Influence of the degree of polarization on beam wander of partially coherent Laguerre-Gaussian-Schell model (LGSM) beams propagating in a turbulence atmosphere is investigated. Based on the cross-spectral density function and the extended Huygens-Fresnel integral principle, the expression for beam width and beam wander of partially coherent LGSM beams in theory is developed. In different transmission distances, turbulence strength and coherence length, influence of the degree of polarization on beam wander of partially coherent LGSM beams is illustrated numerically. The numerical results show that beam wander of a LGSM beam with larger degree of polarization and less coherent length is smaller. Therefore, in free-space optical (FSO) communication, we can choose beams with larger degree of polarization and smaller coherent length to reduce the beam wander.

Based on the model developed recently for describing a spatial power spectrum function of clear oceanic water and the extended Huygens-Fresnel integral in linear media, the effects of oceanic turbulence on propagation properties of a multi-Gaussian Schell-model (MGSM) beam is studied. The analytic expressions such as the spectral density, the degree of coherence and the propagation factor M2 of the beam are derived. Numerical results show that, the oceanic turbulence has a significant influence on propagation properties of a MGSM beam. With the suitable choice of beam parameters, the center of the intensity profile not only forms a plateau in the far-field but also the formed plateau can keep a long distance in oceanic turbulence. Furthermore, a MGSM beam with a large source parameter N could further reduce turbulence-induced spreading effect.

Narrowband sodium fluorescence lidar can be used to measure wind and temperature of sodium layer from 80 km to 110 km, which is the development trend of high-altitude atmospheric sounding. This paper reports a most recently developed fiber-coupled all-solid-state narrowband sodium fluorescence lidar, introducing the whole design, key technologies and the preliminary measurement results. This system has achieved the sodium number density and temperature detection of the sodium layer over Beijing. This all-solid-state lidar has good stability, high reliability and less hardware adjustments, which provides a good means for sodium layer measurement.

Optical phase array scanning method is different from traditional mechanical scanning method as well as flat mirror, which can achieve inertialess random-access. AlGaAs waveguide optical phased array lidar has highlighted advantages in scanning speed, sweep range, etc. But the advantages bring difficulties in designing receiving system. Based on the AlGaAs waveguide phased array scanning lidar system, we design a direct detection and a heterodyne detection of the receiving system and analyze their characteristics of signal noise ratio. In the direct detection solution, in order to reduce background noise, multi aperture array receiving optical system is used. Aiming at the weak echo signal, we choose avalanche photo diode (APD) photoelectric detectors. In the heterodyne detection solution, for its large scan angle, we use the Airy method to achieve big angle coherent detection. Finally, the advantages and disadvantages of the two solutions are compared.

A high efficient terminal polarization-converting system is designed based on combination of axicons and wave plates to transform naturally polarized laser to linearly polarized laser at real time to resolve difficulty of generating high power linearly polarized laser. Energy conversion efficiency is 97.3% with an enhancement of extinction ratio from 18.3% to 99%. The system also keeps excellent far field divergence. The experiment proves that this polarization-converting method will not affect laser structure. The controlling method is, feedback and controlling system is not needed. The property is stable and reliable. It can absolutely be applied to the polarization-conversion of high power laser.

In order to compensate the time dispersion between photocathode and anode in the streak tube, a time focus and time collimation system for electron bunch is presented. The time focus system is used to compensate the time dispersion in the process of accelerating. Then, the compensated electron pulse traverses the time collimation system. The energies of the electrons are equal as they emerge from the time collimation system. Therefore, the pulse width of the electron bunch is invariable in the latter transmission process. The system is simulated by using the Monte Carlo method and the finite difference method. The electron pulse with width of 500 fs is generated at the photo-cathode. The width of the electron pulse is shortened to 131 fs by using the time focus system. The time compression ratio is 3.8:1. Then, the pulse width maintains 131 fs by using the time collimation system. The time collimation ratio is 16.8%.

