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RSS2010 Vol. 34, No. 6
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2010, 34(6): 721-724.
doi: 10.3969/j.issn.1001-3806.2010.06.001
[Abstract]
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Abstract:
Fibered Q-switches are critical components of Q-switched all-fiber lasers.Presently,the useful fibered Q-switches mainly include passive Q-switches based on stimulated Brillouin scattering (SBS) effect,active Q-switches based on two-beam interference principle and some active Q-switches in special design.The repetition rates of the Q-switches based on SBS effect are not stable and adjustable.The Q-switches based on two-beam interference principle belong to slow Q-switches.Because the technologies of other active Q-switches are not yet mature,it is inevitable to develop active fibered Q-switches with high efficiency.
Fibered Q-switches are critical components of Q-switched all-fiber lasers.Presently,the useful fibered Q-switches mainly include passive Q-switches based on stimulated Brillouin scattering (SBS) effect,active Q-switches based on two-beam interference principle and some active Q-switches in special design.The repetition rates of the Q-switches based on SBS effect are not stable and adjustable.The Q-switches based on two-beam interference principle belong to slow Q-switches.Because the technologies of other active Q-switches are not yet mature,it is inevitable to develop active fibered Q-switches with high efficiency.
2010, 34(6): 725-728.
doi: 10.3969/j.issn.1001-3806.2010.06.002
Abstract:
In order to study the shape of the extreme ultraviolet(EUV) collector mirror and liquid droplets drift of the EUV light source system,the parameters for the collector mirror were calculated.The images of the intermediate focus were simulated with ZEMAX when the liquid droplets drifted 50μm,100μm,150μm from top to bottom and from left to right.The results show that the drift of the liquid micro-droplets in the upper and the lower direction have great influence on the imaging of the intermediate focus point,the drift should be controlled below 20μm in this direction,and the drift of the liquid micro-droplets in the optical axis direction have smaller influence on the imaging of the intermediate focus point.
In order to study the shape of the extreme ultraviolet(EUV) collector mirror and liquid droplets drift of the EUV light source system,the parameters for the collector mirror were calculated.The images of the intermediate focus were simulated with ZEMAX when the liquid droplets drifted 50μm,100μm,150μm from top to bottom and from left to right.The results show that the drift of the liquid micro-droplets in the upper and the lower direction have great influence on the imaging of the intermediate focus point,the drift should be controlled below 20μm in this direction,and the drift of the liquid micro-droplets in the optical axis direction have smaller influence on the imaging of the intermediate focus point.
2010, 34(6): 729-732.
doi: 10.3969/j.issn.1001-3806.2010.06.003
Abstract:
In order to study effect of laser incident angles on welding performance of galvanized sheet,firstly orthogonal test was adopted to obtain ideal welding parameters at normal incidence through analyzing the weld topography,tension and shear load.Then galvanized sheet welding tests at different incident angles were carried out under the same ideal parameters at vertical incidence.The transverse weld topography,the connect width between plates and tension and shear load were analyzed when the incident angle changed.The research results show that fine weld topography and greater tension and shear load can be obtained at incident angle less than 30°;the connect width between plates has an significant influence on tension and shear load;slight change of the gap between plates will bring large effect on the critical incident angle.
In order to study effect of laser incident angles on welding performance of galvanized sheet,firstly orthogonal test was adopted to obtain ideal welding parameters at normal incidence through analyzing the weld topography,tension and shear load.Then galvanized sheet welding tests at different incident angles were carried out under the same ideal parameters at vertical incidence.The transverse weld topography,the connect width between plates and tension and shear load were analyzed when the incident angle changed.The research results show that fine weld topography and greater tension and shear load can be obtained at incident angle less than 30°;the connect width between plates has an significant influence on tension and shear load;slight change of the gap between plates will bring large effect on the critical incident angle.
2010, 34(6): 733-735,815.
doi: 10.3969/j.issn.1001-3806.2010.06.004
Abstract:
In order to determine the cloud base,cloud peak and cloud top from the lidar backscatter profile,the differential retrieval method was put forward.The study was focused on distinguishing the single layer from the multi-layer cloud when confronted several backscatter signal peaks.The structure of the lidar used in the experiment was introduced;then the cloud height,cloud thickness and cloud optical depth detected from the lidar in May in Hefei was investigated.The related theory analysis and experiment were presented.In order to test the feasibility of the cloud detection approach,the results obtained from the lidar were compared with those obtained from Finland ceilometer Vaisala (detecting range:0km～7km) after both the instruments aiming at the cloud in the same region.Results show that the data below 7km were identical;the data above the 7km were consistent with those from satellite SAGE Ⅱ.The high layer clouds detected in Hefei,also called cirrus,were mostly thin cirrus with the cloud peak varying from 9km to 12km.The method of cloud detection is helpful for the future cloud retrieval and satellite validation.
In order to determine the cloud base,cloud peak and cloud top from the lidar backscatter profile,the differential retrieval method was put forward.The study was focused on distinguishing the single layer from the multi-layer cloud when confronted several backscatter signal peaks.The structure of the lidar used in the experiment was introduced;then the cloud height,cloud thickness and cloud optical depth detected from the lidar in May in Hefei was investigated.The related theory analysis and experiment were presented.In order to test the feasibility of the cloud detection approach,the results obtained from the lidar were compared with those obtained from Finland ceilometer Vaisala (detecting range:0km～7km) after both the instruments aiming at the cloud in the same region.Results show that the data below 7km were identical;the data above the 7km were consistent with those from satellite SAGE Ⅱ.The high layer clouds detected in Hefei,also called cirrus,were mostly thin cirrus with the cloud peak varying from 9km to 12km.The method of cloud detection is helpful for the future cloud retrieval and satellite validation.
Diffraction efficiency analysis of reflective holographic phase gratings in paraelectric KTN crystal
2010, 34(6): 736-738,742.
doi: 10.3969/j.issn.1001-3806.2010.06.005
Abstract:
The holographic grating storage in photorefractive crystal in paraelectric phase is an available approach to develop a new style electroholography switch.In order to improve the diffraction efficiency,the analytic expression was deduced combining Kogelnik coupling wave theory with the Kukhtarev equations.Then the parameters affecting the diffraction efficiency were analyzed.It's found that the diffraction efficiency can be increased by the methods such as aparting the incident angle far from 45°,increasing the crystal thickness and electric field.A low diffraction efficiency district exists at incident angles in vicinity of 45°.Diffraction efficiency is sensitive to incident angles,crystal thickness and applied electric field.A small change of these factors may bring a great difference of the diffraction efficiency.The influence of absorption of crystal on reading diffraction efficiency is negligible.The results provide useful guidelines to choose optimal parameters for high reading diffraction efficiency in practice.
The holographic grating storage in photorefractive crystal in paraelectric phase is an available approach to develop a new style electroholography switch.In order to improve the diffraction efficiency,the analytic expression was deduced combining Kogelnik coupling wave theory with the Kukhtarev equations.Then the parameters affecting the diffraction efficiency were analyzed.It's found that the diffraction efficiency can be increased by the methods such as aparting the incident angle far from 45°,increasing the crystal thickness and electric field.A low diffraction efficiency district exists at incident angles in vicinity of 45°.Diffraction efficiency is sensitive to incident angles,crystal thickness and applied electric field.A small change of these factors may bring a great difference of the diffraction efficiency.The influence of absorption of crystal on reading diffraction efficiency is negligible.The results provide useful guidelines to choose optimal parameters for high reading diffraction efficiency in practice.
