Based on the nonlinear small-scale self-focusing effect of pump laser, the influences of optical Kerr medium type, pump laser beam quality, and optical Kerr medium length on the beam smoothing effect are analyzed. The research results show that in the radial smoothing scheme based on dynamic wavefront control, an excellent beam smoothing effect is obtained with nitrobenzene instead of CS2 as the optical Kerr medium when the pump laser peak intensity is constant. In the practical applications, since the small-scale self-focusing effect of pump laser is aggravated with the increase of pump laser peak intensity or optical Kerr medium length, it is necessary to select suitable parameters of pump laser and optical Kerr medium for a good beam smoothing effect. Thus the influence of small-scale self-focusing effect of pump laser can be avoided.

For the case that the minimum mean square error (MMSE) algorithm can not be used to realize the demultiplexing of mode-division multiplexing (MDM) when the mode dependent loss (MDL) is large, a demultiplexing method based on the successive interference cancellation (SIC) is proposed in order to nearly reach the performance of the maximum likelihood (ML) detection method. This method reduces the interference of the maximum power signal to the other signals and the aim for the compensation of MDL is obtained. Then the MMSE method is adopted to demultiplex the original signals. For the demultiplexing of a 6×6 MDM system under different coupling strengths as well as with and without MDL, the simulation results show that, the SIC-MMSE method always achieves good performance compared with the MMSE algorithm. The computational complexity is similar with that of the MMSE algorithm. With the differential mode group delay (DMGD) at 9 ps/km and coupling strength at -5 dB, the optical signal to noise ratio (OSNR) by the SIC-MMSE algorithm improves by 3 dB at a transmission distance of 1200 km compared with that of the MMSE algorithm.

The influence of the mean wavelength of a broad-spectral source on the scale factor is analyzed. The systematic models of the scale factors for the open-loop and closed-loop fiber optic gyroscopes are preliminarily established. The mechanism influences of the mean wavelength and the second feedback loop on the scale factor are discussed in detail. The corresponding experiments are conducted. The experimental results coincide well with the theoretical analysis results and the validity of the proposed systematic model is verified.

In order to guarantee the precision of hydroxyl (OH) tagging velocimetry measurement in combustion flow field, we investigate a background noise removal method. Based on the analysis of noise characteristics of hydroxyl tagging velocimetry experimental data in combustion flow fields, we construct a numerical model of noise attenuation. For the background noise such as local combustion OH fluorescence interference and flow stray light, we adopt a spatial filtering method based on Hough transform. As for the physical, electrical, optical and sensor noises of the measurement system, we present a noise removal method of wavelet transform to improve signal-to-noise ratio. The background noise suppression method combining spatial filtering and wavelet transform is proposed to suppress system noise effect on the spatial filtering algorithm precision, and optimize the spatial filtering results. The research results show that the peak signal-to-noise ratio is improved by 16.79 dB, and signal-to-noise ratio is improved by 13.91 dB after imaging processing. The experimental data of combustion flow field are processed, which effectively suppresses background noise, achieves the effect of image preprocessing, and meets the requirement of measurement accuracy of laser diagnostic system for measurement accuracy.

Aiming at the problems of image hue and brightness distortion in sky regions when dealing with fog images by the classic dark channel theory algorithm, we propose a fog image enhancement algorithm based on the boundary constraint weighted least squares filtering. According to the histogram property of fog image, we reduce the boundary condition and obtain the initial transmittance. The transmission is smoothed by weighted least squares filtering method and tolerance mechanism. The enhanced image is obtained by using the model of dark channel theory. The research results show that the proposed algorithm is better than the existing dark channel algorithm in terms of dehazing effect and image visibility.

Multi-focal photon-sieve arrays with different phase shift steps are designed. The imaging of the USAF1951 resolution board is obtained by phase-shifting digital holography, and the phase-shifting function of the photon-sieve array is verified in optical waveband. The experimental results shows that multi-focal photon-sieve arrays can eliminate zero-order image and conjugate image under different phase shift steps, and the system resolution is consistent with theoretical expected result. As a kind of amplitude diffractive lens, the multi-focal photon-sieve array has a wide application prospect in the fields of X-ray holography and biological cell microscopy.