Terahertz (THz) radiation lies between the infrared and microwave regions of the electromagnetic spectrum. Because of organisms’ unique response to the THz wave, THz wave applications in biomedical research, especially in its interactions with biological tissues become a hot spot. Whether the THz wave has the photodynamic effect by exciting the photosensitizer is explored in the study. The wide spectrum (1-3 THz) of pulse terahertz is used as a light source to excite the photosensitizer-hematoporphyrin monomethyl ether (HMME) for 30 min, and then DPBF is used as singlet oxygen scavenger to test the yield of singlet oxygen. HepG2 cells in conventional culture are illuminated with the same dose of terahertz wave, the cell morphology is observed by an optical microscope, the cell activity is determined by MTT method. The singlet oxygen production in PS+THz group is significantly higher than that of pure THz wave irradiation (21.04% vs. 2.39%). Compared to control cells, HepG2 cells in PS+THz group are slightly rounded and have a tendency to shrink. The activity of HepG2 cells incubated in HMME (HMME+THz group) is reduced to 81.13% after irradiation by THz wave (99.21% in THz group). The experimental results show that the THz wave of wide spectrum (1-3 THz) and nanojoule energy can excite the photosensitizer of HMME with excitation efficiency of about 20%.

A pulsed optical parametric oscillator model based on MgO-doped periodically poled lithium niobate crystal is established. The influence of seed intensity on conversion efficiency of the signal in the optical parametric oscillator is numerically investigated. The simulation results show that increasing the seed intensity can restrain multi-longitudinal-mode operation, and promote the conversion efficiency of the seed longitudinal mode remarkably. The conversion efficiency can not be promoted because of gain saturation if the seed intensity reaches the order of μW/mm2. The upper limit of gain saturation is affected by back-conversion, which leads to insufficient utilization of the pump energy. A prospect is given that back-conversion can be avoided in an optical parametric amplifier with a simpler structure by optimizing the crystal length. The pump energy thus can be utilized more sufficiently and the conversion efficiency of the single longitudinal mode is expected to be improved further.

In order to predict and control the polymer temperature field of laser melting molding process, the finite element analysis model of CO2 laser scanning irradiation polymethylmethacrylate (PMMA) is built based on the principles of heat transfer and energy balance. Numerical simulation of the laser melting process of the sample is carried out at low power CO2 laser scanning irradiation, the effects of laser parameters such as laser power, scanning time, scanning speed and spot diameter on samples three-dimensional transient temperature field are investigated, and the intrinsic relationship between laser parameters and sample temperature is analyzed. Simulation results show that the highest temperature of the sample wavily increases and the minimum temperature linearly increases, the temperature difference increases with scanning time increasing, and the sample substrate can be controlled at softening temperature or melting range to select appropriate parameters of the laser. The simulation results are in good agreement with the experimental research of the laser melting and molding, which can provide a reference to study the mechanism of polymer laser melting and molding process embodiments.

The temperature field in 316L stainless steel subjected to laser cladding is analyzed by ANSYS software. Based on the three-dimensional physical model, a study is made to analyze the temperature field distribution, the variation of the temperature gradient of the nodes irradiated by the laser beam and the effect of different scanning paths of laser beam on temperature field in the laser cladding process. Results show that the temperature contours and the heat are intensive and concentrated respectively in the front of melt pool and the regions of the clad overlapping, where cracks are easy to form. In addition, the temperature gradients of the nodes irradiated by the laser beam in the short scanning path are lower than that in the long scanning path. Moreover, compared to the long scanning path, the short scanning path is more conducive to the combination of cladding layer and the substrate and the continuity of laser cladding.