2010, 34(6): 739-742.
doi: 10.3969/j.issn.1001-3806.2010.06.006
Abstract:
The optical transmission property of Ag-air nanofilm was studied based on Bloch's theorem and the transfer matrix method.At a given incident angle,there are some discrete frequency channels;at a given frequency,there are also some discrete spatial channels.Through changing the thickness of air,the positions of frequency channels and spatial channels can be easily adjusted.The loss of Ag influences the transmittance but does not change the position of filtering channel.Through decreasing the thickness of Ag layer,the loss cannot influence the filtering function of the Ag-air structure.The results indicate that the Ag-air structure can be used as a multi-channel frequency filter and spatial filter.
The optical transmission property of Ag-air nanofilm was studied based on Bloch's theorem and the transfer matrix method.At a given incident angle,there are some discrete frequency channels;at a given frequency,there are also some discrete spatial channels.Through changing the thickness of air,the positions of frequency channels and spatial channels can be easily adjusted.The loss of Ag influences the transmittance but does not change the position of filtering channel.Through decreasing the thickness of Ag layer,the loss cannot influence the filtering function of the Ag-air structure.The results indicate that the Ag-air structure can be used as a multi-channel frequency filter and spatial filter.
2010, 34(6): 743-746,769.
doi: 10.3969/j.issn.1001-3806.2010.06.007
Abstract:
To measure optical parameters of biological tissues,CCD diffusing reflection and transmission measurements were introduced.Analyzing the CCD photograph of diffusing reflection distribution on the specimen surface,the reduced scattering coefficient and absorption coefficient of biological tissue simulating liquid (intralipid-20% diluents),beef,pork and chicken were derived from nonlinear regression of the diffusion equation with spatially resolved steady-state diffuse reflectance which was measured by the CCD diffusing reflection measuring equipment.The scattering coefficient was derived from linear regression of the Beer-Lambert equation with transmission light intensity of biological tissue simulating liquid of different titer which was measured by the CCD transmission measuring equipment,and then the reduced scattering coefficient was also deduced.Optical parameters of the same specimen measured by CCD diffusing reflection and transmission measurements were compared with those measured by others,and they were coherent.It is shown that the experimental CCD equipment and the treatment methods used to measure optical parameters have a high accuracy.
To measure optical parameters of biological tissues,CCD diffusing reflection and transmission measurements were introduced.Analyzing the CCD photograph of diffusing reflection distribution on the specimen surface,the reduced scattering coefficient and absorption coefficient of biological tissue simulating liquid (intralipid-20% diluents),beef,pork and chicken were derived from nonlinear regression of the diffusion equation with spatially resolved steady-state diffuse reflectance which was measured by the CCD diffusing reflection measuring equipment.The scattering coefficient was derived from linear regression of the Beer-Lambert equation with transmission light intensity of biological tissue simulating liquid of different titer which was measured by the CCD transmission measuring equipment,and then the reduced scattering coefficient was also deduced.Optical parameters of the same specimen measured by CCD diffusing reflection and transmission measurements were compared with those measured by others,and they were coherent.It is shown that the experimental CCD equipment and the treatment methods used to measure optical parameters have a high accuracy.
2010, 34(6): 747-749,801.
doi: 10.3969/j.issn.1001-3806.2010.06.008
Abstract:
In order to analyze influence of the turbulent aberrations on orbital angular momentum states of laser beam propagating in slant atmosphere-channel,effect of z-tilt aberration,astigmatism aberration and coma aberration on the detection probability of the orbital angular momentum states of laser beam was simulated and the impact regularity of the three aberrations as a function of index-of-refraction,propagation distance and zenith angle of communication channel on the detection probability of the orbital angular momentum states was obtained.The results show that with the increase of the zenith angle of communication channel,the atmospheric turbulence and the channel distance,the detection probability of the orbital angular momentum states of laser beams induced by z-tilt aberration decreases more.For turbulence coma aberration,only when the zenith angle of communication channel increases,the detection probability of the orbital angular momentum states of laser beams will decrease more.The effect of astigmatism aberration on the detection probability of the orbital angular momentum states of laser beam is independent of the change of these three factors and can be ignored.
In order to analyze influence of the turbulent aberrations on orbital angular momentum states of laser beam propagating in slant atmosphere-channel,effect of z-tilt aberration,astigmatism aberration and coma aberration on the detection probability of the orbital angular momentum states of laser beam was simulated and the impact regularity of the three aberrations as a function of index-of-refraction,propagation distance and zenith angle of communication channel on the detection probability of the orbital angular momentum states was obtained.The results show that with the increase of the zenith angle of communication channel,the atmospheric turbulence and the channel distance,the detection probability of the orbital angular momentum states of laser beams induced by z-tilt aberration decreases more.For turbulence coma aberration,only when the zenith angle of communication channel increases,the detection probability of the orbital angular momentum states of laser beams will decrease more.The effect of astigmatism aberration on the detection probability of the orbital angular momentum states of laser beam is independent of the change of these three factors and can be ignored.
2010, 34(6): 750-752,797.
doi: 10.3969/j.issn.1001-3806.2010.06.009
Abstract:
More attention was paid to research of speckles because of their measurable intensity and certain phase.Now speckles are used extensively in the field of non-destructive test.The electronic speckle pattern interferometry (ESPI) is always full of a lot of noise.Generally,the information about deformation recorded by the fringe is mainly distributed in the low frequency domain,whereas the noise is in the high frequency part.In order to obtain the continuous phase distribution of the deformed object,it is necessary to take some proper methods to remove the noise in the fringe.Homomorphic filtering is a frequency domain operation to compress image intensity area and enhance contrast.A new filter based on the principle of homomorphic filtering was designed,which was used for three-step phase-shifting electronic speckle image processing.A theoretical analysis was also proposed in detail.The experimental results show that the speckle noise was removed to the large extent and the contrast of ESPI fringes can be increased by the proposed method.
More attention was paid to research of speckles because of their measurable intensity and certain phase.Now speckles are used extensively in the field of non-destructive test.The electronic speckle pattern interferometry (ESPI) is always full of a lot of noise.Generally,the information about deformation recorded by the fringe is mainly distributed in the low frequency domain,whereas the noise is in the high frequency part.In order to obtain the continuous phase distribution of the deformed object,it is necessary to take some proper methods to remove the noise in the fringe.Homomorphic filtering is a frequency domain operation to compress image intensity area and enhance contrast.A new filter based on the principle of homomorphic filtering was designed,which was used for three-step phase-shifting electronic speckle image processing.A theoretical analysis was also proposed in detail.The experimental results show that the speckle noise was removed to the large extent and the contrast of ESPI fringes can be increased by the proposed method.