In order to realize 894.6 nm single mode laser output with low threshold, high stability, we design vertical cavity surface emitting laser (VCSEL) devices with different mesa etching structure and study the influences of mesa diameter, oxide aperture shape and size on lasing performance. The research results show that the larger of the mesa in VCSEL device, the higher the threshold current; the more circular the oxide aperture, the higher the single mode suppression ratio. VCSEL devices with diameter of 4.4 μm circular oxide aperture is achieved, and the device can realize 894.6 nm single mode laser output with driving current of 0.6 mA and working temperature of 70-90 ℃, and the side mode suppression ratio is higher than 35 dB.

Copper-based shape memory alloys Cu-13.5Al-4Ni-0.5Ti with high relative density, high strength and high hardness are fabricated by selective laser melting (SLM). The microstructures are characterized and the tensile properties at room temperature and 300 ℃ are evaluated, respectively. The results show that the maximum relative density of 99.5% is obtained when the laser input energy is 110 J·mm-3. The lath martensite extending in parallel in the microstructure of the sample grows across the melting tracks and the average grain size is about 43 μm, The grain size of the SLM-fabricated sample is smaller than that of the casting sample. The average tensile strength and percentage elongation after fracture of the SLM-fabricated sample are (541±26) MPa and (7.63±0.39)% at room temperature, respectively, and the tensile strength is increased to (611±9) MPa at 300 ℃, and the percentage elongation after fracture is increased to (10.78±1.87)%. The SLM-fabricated alloy shows a good application potential in the high temperature fields.

Based on the feature learning ability of deep convolutional neural networks, a weld feature extraction method based on fully convolutional networks is proposed. In this method, the fully convolutional networks is used to predict the pixels containing the feature information of the weld, and the edge feature information of weld is supplemented by the fusion of low-level and high-level feature information. The results show that the method can get the weld position accurately under the interference of strong arc and soot particles, and has the advantages of strong anti-interference ability and accurate recognition.

TC4 alloy cladding layer is prepared on TC4 titanium alloy substrate with laser additive manufacturing (LDM) technology, and the microstructure, microhardness and electrochemical corrosion resistance of the cladding layers in sulfuric acid solution are studied. The results show that the main phase of the cladding layers is α-Ti, and the fine acicular α' martensite is formed near the β grain boundary, showing orthogonal basket-weave microstructure. With the increase of the scanning speed, the average microhardness of the cladding layers increases first and then decreases, the corrosion current density decreases first and then increases, and the charge transfer resistance increases first and then decreases, that is, its corrosion resistance also strengthens first and then weakens. In contrast, when the scanning speed is 10 mm/s, the cladding layer has the highest average microhardness (390 HV), minimum corrosion current density (1.2337 μA·cm -2), and maximum charge transfer resistance (11500 Ω·cm -2), and at this time, the cladding layer has better resistance to electrochemical corrosion.

Multiple-pulse laser shock micro-bulging experiments of T2 pure copper foils are conducted. The effects of laser power density, initial grain size and foil thickness on forming limit are investigated. Macro and micro fracture morphology of broken work are analyzed. The fracture mode of copper foils in multiple-pulse laser shock micro-bulging is discussed, and the mechanisms of four fracture modes are analyzed. Research results show that the laser power density has a significant influence on the maximum pulse number before fracture occurrence. In addition, the forming limit of foil cannot be increased through multiple-pulse forming method. Both grain size and feature size have a significant impact on the forming limit of multiple-pulsed laser shock micro-bulging. There are four fracture modes in multiple-pulse laser shock micro-bulging, that is, tensile fracture, shear fracture, mixed fracture and spallation.

The Cu80Fe20 immiscible coating is fabricated by laser cladding technique and the effects of scanning speed on the liquid phase separation characteristics, microhardness and wear resistance of the immiscible coating are investigated. The research results indicate that the delamination phenomenon appears in the Cu80Fe20 immiscible coatings; a large amount of Fe-rich particles consist of body-centered-cubic (bcc) α-Fe, face-centered-cubic (fcc) γ-Fe are dispersed in the upper fcc ε-Cu matrix, and a large amount of ε-Cu Cu-rich particles are distributed in the lower α-Fe matrix. With the increase of the laser scanning speed, the cooling rate of the molten pool increases and the size of Fe-rich particles decreases, while the surface density of Fe-rich particles increases, the spacing of neighbouring Fe-rich particles decreases, and therefore the shadow protection effect of Fe-rich particles on the Cu-rich matrix is enhanced, leading to the improvement in microhardness and wear resistance of the immiscible coating, which are both higher than those of brass.