CrNiAlCoMoB0.5high-entropy alloy (HEA) is prepared on 45# steel bylaser cladding. The microstructure and corrosion resistance properties of this HEA coating are studied. The results show that the corrosion resistance properties of the HEA are remarkable, corrosion electric potential Ecorr and corrosion currect Icorr of CrNiAlCoMoB0.5HEA are equal to those of 304 stainless steel in 3.5%NaCl (mass fraction) while the resistance to pitting is better. Compared with 304 stainless steel, the ability of passivating of HEA coating is weaker. In 1 mol/L H2SO4 electrolytic solution, the Ecorr and Icorr of HEA coating and 304 stainless steel are in an order of magnitude, which means corrosion resistance of CrNiAlCoMoB0.5 coating is remarkable. Corrosion behavior of the HEA coating is intergranular corrosion while 304 stainless steel is irregular flake corrosion. In 1 mol/L NaOH electrolytic solution, Ecorr of CrNiAlCoMoB0.5HEA coating is lower than that of 304 stainless steel, which shows that the tendency of corrosion is larger. Meanwhile, Icorr of the HEA coating is smaller, the corrosion resistance of CrNiAlCoMoB0.5HEA coating is better, and the ability of passivating is equal to that of the 304 stainless steel.

Dissimilar metal butt joints of 1 mm thickness 6061 aluminum alloy and 1 mm 304 stainless steel are welded with filler material by fiber laser welding-brazing method. The mathematical model of relationships between welding parameters and tensile strength is established based on the response surface methodology. Effects of different parameters on the tensile strength are discussed. Afterwards, the tensile strength is used as an optimization goal and the optimum welding parameters are determined with the aid of the numerical optimization method. In order to test the suitability of the mathematical model, the optimized process parameters are used to carry out the welding experiment. The interaction effects of welding parameters on the tensile strength is significant. The results indicate that the maximum tensile strength of the welded joints can reach 180 MPa and the thickness of the intermetallic compounds is almost 2.85 μm.

During the laser cladding process, the traditional methods of microstructure adjustment are to change the laser processing parameters, such as laser power, scanning speed and the size of laser beam. However, these methods only change the boundary of heat transfer of laser cladding layer, the regulation effect is limited. In order to achieve the directional control of heat and mass transfer behavior in laser cladding layer and regulate the shape, the size and the direction of the solidification microstructure effectively, one method using the synergistic effect of electric-magnetic field is proposed. This method can induce the Lorenz force, whose direction, magnitude and frequency are controllable. As a means of volume force, the controllable Lorenz force can drive or drag the convection of the molten pool, which affects the solidification process and realizes the adjustment of microstructure. In this research, the higher influence degree of electric-magnetic synergistic effect is verified numerically and experimentally. The application of this method can improve the fatigue life of the high temperature resistance of turbine parts and decrease the internal defects in the solidification microstructure. Meanwhile, this method can be not only applied in laser cladding process, but also used in laser remelting, laser alloying and laser welding process.

To solve the problem that the adjusting of welding parameters depend on experience, experimental scheme of TC4 light gauge laser welding is designed with orthogonal regressive rotation design. Mathematic model of laser welding parameter (current, pulse width, frequency) and prediction response numeric (tensile-strength) is established based on response surface. Influence regular pattern of each processing parameter for welding procedure is analyzed by the mathematic prediction model. As the analysis shows that welding current has main effects on the tensile properties of the laser welding joint and not only the influence of pulse width and frequency on the tensile properties of the joint has obvious interaction, but also the impact effects of any single factor for pulse width or frequency are less than welding current. Best-fit welding parameters for TC4 sheet of δ=1.5 mm are obtained, and relevant test on which is performed. The results show that the mathematic model is consistent with the actual well.

To realize laser gradient modified destressing restoration of aerial titanium alloy impairment, experiments of functionally gradient reparative layers (FGRL) and non functionally gradient layers (N-FGL) on Ti600 substrate by pulsed Nd:YAG have been carried out. The microstructures and elementary distribution regularities of FGRL are investigated. The thermal shock and thermal fatigue properties of FGRL and N-FGL are examined contrastively. It is found that a rapidly solidified microstructure consisted of in situ synthesized TiC reinforced phase distributed on FGRL in the form of globular grains has three main different shapes: bulky or imperfect arborescent crystal, fine or approximately equiaxial crystal and chopped fibriform crystal. With the increasing of original Cr3C2 content, the number and size of arborescent crystal increase obviously. Resisting thermal shock and thermal fatigue properties indicate that gradiently transitional components of FGRL can relax thermal stress effectively. The main surface oxidation morphology of FGRL possesses densely fine fibrous crystal. Otherwise, that is uniformly polygonal and crassitude TiO2 crystal to Ti600.

