A narrow single pass band tunable microwave photonic filter (MPF) is designed and experimentally demonstrated based on the theory of wavelength-selective amplification of Fabry-Perot (F-P) laser with optical injection. Through changing the injection locking parameters, we investigate the influences of injection locking parameters on the the central frequency, insertion loss, and out-of-band suppression ratio, and the relationship between the wavelength power amplification and the cavity mode red-shift. The experimental results show that, when the injection power ratio, detuning frequencies of the master slave lasers and bias current are properly adjusted, the out-of-band suppression ratio of MPF is 27.9 dB, the 3 dB passband is 275 MHz and the frequency of MPF can be tuned from 9 GHz to 32 GHz. The proposed structure is useful for applications such as filters frequency selection and optic-electric oscillation, where require high frequency and wideband tunability.

To reduce the influences of noise and time delay on positioning accuracy in indoor visible light positioning, a new indoor light-emitting diode (LED) visible light positioning algorithm is proposed. A honeycomb topology structure is introduced to locate the indoor visible light, and its beacon node is selected adaptively. The influence of the noise on the received optical power is studied, and a mean model is used to correct the received optical power. However, the time delay of conventional time division multiplexing system is too long, and thus the clock synchronization error occurs easily. In order to meet the high precision real-time positioning, an improved time division multiplexing network system is used. A network source center node is selected through the cell division. The partial time slot is reused through time slot competing so that the contradiction between the frame length and the number of LED nodes is solved. The simulation results show that the proposed algorithm can effectively reduce the influences of target moving and clock synchronization error on positioning accuracy, and improve the real-time performance and the stability of the indoor positioning system.

The distributed polarization coupling data measured by optical coherence domain polarizer in polarization maintaining optical fiber coil (PMFC) of fiber optic gyroscope is analyzed, and a polarization coupling amplitude model of measurement point is established. It is found that the polarization amplitude coupling is modulated by broadband source coherence function, and there exists pseudo polarization coupling measurement data. Based on this, a data processing algorithm for distributed polarization coupling data is proposed and implemented. PMFC is fabricated to conduct distributed polarization coupling tests at different temperatures, and the true coupling position and intensity information are extracted. The estimation model of secondary polarization coupling error of PMFC is established, and the bias drift error of fiber optic gyroscope induced by the distributed polarization coupling in fiber coil at different temperatures is estimated. With a high precision polarization maintaining fiber coil analyzer, the bias drift of fiber coil gyroscope is measured at corresponding temperature experimentally. The estimated results agree with the experimental results well.

The limited transmission distance and coverage of point-to-point ultraviolet (UV) communication can be improved with an UV self-organization (Ad Hoc) network. Combined with the channel characteristics of UV communication, a design scheme of UV network communication transceiver device is proposed. Based on this scheme, an UV Ad Hoc network node localization algorithm is proposed, which can obtain the relative position between the nodes with the communication distance and sector information between nodes. Based on the wireless Ad Hoc multicast on-demand distance-vector routing protocol, a routing protocol of UV space division multiplexing Ad Hoc network is proposed and simulated. The simulation results under different moving areas and numbers of nodes show that under the premise of meeting communication requirements such as number of message sent, delay and packet loss rate, fewer nodes should be chosen in a certain moving area, and when the number of nodes is constant, a small moving area should be selected.

Based on the fiber network built by fiber Bragg grating (FBG), the PSO algorithm combined with the least squares support vector machine (LSSVM) was applied to the damage identification problem of 304 steel plate. Information feature of FBG center wavelength variation was used as input quantity and the damage location of steel plate structure was used as output quantity. LSSVM-based damage identification prediction model was constructed. The model was compared with the back-propagation (BP) neural network prediction model constructed under the same conditions. Damage location of steel plate structure was identified by kernel parameter σ and regularization parameter γ of LSSVM damage identification model, which was optimized by PSO algorithm. In the experimental area of 300 mm×300 mm×1 mm steel plate, 34 groups of samples were tested for damage location identification. The results show that the injury position of 33 groups is accurately identified in the 34 samples, and the accuracy rate is 97.06%. The PSO-based LSSVM damage prediction model has a self-diagnostic function.

