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RSS2008 Vol. 32, No. 3
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2008, 32(3): 225-227,243.
[Abstract]
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Abstract:
An analytic model was derived to describe the shock wave attenuation in plexiglass.Experimental measurements were also presented with a well-designed optical fiber sensor based on detection beam deflection.The velocity and pressure of the shock wave were achieved at different distances.Good agreement between the experimental and calculated values of the shock wave pressure was established.
An analytic model was derived to describe the shock wave attenuation in plexiglass.Experimental measurements were also presented with a well-designed optical fiber sensor based on detection beam deflection.The velocity and pressure of the shock wave were achieved at different distances.Good agreement between the experimental and calculated values of the shock wave pressure was established.
2008, 32(3): 228-230,239.
Abstract:
The all optical pulses replicating technique for equivalent-time sampling based on active fiber loop replicator was presented.The analysis showed replication error of active fiber loop replicator caused by nonlinear gain and amplified spontaneous emission of semiconductor optical amplifier could be reduced by holding light injecting.The nonlinear errors of active fiber loop replicator and amplified spontaneous emission(ASE) noise adding in output pulses sequence were discussed.The output waveform and distribution of random error caused by ASE noise were measured too.The results show that activ fiber loop replicator is suitable to generate pulses sequence for equivalent-time sampling with waveform identity.
The all optical pulses replicating technique for equivalent-time sampling based on active fiber loop replicator was presented.The analysis showed replication error of active fiber loop replicator caused by nonlinear gain and amplified spontaneous emission of semiconductor optical amplifier could be reduced by holding light injecting.The nonlinear errors of active fiber loop replicator and amplified spontaneous emission(ASE) noise adding in output pulses sequence were discussed.The output waveform and distribution of random error caused by ASE noise were measured too.The results show that activ fiber loop replicator is suitable to generate pulses sequence for equivalent-time sampling with waveform identity.
2008, 32(3): 231-233,251.
Abstract:
In order to study the effect of laser remelting on the property of the nanocrystalline nickel coating prepared by jet electrodepositing on the substrate of 45# carbon steel,the coatings' surface morphology and the size of crystal were analyzed with scanning electron microscope and X-ray diffractometry,the microhardness and corrosion resistance of coatings were also tested,and the effect of laser remelting were discussed in theory and experiment.The results showed that the average size of crystal of jet electrodeposited nickel coating was 13.7nm under the optimum processing parameters.After laser remelting,the size of crystal of coating was greatly diminished,the bonding state between the coating and substrate becomes from mechanical combination to metallurgical combination,and the coating's microhardness,the corrosion resistance were obviously increased.This result has certain theory and practical significance in promoting laser processing technique in the application of nano-materials.
In order to study the effect of laser remelting on the property of the nanocrystalline nickel coating prepared by jet electrodepositing on the substrate of 45# carbon steel,the coatings' surface morphology and the size of crystal were analyzed with scanning electron microscope and X-ray diffractometry,the microhardness and corrosion resistance of coatings were also tested,and the effect of laser remelting were discussed in theory and experiment.The results showed that the average size of crystal of jet electrodeposited nickel coating was 13.7nm under the optimum processing parameters.After laser remelting,the size of crystal of coating was greatly diminished,the bonding state between the coating and substrate becomes from mechanical combination to metallurgical combination,and the coating's microhardness,the corrosion resistance were obviously increased.This result has certain theory and practical significance in promoting laser processing technique in the application of nano-materials.
2008, 32(3): 234-236,247.
Abstract:
A theoretical model was proposed to calculate the lasing wavelength of free running ytterbium-doped fiber lasers.Based on this model,the relationship between lasing wavelength and fiber length,cavity loss,doping concentration as well as working temperature was obtained,which can help design tunable fiber lasers and fiber lasers with required lasing wavelengths.An approximation was introduced to deal with the temperature dependence of absorption and emission cross section of the doped fiber.The applicability of this model was examined by comparing calculation results with published experiment data.
A theoretical model was proposed to calculate the lasing wavelength of free running ytterbium-doped fiber lasers.Based on this model,the relationship between lasing wavelength and fiber length,cavity loss,doping concentration as well as working temperature was obtained,which can help design tunable fiber lasers and fiber lasers with required lasing wavelengths.An approximation was introduced to deal with the temperature dependence of absorption and emission cross section of the doped fiber.The applicability of this model was examined by comparing calculation results with published experiment data.
2008, 32(3): 237-239.
Abstract:
In order to explore a 56J high-energy high-frequency lamp-pumped pulsed Nd:YAG solid-state laser,the main factors affecting the laser output were studied and the relation between the output power and input power and reflectivity was simulated.Then some effective measures were adopted to improve the efficiencies of the laser in experiments.As a result,a high energy Nd:YAG laser was obtained whose pulse width tunable between 0.1ms and 10ms,frequency tunable between 1Hz and 1kHz.When the laser inputs 12kW electrical power,its maximum single pulse energy was up to 56J,maximum average power is up to 500W with its beam parameter product 16.5mm·mrad,total electro-optics efficiency 4.2%,the stability of output power ±2%.The experimental results are corresponding to the theoretical ones.
