Arrangements of point light sources array with 365 nm ultraviolet LED and focusing lens are designed and optimized. Area light source with uniform illumination and high intensity is achieved based on arrangements system. Lithography experiment with contact exposure method is realized with the optimized area optical source. Lithographic patterns are consistent with mask. The lithography method based on uniform area optical source from 365 nm LED arrays has advantages of simple structure, energy conservation and environmental protection.

In the research of color digital holography with CCD-recording and lens-imaging, each monochromatic image could be regarded as an objective image projected on the CCD sensitive plane. Based on single fast Fourier transform (1-FFT) reconstruction method via zero-padding, a new reconstruction method in color digital holography is proposed. According to this method, not only the size of reconstructed images in different monochromatic light is same, but also the influence of lens′s chromatic aberration can be taken into account. The study demonstrates that the influence of lens′s chromatic aberration is equivalent to an offset of reconstructed image apart from ideal imaging plane. Fortunately, in digital holography the reconstructed image has a certain focal depth. Thus, the influence of lens′s chromatic aberration may be ignored in most cases. Depending on nominal lens′s focal length supplied by manufacturer, a reconstructed color image that meets practical requirement can be got.

In order to improving the ability of objective recognition with optical joint transform correlator (JTC). A novel algorithm for the correlator output image is proposed. The experimental results show that this algorithm can accurately identify the object with rotated range form -4° to +10° and scale range from 70% to 140%, improve tremendously the distortion unchanged tolerance.

Defect detection of three-dimensional structures is essential for intelligent laser robot system. A method to detect structural damages in robot laser remanufacturing is presented, and a high precision algorithm is proposed to predict edge locations of damaged part. Initial edge points of the damaged parts are identified using normal-vector technique based on accumulation of the characteristic areas of the mesh vertices. A three-step optimization strategy is proposed to solve gaps, branches, and serrated boundaries of the initial edges. Finally, closed defect edges are predicated with high accuracy. The proposed method is fast for structural damage detection with high precision, which is necessary for industrial applications of intelligent laser robot system.

AZ31B magnesium alloys and 201 stainless steel are joined by laser welding-brazing process with Mg based filler. The welding characteristics including influence of processing parameters on weld appearance, mechanical properties and fracture behavior are studied. Results indicate that satisfactory appearance of welds without evident defects can be achieved by dual beam laser-brazing process with filler. A wide processing window is obtained. The tensile-shear test shows that fracture occurred at two places, weld seam and heat affect zone (HAZ) at the welding side of Mg alloys. The maximum shear strength can reach 193 MPa, which is 71% of that of Mg base metal. The microstructure observed indicates that seam and HAZ are weak parts, which results in failure of joint due to presence of coarse grains. Metallurgical reaction occurs at the brazing side, where reaction layer with thickness of 1~2 μm forms.

Aiming at the disadvantages of existing powder feeding nozzle, which include powder convergent inferior, powder outlet is easy to block and thermal deformation, designed a four hole coaxial powder feeding nozzle. The center of nozzle is laser beam as well as shielding gas channel and the four holes which along the center bore axially uniform distribution is powder channel. Numerical calculation model is established by using FLUENT software on the powder flow numerical simulation under the condition of the powder feeding channel outlet in different shape and different dip angle, and the optimal scheme is selected. The results show that the contraction of export and the powder channel angle of 70° is beneficial to improve the cladding forming effect with other process parameters invariable. Finally, with the developed powder feeding nozzle for powder together, laser cladding forming test and so on, validates the experimental effect of powder feeding nozzle.

