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Showing papers in "Chinese Journal of Lasers in 2004"


Journal Article
TL;DR: In this paper, the authors presented a scheme to detect the resonance point using two frequency serrodyne modulation, and used the Lorentzian function to describe the expression of the output power at the exit port of the fiber ring resonator taking the temporal coherence of the laser into account.
Abstract: Resonator fiber optic gyro (R FOG) is an inertial rotation sensor with high accuracy which is based on the Sagnac effect The signal detection system has important role in the R FOG The detecting precision influences the maximum resolution of the gyro directly The fiber ring resonator is the core sensing element in the R FOG This paper presents the scheme to detect the resonance point using two frequency serrodyne modulation, and uses the Lorentzian function to describe the expression of the output power at the exit port of the fiber ring resonator taking the temporal coherence of the laser into account According to near linear relationship between amplitude of the square waveform and the resonant frequency deviation near the resonant point, frequency feedback time after time is used for frequency tracking for both clockwise (CW) and counterclockwise (CCW) waves Therefore, complex root finding process can be avoided Simulation shows that both CW and CCW waves can be locked at the resonance frequency of the resonator quickly by frequency feedback operation

13 citations


Journal Article
TL;DR: In this paper, through numerical simulation and experimental validation, the Twomey algorithm applied in the foregoing measuring methods was improved and the reasonable results of particle size distribution were got As a result, the Philip-Twomey-NNLS algorithm combined with generalized cross validation (GCV) technique is proved effective to handle the inverse problem in particle sizing.
Abstract: Inverse problem is always encountered in particle sizing techniques based on the light or acoustic scattering Here, through numerical simulation and experimental validation, the Twomey algorithm applied in the foregoing measuring methods was improved and the reasonable results of particle size distribution were got As a result, the Philip-Twomey-NNLS algorithm combined with generalized cross validation (GCV) technique is proved effective to handle the inverse problem in particle sizing

11 citations


Journal Article
TL;DR: In this article, a fiber-coupled diode-end-pumped Nd∶YVO_4 laser with 0.3 at.-% dopped concentration and 10 mm length was reported.
Abstract: A fiber-coupled diode-end-pumped Nd∶YVO_4 laser with a Nd∶YVO_4 crystal of 0.3 at.-% dopped concentration and 10 mm length was reported in this paper. CW TEM_ 00 mode output of 14.85 W was obtained at a pump power of 27.365 W, resulting in an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%. The effect of dopped concentration and crystal length on the performance of Nd∶YVO_4 was also analyzed.

11 citations


Journal Article
Yang Ruike1
TL;DR: In this paper, the attenuation characteristics of a single scattering of sand and dust particles with a special size distribution were studied with Mie theory, and the average scattering cross section, albedo, asymmetry factor, and phase function were calculated.
Abstract: The study on laser transmission and scattering characteristics in complex environments is the basis research of light scattering from target and environment. The severe attenuation caused by laser propagation in sand and dust storms was mainly discussed in this paper. The attenuation characteristic of laser was studied with Mie theory for single scattering of sand and dust particles with special size distribution. Based on Mie theory, the average scattering cross section, albedo, asymmetry factor, and phase function were calculated. The laser multiple scattering and attenuation characteristics of slanting transmission in the layering sand dust atmosphere were studied by using four-flux model method and Monte-Carlo method, and the relationship between attenuation and visibility in difference heights was also given. Finally, after considening of multi-scattering, numerical calculations of specify attenuation were made for laser signal of 1.06 μm in sand and dust atmosphere by using the above two methods respectively, and the results were compared to the condition of single scattering. It is shown that biggish error can be brought in the low visibility take no account of multiple scattering, and that the more layers of the sand and dust atmosphere is divided into for slanting transmission, the more accurate the result is.