2010, 34(6): 753-756.
doi: 10.3969/j.issn.1001-3806.2010.06.010
Abstract:
In order to improve the efficiency of ultrasound excited by pulsed laser in a thin tube,a laser-ultrasonic model of an aluminum tube irradiated by a ring laser was established based on thermo-elastic theory of laser-ultrasound.The transient temperature field of the interior surface of the aluminum tube irradiated by a pulse ring laser was simulated by means of finite element method.Then the evolution curves of the temperature with time,radial and axial variables were obtained.Furthermore, the formation and variation of temperature gradient in the interior of aluminum tubes was analyzed.Results show that transient temperature field can be set up in a few tens of nanoseconds under the irradiation of a pulsed ring laser.Enormous temperature gradient produces in this process and a very strong ultrasonic wave appears subsequently in the aluminum tube.Because temperature gradient distributes on the entire circle,the ultrasonic wave spreading in tube attenuates slowly,which is useful for ultrasonic detection on large region along circle and axis of the tube.The results may provide valuable reference for the laser-generated thermo-elastic ultrasonic guided wave pipeline.
In order to improve the efficiency of ultrasound excited by pulsed laser in a thin tube,a laser-ultrasonic model of an aluminum tube irradiated by a ring laser was established based on thermo-elastic theory of laser-ultrasound.The transient temperature field of the interior surface of the aluminum tube irradiated by a pulse ring laser was simulated by means of finite element method.Then the evolution curves of the temperature with time,radial and axial variables were obtained.Furthermore, the formation and variation of temperature gradient in the interior of aluminum tubes was analyzed.Results show that transient temperature field can be set up in a few tens of nanoseconds under the irradiation of a pulsed ring laser.Enormous temperature gradient produces in this process and a very strong ultrasonic wave appears subsequently in the aluminum tube.Because temperature gradient distributes on the entire circle,the ultrasonic wave spreading in tube attenuates slowly,which is useful for ultrasonic detection on large region along circle and axis of the tube.The results may provide valuable reference for the laser-generated thermo-elastic ultrasonic guided wave pipeline.
2010, 34(6): 757-760.
doi: 10.3969/j.issn.1001-3806.2010.06.011
Abstract:
In order to investigate 1555nm high power fiber amplifiers with different gain length,a two-stage hybrid structure was employed,in which an erbium-doped fiber amplifier(EDFA) was used as a pre-amplifier for signal amplification and higher signal-noise ratio and an erbium/ytterbium co-doped double-cladding fiber amplifier (EYCDFA) was used as a master amplifier. The EYCDFA with special double-cladding configuration can couple more pump power into the system.The optimal,length of erbium-ytterbium co-doped fiber was investigated experimentally and analyzed theoretically.Under the conditions of 10mW signal power,318.58mW EDFA pump power,11.71W EYCDFA pump power and 14m gain length,2.11W output power was achieved.Amplified spontaneous emission spectrum appeared in L-band because of the over long gain fiber.It shows that there exists an optimal length at certain pump power and signal power,and the result is good for the study of high-power fiber amplifiers.
In order to investigate 1555nm high power fiber amplifiers with different gain length,a two-stage hybrid structure was employed,in which an erbium-doped fiber amplifier(EDFA) was used as a pre-amplifier for signal amplification and higher signal-noise ratio and an erbium/ytterbium co-doped double-cladding fiber amplifier (EYCDFA) was used as a master amplifier. The EYCDFA with special double-cladding configuration can couple more pump power into the system.The optimal,length of erbium-ytterbium co-doped fiber was investigated experimentally and analyzed theoretically.Under the conditions of 10mW signal power,318.58mW EDFA pump power,11.71W EYCDFA pump power and 14m gain length,2.11W output power was achieved.Amplified spontaneous emission spectrum appeared in L-band because of the over long gain fiber.It shows that there exists an optimal length at certain pump power and signal power,and the result is good for the study of high-power fiber amplifiers.
2010, 34(6): 761-765.
doi: 10.3969/j.issn.1001-3806.2010.06.012
Abstract:
In order to fabricate a porous hard bone scaffold mold with biological compatibility,it was made of hydroxyapatite based bioceramic because of the viscosity and support effect of bioceramic slurry.Then the microstructure of the solidified scaffolds after laser sintering and high-temperature post-process was observed with a scanning electron microscope.Furthermore, the surface roughness was measured with an atomic force microscope.The results show that the density and the surface finish of scaffolds can be increased after post process,which is good for the attachment and growth of osteoblast-like cells.
In order to fabricate a porous hard bone scaffold mold with biological compatibility,it was made of hydroxyapatite based bioceramic because of the viscosity and support effect of bioceramic slurry.Then the microstructure of the solidified scaffolds after laser sintering and high-temperature post-process was observed with a scanning electron microscope.Furthermore, the surface roughness was measured with an atomic force microscope.The results show that the density and the surface finish of scaffolds can be increased after post process,which is good for the attachment and growth of osteoblast-like cells.
2010, 34(6): 766-769.
doi: 10.3969/j.issn.1001-3806.2010.06.013
Abstract:
In order to study effect of porous silicon (PS) porosity on the optical and electrical properties of ZnS/PS composites,ZnS film was deposited on PS substrates with different porosities by means of pulsed laser deposition.The crystalline structure,surface morphology of ZnS film on PS substrates and optical,electrical properties of ZnS/PS composites were studied by means of X-ray diffraction,scanning electron microscope,photoluminescence (PL) spectra and Ⅰ-Ⅴ characteristics respectively.The results show that ZnS film deposited on PS substrates have a crystalline structure of cubic phase growing in preferred orientation along β-ZnS(111)direction.With the increase of PS substrate porosity,the intensity of diffraction peak of ZnS film decreases and some voids and cracks appears in ZnS film.In the PL spectra of ZnS/PS composites,the PL peak of PS has a blue shift compared with original PS.The larger the porosity of PS substrate,the greater the blue shift.With the increase of PS substrate porosity,a new green light emission at about 550nm appears which is attributed to defect-center luminescence of ZnS.The blue,green emission of ZnS combined with the red emission of PS,ZnS/PS composites exhibit intense while light emission.Based on the Ⅰ-Ⅴ characteristics,ZnS/PS heterojunctions exhibit the similar rectifying properties to the common diode. Under forward bias conditions,the current density is large and the voltage drop is small,on the contrary,under reverse bias conditions,the current density is nearly zero.With the increase of PS substrate porosity,the forward current increases.The research results lay a foundation for the realization of solid state white light emission devices.
In order to study effect of porous silicon (PS) porosity on the optical and electrical properties of ZnS/PS composites,ZnS film was deposited on PS substrates with different porosities by means of pulsed laser deposition.The crystalline structure,surface morphology of ZnS film on PS substrates and optical,electrical properties of ZnS/PS composites were studied by means of X-ray diffraction,scanning electron microscope,photoluminescence (PL) spectra and Ⅰ-Ⅴ characteristics respectively.The results show that ZnS film deposited on PS substrates have a crystalline structure of cubic phase growing in preferred orientation along β-ZnS(111)direction.With the increase of PS substrate porosity,the intensity of diffraction peak of ZnS film decreases and some voids and cracks appears in ZnS film.In the PL spectra of ZnS/PS composites,the PL peak of PS has a blue shift compared with original PS.The larger the porosity of PS substrate,the greater the blue shift.With the increase of PS substrate porosity,a new green light emission at about 550nm appears which is attributed to defect-center luminescence of ZnS.The blue,green emission of ZnS combined with the red emission of PS,ZnS/PS composites exhibit intense while light emission.Based on the Ⅰ-Ⅴ characteristics,ZnS/PS heterojunctions exhibit the similar rectifying properties to the common diode. Under forward bias conditions,the current density is large and the voltage drop is small,on the contrary,under reverse bias conditions,the current density is nearly zero.With the increase of PS substrate porosity,the forward current increases.The research results lay a foundation for the realization of solid state white light emission devices.
