Metasurfaces have been widely used to generate cylindrical vector beams (CVB) owing to its inherent advantages of high efficiency and compact structure. However, a disadvantage of this method is that the polarization order of the generated CVB is hard to be changed, because the structure of metasurface is fixed. To solve this problem, we experimentally demonstrate a simple and efficient method to manipulate the polarization order of CVB through modes addition and subtraction operation at the working wavelength of 1550 nm. By two cascaded metasurfaces, the subtraction operation of polarization orders is realized. Further, a half wave-plate inserted between two metasurfaces is used to reverse polarization orders, in order that the add computation of polarization orders is realized. Experimental results are in good agreement with the calculation results through Jones matrix, and the polarization order of CVB can be adjusted from -8 to 8 with step length of 2 by modes addition and subtraction.

Tissue phantoms with different optical parameters are designed to study the influence of absorption and scattering on tissue fluorescence and diffuse reflection spectra. An empirical recovery algorithm is optimized to correct the influence of absorption and scattering and obtain the intrinsic fluorescence spectrum of tissues. The results reveal that the empirical recovery algorithm (experience parameters kx and km are 0.9 and -0.8, respectively) can effectively reduce the influence of absorption and scattering on the fluorescence intensity, and the fluorescence intensity is linearly correlated with the concentration of fluorescence components. When we apply spectral recovery algorithm to the screening of diabetes based on skin tissue fluorescence spectrum, the results reveal that, comparing to the fluorescence spectrum before recovery, the area under receiver operating characteristic (ROC) curve increases from 0.54 to 0.81; besides, the sensitivity also increases from 38.6% to 77.6% when the specificity is 70.6%. Therefore, this study makes a major contribution to research on clinical application by optimizing fluorescence spectrum empirical recovery algorithm with tissue phantoms.

With the development of infrared optical fiber technology, it is urgent to develop an infrared low loss chalcogenide optical fibers with perfect-structure and high nonlinearity. In this paper, the two kinds of glass samples of As40Se58Te2 and As40Se60 are prepared by the traditional vacuum melt-quenching method and dynamic distillation purification process. Then we obtain a fine-structured chalcogenide optical fiber prefabricated rod prepared by two multi-step extrusion method. After that, the preform is drawn into a low loss step type single-mode chalcogenides glasses fiber under the protection of polyether sulfone (PES) polymer. The results show that the distillation process can effectively remove most of the impurities in the chalcogenide glasses. 2% mole percent of Se is replaced by Te, which can effectively achieve a small numerical aperture (NA) and single-mode transmission characteristics. The single-mode chalcogenides fiber loss test is measured by the truncation method with a Fourier transform infrared spectroscopy spectrometer. The minimum loss of this fiber can be reduced to 1.66 dB/m at 6.06 μm and these glasses working band is from 2.5 to 12 μm. The output of a supercontinuum spectrum covering 1.5-13.2 μm (40 dB bandwidth) is obtained with an optical parametric amplifier (OPA) as the pump source. The fiber has good mid-far infrared transmission performance and extremely high optical nonlinearity.

We design a multi-mode multiplexer/de-multiplexer based on parallel mode couplers. The multi-mode multiplexer/de-multiplexer consists of two single mode fibers and a few-mode fiber. According to the effective refractive index matching principle, the parameters of fiber are determined. The influence of different core distances on the performance of multi-mode multiplexer/de-multiplexer is analyzed, and the optimum core distance is determined. The working wavelength bandwidth corresponding to the multi-mode multiplexer/de-multiplexer is analyzed. Simulation results show that the multi-mode multiplexer/de-multiplexer can achieve the multiplexing of LP01, LP11 and LP02 modes without the need of a mode converter, the optimal coupling length is 4530 μm, and the wavelength bandwidth is 60 nm.

We propose a technique to separate the upper and the lower sidebands of an optical carrier based on orthogonal optical coherent receiving, which can be used in Brillouin scattering distributed fiber-optic sensing systems to separate Stokes and anti-Stokes scattering without loss. In the orthogonal optical coherent receiving technology, phase information of the optical field is preserved. So the upper and the lower sidebands can be arranged in coherent addition or cancellation states in different outputs, and the separation of the upper and the lower sidebands is realized. The results show that the technique can output the upper and lower sidebands from different ports, with a good linear relationship between input power and output power. The crosstalk between the separated upper and lower sidebands can be less than -20 dB. Compared with frequently employed optical filtering, this technique has no temperature sensitive component and shows good stability and robustness.

