Journals >Chinese Journal of Lasers
Contents
2004
Volume: 31 Issue 4
29 Article(s)
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Research Article
Research on Real-Time Measuring the Instantaneous Discharging Characteristic for High Power Laser Power Conditioning System
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Developing with the research on ICF, more and more attention is paid to the high power laser power conditioning system. In order to obtain accurate experiment data for researching on transmission efficiency of the high power laser power conditioning system, the structure of the controlling, measuring system and its reaDeveloping with the research on ICF, more and more attention is paid to the high power laser power conditioning system. In order to obtain accurate experiment data for researching on transmission efficiency of the high power laser power conditioning system, the structure of the controlling, measuring system and its real-time measure method for the characteristic data during the instantaneous discharging process of the xenon flash lamp were presented. A quantified-transmit model was adopted to measure and transmit the characteristic data, and it realized not only separating high voltage, but also preventing from being disturbed during long-distance transmission to ensure measuring precision. Cooperating to the modularize design of the system, the control function was divided into several threads to enhance the ability of real-time and harmony, and it realized the remote controlling high power system by low one effectively. The results show that the precision of the system is satisfied with the requirement of analysis and now the system is applied in experiment and research on power conditioning system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 407 (2004)
Thermal Distortions in Calcium Fluoride, Potassium Chloride and Fused Silica Windows at 1.315 μm
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A time-dependent, two-dimensional theory is developed to calculate thermally induced stress, strain and deformations by use of separation of variables in Fourier law and thermoelastic potential method in stess-strain equilibrium equation. The beam distortion induced by thermal effects for calcium fluoride, potassium chA time-dependent, two-dimensional theory is developed to calculate thermally induced stress, strain and deformations by use of separation of variables in Fourier law and thermoelastic potential method in stess-strain equilibrium equation. The beam distortion induced by thermal effects for calcium fluoride, potassium chloride and fused silica windows at 1.315 μm are deduced and analyzed. The calculations show that thermal lensing affects on beam the most among those three factors and birefringence can be neglected. Moreover, calcium fluoride window has the smallest PV value in beam phase distortions of them and potassium chloride window results in beam distortion the most badly..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 412 (2004)
Application of the Scalar PML-FDTD Method for Simulation of Weakly Guiding Optical Devices
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The scalar finite-difference time-domain (FDTD) method is used in the simulation of weakly guiding optical devices. The perfectly matched layer (PML) boundary condition for the scalar FDTD is implemented and verified by the simulation for the parallel-slab directional coupler. It is shown that the result is in good agrThe scalar finite-difference time-domain (FDTD) method is used in the simulation of weakly guiding optical devices. The perfectly matched layer (PML) boundary condition for the scalar FDTD is implemented and verified by the simulation for the parallel-slab directional coupler. It is shown that the result is in good agreement with the exact solutions. This method can be used as a powerful CAD tool in the analysis of weakly guiding optical devices..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 417 (2004)
Mathematic Model of Ray-Path of Four-Quadrant Photoelectric Detector
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Mathematic model of detector is the basis of precise detection. A complete mathematical model of four-quadrant photodetector has been built by analyzing the ray-path of photodetector in this paper. In the model, the effects of the offset of fixed position of four-quadrant photodetector happened when photodetector was bMathematic model of detector is the basis of precise detection. A complete mathematical model of four-quadrant photodetector has been built by analyzing the ray-path of photodetector in this paper. In the model, the effects of the offset of fixed position of four-quadrant photodetector happened when photodetector was being installed, the distance between photosurface and focus of photodetector, and other architecture parameters of photodetector on the conversion from light to electricity are considered. On the basis of building the models of photodetector in three particular positions, viz. pitching departure position, orientation departure position, rolling departure position, the common relation expressions