The fluxless fusion welding-brazing result between 6061 aluminum alloy and galvanized steel with filler material is studied by using rectangular laser beam. The dependence of the mechanical properties on solidification behavior is established based on the joint formation and the weld microstructure. The results indicate that a fusion welding-brazing weld of AA6061 and galvanized steel without flux can be achieved using the welding with filler powder. By optimizing the welding parameters, the favorable weld without crack and porosity can be achieved. The weld width and the thickness of intermetallic compounds layer increase with laser energy input increasing. The intermetallic in the weld is composed of Al-Fe and Al-Fe-Si system phases. Specimens are fractured at the weld/steel interface with the brittle characteristic during tensile test. The weakness of the joint is the weld interface. The maximum intensity of 152.5 N/mm is obtained. Al5Fe2Zn0.4 and α-Al are found in the fracture surface on the aluminum side. The intensity of joint is both determined by weld width and the thickness of intermetallic compound layer.

Supersonic chemical oxygen iodine laser is a complex process including flow, chemical reactions and lasing. In process of power extraction, output of laser has a direct influence on flow fields and species, which will affect beam quality and power of lasers. Influence of power extraction on inner flow field of the laser has been numerically investigated based on computational fluid dynamic coupling procedures of paraxial wave function. Numerical results show that as power extraction process takes place, consumption of singlet delta oxygen is enhanced since pumping reaction is accelerated, concentration of iodine molecule is elevated, and changing direction of intracavity temperature via power extraction process depends on extraction efficiency. Intracavity temperature arises in high extraction efficiency cases and decreases in low extraction efficiency cases. Computational method in this paper provides an effective tool for research and development of chemical oxygen iodine lasers.

Using a resonant two-stage amplified system structure and the laser unit block design methods, high-power pulsed solid-state lasers for industrial are developed. The average output power of 957 W runs continuously for 2 h. The technical parameters such as power instability of 2.5%, photoelectric conversion efficiency of 3%, beam quality of 22 mm·mrad are achieved, and the laser is coupled into the 0.6 mm fiber. In the amplification stage behind the highest output power is up to 1125 W.

In order to describe the acoustic wave quantitatively induced by laser breakdown, an improved method for computing underwater acoustic wave induced by laser breakdown is presented based on model of point source. Acoustic wave induced by laser breakdown with single and multiple regions is computed based on wave equation and underwater explosion theory. The characteristic of acoustic signal such as pressure waveform, sound source level, transmitting and directivity is analyzed quantitatively, and it is verified through the experiment data contrast. The results show that the coincidence between the computed and experimental data validates the theoretical model. As the laser energy increases from 0.1 J to 0.8 J, the sound source level increases from 182.4 dB to 188.2 dB, but when the laser energy exceeds 0.3 J, sound source changes slightly. The power of acoustic signal is highest in vertical direction of cylindrical region of plasma, and lowest in parallel direction. The intensity of acoustic wave makes an inverse proportion to the square of distance in all directions.

In order to resolve the complicated structure and higher cost problems with current vectorial polarized beams (VPB) generating devices, a new method of generating vectorial polarized beams is proposed by using a ring device with many linear polarizer components concentric circles which is called polarization axis finder (PAF). Based on the special structure property of PAF, nature light emitted by a light emitting diode (LED) encounters the PAF, and then the azimuthally polarized beam (APB) is formed. A polarization transformation of APB to radially polarized beam (RPB) is consisted of two half-wave plates with angle of 45° between the two fast axes. The intensity distributions with different polarizer directions for vectorial polarized beams are observed. The experimental results generally agree with the results previously reported, which can verify the validity and practicality of this method.

For the special power requirements of the laser module, which is consist of the multiple laser diode (LD) chips series driven and the power of synthetic by combining the fiber, a small high-efficiency laser current source component is designed and developed, and a small high-efficiency semiconductor cooling thermal electrical cooler (TEC) fiber-coupled laser module temperature controlling component is presented as well. The component operating temperature range is from -45 ℃ to 55 ℃, and the result that the design can meet the performance requirements has been proved in the experiment. The mathematical model of LD module driving current source circuit is established. The digital design method of a laser current source controlling circuit is presented, and achieved using ADuC831. The temperature controlling component structure of a LD module based on the TEC is introduced, a simplified mathematical model of the temperature control component is established, and the coefficient of performance of the TEC ξ, the controlling side of the heat Qc and the operating current I of TEC are optimized to solve the problem of laser output wavelength drifting with temperature.

