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RSS2008 Vol. 32, No. 2
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2008, 32(2): 113-115.
[Abstract]
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Abstract:
The locking range in coherently combined fiber lasers was studied by means of the reflection distribution function of the tunable fiber gratings.After comparing the threshold,it was seen that the oscillation wavelength of the coherent radiation occurred near the average of the two Bragg wavelengths.The result shows that the constituent lasers can be coherently combined when the Bragg wavelength difference between the two fiber gratings is small enough.
The locking range in coherently combined fiber lasers was studied by means of the reflection distribution function of the tunable fiber gratings.After comparing the threshold,it was seen that the oscillation wavelength of the coherent radiation occurred near the average of the two Bragg wavelengths.The result shows that the constituent lasers can be coherently combined when the Bragg wavelength difference between the two fiber gratings is small enough.
2008, 32(2): 116-118,121.
Abstract:
In order to study the optical polarization property of porous anodic alumina template,the homogeneous and ordered porous anodic alumina(PAA) temple was prepared by twice-anodic oxidation in H2SO4 solution.The morphological,structural and optical polarization property of the obtained PAA was characterized and analyzed.It is revealed the the PAA is anodized at low room temperature with a large current density.The aluminum is only partially oxidized and there is residual aluminum located between pores which formed nanoarray.The result of X-ray diffractogram shows that the PAA is anodic alumina amorphous state,and the transmission and polarization spectrum have indicated that PAA has better transmittance and some extinction ratio in the visible region and the near infrared region.The obtained results is favor of fabricating micropolarizers with anodic alumina film with implanted nanohole metallic arrays.
In order to study the optical polarization property of porous anodic alumina template,the homogeneous and ordered porous anodic alumina(PAA) temple was prepared by twice-anodic oxidation in H2SO4 solution.The morphological,structural and optical polarization property of the obtained PAA was characterized and analyzed.It is revealed the the PAA is anodized at low room temperature with a large current density.The aluminum is only partially oxidized and there is residual aluminum located between pores which formed nanoarray.The result of X-ray diffractogram shows that the PAA is anodic alumina amorphous state,and the transmission and polarization spectrum have indicated that PAA has better transmittance and some extinction ratio in the visible region and the near infrared region.The obtained results is favor of fabricating micropolarizers with anodic alumina film with implanted nanohole metallic arrays.
2008, 32(2): 119-121.
Abstract:
A new approach has been brought forward to obtain glow discharge in non-chain HF/DF laser.It has been shown a volume discharge is forming in non-uniform electric-field without preionization in SF6 and C2H6 mixtures,the energy deposition up to 200J/L.The discharge in the pin-plane gap is a diffuse jet expanding towards the anode with a bright plasma domain at the cathode.The discharge in the plane-plane gap is presented with many diffuse channels attached to bright circular cathode spots that diverge towards the anode,with the channels overlapping,form a spatially uniform glow discharge.The experimental results indicate that the new discharge type in SF6 and C2H6 mixtures is promising for creation of high energy and high frequency HF/DF laser.
A new approach has been brought forward to obtain glow discharge in non-chain HF/DF laser.It has been shown a volume discharge is forming in non-uniform electric-field without preionization in SF6 and C2H6 mixtures,the energy deposition up to 200J/L.The discharge in the pin-plane gap is a diffuse jet expanding towards the anode with a bright plasma domain at the cathode.The discharge in the plane-plane gap is presented with many diffuse channels attached to bright circular cathode spots that diverge towards the anode,with the channels overlapping,form a spatially uniform glow discharge.The experimental results indicate that the new discharge type in SF6 and C2H6 mixtures is promising for creation of high energy and high frequency HF/DF laser.
2008, 32(2): 122-124.
Abstract:
In order to study the effect of TiB2 on microstructure and sliding wear resistance of Co-based alloy coating,laser clad Co-base alloy and metal-ceramics layers of Co-based TiB2 was obtained on low carbon steel surface by means of 5kW continuous wave CO2 laser.The results showed that TiB2/Co metal-ceramics composite coating was mainly consisted of γ-Co,Cr23C6,TiB2,TiC and CO3Ti;the Co-based alloy coating was consisted of developed dendrite and hypoeutectic structure.Cinquefoil grain and fine eutectic structure were observed in the TiB2/Co metal-ceramics coating;the microhardness and sliding wear resistance of the TiB2/Co metal-ceramics coating were more excellent than that of Co-based alloy coating.These results are expected to provide available reference for further research of laser cladding metal-ceramics.
In order to study the effect of TiB2 on microstructure and sliding wear resistance of Co-based alloy coating,laser clad Co-base alloy and metal-ceramics layers of Co-based TiB2 was obtained on low carbon steel surface by means of 5kW continuous wave CO2 laser.The results showed that TiB2/Co metal-ceramics composite coating was mainly consisted of γ-Co,Cr23C6,TiB2,TiC and CO3Ti;the Co-based alloy coating was consisted of developed dendrite and hypoeutectic structure.Cinquefoil grain and fine eutectic structure were observed in the TiB2/Co metal-ceramics coating;the microhardness and sliding wear resistance of the TiB2/Co metal-ceramics coating were more excellent than that of Co-based alloy coating.These results are expected to provide available reference for further research of laser cladding metal-ceramics.
