To adapt to compact space requirements of high power laser system, a far-field and near-field coupling scheme based on second order ghost image is used in high power laser collimation technology. A sensitive small-size collimation optical system is designed and built. We present complete test scheme and verify its feasibility. The near-field measurement sensitivity is 7.04 μm/pixel and the far-field measurement sensitivity is about 18.14 (″)/pixel. The influence of far-field change on near-field is researched and used to optimize beam collimation. Compared with traditional collimation system of far- and near-field separation, this scheme sharply reduces the number of light paths and devices under the condition of imaging quality and resolution assured. It is more convenient to feedback the interaction effect and collimation of far-field and near-field.

Transdermal drug delivery by microneedles combines the advantages of both injection and transdermal drug delivery techniques, greatly enhances the percutaneous absorption of macromolecular drugs with almost no damage to skin, thus has good prospect. However, this technology is still in its infancy, and it is necessary to study the penetration depth of microneedles in the skin and absorption/release behavior of drug particles by means of imaging. A swept source optical coherence tomography system is developed, which uses the Bessel beam, generated by a circular Dammann grating, to illuminate samples. This system exhibits high lateral resolution along an axially extended focal range, the effective depth of focus of the measured system is 1.68 mm and the lateral resolution around the confocal position is 3.61 μm, which can meet the imaging requirements for transdermal drug delivery by microneedles. The proposed system is used to image the dissolving microneedles before and after inserting into the skin, the edge of microneedles, penetration depth and microchannels left on the skin are clearly visible, and the dissolution process of microneedles in skin is observed.

Based on the design method of response surface methodology, pulsed laser welding process experiment of in vitro skin tissue is performed to obtain the tensile strength and peak temperature data of tissue incision. On the basis of single factor experiment, the multivariate nonlinear mathematical regression model is established by using laser power, spot moving speed and laser frequency as the three influencing factors. Correlation coefficients of the regression model are obtained by analysis of variance and regression analysis as follows: correlation coefficient of incision tensile strength is 0.9131, correlation coefficient of incision peak temperature is 0.9985. The results of model analysis show that the main effect and interactions of laser power, spot movement speed and laser frequency have a great influence on the incision performance. The main effect that has the greatest influence on the tensile strength of incision is laser power, and the interaction effect is laser power and spot movement speed. The main effect that has the greatest influence on the peak incision temperature is laser power, and the interaction effects are laser power and spot movement speed, laser power and laser frequency, and spot movement speed and laser frequency. Finally, the optimal combination of laser process parameters is obtained based on the regression model. The experimental results show that the response values of regression model are consistent with the experimental results, and the incision strength meets the requirements.

Quarter-wave plate is a key component in fiber current sensing system. A quarter-wave plate fabricating technique is proposed and demonstrated. The two sections of high-birefringence fibers (HBF) with approximately equal length are orthogonally fused and the angle between their fast axes is 90°. Stretching one of two fibers can adjust the phase difference between the two fibers to be π/2 precisely. A high-birefringent fiber loop mirror (Hi-Bi FLM) is realized by the two fibers fused to 3 dB coupler and the phase difference is determined by real-time detection of the transmissivity of the Hi-Bi FLM. The transmissivity function of the Hi-Bi FLM is deduced and the variation of the transmissivity is analyzed in detail. The phase difference is confirmed experimentally based on the transmissivity curve and its slope. The fabricating technique which has been achieved experimentally, and has excellent features, such as high accuracy and convenient operation.

In order to achieve low-cost, low-complexity and high-precision indoor localization system, we propose a fingerprint based visible light indoor localization method. In the method, the light emmiting diode (LED) is employed as the transmitter. Based on the received signal strengths (RSS) of visible light, the triangulation method and fingerprint based hybrid positioning algorithm are combined to achieve indoor high precision localization. The proposed method can be divided into two phases. First, the triangulation method is used to obtain the coarse range of the mobile terminal (MT). Then, the fingerprint based method which is constrained by the coarse range is used to get a fine estimate of the MT. Experimental results show that the averaged positioning error of the proposed method is improved by 64.71% compared with that of the traditional RSS based visible light indoor localization method. Besides, the proposed method can achieve better localization performance at lower computational complexity compared with the traditional fingerprint based method.