2010, 34(6): 770-773.
doi: 10.3969/j.issn.1001-3806.2010.06.014
Abstract:
In order to compare the propagation characteristics of chirped-pulse propagating in homogeneously and inhomogeneously broadening mediums,they were analyzed and simulated by means of split-step Fourier method.Then they were proved in experiments.The effect of gain narrowing,gain saturation and self phase modulation on temporal shape and power spectra in both mediums were obtained.It is found that the effect of gain narrowing is more obvious and the effect of gain saturation is inhibited well in inhomogeneously broadening medium,and power spectra in both mediums are broadened,which is more symmetry in inhomogeneously broadening medium and distortive in homogeneously broadening medium.These results are useful to study the propagation features of chirped-pulse in comprehensive broadening mediums.
In order to compare the propagation characteristics of chirped-pulse propagating in homogeneously and inhomogeneously broadening mediums,they were analyzed and simulated by means of split-step Fourier method.Then they were proved in experiments.The effect of gain narrowing,gain saturation and self phase modulation on temporal shape and power spectra in both mediums were obtained.It is found that the effect of gain narrowing is more obvious and the effect of gain saturation is inhibited well in inhomogeneously broadening medium,and power spectra in both mediums are broadened,which is more symmetry in inhomogeneously broadening medium and distortive in homogeneously broadening medium.These results are useful to study the propagation features of chirped-pulse in comprehensive broadening mediums.
2010, 34(6): 774-777.
doi: 10.3969/j.issn.1001-3806.2010.06.015
Abstract:
In order to measure various low-level aberration and irregular higher-order aberration of the human eyes accurately,the wave-front aberration measurement method with subjective visual compensation was proposed,which could ensure more accurate and realistic measuring results.The result shows the wave-front aberration obtained from subjective visual compensation measuring method smaller than objective measurement,which is the result of adaptive correction.In addition, when watching different sighting targets,the fluctuation value of wave front aberration is small.Therefore,a conclusion can be drawn that the subjective visual compensation measuring method takes into consideration the actual condition of human eyes when watching targets,which contributes to aberration measuring improvement and obtains results that match realistic state.The conclusion is positive and beneficial to the aberration treatment of human eyes.
In order to measure various low-level aberration and irregular higher-order aberration of the human eyes accurately,the wave-front aberration measurement method with subjective visual compensation was proposed,which could ensure more accurate and realistic measuring results.The result shows the wave-front aberration obtained from subjective visual compensation measuring method smaller than objective measurement,which is the result of adaptive correction.In addition, when watching different sighting targets,the fluctuation value of wave front aberration is small.Therefore,a conclusion can be drawn that the subjective visual compensation measuring method takes into consideration the actual condition of human eyes when watching targets,which contributes to aberration measuring improvement and obtains results that match realistic state.The conclusion is positive and beneficial to the aberration treatment of human eyes.
2010, 34(6): 778-780,784.
doi: 10.3969/j.issn.1001-3806.2010.06.016
Abstract:
To study the influence of temperature change on carbon monoxide absorption spectral lines,at first,the temperature-relative parameters,such as carbon monoxide absorption spectral lines intensity,comprehensive widened line shape function and absorption coefficients were obtained based on high-resolution transmission molecular absorption database.Then starting from absorption spectrum principle,the temperature-relative parameters were simulated with MATLAB and the temperature-relative curves were drawn.The results show that the effect of temperature on carbon monoxide absorption spectral lines,especially on the comprehensive widened line shape function,is complex and that different laser frequencies also affect the relationship of temperature and comprehensive widened line shape function and the absorption coefficients,which gives some advice for the absorption and measurement of carbon monoxide in practical application.
To study the influence of temperature change on carbon monoxide absorption spectral lines,at first,the temperature-relative parameters,such as carbon monoxide absorption spectral lines intensity,comprehensive widened line shape function and absorption coefficients were obtained based on high-resolution transmission molecular absorption database.Then starting from absorption spectrum principle,the temperature-relative parameters were simulated with MATLAB and the temperature-relative curves were drawn.The results show that the effect of temperature on carbon monoxide absorption spectral lines,especially on the comprehensive widened line shape function,is complex and that different laser frequencies also affect the relationship of temperature and comprehensive widened line shape function and the absorption coefficients,which gives some advice for the absorption and measurement of carbon monoxide in practical application.
2010, 34(6): 781-784.
doi: 10.3969/j.issn.1001-3806.2010.06.017
Abstract:
Based on both the coupled nonlinear Schrödinger equations,the nonlinear propagation of two femtosecond laser pulses in the different regimes of photonic crystal fibers was solved by solving the equation group with the slip-step Fourier method.The effect of the pump pulse power,pump frequency chirp and various pulse widths on signal pulse compression was discussed in detail.The numerical results show that the signal pulse can be compressed through cross-phase modulation and the optimum fiber length can be obtained.It is also found that the compression factor increases with initial positive chirp and power, however,the optimum fiber length decreases.In order to obtain larger compression factor,pump pulses with narrow pulse-width are desirable selected.These results offer theoretical references for weak signal pulse compression by using photonic crystal fibers.
Based on both the coupled nonlinear Schrödinger equations,the nonlinear propagation of two femtosecond laser pulses in the different regimes of photonic crystal fibers was solved by solving the equation group with the slip-step Fourier method.The effect of the pump pulse power,pump frequency chirp and various pulse widths on signal pulse compression was discussed in detail.The numerical results show that the signal pulse can be compressed through cross-phase modulation and the optimum fiber length can be obtained.It is also found that the compression factor increases with initial positive chirp and power, however,the optimum fiber length decreases.In order to obtain larger compression factor,pump pulses with narrow pulse-width are desirable selected.These results offer theoretical references for weak signal pulse compression by using photonic crystal fibers.
2010, 34(6): 789-793.
doi: 10.3969/j.issn.1001-3806.2010.06.019
Abstract:
To study the effect of residual chirp on ultrashort pulse width measurement by means of the second harmonic autocorrelation,starting from its measurement principle,the effect was simulated for ultrashort laser pulses with different chirps at center wavelength of 800nm and pulse width of 100fs.The results show that the measured value would be larger than factual value with positive chirp,smaller with negative chirp.Moreover,the measurement error will be augmented with the chirp.The effect of the thickness of β-BaB2O4 (BBO) crystal on the pulse width measurement was also discussed numerically.It is found that choosing thin nonlinear crystal could control the measurement error effectively.Using the nonlinear crystal width of L≤0.5Ld, the measurement error caused by chirp can be controlled to an ideal range.
To study the effect of residual chirp on ultrashort pulse width measurement by means of the second harmonic autocorrelation,starting from its measurement principle,the effect was simulated for ultrashort laser pulses with different chirps at center wavelength of 800nm and pulse width of 100fs.The results show that the measured value would be larger than factual value with positive chirp,smaller with negative chirp.Moreover,the measurement error will be augmented with the chirp.The effect of the thickness of β-BaB2O4 (BBO) crystal on the pulse width measurement was also discussed numerically.It is found that choosing thin nonlinear crystal could control the measurement error effectively.Using the nonlinear crystal width of L≤0.5Ld, the measurement error caused by chirp can be controlled to an ideal range.
