pulses in experiments.
The modulating characteristics of Mach-Zehnder modulator and pulse-amplitude equalization condition were demonstrated in detail.By adjusting the direct-current bias voltage and modulation depth,the shape of transmission curve can be controlled.Mode locking pulse train and the modulator transmission curve were numerically studied in time domain at 5GHz of modulation frequency.The pulse train and modulation curves for mode-locking pulse in the second to seventh order were simulated and analyzed with MATLAB software.The numerical result shows that: equalization of pulse-amplitude occurs only when the transmission coefficient in the modulator is uniform; amplitude-equalized pulses can be obtained both in the linear region and the nonlinear region; when the rational harmonic mode-locking order p is larger than 4, the value of modulation depth affects the pulse-amplitude equalization severely.The figure in the paper is laconic and the result is helpful to get amplitude equalized mode-locked pulses in experiments.
2009, 33(2): 172-175,179.
Abstract:
In order to obtain certain laser pulse with millijoule(mJ) order energy and nanosecond(ns) order pulse width after amplifying the pulsed seed laser, and to find the impact of repetition rate and simulated Raman scattering on laser pulse output, the dynamic model of a three-class ytterbium-doped double-clad fiber pulsed amplifier was established on the base of master oscillator power amplifier.Then the pulse energy,peak power,average power,pulse width and stimulated Raman scattering effect,arose from an amplifier of the pulsed seed laser with 10nJ energy and 100ns pulse width at different pulse repetition frequency,were simulated.The simulation results show that output laser energy and waveform are so slightly affected by the frequency that its effect can be ignored when the pulse repetition frequency is less than 200Hz,and that the Raman effect almost has little impact on the output property of each class amplifier if suitable parameters are selected.According to the numerical analysis,mJ order energy can be obtained from a three-class fiber amplifier with suitable parameters.
In order to obtain certain laser pulse with millijoule(mJ) order energy and nanosecond(ns) order pulse width after amplifying the pulsed seed laser, and to find the impact of repetition rate and simulated Raman scattering on laser pulse output, the dynamic model of a three-class ytterbium-doped double-clad fiber pulsed amplifier was established on the base of master oscillator power amplifier.Then the pulse energy,peak power,average power,pulse width and stimulated Raman scattering effect,arose from an amplifier of the pulsed seed laser with 10nJ energy and 100ns pulse width at different pulse repetition frequency,were simulated.The simulation results show that output laser energy and waveform are so slightly affected by the frequency that its effect can be ignored when the pulse repetition frequency is less than 200Hz,and that the Raman effect almost has little impact on the output property of each class amplifier if suitable parameters are selected.According to the numerical analysis,mJ order energy can be obtained from a three-class fiber amplifier with suitable parameters.
2009, 33(2): 176-179.
Abstract:
In order to calculate the optical transmittance of water vapor in the strong absorption bands fleetly,the application of the correlated k-distribution(CkD) method in the calculation of the optical transmittance of water vapor in the strong absorption bands was studied, and the corresponding program was designed and developed.The technical details in the CkD method, including the chose of integration grid points, the interpolation of the absorption coefficients in the inhomogeneous atmosphere was also discussed.Tested on the six standard atmospheric models, good results were obtained.The results indicate that the CkD algorithm is accurate and efficient in the calculation of atmospheric transmittance of water vapor in the strong absorption bands, and the CkD practical in actual application.
In order to calculate the optical transmittance of water vapor in the strong absorption bands fleetly,the application of the correlated k-distribution(CkD) method in the calculation of the optical transmittance of water vapor in the strong absorption bands was studied, and the corresponding program was designed and developed.The technical details in the CkD method, including the chose of integration grid points, the interpolation of the absorption coefficients in the inhomogeneous atmosphere was also discussed.Tested on the six standard atmospheric models, good results were obtained.The results indicate that the CkD algorithm is accurate and efficient in the calculation of atmospheric transmittance of water vapor in the strong absorption bands, and the CkD practical in actual application.
2009, 33(2): 180-183,186.
Abstract:
In order to analyze the property of optical soliton communication system, split-step Fourier method was used to calculate the nonlinear Schrödinger equations.The simulation results showed that the transmission characteristics of pulse became deteriorated as the parameters of polarization mode dispersion increased.At last, the interaction between solitions was analyzed and the measure for improving the optical soliton communication system was proposed.
In order to analyze the property of optical soliton communication system, split-step Fourier method was used to calculate the nonlinear Schrödinger equations.The simulation results showed that the transmission characteristics of pulse became deteriorated as the parameters of polarization mode dispersion increased.At last, the interaction between solitions was analyzed and the measure for improving the optical soliton communication system was proposed.