The topology dynamic optimization problem for inter-satellite laser links of global navigation satellite system (GNSS) is studied according to the technical characteristics of inter-satellite laser links. The requirements of communication, high-accuracy measurement and autonomous orbit determination for navigation satellite crosslink are also considered. The periodic tables of inter-satellite laser links for navigation satellite are established via the finite state automation (FSA), and a multi-objective optimization model of topology is set up considering the three engineering constraints as follows: satellite platform, orbit dynamics, acquisition and tracking performance of laser terminal. The two quantitative indices of networks delay and position dilution of precision (PDOP) are used to evaluate the performance of communication and high-accuracy measurement. An improved algorithm based on multi-objective simulated annealing (MOSA) is proposed and used to solve the global optimization topology structure. Dynamic optimizations can be performed especially when some satellites or inter-satellite laser links are unavailable. Meanwhile, a link exchange method with conflict avoidance is applied, as well as an improved multi-sources minimum delay routing algorithm. Finally, simulation results show that the optimized topology has good communication and measurement performance and effectively improves networks delay and PDOP in GNSS which is comprised of 24 mesospheric earth orbit (MEO) and 3 inclined geo-synchronization orbit satellite (IGSO) satellites, and the requirements of both high-speed data and high-accuracy measurement are achieved even if individual satellites or inter-satellite laser links are unavailable.

The second harmonic generation (SHG) characteristics of erbium doped femtosecond fiber lasers with different thicknesses of periodically poled lithium niobate crystals (PPLNs) are studied. Based on nonlinear polarization rotation mode locking and chirped pulse amplification, an erbium doped femtosecond fiber laser output with repetition rate of 100 MHz, output power of 423 mW, and pulse width of 80 femto-second (fs) is achieved at 1560 nm. Then we obtain 780 nm femtosecond lasers through SHG with three different PPLN crystals respectively. The thicknesses of PPLN crystals are 0.5, 1 and 10 mm. For 0.5 mm crystal, the SHG pulses with 104 fs width, 100.4 mW output power and 23.7% energy conversion efficiency can be obtained. For 1 mm crystal, the SHG pulses with 161 fs width,165.0 mW output power and 39% energy conversion efficiency can be obtained. For 10 mm crystal, the SHG pulses with 305 fs width, 185.5 mW output power and 43.7% energy conversion efficiency can be obtained. In addition, we explain how do energy conversion efficiency and pulse width of SHG pulses change with thickness of PPLN crystals. The experimental data provide a useful reference for the research of femtosecond optical pulses generated by mode-locked fiber laser at 780 nm band.

A passively Q-switched solid-state Tm∶YAG laser with MoS2 as saturable absorber is reported. In this laser, a 785 nm narrow linewidth diode laser is taken as pump source, a plano-plano cavity is used, and MoS2 nanosheets are served as saturable absorber. Passive Q-switching can be achieved successfully in 2 μm wavelength region. When the absorbed pump power is at 2.02 W, the Q-switched laser pulses are obtained with the maximum average output power of 421 mW, the minimum pulse width of 423 ns, the pulse repetition rate of 49.36 kHz and the maximum pulse energy of 8.53 μJ. The results indicate that MoS2 is a kind of saturable absorber that can be used in solid-state laser in 2 μm wavelength region. Furthermore, it provides a potential way to obtain 2 μm pulse laser.

Position shaking of reference center wavelength is the main factor which affects the accuracy of absolute wavelength calibration. In this case, peak-detection algorithms are proposed to find the real-time position of center wavelength. Five peak-detection algorithms are analyzed and compared by simulations and experiments. The error of Gaussian nonlinear curve fitting algorithm is 0.15 pm, which is the lowest in all the test algorithms. The influence of power threshold value upon the five peak-detection algorithms is studied, and the importance of threshold optimization is clear and definite for reducing peak-detection errors. After threshold value optimization, the Gaussian nonlinear curve fitting algorithm performs the best, as its lowest error is 0.04 pm and the average error is 0.06 pm. Thus, Gaussian nonlinear curve fitting algorithm meets the requirement of calibration accuracy. By analyzing factors which cause error in the peak-detection algorithms, we find that the signal noise ratio turns out to be the major factor which dominates the errors of Gaussian nonlinear curve fitting algorithm. Therefore, noise suppression is the best way to achieve high overall accuracy of absolute wavelength calibration.