2008, 32(2): 125-127.
Abstract:
To attain high power laser with high beam quality,experiments were performed for partially end-pumped Nd:YVO4 slab laser.With the help of a self-assembly 5bar LD array stack and the wave-guide beam reshaping system,the pumped light was coupled into slab crystal.38W CW laser beam was attained with hybrid resonator operation when pumped power was 134W,and the slope efficiency was 44%.When the output laser power was 38W,M2 value in unstable resonator direction was 1.56,and M2 value in stable resonator direction was 1.78.The experimental results indicated that high power laser could be attained with high beam quality,concerning with good thermal effect.The input-output power curve was not flat-topping and reflexed.The experiment results indicated that this laser could be improved more.
To attain high power laser with high beam quality,experiments were performed for partially end-pumped Nd:YVO4 slab laser.With the help of a self-assembly 5bar LD array stack and the wave-guide beam reshaping system,the pumped light was coupled into slab crystal.38W CW laser beam was attained with hybrid resonator operation when pumped power was 134W,and the slope efficiency was 44%.When the output laser power was 38W,M2 value in unstable resonator direction was 1.56,and M2 value in stable resonator direction was 1.78.The experimental results indicated that high power laser could be attained with high beam quality,concerning with good thermal effect.The input-output power curve was not flat-topping and reflexed.The experiment results indicated that this laser could be improved more.
2008, 32(2): 128-130,179.
Abstract:
In order to study the photoluminescence property of zinc sulfide/porous Si composites,porous Si samples were prepared by electrochemical anodization,and zinc sulfide films were deposited on porous Si substrates by pulsed laser deposition.The photoluminescence spectra were measured.The results showed that,under different excitation wavelengths(340nm,360nm,390nm),the photoluminescence spectra of zinc sulfide/porous Si composites were different,and the relative(blue/red) integrated intensities were also different;When zinc sulfide films were grown at different temperatures(100℃,250℃,350℃),zinc sulfide/porous Si composites also presented different photoluminescence property,with the increase of growth temperature,the luminescence intensity of zinc sulfide increased but the luminescence intensity of porous Si decreased;When porous Si substrates were prepared at different current densities(3mA/cm2,9mA/cm2,11mA/cm2),the optical property of zinc sulfide/porous Si composites was also different.Under proper preparing current density conditions of porous Si,the blue,green emission from zinc sulfide combining with the red emission from porous Si,a broad photoluminescence band(450nm~700nm) in the visible region was obtained,exhibiting intensively white light emission.This offers a cheap route for the realization of white light-emitting diodes.
In order to study the photoluminescence property of zinc sulfide/porous Si composites,porous Si samples were prepared by electrochemical anodization,and zinc sulfide films were deposited on porous Si substrates by pulsed laser deposition.The photoluminescence spectra were measured.The results showed that,under different excitation wavelengths(340nm,360nm,390nm),the photoluminescence spectra of zinc sulfide/porous Si composites were different,and the relative(blue/red) integrated intensities were also different;When zinc sulfide films were grown at different temperatures(100℃,250℃,350℃),zinc sulfide/porous Si composites also presented different photoluminescence property,with the increase of growth temperature,the luminescence intensity of zinc sulfide increased but the luminescence intensity of porous Si decreased;When porous Si substrates were prepared at different current densities(3mA/cm2,9mA/cm2,11mA/cm2),the optical property of zinc sulfide/porous Si composites was also different.Under proper preparing current density conditions of porous Si,the blue,green emission from zinc sulfide combining with the red emission from porous Si,a broad photoluminescence band(450nm~700nm) in the visible region was obtained,exhibiting intensively white light emission.This offers a cheap route for the realization of white light-emitting diodes.
2008, 32(2): 131-133,136.
Abstract:
In order to reconstruct three-dimension micro-object wave field accurately,the reconstruction method with collimating reference wave to reconstruct digital hologram with large numerical aperture was studied by using Fresnel diffraction formula and sampling theorem.The reason that spherical reference wave can't be used to reconstruct a large numerical aperture hologram was analyzed.The expression of reconstructed phase image was presented.As result of the measure error of the recording distance and the offset of the point source,the distortion of the phase image reconstructed with collimating reference wave was also analyzed.Both theoretical analysis and computer simulation show that accurate intensity reconstruction can be obtained as long as a high quality hologram is recorded.Only if the recording distance and the offset of the point source are accurately measured,the correct phase reconstruction can be obtained.Due to a measure error,a quadratic function distortion of the reconstructed phase distribution appears.So it is important to measure the recording parameters accurately in experiment.
In order to reconstruct three-dimension micro-object wave field accurately,the reconstruction method with collimating reference wave to reconstruct digital hologram with large numerical aperture was studied by using Fresnel diffraction formula and sampling theorem.The reason that spherical reference wave can't be used to reconstruct a large numerical aperture hologram was analyzed.The expression of reconstructed phase image was presented.As result of the measure error of the recording distance and the offset of the point source,the distortion of the phase image reconstructed with collimating reference wave was also analyzed.Both theoretical analysis and computer simulation show that accurate intensity reconstruction can be obtained as long as a high quality hologram is recorded.Only if the recording distance and the offset of the point source are accurately measured,the correct phase reconstruction can be obtained.Due to a measure error,a quadratic function distortion of the reconstructed phase distribution appears.So it is important to measure the recording parameters accurately in experiment.
