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RSS2009 Vol. 33, No. 4
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2009, 33(4): 337-339,343.
doi: 10.3969/j.issn.1001-3806.2009.04.001
[Abstract]
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Abstract:
In order to study the thermal focal length in LD corner-pumped composite slab lasers more clearly,the theoretical temperature distribution and the thermal focal length in a LD corner-pumped Nd:YAG/YAG composite slab were calculated with the finite-element method.Moreover,the thermal focal length of the slab was measured with CCD under non-lasing conditions.A comparison between the theoretical results and the experimental results was made.The result showed that the experimental thermal focal length transformation was in accordance with the theoretical computation.
In order to study the thermal focal length in LD corner-pumped composite slab lasers more clearly,the theoretical temperature distribution and the thermal focal length in a LD corner-pumped Nd:YAG/YAG composite slab were calculated with the finite-element method.Moreover,the thermal focal length of the slab was measured with CCD under non-lasing conditions.A comparison between the theoretical results and the experimental results was made.The result showed that the experimental thermal focal length transformation was in accordance with the theoretical computation.
2009, 33(4): 340-343.
doi: 10.3969/j.issn.1001-3806.2009.04.002
Abstract:
High signal-to-noise ratio(SNR)is very important in the interaction between high energy ultra-short laser and materials.In order to increase the SNR of ultra-short laser,the saturation absorption property of Nd:glass laser at the neighborhood of 800nm was studied.The relationship between the nonlinear transmissivity and normalized energy density of the combined Nd:glass system was obtained after solving the rate equations.For an optional 800nm laser pulse,making use of the frequency differences between amplified spontaneous emission pulse,modulation pulse and the main laser pulse,combining different types of Nd:glass material of optimizing the comprehensive data of the density,thickness.etc,the absorption spectrum of the combined Nd:glass system was designed reasonably.Computation results indicate that the noise is compressed effectively,and the SNR is increased a lot.
High signal-to-noise ratio(SNR)is very important in the interaction between high energy ultra-short laser and materials.In order to increase the SNR of ultra-short laser,the saturation absorption property of Nd:glass laser at the neighborhood of 800nm was studied.The relationship between the nonlinear transmissivity and normalized energy density of the combined Nd:glass system was obtained after solving the rate equations.For an optional 800nm laser pulse,making use of the frequency differences between amplified spontaneous emission pulse,modulation pulse and the main laser pulse,combining different types of Nd:glass material of optimizing the comprehensive data of the density,thickness.etc,the absorption spectrum of the combined Nd:glass system was designed reasonably.Computation results indicate that the noise is compressed effectively,and the SNR is increased a lot.
2009, 33(4): 344-346,350.
doi: 10.3969/j.issn.1001-3806.2009.04.003
Abstract:
In order to study light's propagation in terms of multiple scattering in complex geometrical or heterogeneous media,especially in atmosphere,semi-analysis Monte Carlo method was used,and relative returned signals of the lidar under different atmospheric conditions and systematic parameters were emulated.Consequently,time-relative returned signal curve was derived.And the influence of field of view(FOV)on the returned signal was discussed in detail.It is concluded that while FOV is very narrow,the curve is nearly as the same of single scattering curve,and that with the augment of FOV,single scattering decreases,multiple scattering enhances.
In order to study light's propagation in terms of multiple scattering in complex geometrical or heterogeneous media,especially in atmosphere,semi-analysis Monte Carlo method was used,and relative returned signals of the lidar under different atmospheric conditions and systematic parameters were emulated.Consequently,time-relative returned signal curve was derived.And the influence of field of view(FOV)on the returned signal was discussed in detail.It is concluded that while FOV is very narrow,the curve is nearly as the same of single scattering curve,and that with the augment of FOV,single scattering decreases,multiple scattering enhances.
2009, 33(4): 347-350.
doi: 10.3969/j.issn.1001-3806.2009.04.004
Abstract:
In order to study how the collimation of chromium(Cr)atomic by means of 1-D Doppler laser varying with laser power,laser detuning and interaction length after pre-collimation,the correlation between the coUimation and laser parameters was obtained after simulation with the fourth-order Runge-Kutta type algorithm at an adaptive step size.The results show that after precollimated by a slit in 5mm long,600mm far away from the downstream,the best collimation results can be obtained at laser power of 20mW,laser detuning of -0.5.Γ(Γ is the natural line-width of(Cr),and twice of the minimum interaction zone.
In order to study how the collimation of chromium(Cr)atomic by means of 1-D Doppler laser varying with laser power,laser detuning and interaction length after pre-collimation,the correlation between the coUimation and laser parameters was obtained after simulation with the fourth-order Runge-Kutta type algorithm at an adaptive step size.The results show that after precollimated by a slit in 5mm long,600mm far away from the downstream,the best collimation results can be obtained at laser power of 20mW,laser detuning of -0.5.Γ(Γ is the natural line-width of(Cr),and twice of the minimum interaction zone.
