Journals >Chinese Journal of Lasers
Contents
2006
Volume: 33 Issue 6
32 Article(s)
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Research Article
Scheme on Acquisition and Disposal for Raman Lidar System
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Detecting the atmospheric CO2 reliably is becoming more and more important due to environment problems and climate changing. Raman light detection and range (lidar) system monitoring the atmosphere is a novel technique. It is a key factor to acquire the back signals of Raman lidar efficiently. The paper not only analyzDetecting the atmospheric CO2 reliably is becoming more and more important due to environment problems and climate changing. Raman light detection and range (lidar) system monitoring the atmosphere is a novel technique. It is a key factor to acquire the back signals of Raman lidar efficiently. The paper not only analyzes the principle of Raman lidar and the theoretical basis of signal processing, but also designs two schemes for collecting Raman signals, which include single channel and double channels, and demonstrates the methods of signal processing separately. The paper resolves the noise interference in collecting signals process, and gets the satisfied conclusion by contrasting the two results of the two schemes. Moreover, the signal-to-noise ratio (SNR) is calculated for the lidar system. The calculated results indicate that the SNR (for 1 km) is up to 10 for single channel, however, up to about 20 for double channels..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 734 (2006)
Influence of Focusing System Structure on Propulsion Performance of Laser Thruster
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Focusing system is one of the most important components of laser thruster when it is also used as a nozzle at the same time. Such parameters change with generatrix equation of inner surface of focusing system as the shape and the size of ignition zone, nozzle length and the distance between ignition zone and inner surfFocusing system is one of the most important components of laser thruster when it is also used as a nozzle at the same time. Such parameters change with generatrix equation of inner surface of focusing system as the shape and the size of ignition zone, nozzle length and the distance between ignition zone and inner surface of nozzle. All these parameters have effects on the propulsion performance of laser thruster. Four kinds of ignition modes are set up according to different nozzle structures. The results of numerical calculation and experiment are coincident. When injecting energy is not larger than 60 J and the diameter of nozzle exit is constant, the impulsion performance of laser thrusters with a parabolic focal point is found better than that of those owing a round one, and the coupling coefficient of the former is about 38.84×10-5 N·s/J. And the impulse coupling coefficient is not sensitive to nozzle length and the distance between ignition zone and inner surface of nozzle. The results are very useful to design nozzle structure of laser thruster that works in air-breathing mode..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 739 (2006)
Simulated Close-Loop Target Tracking System
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
One target motion simulation method and experimental system were presented. The simulation system was constructed with the advantages of laser, such as high brightness, small divergency, small spot size. The transform from angle motion to two-dimensional (2D) space motion of small target was made with the technique of One target motion simulation method and experimental system were presented. The simulation system was constructed with the advantages of laser, such as high brightness, small divergency, small spot size. The transform from angle motion to two-dimensional (2D) space motion of small target was made with the technique of complex multi-axis and space projection. The inner close-loop control of motor was achieved by multimedia timer. The rolling speed was controlled with the technique of pulse width modulation (PWM). With these technique, the simulation precision was advanced. The moving velocity of simulation target was up to 10°/s. It′s precision was about less than 0.1°/s . The normalized standard deviation was 0.09. The system was small and easy to accomplish in engineering. It can be used as the simulation platform to verify the target acquiring, tracking system for a moving target within 2D space. The tracking standard deviation of the tracking system was 0.2 mrad..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 743 (2006)
Characteristics of Off-Axially Cut Nd:YVO4 Crystal for Laser
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The characteristics of 45°-off-axially-cut and a-cut Nd:YVO4 crystal, were compared for continuous wave (CW) and passively Q-switching operations by Cr4+:YAG crystal as the intracavity saturable absorber. By analyzing the experimental results, the 45°-off-axially-cut Nd:YVO4 exhibited parts of properties of tThe characteristics of 45°-off-axially-cut and a-cut Nd:YVO4 crystal, were compared for continuous wave (CW) and passively Q-switching operations by Cr4+:YAG crystal as the intracavity saturable absorber. By analyzing the experimental results, the 45°-off-axially-cut Nd:YVO4 exhibited parts of properties of the a-cut and c-cut crystals for CW passively Q-switching operations respectively, due to the competition between π polarization and σ polarization simulated emissions. With the laser diode (LD)-pump power of 1340 mW, a peak power of 0.6- kW with a 6.5-ns pulse width and 18.7-kHz repetition rate was obtained..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 748 (2006)