2008, 32(2): 134-136.
Abstract:
After summarizing the history and principles of laser induced breakdown spectroscopy(LBS),the classification,application fields of LBS and recent study trends of LBS in biomedicine are introduced systematically.Finally a conclusion is drawn that LBS is an effective technology,and that LBS technology has great practical value,so more and more researchers become interested in the application of LBS in biomedicine field.
After summarizing the history and principles of laser induced breakdown spectroscopy(LBS),the classification,application fields of LBS and recent study trends of LBS in biomedicine are introduced systematically.Finally a conclusion is drawn that LBS is an effective technology,and that LBS technology has great practical value,so more and more researchers become interested in the application of LBS in biomedicine field.
2008, 32(2): 137-139.
Abstract:
Measuring temperature distribution of laser penetration welding keyhole is one of the important ways to study the foundational theory of keyhole.The object is to get the 2-D temperature distribution of plasma in non-symmetry case,dividing one dimension spectrum information into symmetry and non-symmetry part by variable separation approach,computing plane 2-D distribution of antimere by numerical method based on Abel transform,the plane 2-D distribution in non symmetry case can be obtained.A hypothetical function is calculated with this method,error analysis proves that it describes real distribution for small global error accurately.It is important for the study of the foundational theory of the laser penetration welding keyhole.
Measuring temperature distribution of laser penetration welding keyhole is one of the important ways to study the foundational theory of keyhole.The object is to get the 2-D temperature distribution of plasma in non-symmetry case,dividing one dimension spectrum information into symmetry and non-symmetry part by variable separation approach,computing plane 2-D distribution of antimere by numerical method based on Abel transform,the plane 2-D distribution in non symmetry case can be obtained.A hypothetical function is calculated with this method,error analysis proves that it describes real distribution for small global error accurately.It is important for the study of the foundational theory of the laser penetration welding keyhole.
2008, 32(2): 140-142,146.
Abstract:
A set of ultraviolet detecting experiment system was designed to study the target location in solar blind ultraviolet detecting.A kind of location algorithm based on the target image was brought forward.Target azimuth was calculated by the location of target on the image plane.The detecting system and algorithm were analyzed and validated in experiment.With 30m between the deuterium lamp and the detecting system,the measure precision of target azimuth angle can reached 0.5°.The result shows that the location algorithm is feasible.The result helps to carry out farther distance experiment and improve the system.
A set of ultraviolet detecting experiment system was designed to study the target location in solar blind ultraviolet detecting.A kind of location algorithm based on the target image was brought forward.Target azimuth was calculated by the location of target on the image plane.The detecting system and algorithm were analyzed and validated in experiment.With 30m between the deuterium lamp and the detecting system,the measure precision of target azimuth angle can reached 0.5°.The result shows that the location algorithm is feasible.The result helps to carry out farther distance experiment and improve the system.
2008, 32(2): 143-146.
Abstract:
In order to implement negative coefficients filters based on photonics in optical communication,a novel and simple technique for obtaining negative coefficients was adopted by means of the conversion of phase-modulated to intensity-modulated.A two-tap microwave band-pass filter with a negative coefficient was demonstrated.The filter not only achieves the negative coefficients but also improves the performance.
In order to implement negative coefficients filters based on photonics in optical communication,a novel and simple technique for obtaining negative coefficients was adopted by means of the conversion of phase-modulated to intensity-modulated.A two-tap microwave band-pass filter with a negative coefficient was demonstrated.The filter not only achieves the negative coefficients but also improves the performance.
2008, 32(2): 147-150.
Abstract:
To employ lidar for short distance detecting,the geometrical factor must be previously know.Theoretical analysis and experimental study are applied for determination of lidar geometrical factor.Firstly,the geometrical factors are analyzed for lidar with biaxial or coaxial transmitter-receiver.A full focusing filling factor is introduced.Equations of two kinds of filling factors related to geometrical factor are deduced based on geometrical optics.The theoretical range of geometrical factor's value is reached based on these equations.Secondly,a method is introduced for determination of geometrical factor by fitting lidar's back signal of far distance for inversing the signal of short distance.As an example,the geometrical factor profile of AML-2 lidar made in Chinese Academy of Science is determined experimentally with this method.The experimental results are accordant with the theoretical analysis.
To employ lidar for short distance detecting,the geometrical factor must be previously know.Theoretical analysis and experimental study are applied for determination of lidar geometrical factor.Firstly,the geometrical factors are analyzed for lidar with biaxial or coaxial transmitter-receiver.A full focusing filling factor is introduced.Equations of two kinds of filling factors related to geometrical factor are deduced based on geometrical optics.The theoretical range of geometrical factor's value is reached based on these equations.Secondly,a method is introduced for determination of geometrical factor by fitting lidar's back signal of far distance for inversing the signal of short distance.As an example,the geometrical factor profile of AML-2 lidar made in Chinese Academy of Science is determined experimentally with this method.The experimental results are accordant with the theoretical analysis.
2008, 32(2): 151-153,156.
