Showing papers in "Chinese Journal of Lasers in 2006"

Progress of Millimeter Wave Subcarrier Optical Fiber Communication Technologies

Abstract: Progresses of millimeter wave subcarrier fiber communication technology(ROF) for future generation mobile communication are summarized in this paper.The basic structure and key technologies of ROF are reviewed with emphasis put on the millimeter wave subcarrier transmitters and related optical technology,including external-modulation,radio up-conversion method,optical heterodyne,and millimeter wave modulated pulse transmitters and so on.Moreover,progresses of receiver technologies,systematic technologies and related applications of ROF are also introduced briefly at the end of the paper.

ICF Laser Glasses

Abstract: The composition and properties of neodymium-doped silicate,phosphate and fluorophosphates glasses used for inertial confinement fusion(ICF) research-simultaneous high energy and high peak power(10~(11)～10~(15) W) are reviewed.Optical and spectroscopic properties of different glasses for ICF laser application are compared,the parameters considered include linear and nonlinear refractive indices,stimulated emission cross section,fluorescent lifetime of neodymium ion in~4F_(3/2)→~4I_(11/2) transition.Some special technologies include continuous melting process of phosphate laser glass,dehydroxylation,elimination of platinum inclusion on the large scale laser glasses are discussed.

Manufacturing Features Comparing between Computer Control Active-Lap and Computer Control Optical Surface for Large Aspheric Optics

Abstract: Computer control active-lap(CCAL) and computer control optical surface(CCOS) are two new manufacturing technologies which are different from the classical manufacturing technology for large aspheric mirrors manufacturing,the manufacturing removal function models are found respectively aimed at these two manufacturing tools,and the manufacturing features are analyzed from the viewpoint of theoryCCOS possesses the ability of partly grind and polish,but tends to generate mid-and high-spatial frequencies error; CCAL can control the mid-and high-spatial frequencies error effectively,but has nothing for aperture grind and polishThe mid-and high-spatial frequencies error generated by these two manufacturing technologies are further discussed by the methods of power spectral density(PSD) and phase gradient based on the mirror testing data from ZYGO interferometer and Hartmann-Shack wavefront sensor during the experiment of diameter of 1300 mm aspheric mirror manufactureA new manufacturing technology for large aspheric mirrors combining the technologies of the CCAL and CCOS is proposed

Characteristics of Hologram Readout in LiNbO_3∶Fe∶Ru Crystal

Abstract: The readout characteristics for the hologram recorded in the novel LiNbO_3∶Fe∶Ru crystal have been investigated in order to resolve the problem of hologram data erasure during readout. Grating readout characteristics for two-center and single-center recording are analyzed, and the simulating calculation is performed through jointly solving the two-center material equations and coupled-wave equations. The results show that the readout time constant for a saturated grating recorded by two-center method is much shorter than that in LiNbO_3∶Fe∶Mn; an efficient hologram can be realized with one-color recording, the readout time constant is much larger than the recording time constant, and the quasi-nonvolatile readout can be observed. The analysis shows that Ru perhaps is much easier to be excited than Mn by red light, so the grating persistence would decrease; red light can act as recording light and sensitizing light in one-color scheme, and the grating recorded in Fe can be transferred to Ru, which is weakly sensitizing to red light.

Optical Kerr Effect in Phase Modulation Spectroscopy Resonator Fiber Optic Gyro

Abstract: 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 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.