For grating-feedback extended-cavity diode laser (ECDL) whose output frequency is susceptible to environmental interference, with two channel feedback loops for grating and injection current, the frequency stabilization system based on modulation-free polarization spectroscopy is optimized. Its resonant frequency is extended to 155 kHz. The laser frequency fluctuation caused by low frequency random disturbance under open loop is greatly suppressed. It can be suppressed to 1/13570 at 120 Hz. Now that laser frequency fluctuation near the atomic transition center frequency can be measured by use of the polarization spectra, and the acoustic response characteristics of ECDL are depicted experimentally with the analysis of laser frequency fluctuation and sound stimulant signal. By contrasting the acoustic response characteristics of ECDL with or without the soundproofing case, the sound insulating effect could be mapped directly. Experiment results show that sound insulating effect resulted from different frequency can deteriorate from 12.8 to 0.14. The measurement of insulating effect can also act as the experimental criteria for optimizing the design of laser mechanical structures and sound insulation systems. Furthermore,this system could be helpful for the development of acoustic precise measurement.

A fiber-optic ring laser based on semiconductor optical amplifier (SOA) is proposed. In a certain range, a single frequency output of the laser can be realized. At the same time, a new pulse instability phenomenon is found in the laser. This instability phenomenon and current regulation direction is related. The analysis and comparison experiments show that this phenomenon is caused by the photothermal effect of phase-shifted fiber gratings, and weakening the photothermal effect can make the laser output more stable.

Although the traditional 1064 nm frequency-stabilized laser can achieve high frequency stability and uncertainty, its volume is relatively large and the system design is more complicated. For some practical applications where the laser frequency stability is not critical, such as hyperspectral resolution aerosol detection laser radar, the simplicity and volume reduction of the system become more of a concern. A miniaturized compact 1064 nm frequency-stabilized laser is built by using iodine molecule absorption lines combined with frequency modulation spectroscopy technology. The system has compact structure. By monitoring with a high stable wavemeter, the accuracy of Allan deviations is less than 0.1 MHz at 10000 s. The frequency-stabilized 1064 nm laser system has been used as a seeder laser for a single-frequency pulsed light source of the hyperspectral aerosol detection laser radar.

The ultrashort pulse laser, which has a wide application prospect, can weld the glass directly. It does not need to add the absorbing medium between the two pieces of glass and does not need thermal treatment for the material. The welding of two pieces of fused silica is successfully achieved using the thermal accumulation effect of femtosecond laser pulses. In addition, the dependence of welding quality on laser repetition frequency and power is investigated. The welding zone of fused silica comprises three parts, e.g., the circular cavity on the top, the molten area in the middle and the linear damage structure at the bottom, and all the three parts make contributions to the welding strength of fused silica. The experiments show that with a laser repetition frequency of 500 kHz, the molten zone area increases with the increase of the laser power, but the welding strength increases first and then decreases. When the laser power keeps as 4.14 W, both molten zone area and welding strength decrease with the increase of laser repetition frequency. Furthermore, two pieces of aluminosilicate glass and soda-lime glass are also successfully welded and the welding end surface morphologies of the glass with different components are compared.

The experiment of laser cladding deposition is conducted via the addition of modifier B to TC4 powder. The induction heating is introduced during the deposition process, and the microstructure change of the TC4 cladding layers under different process conditions is investigated. The results show that, when the modifier B and the induction heating both take roles, the obtained grains are fine, the distribution is uniform, there are no obvious β columnar crystals, and the microstructure shows a typical basket-weave one. When the induction heating temperature is 900 ℃ and the mass fraction of B is 0.1%, 0.05% and 0.025%, respectively, the microstructures are composed of a large amount of lamellar α phases and a small amount of primary α phases, the grain length is 11-18 μm and the width is 4.40-6.90 μm.

The energetic polymer glycidyl azide polymer (GAP) is taken as the ablation target and the nano-carbon powder and infrared dye are taken as dopants. The plume of GAP is observed by the microscale plume observation system, and the influences of doping concentration, target thickness and laser ablation mode on GAP ablation characteristics and propulsion performance are analyzed. The results show that the utilization rate of absorber-undoped GAP is very low in the laser ablation process. The propulsion performance of GAP doped with nano-carbon powder is significantly improved, which is sensitive to the target thickness, and the thin GAP doped with nano-carbon powder is more suitable as the target of laser ablation micro-thruster in the transmission mode. The gasification of polymer doped with infrared dye is substantially improved and the plume is weakly affected by the target thickness in the transmission mode. The infrared dye is considered suitable as the polymer target of the laser ablation micro-thruster in the reflection mode.