In order to explore a 56J high-energy high-frequency lamp-pumped pulsed Nd:YAG solid-state laser,the main factors affecting the laser output were studied and the relation between the output power and input power and reflectivity was simulated.Then some effective measures were adopted to improve the efficiencies of the laser in experiments.As a result,a high energy Nd:YAG laser was obtained whose pulse width tunable between 0.1ms and 10ms,frequency tunable between 1Hz and 1kHz.When the laser inputs 12kW electrical power,its maximum single pulse energy was up to 56J,maximum average power is up to 500W with its beam parameter product 16.5mm·mrad,total electro-optics efficiency 4.2%,the stability of output power ±2%.The experimental results are corresponding to the theoretical ones.
2008, 32(3): 240-243.
Abstract:
According to the liquid separation property of Cu-base alloy,the Cu-base coating is obtained on the aluminum alloy by CO2 laser cladding for improving the surface strength of aluminum alloy.The results show that the matrix of the coating is Cu-base solid solution,and the main reinforcing phase is laves phase,which shows a dispersion distribution character.The reinforcing phase shows a composite structure of "Mo-rich core"+"surrounding phase".This is mainly caused by the separation of Mo-rich cores,which furnish the liquid separation with heterogeneity nucleation surface.The microhardness test shows that the microhardness of the coating is about 270HV0.05,two times higher than that of the substrate ZL104 aluminum alloy.
According to the liquid separation property of Cu-base alloy,the Cu-base coating is obtained on the aluminum alloy by CO2 laser cladding for improving the surface strength of aluminum alloy.The results show that the matrix of the coating is Cu-base solid solution,and the main reinforcing phase is laves phase,which shows a dispersion distribution character.The reinforcing phase shows a composite structure of "Mo-rich core"+"surrounding phase".This is mainly caused by the separation of Mo-rich cores,which furnish the liquid separation with heterogeneity nucleation surface.The microhardness test shows that the microhardness of the coating is about 270HV0.05,two times higher than that of the substrate ZL104 aluminum alloy.
2008, 32(3): 244-247.
Abstract:
Thermal change and its difference on the optical penetration depth of human benign prostatic hyperplasia(BPH) tissue was measured with a double-integrating-sphere setup at 532nm,670nm,830nm and 1064nm. The optical properties of BPH tissue were assessed from the measurement results using the inverse adding-doubling method.The results of measurement showed that,in exposure temperature range from 20℃ to 80℃,the optical penetration depth of BPH tissue at 532nm,670nm,830nm and 1064nm increased with increase of wavelengths,the optical penetration depth of BPH tissue at 532nm,670nm,830nm and 1064nm varied with a change of exposure temperature by thermal effect,change of the optical penetration depth of BPH tissue at 1064nm was significantly bigger than that of BPH tissues at 532nm,670nm and 830nm,respectively with increase of exposure temperature.Maximal optical penetration depths of BPH tissue at 532nm,670nm,830nm and 1064nm were respectively 0.404mm,0.539mm,0.699mm and 5.917mm at exposure temperature of 50℃,50℃,50℃ and 70℃,respectively,andminimal optical penetration depths were respectively 0.251mm,0.449mm,0.621mm and 1.542mm at exposure temperature of 20℃,20℃,80℃ and 60℃.The results of measurement indicated a few useful reference data for treatment of BPH using optical and thermal properties of laser.
Thermal change and its difference on the optical penetration depth of human benign prostatic hyperplasia(BPH) tissue was measured with a double-integrating-sphere setup at 532nm,670nm,830nm and 1064nm. The optical properties of BPH tissue were assessed from the measurement results using the inverse adding-doubling method.The results of measurement showed that,in exposure temperature range from 20℃ to 80℃,the optical penetration depth of BPH tissue at 532nm,670nm,830nm and 1064nm increased with increase of wavelengths,the optical penetration depth of BPH tissue at 532nm,670nm,830nm and 1064nm varied with a change of exposure temperature by thermal effect,change of the optical penetration depth of BPH tissue at 1064nm was significantly bigger than that of BPH tissues at 532nm,670nm and 830nm,respectively with increase of exposure temperature.Maximal optical penetration depths of BPH tissue at 532nm,670nm,830nm and 1064nm were respectively 0.404mm,0.539mm,0.699mm and 5.917mm at exposure temperature of 50℃,50℃,50℃ and 70℃,respectively,andminimal optical penetration depths were respectively 0.251mm,0.449mm,0.621mm and 1.542mm at exposure temperature of 20℃,20℃,80℃ and 60℃.The results of measurement indicated a few useful reference data for treatment of BPH using optical and thermal properties of laser.
2008, 32(3): 252-254,258.
Abstract:
In order to improve the accuracy of directional detection with the same number of optical channels in the fiber-array laser receiving antenna,a new directional detection algorithm was been proposed,in which the two-dimension waveform data of time delay was expanded into three-dimension data,and the angles were calculated based on the matrix of echoed laser intensity,and the suppression of false alarm was also considered.Comparing the angular resolution with this algorithm before and after,its absolute accuracy was improved significantly from 5° to 2°.It is seen that this algorithm can obviously improve the accuracy of directional detection.
In order to improve the accuracy of directional detection with the same number of optical channels in the fiber-array laser receiving antenna,a new directional detection algorithm was been proposed,in which the two-dimension waveform data of time delay was expanded into three-dimension data,and the angles were calculated based on the matrix of echoed laser intensity,and the suppression of false alarm was also considered.Comparing the angular resolution with this algorithm before and after,its absolute accuracy was improved significantly from 5° to 2°.It is seen that this algorithm can obviously improve the accuracy of directional detection.