between light signals, the offset of mounted position of four-quadrant photodetector, the distance between photosurface and focus of photodetector, and the electricity signal, the output signal are given. Comparing the waveforms of the output signals of the mathematic model of the photodetector and that of practical output signals of detector, it is found that the waveforms of model resembled that of detector in appearance. Comparing the feature parameters of the output signals of model and that of practical output signals, viz. the slope and intercept of tangent on crossover point of outputs, it is found that the differences are less than 0.01. So the relation between the inputs and outputs of the mathematical model was consistent with that between the inputs and outputs of the detector, and the model can be used in practical detection. And a foundation for the profound research and application of photodetector, detection without experiment samples is founded..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 421 (2004)
Study on Background Light Compensation of Photo-Electric Position Sensitive Detector
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
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 tThe 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..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 427 (2004)
A Configuration of Optical Fiber Current Transducer for Elimination of Vibration Effect
[in Chinese], [in Chinese], and [in Chinese]
Optical fiber current transducers based on Faraday effect have a lot of advantages over conventional current transducers and have been studied extensively. The intrinsic birefringence of the sensing fiber is the main cause which affects the measuring precision, and how to eliminate it is the key research topic. The birOptical fiber current transducers based on Faraday effect have a lot of advantages over conventional current transducers and have been studied extensively. The intrinsic birefringence of the sensing fiber is the main cause which affects the measuring precision, and how to eliminate it is the key research topic. The birefringence is not only affected by the features of fiber itself but also is under the influence of environment factors such as temperature and vibration. When a optical fiber current transducer is intensely vibrated, the mechanical stress will change the intrinsic birefringence of the sensing fiber, affecting the output light state of polarization and deteriorating the measuring precision. In this paper a symmetrical transducer configuration with two identical light sources and photodiodes is presented. Two counter-propagating light beams are formed in the sensing fiber and stress-induced linear birefringence is compensated by its reciprocal nature. The experimental results show that this configuration can obviously improve the performance of the transducer and the signal linearity is achieved under ±0.3% with the sensor head exposed to a vibration level of acceleration 10 g..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 469 (2004)
Stress Sensitivity Enhanced in-Fiber Bragg Grating Pressure Sensor
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
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 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..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 473 (2004)
Beam Transmission
Application of Phase Conjugation System with Pretilting Lens to Trace and Aiming at Moving Target with Intense Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In the process of laser propagation in the atmosphere, the technique of optical phase conjugation can be used to compensate for the wavefront aberration produced by the atmospheric turbulence or bloom effects. Pretilting mirror method to realize the tracing and aiming at moving target and to compensate for the wavefronIn the process of laser propagation in the atmosphere, the technique of optical phase conjugation can be used to compensate for the wavefront aberration produced by the atmospheric turbulence or bloom effects. Pretilting mirror method to realize the tracing and aiming at moving target and to compensate for the wavefront aberration was presented, also indoor simulating experiment is studied. The effectiveness of this method has been proved by experiment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 461 (2004)
Biomedical Photonics and Laser Medicine
Effects of Ketamine in Combination with 468.7 mJ/cm2 He-Ne Laser Irradiation on Proliferation in Human Skin Fibroblasts