A two-dimensional (2D) holographic polymer-dispersed liquid crystal (H-PDLC) variable line-space grating is fabricated by interference between cylindrical wave and plane wave. In order to separate polymer from liquid crystal more evidently, we use a 532 nm laser with exposure intensity of 16 mW/cm2 in experiment, and two exposure time is 2 s and 60 s, respectively. We use double exposure and rotate the sample 60° to form 2D hexagonal lattice H-PDLC variable line-space grating. The theoretical periodic variation rang of grating, diffraction properties, electronic control characteristics and analysis of parameters affecting the periodic change of grating are studied, respectively. The results show that, in the circular range with a radius of 6 mm, the periodic variation range of the grating is 1.804-2.281 μm, which is basically consistent with the theoretical calculation. The first-order diffraction efficiency is 18.3% without external voltage, and the zero-order diffraction efficiency increases from 15.6% to 73% with an applied voltage of 90 V. Due to variable period and electronic control characteristics, this grating has potential application in diffraction optics, such as the research of tunable multi-wavelength organic laser for dye-doped 2D H-PDLC grating.

We built a set of four-outputs Nd∶glass pump source system with stable energy output, uniform spot and time-domain approximate square waveform. The system can achieve output of 4×180 J at 1053 nm in fundamental frequency and 4×80 J at 526.5 nm in double frequency. The main structure consists of 4 parts, which are the front-end seed source, the regenerative amplifier, Nd∶glass rod amplifier chain and the KDP frequency doubling crystal. Those two fundamental frequency beams with vertical polarization are combined by the polarizer. The 526.5 nm double frequency laser pulse with the same directivity and polarization is obtained after Type-Ⅱ phase matching frequency-doubling KDP crystal. As a result, the compact dual pulse pump source for the Ti∶sapphire amplifier is realized.

The thermal effect of large aperture active mirror disk Nd∶LuAG ceramic laser gain medium under high power diode pump is analyzed and the wavefront distortions caused by the thermal effect is also studied. In simulation, the size of the disk Nd∶LuAG ceramic is 64 mm×6 mm, the peak pump power is 58.5 kW, the spot size of the pump is 32 mm×35 mm and the incident angle of laser beams is 15°. Simulation results show that the maximum temperature of disk Nd∶LuAG ceramic is 55.6 ℃ at pumping state, and the negative focal length is FH=-65.78 m and FV=-77.28 m in horizontal and vertical directions, respectively. The simulated wavefront distortions peak valley value is 4.33λ(the light wavelength λ is 1064 nm), which is caused by defocus mainly. On this basis, corresponding experimental facilities are set up to measure the temperature distribution of Nd∶LuAG ceramic and the wavefront distortions introduced by laser beams. Simulation results are in good agreement with the experiment. Simulative and experimental analysis results provide important references for the optimization of the pumping uniformity and the improvement of the laser beam quality of Nd∶LuAG ceramic laser amplifier system.

The influence of the etalon effect on the laser output of the uncoated alkali vapor cell windows on the inner surface is experimentally studied. The research results show that the two inner surfaces have different spot patterns when they are used as the laser output surface, and both of the cases are accompanied by parasitic spots. The parasitic spots are caused by the wedge angle of the two windows of alkali vapor cell. The experimental and theoretical results of the threshold at different output coupling rates are compared. It is verified that the uncoated inner surface of the alkali vapor cell has etalon effect and multiple reflections. When the alkali cell replaces output coupling mirror, the etalon effect is the main factor of the laser output. In this case, the rubidium laser of 1.8 W is obtained, whose optical efficiency is 10.2% and slope efficiency is 15.8%.

A novel antireflection all-fiber laser is presented. The oscillator-amplifier integration is utilized to suppress the effect of the reflection light on the stability of the fiber laser, and obtain efficient output with high power and beam quality. The fiber laser system is set up. The output power more than 2 kW with an optical-optical efficiency of 81.6% is obtained, and the beam quality M2 is better than 1.4.The high-reflected metal is used to verify antireflection ability of the laser. The experimental results show that the system has good long-term stability under full power output.