2008, 32(3): 255-258.
Abstract:
In order to study the essential characteristic of airborne particle counter signal transmission,some basic characteristics of airborne particle counter are studied with proceeding from single particle signal,including collecting characteristic of scattered light and photoelectric transfer characteristic.Based on these,statistics characteristic of signal distribute of single particle group and signal transmission characteristic of mixed particles group were analyzed.At the same time,the experiment was performed and the result is consistent with the theory with the correlation coefficient more than 0.9.Results indicate the essence of airborne particle counter signal transmission is changing particle's diameter distribute way to corresponding pulse signal amplitude distribute way with linear transform.All these establish the theoretical foundation for promoting the instrument's development toward the large flow and high sensitivity.
In order to study the essential characteristic of airborne particle counter signal transmission,some basic characteristics of airborne particle counter are studied with proceeding from single particle signal,including collecting characteristic of scattered light and photoelectric transfer characteristic.Based on these,statistics characteristic of signal distribute of single particle group and signal transmission characteristic of mixed particles group were analyzed.At the same time,the experiment was performed and the result is consistent with the theory with the correlation coefficient more than 0.9.Results indicate the essence of airborne particle counter signal transmission is changing particle's diameter distribute way to corresponding pulse signal amplitude distribute way with linear transform.All these establish the theoretical foundation for promoting the instrument's development toward the large flow and high sensitivity.
2008, 32(3): 259-261.
Abstract:
Applying the Huygens-Fresnel diffractive integral,the on-axis intensity distribution and the phenomena of focal shift and focal switch are theoretical studied when a partially coherent annular light is focused by a lens.The results show that the amount of the focal shift depends on not only the Fresnel number of the annular beam,but also the spatial coherence and the central obstruction ratio of the incident partially coherent light.It is also shown that the greater the Fresnel number,the smaller the focal shift;the higher the spatial coherence,the smaller the focal shift.For a fixed Fresnel number,the larger the central obstruction ratio is,the larger the focal shift is.For a given spatial coherence,the phenomenon of focal switch will occur as the Fresnel number decreases.The results are helpful to the research of the focus of partially coherent annular beam.
Applying the Huygens-Fresnel diffractive integral,the on-axis intensity distribution and the phenomena of focal shift and focal switch are theoretical studied when a partially coherent annular light is focused by a lens.The results show that the amount of the focal shift depends on not only the Fresnel number of the annular beam,but also the spatial coherence and the central obstruction ratio of the incident partially coherent light.It is also shown that the greater the Fresnel number,the smaller the focal shift;the higher the spatial coherence,the smaller the focal shift.For a fixed Fresnel number,the larger the central obstruction ratio is,the larger the focal shift is.For a given spatial coherence,the phenomenon of focal switch will occur as the Fresnel number decreases.The results are helpful to the research of the focus of partially coherent annular beam.
2008, 32(3): 262-264.
Abstract:
In order to validate the technical feasibility of air plasma channel with nanosecond ultraviolet laser,the interaction between air and 248nm ultraviolet laser was studied in laboratory.The air ionization threshold was measured in room.Continuous plasma channel was set up.The conducting experiments of plasma channel were carried out with direct current.Flash plasma channel length is about 8mm with 180mJ laser pulses.The conductive plasma channel length is about 20mm.It is possible to establish the continuous laser plasma conducting channel with nanosecond ultraviolent laser.
In order to validate the technical feasibility of air plasma channel with nanosecond ultraviolet laser,the interaction between air and 248nm ultraviolet laser was studied in laboratory.The air ionization threshold was measured in room.Continuous plasma channel was set up.The conducting experiments of plasma channel were carried out with direct current.Flash plasma channel length is about 8mm with 180mJ laser pulses.The conductive plasma channel length is about 20mm.It is possible to establish the continuous laser plasma conducting channel with nanosecond ultraviolent laser.
2008, 32(3): 265-267,271.
Abstract:
For improving the precision of the parameter estimate,a set of pre-processing methods including filtering and normalization were proposed for the initial experimental signal according to the characteristics of the optical feedback self-mixing interference signal.The proposed approach implements filtering of noise effectively and flat the signal.The pre-processed OFSMI experimental signal tallied much with the theoretic signal.Estimating parameters using the initial and the pre-processing signal separately,comparison results show that the latter can make the accuracy of the line width spreading factorand the optical feedback level factor C improve by 5.52% and 4.55% respectively.
For improving the precision of the parameter estimate,a set of pre-processing methods including filtering and normalization were proposed for the initial experimental signal according to the characteristics of the optical feedback self-mixing interference signal.The proposed approach implements filtering of noise effectively and flat the signal.The pre-processed OFSMI experimental signal tallied much with the theoretic signal.Estimating parameters using the initial and the pre-processing signal separately,comparison results show that the latter can make the accuracy of the line width spreading factorand the optical feedback level factor C improve by 5.52% and 4.55% respectively.
2008, 32(3): 268-271.