Experimental Research on the Characteristic Measurement of the Short Pulses before and after Propagating in Dispersion-Flattened Fiber

Abstract: The second-harmonic generation frequency-resolved optical gating(SHG-FROG) is a new measurement technique of short optical pulses developed in recent years.It can be used to exactly measure more characteristic parameters of the pulses than the other measurement techniques.Recently,the experimental research on the characteristic measurement of the short pulses before and after propagating in dispersion-flattened fiber(DFF) is completed by use of SHG-FROG analyzer,obtained the FROG trace,autocorrelation curve,autocorrelation spectral curve,waveform and phase curve,temporal width,spectral width,chirp and other parameters,compared with the propagation theory of Gauss pulse in a single-mode fiber.The results show that the measured parameters are consistent with the predictions of the theory.The pulses from the laser are near transform-limited Gauss pulses with negative linear chirp.After the pulses propagate over 12.7 km of DFF,the spectral width is almost unchanged,the temporal width is about three times as wide as that of input pulse,the chirp is about four times as large as that of input pulses.FROG technology is an effective means of measuring short optical pulses.

Tunable Differential Phase-Shift Keying Demodulator Using the Mach-Zehnder Interferometer

Abstract: Tunable differential phase-shift keying (DPSK) demodulator based on fiber Mach-Zehnder interferometer (MZI) is investigated, which has advantages of low insertion loss, high isolation, good stability, and tunable phase Operation principle for DPSK demodulation is analyzed Temperature of the fiber arm is set by the temperature control system, in which the tuning range is 20 ℃ and the resolution is 01 ℃ In the experiment, 40 Gb/s DPSK signal was demodulated successfully, and the extinction of the demodulated signal is 145 dB With the help of temperature control, the experimental results have a long-time stability and can be switched between constructive interference and destructive one

Polarization Effect of 150 nm Subwavelength Aluminum Wire Grating in Near Infrared

Abstract: The 150 nm subwavelength aluminum wire grating was fabricated with nano-imprint technique and reactive ion etching process,and the polarization effect of this grating was also studied both experimentally and theoretically in visible and near infraredThe transmission spectra of transverse electric(TE) and transverse magnetic(TM) wave for this grating sample were measured by spectrophotometer,respectively,which have good agreements with the numerical results of rigorous coupled wave analysis(RCWA)Results show that such grating is sensitive to the polarization of incidence,polarization paralleled to the gratings will be totally reflected while the orthogonal polarization will be transmitted close to 90%Such performance is uniform with wide variations in wavelength and the angle of incidenceIn addition,different metals were simulated to generate a lower reflectivity of TM wave,so as to give further discussion on the improvement and applications of such grating

Retrieval Method for Aerosol Mass Concentration Vertical Distribution

Abstract: Retrieval method for aerosol mass concentration vertical distribution with lidar is one of research contents in environment monitoring fields.Making use of the extinction coefficients on ground gained by lidar and corresponding mass concentrations gotten by the tapered element oscillating microbalance(TEOM),the relationship between extinction coefficient and mass concentration can be disclose,then the mass concentration vertical distribution can be retrieved through the extinction coefficient vertical distribution. Based on it,two models are adopted,and confirmed by some experiments.It is indicated that the aerosol mass concentration vertical distributions retrieved by both the models are consistent with each other,and consistent with facticity.The models are maneuverable and simple,and can monitor online and real-time.

In Situ Synthesized NbC Particulate Reinforced Ni-Based Composite Coatings by Laser Cladding

Abstract: Laser cladding is the one of the efficient methods for the surface hardening and modifying of metal material.Using this technology,NbC particulate reinforced Ni-based composite coating has been successfully in situ synthesized on steel A3 substrate by prior to pasting.The microstructure observation and hardness test on the cross-section of the laser clad layer were performed.And that X-ray diffraction(XRD) analysis and tribotesting on the surface of the coatings were also accomplished.The microstructural and metallographic analyses by a scanning electron microscope(SEM),energy-dispersive spectrometer(EDS) and X-ray diffractometer reveal that the coating epitaxial growing from the substrate with excellent bonding between the coating and substrate is ensured by the strong metallurgical interface and suggest the presence of the in situ synthesized NbC particles in the clad layer.These NbC particles together with the carbide dendrites present as reinforcements of the composite coatings and are homogenously dispread in the γ(Ni Fe) matrix.The experimental results show that the composite coating gives high average hardness of HV_0.31200 and excellent wear resistance,which is 2.5 times as high as that of pure Ni60 coatings.The improvement of wear resistance is due to the presence of the substantive in situ synthesized NbC particles and their homogenous distribution in the coatings.