8 citations


Journal Article
TL;DR: In this article, a numeric model is established based on ANSYS software to calculate the three-dimensional transient temperature field of the continuous moving laser molten pool, and the calculated results show that when laser scanning on the top surface of 45# steel base plate from one point to another point along straight line, due to thermal conductivity, the temperature of laser molten pools increases with time increasing.
Abstract: In order to calculate the three-dimensional transient temperature field of the continuous moving laser molten pool, a numeric model is established basing on ANSYS software In the established model, the influences of the surface temperature of material on laser absorptivity and phase change of material on temperature field of laser molten pool are taken into consideration The analysis on the time-depended temperature field of laser molten pool is also conducted During laser processing, the heating and cooling process of laser molten pool can be acquired by the numeric model The calculated results show that when lasers scanning on the top surface of 45# steel base plate from one point to the another point along straight line, due to thermal conductivity, the temperature of laser molten pool increases with time increasing The calculated result also indicates that the position of the highest temperature point on the laser molten pool surface is slightly lagged the position of the center point of the laser beam Under the same laser process parameter conditions, the calculated result agrees with the experimental result, this indicates that the established numeric model is correct and reliable

8 citations


Journal Article
Mo Chang1
TL;DR: In this paper, a method for background light compensation of photo electric position detector based on the artificial neural network is presented, which is trained to properly represent the nonlinear mapping between sensor reading and their represent output accurately at different background light.
Abstract: The position sensitive detector (PSD) is photo electronic sensor which can detect the position of a light spot travelling over its surface, and convert the position of light spot to simple electric current signal. The most important problem to use the PSD is how to overcome the influence of background light action on the PSD. Based on the PSD analyses, it is found that the signal of PSD is nonlinear when there exist background light. A method for background light compensation of photo electric position detector based on the artificial neural network is presented in this paper. In order to compensate background light over a full range, the neural network is trained to properly represent the nonlinear mapping between sensor reading and their represent output accurately at different background light. It is revealed from the computer simulation that the influence of background light fluctuation can be eliminated effectively, and a desired linear relationship between the sensor input and the neural network output can be obtained.

6 citations


Journal Article
Wang Qing1
TL;DR: In this article, a Sagnac loop is used to feed back the output of C-band ASE, the reflected C-ASE propagates along single direction in the fiber and is amplified in expending inversion population, so that the utility of pump power for L-band amplified spontaneous emission is increased.
Abstract: Optical wideband source of L-band amplified spontaneous emission (ASE) from erbium doped fiber has extensive application in fiber sensors and device testing; here the pump power conversion is one of the key technique In this work, based on the secondary pumping mechanism by C-band power for L-band signal, a Sagnac loop is used to feed-back the output of C-band ASE, the reflected C-ASE propagates along single direction in the fiber and is amplified in expending inversion population, so that the utility of pump power for L-band ASE is increased Experimentally, the total output power was 14 dBm at 125 mW 980 nm pumping ie pump power conversion efficiency up to 20% was achieved Without gain flatten filter, the 1 dB bandwidth was 311 nm (15689~1600 nm), so that high pump conversion efficiency and broad L-band ASE source was demonstrated

6 citations


Journal Article
TL;DR: In this article, the authors presented the theoretic and experimental results of interferometric polarization-maintaining fiber micro-vibration vector sensor with phase generated carrier (PGC) technology.
Abstract: The theoretic and experimental result of interferometric polarization-maintaining fiber micro-vibration vector sensor are represented. Because of polarization-maintaining fiber structure, the sensor avoided instability of polarization. With phase generated carrier (PGC) technology, the influence of initial phase of interferometer was sliminated. Based on these methods, the stable signal detect was realized by the fiber optic micro-vibration vector sensor. The measured natural frequency of the system was 370 Hz, which agrees with the theoretic result 375 Hz. The acceleration sensitivity in experimental results reached 340 rad/g in frequency band of 5~200 Hz, and it matched 356 rad/g predicted by theory. Vector character of the sensor was obtained too. The acceleration sensitivity in 45° was 0.7 times of that in 0° and the orthogonal crosstalk coupling was -26 dB below. In the system, minimum measurable phase was 10 -5 rad and minimum measurable acceleration reached 3×10 -8 g.

6 citations


Journal Article
TL;DR: In this paper, a new aspect of CO 2 laser beam welding of aluminum with an electrical current technique was reported, where a DC power source was used to supply current to the weld pool.
Abstract: By using of the magnetohydrodynamic effect of electrical current, a new aspect of CO 2 laser beam welding of aluminum with an electrical current technique was reported. A DC power source was used to supply current to the weld pool. One pole of the source was connected with a tungsten electrode which was set in front of the weld pool and the other with the work piece in the rear of the weld pool. In so doing a closed electrical circuit was built. When the electrical current flows in the weld pool, a magnetic field is induced and electromagnetic forces are generated in it, which change the fluid flow and the heat exchange condition of the weld pool. So far the experimental results have shown that the weld depth and area increase and the weld seam becomes more slender when the current is up to a certain value, e.g. 200 A. In the experimental conditions, the weld depth increases maximum nearly by 32% and the weld area nearly by 20%, but the weld width decreases maximum nearly by 28%.