Abstract:
In order to study the transmitting characteristics of single-mode Gaussian beam passing through polarizing prism,after analyzing the optical path difference in two coherent beams,the interference effect at the cementing layer of Semarmont prism was analyzed in detail.The results reveal that for single-mode Gaussian beam,the transmission of the polarized light oscillates in period with one of the three parameters,i.e.,the incident angle at the interface of the cementing layer,the thickness of the cementing layer and the refracting index of cement.The shape of the transmitted beam will change with them too.Comparatively,the effect of prism on o light is more than e light.In general,the effect on the transmitted Gaussian beam less than 3%,so the effect of Semarmont prism on the transmitting characteristics of Gaussian beam can be neglected in practice if the requirement is not extraordinary strict.
In order to study the transmitting characteristics of single-mode Gaussian beam passing through polarizing prism,after analyzing the optical path difference in two coherent beams,the interference effect at the cementing layer of Semarmont prism was analyzed in detail.The results reveal that for single-mode Gaussian beam,the transmission of the polarized light oscillates in period with one of the three parameters,i.e.,the incident angle at the interface of the cementing layer,the thickness of the cementing layer and the refracting index of cement.The shape of the transmitted beam will change with them too.Comparatively,the effect of prism on o light is more than e light.In general,the effect on the transmitted Gaussian beam less than 3%,so the effect of Semarmont prism on the transmitting characteristics of Gaussian beam can be neglected in practice if the requirement is not extraordinary strict.
2008, 32(3): 274-277.
Abstract:
For analyzing the diffraction property of an axicon in quasi-monochromatic illumination,based on the analyses of the diffraction property of an axicon illuminated by a monochromatic plane wave and the property of quasi-monochromatic light that it can be regarded as superposition of monochromatic components of differential frequencies,the intensity distribution of the diffraction pattern of an axicon in quasi-monochromatic light was deduced.According to the numerical simulation and experimental results,the difference between the diffraction patterns generated by quasi-monochromatic light and monochromatic light was compared.Results show that the intensity distribution of an axicon in quasi-monochromatic light is given by the sum of intensity of individual component,and the diffraction fringes are less than those produced by monochromatic light.Moreover the off-axis intensity attenuates more rapidly than that of monochromatic waves.
For analyzing the diffraction property of an axicon in quasi-monochromatic illumination,based on the analyses of the diffraction property of an axicon illuminated by a monochromatic plane wave and the property of quasi-monochromatic light that it can be regarded as superposition of monochromatic components of differential frequencies,the intensity distribution of the diffraction pattern of an axicon in quasi-monochromatic light was deduced.According to the numerical simulation and experimental results,the difference between the diffraction patterns generated by quasi-monochromatic light and monochromatic light was compared.Results show that the intensity distribution of an axicon in quasi-monochromatic light is given by the sum of intensity of individual component,and the diffraction fringes are less than those produced by monochromatic light.Moreover the off-axis intensity attenuates more rapidly than that of monochromatic waves.
2008, 32(3): 278-280.
Abstract:
To investigate the influence of thermal deformation of high-power laser output windows on the beam quality,the Strehl ratio formula and the far-field normalized intensity under thermal aberration were induced with the thermal effect of the refractive index of the materials considered.The influence of the thermal aberration of the output windows on the Strehl ratio and the far-field normalized intensity were analyzed and discussed.The results show that under the same laser radiation,in the presence of temperature effect of refractive index,the far-field Strehl ratio of Al2O3 changes the slowest with the laser radiation power among the three materials.
To investigate the influence of thermal deformation of high-power laser output windows on the beam quality,the Strehl ratio formula and the far-field normalized intensity under thermal aberration were induced with the thermal effect of the refractive index of the materials considered.The influence of the thermal aberration of the output windows on the Strehl ratio and the far-field normalized intensity were analyzed and discussed.The results show that under the same laser radiation,in the presence of temperature effect of refractive index,the far-field Strehl ratio of Al2O3 changes the slowest with the laser radiation power among the three materials.
2008, 32(3): 281-283.
Abstract:
In order to determine the diffusivity of vitamin B6,a real-time laser holographic interferometer was employed.The diffusion coefficients of vitamin B6 in aqueous solution and in biologic brine were obtained at 298.15K respectively.The results show that,the diffusion coefficient of vitamin B6 in aqueous solution decreases unilaterally with the concentration of vitamin B6,but in biologic brine the diffusion coefficient increases up to a maximum and then decreases remarkably with the concentration of vitamin B6,it is mainly due to the special self-structure of vitamin B6 and the effect of different interaction existing in different solution.The above characteristic hasn't been reported so far in literature.Relative explanation and discuss were given in this paper according to the integrated effect of H-bond action,interaction between particles,ion intensity and friction resistance between solute and solvent,etc.The results are important to the medical field.
In order to determine the diffusivity of vitamin B6,a real-time laser holographic interferometer was employed.The diffusion coefficients of vitamin B6 in aqueous solution and in biologic brine were obtained at 298.15K respectively.The results show that,the diffusion coefficient of vitamin B6 in aqueous solution decreases unilaterally with the concentration of vitamin B6,but in biologic brine the diffusion coefficient increases up to a maximum and then decreases remarkably with the concentration of vitamin B6,it is mainly due to the special self-structure of vitamin B6 and the effect of different interaction existing in different solution.The above characteristic hasn't been reported so far in literature.Relative explanation and discuss were given in this paper according to the integrated effect of H-bond action,interaction between particles,ion intensity and friction resistance between solute and solvent,etc.The results are important to the medical field.
2008, 32(3): 284-286.