Selective laser melting(SLM) technology is adopted to form AlSi10Mg alloy and the microstructure and tensile property at room temperature are studied. The results show that SLM formed AlSi10Mg alloy has fine microstructure and high room temperature tensile properties, and the microstructure and strength show obvious anisotropy. The high cooling rate in SLM process refine the previous α-Al dendrites significantly, and the different solidification conditions in the core and boundary of melt pool can not only lead to different scales of α-Al dendrites, but determine the growth morphology of α-Al dendrites, which follows the law of epitaxial growth. Combination of the morphology and evolution of Al-Si eutectic structure of sample in different orientations, the anisotropy of microstructure is investigated. Furthermore, the strength of tensile samples along deposition (L) and scanning (T) directions is almost the same, while the elongation shows double relationship, so the different mechanical properties are due to its anisotropy of ductility. The SEM morphology of tensile fracture presents the crack mechanism, the size of the dimple, morphology of Al-Si eutectic structure and formation of micro cracks prove that the crack mode is intergranular fracture. The experimental results show that the microstructure and properties of SLM formed AiSi10Mg are higher than those of conventional cast components, which make SLM technology realizable in engineering application of typical components manufacturing in the field of aero engine control system.

As for the problem that there occur warpage and deformation in the selective laser melting (SLM) forming process, a three-level progressive model of heat source-locality-structural parts is established and the layer by layer building process in SLM forming is simulated by the birth-death element method. The inherent strain is applied layer by layer to obtain the deformation prediction results of SLM forming of macroscopic structural parts. The comparison between the simulation results and the actual molded parts shows that the inherent strain finite element method can be used to effectively predict the deformation of SLM forming parts.

The 100 mm thickness SUS304 stainless steels are welded by the ultra-narrow gap laser welding, and the microstructures and mechanical properties of the joints are analyzed. The results show that the hundred-millimeter-grade thickness plates can be effectively welded by the ultra-narrow gap laser welding and the welds present good surface appearances. The microstructures of the joints are composed of austenite and small amount of ferrite, and the grains are with the cellular equiaxed shapes. The tensile strength of the joints is 658 MPa and the tensile fracture is located at the cellular grain zone near the fusion line. The fracture morphology shows fine equiaxed dimples and tearing ridges, which indicates that the fracture is ductile. The microhardness at the equiaxed grain zone is obviously higher than that at the cellular grain zone.

An orthogonal re-heating double pulse laser-induced breakdown spectroscopy (RDP-LIBS) experimental setup is built. The Coptis Chinensis is selected as the research target and the spectral intensities and signal-to-background ratios of its characteristic spectral lines are used to evaluate the spectral characteristics. The detection sensibility is improved by the optimization of detection delay, the combination of two laser energy values, the pulse interval and other experimental parameters. Compared with those by the single pulse laser-induced breakdown spectroscopy (SP-LIBS) technique, the enhancement factor of spectral intensities by the RDP-LIBS technique for the four characteristic spectral lines of Fe, Al, Ca and CN are 4.0, 5.5, 10.0 and 3.5 times, respectively. The electron excitation temperature and the electron number density of plasma by the RDP-LIBS technique are both higher than those by the SP- LIBS technique.

The as-deposited and as-forged Ti60A titanium alloys are fabricated by the laser additive manufacturing technique, and the oxidation experiment under the temperature of 600-800 ℃ is conducted. The change laws of the weight increase and the microhardnesses of samples under different oxidation conditions are investigated. The results show that, the surface oxidation products of the as-deposited and as-forged Ti60A alloys mainly consist of TiO2 and Al2O3. The formation of the oxidation layers is caused by the combined action of the inward diffusion of the oxygen into the matrix and the outward diffusion of Al and Ti elements. Under the same experimental conditions, compared with those of the as-forged alloy, the weight increase of the as-deposited Ti60A alloy is smaller, the surface oxidation layer is thinner and denser, the diffusion depth of oxygen element is smaller, and the high-temperature oxidation resistance property is much better.