Investigation of Frequency Null-Drift in Polarimetric Fiber Laser Current Sensors
[in Chinese], [in Chinese], and [in Chinese]
The advantage of the polarimetric fiber laser current sensors over other types of current sensors is direct readout of electrical current, measured as a difference of two beat-frequencies. In this paper, frequency null-drift caused by the deviation of the polarization rotation angle in the Faraday rotation mirror (FRM)The advantage of the polarimetric fiber laser current sensors over other types of current sensors is direct readout of electrical current, measured as a difference of two beat-frequencies. In this paper, frequency null-drift caused by the deviation of the polarization rotation angle in the Faraday rotation mirror (FRM) from 90° is analyzed, and that it is the main source of unstability to variation of temperature is emphasized. Experimental results of this type of current sensors confirm the theoretical predicts and indicate that the suggested method to reduce the frequency null-drift is effective..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 791 (2006)
Beam Transmission
Influence of Manufacture Error with Non-Circular Symmetry in an Axicon on the Bessel Beams Quality
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Based on Huygens-Fresnel diffraction integral theory and stationary phase method, the influence of the axicon with non-circular symmetry manufacture error on the zeroth order Bessel beam (J0 beam) is analyzed. The numerical simulation is compared with the beam patterns photographed by a charge coupled device (CCD) cameBased on Huygens-Fresnel diffraction integral theory and stationary phase method, the influence of the axicon with non-circular symmetry manufacture error on the zeroth order Bessel beam (J0 beam) is analyzed. The numerical simulation is compared with the beam patterns photographed by a charge coupled device (CCD) camera. Results show that if the cross-section of the axicon is ideally manufactured in circular symmetry, the field distribution behind the axicon is approximately an ideal Bessel beam. But if non-circular symmetry manufacture error exists, with the cross-section as an oval, the diffraction beam patterns will deviate the J0 beam. The greater is the difference between elliptical semimajor axis and semiminor axis, the larger is the deviation from the J0 beam. The experimental results fit the theoretical simulation very well..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 809 (2006)
Biomedical Photonics and Laser Medicine
Changes and Thermal Coagulation of Human Liver Tissue Induced Changes in the Optical Properties of Liver Tissue at KTP/YAG Laser in vitro
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Pathological changes and thermal coagulation of human liver tissue induced changes of the optical properties of liver tissue at 532 and 1064 nm wavelengths of laser in vitro. The measurements were performed using a double-integrating-sphere setup, and the optical parameters were assessed from these measurements using tPathological changes and thermal coagulation of human liver tissue induced changes of the optical properties of liver tissue at 532 and 1064 nm wavelengths of laser in vitro. The measurements were performed using a double-integrating-sphere setup, and the optical parameters were assessed from these measurements using the inverse adding-doubling method (IAD). The results of measurement showed that the absorption coefficients of normal liver tissues at 532 and 1064 nm are significantly bigger than those of liver tumors at the same wavelength respectively. When liver tissues were coagulated by heat, the absorption coefficients of normal and tumorous liver tissues of thermal coagulation at 532 nm significantly increase, the absorption coefficient of normal liver tissues of thermal coagulation at 1064 nm significantly decreases, and the absorption coefficient of liver tumors of thermal coagulation at 1064 nm significantly increases. The scattering coefficients of normal liver tissue at 532 and 1064 nm are significantly smaller than those of liver tumors at the same wavelength. When liver tissues were coagulated by heat, the scattering coefficients of normal and tumorous liver tissue of thermal coagulation significantly increase. The anisotropy factors of normal liver tissue at 532 and 1064 nm are obviously bigger than those of liver tumors at the same wavelength respectively. When liver tissues were coagulated by heat, the anisotropy factors of normal and tumorous liver tissue of thermal coagulation at 532 and 1064 nm obviously decrease..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 852 (2006)
Mathematics Modeling and Clinic Experiment of Photodynamic Therapy for Port Wine Stain
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Treatment of port wine stain (PWS) by photodynamic therapy (PDT) has been under development over last years. To study the acting factors on vascular selectivity of photodynamic and help the doctor confirm therapy plan in clinic, the mathematics modeling of photodynamic therapy treating port wine stain is built. The modTreatment of port wine stain (PWS) by photodynamic therapy (PDT) has been under development over last years. To study the acting factors on vascular selectivity of photodynamic and help the doctor confirm therapy plan in clinic, the mathematics modeling of photodynamic therapy treating port wine stain is built. The modeling include light distribution in tissue, production of singlet oxygen, diffusion of photosensitizers and photobleaching. Using the model, a problem of therapeutic effect in clinic is analyzed and a new therapy scheme is recommended. The scheme is proved to be effective in the clinic experiment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 857 (2006)