5 citations


Journal Article
Fu Hai1
TL;DR: In this paper, a novel model of high sensitivity in fiber Bragg grating (FBG) pressure sensor is proposed, and the relation between relative shift of Bragg wavelength and the pressure applied on the sensor is derived, and analytical expression of pressure sensitivity coefficient is also given.
Abstract: To enhance the sensitivity of the in fiber Bragg grating (FBG) sensor is one of the effective ways to improve the resolution of the FBG sensing system. Based on effect of FBG stress sensitivity enhancement by encapsulating the FBG with elastic polymer and a metal bellows, a novel model of high sensitivity FBG pressure sensor is proposed. The relation between relative shift of Bragg wavelength and the pressure applied on the sensor is derived, and the analytical expression of pressure sensitivity coefficient is also given. It indicates that the relation between the relative shift of Bragg wavelength and applied pressure is linear, and the pressure sensitivity coefficient can be enhanced by properly selecting the parameters of the elastic part and the metal bellows, such as the elastic modulus of the elastic part and the elastic constant of the bellows, and the size of them. The experimental pressure sensitivity coefficient of the sensor is -4.35×10 -9 Pa -1 (-6.74 nm/MPa), which is 2197 times of that of the bare FBG, the theoretical value of the sensor is -4.6×10 -9 Pa -1 , they fit very well.

5 citations


Journal Article
TL;DR: In this paper, the photoconductive effect and heat effect in semiconductor HgCdTe detectors when they are irradiated by laser were considered simultaneously, and a transportation model of the photoconductor carriers and heat transmission model were established.
Abstract: Photoconductive effect and heat effect in semiconductor photoconductive detectors when they are irradiated by laser were considered simultaneously. A transportation model of photoconductive carriers and heat transmission model were established. The photoconductive carriers consistency and the heat equilibrium carriers consistency in PC-type HgCdTe detectors under various laser irradiation density were calculated. Instantaneous change behaviors of the detectors were imitated further. The imitative results are identical with experimental results.

Journal Article
TL;DR: In this article, a diffractive optical element (DOE) with 8 levels is designed to implement the wavefront transformation with two dimensional weighed serial iterative algorithm, which realizes the transformation of beam shape and the uniform distribution of the amplitude at the same time.
Abstract: A diffractive optical element (DOE) with 8 levels is designed to implement the wavefront transformation with two dimensional weighed serial iterative algorithm. The DOE converts a circular Gaussian laser beam into a 10 μm×10 μm flat top square focused spot, which realizes the transformation of beam shape and the uniform distribution of the amplitude at the same time. The DOE is applied to high density holographic storage, and it meets the needs of the uniform distribution of the incident focused spot. The simulated results show that the energy transformation efficiency is up to 91.2%, the uniformity error is 4.6%, and the error is below 0.023%, which nearly satisfy the need. The tolerance of the incident beam and the focus is analyzed too. Three sets of masks on 8 levels phase DOEs have been processed.

Journal Article
Wang Yue-feng1
TL;DR: In this article, the authors investigated the thermal and mechanical damage mechanism of optical material induced by continuous-wave laser and solved the equations of heat conduction and thermoelastic dynamics through integral transform method.
Abstract: Laser induced damage in optical components is a limiting factor to the improvement of high-power laser. Using K9 glass irradiated with the CO2 continuous-wave laser as an example, the thermal and mechanical damage mechanism of optical material induced by continuous-wave laser is investigated. The equations of heat conduction and thermoelastic dynamics are solved through integral-transform method. Transient distribution of temperature field and thermal stress field is described. It is found that the definition of the thermal diffusion length is not applicable when incident laser is Gaussian beam; therefore, the dependence of the site of the maximal thermal stress on irradiation time is derived by curve fitting method, then the analytical solution of the damage threshold intensity is calculated. Because the stress damage threshold intensity is smaller than the melting damage threshold intensity, permanent damage in optical material is produced when circumference stress exceeds the tensile strength. The damage morphology of K9 glass induced by laser is proved to be cleavage burst. The model exhibits good agreement with the experiment result.