Progress in Nonlinear Optics with Photonic Crystal Fibers

Abstract: Photonic crystal fibers(PCFs),also called holey fibers(HFs) or microstructure fibers(MFs),are a new class of single-material optical fibers with wavelength-scale air holes running down the entire length.PCFs were first developed in 1996 and have subsequently been the focus of increasing scientific and technological interest,due to their unique and promising properties.The manufacturing,principles,basic properties and applications of PCFs are briefly described.A detailed review of the research on the nonlinear effects and the possible applications of these effects of PCFs are presented.

Experimental Measurement of Metal Powder Stream Concentration Field in Laser Manufacturing

Abstract: The research on the distributions of metal powder stream from co-axial nozzle is very interested in laser manufacturing.The paper was focused in the concentration field of powder stream.Theoretic model of concentration field of powder stream from the co-axial nozzle has been established.A new digital particle image measurement technique has been developed to measure the concentration field of powder stream.The system mainly consists of Nd~+∶YAG laser and charge coupled device(CCD) camera.It is shown that focus parameters and concentration distribution of powder stream can be measured by the technique.The system could be a useful device for laser manufacturing after further developed.

Simulation on High Concentration Effects of Transmission Fluctuation Spectrometry

Abstract: The transmission fluctuation spectrometry (TFS) is a new method developed in recent years,in which the particle size distribution and particle concentration can be measured simultaneously,and real-time online measurements can be realized.The spectral analysis of the transmission fluctuations in the frequency domain is presented and a 2nd order low pass filter with the quality of 0.707 is employed.By numerical simulation,the empirical expression of the normalized deviation of the transition functions between the multi-layer particle system and the monolayer particle system is obtained.And the high concentration effects on the transmission fluctuation spectrum are discussed.The results show that the high concentration effects are related to the concentration of the suspension,number of layers and beam-to-particle diameter ratio.The high concentration effects can change the transition function of TFS in two aspects: the shift in frequency response and the step height.Generally,the shift in frequency of the transition function is domained by particle overlapping,while the step height is affected by both the monolayer structure and particle overlapping.

Generation of Terahertz Wave Based on Optical Methods

Abstract: The terahertz(THz) technique has attracted much attention from a variety of applications in fundamental and applied research field,such as physics,chemistry,life sciences,medical imaging,safety inspection,radio astronomy,modern communication,weapon guidance and so on.THz radiation source is a crucial part of THz techniques system.Some typical techniques of the generation of THz radiation based on the optical methods,especially the nonlinear optical process such as difference frequency generation(DFG) and THz parametric generation(TPG) based on stimulated polariton scattering process,are briefly introduced and reviewed.The future of these two kinds of THz generation methods is also forecast.

Dual-Wavelength High Altitude Detecting Lidar Technology

Abstract: Based on the Rayleigh and sodium fluorescence lidar technologies,a dual wavelength high altitude atmosphere detection lidar by combining the above two lidar mechanisms into one lidar facility through the employment of some special technologies,such as the twice frequency doubling to use the residual fundamental optical energy and the dual optical fiber in the focal plane for spectra separation,has been establishedIn this way,the simultaneously detecting the atmosphere at the altitude of 30～(80 km) by Rayleigh scattering and 80～(110 km) by sodium fluorescence in one lidar facility has been realized,and therefore an effective new facility to detect much wider range of atmosphere has been providedIn this paper,the principle,key technologies and the performance of this dual wavelength high altitude lidar are reported