2010, 34(6): 794-797.
doi: 10.3969/j.issn.1001-3806.2010.06.020
Abstract:
In order to identify alcohol-free beer and ordinary beer quickly and accurately,a recognition model of the alcohol-free beer was established,which was based on fluorescent spectroscopy and probabilistic neural network.It was found experimentally that both alcohol-free beer and ordinary beer excited by ultraviolet-visible light could generate strong fluorescence. The fluorescent spectrum for alcohol-free beer is within a range from 420nm to 620nm,its peak wavelength of the fluorescence is about 490nm.The approximate coefficients,obtained by wavelet transform,were used as the network data,and a probabilistic neural network was trained and constructed.The trained probabilistic neural network was employed to recognize sixty beer samples,and the recognition rate was up to 98.33%.The whole research outcomes will provide a new method for recognizing alcohol-free beer.
In order to identify alcohol-free beer and ordinary beer quickly and accurately,a recognition model of the alcohol-free beer was established,which was based on fluorescent spectroscopy and probabilistic neural network.It was found experimentally that both alcohol-free beer and ordinary beer excited by ultraviolet-visible light could generate strong fluorescence. The fluorescent spectrum for alcohol-free beer is within a range from 420nm to 620nm,its peak wavelength of the fluorescence is about 490nm.The approximate coefficients,obtained by wavelet transform,were used as the network data,and a probabilistic neural network was trained and constructed.The trained probabilistic neural network was employed to recognize sixty beer samples,and the recognition rate was up to 98.33%.The whole research outcomes will provide a new method for recognizing alcohol-free beer.
2010, 34(6): 798-801.
doi: 10.3969/j.issn.1001-3806.2010.06.021
Abstract:
In order to improve the transmission of the output light and reduce the sideband energy with almost the same main intensity,a novel filter based on optical rotatory dispersion effect was introduced.Starting from its principle,its characteristics were analyzed.Compared with a multistage quartz crystal filter,the primary improvement of the novel filter was to reduce the number of needed polariscopes.Compared with a three-level quartz ciystal optical filter,the structure and filtering characteristics of the novel filter were analyzed taking different loss into account.The filtering characteristics were measured with a spectrophotometer.The results show that this novel filter can reduce the loss of the output light and the second sideband energy obviously,which is useful for the observation spectrum.
In order to improve the transmission of the output light and reduce the sideband energy with almost the same main intensity,a novel filter based on optical rotatory dispersion effect was introduced.Starting from its principle,its characteristics were analyzed.Compared with a multistage quartz crystal filter,the primary improvement of the novel filter was to reduce the number of needed polariscopes.Compared with a three-level quartz ciystal optical filter,the structure and filtering characteristics of the novel filter were analyzed taking different loss into account.The filtering characteristics were measured with a spectrophotometer.The results show that this novel filter can reduce the loss of the output light and the second sideband energy obviously,which is useful for the observation spectrum.
2010, 34(6): 802-805.
doi: 10.3969/j.issn.1001-3806.2010.06.022
Abstract:
In order to obtain high bright and high-average-power output of diode pumped solid-state laser,the temperature distribution in the laser medium and thermal lens effects,essential for improving the laser performance,were analyzed.With the help of ZEMAX software,the distribution of pump light in gain material was analyzed when end-pumped by high power LD. Simulation results showed that the optical field distribution was uniform with that in end-pumped structure.Then applying the pump power density in gain material to LASC-AD software,under the condition of the amplifier before and after being seeded, with the pump power of 2400W,the maximum temperature differences were 68℃ and 54.7℃ respectively,maximum thermal stress were 90N/mm2 and 67N/mm2 respectively.Therefore,when the pumping power was lower than 2400W,there was no threat for the laser gain medium under the entire operation of the amplifier.The simulation results have a certain reference value for the design of high-power diode-pumped slab amplifier.
In order to obtain high bright and high-average-power output of diode pumped solid-state laser,the temperature distribution in the laser medium and thermal lens effects,essential for improving the laser performance,were analyzed.With the help of ZEMAX software,the distribution of pump light in gain material was analyzed when end-pumped by high power LD. Simulation results showed that the optical field distribution was uniform with that in end-pumped structure.Then applying the pump power density in gain material to LASC-AD software,under the condition of the amplifier before and after being seeded, with the pump power of 2400W,the maximum temperature differences were 68℃ and 54.7℃ respectively,maximum thermal stress were 90N/mm2 and 67N/mm2 respectively.Therefore,when the pumping power was lower than 2400W,there was no threat for the laser gain medium under the entire operation of the amplifier.The simulation results have a certain reference value for the design of high-power diode-pumped slab amplifier.
2010, 34(6): 806-808,854.
doi: 10.3969/j.issn.1001-3806.2010.06.023
Abstract:
In order to study temperature characteristics of Manakov screening solitons in biased two-photon photorefractive crystals,their intensity profiles were obtained by means of numerical simulation.Moreover,the dynamic evolution of bright-dark Manakov solitons at different temperatures was also analyzed.The results show that,when the temperature of the crystal increases,the peak intensity of two components of the bright-bright Manakov screening solitons will decrease and the full width of half maximum of two components will increase.The dark-dark and bright-dark Manakov screening solitons have the same temperature characteristics as the bright-bright Manakov screening solitons.All the results indicate that the spatial shape of solitons can be regulated by adjusting the temperature of crystals.
In order to study temperature characteristics of Manakov screening solitons in biased two-photon photorefractive crystals,their intensity profiles were obtained by means of numerical simulation.Moreover,the dynamic evolution of bright-dark Manakov solitons at different temperatures was also analyzed.The results show that,when the temperature of the crystal increases,the peak intensity of two components of the bright-bright Manakov screening solitons will decrease and the full width of half maximum of two components will increase.The dark-dark and bright-dark Manakov screening solitons have the same temperature characteristics as the bright-bright Manakov screening solitons.All the results indicate that the spatial shape of solitons can be regulated by adjusting the temperature of crystals.
2010, 34(6): 809-811,831.
doi: 10.3969/j.issn.1001-3806.2010.06.024
Abstract:
The dependence of intensity and position of laser diffraction from capillary waves on incident angles was studied by means of diffraction.When the laser beam obliquely impinges on capillary waves at the different incident angles,the diffraction intensity and position change with the incident angles,and there is a phenomenon of missing orders in the diffraction patterns.Asymmetry of diffraction positions increases with the increase of the incident angle.The theory of laser diffraction from capillary waves at the different incident angles was found,and the analytic expression of the diffraction intensity and position at the different incident angles was obtained.The theoretical and experimental results are in good agreement.The conclusion is valuable for the theory and the application of laser diffraction from capillary waves.
The dependence of intensity and position of laser diffraction from capillary waves on incident angles was studied by means of diffraction.When the laser beam obliquely impinges on capillary waves at the different incident angles,the diffraction intensity and position change with the incident angles,and there is a phenomenon of missing orders in the diffraction patterns.Asymmetry of diffraction positions increases with the increase of the incident angle.The theory of laser diffraction from capillary waves at the different incident angles was found,and the analytic expression of the diffraction intensity and position at the different incident angles was obtained.The theoretical and experimental results are in good agreement.The conclusion is valuable for the theory and the application of laser diffraction from capillary waves.