A fluorescence microscope detection system based on digital micromirror device (DMD) is designed. The system not only can realize the fluorescence imaging of the sample, but also can detect the real-time change of the fluorescence signal energy in different regions of the sample. The video information with different frame rates in multi-channel is fast loaded by DMD in the experiment to realize the segmentation of the excitation beam and frequency modulation. The fluorescence information of the sample is collected by photomultiplier tube (PMT) and then is processed by means of analog-to-digital conversion, Fourier transform, filtering and demodulation, and the relationship curve between intensity of fluorescence signal in different channel regions and time. The experimental results show that adding DMD to fluorescence microscope system can accelerate the integration of multi-channel, the DMD channel can be controlled by computer, and the detection efficiency of the fluorescence microscope can be improved effectively.

To study the scattering characteristics of leukocytes at polarized light incidence, we modify Stokes-Müller matrix elements for polarized light propagation by using the geometric optics approximation theory. On the basis of eccentric sphere model, we numerically simulate the scattering light intensity spatial distribution of the mitochondria free leukocytes with different shapes, sizes and refractive indices with two polarized beams incident, and polarization directions of the two beams are perpendicular to each other. The relationship between the scattering characteristic and cell structure parameters, such as shape, size, and refractive index, is numerically simulated. The three-dimensional distribution of polarized light scattering shows different fringe features under different conditions, which illustrates that the distribution is relevant to physical parameters and optical parameters. The analysis of differences, ratios, and ratios of difference to sum of the scattering intensity shows that the backscattering of the polarized light can reflect rich structural information and optical information in the cell.

In order to maximize the discrete-input continuous-output memoryless channel (DCMC) transmission capacity under certain restriction of modulation scheme in wireless optical multiple input multiple output (MIMO) communication (SM-OMIMO) system with spatial modulation (SM), a novel adaptive power allocation algorithm (PAA) is proposed by the Monte Carlo simulation process. Power allocation coefficients are optimized adaptively for any signal noise ratio (SNR). A model of indoor communication environment is built, and DCMC capacity expression of SM-OMIMO is derived. The distribution principle and procedures of the algorithm are analyzed. Performance of the system is simulated. The effects of several allocation algorithms on DCMC capacity are compared under different combinations of transmits and receivers. Simulation results indicate that, under the condition of low SNR, the system DCMC capacity of system obtained by the proposed adaptive PAA is larger than that obtained by PAA with fixed factor and average PAA, and the proposed PAA is easier to achieve saturation value of DCMC capacity under the condition of high SNR. The results clearly demonstrate the diversity characteristics of the channel. Therefore, the adaptive PAA is capable of improving the transmission rate of SM-OMIMO system.

In order to reduce the temperature gradient of the laser irradiation zone of the light guide mirror surface, the three-dimensional steady turbulent flow and heat transfer equations are solved with the finite volume method, and the temperature field of the laser irradiation zone is analyzed. The effects of rectangular channel size, concentration and velocity of coolant on average temperature rise and temperature rise difference of the light guide mirror surface are studied. Accordingly, a dual-channel structure is designed. Results show that for the single channel, the temperature field of the irradiation zone is not symmetrical around the geometric center and the highest temperature point is located at the downstream of the irradiation zone. The heat transfer efficiency can be improved by the increase of the cross-section size and the coolant velocity. In addition, the temperature distributions between the different surfaces of the channels are not the same. The higher the concentration of the ethylene glycol coolant, the worse the heat transfer effect. The average temperature and the temperature rise difference of the dual-channel structure can be reduced by up to 17.79% and 67.97%, respectively, compared with those of the single-channel structure.

Two up-tapers are produced on a single mode fiber with the distance of 4.5 cm by the technology of fiber waist-enlarged fusion, so as to form a new single mode structure fiber with two spherical shapes based on Mach-Zehnder interferometer (MZI). A tunable self-seeded multiwavelength Brillouin erbium-doped fiber laser is designed based on MZI and put in the glycerol solution of different mass fractions. At the wavelength of 980 nm and the pumping power of 200 mW, the multiwavelength of the output laser is tuned from 1558.6 nm to 1562.8 nm, correspondingly to the changes of the effective refractive index of the optical fiber cladding, and the tunable range is about 4.2 nm. The six Brillouin laser wavelengths with the wavelength interval of 0.088 nm and the mean optical signal to noise ratio of more than 15 dB is obtained. The proposed laser has the advantages of simple structure, stable wavelength interval, and has great application prospect in dense wavelength division multiplexing and optical fiber sensing.