2009, 33(2): 184-186.
Abstract:
The spectral characteristics of the displacement of the parallel beam splitting prism,made of iceland crystal,were analyzed theoretically and experimentally.The results indicated that,the maximum angle between the e rays and the e waves,and the displacement of the prism were influenced by the wavelength of the incident light.For a common parallel beam splitting prism with certain length, the displacement decreased with the increase of the wavelength of incident light, and the influence of the wavelength on the walk-off angle in the ultraviolet wave band was larger than that in visible and near-infrared wave band.The obtained result is favor for the design and application of parallel beam splitting prisms in wider scope.
The spectral characteristics of the displacement of the parallel beam splitting prism,made of iceland crystal,were analyzed theoretically and experimentally.The results indicated that,the maximum angle between the e rays and the e waves,and the displacement of the prism were influenced by the wavelength of the incident light.For a common parallel beam splitting prism with certain length, the displacement decreased with the increase of the wavelength of incident light, and the influence of the wavelength on the walk-off angle in the ultraviolet wave band was larger than that in visible and near-infrared wave band.The obtained result is favor for the design and application of parallel beam splitting prisms in wider scope.
2009, 33(2): 187-190.
Abstract:
In order to study the characteristics of the interference patterns of two coherently combined fiber lasers, experimental and numerical computing method was used.Based on the theory and experiments the interferent fringes of coherent combining of fiber lasers were obtained.It is shown that the interference strips are mainly affected by the beam separation, focal length of Fourier transform lens and beam waist, etc.With increasing beam separation, the number of interference fringes increases and the fringe separation and visibility decrease.When the focal length of Fourier transform lens increases the fringe separation and number of fringes do not change obviously, but the visibility increases.This work will be useful for relative experiments.
In order to study the characteristics of the interference patterns of two coherently combined fiber lasers, experimental and numerical computing method was used.Based on the theory and experiments the interferent fringes of coherent combining of fiber lasers were obtained.It is shown that the interference strips are mainly affected by the beam separation, focal length of Fourier transform lens and beam waist, etc.With increasing beam separation, the number of interference fringes increases and the fringe separation and visibility decrease.When the focal length of Fourier transform lens increases the fringe separation and number of fringes do not change obviously, but the visibility increases.This work will be useful for relative experiments.
2009, 33(2): 191-194.
Abstract:
In order to restrict the power dissipation and electromagnetic interference when the flash-lamp-pumped system of solid laser is at the time of burst and preignition, the technology of quasi-resonant triggering and preignition was developed.Based on this technology,a long-pulsed medical Nd:YAG laser was designed to meet the electromagnetic compatibility requirements of national medical electrical equipment.Because parasitic parameters of the pulse transformer can not be eliminated, complicated oscillation should occur in the circuit.Making use of this resonance characteristic of the pulse transformer, the triggering frequency was adjusted the same as the resonant frequency,namely,quasi-resonant state,to ignite flash-lamp.The experiments proved this circuit was reliable and stable.The value of triggering-pulsed peak voltage could descend below 10kV,much lower than the nominal triggering voltage, 16kV.The results show that the circuit completely meets the national electromagnetic compatibility standards on medical electrical equipment.
In order to restrict the power dissipation and electromagnetic interference when the flash-lamp-pumped system of solid laser is at the time of burst and preignition, the technology of quasi-resonant triggering and preignition was developed.Based on this technology,a long-pulsed medical Nd:YAG laser was designed to meet the electromagnetic compatibility requirements of national medical electrical equipment.Because parasitic parameters of the pulse transformer can not be eliminated, complicated oscillation should occur in the circuit.Making use of this resonance characteristic of the pulse transformer, the triggering frequency was adjusted the same as the resonant frequency,namely,quasi-resonant state,to ignite flash-lamp.The experiments proved this circuit was reliable and stable.The value of triggering-pulsed peak voltage could descend below 10kV,much lower than the nominal triggering voltage, 16kV.The results show that the circuit completely meets the national electromagnetic compatibility standards on medical electrical equipment.
2009, 33(2): 195-197,220.
Abstract:
The transmission property of the two-dimension photonic waveguide after introducing layered composite medium cylinder defect was studied by means of the finite-difference time-domain method when changing the radius and refraction index of the cylinder.The results show that more defect states appear in guided gap with the radius and refractive index of the medium cylinder increasing.Even broader guided gap appears when radius of medium cylinder is close to that of air cylinder.Narrow forbidden gap appears in guided gap with big refraction index of the cylinder.The results are very meaningful for design of 2-D photonic crystal devices.