The NiTi-based intermetallic compound coating is in-situ synthesized on the surface of Ti-6Al-4V (TC4) substrate by the laser melting deposition (LMP) technique. The microstructure characteristics, microhardness and electrochemical corrosion resistance of this coating are investigated. The research results show that, this coating is mainly composed of the intermetallic compounds as NiTi, Ni3Ti, NiTi2, Ni4Ti3 and so on. The microhardness of this coating is up to 800 HV, which is about 1.3 times higher than that of the TC4 substrate. Inhomogeneous passive films are formed on the surface of the coating and there also exist many pittings, and thus there is a slight decrease in corrosion resistance of this coating compared with that of the TC4 substrate.

Aiming at the crosstalk of temperature and strain existing in the fiber Bragg grating (FBG) sensor, we use a femtosecond laser and a phase mask to fabricate FBGs in the melting point of two heterogeneous fibers. Because temperature or strain response parameters of the FBGs are different, the simultaneous measurements of temperature and strain can be realized. Temperature and strain response parameters of two kinds of FBGs, including Yb3+doped fiber with SMF-28 fiber FBGs and Er∶Yb doped fiber with SMF-28 fiber FBGs, are measured, respectively. The results indicate that the Er∶Yb doped FBG has a great difference on temperature response parameter but a similar strain response parameter with the SMF-28 fiber FBG, so the Er∶Yb doped fiber with SMF-28 fiber FBGs can be used to realize the simultaneous sensing on temperature and strain measurement. After annealing at 800 ℃, the reflectivity of Er∶Yb doped fiber FBG with SMF-28 fiber FBG can maintain a long-term stability at 700 ℃. It can be used to realize the temperature-strain dual-parameter demodulation below 700 ℃.

The self-assembled Cu92Fe8 immiscible composite coating is fabricated by the laser cladding technique. Its phase separation, microhardness, corrosion resistance and magnetic properties are investigated. The results indicate that the particle size of Cu92Fe8 composite powder decreases significantly after ball milling, which consists of small amounts of body-centered cubic α-Fe and solid solution Cu. During the process of laser cladding, the supercooled Cu92Fe8 melt experiences liquid phase separation, and many spherical Fe-rich α-Fe particles are evenly embedded within the Cu-rich ε-Cu matrix. The microhardness of the self-assembled Cu92Fe8 immiscible composite coating is uniform and slightly higher than that of brass, and its corrosion resistance is slightly worse than that of brass, but its soft magnetic property is better.

In large-scale high-power laser devices, the laser energy density and the system operating speed are mainly limited by the damage growth of the terminal optical element. An adaptive differential window filtering method based on local signal-to-noise ratio is proposed in order to detect the damage state of the element efficiently and accurately. By designing a window function which acts on pixels, the algorithm can judge the target point or background point according to the pixel value and the values of its neighborhood point. And then the segmentation of the seed image is completed. Finally, the damage segmentation is completed by the growth of the seed region. In order to verify the effectiveness of the algorithm, we built an on-line detection simulation platform to obtain the damaged sample image, and the new method mentioned above is used to process the image. The results show that the average recognition rate of the method is above 99% for the damage points with the diameter above 50 μm, which meets the requirement of high-power laser drive system for the detection of small damage. Because the algorithm does not require setting the threshold of the seed image based on experience, it is more automated than the existing local signal-to-noise ratio algorithm.

Detection of latent fingerprints is one of the key steps in material evidence detection. On the basis of the characteristic that the organic components of latent fingerprints will produce fluorescence under ultraviolet excitation, the two-dimensional laser scanning system is adopted to scan the latent fingerprints left on the surface of porous paper with high speed (the 266 nm ultraviolet laser is used as excitation light source). Interference light is filtered by narrow band filter. The experimental parameters are optimized according to the fingerprint stripe contrast, the latent fingerprint fluorescence images is reconstructed by the methods of removing the singular highlights and enhancing the fingerprint stripe contrast. By above methods, clear images of the sweat fingerprints and sebaceous fingerprints left on the surface of five types of porous paper (copy paper, writing paper, student work paper, sticky note and newspaper) can be obtained. The method can realize the non-destructive detection of latent fingerprints on the porous paper. It has important applications in many fields such as criminal investigation and trace detection.