Laser welding experiments for QP1180 high-strength steel sheet are carried out at different welding parameters, and the microstructure, microhardness, tensile properties and bulge properties of the welding joint are investigated. The results show that tempered martensite is formed in tempered zone (soft zone) of heat affected zone, leading to the softening in this zone. Increasing welding speed and reducing heat input can significantly reduce softening degree. The soft zone is strengthened by the constraints, leading to the fracture in base metal, and the strength of the soft zone is equivalent to that of the base metal. Increasing welding speed and weld line offset can obviously improve the bulge test value of the welding sheet. The welding sheet obtained at high welding speed fractures perpendicular to the weld and has high bulge test value, and the welding sheet obtained at low welding speed fractures parallel to the weld along the soft zone and has low bulge test value. Bulge test value improves gradually as the weld line offset increases and approaches to that of the base metal when the offset reaches to 30 mm.

The effects of welding mode, laser-wire distance, energy input on droplet transfer behavior and the weld porosity defects are studied by laser-MAG hybrid welding process of edge joint. The research results show that laser-MAG hybrid welding is more suitable for the edge joint because of the improvement of weld formation and inhabitation of porosity. Laser leading mode is better than arc leading mode for the less weld porosity. A large distance of laser-wire is beneficial for the stability of welding process. The arc energy input mainly affects the weld formation, while the increase of laser power prevents droplet transfer and increases porosity defects at the bottom of the weld.

The multi-imaging characteristics of CO2 laser-tungsten inert gas (TIG) arc hybrid welding plasma are observed by a high-speed camera with a self-made multi-imaging system. The research results show that three regions of the same plasma with decreasing area and increasing light intensity can be obtained at the same time by multiple imaging technology. The color of plasma gradually changes from blue and white to red in argon shielded hybrid welding, and the metal vapor plasma and argon arc plasma can't be distinguished. Since the second imaging, helium arc plasma is almost invisible, and the remaining metal plasma is still bright white. The less linear spectrum of helium radiation in the visible region (relatively weak light intensity) is the main reason why metal plasma can be distinguished clearly in helium protection; the metal plasma and shielding gas plasma are not fully mixed in hybrid welding. And the morphology of the metal plasma can be obvious influenced by the arc plasma.

Laser texture process is carried out on the surface of GCr15 bearing steel by a fiber laser and the morphology of micro texture is observed by the confocal microscope. The effects of power, pulse width and repetition times on texture morphology are analyzed. The experimental results show that with the increment of pulse width, the diameter of textured point increases and the depth of textured point significantly increases in a certain range of pulse width. Under the condition of single pulse,when the pulse width is 1000 μs, textured structure forms a convex profile, and when the pulse width increases to be more than 5000 μs, textured structure forms a concave pit. With the increment of laser power, the diameter and depth of the textured point increase. The heat effect is more obvious with the increase of repetition times. The pit is gradually deepened and then partially filled up. The height of the convex profile is firstly almost invariable and then rapidly increases. The study verifies the feasibility of the same laser to realize concave or convex micro textures simultaneously, and also provides new ideas for processing different surface topography.

The Stellite 12 coating is synthetized on the 304 stainless steel surface by laser cladding, and the effect of the addition of Ti/B4C with different contents on the microstructure and properties of the Stellite 12 coating is discussed. The microstructural growth of the coating is analyzed, and the microhardness and wear resistance of the coating are also tested. The research results show that the Stellite 12 coating is mainly composed of face-centered cube γ-Co and Cr7C3 phases. The in-situ TiC sub-micron particle phase is synthesized with the addition of Ti/B4C. The remaining B4C acts as a heterogeneous nucleation point, and thus a TiC/B4C strengthening phase with sub-micron structure is formed and the particle size gradually decreases. The TiC/B4C particles have an obvious grain refinement effect on the coating. The micro-hardness of the coating gradually increases with the addition of Ti/B4C with the maximum value of 624 HV. In addition, the wear resistance of the coating gradually increases with the addition of Ti/B4C.

The control of brass welding porosity is studied by adopting a new method of the intermediate transition layer. The weld porosities of brass laser welding under the copper intermediate layer condition and brass general butt laser welding are contrasted and analyzed. The research results reveal that the porosities of weld surface and weld interior are greatly reduced under the condition of the intermediate layer. As the welding speed increases, the porosity decreases gradually. The porosity is almost zero when the welding speed is 2.2 mm/s. When the welding parameters are the same, the porosity of the weld under the intermediate layer condition is barely one third of that in the normal butt laser welding of brass sheet. The mechanical properties of welded joint obtained at the intermediate layer condition is superior to that of welded joint obtained at normal butt laser welding. Under the premise of good weld formation, the effectiveness of the new method of the copper intermediate layer to control the porosity defects of brass laser welding is verified.