Combining a long-focus lens with a continuous medium gas target is a scheme with high conversion efficiency in high-order harmonic generation. The quasi-phase matching technique is applied to this scheme. It is expected to further improve high-order harmonic signal intensity. A multi-jet arrays gas target is applied to the generation of high-order harmonic, which is designed according to the quasi-phase matching technique. It is theoretically confirmed by numerical simulation that the multi-jet arrays gas target could improve the harmonic signal intensity compared with traditional continuous medium gas target.

A double-ring cavity fiber laser based on a high roundness microsphere cavity as the single-longitudinal-mode selector is proposed. By the improvement of the melt heating technology and surface cleaning process, microsphere cavities with high roundness and high Q are obtained. We achieve highly efficient coupling between the tapered fiber and the microsphere cavity by using a two-dimensional visual and three-dimensional high-precision coupling system. Through optimizing the polarization of incident light and the diameter of tapered fiber, we obtain whispering gallery mode (WGM) resonance spectrum with coupling efficiency of 99.5%, a 3 dB bandwidth of 1 pm and a side-mode-suppression-ratio (SMSR) of 14.5 dB. The proposed fiber laser produces narrow bandwidth laser spectra with a 3 dB linewidth less than 0.01 nm, a SMSR of 40 dB and a high stability without mode-hopping.

A novel hybrid surface plasmon waveguide structure with rounded metal ridge and low refractive index air gaps is designed. The changes of electric field distribution, normalized mode area, transmission distance, quality factor and Purcell factor with radius of metal ridge curvature are studied at operating wavelength of 489 nm. The results show that the waveguide can achieve a larger radiation enhancement factor while ultra-deep subwavelength optical field can be limited by adjustment of structure parameters. The optimal geometric parameters are as follows: nanowire radius and curvature radius are 95 nm and 20 nm, respectively. Under the optimal parameters, effective mode area is 0.0037λ2, quality factor is 268, Purcell factor is 65 and gain threshold is 0.2768 μm-1. The value of the laser enhancement is calculated as 69800. Resonant cavity of the laser has superior local ability and laser enhancement ability, and can realize low threshold excitation of ultra-deep subwavelength.

A nonlinear phase shift test method of high power laser facility based on enumeration thought is proposed for no-chirp laser pulse. Combined with the pulse waveform and the variation of energy flow, the theoretical distribution of broadening spectrum after pulse amplification is obtained under different nonlinear phase shift hypotheses. The theoretical distributions of the broadening spectra are compared with the measured ones. Then hypothetical values of the nonlinear phase shifts corresponding to the theoretical broadening spectra are the results of the measurements when the residuals are the minimum. This technique and method are not limited by the pulse time waveform,which effectively improve the confidence of the measurement results.

25 mm thick 27SiMn high strength steels are welded with the fiber laser-metal active gas (MAG) hybrid welding method, and the microstructures and mechanical properties of the welding joints are analyzed. The results show that the weld seam and heat affected zone of the root-face pass of the joints are mainly composed of martensite. The weld seam of the filler pass mainly consists of intragranular acicular ferrite, a small amount of pre-eutectoid ferrite and upper bainite, and the microstructure of the heat affected zone is mainly martensite. The microhardness distribution of welding joints is not uniform and the highest microhardness of the root-face pass is at the weld seam. The highest microhardness of the filler pass is in the coarse grain area, and the lowest microhardness is in the base metal. Tensile specimens are all broken in base metals. The impact experimental results show that the brittle fracture zone and toughness fracture zone exist in the impacted fracture of the weld at the root-face pass, while the toughness fracture zone is observed in the impacted fracture of the weld at the filler pass.

The ultra-short pule laser with the wavelength of 1064 nm and the pulse width of 10 ps is used as filamentation excitation source to induce the self-focusing effect inside sapphire creating a long filamentation trace, and the length of the filamentation trace breaks through the limitation of Rayleigh length. On the basis of different phases between filamentation region and the rest of the sapphire, we obtain fine cutting-surface of sapphire with roughness of 800 nm with the help of chemical corrosion. Arbitrary cutting paths can be achieved by this technique. The filamentation characteristics of picosecond laser and the processing parameters for the presented technique are studied. The laser power threshold of self-focusing effect is determined to be 2.78×106 W. The effects of picosecond laser peak power, focusing position and the number of pulses on the initial position of filamentation and cutting quality are investigated. The processing parameters for realizing high precision cutting of sapphire are obtained.