2009, 33(4): 351-354.
doi: 10.3969/j.issn.1001-3806.2009.04.005
Abstract:
After comparing the linear,nonlinear,and phase transition property of laser protection materials,the optical limiting properties of semiconductor materials,metal phthalocyanine coordination(MPC)compounds,C60,and its derivatives, inorganic metal cluster compounds,and carbon nanotubes were comprehensively analyzed.Because of the advantages of low optical limiting threshold value,wide optical limiting bandwidth and short response time for carbon nanotube materials,its research progress in optical limiting application was further expounded.It is pointed out that carbon nanotube optical limiting material needs the further in-depth research in the aspects of materialization and devise development for better application in the optical limiting field.
After comparing the linear,nonlinear,and phase transition property of laser protection materials,the optical limiting properties of semiconductor materials,metal phthalocyanine coordination(MPC)compounds,C60,and its derivatives, inorganic metal cluster compounds,and carbon nanotubes were comprehensively analyzed.Because of the advantages of low optical limiting threshold value,wide optical limiting bandwidth and short response time for carbon nanotube materials,its research progress in optical limiting application was further expounded.It is pointed out that carbon nanotube optical limiting material needs the further in-depth research in the aspects of materialization and devise development for better application in the optical limiting field.
2009, 33(4): 355-358.
doi: 10.3969/j.issn.1001-3806.2009.04.006
Abstract:
In order to develop a frequency-stabilized cavity-dumped RF waveguide CO2 laser to be used in a pulsed heterodyne imaging lidar,a laser system,composed of a pulsed master laser(MO)and a continuous wave local laser(LO)was studied,in which the same original blazed diffraction grating was set on the total reflective end of LO and MO because of the ceramic-plate folded-channel structure,so the physical length was shorten and the frequency stability of both the LO and MO was improved.In order to increase the width of the cavity-dumped output pulse,a delay circuit was employed to lengthen the falling time of the high voltage applied to the CdTe modulator.The frequency offset between the MO and LO radiation was locked with a piezoelectric ceramic.So the peak power of the MO was about 2.5kW with a pulse width of 30ns(full width at half maximum,FWHM)at a repetition rate of 70kHz,and the frequency offset between the MO and LO radiations was less than 1MHz in a short term.The testing results show that the laser system can meet the requirement of the pulse heterodyne imaging lidar system.
In order to develop a frequency-stabilized cavity-dumped RF waveguide CO2 laser to be used in a pulsed heterodyne imaging lidar,a laser system,composed of a pulsed master laser(MO)and a continuous wave local laser(LO)was studied,in which the same original blazed diffraction grating was set on the total reflective end of LO and MO because of the ceramic-plate folded-channel structure,so the physical length was shorten and the frequency stability of both the LO and MO was improved.In order to increase the width of the cavity-dumped output pulse,a delay circuit was employed to lengthen the falling time of the high voltage applied to the CdTe modulator.The frequency offset between the MO and LO radiation was locked with a piezoelectric ceramic.So the peak power of the MO was about 2.5kW with a pulse width of 30ns(full width at half maximum,FWHM)at a repetition rate of 70kHz,and the frequency offset between the MO and LO radiations was less than 1MHz in a short term.The testing results show that the laser system can meet the requirement of the pulse heterodyne imaging lidar system.
2009, 33(4): 359-361,365.
doi: 10.3969/j.issn.1001-3806.2009.04.007
Abstract:
In order to measure the displacement under the condition of moderate optical feedback self-mixing interference,a displacement measurement method based on phase unwrapping was introduced. Firstly,the system parameters C and α were measured respectively. Secondly,the external cavity phase with optical feedback was recovered after finding the special points of self-mixing interference signal,namely the peak,valley and transition points. Finally,the displacement information of the external moving object was obtained after processing the external cavity phase. Simulation and experimental results proved its feasibility. Experiment results show that the error of the system is ±30nm within the oscillating displacement up to 10 μm. This method is helpful for high precision measurement of micro displacement and vibration.
In order to measure the displacement under the condition of moderate optical feedback self-mixing interference,a displacement measurement method based on phase unwrapping was introduced. Firstly,the system parameters C and α were measured respectively. Secondly,the external cavity phase with optical feedback was recovered after finding the special points of self-mixing interference signal,namely the peak,valley and transition points. Finally,the displacement information of the external moving object was obtained after processing the external cavity phase. Simulation and experimental results proved its feasibility. Experiment results show that the error of the system is ±30nm within the oscillating displacement up to 10 μm. This method is helpful for high precision measurement of micro displacement and vibration.
2009, 33(4): 362-365.
doi: 10.3969/j.issn.1001-3806.2009.04.008
Abstract:
In order to study the influence of different laser parameters on the microstructure and property of the melted layer of Mg alloy,two laser melting techniques at high power,rapidly scanning speed(13J/mm2～33J/mm2)and low power,slowly scanning speed(100J/mm2～250J/mm2)were used to melt the surface of Mg alloy respectively. The results showed that the melted layers with both the techniques were composed of α-Mg and β-Mg17Al12 phases,however,the melted layers at low power,slowly scanning speed had more β-Mg17Al12,about 16%. The microstructure of the melted layers were typical dendrite,however,the dendritic spacing of the melted layers at high power,rapidly scanning speed was much smaller. The microhardness and wear resistance of the melted layers at high power,rapidly scanning speed were 1.5 and 3 times of that of the melted layers at low power, slowly scanning speed,respectively. The melted layers at high power,rapidly scanning speed had better corrosion resistance too.