The characteristics of cryogenically cooled 946 nm Nd∶YAG laser under 885 nm low quantum defect pumping are studied. The Boltzmann distribution fraction of the upper and lower laser levels as a function of temperature is introduced into the laser rate equation, and the change rule of small signal gain and laser threshold at low temperature is analyzed qualitatively. A cryogenic system is developed to study the output characteristics of the 946 nm laser at low temperature. A maximum 165 mW laser output with the slope efficiency 36% is achieved at 210 K. The slope efficiency is increased by 71% compared with the room temperature operation. The gain of 1061 nm laser enhanced at low temperature is observed and analyzed. When the temperature is lower than 190 K, the gain of 1061 nm laser significantly increases and 1061 nm laser competes with 946 nm laser, resulting in a decrease of 946 nm laser output.

Semiconductor laser chips with 976 nm wavelength, broad stripe and high power are designed and realized. The epitaxial structure design of an asymmetric and large waveguide, and metal organic chemical vapor phase epitaxy technology are used to grow epitaxial materials with low loss and high conversion efficiency. The semiconductor laser chips with 190 μm stripe width, 4 mm length and 976 nm wavelength are packaged and packaged as chip-on-submount. The test results show that the threshold current of package-device at room temperature is 1.05 A, slope efficiency is 1.12 W/A, and the maximum conversion efficiency is 68.5%. Even at the elevated temperature of 40 ℃ and the output power of 19.5 W, the conversion efficiency reaches 60%. Nine devices are aging-tested at 40 ℃ and 15 A for 4740 hours, and no failure occurs. There are no changes in power-current curves and spectra before and after aging-test, which proves high stability and reliability of the laser chips.

High precision repetition rate stabilization is realized in an all polarization-maintaining nonlinear amplifying loop mirror (NALM) mode-locked Yb-fiber laser. An additional Er-fiber is added in the nonlinear loop to control the optical length by the resonance-enhanced nonlinearity modulation technique. Moreover, an integrated nonreciprocal device with linear phase shift effectively reduces the mode-locking threshold. By optimizing both the pump power from two laser diodes for mode locking and the nonlinear refractive index modulating, we can obtain the shortest pulse of 590 fs and repetition rate of 20.48 MHz, the peak-to-peak fluctuation of repetition rate is less than 0.4 mHz, and the corresponding standard deviation is 0.1 mHz.

The relationship between transverse mode instability effect and stimulated Raman scattering (SRS) in Ytterbium doped all-fiber laser oscillator is studied. In the single-end pumped 1.5 kW class all-fiber laser oscillator with core diameter of 20 μm, when the stimulated Raman scattering reaches to a certain value, the transverse mode instability effect appears, in this case, the power in the laser oscillator decreases. The decreased power is stripped out of the laser oscillator by the cladding light stripper. It is found in the experiment that the enhancement of the stimulated Raman scattering spectrum, the decrease of the fiber laser power, and the increase of the temperature of the cladding light stripper have an inherence relationship. By shortening the fiber in the laser to mitigate the stimulated Raman scattering, we can increase the transverse mode instability threshold in the single-end pumped laser oscillator up to 2 kW. Similar results by increasing transverse mode instability threshold employing suppression the stimulated Raman scattering are also validated in the double-side pumped all-fiber laser oscillator with fiber core diameter of 25 μm, and laser output greater than 5 kW is demonstrated. The experimental results validates that when the nonlinear effect is somewhat strong, the stimulated Raman scattering is the reason for the transverse mode instability. By mitigating the stimulated Raman scattering effect, we can also increase the transverse mode instability threshold.

External cavity feedback spectral beam combining (SBC) of two fiber lasers is investigated experimentally. A transmission grating is employed as the beam combining element and the SBC of a 1060 nm laser and a 1080 nm laser is achieved. The beam quality of 1.328 in SBC direction is obtained, while the beam quality in the other direction is 1.257. The output power of the SBC system is 57.3 W with a combining efficiency of 91.7%. Based on the configuration in this experiment, the requirement on the bandwidth of a single laser participating in the SBC can be significantly relieved. The experiment results verify the feasibility of multi-channel SBC. The SBC output power can be improved by the increase of the channels of the SBC system.