Current target recognition method application platform is difficult to achieve small size and low cost, the detection imaging of the laser fuze is obtained by the line scanning. The sample matrix of the DHGF algorithm is obtained, and a quaternary evaluation algorithm based on laser line scanning imaging fuze is established for recognition model of typical target, which uses Delphi method to determine target contour similarity index set. Analytic hierarchy process (AHP) is adopted to determine the index weight distribution, and grey system theory is applied to determine evaluation gray level to get single factor fuzzy evaluation matrix. Fuzzy mathematics theory is applied to evaluate target recognition results. The algorithm overcomes the ambiguity and uncertainty in target recognition process in the case of small sample data. The simulation of a typical target is completed, and the simulation results show that the proposed algorithm has ability to recognize typical targets. The research can provide a reference to laser scanning imaging target recognition.

The performance of a visible optical communication system is limited by the effect of severe light power attenuation in application scenes of non-line-of-sight (NLOS) propagation such as shadow occlusion, etc. Thus, we propose a kind of optical receiving antenna coupled with spherical bionic compound eye micro-lens group and a compound parabolic concentrator. By using TracePro to analyze the non-imaging characteristics of bionic compound eye of spherical surface, we find that the ratio of energy collection increases with the decrease of angle of the neighbor's eye axis when the area of detection surface is certain. When the included angle between adjacent optical axes is less than local optimal value, the energy collection rate is more than 90%, which is close to the optimum. There is a positive correlation between the local optimal value of the angle of the optical axis and the area of the detector. With the increase of angle of the neighbor's eye axis, the character of large field of vision (FOV) of bionic compound eye is gone. For the application of NLOS link of indoor visible light communication, the antenna gain can reach 56.45 and the angle of FOV is larger than 90°. Compared with the ordinary single-lens antenna, it is clear that the bionic compound eye multilevel coupling optical antenna can maintain a high light feeding power in the case of severe shading, and the average power is increased by 20 dBm. It also shows that the design of the optical antenna with large FOV and high gain characteristics can effectively improve the anti-shadowing performance of indoor visible light communication system.

At present, the height profile of PM2.5 mass concentration is difficult to detect directly. However, a certain relationship can be used to transfer the height profile of aerosol backscattering coefficient detected by lidar to the height profile of PM2.5 mass concentration. The hygroscopic factor of aerosol is a key parameter in the process of transferring the profile of aerosol backscattering coefficient to that of PM2.5 mass concentration. The near ground height distribution profile of aerosol backscattering coefficient can be detected by the lidar system, while the PM2.5 mass concentration and atmospheric relative humidity are measured by PM2.5 monitor. The two instruments are placed at the same location and probed simultaneously to obtain the aerosol backscattering coefficient, PM2.5 mass concentration and atmospheric relative humidity at the same time. Under the guidance of the theory, the expression hygroscopic factor is calculated by fitting the related experimental data. By fitting the detection data aerosol backscattering coefficient, PM2.5 mass concentration and atmospheric relative humidity in Hefei area from May 2016 to October 2017, the change law of the hygroscopic factor between PM2.5 mass concentration and aerosol backscattering coefficient is obtained.

In the implosion physics experiment, several groups of laser pulses interact with the target at different times and produce several transient physical processes. Accurately diagnosing the time sequence relationship between these lasers and the transient process generated by the laser and the target is very important for successfully obtaining the relevant parameters of the experimental state. A time sequence diagnosis method of implosion physics experiment based on the electromagnetic radiation is proposed. It can produce intense electromagnetic pulse radiation when the laser is interacting with metal targets. The time sequence relationship between different lasers and target action processes can be obtained. It provides an important basis for judging and controlling the time sequence between different lasers and target actions. The experimental tests on Shenguang III host large laser devices show that the time sequence diagnosis method of the implosion physical experiment based on the electromagnetic radiation can accurately determine the time sequence relationship between the preliminary pulse laser, the main pulse laser and the interaction between backlight laser and cavity target and flat backlight target. This method has the advantages of simple operation and high measurement precision. It is of great significance to accurately grasp the time relationship between laser and target interaction and improve experimental accuracy.

The precision temperature control method of the optical frequency discriminator and its influence on optical transmission spectrum and measurement error are studied. A double-deck temperature controlling structure and corresponding circuit are designed, and the influence of the wire resistance is reduced by using a three-wire equal length method and dual switchable current source, and the mismatch of the current source is eliminated. The analog and digital hybrid temperature control method based on field-programmable gate array (FPGA) is studied. Control experiment with different temperature set points show that the temperature control accuracy is 0.0062 ℃ and the temperature measurement error is 0.0036 ℃. The influence of the temperature control accuracy on the spectral line movement and transmittance of the optical frequency discriminator is tested with a single-frequency ultraviolet laser. The transmittance spectrum line translation under this temperature control accuracy is 0.11 MHz, resulting in a speed measurement error of 0.0195 m/s.