2010, 34(6): 812-815.
doi: 10.3969/j.issn.1001-3806.2010.06.025
Abstract:
In order to realize the laser quenching heat treatment of cams,according to three preconditions for getting uniform hardened layer,combining with movement forms of laser processing machines,the mathematical models of relative movement were established about laser beam and the cam surface in the laser quenching process,the theoretic analysis and algorithm research were carried out for the laser head's movement,and the formulas of X,ω,B three-axis motion were derived. The result shows that the laser quenching heat treatment of the cam can be controlled feasibly,and it lays a theoretical foundation for the process of complex parts.
In order to realize the laser quenching heat treatment of cams,according to three preconditions for getting uniform hardened layer,combining with movement forms of laser processing machines,the mathematical models of relative movement were established about laser beam and the cam surface in the laser quenching process,the theoretic analysis and algorithm research were carried out for the laser head's movement,and the formulas of X,ω,B three-axis motion were derived. The result shows that the laser quenching heat treatment of the cam can be controlled feasibly,and it lays a theoretical foundation for the process of complex parts.
2010, 34(6): 816-818,822.
doi: 10.3969/j.issn.1001-3806.2010.06.026
Abstract:
In order to obtain a more perfect theory of two-photon screening-photovoltic solitons,the theory of spatial solitons in biased two-photon photovoltaic photorefractive crystals were amended theoretically under the condition that spatial width of the beam was not much smaller than the width of crystal.The numerical integral solutions for both the bright and dark solitons were presented.The result shows that different from screening solitons originating from the spatially nonuniform screening of the external electric field and photovoltaic solitons originating from the photovoltaic effect,two-photon screening photovoltaic solitons originates from both the spatially nonuniform screening of the external electric field and the photovoltaic effect.When the photovoltaic effect is neglected,the screening-photovoltaic solitons are the screening ones and their space charge field is the space charge field of the screening solitons.When the external field is absent,the screening photovoltaic solitons are the photovoltaic ones on the open and closed circuit conditions and their space charge field is of the photovoltaic solitons.
In order to obtain a more perfect theory of two-photon screening-photovoltic solitons,the theory of spatial solitons in biased two-photon photovoltaic photorefractive crystals were amended theoretically under the condition that spatial width of the beam was not much smaller than the width of crystal.The numerical integral solutions for both the bright and dark solitons were presented.The result shows that different from screening solitons originating from the spatially nonuniform screening of the external electric field and photovoltaic solitons originating from the photovoltaic effect,two-photon screening photovoltaic solitons originates from both the spatially nonuniform screening of the external electric field and the photovoltaic effect.When the photovoltaic effect is neglected,the screening-photovoltaic solitons are the screening ones and their space charge field is the space charge field of the screening solitons.When the external field is absent,the screening photovoltaic solitons are the photovoltaic ones on the open and closed circuit conditions and their space charge field is of the photovoltaic solitons.
2010, 34(6): 819-822.
doi: 10.3969/j.issn.1001-3806.2010.06.027
Abstract:
In order to obtain high precision,high efficiency and low ripple current drivers in pump-modules of fiber amplifiers,a new laser diode (LD) driving circuit,composed of modules of driver and serial interface and so on,was designed. A switching power-converter current source based LM2676 was designed to drive LD at higher conversion efficiency.The circuit is capable of delivering up to 2.5A current to a laser load with precision of 0.1%,efficiency larger than 85% and current ripple of 0.5 mA because of a LC filter.Meanwhile long-distance reading and setting of the pump-module LD driver can be achieved by the design of serial device circuit control system.Results indicate that the circuit meets the theory design demands and can be applied in pump-modules of fiber amplifiers.
In order to obtain high precision,high efficiency and low ripple current drivers in pump-modules of fiber amplifiers,a new laser diode (LD) driving circuit,composed of modules of driver and serial interface and so on,was designed. A switching power-converter current source based LM2676 was designed to drive LD at higher conversion efficiency.The circuit is capable of delivering up to 2.5A current to a laser load with precision of 0.1%,efficiency larger than 85% and current ripple of 0.5 mA because of a LC filter.Meanwhile long-distance reading and setting of the pump-module LD driver can be achieved by the design of serial device circuit control system.Results indicate that the circuit meets the theory design demands and can be applied in pump-modules of fiber amplifiers.
2010, 34(6): 823-827.
doi: 10.3969/j.issn.1001-3806.2010.06.028
Abstract:
In order to reduce the influence of differential loss on the performance of four-frequency differential laser gyros, zero drift resulting from differential loss was analyzed theoretically according to semi-classical theory of gas lasers.Modes in the four-frequency differential laser gyro have different round trip loss due to different polarization,propagating direction.Light intensity and frequency of the lasing mode relate to the round trip loss,so zero drift will appear if influence of differential loss is not removed in the difference frequency.With self consistent equations,effects of detuning frequency,magnetic field,cavity length,reciprocal biasing,Faraday biasing,Doppler broadening and gas pressure on three coefficients of differential loss were analyzed.The results show that zero drift caused by differential polarization loss can be eliminated by application of magnetic field.However,zero drifts caused by differential direction loss and magnetic circular dichroism loss cannot be eliminated by varying magnetic field or detuning frequency.Coefficients of differential loss can be changed by changing gas pressure and neon isotope ratio.Therefore,besides reduction of differential loss themselves,optimization of gain medium will play a certain role in reducing zero drift caused by differential loss.
In order to reduce the influence of differential loss on the performance of four-frequency differential laser gyros, zero drift resulting from differential loss was analyzed theoretically according to semi-classical theory of gas lasers.Modes in the four-frequency differential laser gyro have different round trip loss due to different polarization,propagating direction.Light intensity and frequency of the lasing mode relate to the round trip loss,so zero drift will appear if influence of differential loss is not removed in the difference frequency.With self consistent equations,effects of detuning frequency,magnetic field,cavity length,reciprocal biasing,Faraday biasing,Doppler broadening and gas pressure on three coefficients of differential loss were analyzed.The results show that zero drift caused by differential polarization loss can be eliminated by application of magnetic field.However,zero drifts caused by differential direction loss and magnetic circular dichroism loss cannot be eliminated by varying magnetic field or detuning frequency.Coefficients of differential loss can be changed by changing gas pressure and neon isotope ratio.Therefore,besides reduction of differential loss themselves,optimization of gain medium will play a certain role in reducing zero drift caused by differential loss.
2010, 34(6): 828-831.
doi: 10.3969/j.issn.1001-3806.2010.06.029
Abstract:
In order to describe the refractive index profiles of Y-branch waveguide in x and y direction with only one expression,after analyzing the construction of glass substrate and the ion exchange process,an expression based on the product of refractive index distribution functions on the horizontal direction and the vertical direction was put forward by means of inverse variable separation method.Then the refractive index profiles were simulated with MATLAB.A 12 Y-branch optical waveguide was fabricated on BK7 glass substrate by means of Tl+-Na+ ion-exchange method,and its refractive-index profiles was measured by means of interference method.The simulated profiles were in good agreement with experimental results.The results show that the refractive-index distribution of Y-branch optical waveguide in cross-section can be reconstructed by the improved function n(x,y) easily.