The stationary magnetic and electric fields are coupled to form the directional Lorentz force. Based on the multi-physics field coupling theory and the mesh deformation method, the molten pool model under the effect of the directional Lorentz force is built, and the bubble movement process in molten pool is simulated by the discrete element method. The comparison of numerical results with and without directional Lorentz force but both under the same laser cladding process conditions indicates that the directional Lorentz force possesses an excellent ability to regulate pores. When the direction of the Lorentz force is upward, the maximum velocity of molten pool is suppressed by 62.5%, the gas bubble movement direction deflects downward, and the pores in cladding layers increase obviously. When the direction of the Lorentz force is downward, the maximum speed of molten pool is suppressed by 25%. Nevertheless, for the reason of the increase of the bubble buoyancy, the bubble is accelerated and escapes from the melting pool, and a dense cladding layer without any pores is obtained. The simulation results agree well with the experimental ones, which confirms the reliability of this simulation model.

The IC10 single crystal superalloys are welded by the laser welding process, and the effects of welding speed on joint weld forming, cross-section morphology and microstructure are analyzed. The results show that the surface and back widths of welds increase with the decrease of welding speed. The cross-sections of welds under different welding speeds all show a typical goblet shape. The welds mainly consist of fine grains, cellular crystals and columnar crystals. The welding cracks extending along the grain boundaries always occur in welds under different welding speeds. The growing direction of the grains in joints tends to be the same, which increases the cracking susceptibility of joints.

An experiment of 355 nm all-solid-state ultraviolet laser direct writing and etching of borosilicate glass is conducted to investigate the effects of laser energy density, repetition frequency, scanning speed, scanning distance and number of scanning on the etching results based on the single variable method. The research results show that, serious collapse phenomena occur in glass if laser energy density is too large. The plasma shielding effect increases and the etching depth decreases with the increase of laser energy density. With the decrease of repetition frequency, the channel edge fragmentation gradually reduces and the etching depth increases. The reduction of scanning distance can effectively improve the channel bottom surface flatness. The etching depth increases with the increase of number of scanning and simultaneously the channel taper increases. Under the optimal processing parameters, the direct writing and etching of L-shaped micro-channel with a width of 84.8 μm, an etching depth of 178 μm, a flat bottom surface and a channel verticality of 89.580° is realized.

The relationship between circumferential offset and inclination angle is obtained via the establishment of the model of the circumferential thin-walled cylinder. By the optimization of circumferential offset angle and based on the laser cladding net shaping technique, a circumferential cantilever thin-walled cylinder with stable structure and relatively small errors in height and width is obtained. The results show that the requirements of cladding can be met when the offset angle is 0.75° and the inclination angle is 25.95° of cladding specimens. In addition, the circumferential deviation of 0.11 mm and Z-axis increment of 0.224 mm are the optimal process parameter set.

Based on the finite-difference time-domain (FDTD) method, the terahertz (THz) polarization characteristics of a metal wire grid structure are simulated and analyzed. The influences of duty ratio and metal layer thickness on the polarization characteristics are investigated. It is found that the periodic high transmission phenomenon in the range of 0.1-10 THz occurs with the increase of the metal layer thickness. The metal wire grid THz polarizer is fabricated by the femtosecond laser micro-machining technique, which is tested by the time-domain terahertz spectroscopy system. The experimental results are consistent with the simulation ones. The extinction ratio of the polarizer is in the range of 40 dB-45 dB and the polarization degree is 1, which indicates that the polarizer possesses a good polarization characteristic.

The experiment of laser remelting of crystalline Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2 alloy matrix by a fiber laser with a power of 500 W is conducted, and the effects of different processes on the molten pool morphology and crystallization are investigated. The results show that, as for the single track remelting process, the amorphous microstructure occurs easily in the molten pool and the molten pool morphology is gradually transformed from the coronal shape to the funnel shape with the decrease of scanning speed. As for the overlap remelting process, the crystallization belt in the heat-affect zone induced by weld overlap is formed in the remelting zone when the scanning width is large, but when the scanning width is relatively small, the pool width is close to the scanning width and the remelting zone is basically amorphous due to the significant heat accumulation effect. In the surface scanning process, the keyhole effect is prominent due to thermal accumulation, the penetration depth of molten pool increases significantly, and there occurs a small amount of pores at the bottom of molten pool.