The diffusing non-contact measurement method is effective for measuring incident laser power density. However, the strong laser irradiates diffusing metal plane for a long time, which once makes the temperature of target plane rise to a degree, causing the surface reflection descend significantly. The measuring results are affected. Based on the finite element method, considering hot source and wind convection, the temperature changes of Al plane coated Au film are simulated under strong laser irradiation, the results show that the energy absorption is the key factor to temperature rising. The energy absorption of diffusing surface can be designed similar to smooth surface, reducing the temperature of target plane effectively. the optimum design reference for diffusing metal target plane is provided.

Chemical oxygen iodine Laser (COIL) power is restricted by the reflectivity of COIL mirrors who are important parts of COIL, so the reflectivity of COIL mirrors must be tested precisely. The precision of measurement system is high for the high reflectivity of COIL mirrors based on cavity ring-down spectroscopy, the reflectivity for an 45° optical mirror of COIL mirrors is 99.979%. Uncertainty of measurement system for the high reflectivity of COIL mirrors are based on cavity ring-down length, cavity mirrors ring-down time and tested mirrors ring-down time. By studying the vertex of curve ring-down and tests repetition, it is found that vertex of curve and tests repetition are sensitive. When ring-down curve is managed, the vertex of curve is properly choosed. Uncertainty analysis of measurement system for the high reflectivity of COIL mirrors has been done, expanded uncertainty is 0.0152%.

Detection for mode dynamics of fiber ring laser is a key problem for experiments and applications. On the condition of the different pumping intensity and long-time operation laser can appear complex mode dynamic phenomenon. Output of the intensity can be obtained easily based on the current experimental condition, but more exact mode dynamic characteristic is still difficult to be obtained. One type of mode hopping detection for fiber ring laser based on optic heterodyne is set up. Real-time mode hopping and frequency drift of fiber ring laser is detected. Time-frequency fall graph of mode characteristic and the mode intensity time series can be acquired. According to the experimental results, the output of fiber ring laser mode dynamics is detected and analysis for mode intensity can be obtained. This method plays an imperative role in laser control systems and frequency dynamics analysis.

The relationship between the output performance and the working temperature of the fiber laser is studied both in theory and experiment. A numerical model based on laser rate equations concerning the change of pump wavelength is built up and used to calculate and analyze the temperature shift influence of some key components on the change of laser performance. By building the experiment configuration with 915nm wavelength pump light input, the output power and spectrum of the fiber laser are measured while changing the temperature of certain devices like laser diode (LD), grating and doped fiber. Compared with the calculation result, the experimental results suit the model simulation. The fiber laser holds working stability with about 140 W output in the set cooling range of temperature from 15 to 40℃. The temperatures of all the key components except the pump stripper are controlled below 55℃. The fiber laser has certain good performance under different temperature conditions.

High beam quality, high power fiber coupled diode laser has extensive requirements in the field of industrial processing applications. Micro-optics beam transform system (BTS) has been employed to transform the beam emitted from standard cm-bar semiconductor with 19 emitters, the beam quality along the slow axis has been improved. Compact spatial multiplexing module is designed, and balanced beam quality in both directions of combined beam is achieved, four spatial multiplexing modules are employed in polarization multiplexing and wavelength multiplexing, the output beam is coupled into a fiber with core diameter of 400 μm, numerial aperture (NA) of 0.22. The maximum fiber-coupled output power of 1070 W, the coupling efficiency of 96.3%, and the electro-optical conversion efficiency of 43% are achieved. The instability of output power is less than 1%, by measuring the maximum output power for 1 h.

By reducing the Al concentration in waveguide layer and optical confinement layer,stabilizing the epi-growth condition and combining with standard broad-area-laser processing technology,we obtain a continuous output power of 823 mW when working at 15 ℃,the peak wavelengh is 1.96 μm with 0.5 A injection current.In pulsed condition of 1000 Hz and 5% duty cycle, the maximum output power of about 1.86 W is gotten.