Journal Article
TL;DR: In this paper, the hollow lens duct is introduced for the application in the coupling of pump radiation from extended two dimensional semiconductor laser diode arrays into solid state laser gain media.
Abstract: The hollow lens duct is introduced for the application in the coupling of pump radiation from extended two dimensional semiconductor laser diode arrays into solid state laser gain media. With the help of numerical analysis of three dimension ray tracing, a computer simulation program for longitudinal pump laser diode (LD) coupling system was developed. Based on the result of simulation, a coupling system for large aperture high power LD arrays using hollow lens duct was build. Coupling efficiency beyond 90% was reached with perfect pumping uniformity on the surface of gain material. An experience formula for hollow lens duct design was deduced at the same time, it would be very helpful in designing coupling system of large scale diode pumped solid state lasers (DPSSLs).

Journal Article
TL;DR: In this paper, optical tweezers can be used in measuring nanometer displacements of a particle with several micron diameters, error sources are analyzed The dynamic image analysis methods including the gray centroid method and new developed methods: exponent centroid and parabolic fit method are discussed and compared A numerical simulation method was developed to evaluate errors caused by these different methods and compared the errors of three data processing methods.
Abstract: Optical Tweezers can be used in measuring nanometer displacements of a particle with several micron diameters Methods of measurement and data processing, error sources are analyzed The dynamic image analysis methods including the gray centroid method and new developed methods: exponent centroid method and parabolic fit method are discussed and compared A numerical simulation method was developed to evaluate errors caused by these different methods and compared the errors of three data processing methods The result shows that the parabolic fit method has a high precision with fewer computing time when the background noise is the main noise source The position of a fixed particle is measured by the quadrant detect (QD) method and the dynamic image analysis method The measurement standard deviation is 1 nm and 03 nm respectively Based on nanometer displacement measurement, the trap stiffness can be got Finally, a sub-PicoNewton external force which is applied on the particle is measured successfully It shows that the resolution of force measurement can reach femto Newton order

Journal Article
TL;DR: The fundamental principle of the recording and numerical reconstruction of the synthetic aperture digital holography is introduced, and two numerical reconstructed methods are proposed: one is the numerical reconstructed complex amplitude superposition or intensity superposition from the single reference beam sub hologram, and the other one isThe numerical reconstructedcomplex amplitude superpositions of the multi reference beams sub holograms.
Abstract: This paper introduces the fundamental principle of the recording and numerical reconstruction of the synthetic aperture digital holography, and proposes two numerical reconstructed methods: one is the numerical reconstructed complex amplitude superposition or intensity superposition from the single reference beam sub hologram, the other one is the numerical reconstructed complex amplitude superposition or intensity superposition of the multi reference beams sub hologram. The experimental research results show: Synthetic aperture technique can improve the resolution of digital holography evidently. Comparing with the conventional numerical reconstructed method of direct combined sub hologram, the proposed two kinds of numerical reconstructed methods are the same in improving the resolution of reconstructing image of digital holography, but the difficulty of recording and reconstruction of synthetic aperture digital holography by the intensity superposition method is decreased.

Journal Article
TL;DR: In this article, a composite light source is employed to decrease the measurement errors caused by the light intensity changes, which can be used to measure micro-vibrations with a high accuracy in real time.
Abstract: A novel LD-SPM interferometer, which can be used to measure micro-vibrations with a high accuracy in real time, is proposed. In this paper, a composite light source is employed to decrease the measurement errors caused by the light-intensity changes. Experiments verify the usefulness of the interferometer.

Journal Article
TL;DR: In this paper, composite coatings of Al 2O_3 nanocrystalline/Ni-based powder produced by transverse flow CO 2 laser on Ni-based superalloy were introduced.
Abstract: Composite coatings of Al_2O_3 nanocrystalline/Ni-based powder produced by transverse flow CO_2 laser on Ni-based superalloy were introduced. With Olympus Pme-3 type optical microscope, Philip-XL 30 type scanning electronic microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), the microstructure, chemical composition and distribution of nano particles of the cross-sections of the coatings were analyzed. The results showed that columnar dendrite grew perpendicularly to the interface without nano Al_2O_3 particles. And the growth morphologies of dendrite transformed from long columnar to short form by adding nano additives. Non-directional dendrite growth at the interface and equaxied dendrite across the section of the clad appeared with the additive amount of Al_2O_3 particles to 1%. The solidified microstructure was greatly refined because the nano Al_2O_3 accelerated nucleation ahead of the advancing interface of solid/liquid and held back crystal growth by its concentration. Nano particles prevented the formation of cracks in the coatings.