In order to realize real-time measurement with high precision and high reliability, we propose a Zemax simulation based energy analysis method of optical system for laser tracking measurement. Based on the principle of optical system for laser tracking measurement, the energy model is established. The influence of non-ideal optical elements on the energy of optical system is analyzed by Zemax simulation. The simulation results show that the best interference pattern is obtained when the interference beam split ratio is 5∶5 and the tracking beam split ratio is 7∶3. In this situation, the interference signals from the four receivers have close energy, and the visibility of fringe pattern reaches 0.89. The visibility of fringe pattern of the four received interference signals will degrade when the reflectivity of polarization beam splitters is under non-ideal conditions. The non-ideal transmittance of the polarization beam splitters does not affect the visibility of fringe pattern. The research is useful for the laser tracking measurement system, mainly in terms of precision improvement, reliability evaluation, optical system design, and optical element selection.

Both numerically and experimentally, the temporal coherence of parametric fluorescence pumped by picosecond laser is studied. The influence of pump power and pump pulse width on temporal coherence of parametric fluorescence is investigated using the two-time mutual coherence function in the presence of walk-off between the signal and idle. The numerical simulations show that a suitable pump power and a relatively short pump pulse width are very important to increase the temporal coherence of optical parametric fluorescence while a too high pump power or a relatively long pump pulse width can reduce the temporal coherence. Using the periodically poled lithium niobate crystal, the theoretical result is preliminarily proved experimentally.

In view of the problem of the low key generation rate for the measurement device independent quantum key distribution (MDI-QKD) protocol based on weak coherent sources (WCS) and orbital angular momentum (OAM), the MDI-QKD protocol based on odd coherent sources (OCS) and OAM is investigated, and its performance and parameters are analyzed. The relationships between key generation rate, quality factor of detector and secure transmission distance are investigated. The performance comparison between the MDI-QKD protocol based on OCS and OAM and the MDI-QKD protocol based on WCS and OAM is compared. The simulation results show that the key generation rate decreases with the increase of secure transmission distance. The adoption of OCS makes up the deficiency of WCS and reduces the photon number greatly, while the adoption of OAM can solve the problem of the dependence defect of the base and increase the maximum secure transmission distance, which provides an important theoretical reference for the practical quantum key distribution protocol.

Because the amplitude of diffraction waves from the internal defects is weak and the depth information of the defects cannot be obtained by transmission bulk waves, it is still difficult to inspect the small internal defects of material by using laser ultrasonics (LU) in nondestructive conditions. In order to achieve remote nondestructive testing of internal tiny defects, we propose a double shadow method based on the LU reflected shear waves. By combining the advantages of the ultrasonic transmission method and the reflection echo-wave method, this method utilized the time of flight method to inspect the internal defects based on the twice attenuation effect of the defects on the reflected shear waves. The cross-correlation algorithm is used to calculate the time delay of the surface acoustic wave and the reflected shear wave, respectively. On basis of the accurate measurement of the distance between the pump and probe lasers, the distance between the two shadow positions and the thickness of the sample, the internal defect of 0.8 mm diameter is successfully detected by the double shadow method, and the depth position of the defect is measured. By comparing with the result of X-ray digital radiography imaging and the detection of conventional ultrasound transducers, the experimental results demonstrate that the LU method has the ability to inspect the internal tiny defects and locate the position of the defects accurately under nondestructive conditions.

In order to achieve a temperature sensor with a higher sensitivity, a theoretical model is proposed. The theoretical model is based on parity-time (PT) symmetry structure with a defect cavity composed of thermo-optical material. The refractive index of thermo-optical material is dependent on temperature. The changes of temperature will influence the transmittance of the defect mode in the structure. The transmittance spectra are calculated by the transfer matrix method. It is found that with the change of temperature, the transmittance value of the defect mode changes much larger than the location changes of the defect mode. Thus, the change of transmittance value with temperature is used for temperature sensing. Due to the unique gain amplification of the structure, the maximum sensitivity of the sensor is 6.82 dB·K-1. and the detecting range can reach 44.4 K. Through the modulation of structural parameters, the sensor can work with high sensitivity in small temperature range, or with low sensitivity in big temperature range.