To research the beam quality of high power vertical cavity surface emitting lasers (VCSELs) singledevices,the impact of the factors such as the current, the aperture, the substrate thickness on the M2 factor, the far field divergence angle, near field and far field intensity distributionsis analyzed. It'sconcluded that, the current density of active area tends to be uniform with the increasing current until the current gets crowded, which inducesall partsemitting and has a circular symmetric beam distribution.The beam quality factor will be smaller with the improved beam quality. On the other hand, with the increasing aperture size of the active region, the lasing intensitydistribution becomes more uneven. While, beam quality will be worse with the increasing aperture size.For the effect of substrate thickness on the beam quality, all the factorsare considered, the optimum substrate thickness is about 100 μm. In order to obtain high power and high beam quality for the VCSELs single device, the oxidation diameter of 650 μm and P side electrode diameter of 580 μm are chosen, which can realize the uniform distribution of current density in the active region and the effective limits on current. This study provides a basis for looking for an effective method to improve the beam quality.

In high power all fiber laser systems, the backward stimulated Raman Stokes light will be absorbed in combiners and converted into heat finally, which can cause damage to devices and restrain output power. Forward Raman compatible fiber laser concept is put forward to suppress the backward Raman Stokes light by injecting an auxiliary seed. The model of master oscillator power amplifier (MOPA) with stimulated Raman scattering (SRS) effect is simulated and the characteristics of backward Raman Stokes light are discussed. The effects of different auxiliary seeds injections on the increase of output power are compared. Results of simulations have illustrated that the output power of the system can be increased by more than one time when the certain power and wavelength auxiliary seed are injected.

In order to calculate the intensity distribution of ring resonators, a numerical model is obtained with Collins’ formula and finite element propagation matrix method. The intensity distribution of planar resonator is unsymmetrical due to astigmatism. The axis mode has an elliptic facula, but high order mode can be detached. When increasing the coordinate rotation angle in the nonplanar ring resonator, components in the tangential plane and sagittal plane are coupled. The intensity distribution of high order modes changes with the coordinate rotation angle which shows the influence of coordinate rotation angle on the field modes. The intensity distribution of ring resonator with 90° rotation is nearly axis-symmetrical, but it is different from that in the linear resonator.

The 444 nm blue laser diode pumped Pr3+:GdLiF4solid-state red laser is reported. The Pr3+:GdLiF4crystal with the Pr3+ doped concentration of 1.01% is cut along a direction with the dimensions of 2.7 mm×2 mm×4 mm(a×c×a). Under the laser diode pumped, a continuous wave red light of 639.3 nm is obtained through the plane concave cavity. Several of laser input and output characteristics are gained through optimization of many times. The maximum output power is 153 mW when the pump power at 3 W and the transmittance of the output coupler is 3%. The slope efficiency is 6.78%, and the pump threshold is 750 mW.

In this paper, the damage process and mechanism of diode pumped alkali vapor laser (DPAL) windows have been experimental studied and analyzed. The results show that two different processes exist in DPAL windows (take glass as example): the heat induced physical damage and the reaction (between alkali and hydrocarbon) induced chemical damage. The mechanism of these two processes has been analyzed. The research method in this paper can be applied to study the performance of other DPAL windows.

We have prepared a ridge waveguide distributed feedback (DFB) laser emitting at 1.5 μm. To gain maximum output power of the laser, we choose asymmetric cladding layer structure. By simulation, it is found that while the lower cladding is 450 nm, the laser has minimum inner loose coefficient, and first order mode (m=1) can has minimum limiting factor. The loose coefficient of prepared tube core is 9.78 cm-1, which matches well with the loose coefficient of simulation 9.3 cm-1. Under the direct current of 600 mA, the maximum power of prepared Fabry-Perot (F-P) cavity laser is greater than 114mW. Under the direct current of 225 mA, the prepared DFB laser with single-wavelength has side-mode suppression ratio of 45dB, output power of 40 mW and spectrum line width smaller than 400 kHz.