Transverse Mode Distribution of THz Wave by THz Imaging Technology

Abstract: The transverse mode distribution of THz wave near the position of focus point was studied in this paper.It is important to know the transverse distribution of THz wave,which can be referenced as an evidence of sample positioning in THz spectroscopy and THz imaging experiments.By using THz point-by-point imaging technology,THz transverse mode distribution in the positions,where samples are usually placed,is analyzed qualitatively.By applying "slit method",the beam width of THz wave was measured.The results show that the shapes of the transverse modes of THz wave in different positions around the focus have much difference.To the maximum wavelength of about(1.5 mm) of THz wave in the system,the minimum diameter of THz beam at the focus point is around(1.0 mm.) The results provide a basic reference for further application of THz Spectroscopy and THz Imaging.

Ultraintense Solid-State Lasers and Applications to the Frontiers of Sciences

Abstract: 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 facilities have been built for picosecond and femtosecond pulses with focused intensities of up to 10~(20)～(10~(22) W/cm~2.) 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.

Study of Silicon Micro-Structuring Using Ultra-Short Laser Pulses

Abstract: The new material “black silicon” formed by arrays of sharp conical spikes on the silicon surface is fabricated under the cumulative ultra-short laser pulses irradiation in different ambient atmospheres. The physical mechanisms of conical spikes evolutions impacting silicon surface under picosecond (ps) and femtosecond (fs) laser irradiations are different. The formation of spikes arrays depends on the pulse duration and ambient atmosphere. Especially, in SF_6 ambient atmosphere, silicon surface micro-structuring evolutions under ps and fs laser irradiations are analyzed in detail. Under the ps laser irradiation, silicon surface is melted before the spike arrays formed; while under the fs laser irradiation, the formation of spike array does not go through the liquid phase. The preliminary experiment shows that the infrared radiation absorptance is more than 80% at the wavelength range of 1.5～16 μm.

Waveform Simulator of Return Signal for Laser Altimeter

Abstract: The establishing process and physical parameters for return signal in the laser altimeter systems are analyzed simply.Under the circumstance that the influence of atmosphere on laser pulse is ignored,the models of return signals and target response function are concluded,which indicates that return signals can be look as the convolution of transmission signal and target response function.In terms of existent laser altimeter—geoscience laser altimeter system(GLAS),the return signals for different observation angles and target models are simulated according to the ways of gridding partition.The simulated output parameters are compared with parameters of computing by using theoretical way.The results show that the agreement of pulse width is(99.5%,) the difference about the total number of photonelectron between this paper and GSFC is(0.4%,) the difference between the height for barycenter of pulse and actual supposed height is 1%.It proves that the way is correct and reliable.

Experimental Study of Long-Period Moiré Gratings

Abstract: Two kinds of special long-period fiber gratings,phase-shift and apodised long-period gratings,were studied by many researchers,because of their special spectral characteristics.According to the theory of long-period moire gratings,with the methods of step-by-step ultraviolet(UV) writing and double-exposure with different grating period,several kinds of long-period moire gratings were fabricated in the hydrogened high-germanium-doped fiber by controlling the period and the first position of both exposure and the exposure-time of each step,which realized the effects of phase-shift and apodization.The results indicated that the moire gratings technology can be well applied in fabricating the special kinds of long-period fiber gratings,such as phase-shifted and apodised gratings.

Modeling and Measuring the Pulse Laser Scattering Echo Power from Whole Dimension Target

Abstract: A theoretical model is presented which computes the pulse laser scattering echo power from the whole dimension target by using the theory of rough surface scattering and of pulse laser scattering combined with the modeling parameter of complex rough surfaceThe directional figure of pulse laser backscattering echo power is given through the measurement of the pulse laser backscattering echo power of the aerial complex scale-modelAn analysis of the experimental error by comparing the theoretical results with experimental data proves that this model is correctComputational results of the pulse laser backscattering echo power from non-cooperative complex space target by the model can pre-estimate the laser scattering characteristic of space target and solve some problems of engineering application about the pulse laser scattering from space complex targets