In order to study the influence of different laser parameters on the microstructure and property of the melted layer of Mg alloy,two laser melting techniques at high power,rapidly scanning speed(13J/mm2～33J/mm2)and low power,slowly scanning speed(100J/mm2～250J/mm2)were used to melt the surface of Mg alloy respectively. The results showed that the melted layers with both the techniques were composed of α-Mg and β-Mg17Al12 phases,however,the melted layers at low power,slowly scanning speed had more β-Mg17Al12,about 16%. The microstructure of the melted layers were typical dendrite,however,the dendritic spacing of the melted layers at high power,rapidly scanning speed was much smaller. The microhardness and wear resistance of the melted layers at high power,rapidly scanning speed were 1.5 and 3 times of that of the melted layers at low power, slowly scanning speed,respectively. The melted layers at high power,rapidly scanning speed had better corrosion resistance too.
2009, 33(4): 366-368,373.
doi: 10.3969/j.issn.1001-3806.2009.04.009
Abstract:
In order to understand the interaction between two or multiple screening-photovoltaic bright spatial solitons,the interaction was numerically simulated. Both in-phase solitons attract each other and soliton fusions do occur at a certain interaction length,which increases monotonously with their initial separation. While in the case of out-of-phase,both the solitons repel each other with a force decreasing monotonously with the initial separation. When the relative phase between the solitons falls within the ranges of(0,π)and(-π,0),energy transfers in reverse direction. When the multiple solitons are in-phase,they will attract each other and the inner ones will fuse together gradually. When the relative initial phase between any two adjacent solitons is π/2,energy transfers among them. When the colliding solitons are out of phase,they propagate stably. The result indicate that the change of interaction between both solitons controlled by relative phase can be applied in all optical switch,and that the interaction result of multiple spatial solitons may be useful for the formation of soliton array and waveguide array.
In order to understand the interaction between two or multiple screening-photovoltaic bright spatial solitons,the interaction was numerically simulated. Both in-phase solitons attract each other and soliton fusions do occur at a certain interaction length,which increases monotonously with their initial separation. While in the case of out-of-phase,both the solitons repel each other with a force decreasing monotonously with the initial separation. When the relative phase between the solitons falls within the ranges of(0,π)and(-π,0),energy transfers in reverse direction. When the multiple solitons are in-phase,they will attract each other and the inner ones will fuse together gradually. When the relative initial phase between any two adjacent solitons is π/2,energy transfers among them. When the colliding solitons are out of phase,they propagate stably. The result indicate that the change of interaction between both solitons controlled by relative phase can be applied in all optical switch,and that the interaction result of multiple spatial solitons may be useful for the formation of soliton array and waveguide array.
2009, 33(4): 369-373.
doi: 10.3969/j.issn.1001-3806.2009.04.010
Abstract:
In order to study how to improve splicing precision between galvanometer processing grids cut by dynamic-optictype laser,a seamless splicing method for grids was introduced. Firstly,the area coefficients of laser points for both axes were compensated with linear interpolation. Then projective transformation was applied to establish the projective transformation matrixes of points in two optional planes to compensate trapezium and diamond distortion of dual galvanometers. After the above compensation,all coordinates in the entire scanning filed accord with a certain linear proportion relationship. Applying this method to cut flexible printed circuit board,experimental results showed that cutting precision and efficiency of this system were much higher than ordinary static-optic-type cutting. The splicing precision between grids of laser cutting system is greatly improved up to the precision and efficiency of the latest foreign system of the same kind.
In order to study how to improve splicing precision between galvanometer processing grids cut by dynamic-optictype laser,a seamless splicing method for grids was introduced. Firstly,the area coefficients of laser points for both axes were compensated with linear interpolation. Then projective transformation was applied to establish the projective transformation matrixes of points in two optional planes to compensate trapezium and diamond distortion of dual galvanometers. After the above compensation,all coordinates in the entire scanning filed accord with a certain linear proportion relationship. Applying this method to cut flexible printed circuit board,experimental results showed that cutting precision and efficiency of this system were much higher than ordinary static-optic-type cutting. The splicing precision between grids of laser cutting system is greatly improved up to the precision and efficiency of the latest foreign system of the same kind.
2009, 33(4): 374-376,380.
doi: 10.3969/j.issn.1001-3806.2009.04.011
Abstract:
In order to study how to shape femtosecond pulses with space-time conversion technique,combining theoretical analysis with computer simulation,femtosecond pulse shaper of 4f system applying Dammann-type filters as mask was analyzed. Firstly,Dammann-type filters including equally-spaced and equal-intensity gratings and unequally-spaced and equal-intensity gratings were designed with gradient algorithm. Then,the relation among the generated multiple ultrafast temporal pulses,the periodic repetition number,the spacing between the components and the wavelength in the spectral plane was discussed. The results showed that the perfect uniformity of the output pulse trains was strongly affected by the number of periodic repetition number. The efficiency and uniformity of the resultant output pulses became lower because of the spacing between the components and the wavelength effect.