Holography and Information Processing
A Novel Synthetical Method for Phase Unwrapping
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A novel synthetical method for phase unwrapping is proposed in this paper. First an effective model to eliminate local branch points without influencing normal points is established. And then, by calculating the mean values of the unwrapped phase along multiple certain directions, the goal of path independence can be aA novel synthetical method for phase unwrapping is proposed in this paper. First an effective model to eliminate local branch points without influencing normal points is established. And then, by calculating the mean values of the unwrapped phase along multiple certain directions, the goal of path independence can be achieved. The feasibilities and the efficiencies of the approach are demonstrated by employing numerical simulations and experiments. It is shown that the proposed method also exhibits strong stability and high efficiency even in presence of serious noises and relatively large under sampled areas..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 795 (2006)
Measurement of Profile Parameters of Holographic Photoresist Grating Mask Made on Top of Chrome Stack in Spectroscopic Way
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to detect the profile of holographic photoresist grating mask made on top of chrome stack, rigorous coupled wave theory (RCWT) was applied to analyze the relationship between zero order reflected spectrum and the profile of grating mask. Zero order reflected spectra range from 400 nm to 700 nm at the incident In order to detect the profile of holographic photoresist grating mask made on top of chrome stack, rigorous coupled wave theory (RCWT) was applied to analyze the relationship between zero order reflected spectrum and the profile of grating mask. Zero order reflected spectra range from 400 nm to 700 nm at the incident angle of 60° were measured in experiment. The standard deviation of differences between experimental curve and theoretic curve of different profiles is calculated for matching,and the duty cycle and groove depth were obtained by the best fitted theoretic spectra corresponding to minimum standard deviation. Results achieved in this way which is a quick in matching and high in error tolerance, agree very well with scanning electron microscope (SEM) pictures. The method is qualified for measurement of groove depth and duty cycle simultaneously for the rectangle-shaped or similar profile of holographic grating mask..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 800 (2006)
Diffractive Characteristics of 1D Metal Gratings with Subwavelength Periodic Structure
[in Chinese], [in Chinese], and [in Chinese]
Rigorous coupled wave approach (RCWA) was used to calculate the value of one-dimensional (1D) subwavelenth metal grating′s maximum period that allows only propagation of the zeroth diffraction order (the maximum period is also called critical periodic point). Assuming the surrounding medium is air, some different refraRigorous coupled wave approach (RCWA) was used to calculate the value of one-dimensional (1D) subwavelenth metal grating′s maximum period that allows only propagation of the zeroth diffraction order (the maximum period is also called critical periodic point). Assuming the surrounding medium is air, some different refractive indexes of the substrate material are chosen to calculate the critical periodic point. It is shown that the critical periodic point is only decided by the refractive indexes of the substrate, no matter which kind of metal, refractive indexes of grating layer, grating period, duty cycle, grating thickness and the polarization and wavelength of incidence are chosen. The results are useful for designing and fabricating novel nano-optics based on 1D subwavelength metal grating by avoiding complicated calculation and the failure of fabricating..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 805 (2006)
Laser Manufacturing
Intensity Distribution Design for Laser-Induced Thermal Loading Based on Numerical Simulation
[in Chinese], [in Chinese], and [in Chinese]
To accomplish laser-induced thermal loading simulation tests for pistons, the Gaussian beam was modulated into multi-circular beam with specific intensity distribution. A reverse method was proposed to design the intensity distribution for the laser-induced thermal loading based on finite element (FE) analysis. FirstlyTo accomplish laser-induced thermal loading simulation tests for pistons, the Gaussian beam was modulated into multi-circular beam with specific intensity distribution. A reverse method was proposed to design the intensity distribution for the laser-induced thermal loading based on finite element (FE) analysis. Firstly, the FE model is improved by alternating parameters of boundary conditions and thermal-physical properties of piston material in a reasonable range, therefore it can simulate the experimental results of the originally designed shaping lens. Secondly, with the validated FE model, the target temperature field is achieved by alternating the intensity field and loading conditions, and the optimal design for the beam shaping lens is subsequently obtained. This reverse design method bridges temperature field and intensity field. The results show that numerical simulation can reduce design cycle and design expense efficiently. Meanwhile, this process can be taken as a kind of virtual experiment which makes the thermal loading test more controllable and predictable..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 842 (2006)