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Based on the photobiomodulation on wound healing of animal models, the stimulative effects of He-Ne laser irradiation on proliferation of human normal skin fibroblasts were used as the cell model to investigate the role of ketamine as an anesthetics in animal model experiments in this paper. The cell proliferation was Based on the photobiomodulation on wound healing of animal models, the stimulative effects of He-Ne laser irradiation on proliferation of human normal skin fibroblasts were used as the cell model to investigate the role of ketamine as an anesthetics in animal model experiments in this paper. The cell proliferation was measured using MTT-based colorimetric assay. The effects of 1.56 mW/cm2 He-Ne laser irradiation on human normal skin fibroblasts for 0, 10, 30, 100, 300 s, and on the cells preincubated with different concentrations of ketamine (0, 0.6, 1.2, 2.0 μg/mL) for 300 s were investigated, respectively. The results show that human normal skin fibroblast proliferation induced by He-Ne laser irradiation (468.7 mJ/cm2) was inhibited when the cells were preincubated with different concentrations of ketamine (0.6, 1.2, 2.0 μg/mL). These results suggest that anesthetics may affect photobiomodulation on wound healing..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 509 (2004)
Holography and Information Processing
Study of Self-adaptive Texture Template and Distortion Correction in Multi-Gray Laser Marking System
[in Chinese], [in Chinese], and [in Chinese]
Recently, multi-gray laser mark is one of the most interesting fields in laser mark. But, the software used in multi-gray laser mark can′t produce living, well-bedded, orthoscopic image. In this paper, based on multi-gray laser mark and 5×5 evenly distributed template, the gray relationship of adjacent pixels is cRecently, multi-gray laser mark is one of the most interesting fields in laser mark. But, the software used in multi-gray laser mark can′t produce living, well-bedded, orthoscopic image. In this paper, based on multi-gray laser mark and 5×5 evenly distributed template, the gray relationship of adjacent pixels is considered. Except for marginal pixels, differential operation has been used to every pixels across the window of the size of 3×3 pixels, then texture characteristics are discriminated locally. Based on the local texture in images, corresponding templates are selected. Furthermore, the distortion for dual galvanometer scanning is corrected with the method of Lagrange second-degree parabola interpolation, where the value of distortion in the direction of x- and y-axes are 80, 90, respectively. The aesthetic appearance of marked images is improved greatly removing the effect of trace of matchboard and distortion of dual galvanometer scanning..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 452 (2004)
Study of Holographic Image Storage in Rewritable Photochromic Fulgide Material
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new type of organic photochromic material―fulgide/PMMA film was investigated as a rewritable holographic recording medium. The bistable absorption spectra of the fulgide/PMMA film were measured. The maximum absorption of the colored state was centered at 513 nm, the peak absorption of the bleached state was at 370 nmA new type of organic photochromic material―fulgide/PMMA film was investigated as a rewritable holographic recording medium. The bistable absorption spectra of the fulgide/PMMA film were measured. The maximum absorption of the colored state was centered at 513 nm, the peak absorption of the bleached state was at 370 nm. Based on the bistable states of the photochromic fulgide, holographic images were stored on the 10 μm film. Argon laser (514.5 nm) was used as recording light. The relation between the diffraction efficiency and the exposure was measured, which showed that the maximal diffraction efficiency was about 1% under the exposure 1 J/cm2 or so. Holographic gratings recorded on the film and diffraction images recovered by the reference beam were obtained. Factors influencing the recovery image′s quality were analyzed. The holographic gratings recorded on the film can be kept for over one year in darkness at room temperature, which can be erased by UV light. The sample can be written, read and erased in many times. The experimental results show that the fulgide can be used as a good rewritable holographic storage material..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 457 (2004)
Laser Manufacturing
Laser Direct Manufacturing W/Ni Telescope Collimation Component
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Laser direct manufacturing (LDM) is intensively developed in recent years to directly and flexibly manufacture metallic components with full metal density, functions and properties, especially for some specific materials or geometry. This paper presents a project work on laser direct manufacturing a novel designed collLaser direct manufacturing (LDM) is intensively developed in recent years to directly and flexibly manufacture metallic components with full metal density, functions and properties, especially for some specific materials or geometry. This paper presents a project work on laser direct manufacturing a novel designed collimation component for out-space hard X-ray modulation telescope. The research work contained the characteristics study of overlap multi-pass laser cladding of tungsten or tungsten nickel alloys, the microstructure analyses and the processing stability of laser direct manufacturing. The research indicated that a triangle shape clad appeared when vertically overlap W and W90Ni10 alloy. The W60Ni40 and W45Ni55 alloys showed good forming capability for manufacturing. With optimized parameters.