In order to study how to shape femtosecond pulses with space-time conversion technique,combining theoretical analysis with computer simulation,femtosecond pulse shaper of 4f system applying Dammann-type filters as mask was analyzed. Firstly,Dammann-type filters including equally-spaced and equal-intensity gratings and unequally-spaced and equal-intensity gratings were designed with gradient algorithm. Then,the relation among the generated multiple ultrafast temporal pulses,the periodic repetition number,the spacing between the components and the wavelength in the spectral plane was discussed. The results showed that the perfect uniformity of the output pulse trains was strongly affected by the number of periodic repetition number. The efficiency and uniformity of the resultant output pulses became lower because of the spacing between the components and the wavelength effect.
2009, 33(4): 377-380.
doi: 10.3969/j.issn.1001-3806.2009.04.012
Abstract:
In order to design a 3-D galvanometric scanner with a large working field,its dynamic response capability,control algorithm and calibration algorithm were studied in detail. After selecting a servo motor with high dynamic response as the executive unit of the scanner,optimizing the scanning path and delay parameters,a 3-D scanner was developed successfully. A precise calibration model was designed to calibrate the scan image. This set of scanner was validated with it running for a long time. The scanner worked stably with repeating location precision of ≤30μm and scanning precision of 100mm ±0.1mm. The results show that the 3-D scanner has important application in large scanning fields.
In order to design a 3-D galvanometric scanner with a large working field,its dynamic response capability,control algorithm and calibration algorithm were studied in detail. After selecting a servo motor with high dynamic response as the executive unit of the scanner,optimizing the scanning path and delay parameters,a 3-D scanner was developed successfully. A precise calibration model was designed to calibrate the scan image. This set of scanner was validated with it running for a long time. The scanner worked stably with repeating location precision of ≤30μm and scanning precision of 100mm ±0.1mm. The results show that the 3-D scanner has important application in large scanning fields.
2009, 33(4): 381-383.
doi: 10.3969/j.issn.1001-3806.2009.04.013
Abstract:
In order to analyze the relationship among the lasing wavelength,length and coupler ratio of erbium-doped fibers, the rate equation based on 3rd energy state was solved and confirmed in experiments. The lasing wavelengths changing with the length and coupler ratio of erbium-doped fibers were obtained. The result shows that the lasing wavelength is shifted to longer wavelength with the decrease of the length of the erbium-doped fiber. The maximum output power occurs at 1563nm when the optimum length of the erbium-doped fiber is 11. 5m. In addition,the lasing wavelength becomes shorter wavelength with the decrease of the coupler ratio. These are good for the optimized design of a tunable erbium-doped fiber laser by varying coupler ratio.
In order to analyze the relationship among the lasing wavelength,length and coupler ratio of erbium-doped fibers, the rate equation based on 3rd energy state was solved and confirmed in experiments. The lasing wavelengths changing with the length and coupler ratio of erbium-doped fibers were obtained. The result shows that the lasing wavelength is shifted to longer wavelength with the decrease of the length of the erbium-doped fiber. The maximum output power occurs at 1563nm when the optimum length of the erbium-doped fiber is 11. 5m. In addition,the lasing wavelength becomes shorter wavelength with the decrease of the coupler ratio. These are good for the optimized design of a tunable erbium-doped fiber laser by varying coupler ratio.
2009, 33(4): 387-390.
doi: 10.3969/j.issn.1001-3806.2009.04.015
Abstract:
The linewidth enhancement factor of a semiconductor laser with moderate and strong feedback was measured by means of folding algorithm based on the optical feedback self-mixing interferometry. The factors affecting the accuracy of the folding algorithm,including the factor of optical feedback level,nonlinear motion of the external target,sampling frequency and location of turning points,was analyzed by processing the simulated signals. It was shown that optical feedback level factor was the premise of accurate measurement of linewidth enhancement factor and the error caused by nonlinear motion of external target could be reduced by using middle interference fringes. The folding algorithm was improved,providing a helpful measure for signal processing.
The linewidth enhancement factor of a semiconductor laser with moderate and strong feedback was measured by means of folding algorithm based on the optical feedback self-mixing interferometry. The factors affecting the accuracy of the folding algorithm,including the factor of optical feedback level,nonlinear motion of the external target,sampling frequency and location of turning points,was analyzed by processing the simulated signals. It was shown that optical feedback level factor was the premise of accurate measurement of linewidth enhancement factor and the error caused by nonlinear motion of external target could be reduced by using middle interference fringes. The folding algorithm was improved,providing a helpful measure for signal processing.
2009, 33(4): 391-392,396.
doi: 10.3969/j.issn.1001-3806.2009.04.016
Abstract:
In order to optimize the structure parameters of 3-D woodpile-type photonic crystals,based on the plane-wave method,the property of complete forbidden bands of woodpile structure was theoretically studied in terms of varying aspect heightto -pitch ratios,filling fractions,and rotation angles. It was found that the gap to midgap ratio changed slightly with a filling fraction ranging from 0.25 to 0.30. The optimum height-to-pitch ratio was about 1.3. The gap to midgap ratio became larger than 0.18 when the rotation angle changed from 40° to 50° and the maximum gap to midgap ratio of 0.2 remained unchanged for the rotation angle ranging from 42° to 48° with height-to-pitch ratio of 1.3. The results show this type of woodpile structure can produce big band gaps in a wider parameter range,which offers convenience for preparing three- dimension photonic crystals in laboratory.