The vibration welding test of a 5 mm thick 5052 aluminum alloy is carried out by a fiber laser. The influences of joint microstructure and residual stress on the tensile properties and fatigue properties are studied. The research results show that the number of columnar crystals in the weld microstructure after vibration welding is significantly reduced, and the microstructure is more uniform and finer than that of an ordinary weld. Under the suitable vibration frequency and vibration acceleration, the residual stress of weld is decreased to 140 MPa, while that of an ordinary weld is up to 335 MPa. Under the tension-tension fatigue condition with a stress ratio of 0.1, the conditional fatigue limits of the base metal and joints are 160 MPa and 120 MPa, respectively. The fatigue source is located in the surface defects and the cracks propagate in a transgranular way. A large number of fatigue striations and secondary cracks are formed in the fractures.

The micro-nano composite structures with different micromorphologies are prepared on the nickel-aluminum bronze alloy surfaces by a picosecond laser, and then surface-modofied by stearic acid. Scanning electron microscopy and X-ray diffraction and others have been performed to characterize the morphologies and chemical composition. The research results show that the contact angle of the surfaces obtained by picosecond laser processing and surface modification of stearic acid is more than 150°. The samples have different surface morphologies and wettability under different laser fluences. With the increase of laser fluence, the sliding angle of the modified sample surface gradually decreases. When laser fluence is 6.85 J/cm2, the sliding angle decreases to 7°. With the further increase of laser fluence, the sliding angle gradually increases again. The corrosion resistance test results show that the surface of superhydrophobic nickel-aluminium bronze alloy has better corrosion resistance. The superhydrophobic surface of nickel-aluminium bronze alloy can be machined with optimized process parameters, which is helpful to improve the corrosion resistance of nickel-aluminium bronze alloy.

The pure Ti components are prepared by the laser melting deposition technique with coaxial powder feeding, and the residual stresses in the different regions on the scanning surfaces of samples are measured by the hole-drilling strain method. The effects of laser power, scanning speed and powder feeding rate on the residual stress distributions on the scanning surfaces of samples are also investigated. The research results show that the highest compressive stress appears in the joint area between the deposited component and the substrate and the other areas exhibit the tensile stresses. Moreover, the lowest stress appears at the top area of samples. The residual stress in the joint area between the deposited component and the substrate is strongly dependent on the laser process parameters, while the latter has a slight effect on the residual stress distribution in the top area. The reasonable choice of laser process parameters can effectively reduce the residual stresses of deposited components.

Taking polystyrene powder as experimental material and dimensional accuracy as evaluation index, we study the effects of laser power, scanning pitch, layer thickness and scanning speed and their interactions on the forming precision of selective laser sintering parts. The mathematical model between process parameters and dimensional accuracy are achieved and the optimal process parameters are obtained by response surface methodology. The research results show that the dimensional deviation rate decreases with the increase of laser power and scanning speed, increases at first and then decreases with the increase of layer thickness, and increases with the increase of scanning pitch. The interaction between laser power and single layer thickness and the interaction between scanning pitch and layer thickness have a significant effect on the dimensional deviation rate. The maximum error between the predicted value of the response surface method and the actual value is less than 7%.

The alloy powders containing Ti-48Al-2Cr-2Nb and niobium are mechanically mixed, and γ-TiAl alloy samples are successfully prepared with the laser additive manufacturing technique. The influence rules of laser power, scanning speed and powder feeding amount on deposition forming are studied, and the microstructure, phase composition, fracture morphology and hardness distribution of the deposited layer are analyzed. The research results indicate that the width and height of the deposited layer increase with the increase of laser power. With the increase of the scanning speed, the width and height of the deposited layer decrease. With the increase of powder feeding amount, the width of the deposited layer increases and the height of the deposited layer is basically unchanged. The deposited samples obtained under the optimum technology parameters are well formed and have no metallurgical defects. The deposited layer consists of a large number of γ phases and a small amount of α2 phases. The compressive yield strength, compression strength and compression ratio are 905 MPa, 1542 MPa and 14.7% respectively along the Z direction of deposited specimen at room temperature. The tensile strength and elongation are 425 MPa and 3.3%, respectively. The fractures of compressive specimen and tensile specimen are both quasi-cleavage fractures.