The GH738 nickel-based superalloy through-groove sample is repaired by laser deposition, and the microstructure and room temperature tensile properties of the repaired sample are analyzed. The results show that the microstructure of repair zone presents typical characteristics of columnar dendrite with epitaxial growth, and the dendrites are perpendicular to the substrate and tend to grow along the deposition height direction through multiple layers. The dendritic orientation in the center of the repair area shows a large deflection. No γ′ phase is found in the repair area, the content of carbide in the area is less, the M23C6 type carbides rich in Cr and Co mainly exist in the dendrite stem, and a few cubic MC carbides with relatively larger size and higher contents of Ti and Mo exist among the dendrites. Compared to the substrate, the size of γ′ phase in the heat affected zone obviously increases, the size of partial γ′ phase exceeds 200 nm and the average distance between them increases obviously. The content of carbide in the heat affected zone reduces, and partial carbides decompose. The room temperature tensile strength and elongation of the laser deposition repair sample is 78.2% and 69.2% of those of the forging, respectively.

A finite element model of laser bending of cross-stiffened integral panel (CSIP) is established by use of sequential coupling method. The deformation process of CSIP is investigated by analyses of the temperature field and the strain field. Then a varying power scanning strategy is proposed to reduce the undesirable deformation. The results show that not only transverse bending but also longitudinal bending occur when the CSIP is scanned with constant parameters. And the skin near scanning line is sunken to somewhat extent. The analyses suggest that the nonuniform transverse bending and the existence of longitudinal plastic strain lead to the concave of skin and longitudinal bending, respectively. The varying power strategy could reduce the undesirable deformation effectively, which reduces the maximum sinkage of skin and relative bending of free end by 80% and 58%, respectively.

Yttrium aluminium garnet (YAG) single crystals and ceramics with different Ce3+-doping concentrations (mole fraction) are prepared. The luminous flux, photoelectric conversion efficiency, color rendering index, and color temperature of Ce∶YAG single crystals and ceramics under laser excitation are also analyzed. Under the excitation of the laser with a current of 2.6 A, the luminous flux of ceramics with a Ce3+-doping concentration of 0.3% is the highest at 617.2 lm. The single crystals with a Ce3+-doping concentration of 0.5% have a high color rendering index of 62 and a color temperature of 5841 K. Under the excitation of the laser with a power of 2.61 W and a power density of 10.8 W·mm-2 at the material center, the optical conversions of Ce∶YAG single crystals and ceramics are both unsaturated and the corresponding optical-to-optical conversion efficiencies are both about 240 lm·W-1. The experimental results show that the ceramics and single crystals are suited to produce high brightness white light under high power density laser excitation.

The ceramic coating is fabricated by laser pyrolyzing of polydimethylsiloxane precursors with titanium powder, and the compositions and structures of the products are also analyzed. The results show that, under the action of a high energy laser, there is a free radical reaction between the titanium powder and the polydimethylsiloxane, and the fabricated multiphase ceramic coating is composed of the crystalline-state SiC, TiC, TiO2 and the amorphous-state SiO2, elemental C, C6H18OSi2. The newly formed TiO2 and TiC ceramic phases can fill the pore of the ceramic coating, which makes the coating surface uniform and dense and the pore number reduced. The addition of metallic titanium powder is also conductive to reducing the mass fraction of free carbons in the multiphase ceramic coating. When the mass fraction of the titanium powder is 5.0%, the mass fractions of Si, O and C element in the coating are 74.44%, 16.48% and 6.19%, respectively.

Up-conversion phosphor BaxNayYzF2x+y+3z+3m∶Er3+m is synthesized by low-temperature combustion synthesis method. The phase and morphology of the phosphor are analyzed by X-ray diffraction and scanning electron microscopy, and the optimal formula is obtained by orthogonal experiment. The effects of doping concentration of Er3+ and Y3+ ions on green and red up-conversion is studied by measuring the up-conversion luminescence property of samples with different doping concentrations. The results show that increasing the doping concentration of Y3+ ion is beneficial to green up-conversion luminescence, increasing the doping concentration of Er3+ ion is beneficial to red up-conversion luminescence.