In order to describe the refractive index profiles of Y-branch waveguide in x and y direction with only one expression,after analyzing the construction of glass substrate and the ion exchange process,an expression based on the product of refractive index distribution functions on the horizontal direction and the vertical direction was put forward by means of inverse variable separation method.Then the refractive index profiles were simulated with MATLAB.A 12 Y-branch optical waveguide was fabricated on BK7 glass substrate by means of Tl+-Na+ ion-exchange method,and its refractive-index profiles was measured by means of interference method.The simulated profiles were in good agreement with experimental results.The results show that the refractive-index distribution of Y-branch optical waveguide in cross-section can be reconstructed by the improved function n(x,y) easily.
2010, 34(6): 832-834,838.
doi: 10.3969/j.issn.1001-3806.2010.06.030
Abstract:
In order to reveal the relationship between blue-violet light signal and the surface quality in cladding process,the blue-violet light signal intensity was measured in real time with a UV-420 device.The blue-violet intensity was obtained at different scanning speeds and laser power.Experimental and analytical results show that the surface quality is good when blue-violet intensity is relatively stabled at 1.7μW/cm2～2.5μW/cm.And the plasma is mainly caused by the breakdown of powder's vaporization.The blue-violet intensity can reflect the surface quality,and it can also provide parameters for closed-loop feedback control.
In order to reveal the relationship between blue-violet light signal and the surface quality in cladding process,the blue-violet light signal intensity was measured in real time with a UV-420 device.The blue-violet intensity was obtained at different scanning speeds and laser power.Experimental and analytical results show that the surface quality is good when blue-violet intensity is relatively stabled at 1.7μW/cm2～2.5μW/cm.And the plasma is mainly caused by the breakdown of powder's vaporization.The blue-violet intensity can reflect the surface quality,and it can also provide parameters for closed-loop feedback control.
2010, 34(6): 835-838.
doi: 10.3969/j.issn.1001-3806.2010.06.031
Abstract:
In order to investigate the stray facula in the in-line digital hologram with an array CCD detector irradiated by short intense laser pulse,variable images were gathered with CCD under laser irradiation or not.Different image grey was analyzed based on the diffraction fringes of the particles and the output electrical signal of the pixel.The stray facula was induced by diffracting dust in the pixels and the abnormal behavior of the reset level due to laser absorption of CCD.Without laser irradiation,the image gathered by CCD was quite abnormal due to the thermal effect and memory effect of CCD.The results showed that the stray facula vanished slowly with the elimination of heat during a long time.Finally,the image gathered by CCD can recover normally and the stray facula vanished completely when the dirty was removed and the time interval of the gathering image was prolonged.
In order to investigate the stray facula in the in-line digital hologram with an array CCD detector irradiated by short intense laser pulse,variable images were gathered with CCD under laser irradiation or not.Different image grey was analyzed based on the diffraction fringes of the particles and the output electrical signal of the pixel.The stray facula was induced by diffracting dust in the pixels and the abnormal behavior of the reset level due to laser absorption of CCD.Without laser irradiation,the image gathered by CCD was quite abnormal due to the thermal effect and memory effect of CCD.The results showed that the stray facula vanished slowly with the elimination of heat during a long time.Finally,the image gathered by CCD can recover normally and the stray facula vanished completely when the dirty was removed and the time interval of the gathering image was prolonged.
2010, 34(6): 839-842.
doi: 10.3969/j.issn.1001-3806.2010.06.032
Abstract:
In order to study the change regularity of photon states in atmospheric turbulence,the photon state detection probability was derived based on facts that transverse spatial wave function of Laguerre-Gaussian beam is the eigenfunction of a photon and transverse spatial wave function of Laguerre-Gaussian beam propagation in turbulent atmosphere approaches to superimposition of all photon state eigenfunctions.Effect of atmospheric turbulence,propagation length,quality factor on detection probability was analyzed.The results present that the change of the photon state largely relies on beam quality factor. With the same quality factor,the measurement weight at the receiving plane is nearly the same.In addition,the total measurement weight from initial photon to state at which the orbital angular momentum increases to a certain value,is equivalent to the total measurement weight of the corresponding decrease.The stronger the turbulence is,the smaller the photon state measurement weight of the initial photon state at the receiving side is.That is also true of the propagating distance.However, distance puts much less effect on photon states than atmospheric turbulence.
In order to study the change regularity of photon states in atmospheric turbulence,the photon state detection probability was derived based on facts that transverse spatial wave function of Laguerre-Gaussian beam is the eigenfunction of a photon and transverse spatial wave function of Laguerre-Gaussian beam propagation in turbulent atmosphere approaches to superimposition of all photon state eigenfunctions.Effect of atmospheric turbulence,propagation length,quality factor on detection probability was analyzed.The results present that the change of the photon state largely relies on beam quality factor. With the same quality factor,the measurement weight at the receiving plane is nearly the same.In addition,the total measurement weight from initial photon to state at which the orbital angular momentum increases to a certain value,is equivalent to the total measurement weight of the corresponding decrease.The stronger the turbulence is,the smaller the photon state measurement weight of the initial photon state at the receiving side is.That is also true of the propagating distance.However, distance puts much less effect on photon states than atmospheric turbulence.
2010, 34(6): 843-846.
doi: 10.3969/j.issn.1001-3806.2010.06.033
Abstract:
For the sake of studying coded modulations between digital pulse modulation(DPM) and channel error coding in optical wireless communication,after introducing time domain structure of DPM,the error performances of on-off keying(OOK), pulse position modulation (PPM) and digital pulse interval modulation (DPIM) systems were analyzed with binary linear block code.Afterward computer simulations were conducted and the relationship between error correction ability of channel code and modulation level of DPM was obtained.Numerical results show that there is no matching issue for an OOK system using binary linear block code because its bijection between Hamming distance and Euclidean distance.For a PPM system,much better coding and modulation gain can be acquired if error correction number of binary linear block code is bigger than modulation level M. Especially,when error correction number is divided exactly by M,the coding gain and coding cost can get to balance.Moreover, channel code is not fit for DPIM since its variable symbol slots which cause error propagation.The conclusions can be used to help design of optical wireless link.
For the sake of studying coded modulations between digital pulse modulation(DPM) and channel error coding in optical wireless communication,after introducing time domain structure of DPM,the error performances of on-off keying(OOK), pulse position modulation (PPM) and digital pulse interval modulation (DPIM) systems were analyzed with binary linear block code.Afterward computer simulations were conducted and the relationship between error correction ability of channel code and modulation level of DPM was obtained.Numerical results show that there is no matching issue for an OOK system using binary linear block code because its bijection between Hamming distance and Euclidean distance.For a PPM system,much better coding and modulation gain can be acquired if error correction number of binary linear block code is bigger than modulation level M. Especially,when error correction number is divided exactly by M,the coding gain and coding cost can get to balance.Moreover, channel code is not fit for DPIM since its variable symbol slots which cause error propagation.The conclusions can be used to help design of optical wireless link.