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 482 (2004)
Study on Graded Bioceramic Coating Cladded by Laser Beam
[in Chinese], [in Chinese], and [in Chinese]
Titanium alloy with hydroxyapatite (HA) coating, which has excellent mechanical properties and biocompatibility, is a promising artificial implant. In material and biomedical science, many efforts are made to develop this composite. At elevated temperature, CaCO3 reacts with CaHPO3?2H2O to form HA. And laser-melting teTitanium alloy with hydroxyapatite (HA) coating, which has excellent mechanical properties and biocompatibility, is a promising artificial implant. In material and biomedical science, many efforts are made to develop this composite. At elevated temperature, CaCO3 reacts with CaHPO3?2H2O to form HA. And laser-melting technique can produce ceramic coatings well bonded with substrate. So the experiment on synthesizing and cladding HA coating on TC4 surface can be made, simultaneously. 80CaCO3-20CaHPO3?2H2O with 1% Y2O3 in addition are used as raw materials. As laser treatment, the power density is 13～15 W/mm2 and the scanning rate is 630 mm/min. A graded bioceramic coating is cladded on Ti6Al4V, which mainly consists of HA. In this coating, as the depth increasing calcium content decreases, but titanium and yttrium change contrarily. The distribution of phosphorus is complex to increase followed by decrease. The porosity decreases from surface to substrate, which is similar to the distribution of micro-hardness..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 487 (2004)
Modeling and Simulating on Laser Remelting Considering Diffusion/Convection and Phase Change Process in the Substrate
[in Chinese], and [in Chinese]
A transient, moving laser beam, three dimensional laser remelting mathematical model considering convection, diffusion and phase change process in laser melting pools and substrate was developed, which is suitable for the prediction of fluid flows, temperature field, liquid fraction field and phase change in solid, liqA transient, moving laser beam, three dimensional laser remelting mathematical model considering convection, diffusion and phase change process in laser melting pools and substrate was developed, which is suitable for the prediction of fluid flows, temperature field, liquid fraction field and phase change in solid, liquid and mash zone. Based on the mathematical mode, this paper developed an fix-grid numerical method. This method need not trace the interface between solid and liquid, and can consider the effect of latent heat released during phase change. The agreement of melting pool depth between prediction and experiment validates the model. The simulation shows that the surface tension and buoyancy drive the liquid metal fluid forming two set eddies in the transverse section, i.e. the first order recirculating,and the second order recirculating. The first order recirculating makes the pool wide and shallow and the second order recirculating digs a pit in the bottom of the pool. The experimental results show a good agreement with the model simulation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 491 (2004)
Study on the Experiment of 40Cr Steel by Laser Shock Processing
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
40Cr steel has been shocked processing by Nd∶YAG laser. In the experiments, the parameters of laser shock processing are as follow40Cr steel has been shocked processing by Nd∶YAG laser. In the experiments, the parameters of laser shock processing are as follow.