In order to optimize the structure parameters of 3-D woodpile-type photonic crystals,based on the plane-wave method,the property of complete forbidden bands of woodpile structure was theoretically studied in terms of varying aspect heightto -pitch ratios,filling fractions,and rotation angles. It was found that the gap to midgap ratio changed slightly with a filling fraction ranging from 0.25 to 0.30. The optimum height-to-pitch ratio was about 1.3. The gap to midgap ratio became larger than 0.18 when the rotation angle changed from 40° to 50° and the maximum gap to midgap ratio of 0.2 remained unchanged for the rotation angle ranging from 42° to 48° with height-to-pitch ratio of 1.3. The results show this type of woodpile structure can produce big band gaps in a wider parameter range,which offers convenience for preparing three- dimension photonic crystals in laboratory.
2009, 33(4): 397-399.
doi: 10.3969/j.issn.1001-3806.2009.04.017
Abstract:
In order to study the performance deterioration induced by polarization mode dispersion(PMD)in a fiber link, the effect of 1st order and 2nd order PMD on the non-return-to-zero(NRZ),return-to-zero(RZ)and chirped return-to-zero(CRZ)codes was analyzed by means of the split-step Fourier method based on the coupled nonlinear Schrodinger equation. The analytical results show that the performance of the optical fiber link is severely deteriorated by PMD,one of the main factors limiting the property of the link. And with the increase of the working speed,the influence of higher-order PMD becomes worse. The effect of PMD can be partially reduced for a right code pattern,i. e.,CRZ code is a little better than RZ code and RZ code is better than NRZ code.
In order to study the performance deterioration induced by polarization mode dispersion(PMD)in a fiber link, the effect of 1st order and 2nd order PMD on the non-return-to-zero(NRZ),return-to-zero(RZ)and chirped return-to-zero(CRZ)codes was analyzed by means of the split-step Fourier method based on the coupled nonlinear Schrodinger equation. The analytical results show that the performance of the optical fiber link is severely deteriorated by PMD,one of the main factors limiting the property of the link. And with the increase of the working speed,the influence of higher-order PMD becomes worse. The effect of PMD can be partially reduced for a right code pattern,i. e.,CRZ code is a little better than RZ code and RZ code is better than NRZ code.
2009, 33(4): 400-402.
doi: 10.3969/j.issn.1001-3806.2009.04.019
Abstract:
In order to study the property of high power fiber amplifiers,the output energy of 10μJ and the peak power of 2.4kW were obtained respectively after the shaped signal pulse is amplified by a two-stage fiber amplifier. However,the pump power was larger than 1.4W,the output energy became unstable and giant pulse was detected. It was found that the output signal was not saturated and there was lots of residual energy in the fiber even the output signal was large up to a few kW. Higher power can be obtained if the design of the fiber amplifier was optimized. The Yb-doped large-mode-area fiber amplifier was simulated, and the result was identical with the experiment result.
In order to study the property of high power fiber amplifiers,the output energy of 10μJ and the peak power of 2.4kW were obtained respectively after the shaped signal pulse is amplified by a two-stage fiber amplifier. However,the pump power was larger than 1.4W,the output energy became unstable and giant pulse was detected. It was found that the output signal was not saturated and there was lots of residual energy in the fiber even the output signal was large up to a few kW. Higher power can be obtained if the design of the fiber amplifier was optimized. The Yb-doped large-mode-area fiber amplifier was simulated, and the result was identical with the experiment result.
2009, 33(4): 403-405,412.
doi: 10.3969/j.issn.1001-3806.2009.04.020
Abstract:
With the eigen matrix method,it analysed the relation between dual defect modes and the thickness of the defect layer in 1-D photonic crystal was analyzed. The results showed that when the thickness of the defect layer was changed totally,the position of dual defect modes at low frequencies was different from that at high frequencies. When the thickness of the material with positive refractive index was solely increased,the position of dual defect layers was red-shifted. On the contrary,the position was blue-shifted when the thickness of the material with positive reflective index was solely increased. The transmissivity of dual defect modes changed intricately. The property can be used to design some specific photonic devices.
With the eigen matrix method,it analysed the relation between dual defect modes and the thickness of the defect layer in 1-D photonic crystal was analyzed. The results showed that when the thickness of the defect layer was changed totally,the position of dual defect modes at low frequencies was different from that at high frequencies. When the thickness of the material with positive refractive index was solely increased,the position of dual defect layers was red-shifted. On the contrary,the position was blue-shifted when the thickness of the material with positive reflective index was solely increased. The transmissivity of dual defect modes changed intricately. The property can be used to design some specific photonic devices.