In order to obtain broadband light absorber, a compound structure model composed of graphene metamaterial layer, air layer and metal layer is designed. The transfer matrix formula is derived to compute the transmission characteristics of the designed structure. The results show that by adjustment of the structure parameters, wavelength bandwidth and angle bandwidth are expanded at the same time under the condition of high absorptance. For the incident angle π/4, the absorptance can achieve above 0.8 in the incident wavelength range of 0.1~6.0 μm. For the incident wavelength 3.5 μm, the absorptance can reach more than 0.9 in the incident angle range of -70° to 70°.

Aiming at three-dimensional (3D) reconstruction of interior space, based on dual two-dimensional (2D) laser radar, the precise calibration method of relative position and pose between two radars were presented, the consecutive collection was achieved, and accuracy point cloud contour was obtained. By the establishment of mathematical model of target parameter from scanning data of static calibration, the position and pose compensation matrix between dual 2D laser radar was obtained, which was converted into precise matrix. We established simulation platform to simulate calibration experiment and realize distortion correction of target parameters. This method was proved to be applicable through analogue acquisition experiments, where the degree of separation of point cloud was less than or equal to 7 mm. Undistorted 3D point cloud contour was acquired through the establishment of hardware platform and indoor contour acquisition experiment after calibration. The experiment results show that the calibration accuracy of relative position and pose between dual 2D laser radar could meet the requirements of 3D reconstruction in interior scene.

A spin-exchange relaxation free (SERF) rubidium atom magnetometer is developed for liquid-state zero-field nuclear magnetic resonance detection. The magnetic resonance curve of the atom is measured by the experiment. It is verified that the magnetometer is working at the status of SERF, and the result is consistent with the theory. Using the method of increasing the intensity of light, the bandwidth of the magnetometer is improved, and the bandwidth demand of the liquid zero field nuclear magnetic resonance is met. The sensitivity of the magnetometer in the frequency range of 20~300 Hz is lower than 18 fT/Hz1/2. A liquid-status zero-filed nuclear magnetic resonance device based on magnetometer is used to measure the the sample of formic acid, and zero-filed nuclear magnetic resonance spectra of formic acid marked by 13C is got. Which verifies the usability of magnetometer.

A demodulated method for fiber Bragg grating (FBG) pulse wave is proposed based on micro-structure Fabry-Perot interferometer (MS-FPI). The proposed MS-FPI is fabricated by splicing single mode fiber and photonic crystal fiber (PCF), and the micro-bubble structure is formed near the splicing end face by the special technology to constitute the Fabry-Perot (F-P) cavity, whose size is about 48 μm. In order to increase mechanical strength, the MS-FPI is coated again and thus can be woven into the fabric as yarn. Its interference spectrum remains nearly unchanged even its bending diameter is up to 4 cm. Besides, it also has very low temperature sensitivity, suitable as a demodulator filter. The proposed demodulated method is analyzed theoretically and studied experimentally. The results indicate that the designed demodulated system achieves linear demodulation in the range of the FBG pulse wave and has better measurement repeatability. The demodulated sensitivity is about 43 mV/pm. The demodulated pulse wave is consistent with the result of the commercial interrogator. By comparing with the photoplethysmography, the correctness of the pulse wave demodulated by designed system is proved.

In order to meet the requirements of high-precision real-time three-dimensional measurement of large-size free-form surface workpieces, a three-dimensional measurement system for an ultra-large scale line-structured light sensor is designed and an onsite calibration approach for the extrinsic parameters of this sensor based on one-dimensional targets is proposed. The experimental results show that the proposed calibration method has a equivalent accuracy to compare with that of the planar-target-based method. Moreover, the proposed calibration method is easier for the accurate fabrication of the one-dimensional targets, more convenient for the onsite calibration process of the extrinsic parameters, and more suitable for the calibration of ultra-large scale line-structured light sensor.

A large cathode magnetic-focusing framing image converter tube is designed and developed. The field curvatures of single magnetic lens and double magnetic lens systems are investigated at electron optical magnification of 2∶1. Based on optical lens imaging principle, the approximate relational expressions of the imaging excitation variation with the best image positions of the off-axis object are derived in the cases of single magnetic lens and separated double magnetic lens systems. It is assumed that the shape of image surface does not change with excitation in a certain scope. Accordingly, a method of field curvature measurement and decrease is proposed. Then, by virtue of Matlab programming, the best image positions for off-axis point objects are simulated, and the image surface equations are fitted, which are experimentally verified by use of the proposed method of field curvature measurement. It is showed that computer simulations agree with the experimental results within a certain field of view. Both of the best image surfaces of two systems are paraboloids of revolution. But the field curvature of double magnetic lens system is obviously smaller than that of single magnetic lens system.