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 495 (2004)
Study on Relationship between Material Properties and Bending Angles in Laser Forming Process of Sheet Metals
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Laser forming process is a new flexible forming process without rigid tool and external force. The sheet metal is formed by internal thermal stress induced by laser. Material properties play an important role in laser forming. A three-dimensional coupled thermal-mechanical finite element model is established in this paLaser forming process is a new flexible forming process without rigid tool and external force. The sheet metal is formed by internal thermal stress induced by laser. Material properties play an important role in laser forming. A three-dimensional coupled thermal-mechanical finite element model is established in this paper. The laser bending process of a sheet blank is simulated numerically using the model. The relationship between the bending angle and material property parameters, such as Young′s modulus, yield strength, thermal expansion coefficient, heat capacity, and thermal conductivity, are studied in detail by FEM simulation. The simulations show that the material with lower Young′s modulus and yield strength can get a larger bending angle. The thermal expansion coefficient is about in direct proportion to the bending angle. The bending angle decreases with the increase of the heat conductivity. The bigger bending angle can be obtained for the material with lower heat specific and density. The research provides a good reference of selecting process parameters for increasing laser forming efficiency..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 499 (2004)
Study on Stress Status of WC Doped Ni-Based Alloy by Laser Cladding
[in Chinese], [in Chinese], and [in Chinese]
For the laser cladding of WC doped Ni-based alloy on 20Cr2NiSiW substrate, the stress status of cladding layer are analyzed .The thermal residual stress of laser cladding layer without preheating is 700 MPa, and phase changing residual stress is 850 MPa. The stress distribution of cladding layer can be ameliorate with For the laser cladding of WC doped Ni-based alloy on 20Cr2NiSiW substrate, the stress status of cladding layer are analyzed .The thermal residual stress of laser cladding layer without preheating is 700 MPa, and phase changing residual stress is 850 MPa. The stress distribution of cladding layer can be ameliorate with preheating before cladding and thermal retardation after cladding. The part of thermal stress is relieved and the residual stress of phase changing is descend. Although the cladding layer still is compressive stress and the heating affected zone is stretching stress, the thermal stress peak is decrease to 510 MPa and shifted from face to intermediate section of cladding layer. The interface peak of stretching stress of phase changing is relieved, and satisfaction of stress status of cladding layer is obtained. On the non preheating cladding layer, the eutectic austenite dendrite growth is along the opposite direction of temperature gradient beginning from interface to face of cladding layer. On the preheating cladding layer, the eutectic austenite dendrite growth is changed from beginning the perpendicular border of cladding pool to intermediate section of layer..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 505 (2004)
Laser Physics
High-Stabilization 85 W All-Solid-State Green Laser Operation
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
This paper reported high power high stabilization 85 W all-solid-state green laser operation, which was pumped by 80×20 W high power laser arrays. The theoretical analysis of the influence of thermal effect and phase mismatching about frequency-doubling crystal on output was presented. The calorific power distribuThis paper reported high power high stabilization 85 W all-solid-state green laser operation, which was pumped by 80×20 W high power laser arrays. The theoretical analysis of the influence of thermal effect and phase mismatching about frequency-doubling crystal on output was presented. The calorific power distribution is numerically simulated and the values of frequency-doubling crystal phase mismatching varying with the change of temperature were given. In experiment, double acousto-optic Q-switching were employed inside single Nd∶YAG rod, high efficiency flat-concave intracavity-frequency-doubled resonance structure. A maximum green power of 85 W was generated at 20.4 kHz repetition rate and 230 ns pulse width when pumped current of laser diodes was 17.3 A with compensating phase mismatch by angle departuring and strong cooling big KTP crystal, leading to ±1.03% instability and 9.7% of optical-optical conversion efficiency..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 385 (2004)
Study on Uniform of Pump Distributivity in a LD Side-Pumped Nd∶YAG Laser