The droplet transition behavior of laser-arc hybrid surfacing with self-shielded flux-cored wire is studied. The results show that the introduction of laser makes the arc wandering probability significantly reduced, arc space stretched, droplet stress state and transition behavior changed. Laser preposition is more beneficial to droplet transfer and arc stability improvement than laser postposition. The optimal process parameters of laser-arc hybrid surfacing with self-shielded flux-cored wire are laser preposition, laser power of 2 kW, laser-arc distance of +4 mm, light spot diameter of 2 mm and laser-arc angle of 30°. When laser-arc distance is small and laser power is 4 kW, the droplet transition mode is changed from repelled transfer to explosive transfer.

As for a two-dimensional function photonic crystal with square structure and point defects, its band gap structure, defect modes and eigenfield distribution of defect modes are studied by using the plane wave expansion method. The refractive index of the dielectric column is chosen as a spatial distribution function, whose coefficients can be adjusted by the altering of the applied electric field and the light field intensities. The research results show that, the adjustability of band gap structure, band gap position, defect modes and eigenfield distribution of defect modes can be realized by adjusting the parameters of the dielectric column, which provides an important theoretical basis and design method for the design of related optical devices.

The rapid location and extraction of urban municipal manhole covers is one of the key problems to be solved in the component management of smart city, and also the key technical problem to be solved in the realization of intelligent management of urban road maintenance. Therefore, we propose an automatic location and extraction method for manhole covers based on mobile mapping system. The ground point cloud is extracted from the surface roughness, the ground points are generated into the ground intensity feature images, and rapid location and extraction of manhole covers are achieved based on the combination of three methods, such as histogram of oriented gradient algorithm, principal component analysis and support vector machine classifier. We obtain the ownership information of manhole covers with synchronous images. Qualitative and quantitative analysis of the method is carried out based on experimental data, the accuracy of automatic extraction of urban manhole covers is 88.495% and the accuracy is 99%. The results also verify the correctness, feasibility, and robustness of the proposed method. This method further promotes the improvement of intelligent working mode of road maintenance department, which not only reduces the danger coefficient of work, improves the detection accuracy, but also transforms the traditional field test into indoor operation mode, and the degree of automation and intelligence increases greatly.

In designing a three-channel non-imaging passive ranging system based on oxygen absorption, determining the absolute spectral sensitivity of the photomultiplier tubes is of great significance to ensure the ranging accuracy of the system. In order to overcome the difficulty of monochromatic light power measurement caused by high sensitivity and saturation of photomultiplier tube, we propose a measurement method of absolute spectral sensitivity of photomultiplier tubes. In this method, a system light source with adjustable flux is constructed using an integrating sphere and an adjustable slit, and a standard detector with known spectral sensitivity is used to measure the radiant power of the monochromatic light source. An absolute spectral sensitivity measurement system for photomultiplier tube is established, and the absolute spectral sensitivity of three H10722-01 photomultiplier tubes is measured with this method. In order to test the effectiveness of the proposed measurement method, a short-range passive ranging experiment is conducted in external field, the measured absolute spectral sensitivity of the photomultiplier tubes is used as the spectral sensitivity parameter of the passive ranging system. The experimental results show that in the range of 60-300 m, the average relative error of distance measurement is 6.25%. The experimental results prove the validity of this absolute spectral sensitivity measurement method.

The multi-conjugate adaptive optics (MCAO) can effectively reduce the disturbance of turbulent atmosphere. For the design and performance optimization of MCAO technology, it is necessary to measure the atmospheric turbulence profiles of the site. The inversion linear equations of the methods based on differential image motion variance or covariance of extended object are obtained through discretization. The discretization error causes the effective field of view (FOV) not to be very wide. A small FOV limits the number of equations, resulting in turbulence profile inversion results being affected by motion variance or covariance measurement errors. In this paper, taking the PML method as an example, we propose a layer integral coefficient matrix method. This method obviously reduces the discretization error, greatly improves the range of observation FOV, reduces the influence of the covariance error on the measurement results, and improves the accuracy of the turbulence profile inversion. The simulation results show that the FOV of the PML method using layer integral coefficient matrix can reach 400″, and the measurement error is also greatly reduced.