The diffraction efficiency of compression gratings in chirped-pulse amplification is very crucial to obtain terawatt femtosecond laser. Although the gratings are located in vacuum chamber with oil free, the gratings illuminated by laser beam are still subjected to carbon contamination in the vacuum condition, and results in degradation of diffraction efficiency. Moreover, additional energy deposition on the surface of grating will lead to irreversible changes of the grating structure or even catastrophic damage. A plasma cleaning technique is introduced to realize cleaning of carbon layer on the grating. The diffraction efficiency of grating is obviously improved after cleaning. It is demonstrated that the plasma cleaning is an effective on-line technique to repeatedly recover the high efficiency of compression gratings before damage occurs due to excessive carbon deposition.

In order to solve the manual detection drawbacks of laser gyroscope cavity adjustment, such as low quality and low efficiency, a multi-sensor information fusion detection method is proposed using a CCD camera and a photomultiplier. The center of the facula and the diaphragm and the loss of laser gyroscope are obtained and then transmitted to the fusion center. After fusion calculation, the integrated judgment is produced. The fusion system utilizes the momentum back-propagation neural network (BPNN) to fuse the multi-source information and output the final decision. And according to the modes of the detected signals and output decision, a three layers topology structure including an input layer, a hidden layer and an output layer is designed. The experimental results indicate that the accuracy of the proposed cavity adjustment detection method is 93.81%, which is higher than the manual step detection method using a single sensor about 6%.

Original model and scaling model for an inner optical system are designed. Considering angular spectrum diffraction theory of light with heat conduction theory and thermal elastic theory, thermal deformation aberration and wavefront pre-compensation are simulated for both models. The scaling model can be numerically transformed to original model. Thermal deformation aberration is studied to indicate that astigmatism aberration is introduced with incident angle of irradiation laser. Thermal deformations and optical quality in scaling model are similar to results in original model, and the two models can realize good numerical reversion

Coherent polarization beam combining (CPBC) of multi-channel fiber lasers is studied theoretically and experimentally. Based on active phase-locking technology, phase of four fiber lasers are locked and coherently combined beam with combining efficiency of 84.9% is obtained, which indicates that coherent polarization beam combining is feasible for multi-channel, multi-module structure and feasible project are proposed.

Semiconductor laser cooling is to provide a low thermal resistance path between heat source and heat sink. Its main purpose is to reduce the external thermal resistance (resistance between the laser chip and the cooling space) to maintain a low temperature gradient and good thermal contact between the heating laser chip and cooling surface. Experimental methods are used to solve the problem of contact resistance according to the study object. Based on the single-chip combined beam module, a overall thermal resistance is analyzed gradually, software simulation and the frequency with red shift method are described for the thermal resistance of laser diode measurement. Single-chip combined beam module overall thermal resistance is less than 0.25 ℃/W. The cooling modules can be used in the 100 W-class semiconductor laser cooling requirements.

The evolution of spikes formed on silicon surface by irradiating femtosecond laser pulses in SF6 as the increase of incident pulse energy is experimentally investigated. The spike height increases with the increase of pulse energy at first and then decreases with the pulse energy continuously increasing. The increase of spike height is all due to the material ejection at the initial stage. While the high energy can not penetrate into the deep layer of silicon completely during the initial several hundreds of laser pulses, more and more energy accumulates on the topmost layer and the silicon surface is maintained in the molten state, which hinders the formation of spike structure. This leads the decrease of the effective number of pulses interacting with silicon, together with the decrease of the spike height.

A series of TiO2 single films with different oxygen partial pressures and baking temperatures are prepared by electron beam evaporation. Both the absorption and the laser induced damage threshold (LIDT) at the wavelength of 1064 nm are measured. The results show that by improving oxygen partial pressure or reducing baking temperature, the film absorption can be reduced obviously. As for the LIDT of the TiO2 films at 1064 nm, it is affected by not only the absorption but also the quality of the substrate surface. When the absorption of the coating is high, the intrinsic absorption is dominant in the laser damage process. However, when the absorption of the coating is low enough, even bits of impurities at the surface of the substrate lead to a sharp decline of the LIDT.