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A mathematic model of the pump power absorption and distribution in the LD side-pumped solid-state laser medium is set up. The pump power distribution in the single diode directly pumped laser rod with different pumped parameters is simulated using the method of ray trace. The effect of the different active medium′s abA mathematic model of the pump power absorption and distribution in the LD side-pumped solid-state laser medium is set up. The pump power distribution in the single diode directly pumped laser rod with different pumped parameters is simulated using the method of ray trace. The effect of the different active medium′s absorption coefficient and distance between the diode and the laser rod on the pump power distribution in the laser rod is studied. The Gauss distribution of the pump power in the multiarray LD side-pumped laser rod is got under the condition of the laser rod with cooling system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 390 (2004)
Study of Green Laser by Intracavity Frequency Doubling of a LD-Array Pumped Nd∶YVO4 Laser
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
CW stable output of 520 mW at 532 nm has been obtained by intracavity frequency doubling with KTP in a single axis crystal Nd∶YVO4 laser pumped by 9.5 W diode laser array. The optical-optical conversion efficiency is 5.5%. Polarization of LD is matched with polarizing absorption of Nd∶YVO4. The beam of the diode-array-CW stable output of 520 mW at 532 nm has been obtained by intracavity frequency doubling with KTP in a single axis crystal Nd∶YVO4 laser pumped by 9.5 W diode laser array. The optical-optical conversion efficiency is 5.5%. Polarization of LD is matched with polarizing absorption of Nd∶YVO4. The beam of the diode-array-laser is well shaped with cylindrical-lens-array. Good mode-matching is realized by using of cavity′s astigmatism..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 395 (2004)
Investigation on a Compound Resonator Nd∶YAG-Cr4+∶YAG Laser with Dual Q-Switching Operation
[in Chinese], [in Chinese], and [in Chinese]
A pratical and novel Nd∶YAG-Cr4+∶YAG laser with dual Q-switching and dual-wavelength output is reported. In the compound resonator couplied with two plano-concave cavities, a single Cr4+∶YAG is both a saturable-absorber of Q-switch at 1.06 μm laser from Nd∶YAG and a laser gain medium at 1.44 μm with 1.06 μm laser as itA pratical and novel Nd∶YAG-Cr4+∶YAG laser with dual Q-switching and dual-wavelength output is reported. In the compound resonator couplied with two plano-concave cavities, a single Cr4+∶YAG is both a saturable-absorber of Q-switch at 1.06 μm laser from Nd∶YAG and a laser gain medium at 1.44 μm with 1.06 μm laser as its intra-cavity pump source. the dual-wavelength laser oscillation with passively Q-switched 1.06 μm laser and gain-switched 1.44 μm laser is realized in the laser. The output energy and pulse duration of 1.06 μm and 1.44 μm laser are 18 mJ, 52 ns and 0.2 mJ, 19 ns respectively, and the pulse duration of the latter is about one of third of the former. The working mechanism of the dual Q-switching is analyzed in theory according to energy levels of the Cr4+∶YAG and the feature of the compound resonator. Based on the rate equations, the relationship between pulse duration of 1.44 μm laser and the intra-cavity power of 1.06 μm laser is derived. The theoretical data (21.7 ns) of pulse duration of 1.44 μm laser is roughly consistent with the experimental resultt (19 ns)..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 399 (2004)
Yb3+-Doped Multi-Wavelength Double Clad Fiber Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
For the double clad fiber laser, differ from ordinary fiber laser, the requirement of a single mode for pumping the fiber laser is needless, furthermore, the pump beam coupling into fiber along nearly whole fiber, consequently, the laser conversion efficiency is improved. In this paper, a novel Yb3+-doped multi-wavelenFor the double clad fiber laser, differ from ordinary fiber laser, the requirement of a single mode for pumping the fiber laser is needless, furthermore, the pump beam coupling into fiber along nearly whole fiber, consequently, the laser conversion efficiency is improved. In this paper, a novel Yb3+-doped multi-wavelength double clad laser pumped by 976 nm laser diode is presented. The output wavelength are 1085, 1090, 1095 and 1100 nm. The laser exhibits 0.33 nm line-width, 1.2 W laser out power, 20 dB signal-to-noise (SNR) and 52% slope efficiency..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 403 (2004)
Validity of Series Expansion Corrections to the Paraxial Approximation of Non-Paraxial Beams
[in Chinese], and [in Chinese]