To suppress the influences of vehicle jolts and the load variations on one-dimensional (1D) laser Doppler velocimeter (LDV), a two-dimensional (2D) LDV is designed. As for the error parameters produced in the usage process of 2D LDV, the Kalman filtering calibration method with the auxiliary of the differential global positioning system (DGPS) is proposed. The effectiveness of this method is verified by an experiment of vehicle load navigation. The maximum horizontal position error and the maximum altitude error of the dead reckoning of the 2D LDV after compensation and the gyroscopes are 5.5 m and 0.36 m, respectively. The experimental results show that this calibration method proposed is effective, and the 2D LDV after compensation can not only greatly improve the horizontal positioning accuracy of navigation, but also give high precision altitude informations.

In order to investigate the performance of photomultiplier tube to meet the needs of on-orbit application requirements of the space remote sensing instruments, we construct a set of quantum efficiency calibration system based on standard vacuum phototube with deuterium lamp, vacuum ultraviolet monochromator, photomultiplier tube, and so on. According to the principle of the cathode quantum efficiency measurement about photomultiplier tube, the photomultiplier tube is transformed into phototube without electron beam multiplying, and the standard transferring from the standard vacuum phototube to the phototube R2078 is realized. On this basis, direct measurement of the quantum efficiency of phototube in ultraviolet-vacuum ultraviolet (UV-VUV) range of 150-300 nm is realized for the first time in China. The measurement results show that, owing to the window material is fused silica, the phototube R2078 has the lowest transmissivity at 155 nm, so the quantum efficiency obtained at 155 nm is the smallest, and the quantum efficiency at 230 nm is the largest. Finally, the uncertainty of the measurement results is analyzed and estimated, and the total synthetic uncertainty is 3.4%.

The spectral pattern of pulsed laser is one of the most important parameters for atmospheric wind and temperature lidar. Accurate detection of the spectral pattern of pulsed laser can provide scientific and effective data for wind and temperature inversion. Since the repetition rate of the laser is usually a few tens of hertz (the repetition period is a few tens of milliseconds) and the pulse width of laser is only a few nanoseconds, the linewidth measurement of pulsed laser is much more difficult than that of continuous laser. In this paper, a system based on Fabry-Perot interferometer (FPI), narrow pulse signal gate integral averager and modulus sampler is built, which can detect the spectral pattern of pulsed laser. The linewidth of the sodium layer wind and temperature lidar is detected by this system. The output linewidth of the pulsed laser is measured with the system to be approximately 123 MHz, which is basically consistent with the measurement result of 120 MHz in foreign countries. This system can be mounted on the lidar for real-time monitoring of the spectral pattern of laser, which can provide technical support for ensuring the accuracy and stability of the wind measurement lidar.

Focusing and imaging through scattering medium based on the optical transmission matrix is a hot topic in the field of optics recently. To measure the optical transmission matrix of the scattering medium and study special properties of the scattering medium, we propose a method named three steps phase shift interferometry to measure the optical transmission matrix of the frosted glass, and analyze eigenvalue distribution characteristics of the optical transmission matrix in Hadamard basis and Cartesian basis. Then combining the optical transmission matrix in Cartesian basis and phase conjugation, we achieve single point and multipoint focusing through scattering medium to verify the controllability of focusing points of the scattering medium. We study properties focusing through scattering medium with the camera in different positions, and measure the depth of focus of the optical system. We verify the lenslike effect of the frosted glass based on the controllability of the focusing points and the depth of focus of the system. The results show that three steps phase shift interferometry has the advantages of less measuring time and high enhancement factors of focusing; The eigenvalue distribution characteristics of the optical transmission matrix in Hadamard basis and Cartesian basis are both following the Gaussian distribution, which agrees well with theoretical prediction, and the correctness of the three steps phase shift interferometry to measure the optical transmission matrix of scattering media is verified; the focusable depth of focus of the system is long, within which the single point and multipoint focusing can be achieved.

The rotation absolute algorithm is stuided for the grating lateral-shearing interferometer, and the first 36-term Zernike polynomials are used to characterize the asymmetric term in the systemic errors of the shearing setup. The research results show that the relatively ideal measurement precision can be obtained after the systemic errors are removed if the absolute algorithm of surface figure testing is used to the testing of wavefront aberration in lens system. In addition, the RMS of the repeatability of the experimental data can approach 0.14 nm.