WSx solid lubrication films are deposited on monocrystalline silicon substrates by pulsed laser deposition (PLD). The composition, morphology and microstructure of the films are characterized by energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and X-ray diffractometer respectively. The tribological behavior is investigated using a ball-on-disk tribometer in atmosphere (relative humidity is 50%~55%). The results show that the composition of the film was controllable while the atom fraction ratio of sulfur to tungsten ranges from 1.05 to 3.75 and the friction coefficient ranges from 0.1 to 0.2. The friction coefficient and film quality deteriorates dramaticly when the ratio of sulfur to tungsten exceeds 2.0. It is well-established that the rank of main influence factors related to the ratio of sulfur to tungsten of the WSx films are argon pressure, temperature, target-substrate distance and laser flux by orthogonal test, and a near-stoichiometric WSx film with dense structure could be grown under optimized growth conditions, including deposit temperature at 150 ℃, distance between target and substrate at 45 mm and laser flux at 5 J/cm2 and argon pressure at 1 Pa.

The far-field propagation model of annular plane beam through Kolmogorov atmospheric turbulence is presented and the nonlinear response characterization, such as so called "dead zone" and nonlinear saturation effect of CCD sensor are considered as well, the theoretical far-filed irradiance profiles of annular beam with obscuring ratio 0.5 under different turbulence strengths and their corresponding measurement results with CCD are calculated. The parameters of peak Strhel ratio RS, beam quality factor β and encircled energy ratio Ree are taken as evaluating far-field spot quality. The influence of dead zone and nonlinear saturation effect of CCD on measurement results of far-field spot profile and beam quality are analyzed, and the approaches to eliminate the measurement errors are discussed.

The azimuthal alignment scale of current azimuth alignment system based on sine wave magnetooptic modulation is narrow. The principle of azimuth alignment system and the mixed signal′s component from the modulator are analyzed, then an azimuth automatic alignment method in spatial wide-angle scale is present. The method of estimate azimuth is established based on the phase comprison between the modulation signal and the atternating current (AC) signal from modulator, and the independent measurement model of the initial light intensity signal is established according to the lower instrument′s initial setting place and running way, then the model of measuring glancing azimuth is presented based on the collected direct current (DC) signal from modulator in wide-angle scale, the lower instrument is controlled by the glancing azimuth signal and turned into the little-angle scale. The model of measuring azimuth accurately in little-angle scale is established based on the collected AC signal from modulator. Two models cooperate together to assurance the azimuth automatic alignment precision in wide-angle scale. The simulation results show that with the method, the system′s theoretic automatical alignment scale is -90°~90°, it can solve the current problem effectively.

In order to realize precise diagnostics for pico-second pulse of peta-watt laser, an auto-correlator especially for single shot pico-second pulse is developed. Optical elements with no dispersion are used in this pico-second auto-correlator′s design, which could improve its precise. Three methods are adopted to testify its characters. Self-calibration is used for time resolution. Over-range is used for time range. Limitation is used for impulse response function. Experiments results show that its time resolution is 0.1 ps/pixel, its time range is 26 ps, and its impulse response function value is 300 fs. So this auto-correlator can fulfill the requirement of precised measurement on pulse width for chirped pulse of pico-second peta-watt laser.

Based on the method of T-matrix, a detailed comparison of the distribution of light scattering Muller matrix elements with scattering angle on the polydisperse model, the monodisperse model and the equal-volume-sphere model of fractal structure of smoke particles is produced by flaming n-heptane, under the laser wavelength of 300, 633 and 800 nm respectively. The results show that scattering light could reflect the characteristics of the fractal structure of smoke particles and the distribution characteristics of primary particles in smoke particles when λ is equal to 300 nm, then the light scattering characteristics of fractal structure of polydisperse model and monodisperse model become identically when λ is equal to 633 nm, meanwhile, the light scattering characteristics of three models about the smoke particles produced by flaming n-heptane tend to be consistency when λ is equal to 800 nm.