Abstract:
In order to design a modular structural reflected polarizing prism which has an equal splitting angle,the construction of the prism was analyzed in theory by combining the reflecting principle in anisotropic crystal and practical application,and a structure angle was found which can make the splitting angle equal.Based on the angle,two aspects of the prism were calculated,i.e.the relationship between the degree of asymmetry and the incidence angle of light wave,and the relationship between the degree of asymmetry and incident wavelength.The results show although the degree of asymmetry has a small fluctuation,the design proposal is still successful.
In order to design a modular structural reflected polarizing prism which has an equal splitting angle,the construction of the prism was analyzed in theory by combining the reflecting principle in anisotropic crystal and practical application,and a structure angle was found which can make the splitting angle equal.Based on the angle,two aspects of the prism were calculated,i.e.the relationship between the degree of asymmetry and the incidence angle of light wave,and the relationship between the degree of asymmetry and incident wavelength.The results show although the degree of asymmetry has a small fluctuation,the design proposal is still successful.
2008, 32(2): 154-156.
Abstract:
In order to increase the lateral shearing distance when light transit the parallel splitting prism,as well as facilitate the path building of rays in the experiment,the prism design was optimized based on the prism light scattering beam principle and Fresnel formula and a new kind of turning composite parallel splitting prism was obtained.Analytical and experimental results prove that the lateral shearing distance is extended accompanying with deflecting function if the prism is with high transmissivity,which is valuable and practical.
In order to increase the lateral shearing distance when light transit the parallel splitting prism,as well as facilitate the path building of rays in the experiment,the prism design was optimized based on the prism light scattering beam principle and Fresnel formula and a new kind of turning composite parallel splitting prism was obtained.Analytical and experimental results prove that the lateral shearing distance is extended accompanying with deflecting function if the prism is with high transmissivity,which is valuable and practical.
2008, 32(2): 157-158,162.
Abstract:
In order clearly to learn the regularity that sensitivity to variations in the input angle of incidence i of a rhomb-type achromatic quarter-wave phase retarder vary with refractive index n,the total reflection phase transformation formula are used to deduce the transmissivity formula of sensitivity to variations in the input angle of incidence i of retarders and refractive index n and draw the theoretical curves.The result indicates that retarders are more sensitive to variations in the input angle of incidence i with refractive index increasing.So the higher refractive index material should be avoided in designing retarders.This application is advantageous in analyzing error in phase retardance measurement.
In order clearly to learn the regularity that sensitivity to variations in the input angle of incidence i of a rhomb-type achromatic quarter-wave phase retarder vary with refractive index n,the total reflection phase transformation formula are used to deduce the transmissivity formula of sensitivity to variations in the input angle of incidence i of retarders and refractive index n and draw the theoretical curves.The result indicates that retarders are more sensitive to variations in the input angle of incidence i with refractive index increasing.So the higher refractive index material should be avoided in designing retarders.This application is advantageous in analyzing error in phase retardance measurement.
2008, 32(2): 159-162.
Abstract:
The role of cubic phase plate in large-depth-of-field diffraction limited system with CCD detector was discussed and the special phase shift phenomena caused by the cubic phase plate was studied.Mathematic functions indicating the relation between axial desfocus parameter ψ,cubic phase plate shape constant α and modulation transfer funetion(MTF) and image shift variable s were deduced.Spoke images for standard imaging system and that with large depth of field were shown when defocus variable w equals to 0,50,150 and 300 times wavelength respectively.Changing optical transfer function and reducing its sensitivity to axial defocus parameter,depth of field for imaging system was enlarged.Along with its enlargement,phase shift appeared simultaneously,which is related with both the extending ratio for depth of field and the constant for cubic phase plate.Thus phase shift could be very small and a satisfactory image might be achieved when the extending ratio was limited to a certain suitable range and a reasonable constant for cubic phase plate was chosen.
The role of cubic phase plate in large-depth-of-field diffraction limited system with CCD detector was discussed and the special phase shift phenomena caused by the cubic phase plate was studied.Mathematic functions indicating the relation between axial desfocus parameter ψ,cubic phase plate shape constant α and modulation transfer funetion(MTF) and image shift variable s were deduced.Spoke images for standard imaging system and that with large depth of field were shown when defocus variable w equals to 0,50,150 and 300 times wavelength respectively.Changing optical transfer function and reducing its sensitivity to axial defocus parameter,depth of field for imaging system was enlarged.Along with its enlargement,phase shift appeared simultaneously,which is related with both the extending ratio for depth of field and the constant for cubic phase plate.Thus phase shift could be very small and a satisfactory image might be achieved when the extending ratio was limited to a certain suitable range and a reasonable constant for cubic phase plate was chosen.
2008, 32(2): 163-165,170.
Abstract:
In order to study passive Q-switch character of the nanoscale-Si-particle embedded in silicon nitride(nano-Si/SiNx)thin film,the film was prepared on single crystal silicon by means of radio frequency magnetron reaction sputtering technique and thermal annealing.In the experiment,these samples were inserted as saturable absorber into the resonator,concave-flat cavity was adopted and Nd:YAG was pumped by a xenon lamp,and the Q-switched waveform of 19ns single pulse width was obtained at repetition rate of 1Hz.Furthermore,the influence of structural characteristic,pump voltage and cavity length on the properties of laser output was investigated.Then,these phenomena observed in the experiment was analyzed and discussed based on the theory of passive Q-switch.In conclusion,nano-Si/SiNx film has potential value in research and applications because of its passive Q-switch character.