2009, 33(4): 406-408,432.
doi: 10.3969/j.issn.1001-3806.2009.04.021
Abstract:
In order to study gain characteristics of forward and backward multi-pumped Raman amplifiers,based on the power propagation equations of multi-pumped Raman fiber amplifiers,the pumped power and signal power along the fiber was calculated combining Ronge-Kuta with shoot calculation method. The calculation results showed that in the forward pumped fiber amplifiers,the signal power was amplified at first because of the interaction between the pumped light,then reduced fast after the peak value,and that in the backward pumped fiber amplifiers,the signal power reduced gradually at first,then increased fast at the end of the fiber. The result is an important reference for the design of the Raman fiber amplifiers.
In order to study gain characteristics of forward and backward multi-pumped Raman amplifiers,based on the power propagation equations of multi-pumped Raman fiber amplifiers,the pumped power and signal power along the fiber was calculated combining Ronge-Kuta with shoot calculation method. The calculation results showed that in the forward pumped fiber amplifiers,the signal power was amplified at first because of the interaction between the pumped light,then reduced fast after the peak value,and that in the backward pumped fiber amplifiers,the signal power reduced gradually at first,then increased fast at the end of the fiber. The result is an important reference for the design of the Raman fiber amplifiers.
2009, 33(4): 409-412.
doi: 10.3969/j.issn.1001-3806.2009.04.022
Abstract:
In order to study the problem of calculating phase shifts in the phase-shifting digital holography,the recording and reconstructing principle of phase-shifting off-axis lenless Fourier transform digital holography was analyzed based on the Fresnel diffraction and holographic theory.Then the complex field expression of four-step phase-shifting digital hologram based on arbitrary phase shifts was deduced.A new method was proposed to calculate arbitrary phase shifts by means of phase subtraction.The experimental results show that compared with the conventional method of four-step phase-shifting,it is not necessary to calibrate phase-shifting devices strictly with this method.The zero-order diffraction and the conjugate image are also eliminated effectively and the ratio of signal to noise is similarly improved.Therefore,the method contributes to the reduction of the complicacy of the measure system and the promotion of the development of four-step phase-shifting digital hologram.
In order to study the problem of calculating phase shifts in the phase-shifting digital holography,the recording and reconstructing principle of phase-shifting off-axis lenless Fourier transform digital holography was analyzed based on the Fresnel diffraction and holographic theory.Then the complex field expression of four-step phase-shifting digital hologram based on arbitrary phase shifts was deduced.A new method was proposed to calculate arbitrary phase shifts by means of phase subtraction.The experimental results show that compared with the conventional method of four-step phase-shifting,it is not necessary to calibrate phase-shifting devices strictly with this method.The zero-order diffraction and the conjugate image are also eliminated effectively and the ratio of signal to noise is similarly improved.Therefore,the method contributes to the reduction of the complicacy of the measure system and the promotion of the development of four-step phase-shifting digital hologram.
2009, 33(4): 413-415,418.
doi: 10.3969/j.issn.1001-3806.2009.04.023
Abstract:
In order to study the dependence of output characteristics on the parameter of multi-order cascaded Raman fiber lasers,the nonlinear coupled equations,describing modeling of multi-order cascaded Raman fiber lasers,were solved.Based on numerical simulation,the effect of fiber length,reflectivity of output coupler and pump power on the output characteristics of a 6-order cascaded Raman fiber laser was obtained.The results showed that the Raman fiber lasers had lower threshold power and could obtain the maximum output power when the fiber length was about 300m,and the reflectivity of the output mirror was about 10%.
In order to study the dependence of output characteristics on the parameter of multi-order cascaded Raman fiber lasers,the nonlinear coupled equations,describing modeling of multi-order cascaded Raman fiber lasers,were solved.Based on numerical simulation,the effect of fiber length,reflectivity of output coupler and pump power on the output characteristics of a 6-order cascaded Raman fiber laser was obtained.The results showed that the Raman fiber lasers had lower threshold power and could obtain the maximum output power when the fiber length was about 300m,and the reflectivity of the output mirror was about 10%.
2009, 33(4): 419-421,425.
doi: 10.3969/j.issn.1001-3806.2009.04.025
Abstract:
In order to understand the effect of the system factors,such as light intensity,magnification,CCD and background,on the reconstructed image of different diameter particles in the process of holographic reconstruction,a series of experiments were performed.The experimental results showed that,by adjusting the light intensity and making the background light intensity closed to the lower limit of CCD threshold,images with smoothing background and high definition were acquired.For particles with diameter less than 20μm and a reconstruction system with a certain magnification,a little higher intensity of reconstruction light was needed for ideal images.It was favorable for image keeping the experimental environment dark.Results show that high quality particle images can be obtained by means of the above methods in the process of particle holographic reconstruction.
In order to understand the effect of the system factors,such as light intensity,magnification,CCD and background,on the reconstructed image of different diameter particles in the process of holographic reconstruction,a series of experiments were performed.The experimental results showed that,by adjusting the light intensity and making the background light intensity closed to the lower limit of CCD threshold,images with smoothing background and high definition were acquired.For particles with diameter less than 20μm and a reconstruction system with a certain magnification,a little higher intensity of reconstruction light was needed for ideal images.It was favorable for image keeping the experimental environment dark.Results show that high quality particle images can be obtained by means of the above methods in the process of particle holographic reconstruction.