Journal Article
TL;DR: In this paper, an InP-based long wavelength resonant cavity enhanced photodetector with InP Air gap reflectors was used to achieve high quantum efficiency and wide frequency bandwidth.
Abstract: High speed and long wavelength photodetector is the key device for high bit rate optical fiber communication systems and optical networks that need wide frequency bandwidth and high external quantum efficiency simultaneously. It is well known that to increase the speed of PIN photodetector, the absorbing layer thickness should be reduced. The reduction of the absorbing layer thickness means a reduction in the quantum efficiency. So for conventional PIN photodetectors, there is a tradeoff between the quantum efficiency and the device frequency bandwidth through the absorbing layer thickness. One effective solution to this conflict is to use a resonant cavity enhanced (RCE) photodetector. In the RCE photodetector, the absorbing layer is put inside a Fabry Perot cavity. This means a very thin absorbing layer thickness can be used to achieve a high quantum efficiency and wide frequency bandwidth. In this paper, analyses of light field distribution in the absorption layer of RCE photodetector based on practical design and manufacture are performed. The expression of light field distribution is used in the continuity equations to the frequency response of the RCE photodetector. The frequency response of long wavelength RCE photodetector is analyzed and calculated. The result of analyses and calculation is almost identical with the measuring result of the wide frequency bandwidth RCE photodetector manufactured. That device is an InP based long wavelength resonant cavity enhanced photodetector with InP Air gap reflectors and has 8 GHz frequency bandwidth and about 60% external quantum efficiency with the active area of 50 μm×50 μm.

Journal Article
TL;DR: In this article, the effects of defocus and welding speed on the size and the appearance of the keyhole and the welding pool were experimentally studied, and a heat transfer model was proposed to obtain the temperature distribution and the fluid velocity distribution around a keyhole by a finite element method.
Abstract: Laser beam welding has gained increasing application in the industry, because of its high ratio of penetration deep to weld width, low heat effects and high welding speed. Keyhole effects are the essential characteristic in laser deep penetration welding. A clear stable keyhole was observed with a high-speed camera in laser welding of GG17 glass. The effects of defocus and welding speed on the size and the appearance of the keyhole and the welding pool were experimentally studied. Under the assumption of the keyhole per thin layer being cylindrical, a heat transfer model was proposed to obtain the temperature distribution and the fluid velocity distribution around the keyhole by a finite element method based on the keyhole observed. Experimental study and simulation show that temperature gradient on the front keyhole wall is steeper than that on the rear, the mass flow rate in the welding pool is about ten times the welding speed, and a new technology for quantitative study of keyhole effects in deep penetration laser welding is developed.

Journal Article
Lu Min1
TL;DR: In this paper, the authors analyzed the self mixing interference effect in the laser diode (LD) with multiple external reflectors and presented the analysis based on the compound cavity effect in lasers.
Abstract: This paper analyzes the self mixing interference effect in the laser diode (LD) with multiple external reflectors and presents the analysis based on the compound cavity effect in lasers. Each external cavity is considered to be an optical thin film, and the reflectance ratio can be get from the theory of the thin film optics. The general expression of the threshold gain and frequency in the compound laser cavity are deduced and some simulation analysis is made at different conditions. A self mixing interference experiment system is build with multiple external reflectors. And some experiment results are presented. It is found from the simulation and experiment that the output of the self mixing interference system with multiple external reflectors is sinusiodal or saw toothed waves which is similar with the three mirror Fabry Perot cavity system. The simulating and experimental results demonstrate the validity of the principle. This principle can be used to analyze the fiber coupled self mixing system and the simulation is accordant with experimental results.

Journal Article
TL;DR: In this paper, a laser diode (LD) end pumped Yb∶YAG (Yb∻Y 3Al 5O 12 ) chip laser has been demonstrated.
Abstract: A laser diode (LD) end pumped Yb∶YAG (Yb∶Y 3Al 5O 12 ) chip laser has been demonstrated. The pumping source is a fiber coupled laser diode array with maximum output power of 13.56 W at 940 nm. The diameter of the fiber is 800 μm. Two lenses with focal length ratio of 30∶12 have been used to compress the pumping light into the laser crystal. 3.06 W continuous wave (CW) output power was obtained from the 8 at. % doped, 1.6 mm thick Yb∶YAG crystal, the whole experiment set was cooled by thermoelectric cooler (TEC) and cooling water, slope efficiency was 33.1%, the M 2 values were measured to be 1.54 and 1.73 in the x and y directions respectively.