In order to studythe output characteristic of the excimer broadband pumped alkali laser (XPAL), the time-dependent rate equationisestablished forthe five-level XPAL, which takes Cs-Ar mixed gas as the gain medium.Using triangle pulse pump, the output laser energy curvesare obtained by simulation when pump pulseenergy, temperature, and concentration of relaxation gas change, and the slope efficiency obtained from the model agrees well with the experimental data.The results show that, the higher the temperature is, the higher the threshold and slope efficiency of the XPAL are, when the other conditionsare fixed;D2 line laser disappears when the concentration of relaxation gas is large enough;and XPAL has the highest efficiency when the temperature is around 515K.

A passively 2 μm Q-switched mode-locked thulium-doped fiber laser by using graphene saturable absorber on tapered fiber is experimently demonstrated. The pulse evolution with the increase of the pump power is discussed in the experiment. Finally stable Q-switched mode-locked pulse is obtained. Stable Q-switched pulse trains occurr at 390 mW pump power and the repetition rate is 19.5 kHz.When the pump power increases to 490 mW, Q-switched mode-locked pulse can be obtained. The Q-switched frequency is recorded with a frequency of 30.2 kHz and the mode-locked frequency is 19.5 MHz. After increasing the pump power to 610 mW, the mode-locked pulses are filled up with the Q-switched envelope. The Q-switched frequency is 44.9 kHz and mode-locked frequency is still 19.5 MHz.

By simulating the diffusion of organic contaminants in the spatial filter with the method of computational fluid dynamics(CFD), the concentration distribution of organic contaminants,in different diffusion times and design models, are got in the spatial filter. Then the model is further optimized on the basis of a preferred design. Ultimately the chance that the organic contaminating optical components is reduced.It has important significance to realize the high power laser system efficient and precise operating.

The influence of detector’s gain on laser disturbing effect has been investigated in the experiment. We firstly measure the noise distribution and grey scale of output image under the different CCD gains, and then define the variable relation of noise grey scale with the increase of CCD gain. According to comparing laser spot image and grey scale distribution under the different gains, it is secondly found that the increase of CCD gain can amplify the weak signal around laser main spot, add the number of saturated pixel and enhance laser disturbing effect. The variable relation between signal grey scale and CCD gain has been also defined by calculating signal grey scale. At last, it is can be achieved to simulate laser disturbing effect under the different gains based on the relation of signal/noise grey scale and CCD gain. The research results can provide technical support and theoretical reference for evaluating laser disturbing effect of electro-optical imaging system under the different gains.

TiC enhanced coating has excellent properties, such as high hardness, wear resistance, oxidation resistance, etc., and it is widely used on the surface of tools and mold. Laser cladding is an ideal method of preparing TiC enhanced coating, but the usually used mechanical mixing powder method is even more difficult to mix the powder even, which directly affects the generation of TiC particles. A new method of sol-gel is used to prepare even TiO2-graphite mixed powder, and the TiC enhanced coating is made by TiO2-C in-situ synthesis through diode laser irradiation on 45# steel substrate. The phases on the coating surface, microstructure and hardness of the enhanced layer are tested by X-ray diffraction, scanning electron microscopy, micro-hardness tester, respectively. The influences of laser power, scanning speed, gas flow on TiC distribution and microstructure of enhanced coating are investigated. The results show that the shape of generated TiC particles in enhanced coating is polygonal or irregular. On the premise that the cladding layer can be formed and TiC particles can be generated, the energy density is smaller and the gas flowing speed is bigger, more TiC particles is generated in the coating. The maximum hardness of enhanced coating reaches 1151 HV0.2 when laser processing specific energy is 250 W·s/mm2 and gas flow rate is 30 L/min.

In-situ tensile test of 2219 aluminum alloy joint by electric current supported laser welding laser under electric current is carried out using scanning electron microscope. In-situ tensile test is employed to study the crack formation, propagation and fracture mode of welded joint, and the micro fracture behavior is studied.The relationships between microstructures and mechanical properties are revealed.The results show that the crack initiation mainly arises on the interface between eutectic phase and matrix and in the matrix between dendrites in the weld zone.The crack propagation is done in two ways of intergranular and transgranular propagation,and the crack propagation is prevented obviously by eutectic phase. The samples break with the mixed model of normal fracture and shear fracture in the weld zone.The effects of electric current on refining solidfication structure, homogenizing eutectic phase and increasing solute solid solution in the weld matrix prevent the crack formation and propagation,which is help the to increase the strength of aluminum alloy welded joint.