Abstract:
In order to measure the photo damage threshold and infrared spectra of Mg:Er:LiNbO3 crystals,the high quality Mgx:Ery:LiNbO3(x=0.02,0.04,0.06,0.08,y=0.01(mole fraction)) crystals were grown by Czochralski technique.The experiment indicated that the photo damage resistance ability of Mg(0.06):Er:LiNbO3 and Mg(0.08):Er:LiNbO3 crystals improved the two orders magnitude over higher than that of LiNbO3 crystals and their OH-absorption peak of infrared spectra shifts to 3535cm-1 nearby.The experiment gained the steady state shoot spectra of Mg:Er:LiNbO3 crystals in wavelength 510nm~580nm finding doped with mole fraction 0.04 of MgO.The results showed that the Mg2+ concentration increased the photo damage resistance ability increased and the lifetime of Mg:Er:LiNbO3 crystal doped with mole fraction 0.04 of MgO was the longest.
In order to measure the photo damage threshold and infrared spectra of Mg:Er:LiNbO3 crystals,the high quality Mgx:Ery:LiNbO3(x=0.02,0.04,0.06,0.08,y=0.01(mole fraction)) crystals were grown by Czochralski technique.The experiment indicated that the photo damage resistance ability of Mg(0.06):Er:LiNbO3 and Mg(0.08):Er:LiNbO3 crystals improved the two orders magnitude over higher than that of LiNbO3 crystals and their OH-absorption peak of infrared spectra shifts to 3535cm-1 nearby.The experiment gained the steady state shoot spectra of Mg:Er:LiNbO3 crystals in wavelength 510nm~580nm finding doped with mole fraction 0.04 of MgO.The results showed that the Mg2+ concentration increased the photo damage resistance ability increased and the lifetime of Mg:Er:LiNbO3 crystal doped with mole fraction 0.04 of MgO was the longest.
2008, 32(3): 287-289,292.
Abstract:
In order to measure the organic aerosol in the atmosphere,based on laser induced fluorescence,a fluorescence lidar model system was put forward for detecting organic aerosol in the atmosphere.The principle of models system measurement was described exhaustively,system model parameters were presented after fully simulating and analyzing,accounting detection capability.The results showed that when the lidar worked at night,the least detectable density of organic aerosol was only a few particles/L within 5km;while during the daytime,the least detectable density could reduce to less than 10 particles/L within 2km due to background radiation.The results show that the lidar model can satisfy the requirement of real organic aerosol detecting,which could provide valuable instructions to the design of a real system.
In order to measure the organic aerosol in the atmosphere,based on laser induced fluorescence,a fluorescence lidar model system was put forward for detecting organic aerosol in the atmosphere.The principle of models system measurement was described exhaustively,system model parameters were presented after fully simulating and analyzing,accounting detection capability.The results showed that when the lidar worked at night,the least detectable density of organic aerosol was only a few particles/L within 5km;while during the daytime,the least detectable density could reduce to less than 10 particles/L within 2km due to background radiation.The results show that the lidar model can satisfy the requirement of real organic aerosol detecting,which could provide valuable instructions to the design of a real system.
2008, 32(3): 293-295,311.
Abstract:
The research progress on laser surface processing of magnesium alloy is reviewed.Laser surface processing techniques of magnesium alloys such as melting,alloying,composite intensifying and cladding developed in recent years are introduced.Its achievements such as improving the hardness,wear and corrosion resistance of magnesium alloys,repairing the finished-product of magnesium alloys are described.Finally some prediction of its future development is also presented.
The research progress on laser surface processing of magnesium alloy is reviewed.Laser surface processing techniques of magnesium alloys such as melting,alloying,composite intensifying and cladding developed in recent years are introduced.Its achievements such as improving the hardness,wear and corrosion resistance of magnesium alloys,repairing the finished-product of magnesium alloys are described.Finally some prediction of its future development is also presented.
2008, 32(3): 296-298,301.
Abstract:
For studying the passively mode-locked character of semiconductor saturable absorber mirror(SESAM),a semiconductor saturable absorber mirror,made by Institude of Semiconductors,Chinese Academy of Sciences,was used to obtain a passivel mode-locked Nd:YAG laser with a simple straight cavity.Stable ps mode-locked pulse train was realized.The mode-locked pulse duration is about 48.2ps measured by autocorrelation.The energy of the train is 24mJ.In addition,the constructure of 1.06μm semiconductor saturable absorber mirror and the theory of passively mode-lock was analyzed.Semiconductor saturable absorber mirror is mainly made up of distributed Bragg reflection(DBR) and saturable absorber.The DBR is made up of different higher and lower refractive index materials.Then the reflection spectrum of different pairs of DBR in semiconductor saturable absorber mirror was simulated,so was the distribution of electric field in DBR.From the results,it can be seen that as the increase of pairs of DBR,the reflectivity of central wavelength also increased;when the pairs is above 13,the reflectivity of central wavelength exceeded 99%.In conclution,semiconductor saturable absorber mirror can replace the traditional passively mode-locked component(such as Cr4+:YAG or organic dye) to be the most perfect component for the mode-lock of solid laser.