It is well known that the paraxial approximation is no longer valid for the beams with large divergence angle and/or small spot size comparable with the wavelength. Thus, a rigorous nonparaxial treatment becomes necessary. As yet, a variety of approaches, such as the perturbation method, power-series expansion, angularIt is well known that the paraxial approximation is no longer valid for the beams with large divergence angle and/or small spot size comparable with the wavelength. Thus, a rigorous nonparaxial treatment becomes necessary. As yet, a variety of approaches, such as the perturbation method, power-series expansion, angular spectrum representation and integral solution of the wave equation etc. have been proposed to treat the beam propagation behavior beyond the paraxial regime. In this paper the validity of series expansion corrections to the paraxial approximation of non-paraxial beams is studied. Detailed numerical calculations for the integral expression and series expansion of the wave equation are performed and compared. It is shown that the series expansion provides a valid correction to the paraxial solution as w0>0.2251λ, with w0 and λ being the waist width and wavelength, respectively. However, the series expansion solution delivers unrealistic results and may become divergent if w0≤0.2251λ. The applicable range of the series expansion approach depends on the waist width, propagation distance and order of the series expansion. The results obtained in this paper are useful for studying the propagation of nonparaxial beams..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 432 (2004)
Axial Light Intensity Characteristics of Gaussian Beam Diffracted by a Wavelength-Order Circular Aperture
[in Chinese], [in Chinese], and [in Chinese]
Based on the accurate expression of light intensity at the transverse plane and the rigorous diffraction formulae, the characteristics of axial light intensity of Gaussian beam diffracted by a wavelength-order circular aperture are investigated. The results show that the axial light intensity characteristics of GaussiaBased on the accurate expression of light intensity at the transverse plane and the rigorous diffraction formulae, the characteristics of axial light intensity of Gaussian beam diffracted by a wavelength-order circular aperture are investigated. The results show that the axial light intensity characteristics of Gaussian diffracted beam are decided by the initial Gaussian half width w0 and the radius of wavelength-order circular aperture R. As to the Gaussian diffracted beams with w0/R≥1, the number and location of extrema of axial light intensity are determined by 2R/λ, and the maximum axial light intensity must be located at N=R2/(λz)=1. Whether the apex and vale of extrema are distinct or not rest with the ratio of w0/R. The larger the ratio, the more distinct the apex and vale are. When the ratio of w0/R is large enough, it trend to the case of planar incident wave. While for the Gaussian diffracted beams with w0/R<1, the axial light intensity exists specifically evolutive law. The number of extrema is reduced step by step and finally disappeared with the initial Gaussian half width diminishing..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 437 (2004)
Fiber Phase-Conjugator in Four-Pass MOPA System with High Repetition Rate
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Using a 200 μm-core multimode optical fiber as the phase conjugator mirror, an LD-pumped Q-switched four-pass MOPA system operated on 100 Hz repetition rate and 20 ns pulse width has been experimental investigated in this paper. As a result, high quality laser beam with energy of 4.1 mJ and energy-stability less than 1Using a 200 μm-core multimode optical fiber as the phase conjugator mirror, an LD-pumped Q-switched four-pass MOPA system operated on 100 Hz repetition rate and 20 ns pulse width has been experimental investigated in this paper. As a result, high quality laser beam with energy of 4.1 mJ and energy-stability less than 10% have been obtained when 4.6 mJ pump energy injected into fiber phase conjugator. The self-oscillating (SO) in amplifier and amplified spontaneous emission (ASE) has been validly suppressed. In additional, the pulse width of laser has been compressed to 4.7 ns. Due to the using of fiber phase conjugating mirror, the deformation formed by the thermal effect from the slab amplifier has been compensated after four passing. The output beam profile resumes the intensity distribution of the oscillator output beam..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 441 (2004)
Computing of the Axial Optical Force Applied by the Femtosecond Laser Trap
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Optical tweezers are one of the most efficient means of manipulating objects on the micrometer scale and biological cells. The sources of the existing optical tweezers are CW light or long-pulse-width light. The concept of femtosecond laser tweezers was proposed. Taking femtosecond pulses as the sampling of CW lasers, Optical tweezers are one of the most efficient means of manipulating objects on the micrometer scale and biological cells. The sources of the existing optical tweezers are CW light or long-pulse-width light. The concept of femtosecond laser tweezers was proposed. Taking femtosecond pulses as the sampling of CW lasers, the theoretical model of the induced axial forces by femtosecond laser pulses exerted on micrometer-sized sphere was established. The major factors that affect the trapping were discussed and suitable beam waists and radii of the trapped particles were demonstrated. The numerical results show that micron-sized particles can be trapped with femtosecond pulses with suitable single pulse energy, beam waist, pulse wavelength and the relative refraction index of the particle to the medium. Considering the axial optical force, the gravity and the Brownian inertial force, the pulsed property of the axial gradient force and the stability condition of femtosecond laser tweezers were also demonstrated..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 445 (2004)