Numerical Simulation of Residual Stress Field for Laser Shock Processing
[in Chinese], [in Chinese], and [in Chinese]
Finite element method (FEM) simulation of laser shock processing (LSP) is an effective method to predict the residual stress field and optimize the laser shock parameters. The FEM is applied to attain the numerical simulation of residual stress field of material treated by laser shock processing. The history of energieFinite element method (FEM) simulation of laser shock processing (LSP) is an effective method to predict the residual stress field and optimize the laser shock parameters. The FEM is applied to attain the numerical simulation of residual stress field of material treated by laser shock processing. The history of energies during explicit dynamic analysis is discussed and is well correlated with the result derived by shock wave theory. The method of solution time choosing for explicit analysis is presented based on the history of energies. Residual stress distribution of single and multiple laser shock is analyzed and validated by experimental result. The analysis results indicate that compressive residual stress of material is uniform on surface and the stress gradient in depth is small. Compressive residual stresses and plastically affected depth are extensively increased and gradually reach the saturated state by multiple laser shock..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 846 (2006)
Laser Physics
Ultraintense Solid-State Lasers and Applications to the Frontiers of Sciences
[in Chinese]
Peak output powers of solid-state laser facilities have tremendously increased by a few orders of magnitude since the middle of last eighties due to the combination of the technique of chirped pulse amplification (CPA), advanced high-power laser technologies and novel laser materials. Petawatt (PW) level laser facilitiPeak output powers of solid-state laser facilities have tremendously increased by a few orders of magnitude since the middle of last eighties due to the combination of the technique of chirped pulse amplification (CPA), advanced high-power laser technologies and novel laser materials. Petawatt (PW) level laser facilities have been built for picosecond and femtosecond pulses with focused intensities of up to 1020～1022 W/cm2. Laser intensities play dominant roles in understanding the physics of laser-plasma interactions and, therefore, different intensities open different physics areas to study. Such high laser intensities are able to produce extreme conditions: ultraintense electric and magnetic fields, and ultrahigh pressure, leading to the emerging of strong-field physics. A numbrer of multidisciplinary frontiers have been explored, such as particle acceleration, intense radiation source, advanced light source, attosecond physics, fast ignition fusion, superhot matter, nuclear physics, ultrafast proccess diagnosing, laser astrophysics, nonlinear quantum electrodynamics (QED) and so on. Also, there exist invaluable potentials in material, biological and medical applications..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 721 (2006)
Tm:Ho:GdVO4 Laser at 2 μm Using Laser-Diode Double-End Pumping
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Continuous wave (CW) and quasi continuous wave (QCW) Tm: Ho: GdVO4 solid laser at 2.049 μm using laser-diode (LD) double-end pumping is reported. The fibre-coupled LD emits a maximum power of 27.7 W at 805 nm with a fiber core diameter of 400 μm and a fiber numerical aperture of 0.22. The LD output is divided into two Continuous wave (CW) and quasi continuous wave (QCW) Tm: Ho: GdVO4 solid laser at 2.049 μm using laser-diode (LD) double-end pumping is reported. The fibre-coupled LD emits a maximum power of 27.7 W at 805 nm with a fiber core diameter of 400 μm and a fiber numerical aperture of 0.22. The LD output is divided into two beams with the same power and double-end pumped the laser crystal. The crystal is co-doped with 5% Tm and 0.5% Ho in dimensions 4 mm×4 mm×7 mm. The spectroscopy and energy loss of the Tm: Ho system is analyzed. The crystal is cooled with liquid N2 for improving the output power and extracted efficiency. The output power of 9.4～10.1 W is obtained at 5, 10, 20-kHz Q-switched and CW modes, corresponding to the optical-to-optical efficiency of 34%～36%. Also, the maximal energy per pulse of 1.9 mJ and the maximal peak power of 0.13 MW are obtained. Additionally, both the alteration of the pump power and that of the repetition rate influence the pulse width..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 730 (2006)
Microwave Measurement of Dielectric Film-Enhanced Goos-Hanchen Shift
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The Goos-Hnchen shift (GH shift) of reflected beam is resonance enhanced under some conditions when the incident beam transmits from the high-refractive index prism to the low-refractive index dielectric thin-film and is totally reflected from the film-air interface. In this paper, the GH shift versus the film thicknesThe Goos-Hnchen shift (GH shift) of reflected beam is resonance enhanced under some conditions when the incident beam transmits from the high-refractive index prism to the low-refractive index dielectric thin-film and is totally reflected from the film-air interface. In this paper, the GH shift versus the film thickness is directly measured by microwave technology. The experimental measurements confirm the theoretical prediction..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 753 (2006)