For studying the passively mode-locked character of semiconductor saturable absorber mirror(SESAM),a semiconductor saturable absorber mirror,made by Institude of Semiconductors,Chinese Academy of Sciences,was used to obtain a passivel mode-locked Nd:YAG laser with a simple straight cavity.Stable ps mode-locked pulse train was realized.The mode-locked pulse duration is about 48.2ps measured by autocorrelation.The energy of the train is 24mJ.In addition,the constructure of 1.06μm semiconductor saturable absorber mirror and the theory of passively mode-lock was analyzed.Semiconductor saturable absorber mirror is mainly made up of distributed Bragg reflection(DBR) and saturable absorber.The DBR is made up of different higher and lower refractive index materials.Then the reflection spectrum of different pairs of DBR in semiconductor saturable absorber mirror was simulated,so was the distribution of electric field in DBR.From the results,it can be seen that as the increase of pairs of DBR,the reflectivity of central wavelength also increased;when the pairs is above 13,the reflectivity of central wavelength exceeded 99%.In conclution,semiconductor saturable absorber mirror can replace the traditional passively mode-locked component(such as Cr4+:YAG or organic dye) to be the most perfect component for the mode-lock of solid laser.
2008, 32(3): 299-301.
Abstract:
In order to study the splitting angle and light intensity splitting ratio changing with the structure of a single-element polarized beam splitting prism,at first how the o light and e light changing with the orientation of principal axis,the structure angle of the prism and the incident angle was analyzed theoretically.Then how the splitting angle and light intensity splitting ratio changing with different incident angles was measured experimentally.The mathematical expression of the splitting angle and light intensity splitting ratio changing with the orientation of principal axis,the structure angle of prism and the incident angle was deduced,and the experimental data of the splitting angle and light intensity splitting ratio changing with the incident angle were obtained.The results indicate: The tested result is well concordant with the theoretical calculation,and the splitting angle is about 1/2 of the incident angle.
In order to study the splitting angle and light intensity splitting ratio changing with the structure of a single-element polarized beam splitting prism,at first how the o light and e light changing with the orientation of principal axis,the structure angle of the prism and the incident angle was analyzed theoretically.Then how the splitting angle and light intensity splitting ratio changing with different incident angles was measured experimentally.The mathematical expression of the splitting angle and light intensity splitting ratio changing with the orientation of principal axis,the structure angle of prism and the incident angle was deduced,and the experimental data of the splitting angle and light intensity splitting ratio changing with the incident angle were obtained.The results indicate: The tested result is well concordant with the theoretical calculation,and the splitting angle is about 1/2 of the incident angle.
2008, 32(3): 302-304.
Abstract:
In order to solve the splice loss problem of photonic crystal fiber,the full vector model was adopted to calculate the mode field radius,air hole radius as well as its relation with doping concentration in total-internal-reflection fiber and high-nonlinearity fiber.Based on the results,the splice loss of photonic crystal fiber and single mode fiber was analyzed in detail.The calculation indicates that the mode-field unbalance is the main reason of splice loss for total-internal-reflection fibers and high-nonlinearity fibers.An appropriate modification of mode field match can reduce the splice loss to a minimum value.
In order to solve the splice loss problem of photonic crystal fiber,the full vector model was adopted to calculate the mode field radius,air hole radius as well as its relation with doping concentration in total-internal-reflection fiber and high-nonlinearity fiber.Based on the results,the splice loss of photonic crystal fiber and single mode fiber was analyzed in detail.The calculation indicates that the mode-field unbalance is the main reason of splice loss for total-internal-reflection fibers and high-nonlinearity fibers.An appropriate modification of mode field match can reduce the splice loss to a minimum value.
2008, 32(3): 305-307.
Abstract:
The purpose of the paper is to study cross-phase modulation of pulse pairs with different shapes in optical fibers with quintic nonlinearity.Starting from the extended coupled nonlinear Schrdinger equations including quintic nonlinearity,the expressions for the nonlinear phase shifts and frequency chirps of different pulse pairs were derived,and the phase shifts,chirps and power spectra of pulse pairs with different shapes were simulated,compared and analyzed.The results show that,the powerful negative quintic nonlinearity can greatly influence the central regimes of the curve shapes of the phase shifts,chirps and spectra.While the positive quintic nonlinearity(weak negative quintic nonlinearity) can only increase(decrease) the phase shifts,chirps,the spectral width,and the number of spectral peaks.The soliton pairs are similar to Gaussian ones in terms of their spectral shapes.Depending on the quintic nonlinearity coefficients,the spectral peaks with the maximum energy may distribute in the vicinity of the center or near the edge.The super-Gaussian pairs are also similar to each other in terms of their spectral shapes.But the energy remains mainly on the central peak.To some degrees,this investigation may contribute to the pulse compression,optical switching devices and improving the performance of optical fiber communication systems,etc.
The purpose of the paper is to study cross-phase modulation of pulse pairs with different shapes in optical fibers with quintic nonlinearity.Starting from the extended coupled nonlinear Schrdinger equations including quintic nonlinearity,the expressions for the nonlinear phase shifts and frequency chirps of different pulse pairs were derived,and the phase shifts,chirps and power spectra of pulse pairs with different shapes were simulated,compared and analyzed.The results show that,the powerful negative quintic nonlinearity can greatly influence the central regimes of the curve shapes of the phase shifts,chirps and spectra.While the positive quintic nonlinearity(weak negative quintic nonlinearity) can only increase(decrease) the phase shifts,chirps,the spectral width,and the number of spectral peaks.The soliton pairs are similar to Gaussian ones in terms of their spectral shapes.Depending on the quintic nonlinearity coefficients,the spectral peaks with the maximum energy may distribute in the vicinity of the center or near the edge.The super-Gaussian pairs are also similar to each other in terms of their spectral shapes.But the energy remains mainly on the central peak.To some degrees,this investigation may contribute to the pulse compression,optical switching devices and improving the performance of optical fiber communication systems,etc.