2009, 33(4): 422-425.
doi: 10.3969/j.issn.1001-3806.2009.04.026
Abstract:
In order to identify correlation peak better in the research of target recognition technology based on coherent optics,combining the genetic algorithm(GA)and the artificial neural network(ANN),based on GA and back propagation(BP)neural network,a correlation peak identification system was built with GA optimizing the initial weights and thresholds of the ANN.The optimized identification system could not only avoid the tendency of local minimum and slow convergence speed in ANN training,but also overcome the shortage of local precise searching capacity in GA.It realizes the superiority complementation between the both the methods,and is helpful to solve the problem of recognizing correlation peak.The testing results show that the improved method makes full use of the advantages of GA and BP algorithm,and gets much better interpretation effect.
In order to identify correlation peak better in the research of target recognition technology based on coherent optics,combining the genetic algorithm(GA)and the artificial neural network(ANN),based on GA and back propagation(BP)neural network,a correlation peak identification system was built with GA optimizing the initial weights and thresholds of the ANN.The optimized identification system could not only avoid the tendency of local minimum and slow convergence speed in ANN training,but also overcome the shortage of local precise searching capacity in GA.It realizes the superiority complementation between the both the methods,and is helpful to solve the problem of recognizing correlation peak.The testing results show that the improved method makes full use of the advantages of GA and BP algorithm,and gets much better interpretation effect.
2009, 33(4): 426-428,436.
doi: 10.3969/j.issn.1001-3806.2009.04.027
Abstract:
In order to make a laser beam expander work a long time under high power laser radiation,on the base of the traditional multi-wavelength laser-beam expander,a two-serial expander with magnification of 2.3 and 6 respectively was designed through modifying the optical material and configuration.The expander was optimized and its image quality was analyzed with optical design software.After the expander was manufactured,experiments were performed in practical environment.It could work for a long time under laser radiation with pulse interval of 5s at high peak power up to 20MW,the output beam diameters were 24.5mm and 154.8mm respectively at 1m behind the expender with the characteristic of Gaussian-beam kept very well.The result indicates that the expender meets the design requirement and is practical.
In order to make a laser beam expander work a long time under high power laser radiation,on the base of the traditional multi-wavelength laser-beam expander,a two-serial expander with magnification of 2.3 and 6 respectively was designed through modifying the optical material and configuration.The expander was optimized and its image quality was analyzed with optical design software.After the expander was manufactured,experiments were performed in practical environment.It could work for a long time under laser radiation with pulse interval of 5s at high peak power up to 20MW,the output beam diameters were 24.5mm and 154.8mm respectively at 1m behind the expender with the characteristic of Gaussian-beam kept very well.The result indicates that the expender meets the design requirement and is practical.
2009, 33(4): 429-432.
doi: 10.3969/j.issn.1001-3806.2009.04.028
Abstract:
In order to study the effect of illuminating beam on output correlation spots,for a given target image,the relation among the output correlation peak value,the parameters of Gaussian beam and the location of the image on the input plane was simulated with the joint transform correlator illuminated by Gaussian beam.It was found that the output correlation peak value decreased with the decrease of the waist radius of Gaussian beam and the increase of the interval between target image on input plane and the center of Gaussian beam.Simulation results show that the ratio of amplitude of the center of Gaussian beam before and after beam expansion should be 5.7 if the waist radius of 1mm is expanded to 32mm,where the output correlation peak value at the edge of the facula is 90% of that at the center,and that in order to output high correlation peak value when images locate any place on the input plane,the waist radius of Gaussian beam must be expanded big enough.
In order to study the effect of illuminating beam on output correlation spots,for a given target image,the relation among the output correlation peak value,the parameters of Gaussian beam and the location of the image on the input plane was simulated with the joint transform correlator illuminated by Gaussian beam.It was found that the output correlation peak value decreased with the decrease of the waist radius of Gaussian beam and the increase of the interval between target image on input plane and the center of Gaussian beam.Simulation results show that the ratio of amplitude of the center of Gaussian beam before and after beam expansion should be 5.7 if the waist radius of 1mm is expanded to 32mm,where the output correlation peak value at the edge of the facula is 90% of that at the center,and that in order to output high correlation peak value when images locate any place on the input plane,the waist radius of Gaussian beam must be expanded big enough.
2009, 33(4): 433-436.
doi: 10.3969/j.issn.1001-3806.2009.04.029
Abstract:
A method was proposed to decrypt the original image from an only ciphertext encrypted from a symmetrical image.Through inverse Fresnel transform of the ciphertext holograph,the intensity of the frequency spectrum can be received by CCD and sent into a computer.According to the characteristics of autocorrelation and complex-convolution in discrete Fresnel transform,the coefficients are classified and ranked,so that the input light wave can be recovered and the original image can be obtained.The effect of the symmetrical deviation on the quality of the decrypted image was also studied.The investigation indicates that the original image can be decrypted by means of discrete Fresnel diffraction.