Theoretical and Experimental Studies on Second-Order Soliton Compression Based on Dispersion Flattened Fiber
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Using second-order soliton compression effect in 4.28 km dispersion flattened fiber (DFF), the 5.8 ps pulse with the repetition rate of 10 GHz generated from a regeneratively mode-locked fiber laser (RMLFL) was compressed into pulse with pulse-width of 1.74 ps. The compression factor was 3.3. The experimental results aUsing second-order soliton compression effect in 4.28 km dispersion flattened fiber (DFF), the 5.8 ps pulse with the repetition rate of 10 GHz generated from a regeneratively mode-locked fiber laser (RMLFL) was compressed into pulse with pulse-width of 1.74 ps. The compression factor was 3.3. The experimental results agree well with the theoretical results. Compared to adiabatic soliton compression (ASC) based on dispersion decreasing fiber (DDF), this scheme can greatly lower the input power for the same soliton order numbers. Moreover, for the input pulses with different wavelength and pulse width, compression condition can be satisfied by adjusting input power and choosing proper fiber length, which is determined by the non-dispersion-decreasing characteristics of DFF. Despite the compression factor is small, it still meets requirement..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 756 (2006)
Gain of Cascaded Two-Pump Fiber-Optical Parametric Amplifier with High Order Dispersion
[in Chinese], [in Chinese], and [in Chinese]
By the use of a set of coupled equations, the gain expression of two-pump fiber optical parametric amplifier (FOPA) with three-section nonlinear fibers is deduced theoretically. It is indicated that the parametric gain has a relationship with the pumps power, the fiber′s length and the fiber′s dispersion characteristicBy the use of a set of coupled equations, the gain expression of two-pump fiber optical parametric amplifier (FOPA) with three-section nonlinear fibers is deduced theoretically. It is indicated that the parametric gain has a relationship with the pumps power, the fiber′s length and the fiber′s dispersion characteristic as well. From abnormal dispersion region to normal dispersion region, the bandwidth reduced and became flattened. Assume the fiber′s second-order dispersion keeps constant, with the increase of the fiber′s fourth-order dispersion, the bandwidth is reduced accordingly. By using multi-section fiber arrangement, the parametric gain can be flattened by adjusting the fiber′s parameters..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 760 (2006)
Analysis of Laser-Induced Surface Rayleigh Wave′s Polarity in Hollow Cylinders by Finite Element Method
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The transient temperature fields and the surface acoustic waves generated by a pulsed line-source laser in thick hollow cylinders are analyzed by using a finite element method. A series of the time domain waveforms of the surface normal displacements are shown for different angles between the source and the detection pThe transient temperature fields and the surface acoustic waves generated by a pulsed line-source laser in thick hollow cylinders are analyzed by using a finite element method. A series of the time domain waveforms of the surface normal displacements are shown for different angles between the source and the detection point from =5° to =180° in an anti-clockwise direction. And the surface acoustic waves generated in hollow cylinders with the same thickness and the different outer radii are compared. The numerical results denoted that the main features of the surface waves are three kinds of waves—the surface skimming longitudinal wave, head wave and the Rayleigh wave. And the first Rayleigh pulse′s polarity changes gradually with the propagating angle increment. The Rayleigh pulse is monopolar (negative) near the source, becomes bipolar completely at the point of =90° and monopolar (positive) at =180°. If neglected the diffraction effects, the polarity of the first Rayleigh pulse is only determined by the angle between the source and the detection point, and not related to the size of the specimen..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 765 (2006)
Influences of Wave Vector Direction on Energy Bands and Applications of Two-Dimensional Photonic Crystals
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The influences of the wave vectors off the periodic plane on the distribution of energy bands of triangular, honeycomb and square lattices are analyzed by plane wave method. The rods and background of these lattices are all composed of two mediums with dielectric constants equal to 13 and 1. With the increase of wave vThe influences of the wave vectors off the periodic plane on the distribution of energy bands of triangular, honeycomb and square lattices are analyzed by plane wave method. The rods and background of these lattices are all composed of two mediums with dielectric constants equal to 13 and 1. With the increase of wave vectors off periodic plane, many changes will take place in the dispersion relation of these lattices: the band gaps of wave vectors in the periodic plane will decrease gradually and even disappear; a region, which does not exist modes, will appear in the low frequency range and it will be broaden with the increase of wave vectors off periodic plane; new degenerated energy levels appear and primarily degenerated levels will disappear; the energy bands tend to become flat; the absolute band gaps can easily form among the lowest energy bands. By the analyses of the band gaps of three lattices, some conclusions can be obtained: the width of absolute band gaps in triangular and honeycomb lattices are larger than those of square lattices, which make triangular and honeycomb lattices lower the rate of spontaneous radiation more effectively than square lattices; the width of band gaps of triangular lattices in the leaky region is larger than that of honeycomb lattices, which made triangular lattices be more appropriate to be used as reflect mirror than honeycomb lattices..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 770 (2006)