The transmission property of the two-dimension photonic waveguide after introducing layered composite medium cylinder defect was studied by means of the finite-difference time-domain method when changing the radius and refraction index of the cylinder.The results show that more defect states appear in guided gap with the radius and refractive index of the medium cylinder increasing.Even broader guided gap appears when radius of medium cylinder is close to that of air cylinder.Narrow forbidden gap appears in guided gap with big refraction index of the cylinder.The results are very meaningful for design of 2-D photonic crystal devices.
2009, 33(2): 198-200,204.
Abstract:
In order to study the relation between tuning characteristics and bistability characteristics, after establishing H parameter simplified model and taking carrier density for the characteristic of threshold, an analytical expression for the tuning range was derived.Then the maximum residual reflectivity for anti-resonance was analyzed,the effect of reflectivity in laser output terminal and residual reflectivity on tuning range and hysteresis loop width was simulated, and the maximum hysteresis loop width was obtained.Based on the model,the relation between tuning and bistability characteristics can be clarified.
In order to study the relation between tuning characteristics and bistability characteristics, after establishing H parameter simplified model and taking carrier density for the characteristic of threshold, an analytical expression for the tuning range was derived.Then the maximum residual reflectivity for anti-resonance was analyzed,the effect of reflectivity in laser output terminal and residual reflectivity on tuning range and hysteresis loop width was simulated, and the maximum hysteresis loop width was obtained.Based on the model,the relation between tuning and bistability characteristics can be clarified.
2009, 33(2): 201-204.
Abstract:
In order to study the effect of quintic nonlinearity on the optical pulse propagating in the optical fiber, the extended nonlinear Schrödinger equation, including the quintic nonlinearity, was solved by means of split-step Fourier transform.The results showed that the negative quintic nonlinearity stretched the pulse while the positive one compressed the pulse width.Less quintic nonlinearity produced less modulation instability of the optical pulse, thus the optical pulse almost maintained the pulse envelope.While the absorbed coefficient was neglected,the propagation of the pulse was adiabatic.For the positive quintic nonlinearity, some proper absorbed coefficient could slow down the modulation instability.If the quintic nonlinear coefficient were fixed,the effect of quintic nonlinearity would be more obvious when the input peak power of the pulse increased.
In order to study the effect of quintic nonlinearity on the optical pulse propagating in the optical fiber, the extended nonlinear Schrödinger equation, including the quintic nonlinearity, was solved by means of split-step Fourier transform.The results showed that the negative quintic nonlinearity stretched the pulse while the positive one compressed the pulse width.Less quintic nonlinearity produced less modulation instability of the optical pulse, thus the optical pulse almost maintained the pulse envelope.While the absorbed coefficient was neglected,the propagation of the pulse was adiabatic.For the positive quintic nonlinearity, some proper absorbed coefficient could slow down the modulation instability.If the quintic nonlinear coefficient were fixed,the effect of quintic nonlinearity would be more obvious when the input peak power of the pulse increased.
2009, 33(2): 205-208,212.
Abstract:
Laser drilling is a complex physics process, which involves multiple material state transformation.In order to simulate the process,the material's state transformation change with heating time is equivalent to the change of power density distribution change with time in the infinite medium.Based on the analytic solution of thermal diffusion equation of the infinite medium with constant thermal physical properties, approximate mathematics expressions of laser drilling were formulated.Corresponding software was edited to simulate drilling process.The simulation computation shows that the designed software can simulate a logical process of the cavity formation.If the computation parameters are changed,the holes with different shapes will be obtained.The investigation can used to improve the laser processing technology and provide a fast and efficient tool to estimate thermal damage induced by the laser irradiation.
Laser drilling is a complex physics process, which involves multiple material state transformation.In order to simulate the process,the material's state transformation change with heating time is equivalent to the change of power density distribution change with time in the infinite medium.Based on the analytic solution of thermal diffusion equation of the infinite medium with constant thermal physical properties, approximate mathematics expressions of laser drilling were formulated.Corresponding software was edited to simulate drilling process.The simulation computation shows that the designed software can simulate a logical process of the cavity formation.If the computation parameters are changed,the holes with different shapes will be obtained.The investigation can used to improve the laser processing technology and provide a fast and efficient tool to estimate thermal damage induced by the laser irradiation.
2009, 33(2): 209-212.