The electron probe micro-analyzer (EPMA) technology is used to analyze and study various forms of platinum (Pt) particle inclusions in continuous-smelted Nd∶glass before and after intense laser irradiation. After intense laser irradiation, platinum particle inclusions exhibit three typical EPMA morphology. Their forms come from the joint result of the thermal stress and vapor pressure caused by platinum particles absorbing laser energy. The thermodynamic properties of Nd∶glass also have an effect on the morphology. The phenomenon of Pt-Zr-Sn being co-wrapped is found by comparing the EPMA distribution characteristics of zirconium and stannum impurity inclusions.

A method to acquire the coordinates of camera and measured surfaces in the deflectometry is proposed. A circular window glass is tested by the slope calculation and the shape reconstruction. The final test results by the proposed method are close to those by the interferometer and the Zhang's calibration method, and the feasibility and correctness of the proposed method are proved. The research results show that the calibration by the proposed method is simple and flexible. This method can be used to achieve the global calibration of cameras and the measured surfaces, and is suitable for the calibration of online measurements.

Based on laser-induced incandescence (LII) and cavity ring-down spectroscopy (CRDS), we establish a measurement setup for the study of flame soot particles, and characterize the performance parameters. The measurement results of the path-integrated attenuation coefficient of soot particles show that the two-color LII test system and the CRDS system are independent of each other. When the two-color LII and CRDS systems are opened at the same time, the measured path-integrated attenuation coefficient increases first and then decreases with the increase of the height above the burner, and the measurement results of the two systems have good correlation. By optimizing the fitting model and removing the system noise, we obtain a better cavity ring-down signal fitting results.

To solve the problem of low recognition rate of perimeter intrusion behaviors, an improved empirical mode decomposition algorithm is used in the perimeter intrusion behaviors classification of fiber Bragg gratings. In this algorithm, the intrusion signal is extracted from the overall signal by using the short time average zero-crossing rate algorithm, and the double extreme wave prolongation is used to decompose the end effect of empirical mode decomposition algorithm. The improved algorithm is employed to decompose the intrusion signal and the characteristics of the effective components are extracted. Support vector machine is used to identify the intrusion behaviors. The nonintrusive behavior and four different invasion behaviors such as climbing, shearing, colliding, and touching are used to classify and recognize in outdoor environment. The results show that the proposed method can effectively identify different intrusion behaviors, and the recognition rate is greater than 96%.

Aiming at the problem of underwater short-range detection of incoming targets, a random positioning method driven by fluid dynamics is proposed. The single-beam pulse laser driven by the navigation hydrodynamic force is used to dynamically scan, and the scanning periodic is recorded by the magnetic sensor. Based on the heavy tail function, the target echo equation is derived, and the magnetic dipole equivalent model of the magnetic detection system is established. The optical magnetic measurement signals are calculated respectively by using the peak detection method and the threshold detection method. The underwater short-range target acquisition model and the azimuth detection accuracy equivalent model are established. The influence mechanism of laser emission power, pulse width, threshold, and noise on measurement accuracy is studied. The results show that the azimuth measurement accuracy and target capture rate increase with the increase of the laser emission power, and decrease with the increase of the pulse width and the receiving circuit noise voltage. The azimuth measurement accuracy reaches the maximum when the detection threshold is 300 mV. The capture rate varies slightly with the increase of the threshold. When the threshold is close to the peak of the echo pulse, the target capture rate decreases rapidly.

Based on the analysis of the influence of optical system on tracking detection and combined with the instrumental functions, a smart method based on glued lens is proposed to reduce tracking offsets. The tracking optical path in the femtosecond laser tracker is optimized. At the same time, the optical path for collimation and expanding is improved, and the optical system is refined. The influence mechanism of receiving laser power and stray light in the optimized optical system on tracking detection is analyzed in detail. Based on the optimal design of the optical system, the experimental system is established and the detection experiment is conducted. The research results show that the tracking detection accuracy can reach 3 μm after compensation, which meets the precision tracking requirements of instruments.