Materials and Thin Films
Influences of Deposition Temperature on Residual Stress of HfO2 Films Prepared by Electron Beam Evaporation
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
HfO2 films were prepared by electron beam evaporation on BK7 glass and fused silica substrates. The residual stress was measured by viewing the substrate deflection using ZYGO interferometer. The results show that the residual stresses of HfO2 films on both substrates are tensile and increase with the increase of deposHfO2 films were prepared by electron beam evaporation on BK7 glass and fused silica substrates. The residual stress was measured by viewing the substrate deflection using ZYGO interferometer. The results show that the residual stresses of HfO2 films on both substrates are tensile and increase with the increase of deposition temperature firstly, then decrease. The main origin mechanisms of residual stress are different. For films on BK7 glass substrate, the intrinsic stress is the determinate factor. While for films on fused silica substrate, the evolution of the residual stress is mainly due to the thermal stress in lower temperature. The microstructure of the HfO2 films was inspected by X-ray diffraction (XRD). It is found that the microstructure of the films transmitted from amorphous to polycrystalline, which is corresponding to the variation of the residual stress. The differences of the film residual stress for two substrates may be due to the evolution of the microstructure as the increasing of the deposition temperature and differences of properties between two kinds substrates..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 827 (2006)
a-Axis Oriented Bi4Ti3O12 Thin Films Deposited on Si(111) by Femtosecond Laser Ablation
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The crystalline grains of Bi4Ti3O12 thin films are tended to c-axis-orientation in a usually deposited process on planar substrates, but the piezoelectric and ferroelectric storage devices largely utilize the a-axis-oriented component of spontaneous polarization. So, it is importance to investigate the way to gain a-axThe crystalline grains of Bi4Ti3O12 thin films are tended to c-axis-orientation in a usually deposited process on planar substrates, but the piezoelectric and ferroelectric storage devices largely utilize the a-axis-oriented component of spontaneous polarization. So, it is importance to investigate the way to gain a-axis-oriented Bi4Ti3O12 thin films. The polycrystalline Bi4Ti3O12 thin films successfully prepared by femtosecond laser deposition on Si(111) wafers are reported in this paper. The structural properties and crystallographic orientation of the films were investigated by X-ray diffraction (XRD) method in 2θ only scan, the surface morphology of the films was observed using the field scanning electron microscope (FSEM). The Bi4Ti3O12 thin film deposited at room temperature (20 ℃) was highly c-axis-oriented; but the film deposited at 500 ℃ was highly a-axis-oriented. It was observed that the films were composed of well-distributed grains, the grains of the 20 ℃-sample was about 20 nm in diameters, the grains of the 500 ℃-sample was 30～200 nm, large particles (≥1 μm) were not found in the surface of the two samples. A Fourier-transform infrared spectroscopy (FT-IR) was used to measure the transmittance and reflectance of the film deposited on quartz at room temperature, and then to determine the optical forbidden gap of the film, the optical forbidden gap of it was 1.0 eV. The remnant polarization (Pr) of the a-axis-oriented sample was measured to be 15 μC/cm2 by RT-66A the coercive force (Er) was 48 kV/cm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 832 (2006)
Laser-Induced Damage of Flat Polarizer Prepared by Electron Beam Evaporation
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The flat polarizer was prepared by electron beam evaporation and its optical performance was measured by Lambda900 spectrometer. The transmission of P-polarization is more than 98%, the transmission of S-polarization is less than 0.5%, its extinction ratio is more than 200:1, and its spectral bandwidth is 20 nm near 10The flat polarizer was prepared by electron beam evaporation and its optical performance was measured by Lambda900 spectrometer. The transmission of P-polarization is more than 98%, the transmission of S-polarization is less than 0.5%, its extinction ratio is more than 200:1, and its spectral bandwidth is 20 nm near 1053 nm. The laser-induced damage thresholds (LIDTs) of P-polarization and S-polarization are 17.2 J/cm2 and 19.6 J/ cm2, respectively, measured at 1064 nm wavelength,12-ns pulse width and the incident angle of 60°. The morphology of the laser-induced damage was characterized by Nomarski microscopy and its depth was measured by Alpha-500 step meter. Two distinct damage morphologies (defect and delamination) were observed when polarizer was tested in P-polarization. The character of interface caused the outer layer delamination damage morphology and which happened at hafnia-silica interface of the outer layer. The defect damage was induced by the defects in the film, and it appeared in the interior of the polarizer. In the case of S-polarization,the outer layer delamination damage morphology,which was induced by standing electric field was also observed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 837 (2006)