Ultrafast magnetization precession in the FePt film with weak magnetocrystalline anisotropy is studied using the all-optical method. The magnetization precession is induced by femtosecond laser pulses, and its dynamics is measured by time-resolved magneto-optical Kerr spectroscopy. After fitting and theoretical analyzing, field-dependent and excitation-energy-dependent precession frequency and Gilbert damping factor are obtained. Frequency equation deduced based on micromagnetics and the experimental condition can well explain the nonlinear field-dependence of precession frequency. Frequency is found to increase with the increasing excited energy, and can be attributed to the higher equilibrium temperature. In addition, intrinsic damping factor which is much smaller than that observed in L10-FePt film reported in recent literature is obtained. The effective damping rapidly decreases with the increasing field, and that can be attributed to the magnetic inhomogeneity. Moreover, it is found that increase of excited energy can slow down energy dissipation of the uniform magnetization precession.

In order to reduce the influence of airborne platform’s vibration on the accuracy of measurements, the propagation models are established for laser beam pointing error of airborne light detection and ranging (LiDAR). The platform’s vibration is decomposed into linear-vibration and angular-vibration. Then error propagation models for the two types of vibration are built respectively. Rules of that positioning accuracy influenced by linear-vibration and angular-vibration are also studied. The results show that linear-vibration of x would bring positioning error of y and z only when there is a slope on the measured ground, while the positioning accuracy of x is isolated from the other two directions. Angular-vibration has a significant influence on the accuracy of horizontal positioning. Positioning accuracies of y and z are only influenced by rolling vibration, while the pitching and yawing vibration are two main source of positioning error of x.

Currently, image retrieval is based on images color, texture, shape and other characteristics to match. The speed and accuracy of retrieval can not meet the needs of users. Image retrieval based on scale invariant feature transform (SIFT) is carried on. But there are too many feature points and dimensions, which has an impact on real-time retrieve. Locality preserving projections (LPP) in SIFT is used to reduce dimension in order to reduce number of feature points. The enhanced approximate nearest neighbor method is used to improve the accuracy of the match. A secondary judgment mechanism is added, when it is matching. If they are possible match points, handshake confirmation is executed. Experimental results show that based on the experimental verification of 20 images in image library, the improved SIFT algorithm improves the timeliness and matching rate of image retrieval. So that, it can be well applied in image retrieval.

Aiming at the characteristics of pulse laser such as high peak power, low repetition frequency, limited duty cycle and so on, the existing optical wireless communication modulation schemes are analyzed and improved, symbol structure of the improved modulation schemes are given, their performance of average transmission power, bandwidth requirement, and transmission capacity are analyze and compared. Deduce the packet error rate based on the ideal additive white Gaussian noise channel model. Theoretic analysis and simulation show that pulse midth modualation has the largest transmission capacity.If it is used to modulate pulse laser, it can not only overcome the limitations of pulse laser, but also achieve good performance, so it has application mospect in optical wireless communication system to some extent.

A single pump polarization-insensitive and widely tunable all-optical wavelength conversion for 10 Gbit/s non-return-to-zero (NRZ) signal is experimentally demonstrated by means of four-wave-mixing (FWM) in highly nonlinear photonic crystal fiber (PCF). The residual birefringence in the 50 m dispersion-flattened guarantees the FWM-based wavelength conversion to be polarization insensitive when the pump polarization is exactly at 45° to the birefringent axes of the PCF. Experimental results show that the polarization dependence of FWM in the PCF can be decreased to be less than 1 dB over 28 nm of wavelength tunable operation.The conversion efficiencies are better than -13 dB and the Q factor of idler signal is larger than 7 over the conversion range with signal polarization change.