Au-nanorod modified fiber surface enhanced Raman scattering (SERS) probes were fabricated by laser-induced self-assembly method in a meniscus. The influences of laser radiation power and laser radiation time on the performances of fiber probes were studied in detail. Under an optimized experimental condition as 70 mW laser power and 7 min radiation time, the fiber SERS probes with high sensitivity and good repeatability have been prepared. Further, these optimized fiber SERS probes were used to detect two typical pesticide residues of thiram and methyl parathion (MP) by combining with a portable Raman spectrometer. High detection sensitivity as 10-7 mol/L for thiram and 5×10-7 mol/L for MP, and good detection repeatability with the relative standard deviation less than 6% were observed. This laser-induced self-assembly method in a meniscus has the advantages of easy operation, low cost and short preparation time, which is very useful for the fast preparation of fiber SERS probes with high sensitivity. These optimized fiber SERS probes may have potential applications in rapid and high sensitivity detection of various pesticide residues.

An enhanced phase sensitive optical time-domain reflectometer (-OTDR) vibration sensing system based on weak fiber Bragg grating arrays is designed. A weak reflection signal from the fiber Bragg grating (FBG) with a relatively large reflectivity is used instead of the Rayleigh scattering signal in the -OTDR system. The perturbation behaviors in the optical fiber lines are determined based on the intensity variation of the interference signal between the adjacent weak FBG reflection signals and the time division multiplexing technique is used to locate external vibration points precisely. The results show that, by this system, the detection and demodulation of the vibration signal are simpler than those by -OTDR, the distributed measurement is simultaneously fulfilled, and any vibration signals in the frequency range of 10-500 Hz can be demodulated. The system has the practical application value in perimeter surveillance systems.

Based on the Mach-Zehnder interferometer, the detection principle of quantum interferometric radar based on coherent state light source is analyzed. The influence of intensity fluctuation and atmospheric loss caused by atmospheric scintillation on the performance of quantum interferometric radar is studied systematically. Then, the atmospheric channel is regarded as dissipation-fluctuation channel. Based on the classical statistical theory of turbulence, the probability distribution of transmission coefficient (PDTC) function P(T) is derived. Furthermore, P(T) is used to investigate the sensitivity and resolution of the quantum interferometric radar, especially the influence of average transmission coefficient T-A and the scintillation index β2D on the detection performance of the quantum interferometric radar. These research results exhibit that, in a high-loss environment, the fluctuation of transmission caused by atmospheric scintillation is able to improve the sensitivity and resolution of the coherent state quantum interferometric radar remarkably.

We propose a sensor based on etched double-cladding fiber (DCF) coated with nanofilm. The coupling mode, resonant wavelength and the best sensing interval can be adjusted by control of the etching time and coating thickness. The evolution of mode behaviors and refractive index (RI) sensitivity as DCF cladding thickness decreasing is theoretically analyzed. In the experiment, 2000 layers of Al2O3 nanofilms are coated on a DCF with an outer diameter of 59 μm to achieve a sensitivity of 1200 nm/RIU in the RI range from 1.336 to 1.356, in which RIU is RI unit. The RI sensitivity of proposed fiber is 24 times than that of bare DCF. The sensor has the advantages of high sensitivity, good consistency, controllable coupling mode, and customizable sensor parameters. It is expected to have great application value in biomedicine, chemical detection and so on.

Aiming at the low signal-to-noise ratio (RSN) and difficult extraction of coherent lidar echo signal in the far field, we propose pulse coding technology to improve the RSN and dynamic range of the system, then we study the encoding and decoding principle of Golay code in coherent lidar system, and theoretically analyze RSN improvement of the system by using pulse coding technology. We simulate the echo signal of coherent Doppler lidar based on the atmospheric slices model, and obtain the wind velocity of the pulse coding system based on the decoding principle. The simulation results show that, when the Golay code pulse is used as the detection pulse of the coherent lidar, the wind velocity error is less than 3 m·s-1 in the range of 0~5.3 km with the distance resolution of 60 m and the time resolution of 1 s. In the same measurement time, the coherent lidar with pulse coding technique can improve the detection distance by 2.5 km compared with the traditional pulse coherent lidar, which improves the RSN of the far-field weak signal.