In order to study passive Q-switch character of the nanoscale-Si-particle embedded in silicon nitride(nano-Si/SiNx)thin film,the film was prepared on single crystal silicon by means of radio frequency magnetron reaction sputtering technique and thermal annealing.In the experiment,these samples were inserted as saturable absorber into the resonator,concave-flat cavity was adopted and Nd:YAG was pumped by a xenon lamp,and the Q-switched waveform of 19ns single pulse width was obtained at repetition rate of 1Hz.Furthermore,the influence of structural characteristic,pump voltage and cavity length on the properties of laser output was investigated.Then,these phenomena observed in the experiment was analyzed and discussed based on the theory of passive Q-switch.In conclusion,nano-Si/SiNx film has potential value in research and applications because of its passive Q-switch character.
2008, 32(2): 166-170.
Abstract:
First of all,the principle of laser welding of plastics is explained.Then,several new methods,characteristics and applications of laser welding of plastics are introduced,such as contour welding,simultaneous welding,quasi-simultaneous welding,mask welding,radial welding,Globo welding and diffractive welding.At last,present status and development trend of laser welding of plastics are summarized.It can be seen that the current study mainly focuses on two-dimension welding,while research on three-dimension welding is scarce.Laser welding of plastics is becoming a hot phenomenon in laser welding field.It might replace the traditional welding methods of plastics.
First of all,the principle of laser welding of plastics is explained.Then,several new methods,characteristics and applications of laser welding of plastics are introduced,such as contour welding,simultaneous welding,quasi-simultaneous welding,mask welding,radial welding,Globo welding and diffractive welding.At last,present status and development trend of laser welding of plastics are summarized.It can be seen that the current study mainly focuses on two-dimension welding,while research on three-dimension welding is scarce.Laser welding of plastics is becoming a hot phenomenon in laser welding field.It might replace the traditional welding methods of plastics.
2008, 32(2): 171-173.
Abstract:
In order to analyze the back signals and the signal-noise-ratio for the detection of He density in thermosphere by means of resonant lidar,the effective backscattering cross-section of about 10-17m2 was obtained after computer simulation.The size of the back signal was analyzed through numerical simulation with neglecting and considering the background signal respectively.Results showed that the signal-noise-ratio for current system was low,and that the range of the resolving power Δz should be decreased and the integral time τ should be extended in order to improve the signal-noise-ratio.There results are helpful for the detection of He density in thermosphere by means of resonant lidar.
In order to analyze the back signals and the signal-noise-ratio for the detection of He density in thermosphere by means of resonant lidar,the effective backscattering cross-section of about 10-17m2 was obtained after computer simulation.The size of the back signal was analyzed through numerical simulation with neglecting and considering the background signal respectively.Results showed that the signal-noise-ratio for current system was low,and that the range of the resolving power Δz should be decreased and the integral time τ should be extended in order to improve the signal-noise-ratio.There results are helpful for the detection of He density in thermosphere by means of resonant lidar.
2008, 32(2): 174-176,179.
Abstract:
In order to study property of polyvinyl alcohol films doped with methlyene blue under low power continuous-wave laser radiation generated by He-Ne laser,degenerate four-wave mixing(DFWM) was used to study relations of phase-conjugate(PC) signal along with incidence time,forward-pump beams and backward-pump beam.The PC signal influence from induced holographic transmission and reflection gratings were studied.We observed a maximum PC reflectivity of 0.27% in these dye-doped polyvinyl alcohol films.The result of research is helpful in nonlinear effect study in dye-doped solid.
In order to study property of polyvinyl alcohol films doped with methlyene blue under low power continuous-wave laser radiation generated by He-Ne laser,degenerate four-wave mixing(DFWM) was used to study relations of phase-conjugate(PC) signal along with incidence time,forward-pump beams and backward-pump beam.The PC signal influence from induced holographic transmission and reflection gratings were studied.We observed a maximum PC reflectivity of 0.27% in these dye-doped polyvinyl alcohol films.The result of research is helpful in nonlinear effect study in dye-doped solid.
2008, 32(2): 177-179.
Abstract:
In order to control accurately the lasing wavelength of the fiber grating external cavity semiconductor laser(FGECSL),after determining the mode distribution based on the phase condition,the influence of the air gap between the head of fiber and the front face of F-P LD on the lasing wavelength of FGECSL was through numerical simulation.The results show that the variation of the air gap will result in the lasing wavelength rippling around the Bragg wavelength of fiber grating(FG),and the amplitude of fluctuation becomes smaller with the increase of the external cavity length.For a fixed length of external cavity,the lasing wavelength can be accurately located in the Bragg wavelength of FG through adjusting the air gap carefully.
In order to control accurately the lasing wavelength of the fiber grating external cavity semiconductor laser(FGECSL),after determining the mode distribution based on the phase condition,the influence of the air gap between the head of fiber and the front face of F-P LD on the lasing wavelength of FGECSL was through numerical simulation.The results show that the variation of the air gap will result in the lasing wavelength rippling around the Bragg wavelength of fiber grating(FG),and the amplitude of fluctuation becomes smaller with the increase of the external cavity length.For a fixed length of external cavity,the lasing wavelength can be accurately located in the Bragg wavelength of FG through adjusting the air gap carefully.