Research and measurement of feedback strength of optical feedback self-mixing interferometry systems
2010, 34(6): 847-850.
doi: 10.3969/j.issn.1001-3806.2010.06.034
Abstract:
In order to obtain feedback strength of optical feedback self-mixing interferometry (OFSMI) systems exactly, OFSMI signals were simulated and analyzed and Lang-Kobayashi equations were solved.It is found that separation between the minimum of the up-side interferometric fringes and the maximum of down-side interferometric fringes grows as the optical feedback strength factor increases.Some interferometric fringes disappear when the factor is greater than 7.8.Besides,a formula about feedback strength factor was deduced from hysteresis phenomenon and a measurement model was set up.The simulation and experimental results show that OFSMI signal fringes are related to the optical feedback strength factor.The proposed model based on the formula about the factor can be used to judge regimes of OFSMI measurement systems and the value of optical feedback strength factor can be figured out when it is between 1 and 7.8.
In order to obtain feedback strength of optical feedback self-mixing interferometry (OFSMI) systems exactly, OFSMI signals were simulated and analyzed and Lang-Kobayashi equations were solved.It is found that separation between the minimum of the up-side interferometric fringes and the maximum of down-side interferometric fringes grows as the optical feedback strength factor increases.Some interferometric fringes disappear when the factor is greater than 7.8.Besides,a formula about feedback strength factor was deduced from hysteresis phenomenon and a measurement model was set up.The simulation and experimental results show that OFSMI signal fringes are related to the optical feedback strength factor.The proposed model based on the formula about the factor can be used to judge regimes of OFSMI measurement systems and the value of optical feedback strength factor can be figured out when it is between 1 and 7.8.
2010, 34(6): 851-854.
doi: 10.3969/j.issn.1001-3806.2010.06.035
Abstract:
A simple method was presented to determine various higher order chirps in ultrashort laser pulses based on interferometric autocorrelation (IAC) envelope width.This method is highly sensitive to chirp,dependence of envelope width of IAC on different magnitude of the chirp and its order.Through the Gaussian intensity of the linear chirp,square and cubic chirp pulses were analyzed and numerical calculated,IAC envelope width as a functions of the normalized mean chirp for different orders of chirp were obtained.The theoretical analysis was supported by experimental envelope width,IAC signals obtained using laser chirped pulses from a CW dye ring laser in the colliding pulse mode (CPM) locked regime.According to the characteristics of IAC envelope,the square chirp pulse was determined,the envelope width was measured 1.15 and the chirped ultrashort laser pulse was measured 1.0.The results show that the order of chirp can be determined according to the chirp characteristics of the two wings of IAC envelope and that the value of the chirp can be estimated according to its dependence on the envelope width. Chirp of ultrashort laser pulses can be determined easily based on the IAC envelope width.
A simple method was presented to determine various higher order chirps in ultrashort laser pulses based on interferometric autocorrelation (IAC) envelope width.This method is highly sensitive to chirp,dependence of envelope width of IAC on different magnitude of the chirp and its order.Through the Gaussian intensity of the linear chirp,square and cubic chirp pulses were analyzed and numerical calculated,IAC envelope width as a functions of the normalized mean chirp for different orders of chirp were obtained.The theoretical analysis was supported by experimental envelope width,IAC signals obtained using laser chirped pulses from a CW dye ring laser in the colliding pulse mode (CPM) locked regime.According to the characteristics of IAC envelope,the square chirp pulse was determined,the envelope width was measured 1.15 and the chirped ultrashort laser pulse was measured 1.0.The results show that the order of chirp can be determined according to the chirp characteristics of the two wings of IAC envelope and that the value of the chirp can be estimated according to its dependence on the envelope width. Chirp of ultrashort laser pulses can be determined easily based on the IAC envelope width.
2010, 34(6): 855-860.
doi: 10.3969/j.issn.1001-3806.2010.06.036
Abstract:
Up-conversion fluorescent mechanisms were briefly introduced.The methods of improving frequency up-conversion efficiency of rare-earth doped luminescent materials,mainly including changing the substrate phonon distribution, adding the sensitizer,changing the ratio of substrate materials components,and application of new technology,such as surface enhanced fluorescence,pumping methods,new materials synthesis and so on,were reviewed in detail.Furthermore,the research trends of up-conversion luminescent materials in the future were prospected in combination with fluorescence enhancement mechanisms.
Up-conversion fluorescent mechanisms were briefly introduced.The methods of improving frequency up-conversion efficiency of rare-earth doped luminescent materials,mainly including changing the substrate phonon distribution, adding the sensitizer,changing the ratio of substrate materials components,and application of new technology,such as surface enhanced fluorescence,pumping methods,new materials synthesis and so on,were reviewed in detail.Furthermore,the research trends of up-conversion luminescent materials in the future were prospected in combination with fluorescence enhancement mechanisms.
2010, 34(6): 861-864.
doi: 10.3969/j.issn.1001-3806.2010.06.037
Abstract:
In order to study the effect of liquid velocity on laser output field,the output characteristics for hard-edge positive branch unstable resonators in transverse-flow liquid lasers were simulated with finite element difference method algorithm. The thermal flow field for different liquid velocities was analyzed by means of finite element method.The beam quality and laser spot center (peak intensity) were studied when the pump light was plane wave.The offset of spot center was observed in the experiment.The result is that the laser quality is tending to the constant and the laser spot center is biased to the pumped side when the liquid velocity is larger than 1m/s.
In order to study the effect of liquid velocity on laser output field,the output characteristics for hard-edge positive branch unstable resonators in transverse-flow liquid lasers were simulated with finite element difference method algorithm. The thermal flow field for different liquid velocities was analyzed by means of finite element method.The beam quality and laser spot center (peak intensity) were studied when the pump light was plane wave.The offset of spot center was observed in the experiment.The result is that the laser quality is tending to the constant and the laser spot center is biased to the pumped side when the liquid velocity is larger than 1m/s.
2010, 34(6): 785-788.
doi: 10.3969/j.issn.1001-3806.2010.06.018
Abstract:
To examine the chaotic dynamics and its application in communication of a unidirectionally coupled vertical-cavity surface-emitting laser (VCSEL) system,the synchronization performance of polarization modes of two unidirectionally coupled VCSELs were simulated.An encryption scheme was proposed,where the phases of the polarization states of the master laser were modulated.It was demonstrated that high synchronization could be achieved between corresponding polarization components of the master laser and the slave laser.Moreover,there were two distinct synchronization regimes,i.e.complete synchronization and injection locking synchronization.The transmitted digital information was successfully recovered at each polarization branch of the slaver laser.The results open an opportunity for multichannel chaotic communication by utilizing different polarization components in single-mode or multi-transverse-mode VCSELs.
To examine the chaotic dynamics and its application in communication of a unidirectionally coupled vertical-cavity surface-emitting laser (VCSEL) system,the synchronization performance of polarization modes of two unidirectionally coupled VCSELs were simulated.An encryption scheme was proposed,where the phases of the polarization states of the master laser were modulated.It was demonstrated that high synchronization could be achieved between corresponding polarization components of the master laser and the slave laser.Moreover,there were two distinct synchronization regimes,i.e.complete synchronization and injection locking synchronization.The transmitted digital information was successfully recovered at each polarization branch of the slaver laser.The results open an opportunity for multichannel chaotic communication by utilizing different polarization components in single-mode or multi-transverse-mode VCSELs.