When we construct a large distributed sensing network by fiber Bragg grating (FBG), under the condition of same bandwidth, we fabricate as many fiber gratings as possible to increase the number of sensors, which leads to overlapping spectra and makes FBG central wavelength recognition difficult and reduces the demodulation accuracy. In order to solve this problem, we propose an improved particle swarm optimization (PSO) algorithm to improve the recognition accuracy of the central wavelength. First, the overlapping spectra model is established by spectral shape multiplexing technology. Then, the temperature experiment system is built to get the overlapping spectral signals, and the weight factor and the learning factor in the PSO algorithm are improved. Finally, the proposed algorithm is used to optimize the parameters of the overlapping spectra model, and it is compared with the six optimization algorithms. Simulation result and experimental result show that the proposed algorithm has the characteristics of fast convergence speed, short running time and high wavelength recognition accuracy compared with the contrast algorithm, and the wavelength demodulation error is less than 1 pm, which verifies the effectiveness and feasibility of the algorithm.

Single part information of building represented by three-dimensional point cloud or model representation is a key information factor in numbers of applications, such as urban planning, municipal management and digital city construction. Using dense matching point cloud generated by aerial images, we propose a new algorithm for rapidly single part of building extraction in complex construction area. On the basic of ground filtering and clustering after horizontal point cloud extraction, the algorithm projects all the point cloud clusters into the two dimensional grid. Non-roof segments are removed based on building fa ade and clusters' geometrical characteristic. Then, topological relationships between clusters computed based on grid images are adopted to generate the range of single part of the building. And the single part point clouds are extracted finally. Experimental results show that the average recall and the average precision of single part of building extraction are 92.6% and 89.9%, and it means that it is efficient for our algorithm to extract single part of building in complex urban area.

Aimed at eliminating the fluorescence interference from containers of the sample in the detection of Raman spectroscopy, a dual-axis confocal detection scheme is proposed based on the characteristic that the fluorescence generated by the container and the Raman signal of the sample are not confocal. The experimental results show that the fluorescence interference signals from the container are reduced by an order of magnitude,and the intensity of Raman signal decreases by about 30%. The dual-axis confocal Raman detection scheme can solve the mixed reception problem of Raman signal and fluorescence in the conventional coaxial confocal Raman detection scheme, solve the limitation of the dynamic detection range of Raman signal caused by the fluorescence interference, and achieve the effective detection of Raman signal of the material in fluorescent material containers.

Due to the complex matrix effects in bulk water, the application of laser induced breakdown spectroscopy (LIBS) in online continuous detection and analysis of liquid sample is limited. Thus, we propose a new method of LIBS assisted by micro hole spraying technology. The essence of this method is to transform the flowing liquid sample into dense droplets and spurt out continuously through a micron hole matrix and piezoelectric ceramic in order to assist the analysis of LIBS. A detection experimental system is established, composing of a micro hole ultrasonic system, a 1064 nm Nd∶YAG laser and a fiber optic spectrometer. A series of experiments and analysis are carried out to detect the calcium element dissolved in pure water with the detection experimental system. The optimum experimental parameters, the physical properties of plasma and the analysis ability of this method are studied. The results show that the limit of detection for calcium element is as low as 0.96 mg/L. And there is a good linearity between spectral peak intensity and concentration within the range of 0-1124 mg/L.

In this paper, we apply the auto-focusing algorithm, which is based on the image sharpness evaluation function, to collinear double pulse laser-induced breakdown spectroscopy (DP-LIBS). Through the control software based on LabVIEW, the collinear DP-LIBS experiment system, CCD camera and three-dimensional mobile platform are effectively controlled. Image sharpness evaluation, the auto-focusing algorithm, and the three-dimensional mobile platform are combined to achieve sample auto-focusing function. The results show that the optimal interval between the two lasers is 0.55 μs. The stability of the atomic spectral line is higher than that of the ion line. The relative standard deviation of the spectral strength decreases from 16.7% to 6.7%. The quantitative analysis of the steel samples shows that the correlation coefficients of Cr and Mn measurements increase from 0.851 and 0.639 to 0.947 and 0.923, respectively. Overall, the auto-focusing system can improve signal stability and measurement accuracy.