The history, present situation and future development trend of volume holographic storage technology are reviewed based on the timeline. The principle and characteristic of volume holographic data storage are introduced and the development process at home and abroad is summarized. Then key techniques such as driver technology, recording materials, channel processing technology are summarized respectively. The Latest development of phase encoded and polarization volume holographic data storage is introduced. Finally, the technical problems that affect the practical application of volume holographic storage are analyzed. It is considered that the inter-page crosstalk noise, the material scattering noise and the material shrinkage are the three bottlenecks that limit the storage density, which need to be solved in the follow-up study.

Operation characteristics of an injection-seeded terahertz parametric oscillator based on ring-cavity configuration are reported. The nonlinear crystal used in the experiment is MgO∶LiNbO3. The terahertz wave is emitted perpendicularly to the output surface. The Stokes ring-cavity is constituted by three mirrors and total reflection surface of MgO∶LiNbO3 crystal. The pumping source is a Q-switched laser, whose output wavelength is 1064.2 nm and pulse width is 7.5 ns. When the pumping pulse energy is 105.5 mJ and the transmittance of the Stokes wave output coupler is 20.1%, the maximum terahertz pulse energy output leads to the output voltage of 3.3 V, and the corresponding Stokes pulse energy is 16.1 mJ and the pumping energy threshold is about 10 mJ. Under the same pumping conditions, the output energy and pumping pulse energy threshold of the injection-seeded terahertz parametric oscillator based on ring-cavity configuration and injection-seeded terahertz parametric generator are compared with that of a ring-cavity terahertz parametric oscillator without seed injection. The results show that the injection-seeded ring-cavity terahertz parametric oscillator based on ring-cavity configuration has higher output energy and lower pumping energy threshold, and the oscillator has more obvious advantage in energy output when the pumping energy is smaller.

The intensity noise caused by the relaxation oscillation in lasers has a great influence on the system noise in the distributed feedback fiber laser hydrophone. The transmission process of the intensity noise in the digital realization of the NPS (Naval Postgraduate School) algorithm is analyzed, and it is found that the non-ideal characteristic of the derivation operation is the reason for the introduction of intensity noises in the demodulation results. An improved symmetric demodulation algorithm is proposed, where the intensity noise is canceled before entering the derivation operation and the way of the intensity noise transferring to the demodulation results is eliminated. The experimental results show that the demodulated phase noise suppression at 1 kHz reaches 30 dB when the relative intensity noise at the relaxation oscillation peak is -84 dB·Hz-1. The improved algorithm is compared with the arctangent method where the derivative operation is not needed and is further verified to suppress the intensity noise introduced by the derivation.

A distributed feedback (DFB) fiber laser accelerometer sensor with a vertically encapsulated structure is designed. The theoretical models of the acceleration sensitivity and the dimension parameters of the mass block are established. Based on the finite element software, the frequency response performance of this accelerometer sensor is simulated. The prototype sample of the sensor is fabricated and tested. The experimental results show that the average acceleration sensitivity of the fabricated DFB fiber laser accelerometer sensor reaches -119.1 dB in the spectral range of 10 to 4000 Hz, and the resonant peak appears near the frequency of 5000 Hz, which agrees well with the theoretical and simulated results. The working frequency band of the fiber laser accelerometer sensor is effectively broadened towards high frequency, which can better meet the requirements of engineering applications of DFB fiber laser accelerometer sensors in the high frequency field.

Based on the resonance principle of waveguide coupled gratings and optical sensing properties of porous silicon, a refractive index sensing model of waveguide coupled gratings nano-heterostructure is proposed. According to the theory of Goos-Hnchen displacement and phase matching conditions of waveguide coupled gratings resonance, the relationship model between the resonant wavelength and the refractive index of the detected sample is established, and the refractive index sensing properties of the refractive index sensing structure are analyzed. Taking the porous silicon as bearing units of detected samples according to its effective bearing mechanism, we analyze the sensitivity and the quality factor Q of the refractive index sensing structure by detecting solutions of ethylene glycol with different concentrations. The results show that the sensitivity of the refractive index sensing structure to the solution of ethylene glycol is 2.2 nm/1%, and the Q value is 226, which proves the validity of this sensing structure. The sensing structure can detect the samples with low concentration.