Frequency stability of two independent lasers with the same model is measured by using beat frequency technology. By using the theory of beat frequency, frequency stability of the beat signal is deduced, which can be expressed by the sum of squares of the frequency stability of the reference laser and the measured laser. From the above relationship, the frequency stability of measured laser with the same model with reference laser can be obtained. Two independent lasers (TLB-6017) with the same model produced by New Focus company are used in the experimental measurement, and the results show that the frequency stability of the measured laser is about 1.36×10-8 and the frequency shift is 5.1 MHz at the averaging time of 1 s. Frequency stability is in the same level with the technical specification (frequency stability is about 1×10-8 and frequency shift is about 5 MHz at the averaging time of 1 s), and the relative error of frequency shift is about 2%. The provided method avoids conventional limitations which need a higher stability laser as reference laser.

A new method is proposed to enhance dynamic range single-short measurement of nanosecond optical pulses. A fiber pulse replication loop system is developed to generate temporal replicated pulse train with an exponential decay curve, and the effective loop gain is 0.955. By compensating each pulse to the same amplitude and averaging 18 pulses in the front of the replicated pulse train, the dynamic range can be improved more than 2.74 times. It can meet the need of 1001 high dynamic range inertial confinement fusion pulse measurement by combination PIN diode in conjunction with oscilloscopes.

Based on the rotating-compensator ellipsometry (RCE), a method of phase retardation measurement of wave plates based on the self-calibration method is presented. The new method takes retardation of compensator as an unknown parameter, constructs four nonlinear equations, and calculates the retardation of wave plates under test. The method uses the self-calibration of compensator to eliminate the systematic error caused by its retardation′s inaccurate calibration. Especially, it is more convenient for retardation measurement in many wavelengths. Based on this, the measuring accuracy of system is analyzed and simulated. It is found that the maximal systematic error and random error are 0.036° and 0.04°, respectively, over all the samples. Besides, a quarter wave plate (QWP), a half wave plate (HWP), a 127° wave plate and the air (without sample) are measured at 517.3, 525.0 and 532.4 nm, respectively, to evaluate the performance of the system, where the retardation of air indicates the measuring accuracy of the system, and is consistent with error analysis.

A novel dual-wavelength (DW) sampled fiber Bragg grating (FBG) is proposed. Phase shift between two adjacent FBG units is achieved by increasing direct current (DC) refractive index of FBG. The FBG with only identical ±1 order reflective spectrum is optimized with cosine sampling function. This method has the advantages of flexible wavelength design, low fabrication precision and low cost. Comparison between uniform DC phase shift FBG, sample DC phase shift FBG and traditional discrete phase shift FBG is made. Uniform DC phase shift FBG and sample DC phase shift FBG are fabricated, which show a good agreement with theory. DW filter with channel spacing 0.08 nm is fabricated, and the experiment results verify the feasibility of this proposed method.

To expand the range of strain measurement, a new method is proposed by using two distributed feedback (DFB) lasers as light source of optical time domain reflectometry-fiber Bragg grating (OTDR-FBG) sensing system. The corresponding nanosecond pulse driving circuits and the temperature control circuits are also designed. The driving pulse widths of two lasers are 3.10 ns and 3.18 ns, and the pulse amplitudes are 4.40 V and 4.08 V, respectively. The temperature control circuits have the accuracy of ±0.04 ℃. According to the measurement, the nanosecond pulses and temperature control accuracy can meet the requirements of OTDR-FBG sensor system.