Flow Field Moire Tomography Based on Phase Unwrapping and a New Iterative Reconstruction Algorithm

Abstract: Moire tomography is applied in fully quantitative measurement of temperature distribution.Rotary moire deflectometer is designed to capture multidirectional optical projections,and moire patterns of temperature field can be obtained in 180 degrees.The information of fringe pattern is Abstracted by phase unwrapping using Fourier transform.The temperature distribution of asymmetric flow field is calculated from incomplete projection data by a new iterative reconstruction algorithm,which is derived from basic moire deflection formula and discrete element reconstruction technique.The deflection angle is applied directly in iteration,which is completely different from the previous transform methods and existing series expansion methods.In experiment,the asymmetric temperature distribution was reconstructed by 8 projections with different view angles,and some measurement errors were discussed.The results prove that it is an accurate and practical tomography technique.

Experimental Study of Smoothing by Spectral Dispersion

Abstract: To improve the ability of beam smoothing in the device of inertial confinement fusion(ICF) in China,the theory of smoothing by spectral dispersion(SSD) is studied,and some experiments are carried out to analyze the mechanism of SSD in contrast with another technology of smoothing—distributed phase plane(DPP).It is found that the uniformity of focal spot in direction of dispersion is improved markedly using sinusoidal phase modulation(PM) and dispersion in SSD.And the intensity modulation of focal spot in this direction is smoothed by SSD.According to the experiments results,the changes of spectral intensity of spatial frequency at low-mode are very limited,and at high-mode are obviously;the nonuniformity varies from 40% to 12.5%.The ability of smoothing depends on the parameter of SSD.It also shows that the color cycle is very important in the process of smoothing,although the smoothing by broaden of laser spectral width for PM is poor.

Theoretical Analysis of Fiber Bragg Grating Characterization by Applying Transverse Force

Abstract: Fiber Bragg grating(FBG) characteristics by applying a transverse force to a middle section were studied theoretically and experimentally.A numerical simulation based on the transfer matrix method was used to calculate the consequent changes in reflection spectrum.The reflection spectra of the FBG subjected to the transverse force split into two main peaks,and the split point shifted linearly and periodically with the applied force.The linearity expression was presented.The split point was shifted within the bandwidth with the period of(11.06 N,) and in one period the sensitivity of the split point wavelength shift versus the applied force was the ratio of bandwidth to the period,the period was independent of the length under stress.The theory analysis,simulation results and experimental consequents were presented.The experimental consequents were in good agreement with the simulation results.

Comparison of Spectral Radiance Calibrations of Spectroradiometer for Ultraviolet Space Remote Sensing Using Three Calibration Techniques

Abstract: Three techniques of spectral radiance calibration,one based on the flat diffuser and the other two based on internally illuminated integrating sphere,are applied.The radiance responsivities of the spectroradiometer under development for ultraviolet remote sensing in space have been obtained using these three calibration techniques.A preliminary analysis of uncertainties of these techniques points out that the uncertainties in measurements of the diffuser bidirectional reflectance distribution on function(BRDF) and the calculation of the radiance of the flat diffuser are the major sources for the discrepancy among the comparisons of these three techniques.The comparisons of calibration data show that radiance responsivities of the spectroradiometer derived using these three techniques are consistent within the uncertainties (3%) designated to them,respectively.

Study on Fiber Grating Petroleum Pressure Sensor and Its Reliability

Abstract: A high pressure and temperature fiber grating sensor was presented.The sensor was implemented by using three metal tubes.The central elastic metal tube was used to convert pressure into longitudinal strain.The outer tube was only affected by temperature.Fiber grating was fixed on both end of central and outer tube,so as to sense the wavelength increment introduced by the pressure.Temperature compensation scheme was studied,and two fiber Bragg gratings(FBGs)(pressure sensing grating and temperature sensing grating) with similar temperature coefficient were designed.High pressure and high temperature/humidity storage tests were carried out.Results showed that the sensor during the condition of 0～(50 MPa) had a pressure sensitivity up to(31.7 pm/MPa.) After storage of 16 hours under(200 ℃) and immersion into(100 ℃) water for 6 hours,the fiber grating wavelength showed no obviously decay.