The calibration of exterior parameters of a 3D lidar is the basis of an intelligent vehicle perceiving environment through the lidar. Aiming at the major problems of common calibration methods including cumbersome implementation, low precision, and relying on other sensors, we propose a step-by-step automatic calibration algorithm. The first step is to get the ground equation by fitting the ground point cloud, construct the levelness function, and complete the calibration of the pitch angle, roll angle, and longitudinal displacement of the lidar by optimizing the levelness function with the particle swarm optimization (PSO) algorithm. Based on the completion of the first step calibration, the second step calibration needs to collect multi-frame point clouds containing the same calibration pole during the vehicle moving along a straight line. The calibration pole is clustered to get the clustering centers. The linear equation with multi-frame clustering centers is fitted in the two-dimensional plane, and the yaw angle is calculated according to the slope of the fitted straight line. The results show that the precision of the proposed algorithm can reach the magnitude order of 10-5, and the algorithm takes 0.5 s. The calibration precision and efficiency are greatly improved, and actual engineering demands can be satisfied. The two steps are done automatically by the program, and the calibration results with high-precision can be acquired without other sensors.

A direct detection Doppler lidar system with coherent light path which can work in high altitude area is proposed. Design of the optical path system is improved on the basis of coherent lidar system, the atmospheric molecular scattering light is used for wind speed measurement. The optical path of direct detection system is simplified by photoswitch and monostatic telescope. The photoswitch is composed of polarization splitting prism and 1/4 wave plate. The stability of optical path is improved. The etalon with fixed cavity length is adopted. The wavelength of pulse laser is tunable. The tuning range is about 10 GHz after optimization. The simulation design and equipment selection of the system are completed.

To solve the high labor cost and low efficiency problems of complex tank members extraction, we propose a point cloud segmentation algorithm which is applicable to tank of plane bulkhead type. The steps of this approach are as follows: the original point cloud is firstly transformed to the independent coordinate, whose X, Y and Z axes are defined as the longitudinal, transverse and vertical directions of tank, based on seed sets building, normal estimation and linear fitting; then clouds of each tank member are segmented in the best order by plane fitting of random sample consensus (RANSAC) method according to the distribution of complex tank members. Experimental results on two sets of point clouds show that the proposed algorithm can quickly, accurately and automatically segment the clouds of main members from unorganized clouds, which demonstrate the high reliability and practical value of the proposed method.

A new classification method for terrestrial LiDAR point cloud intensity is proposed, which uses the color information of point cloud to constrain the intensity classification. Compared with the existing method solely based on intensity classification, the proposed method uses the color-to-strength supplement to establish the fault-tolerant mechanism of the laser intensity correction results, thus improving the problem of poor classification resulted from the fact that the intensity correction model cannot get the best correction result. The data of intensity and color information of the Faro Focus 3D 120 terrestrial laser scanner are investigated in the experiment. The results indicate that the proposed method can improve the accuracy of the three-dimensional point cloud data classification and can also improve the credibility and reliability of classification results even when the intensity data are poorly calibrated.

Argon and nitrogen are widely used as shielding gas in additive manufacturing. However, the high temperature in localized melting area and the release of oxygen in the row materials can cause the difference of oxygen content between melting zone and shielding environment. Laser-induced breakdown spectroscopy is proposed to measure the trace oxygen content in argon and nitrogen near the melting zone. The experimental calibration curves are obtained from laser-induced spectra of oxygen/argon or oxygen/nitrogen mixture gas with different oxygen contents combined with the ratio of oxygen spectral line intensity to continuous background strength. Detection limits of oxygen concentration are determined to be 31×10-6 in argon and 41×10-6 in nitrogen. By analyzing the formation and decay characteristics of the plasma, we find that the electron temperature of argon plasma is higher than that of nitrogen plasma and the decay of argon plasma is slower than that of nitrogen plasma. Therefore, under the same experimental conditions, spectral line intensity and signal-noise ratio of argon plasma are stronger than that of nitrogen plasma, which lead to lower detection limit of the content of oxygen in argon.