Based on coupled-mode theory and transfer matrix method, the general transfer matrix for evaluating cascaded long-period grating and fiber Bragg grating system (CLBG) is obtained. Through general transfer matrix, the reflection spectrum of CLBG is simulated, and the theoretical simulations agree well with the relationship of two reflected peaks given in the known paper. Effects of the length of fiber between long-period fiber grating (LPG) and fiber Bragg grating (FBG), film refractive index and thickness on coated CLPG are discussed. From simulation results, reflection peaks affected by LPG and FBG in CLBG are sensitive to changes of the film parameters, and resolution on the film refractive index is 2 orders of magnitude higher than that of single coated LPG, which shows that coated CLBG has important application value in sensing field.

A scheme for generation of frequency quadruple optical millimeter-wave signal to overcome chromatic dispersion is proposed. With radio frequency signal phase, bias, modulation index, and base-band signal gain adjustment, a dual-drive Mach-Zehnder modulator is used to generate frequency quadruple optical millimeter-wave signal only carried by one second-order sideband which solves the problem of time shift of code caused by chromatic dispersion, so the transmission distance is extended greatly. Theoretical analysis and simulation results show that the eye diagram keeps open and clear even when the optical millimeter-wave signals are transmitted over 120 km and the power penalty is about 0.45 dB after fiber transmission distance of 60 km. Furthermore, due to one pure optical component carrying no signals, a full duplex radio-over-fiber (RoF) link based on frequency reuse is also built to simplify the base station. The bidirectional 2.5 Gbit/s data is successfully transmitted over 40 km standard single mode fiber with less than 0.6 dB power penalty in the simulation.

A kind of dual-core highly birefringent photonic crystal fibers (PCF) is proposed. The model introduces the asymmetrical structure through replacing the innermost eight air holes with four elliptic air holes. The mode birefringence, coupling length and dispersion characteristics are studied by changing the hole size between the two cores, ellipticity of elliptic air holes and hole pitch. The results show that the mode birefringence is up to 10-2, the coupling length is as short as 0.1367 mm, and the dispersion is very flat from 1.0 μm to 1.6 μm.

Multilevel coded modulation (MLCM) scheme is proposed for the application of combination between pulse position modulation (PPM) and binary correct coding. The bits demodulated from one PPM symbol are divided into different subcode channels by using the multilevel labels structure of multilevel coding, and the multiple-step demodulation and decoding (MSDD) algorithm of the scheme is derived with signal set partitioning and maximum-likelihood detection of PPM. Simulation under weak turbulence shows that PPM MLCM gets 0.85 dB gain over single-level coded modulation under the bit-error rate (BER) of 10-6, and it can provide unequal error protection to in formation with different importance. When the subcode types are given, the system with the subcodes configuration in order of error corrective ability in levels, as well as MSDD being used, will have good error performance, much better than direct parallel decoding method.

In structural health monitoring, performance degeneration of optical fiber Bragg grating (FBG) sensor will seriously affect the whole monitoring system′s stability and accuracy. High temperature, high pressure and many other bad conditions may cause FBG sensor performance degeneration. Therefore, in this paper, the theory that fiber Bragg grating sensor performance degeneration caused by temperature is analyzed. Influences of different kinds of FBG sensor on performance degeneration are analyzed quantitatively by numerical simulation and temperature cycling experiment. The experimental results show that performance degeneration of FBG is related to its own reasons. For normal FBG sensors, its peak value of reflective spectrum decreases with the increasing of the cycle numbers. For FBG sensors containning some hydrogen molecules, with the numbers of cycle increasing, its peak value of reflective spectrum decreases, and its central wavelength shifts towards short wavelength.

The coaxial three-mirror optical system has the advantage of small volume, easy to assembly and high quality image, which can be widely used in the field of aerospace remote sensing. The initial configuration parameters of the system are resolved by using the primary aberration theory, a coaxial field-bias three-mirror optical system with a focal length of 25 m and F number of 12.5 is designed. The design results show that the field of view of the system can attain to 0.6°×0.3° by offsetting the rectangle field with low parasitic light and compact structure, by using the folded mirror, the total length is about f′/6.0~f′/6.6, which is suitable for linear array time-debyed-integration charge coupled device (TDI-CCD) sensor to push-scanning image. The modulation transfer function (MTF) is higher than 0.47 at 50 lp/mm and the image quality of the optical system approaches the diffraction limit. The optical system provides a good option for the field of high-resolution space-to-earth fine observation.