A homodyne Brillouin optical time-domain reflectometry (BOTDR) based on Raman amplification is proposed to achieve the fast and single-end measurement of temperature and strain in long-range distributed optical sensors. In this method, Raman amplification can be used to enhance multi-Brillouin peaks power in order to improve the power of the Brillouin beat peaks, which can effectively improve the signal-to-noise ratio (SNR) and sensing distance of the sensing system. The co-Raman gain，counter-Raman gain and bidirectional-Raman gain are achieved by solving the coupled equation of the Raman amplification and the power distribution of Brillouin beat peak in front-end Raman pumped system is derived. Take a 50 km large effective area fiber (LEAF) as an example, when the front-end Raman pump power is 800 mW, the lowest SNRs of two Brillouin beat peaks appear at the front end of the LEAF and they are respectively 26.4 dB and 21.5 dB. The SNRs in the rear end of the LEAF are 70.9 dB and 46.8 dB, respectively. The results show that by using the proposed method, the optical fiber sensing dynamic range can be increased by 11 times without degrading the measurement accuracy and speed.

The mechanism of temperature effect on fiber length by heat expansion and cold contraction effect have been analyzed theoretically. Experimental verifications have been carried out by different lengths in different wavelengths. Experimental results show that in different wavelengths, single-mode fibers of different lengths change little per km when the variation of temperature is 1 ℃. For fibers of different lengths, when the variation of temperature is 1 ℃, the variation of single-mode fiber length is proportional with fiber length, which is consistent with theoretical analysis results.

For the purpose of measuring micro strain of a stretched metal panel, a measurement system including a fiber sensor is designed, which works at 1550nm central wavelength. The fiber sensor is actually a small circle of multimode fiber, fixed vertically on surface of the metal panel. When the metal panel is stretched, the sensing circle produces strenuous bending loss effect, leading to violent fluctuation of light intensity of back Rayleigh scattering. The measurement system of axial micro strain is set up according to the principle of optical time domain reflectometer and the light intensity of back Rayleigh scattering is acquired so that the strain of metal material is calculated. It can also realize distributed and real time measurement. The experimental results show that sensitive radius range of the bending loss multimode fiber sensor is within 3~6 mm, calibration measurement range of micro strain is about 500~3000 με, measurement precision of micro strain is about 40 με.

Phytoplankton absorption coefficient is an important parameter for ocean optics. The parameter varies widely with different locations and time. In order to model the phytoplankton absorption coefficient, application of the cluster analysis on the retrieval of phytoplankton absorption coefficient based on a non-linear model of phytoplankton absorption coefficient is discussed. The method reduces the error due to different optical properties of phytoplankton in different areas. By calculating adjusted Rand index (ARI) between the second derivative reflectance and absorption spectra at different wavelengths, the spectral range of 555~681 nm is found to be more sensitive than other bands. The spectral band of 555~681 nm is applied to analyze the second derivative reflectance. In situ data are used to validate the cluster analysis method, and it is found that the cluster analysis is effective for phytoplankton absorption model (root mean square error is higher than 0.79). The study is a fundamental research for application of optical remote sensing to retrieving phytoplankton information and ocean component.

Aiming at the communications requirement of inter-satellite links laser ranging, a scheme of using four-quadrant detector as the communications detector and simultaneous tracking for the communications laser is proposed. The system can complete the communications and tracking missions in the condition of single detector. The corresponding communications and tracking compound mode experiment is established in laboratory and the detection performance which includes communications rate, limiting sensibility, photoresponse ability is tested. The calibration and extraction of communications laser miss distance is using low pass filter to deal with the modulate signal by the characters of Manchester code. When the laser spot could not cover all quadrants of the detector, the output communications signal is optimized and selected to improve the signal-to-noise ratio(SNR).The experimental results show that by using the PIN type InGaAs four-quadrant detector which photosensitive surface diameter is 1mm, the communication rate can achieve 10Mbps , the detection limiting sensitivity is -33 dBm and the SNR is 10-7。Initially the feasibility of four-quadrant detector in communications and tracking compound mode is confirmed and will lay the foundations for satellite miniaturization in future.