A method was proposed to decrypt the original image from an only ciphertext encrypted from a symmetrical image.Through inverse Fresnel transform of the ciphertext holograph,the intensity of the frequency spectrum can be received by CCD and sent into a computer.According to the characteristics of autocorrelation and complex-convolution in discrete Fresnel transform,the coefficients are classified and ranked,so that the input light wave can be recovered and the original image can be obtained.The effect of the symmetrical deviation on the quality of the decrypted image was also studied.The investigation indicates that the original image can be decrypted by means of discrete Fresnel diffraction.
2009, 33(4): 437-439,448.
doi: 10.3969/j.issn.1001-3806.2009.04.030
Abstract:
In order to study the focusing property and focal depth of amplitude-modulated Gaussian beam in different numerical-aperture(NA):they were numerically simulated according to the vector diffraction theory based on Debye approximate condition.Simulation results showed that the intensity in the focus plane was in a circular shape in a low NA optical system;while in a high NA optical system,it was in an elliptical shape because of the polarization effect.The focal spot size and focal depth can be adjusted by changing the geometric parameters and the amplitude modulation parameter exponential n of Gaussian beam.
In order to study the focusing property and focal depth of amplitude-modulated Gaussian beam in different numerical-aperture(NA):they were numerically simulated according to the vector diffraction theory based on Debye approximate condition.Simulation results showed that the intensity in the focus plane was in a circular shape in a low NA optical system;while in a high NA optical system,it was in an elliptical shape because of the polarization effect.The focal spot size and focal depth can be adjusted by changing the geometric parameters and the amplitude modulation parameter exponential n of Gaussian beam.
2009, 33(4): 440-442,445.
doi: 10.3969/j.issn.1001-3806.2009.04.031
Abstract:
In order to design and use the splitting Lippich prism and the splitting Grand-Thompson prism,the splitting angle,separation angle and splitting ratio of light intensity were analyzed.The results show:the splitting angle and splitting ratio of light intensity of the splitting Lippich prism and the splitting Grand-Thompson prism are dependent on the structure angle and the vice structure angle;both the prisms have the same splitting angle and different light intensity splitting ratios if they have the same structure angle and vice structure angle.The separation angle about beam o and beame' is dependent on the vice structure angle: the design of splitting Lippich prism is better for the need of normal output of beam o;the design of splitting Grand-Thompson prism is better for the need of a big splitting angle.With optimum design symmetric beam splitting of light intensity can be achieved for both the prisms.The experiment data are in accordance with the theoretical results.
In order to design and use the splitting Lippich prism and the splitting Grand-Thompson prism,the splitting angle,separation angle and splitting ratio of light intensity were analyzed.The results show:the splitting angle and splitting ratio of light intensity of the splitting Lippich prism and the splitting Grand-Thompson prism are dependent on the structure angle and the vice structure angle;both the prisms have the same splitting angle and different light intensity splitting ratios if they have the same structure angle and vice structure angle.The separation angle about beam o and beame' is dependent on the vice structure angle: the design of splitting Lippich prism is better for the need of normal output of beam o;the design of splitting Grand-Thompson prism is better for the need of a big splitting angle.With optimum design symmetric beam splitting of light intensity can be achieved for both the prisms.The experiment data are in accordance with the theoretical results.
2009, 33(4): 443-445.
doi: 10.3969/j.issn.1001-3806.2009.04.032
Abstract:
In order to analyze the variation relation between light intensity splitting ratio and incident angle with He-Ne laser obliquely incident on YVO4 polarizing splitting prism,the mathematical formula of the light beam were deduced according to the geometric relationship,Fresnel formula and phase matching conditions.Through experimental verification,theoretical value accorded with experimental value,then the error was analyzed.It provides important reference information for the development of YVO4 polarizing splitting prisms as polarizing devices.
In order to analyze the variation relation between light intensity splitting ratio and incident angle with He-Ne laser obliquely incident on YVO4 polarizing splitting prism,the mathematical formula of the light beam were deduced according to the geometric relationship,Fresnel formula and phase matching conditions.Through experimental verification,theoretical value accorded with experimental value,then the error was analyzed.It provides important reference information for the development of YVO4 polarizing splitting prisms as polarizing devices.
2009, 33(4): 446-448.
doi: 10.3969/j.issn.1001-3806.2009.04.033
Abstract:
In order to study the energy focus ability of the beam diffracted by a small circular aperture,based on the rigorous vectorial diffraction theory and the accurate expression of light intensity,the power density expression of nonparaxial diffraction beam at the transverse plane,detailed numerical calculation was performed and the different results were compared.It showed that the energy focusability of the diffraction beam depended on the transmission distance,diffraction aperture and facula radius,and appropriate energy focusability could be obtained by controlling some parameters of the optical system.The results have some reference values to the research of energy transmission of the fiber probe.
In order to study the energy focus ability of the beam diffracted by a small circular aperture,based on the rigorous vectorial diffraction theory and the accurate expression of light intensity,the power density expression of nonparaxial diffraction beam at the transverse plane,detailed numerical calculation was performed and the different results were compared.It showed that the energy focusability of the diffraction beam depended on the transmission distance,diffraction aperture and facula radius,and appropriate energy focusability could be obtained by controlling some parameters of the optical system.The results have some reference values to the research of energy transmission of the fiber probe.