In order to realize the high accuracy alignment of co-axial eccentric-pupil three-mirror system, and to improve the image quality, the micro-stress installation of large-aperture aspheric mirror and system benchmarking adjusting techniques are investigated. The optical calibration and mechanical calibration of primary mirror, secondary mirror and third mirror are unified by using optical alignment machining. The assembly of three mirrors, also the aberration adjustment of two-mirror system and three-mirror system are realized by the instruct of wavefront aberration distribution which is gained from Zygo interferometer. The pupil of coaxial three-mirror system is eccentric, and the sweeping direction is vertical with the linear charge coupled device (CCD) direction, the system astigmatism brought by the tilting of folded-axis mirror is removed by rotating the folded-axis mirror and trimming the neighboring circle. Alignment results indicate that the image quality targets of optical system′s each field-view are achieved, the root mean square (RMS) of optical system is less than 0.07λ, and the modulation transfer function (MTF) is larger than 0.57.

An automatic classification method for urban area lidar point clouds is proposed. A segmentation algorithm named topology heuristic segmentation to process regular grid height image is used. A separation for terrain objects and off-terrain objects is carried out with Otsu clustering algorithm and adjacent regions is merged. The typical off-terrain objects could be detected by using topological models, the tree can also be detected by multi-echo ratio of region. An experiment is done with a typical urban cloud points, the result shows that the algorithm has good classification accuracy and strong practical value.

Streak tube imaging lidar (STIL) is a new type of flash laser radar. The characteristic of STIL is wide field of view and high resolution. The exact streak data extraction is crucial in the three-dimensional reconstruction of the target. The deviation caused by the noise and CCD sampling has been ignored by the existing peak detection method. It causes deviation when the data of the streak image is extracted. Based on the analysis of the returned waveform and the theory waveform, a method of streak data extraction algorithm is presented and it not only eliminates the deviation but also filters the system noise effectively. A ladder imaging experiment is designed to verify the accuracy of the algorithm. It shows that this algorithm can improve the accuracy of streak data extraction obviously.

The detection performance of range detection laser radar which uses a single Geiger-mode avalenche photodiode (Gm-APD) with single-pulse is reported. Based on the model of single photon detection with a Gm-APD, research on the detection and false alarm probabilities (PD and PFA) with accumulated single-pulse detection at long dead-time is done. Research on the influence on PD and PFA is done, when the location of target bin in the strobe gate and the mean signal photoelectrons vary. The PD and PFA under different numbers of accumulated detection are compared and analyzed. Theory and numerical results show that accumulated detection can improve the detection performance, and when the accumulated number increases to three times, the detection performance can be very significantly improved; good control of the opening time of the strobe gate can significantly improve the detection performance; when Gm-APD receives a laser pulse, only four photoelectrons can make the detection performance best.

Because the signal noise ratio (SNR) of the optoelectronic information in the Brillouin scattering spectrum of distributed sensing systems is too low, the measured inversion becomes very difficult. In order to extract features for Brillouin scattering spectrum of distributed sensing systems in high accuracy, a novel hybrid algorithm based on Levenberg-Marquardt (L-M) and particle swarm optimization (PSO) is proposed. PSO is applied to get a volume of gross unites which served as the initial value of L-M, then output the result of L-M as the final result. This algorithm overcomes the premature local extremum of PSO and excessive dependence for initial value of L-M. It can ensure the efficiency and precision of the value. Numerical results show that the algorithm can be used in different weight ratios, different line widths, low SNR and scattering spectrum parameter estimation in large scope. The error of the hybrid algorithm is 2.18838 MHz with SNR of 10 dB, which is better than the other two. The experimental results indicate that the new algorithm can extract features for Brillouin spectrum with different pulse widths. It can increase the accuracy of Brillouin scattering spectrum.