Journal Article
TL;DR: In this paper, a short cavity Er/Yb co-oped fiber laser with high output power and high slope efficiency is demonstrated, which is used for dense wavelength division multiplex (DWDM) system.
Abstract: A short cavity Er/Yb co doped fiber laser of high output power and high slope efficiency is demonstrated. Its resonant cavity is composed of a section of single mode Er/Yb co doped fiber and two fiber Bragg gratings with the same reflection wavelength. A fiber grating is used for output of resonant cavity with 60% reflectivity. Its 3 dB bandwidth is measured as 0.16 nm. The other fiber grating is used for high broadband reflector and input of pump light with 99% reflectivity. Its 3 dB bandwidth is measured as 1.02 nm. This fiber laser is pumped by a 980 nm semiconductor laser. Meanwhile, the Er/Yb co doped fiber with different lengths is measured by different pump power, and the optimized length of the fiber is only 13 cm. A short cavity fiber grating laser is done by using 13 cm Er/Yb co doped fiber as gain medium. Its maximum output power is 11 mW and its power stability is better than ±0.01 dB. The laser has a threshold of 35 mW and a slope efficiency of 15 3%. Its 1552 2 nm output spectral 25 dB bandwidth is measured as 0 3 nm. Edge mode suppression ratio 60 dB has been achieved and its wavelength stability is 0 05 nm. This fiber laser is able to be used for dense wavelength division multiplex (DWDM) system.

Journal Article
Huo Yu-jing1
TL;DR: Based on the self-triggering pulsed technique, a novel pulsed time-of-flight laser rangefinding method is proposed to improve the accuracy and measuring speed of laser distance measurement.
Abstract: Based on the self-triggering pulsed technique, a novel pulsed time-of-flight laser rangefinding method is proposed to improve the accuracy and measuring speed of laser distance measurement. The theoretical analysis is carried out, and three basic equations are presented to describe the methods. Furthermore, a measurement device is described and experimental evidence is presented to show the feasibility of measuring distance with 0 5 mm resolution over 20 m ranges.

Journal Article
TL;DR: In this article, the three dimensional intracavity distribution of super Gaussian mirror resonator is analyzed, and the intensity distributions are simulated when the thermal focal length changes. And the influence of the thermal lens effect is discussed.
Abstract: For the conventional unstable resonator, the output laser is deteriorated by the hard edge diaphragm diffraction. Using variable reflective mirror, as a soft edge diaphragm, the intensity distributions of output laser are improved. Gaussian mirror has been used widely, and the super Gaussian mirror is a development for variable reflective mirror. The fast Fourier transform (FFT) algorithm is a convenient method for simulating the intensity distribution of resonator. In this paper, the three dimensional intracavity distribution of super Gaussian mirror resonator is analyzed, and the intensity distributions are simulated when the thermal focal length changes. Then the output intensity distributions are simulated with or without considering the thermal lens effect. And the influence of the thermal lens effect is discussed.

Journal Article
TL;DR: In this paper, numerical simulation for temperature field of femtosecond-picosecond pulse laser ablation on metal surface is performed by finite-difference method (FDM).
Abstract: To describe femtosecond laser ablation on metal surface, the double-temperature equation (DTE) was formatted simply. In this paper, numerical simulation for temperature field of femtosecond-picosecond pulse laser ablation on metal surface is performed by finite-difference method (FDM). It is reasonable to make the DTE simple in femtosecond scale. It is also analysed that the effect of electron-lattice couple coefficient g on surface temperature, and found that g determines the surface temperature rising rate and the electron-lattice couple time. Compared with picosecond pulse laser, the intense of pulse is the main factor of the finally temperature of electron. The ablated depth of femtosecond laser can be controlled as thick as the surface depth of metal.