2008, 32(3): 308-311.
Abstract:
In order to obtain the laser beam with better beam quality,smaller spot diameter and higher power density in rapid prototyping for selective laser melting(SLM),Gaussian beam used in SLM was transmitted and transformed.The theoretic and experimental transmission,transformation and focused characteristic properties were analyzed.The experimental results are consistent with the theoretic ones.The smaller spot with power density above 106W/cm2 which is applicable in SLM,was obtained.When used in 3-D rapid prototyping for SLM of Ni-based alloy and Cu-P alloy powder,it also indicated feasible and effectual,and met the demands of spot diameter and power density.
In order to obtain the laser beam with better beam quality,smaller spot diameter and higher power density in rapid prototyping for selective laser melting(SLM),Gaussian beam used in SLM was transmitted and transformed.The theoretic and experimental transmission,transformation and focused characteristic properties were analyzed.The experimental results are consistent with the theoretic ones.The smaller spot with power density above 106W/cm2 which is applicable in SLM,was obtained.When used in 3-D rapid prototyping for SLM of Ni-based alloy and Cu-P alloy powder,it also indicated feasible and effectual,and met the demands of spot diameter and power density.
2008, 32(3): 312-313.
Abstract:
In order to get high power CW green output,the laser pumped by 9×20W high power laser diode arrays with a type Ⅱ phase matched KTP crystal was developed.Properly enlarging the light waist where KTP crystal was laid to avoid "gray tracks effect".At last,16W CW green laser output and 40% second-harmonic genration conversion efficiency were achieved at pumping current of 19.5A,with compensating phase mismatch by angle departure.The results show that Nd:YAG/KTP are good choice for high power CW green output.
In order to get high power CW green output,the laser pumped by 9×20W high power laser diode arrays with a type Ⅱ phase matched KTP crystal was developed.Properly enlarging the light waist where KTP crystal was laid to avoid "gray tracks effect".At last,16W CW green laser output and 40% second-harmonic genration conversion efficiency were achieved at pumping current of 19.5A,with compensating phase mismatch by angle departure.The results show that Nd:YAG/KTP are good choice for high power CW green output.
2008, 32(3): 314-316.
Abstract:
As one of the ideal and new energy sources in propulsion systems,TEA CO2 laser,with the increasing of single pulse energy,must have high beam quality to acquire high efficiency in long distance transmission.The divergence angle of TEA CO2 laser with stable resonator and improved unstable resonator with a vortex tube cooling system are accurately measured at 1Hz,using diffuse reflection and beam filter method respectively,giving the value of β is 12.53 and 3.28 respectively.Meanwhile,the pulse energy of unstable resonator reduced very little.As the result shown,the improved unstable resonator is much more valuable in propulsion system and the result is helpful in large volume high energy TEA CO2 lasers.
As one of the ideal and new energy sources in propulsion systems,TEA CO2 laser,with the increasing of single pulse energy,must have high beam quality to acquire high efficiency in long distance transmission.The divergence angle of TEA CO2 laser with stable resonator and improved unstable resonator with a vortex tube cooling system are accurately measured at 1Hz,using diffuse reflection and beam filter method respectively,giving the value of β is 12.53 and 3.28 respectively.Meanwhile,the pulse energy of unstable resonator reduced very little.As the result shown,the improved unstable resonator is much more valuable in propulsion system and the result is helpful in large volume high energy TEA CO2 lasers.
2008, 32(3): 317-319.
Abstract:
In order to study the application of laser direct writing technology in the fabrication of strip optical waveguides,the SiO2-TiO2 strip waveguides based on silicon were manufactured using a continuous fiber laser with the wavelength of 1.07μm.The mechanism on the fabrication of strip waveguides by laser direct writing was discussed.The effect of the laser parameter on the width of waveguides was studied.Finally,the propagation mode field and optical loss at the wavelength of 1550nm were measured.The results indicate that the width of strip waveguide increases with the increase of laser power density and the decrease of laser scan velocity at the range of 0.1mm/s~1mm/s.There is no evident influence on the width of the strip waveguide when the laser scan velocity is higher than 1 mm/s.The strip waveguide with a height of 0.4μm and a width of 120μm was obtained by laser direct writing at the optimized parameters.The mode field in the optical waveguide is multi-mode at the wavelength of 1550 nm.The minimum propagation loss is 1.7dB/cm.
In order to study the application of laser direct writing technology in the fabrication of strip optical waveguides,the SiO2-TiO2 strip waveguides based on silicon were manufactured using a continuous fiber laser with the wavelength of 1.07μm.The mechanism on the fabrication of strip waveguides by laser direct writing was discussed.The effect of the laser parameter on the width of waveguides was studied.Finally,the propagation mode field and optical loss at the wavelength of 1550nm were measured.The results indicate that the width of strip waveguide increases with the increase of laser power density and the decrease of laser scan velocity at the range of 0.1mm/s~1mm/s.There is no evident influence on the width of the strip waveguide when the laser scan velocity is higher than 1 mm/s.The strip waveguide with a height of 0.4μm and a width of 120μm was obtained by laser direct writing at the optimized parameters.The mode field in the optical waveguide is multi-mode at the wavelength of 1550 nm.The minimum propagation loss is 1.7dB/cm.