Abstract:
Based on the framework of the coupled modes theory, transmission of the Bragg solitons and interaction of the Bragg solitons were simulated with the finite-difference scheme in Gaussian-apodized fiber Bragg gratings under the condition with the transmission speed irrelevant to the transmission distance.According to the numerical results, the peak power of Bragg solitons changes with different incident peak power and pulse width.And interaction of two solitons relies on their relative phase and amplitude.When the initial pulse is chirped,transmission of Bragg solitons is broadened (positive chirp) or narrowed (negative chirp) and restricted by Gaussian-apodized gratings all the time.
Based on the framework of the coupled modes theory, transmission of the Bragg solitons and interaction of the Bragg solitons were simulated with the finite-difference scheme in Gaussian-apodized fiber Bragg gratings under the condition with the transmission speed irrelevant to the transmission distance.According to the numerical results, the peak power of Bragg solitons changes with different incident peak power and pulse width.And interaction of two solitons relies on their relative phase and amplitude.When the initial pulse is chirped,transmission of Bragg solitons is broadened (positive chirp) or narrowed (negative chirp) and restricted by Gaussian-apodized gratings all the time.
2009, 33(2): 213-216.
Abstract:
Based on the method of filter used to eliminate noise from gray image according to its gray value,median filter was proposed to remove noise from the point cloud data obtained by a 3-D lidar measuring system.A lidar can be used to collect point cloud data from the surface of an object.The quantity of the point cloud data is huge with noise,which is always harmful to surface reconstruction if it is not removed.Based on the character of the point cloud data,an improved algorithm for 2-D median filter and method for segregating noise from point cloud were mainly emphasized.The speed and effect of the process are improved significantly, which demonstrates that median filter can be used to deal with the lidar data.
Based on the method of filter used to eliminate noise from gray image according to its gray value,median filter was proposed to remove noise from the point cloud data obtained by a 3-D lidar measuring system.A lidar can be used to collect point cloud data from the surface of an object.The quantity of the point cloud data is huge with noise,which is always harmful to surface reconstruction if it is not removed.Based on the character of the point cloud data,an improved algorithm for 2-D median filter and method for segregating noise from point cloud were mainly emphasized.The speed and effect of the process are improved significantly, which demonstrates that median filter can be used to deal with the lidar data.
2009, 33(2): 217-220.
Abstract:
To study the scattering characteristic of 1064nm laser in low latitude,improved Mie scattering algorithm was put forward,in which the iterative function was simplified to reduce the storage array, and the endless circulation was truncated to reduce the number of circulation.From the simulation, the distribution of single and bulk scattering was obtained and it was found that the scattering distribution was focused in forward scattering at a small angle, and that the scattered laser might be absolute polarized light.The results show that the new method embodies the advantage of fast convergence and high precision.
To study the scattering characteristic of 1064nm laser in low latitude,improved Mie scattering algorithm was put forward,in which the iterative function was simplified to reduce the storage array, and the endless circulation was truncated to reduce the number of circulation.From the simulation, the distribution of single and bulk scattering was obtained and it was found that the scattering distribution was focused in forward scattering at a small angle, and that the scattered laser might be absolute polarized light.The results show that the new method embodies the advantage of fast convergence and high precision.
2009, 33(2): 221-224.
Abstract:
In order to study the detection principle and experimental technique of the attack directions of cruise missiles based on "cat's eye" effect, the factors that affecting the intensity of the reflection wave were analyzed both quantitatively and qualitatively with the method of ray tracing.Research results show that the relative aperture of optical lens, the incline and defocusing of reflection plane in infrared seeker optical system reduce the intensity of the "cat's eye" reflection.For example,the ratio of the reflection energy of TV seeker and the pulse energy of scanning laser goes down from 43.80% (under the ideal reflection condition) to 1.53% (for the defocusing) and 0% (for the incline) respectively,while the distance between the laser scanning setup and TV seeker is 10000m and the incidence angle of scanning laser is 0.08rad.This results may be useful for the application of missile's optical warning system.
In order to study the detection principle and experimental technique of the attack directions of cruise missiles based on "cat's eye" effect, the factors that affecting the intensity of the reflection wave were analyzed both quantitatively and qualitatively with the method of ray tracing.Research results show that the relative aperture of optical lens, the incline and defocusing of reflection plane in infrared seeker optical system reduce the intensity of the "cat's eye" reflection.For example,the ratio of the reflection energy of TV seeker and the pulse energy of scanning laser goes down from 43.80% (under the ideal reflection condition) to 1.53% (for the defocusing) and 0% (for the incline) respectively,while the distance between the laser scanning setup and TV seeker is 10000m and the incidence angle of scanning laser is 0.08rad.This results may be useful for the application of missile's optical warning system.