Journal Article
TL;DR: A 30 km long range distributed optical fiber Raman temperature sensor (DOFRTS) system has been made, it use new measuring temperature principle of optical fiber amplified anti Stokes Raman spontaneous scattering In the system, 1550 nm erbium doped optical fiber laser, high speed data acquisition card and signal processing technique are used, the problem of weak signal detection is resolved and signal to noise ratio is increased.
Abstract: A 30 km long range distributed optical fiber Raman temperature sensor (DOFRTS) system has been made, it use new measuring temperature principle of optical fiber amplified anti Stokes Raman spontaneous scattering In the system, 1550 nm erbium doped optical fiber laser, high speed data acquisition card and signal processing technique are used By using these technique, the problem of weak signal detection is resolved and signal to noise ratio is increased All components of system are put into an intellectualized constant temperature box and work in constant temperature condition Stability and environment adaptability are improved By appraisal, performance of the system is listed as follows: optical single mode fiber: 31 km, temperature rang: 0~100℃ (can be expanded), temperature measuring uncertainty: ±2℃, temperature resolution: 01℃, measurement time: 432 s, spatial resolution: 4 m The contrast table of the performance of DOFRTS system is given in the paper

Journal Article
TL;DR: In this article, a quantitative analysis of the object image relation and the resolution of digital holography by computer simulation and corresponding experiment is given, and the results show that the object-image relation is the same as that of traditional holographic theory, and if the collimating waves with the same wavelength are used in recording and reconstructing digital hologram, the size and shape of the reconstructed image are the same same as the recorded object.
Abstract: By use of Fresnel diffraction and traditional holographic theory, this paper gives some quantitative analysis of the object image relation and the resolution of digital holography by computer simulation and corresponding experiment The results shows: the object image relation of digital holography is the same as that of traditional holography, and if the collimating waves with the same wavelength are used in recording and reconstructing digital hologram, the size and shape of the reconstructed image are the same as that of the recorded object, and the incidence angle variation of reconstructing wave only make the position of the reconstructed image parallel shift and doesn′t influence the size of reconstructed image The physical meaning of the lateral resolution of digital holography is identical with that of the resolving power of optical image instrument, and the size of the lateral resolution of digital holography is determined by the diffracting limit using CCD′s size as windows at the position of reconstructed image The results of simulation is almost the same as that of experiment

Journal Article
TL;DR: In this paper, a chirp fiber grating to flatten the gain spectrum of L-EDFAs by using layer-peeling method is designed based on the law of causality.
Abstract: Gain flattening of EDFA (erbium-doped fiber amplifier) is a critical issue for WDM (wavelength-division-multiplex) system, and cost efficiency and insertion loss make in-fiber gratings very attractive candidates for this application A chirp fiber grating to flatten the gain spectrum of L-EDFAs by using layer-peeling method is designed This algorithm, based on the law of causality, considers fiber Bragg gratings as a discrete model, which divides the entire grating into a series of discrete, complex reflectors with a distance Δ between the adjacent reflectors, the coupling coefficient at the back of a reflector can be derived from one at the front of this reflector recursively, so coupling coefficient function can be extracted rapidly and accurately The target reflection spectrum of chirp gratings is derived from the ideal transmission spectrum of gain-flattening filters A constant, α, is utilized to control the length of chirp gratings, which is relative with group time delay of reflection spectrums When α is equal to 00024 cm2, the grating has a short length of 35 cm After extracting coupling coefficients of the chirp grating using layer-peeling algorithm, transmission spectrum of the synthesized grating by solving Riccati equation is simulated, numerical analysis indicates that peak-to-peak error function is below 01 dB between ideal and realistic transmission spectrums The variation of group time delay in transmission spectrum is less than 06 ps over entire operation bandwidth; therefore, the grating has no impact of additional chromatic dispersion on system performance

Journal Article
TL;DR: Using the cross mutual spectral density of the partially coherent theory, the self imaging of grating under illumination with arbitrary degree of partial coherence was developed in this article, which can be applied to either continuous or pulsed illuminations with any kind of spectra.
Abstract: Using of the cross mutual spectral density of the partially coherent theory, the self imaging of grating under illumination with arbitrary degree of partial coherence is developed. Both the temporal and the averaged distributions of diffracted intensities at the self imaging distances are formulated, which can be applied to either continuous or pulsed illuminations with any kind of spectra. The theoretical result shows that the ultra short laser pulse and the continuous polychromatic illuminations, whose spectrum distributions are the same, have the similar averaged self image distribution. So, the Talbot effect may help to study the temporal and spectral characteristics of ultra short laser pulses. An experiment using a light emitting diode (LED) as the source of illumination is performed, and the experimental results confirm with the theoretical ones.