2008, 32(2): 180-183.
Abstract:
To study the inspection technology of small pipes inner surface,a method for extracting inner surface section was proposed based on the inner surface image analysis.Firstly,the effective image zone was extracted in terms of geometry characteristic of the light ring.Then the radius of each point on the inner surface was achieved taking the image point which has maximum gray value along the ring radial direction as the section point.The corresponding inner section was inspected based on the method.Experiments show that the measurement accuracy of the inspection method is ±0.1mm.So,the inner surface of small pipes can be inspected with this method.
To study the inspection technology of small pipes inner surface,a method for extracting inner surface section was proposed based on the inner surface image analysis.Firstly,the effective image zone was extracted in terms of geometry characteristic of the light ring.Then the radius of each point on the inner surface was achieved taking the image point which has maximum gray value along the ring radial direction as the section point.The corresponding inner section was inspected based on the method.Experiments show that the measurement accuracy of the inspection method is ±0.1mm.So,the inner surface of small pipes can be inspected with this method.
2008, 32(2): 184-186.
Abstract:
The purpose is to provide insight into the issue of photo-damage selectivity in photodynamic therapy.Monte Carlo simulation was performed using different optical property for normal and tumor tissue.The decay of photodynamic dose with depth was approximately exponential.The greater depth of effect of increasing photodynamic dose obtainable in the tumor/normal simulation is clear as the greater depth of completely selective damage is,which has a threshold photodynamic dose for tissue necrosis and is affected by the photo spot size.For typical photosensitizer retention ratios,it is possible to obtain a shallow but entirely selective depth of tumor necrosis,but to obtain deeper tumor necrosis necessarily means some degree of normal tissue damage.
The purpose is to provide insight into the issue of photo-damage selectivity in photodynamic therapy.Monte Carlo simulation was performed using different optical property for normal and tumor tissue.The decay of photodynamic dose with depth was approximately exponential.The greater depth of effect of increasing photodynamic dose obtainable in the tumor/normal simulation is clear as the greater depth of completely selective damage is,which has a threshold photodynamic dose for tissue necrosis and is affected by the photo spot size.For typical photosensitizer retention ratios,it is possible to obtain a shallow but entirely selective depth of tumor necrosis,but to obtain deeper tumor necrosis necessarily means some degree of normal tissue damage.
2008, 32(2): 187-190,193.
Abstract:
In order to adopt photonic crystal fibers broadly in the passive devices such as fiber press sensors,the stress of photonic crystal fiber cores and cladding,the transversal structure and the refractive index were theoretically analyzed and simulated by means of elastic-optical theory,and the effect of pressure on the pulse phase and mode birefringence in photonic crystal fibers were discussed.The pulse phase fluctuation and mode birefringence variation in photonic crystal fibers were measured by means of coherent interference technology,and the pressure in the photonic crystal fibers was calculated.It is indicated that the photonic crystal fibers might be used as sensitive elements in the fiber press sensors.It is help that the photomic crystal fibers is more application in the fiber press sensors by this result.
In order to adopt photonic crystal fibers broadly in the passive devices such as fiber press sensors,the stress of photonic crystal fiber cores and cladding,the transversal structure and the refractive index were theoretically analyzed and simulated by means of elastic-optical theory,and the effect of pressure on the pulse phase and mode birefringence in photonic crystal fibers were discussed.The pulse phase fluctuation and mode birefringence variation in photonic crystal fibers were measured by means of coherent interference technology,and the pressure in the photonic crystal fibers was calculated.It is indicated that the photonic crystal fibers might be used as sensitive elements in the fiber press sensors.It is help that the photomic crystal fibers is more application in the fiber press sensors by this result.
2008, 32(2): 191-193.
Abstract:
In order to study temperature field distribution in laser melt hardening,a non-destructive direct measurement method was developed.A novel laser molten pool dynamic process measurement system was set up.Thermal radiation image in laser melt hardening molten pool was captured at real time.Temperature field data at different time were obtained by theory analysis and experiment measurement.It is shown cooling process in molten pool includes solidification and temperature declining after solidification.Melting time,solidification time,temperature field distribution and molten pool size could be measured.These information could be used to optimize laser melt hardening process parameters.
In order to study temperature field distribution in laser melt hardening,a non-destructive direct measurement method was developed.A novel laser molten pool dynamic process measurement system was set up.Thermal radiation image in laser melt hardening molten pool was captured at real time.Temperature field data at different time were obtained by theory analysis and experiment measurement.It is shown cooling process in molten pool includes solidification and temperature declining after solidification.Melting time,solidification time,temperature field distribution and molten pool size could be measured.These information could be used to optimize laser melt hardening process parameters.
2008, 32(2): 194-197.
Abstract:
For the sake of studying second-harmonic generation(SHG) and polarization gating(PG) frequency-resolved optical gating(FROG),both techniques measuring the intensity and phase of ultrashort laser pulses,SHG-FROG and PG-FROG traces of several types of common ultrashort pulses were numerically simulated using a matrix approach.Taking SHG-FROG as an example,the amplitude and the phase of these pulses were gleaned from these SHG-FROG traces by the principal component generalized projections algorithm and the SHG-FROG error was less than 10-4.The results show that FROG can accurately measure ultrashort laser pulses.