2008, 32(3): 320-322,326.
Abstract:
In order to increase the conversion efficiency of a multi-disk laser at Brewster angle,the main elements affecting the efficiency were analyzed theoretically and verified by means of experiments.A series of datum about the relation of output energy and intracavity loss were gained.The results indicated that inherence loss due to multi-disk configuration led to low laser efficiency.The dynamic loss limited the ability of continuous laser output,and the pump loss brought a certain effect on the laser efficiency.
In order to increase the conversion efficiency of a multi-disk laser at Brewster angle,the main elements affecting the efficiency were analyzed theoretically and verified by means of experiments.A series of datum about the relation of output energy and intracavity loss were gained.The results indicated that inherence loss due to multi-disk configuration led to low laser efficiency.The dynamic loss limited the ability of continuous laser output,and the pump loss brought a certain effect on the laser efficiency.
2008, 32(3): 323-326.
Abstract:
Various phase unwrapping algorithms have been proposed for the last two decades.They mainly can be grouped into two classes：Path-following and global phase unwrapping algorithms.In order to compare their performances,firstly,different type wrap phases were generated according to computer-simulating inclined and Gaussian planes at various noise levels.Then three representative algorithms were chosen from the two classes respectively and their unwrapping phases and root-mean-square errors were calculated.Lastly,experimental data were compared and analyzed theoretically.The results show that minimum cost flow algorithm based on network programming and ZπM algorithm based on Bayesian reference are more robust,effective,and prior to be chosen or improved in practical application.
Various phase unwrapping algorithms have been proposed for the last two decades.They mainly can be grouped into two classes：Path-following and global phase unwrapping algorithms.In order to compare their performances,firstly,different type wrap phases were generated according to computer-simulating inclined and Gaussian planes at various noise levels.Then three representative algorithms were chosen from the two classes respectively and their unwrapping phases and root-mean-square errors were calculated.Lastly,experimental data were compared and analyzed theoretically.The results show that minimum cost flow algorithm based on network programming and ZπM algorithm based on Bayesian reference are more robust,effective,and prior to be chosen or improved in practical application.
2008, 32(3): 327-329,336.
Abstract:
In order to study the effect of dopant absorption on photonic crystal filters,the peak transmissivity and full width at half maxmum(FWHM) of the filters were calculated based on the complex refractive index and the characteristic matrix.It was found that the peak transmissivity decreased with the increment of the extinction coefficient,however the FWHM increased with the increment of the extinction coefficient.Both the peak transmissivity and the FWHM decreased with the increment of the optical thickness of doping.A valuable conclusion is drawn that the absorption of dopant has to be taken into account for the design of a phonic crystal filter and that the extinction coefficient should be less than 0.002 and the optical thickness of doping should be 2(λ0/4) or so.
In order to study the effect of dopant absorption on photonic crystal filters,the peak transmissivity and full width at half maxmum(FWHM) of the filters were calculated based on the complex refractive index and the characteristic matrix.It was found that the peak transmissivity decreased with the increment of the extinction coefficient,however the FWHM increased with the increment of the extinction coefficient.Both the peak transmissivity and the FWHM decreased with the increment of the optical thickness of doping.A valuable conclusion is drawn that the absorption of dopant has to be taken into account for the design of a phonic crystal filter and that the extinction coefficient should be less than 0.002 and the optical thickness of doping should be 2(λ0/4) or so.
2008, 32(3): 330-333.
Abstract:
In order to analyze the dependence of the nonlinear coefficient and dispersion property on the structural parameters of photonic crystal fibers,a vector effective index model was used.Through analyzation,it is possible to design photonic crystal fibers with high nonlinear coefficient and nearly zero dispersion at wavelengths of around 820nm.Results show that there are huge potential in photonic crystal fibers of high nonlinear flattened dispersion.
In order to analyze the dependence of the nonlinear coefficient and dispersion property on the structural parameters of photonic crystal fibers,a vector effective index model was used.Through analyzation,it is possible to design photonic crystal fibers with high nonlinear coefficient and nearly zero dispersion at wavelengths of around 820nm.Results show that there are huge potential in photonic crystal fibers of high nonlinear flattened dispersion.
2008, 32(3): 248-251.
Abstract:
Laser spot detection is the key technique in the imaging laser detecting system.In order to find the pinpoint direction of the laser source and locate the accurate laser spot position,the arithmetic of sub pixel measurement was put forward.For different laser spots,it was studied with the method of gravity model and the method based on spatial moments both in the theory and experiment.The statistic data of the mean value and root-mean-square of the spots' coordinates at different laser intensity approved that this idea can increase the detecting precision to less than 0.2 pixels while extending the detecting dynamic extension,which is helpful to assure the laser location precisely.
Laser spot detection is the key technique in the imaging laser detecting system.In order to find the pinpoint direction of the laser source and locate the accurate laser spot position,the arithmetic of sub pixel measurement was put forward.For different laser spots,it was studied with the method of gravity model and the method based on spatial moments both in the theory and experiment.The statistic data of the mean value and root-mean-square of the spots' coordinates at different laser intensity approved that this idea can increase the detecting precision to less than 0.2 pixels while extending the detecting dynamic extension,which is helpful to assure the laser location precisely.