Measurement and Metrology
Optical Kerr Effect in Phase Modulation Spectroscopy Resonator Fiber Optic Gyro
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Resonator fiber optic gyro (R-FOG) is a novel optical sensor whose resonant frequency is changed due to the Sagnac effect. The detection technique and system noises affect the detection precision greatly. In the R-FOG based on the phase modulation spectroscopy technique, not only the optical power difference between thResonator fiber optic gyro (R-FOG) is a novel optical sensor whose resonant frequency is changed due to the Sagnac effect. The detection technique and system noises affect the detection precision greatly. In the R-FOG based on the phase modulation spectroscopy technique, not only the optical power difference between the clockwise (CW) and counterclockwise (CCW) light waves induces the bias drift, but also the two different modulation indexes do. The bias drift caused by optical Kerr effect is indistinguishable from the rotational-induced Sagnac frequency shift. Using the optical field overlapping method, the analytical expression for the rotation-rate error due to the optical Kerr effect is derived. For the bias drift caused by the optical Kerr effect does not change with the rotation-rate, using a simple open-loop operation, the drift caused by the optical Kerr effect is observed in the gyro output curve..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 814 (2006)
Micro-Calorimetry Based on Time-Resolved Interferometer
[in Chinese]
A micro calorimetry based on interferometer to measure the light-induced reaction volume and quantity of heat is studied. The principle to get the reaction volume and quantity of heat is introduced. The method is used to investigate the reaction of myoglobin (Mb) with CO after light excitation. Accompanying the reactioA micro calorimetry based on interferometer to measure the light-induced reaction volume and quantity of heat is studied. The principle to get the reaction volume and quantity of heat is introduced. The method is used to investigate the reaction of myoglobin (Mb) with CO after light excitation. Accompanying the reaction of Mb with CO, the quantity of heat and reaction volume are changed which could lead to the variation of the index of refraction of Mb. The thermodynamic information could be obtained through measuring the phase variation. The experiment to get the reaction volume and quantity of heat for the reaction of Mb with CO is done at 273 K to 301 K with a time window of 10-6 s to 10-1 s. The measured reaction enthalpy is 80 kJ/mol, the reaction volume is 10 mL/mol..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 819 (2006)
Measuring Weak Absorptance of Optical Thin Films with Laser Calorimetric Technique
[in Chinese], [in Chinese], Holger Blaschke, and Detlev Ristau
A laser calorimeter in compliance with ISO 11551 was developed to measure the absolute absorptance of optical thin films. Under a typical condition the absorptance sensitivity of the calorimeter was better than 10-6 and the measurement error was estimated to be ～10%. For an uncoated fused silica substrate with 1-mm thiA laser calorimeter in compliance with ISO 11551 was developed to measure the absolute absorptance of optical thin films. Under a typical condition the absorptance sensitivity of the calorimeter was better than 10-6 and the measurement error was estimated to be ～10%. For an uncoated fused silica substrate with 1-mm thickness, the measured absorptance was 3.4×10-6 and the sensitivity was ～1.5×10-7. The laser calorimeter was employed to measure the absorptance of highly reflective dielectric coatings prepared by two different coating techniques. The absolute absorptance of a 0° Ta2O5/SiO2 multilayer mirror prepared by the ion beam sputtering (IBS) technique was as low as 1.08×10-5, and the absorptance of a 45° HfO2/SiO2 multilayer mirror prepared by the ion-assisted deposition (IAD) technique was 6.83×10-5, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 823 (2006)
Optical Communication
Effect of Hetero-Diameters of Cladding Air Holes on Nonlinearity Coefficient of Microstructured Optical Fibers
[in Chinese], and [in Chinese]
The nonlinearity coefficient of microstructured optical fibers (MOFs) is a quantity of great importance in devices based on the nonlinearity of the fibers. The distribution asymmetry of the cladding air holes can make an impact on it. The effect of hetero-diameters of the cladding air holes on the nonlinearity coefficiThe nonlinearity coefficient of microstructured optical fibers (MOFs) is a quantity of great importance in devices based on the nonlinearity of the fibers. The distribution asymmetry of the cladding air holes can make an impact on it. The effect of hetero-diameters of the cladding air holes on the nonlinearity coefficient of a highly nonlinear MOFs with a hexagonal lattice is analyzed by the full-vector finite element method and the error theory. The dependence of the nonlinearity coefficients of the HEx11 and HEy11 modes of the fiber on the diameter of cladding air hole is computed. Subsequently, the dependence of the standard error of the nonlinearity coefficients on the standard error of the diameters of the air holes is obtained. As a result, if the standard error of the diameters of the air holes is given, it is easy to obtain the standard error of the nonlinearity coefficients. When the ratio of the air hole diameter standard error to the designed diameter is 5%, the ratios of the nonlinearity coefficient standard errors of the HEx11 and HEy11 modes to the nonlinearity coefficient of the fiber with uniform cladding air holes are 2.55% and 3.06%, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 775 (2006)