For the sake of studying second-harmonic generation(SHG) and polarization gating(PG) frequency-resolved optical gating(FROG),both techniques measuring the intensity and phase of ultrashort laser pulses,SHG-FROG and PG-FROG traces of several types of common ultrashort pulses were numerically simulated using a matrix approach.Taking SHG-FROG as an example,the amplitude and the phase of these pulses were gleaned from these SHG-FROG traces by the principal component generalized projections algorithm and the SHG-FROG error was less than 10-4.The results show that FROG can accurately measure ultrashort laser pulses.
2008, 32(2): 198-200.
Abstract:
Aiming at temporal spreading of laser pulse by bubbles,theoretic analysis and exploratory research were made for the light scattering properties and the multiple scattering effect of wake bubbles by Mie light scattering theory,and some signal waves of light back-scattering from bubbles at different distance were gained.The results indicate that wake bubbles influence the transmission of laser in water,which makes laser pulse spread in time evidently.
Aiming at temporal spreading of laser pulse by bubbles,theoretic analysis and exploratory research were made for the light scattering properties and the multiple scattering effect of wake bubbles by Mie light scattering theory,and some signal waves of light back-scattering from bubbles at different distance were gained.The results indicate that wake bubbles influence the transmission of laser in water,which makes laser pulse spread in time evidently.
2008, 32(2): 201-203,206.
Abstract:
The main purpose of this paper is to present the simple and fast method for simulating the characteristics of pulse amplification in ytterbium-doped double-clad fiber amplifiers with finite elements model FEMLAB package.The upper-level population distribution in the fiber,the pump power and the amplified spontaneous emission with 915nm forward pumping were studied by using the same parameters with the finite elements model fast Fourier transform.The transient output power,stored energy and gain of Gaussian pulse and square pulse were simulated.These results are in good agreement with those obtained according to fast Fourier transform.Furthermore,these results are more exact.The results show this method is convenient and fast.This method will offer valuable reference in design and parameter optimization of ytterbium-doped fiber amplifiers.
The main purpose of this paper is to present the simple and fast method for simulating the characteristics of pulse amplification in ytterbium-doped double-clad fiber amplifiers with finite elements model FEMLAB package.The upper-level population distribution in the fiber,the pump power and the amplified spontaneous emission with 915nm forward pumping were studied by using the same parameters with the finite elements model fast Fourier transform.The transient output power,stored energy and gain of Gaussian pulse and square pulse were simulated.These results are in good agreement with those obtained according to fast Fourier transform.Furthermore,these results are more exact.The results show this method is convenient and fast.This method will offer valuable reference in design and parameter optimization of ytterbium-doped fiber amplifiers.
2008, 32(2): 204-206.
Abstract:
In order to study the symmetry of Q-switched laser pulse,combined with a electric-optic(EO) modulator and a GaAs saturable absorber,an active-passive Q-switched laser is realized.Especially,the more symmetric and shorter pulse is generated in comparison with only EO-active or GaAs-passive Q-switched laser.The compressed ratio is higher than 40%.In addition,a symmetric factor is defined to describe the temporal symmetry of the pulses and the improvement of the pulsed symmetry is higher than 10%.The coupled rate equations under the plane-wave approximation are used to simulate the Q-switched process of the laser,and the numerical solution accords well with the experimental results.
In order to study the symmetry of Q-switched laser pulse,combined with a electric-optic(EO) modulator and a GaAs saturable absorber,an active-passive Q-switched laser is realized.Especially,the more symmetric and shorter pulse is generated in comparison with only EO-active or GaAs-passive Q-switched laser.The compressed ratio is higher than 40%.In addition,a symmetric factor is defined to describe the temporal symmetry of the pulses and the improvement of the pulsed symmetry is higher than 10%.The coupled rate equations under the plane-wave approximation are used to simulate the Q-switched process of the laser,and the numerical solution accords well with the experimental results.
2008, 32(2): 207-209.
Abstract:
For well understanding of light propagation in photonic crystal micro-cavity,the transmission spectrum of a one-dimensional photonic crystal contained Lorentz dispersive medium was calculated by means of the finite-difference time-domain method.The influence of refractive index inside micro-cavity on amplification properties and resonant frequency of defect modes was analyzed in detail.The results show that dispersive properties inside the micro-cavity lead to frequency shift of the defect modes.In addition,these defect modes can be also amplified as optical gain is introduced into the system.It is shown that lasing threshold of the defect modes can be significantly reduced through carefully adjusting the refractive index of micro-cavity.
For well understanding of light propagation in photonic crystal micro-cavity,the transmission spectrum of a one-dimensional photonic crystal contained Lorentz dispersive medium was calculated by means of the finite-difference time-domain method.The influence of refractive index inside micro-cavity on amplification properties and resonant frequency of defect modes was analyzed in detail.The results show that dispersive properties inside the micro-cavity lead to frequency shift of the defect modes.In addition,these defect modes can be also amplified as optical gain is introduced into the system.It is shown that lasing threshold of the defect modes can be significantly reduced through carefully adjusting the refractive index of micro-cavity.