In order to decrease the limit of detection of elements and improve signal-to-background ratio (SBR) and the stability of characteristic spectral lines of laser-induced breakdown spectroscopy (LIBS) of heavy metals in soil, we study the polarization property of four characteristic discrete spectral lines of Fe, Pb, Ca, Mg elements and continuous background radiation of LIBS in soil, and analyze the limit of detection, SBR and relative standard deviation (RSD) of characteristic spectral lines of elements under the conditions of polarization and no-polarization. The results indicate that the polarization degree of four characteristic spectral lines Fe Ⅰ: 404.581 nm, Pb Ⅰ: 405.780 nm, Ca Ⅰ: 422.670 nm, Mg Ⅰ: 518.361 nm and corresponding continuous background radiation are 0.27, 0.17, 0.25, 0.23 and 0.70, 0.64, 0.69, 0.67, respectively. The polarization resolved LIBS (PRLIBS) technology makes RSD of four characteristic spectral lines Fe Ⅰ: 404.581 nm, Pb Ⅰ: 405.780 nm, Ca Ⅰ: 422.670 nm, Mg Ⅰ: 518.361 nm decrease by 3.28％, 2.2％, 3.24％ and 1.34％, respectively. Continuous background radiation is effectively depressed by PRLIBS technology, and SBR of four characteristic spectral lines is increased by 5.59, 5.67, 5.30, 7.35 times, respectively. Under the conditions of polarization and no-polarization, the limits of detection of heavy metal Pb are 17.4×10-6 and 39.4×10-6, respectively, limit of detection under polarization is 44% that of non-polarization. Above results provide data support for further improving quantitative analysis ability of LIBS on heavy metal in soil.

Laser-induced breakdown spectroscopy (LIBS) usually contains rich element characteristic spectrum peaks. The accurate identification of spectral peaks is the premise and basis for qualitative and quantitative elements analysis in LIBS technique. In this paper, a new method for automatic identification of spectral peaks is proposed to overcome the disadvantages of low accuracy and reliability of traditional spectral peak recognition methods. Firstly, the Voigt function is used to fit the experimental spectrum to overcome the overlapping spectrum and noise interference. Then, the center wavelength, light intensity, full width at half maximum and peak centroid of the fitting spectrum are extracted as the characteristic parameter vector of spectral peak after fitting process. Finally, the similarity analysis of the characteristic parameter vector of spectral peak between the spectrum to be recognized and the spectrum in National Institute of Standards and Technology (NIST) standard spectral database is carried out, so as to realize the automatic recognition of the spectral peak corresponding elements. Experiments are carried out using NIST standard database and LIBS spectra of tea samples, and the effectiveness of the method for spectral element recognition based on LIBS is verified.

A terahertz imaging system based on active ghost imaging method is proposed. The system can achieve high speed and high resolution imaging using one single-pixel detector, breaking through the resolution limit of terahertz devices. Reusable measurement matrix is obtained by the rotation of double random amplitude plates so that the imaging speed is greatly improved. The influence of imaging distance, size of random pattern, sampling number and the relativity of sampling matrix on imaging quality are numerically analyzed. The best parameters are used for experiment. And the motion strategy of double amplitude plates is optimized. Experimental results show that the imaging resolution is 4 mm when the wavelength of terahertz source is 3 mm, and imaging speed is determined by the motor of amplitude plates. The feasibility of terahertz active ghost imaging method is proved.

Detector samples based on resonant tunneling diode (RTD) are fabricated by molecular beam epitaxy. In order to improve the detection responsivity, the detector uses bowtie antenna to enhance the terahertz electric field intensity, in which the antenna structure is designed with reference to 0.2 THz incident frequency. The terahertz source with an output power of 20 mW is used for testing. Current-voltage (I-V) test is performed with and without THz irradiation at room temperature, and the peak voltage is 1.398 V. The difference between the maximum current values is tested, the detector responsivity is calculated to be of 20 mA·W-1 and the noise equivalent power is 15 nW·Hz-0.5. The response of the detector to the terahertz wave in different directions of incidence is measured, and the enhancement of the antenna on terahertz electric field is verified.