Experiment on 2.5 Gbit/s Symbol Overlapping Optical Fast Frequency-Hopping Code Division Multiple Access System
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Experiment on 2.5 Gbit/s symbol overlapping fast frequency-hopping optical code division multiple access (SO-FFH OCDMA) system with single user is designed and demonstrated. Under user′s data rate 2.5 Gbit/s, fiber Bragg grating based optical encoder and decoder are designed and fabricated employing one-coincidence seqExperiment on 2.5 Gbit/s symbol overlapping fast frequency-hopping optical code division multiple access (SO-FFH OCDMA) system with single user is designed and demonstrated. Under user′s data rate 2.5 Gbit/s, fiber Bragg grating based optical encoder and decoder are designed and fabricated employing one-coincidence sequence, which the number of wavelengths is seven and code length is four. The spectra of optical encoder and decoder are measured. Pulse generator generates 2.5 Gbit/s non-return zero (NRZ) pulse signal, which is used to externally modulate amplified spontaneous emission (ASE) broadband source, and then optical signal is fed into optical encoder to spread spectrum. At the receiver, an Erbium-doped fiber amplifier (EDFA) is employed to amplify the encoded optical signal, then optical signal is fed into the decoder, and is also converted into electrical signal by 2.5 Gbit/s receiver module. It can be shown from the waveforms of decoded optical signal and the electronic signal that, user′s data can be decoded correctly at 2.5 Gbit/s data rate. Experiment shows that compared with traditional FFH OCDMA, SO-FFH OCDMA has much higher user′s data rate..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 779 (2006)
Atmospheric 2D-Wireless Optical Code Division Multiple Access Communication System
[in Chinese], and [in Chinese]
Code division multiple access (CDMA) can be adopted to make full use of the broad bandwidth and effectively improve the system performance of wireless optical communication system. Considering the effects of background optical noise, multi-user interference, avalanche photodiode detector (APD) noise, and atmospheric scCode division multiple access (CDMA) can be adopted to make full use of the broad bandwidth and effectively improve the system performance of wireless optical communication system. Considering the effects of background optical noise, multi-user interference, avalanche photodiode detector (APD) noise, and atmospheric scintillation, the system model of atmospheric two-dimensional wireless optical code division multiple access (2D-WOCDMA) communication system with pulse position modulation (PPM) and fiber Bragg grating (FBG) encoder/decoder is presented. And the bit error rate (BER) of this optical CDMA communication system is analyzed in detail. The results show that atmospheric scintillation is one of the important factors which affect the BER performance of this communication system, and the 1550 nm wave band is more suitable for this 2D-WOCDMA communication system. When the atmospheric turbulence is strong (σ2s≥0.2), some new technologies,such as multi-user detection, channel coding and array reception,can be used to improve the system performance. The results also show that the performance of this communication system can be affected by background optical, APD gain and modulation extinction ratio..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 783 (2006)
Sub-Pixel Resolution of CCD in Optical Communication
[in Chinese]
In acquisition, pointing and tracking (APT) system of optical communications, the resolution of detector is very important for whole system. In order to meet the specification of the communications, improve the performance of APT ulteriorly, a new method is put forward in this paper, it is multiple-sampling for detectiIn acquisition, pointing and tracking (APT) system of optical communications, the resolution of detector is very important for whole system. In order to meet the specification of the communications, improve the performance of APT ulteriorly, a new method is put forward in this paper, it is multiple-sampling for detecting data. According to this method, two results of sampling are added together and disposed by procedure, this can make resolution of charge coupled device (CCD) attain sub-pixel. From the simulation of this method, the resolutions of CCD get to 1/2, 1/4 pixel or more. At the same time, this method can also improve the signal-noise-ratio (SNR) of data. So, the method has been proved to be effective to improve the resolution to sub-pixel for CCD in APT system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 788 (2006)
Rapid Communications
[in Chinese]
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 863 (2006)
[in Chinese]
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 33, Issue 6, 864 (2006)
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