2008, 32(2): 210-211,214.
Abstract:
For realizing a stable multiwavelength erbium-doped fiber laser at room temperature,sinusoidal phase modulation and polarization hole burning are introduced in the laser cavity to suppress the mode competition.In the linear cavity,a semiconductor optical waveguide is used as a reflective mirror,and driven by a sinusoidal signal.The semiconductor waveguide can be classified here as two optical devices:a sinusoidal phase modulator and a nonlinear phase retarder.The sinusoidal phase modulator produces frequency shift for the fiber laser,and the nonlinear phase retarder introduces polarization hole burning in the erbium-doped fiber.Stable lasing with multiple wavelengths up to 10 and wavelength spacing of 0.32nm was demonstrated at room temperature.The power fluctuation was less than 3dB.The results that the phase modulation and polarization hole burning is propitious to suppress the mode competition owing to the homogeneous broaden line.
For realizing a stable multiwavelength erbium-doped fiber laser at room temperature,sinusoidal phase modulation and polarization hole burning are introduced in the laser cavity to suppress the mode competition.In the linear cavity,a semiconductor optical waveguide is used as a reflective mirror,and driven by a sinusoidal signal.The semiconductor waveguide can be classified here as two optical devices:a sinusoidal phase modulator and a nonlinear phase retarder.The sinusoidal phase modulator produces frequency shift for the fiber laser,and the nonlinear phase retarder introduces polarization hole burning in the erbium-doped fiber.Stable lasing with multiple wavelengths up to 10 and wavelength spacing of 0.32nm was demonstrated at room temperature.The power fluctuation was less than 3dB.The results that the phase modulation and polarization hole burning is propitious to suppress the mode competition owing to the homogeneous broaden line.
2008, 32(2): 212-214.
Abstract:
In order to analyze the relationships of the light intensity splitting ratio with the incident angle,the prism's structural angle and the incidence wavelength's variation with the light beam coming from natural light's oblique incidence to Glan polarizing splitting prism,the mathematical formula of the light beam are deduced according to the geometric relationship,Fresnel formula and phase matching conditions.Through the analysis,a conclusion is drawn that the light beam assumes the nonlinear relationship with the incidence angle,the prism's structural angle and the incidence wavelength's variation,which provides useful information for the development of Glan polarizing splitting prism as optical devices.
In order to analyze the relationships of the light intensity splitting ratio with the incident angle,the prism's structural angle and the incidence wavelength's variation with the light beam coming from natural light's oblique incidence to Glan polarizing splitting prism,the mathematical formula of the light beam are deduced according to the geometric relationship,Fresnel formula and phase matching conditions.Through the analysis,a conclusion is drawn that the light beam assumes the nonlinear relationship with the incidence angle,the prism's structural angle and the incidence wavelength's variation,which provides useful information for the development of Glan polarizing splitting prism as optical devices.
2008, 32(2): 218-221.
Abstract:
A new normalized first-order spatial amplitude spectrum three-dimension(3-D) recognition method based on grating modulation was presented to speed up and improve ability for 3-D recognition.The theoretical model was established in detail,the properties of rotation and shift were theoretically and practically analyzed to conclude its shift invariant speciality.Experiments showed its flexibility.It can not only recognize 3-D object efficaciously,but also estimate the rotated angle of the 3-D object with higher resolution of ±2°.Because only one frame of sinusoidal grating needs to be projected and only one frame of the deformed fringe pattern needs to be collected in this method,it may be very suitable to be applied in dynamic or on-line 3-D recognition.
A new normalized first-order spatial amplitude spectrum three-dimension(3-D) recognition method based on grating modulation was presented to speed up and improve ability for 3-D recognition.The theoretical model was established in detail,the properties of rotation and shift were theoretically and practically analyzed to conclude its shift invariant speciality.Experiments showed its flexibility.It can not only recognize 3-D object efficaciously,but also estimate the rotated angle of the 3-D object with higher resolution of ±2°.Because only one frame of sinusoidal grating needs to be projected and only one frame of the deformed fringe pattern needs to be collected in this method,it may be very suitable to be applied in dynamic or on-line 3-D recognition.
2008, 32(2): 222-224.
Abstract:
In order to obtain maximum compression ratio and solve the problem of tremendous information transmission and storage under the condition that the images meet the requirement of data processing precision,according to the character of digital image,H.264 was applied to encode object region and background region encoding respectively so that 70 multiple compression picture data and object coordinates in the image coordinate system were obtained.The experimental results illustrated that the object region lossless compression encoding and background region lossy compression encoding were implemented.It not only satisfied the range data processing precision but also reduced the information quantity consumedly.The technique can be applied to process the standard bit images and widely extended in other ranges.
In order to obtain maximum compression ratio and solve the problem of tremendous information transmission and storage under the condition that the images meet the requirement of data processing precision,according to the character of digital image,H.264 was applied to encode object region and background region encoding respectively so that 70 multiple compression picture data and object coordinates in the image coordinate system were obtained.The experimental results illustrated that the object region lossless compression encoding and background region lossy compression encoding were implemented.It not only satisfied the range data processing precision but also reduced the information quantity consumedly.The technique can be applied to process the standard bit images and widely extended in other ranges.