Ni-Coated Nano-Al_2O_3 Composite Coating Prepared by Laser Cladding

Abstract: The experiments of laser cladding Ni-coated nano-Al_2O_3 composite powder were made on 2Cr13 stainless steel using(7 kW) CO_2 laser processing systemThe microstructure and mechanic performances of coating were tested by scanning electronic microscope(SEM),X-ray diffraction(XRD),energy dispersion analyzer of X-ray(EDAX) and microhardness testerThe changes of microstructure and performances after adding nano-particles were analyzedThe results have shown that the dense Fe-Ni(Cr)/Al_2O_3 composite coating can be got by laser claddingThe coating exhibited a cellular dendritic structureThe XRD data revealed that the phases of composite coating include Al_2O_3,iron nickel alloy and iron chromium alloyNano-Al_2O_3 particles enhanced the homogeneous nucleation of metal alloys,refined the crystal grains and strengthened the mechanical properties of coatingThe average hardness of composite coating is about 700HV_(02),15 times higher than that of substrateCompared with substrate,the abrasion proof has increased by 125%

CO_2 Laser Welding of Zinc Coated High Strength Steel

Abstract: Based on many experiments of CO_2 laser welding of 15 mm zinc coated high strength steel to vehicle body,joint microstructure and stress-strain curve of specimen are acquiredGiven special welding technology,theoretical P_c-v curve and P_c-Δf curve of stable deep penetration laser welding are deducedThe unstable sharply gasification of zinc enlarges heat-affected zone(HAZ),debases welding stability and increases the difficulty of protecting condenserThrough optimizing technology parameter,adopting coaxial and side blown protective gas,deep penetration laser welding can effectively avoid softening HAZ of welding of zinc coated high strength steel and can control the gas holeThe experimental result indicates that the content welding quality can be gained on the condition of using N_2 as protective gas,the laser power at(1300 W,) the welding speed at 08～(11 m/min) and defocusing amount at Δf=(-04 mm,) the hardness of welding seam is twice as that of base material

Experiment of Laser-Propulsion Free-Flight

Abstract: An experimental setup is designed to realize the stabilized flight in the laser-propulsion free-flight demonstration.The (4.2 g) paraboloid craft with(10 mm) focus is spin-stabilized to(700 r/m) prior to launch.It was boosted by the transversely excited atmospheric-pressure(TEA) CO_2 laser to(2.6 m) in a flight lasting(1.75 s.) In the experiment,the single laser pulse output energy is(13 J,) the repetition rate is the(50 Hz.) The results indicate that,when the laser output energy is definite,high rotate speed avails to stabilizing the craft,and improving flight altitude properly in the free flight demonstration.

Effect of Intracavity Perturbation on Mode Properties and Tilt Aberration Correction for Unstable Resonators

Abstract: Influence of intracavity tilt perturbation on the outcoupled mode of positive-branch confocal unstable resonators is analyzed by adopting Hartmann-Shack(H-S) wavefront sensor method,and the wavefront recovery calculation is performed.The relations of intracavity perturbation and aberration properties of mode are presented.The intracavity perturbation of the concave mirror has more remarkable effect on outcoupled beam-quality than that of the convex mirror by introducing equivalent perturbation.For a large Fresnel-number resonator,the tilt angle of intracavity mirror has a near linear relation with Zernike tilt coefficient of the output beam.A system for intracavity tilt aberration correction based on H-S wavefront sensor is established to correct low order aberration by control the concave mirror,and the aberration-corrected results are compared.For a small and slow intracavity perturbation,the correction for tilt aberration can reach a satisfied level.