Resonant Enhanced Nonlinearity in Yb∶Er Codoped Fiber Bragg Grating
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In this article, the mechanism of resonant enhanced nonlinearity is introduced in rare-earth doped fibers. The nonlinearity data of several rare-earth doped fibers are presented. The nonlinearity of rare-earth doped fibers is much greated than that of common silica fiber. However, the nonlinearity respond speed in rareIn this article, the mechanism of resonant enhanced nonlinearity is introduced in rare-earth doped fibers. The nonlinearity data of several rare-earth doped fibers are presented. The nonlinearity of rare-earth doped fibers is much greated than that of common silica fiber. However, the nonlinearity respond speed in rare-earth doped fibers is lower than that in common silica fiber. At the same time, the nonlinearity enhancement is correlative with pump and dopant concentration. The resonant enhanced nonlinearity of Yb∶Er codoped fiber Bragg grating has been investigated by experiment. The transmission spectrum of the FBF with various incident powers of 980 nm laser is recorded. The Bragg wavelength was shifted 0.2 nm with 100 mW incident power. This experiment demonstrates that the nonlinearity of rare-earth doped fiber Bragg grating has high nonlinearity coefficient as high 106 times as common silica fiber gratings. This type FBG has some application potentials in all-optical switch..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 449 (2004)
Materials and Thin Films
Design of 193 nm Optical Thin Films under Practical Structure and Optical Parameters
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
193 nm optical thin films are one of the key components in the 100 nm step and scan microlithography systems.The paper analysized the influence of the optical constants of substrates and thin films, the extinction coefficient of high refractive materials and the surface roughness on the reflectance of HR mirrors. It sh193 nm optical thin films are one of the key components in the 100 nm step and scan microlithography systems.The paper analysized the influence of the optical constants of substrates and thin films, the extinction coefficient of high refractive materials and the surface roughness on the reflectance of HR mirrors. It showed that to obtain a mirror with reflectance of more than 98.5%, the extinction coefficient of the high-refractive material must be below 0.0034 and at the same time, with a surface roughness σ≤1 nm. The influence of the water absorption on the optical performance of the coatings was also analysized and the possible reasons resulted in the difference between the practical and theoretical performance were discussed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 477 (2004)
Optical Communication
APD Signal Detecting Method Based on Wavelet Transform
[in Chinese], [in Chinese], and [in Chinese]
Pulse position modulation (PPM) is the most often used modulation technique in space laser communications. As avalanche photodiode detector (APD) has high gain, high sensitivity and fast response, it is a likely candidate to detect laser signals for providing space laser communications needs. This paper discusses the cPulse position modulation (PPM) is the most often used modulation technique in space laser communications. As avalanche photodiode detector (APD) has high gain, high sensitivity and fast response, it is a likely candidate to detect laser signals for providing space laser communications needs. This paper discusses the characteristics and sorts of noises in the APD signal detecting subsystem, as the PPM channel is considered in the space laser communication system. Based on the ability of achieving topical characteristics of signals by the wavelet transform, a method of APD signal detecting based on the wavelet analysis is proposed. Four different threshold limit-selecting methods are applied to choose the wavelet coefficient for signal-recovering. A primary simulation experiment and some analyses are also done. The results show that the adaptive threshold values selecting algorithm is the best one. It can mitigate the effect of the intensive background noise to improve the performance of the APD signal detecting system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 31, Issue 4, 465 (2004)
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