Aiming at the low precision problem of the three-dimensional shape robot measurement system composed of industrial robots and topographic sensors, a three-dimensional shape complex curved surface measurement system based on iGPS (indoor global positioning system) is proposed. The overall design scheme of the proposed measurement system is introduced and a mathematical model is established for it. Experiments on length measurement accuracy and repeated measurement accuracy are carried out. The experimental results verify the accuracy and reliability of this measurement system for large-scale complex curved surface topography measurement. The shape measurement of large-sized workpiece with double arched surface is carried out. The measurement results verify the feasibility of this measurement system.

An evaluation algorithm of the pupil characteristic parameters is proposed, aiming at the practical application requirements of lithography illumination system. By changing the intensity distribution of pupil, this algorithm can be used to simultaneously calculate the pupil ellipticity, non-balance_X, non-balance_Y, non-balance_quad, and other pupil characteristic parameters in different illumination modes. The relay lens set of the 28 nm node scanning lithography illumination system is used as an example and the pupil characteristic parameters under the traditional illumination mode are analyzed. The simulation results show that the maximum value of pupil ellipticity in the full field of view is 0.95%, and the maximum values of non-balance_X and non-balance_Y are 0.18% and 0.19%, respectively. In addition, the maximum value of non-balance_quad is 0.66%. These data satisfy the actual index requirements of the 28 nm node scanning lithography. The proposed algorithm can help to evaluate the pupil performances quickly at the optical design stage.

The diffraction characteristics of the convex blazed grating are investigated by using rigorous coupled-wave analysis. The convex blazed grating with a central period of 2.45 μm, a curvature radius of 51.64 mm, and an aperture of 17 mm is fabricated by using holographic lithography-scanning ion beam etching method. The blazed angle is 6.4°, and the vertex angle is 141°. The results show that the first-order diffraction efficiency of the proposed grating is greater than 40% in the whole visible and near-infrared band, and the first-order diffraction efficiency at blaze wavelength is greater than 75%.

Under room temperature, the influences of different parameters on the formation of femtosecond laser-induced aerosols with relatively large size in a small cloud chamber are studied. The experimental results show that, under sub-saturated condition, the aerosol number density increases with the increase of relative humidity, and 0.3-0.5 μm aerosols are dominated. However, when the environmental relative humidity is near to be saturated, the number density of relative large-size aerosols (with their diameter D≥0.7 μm) is enhanced mostly, and at the end, the number density of 1.0-2.0 μm aerosols is comparable with that of 0.3-0.5 μm aerosols. When the laser irradiation duration and tightened focusing condition are prolonged under this near saturated condition, the number density of different size aerosols increases simultaneously at the same degree, and ultimately the corresponding size distribution does not change too much. Theoretical analysis results show that environmental relative humidity plays a key role for femtosecond laser-induced relative large-size aerosol formation.

Supersonic laser deposition (SLD) is a newly developed laser hybrid manufacturing technology, which combines the advantages of laser irradiation and cold spray. With the synergistic effects of thermal energy from laser irradiation and kinetic energy from high velocity particles impacting, a wider range of materials can be deposited by this technique and unique microstructures and properties can also be obtained. Based on the research results of the authors' team in the field of SLD, the latest research progress at home and abroad from the aspect of technique principle, deposition material range, phase and microstructure, and performance characterization are summarized. And then, the future trend and challenge of SLD technology are prospected from the perspective of process exploration, equipment development and property evaluation.

A miniaturized passive laser heterodyne detection system is built for monitoring atmospheric environment with a near infrared diode laser operating at 1.57 μm as the local oscillator light source. In order to evaluate the performance of the system, we use light emitted by an external cavity laser with narrow linewidth as the signal light mixing with the local oscillator light. The bandwidth of the system is 0.032 cm -1 and the minimum detectable sensitivity is 25 pW, which is 1/68 of the dark current noise power of photodetector. CO2 solar spectral signal is measured with the system. The volume fractions of two main absorption lines are inverted, and the values are all around 396×10-6 with measurement error of 7.6×10-6. The measured results are consistent with the actual CO2 column concentration in the whole atmosphere, and the feasibility of the system for atmospheric environment monitoring is verified.

A laser-induced breakdown spectroscopy system integrated with a micro-imager is developed. The energy stability of laser and background noise level of spectrometer are analyzed with the descriptive statistical method. The stability features of laser-induced breakdown spectroscopy signals in gas and solid samples are emphatically analyzed and compared. The results show that the laser-induced breakdown spectroscopy signals of air have the characteristics of random fluctuation and normal distribution. The laser-induced breakdown spectroscopy signals of aluminum alloy have the characteristics of position sensitivity and non-random fluctuation. Compared with that of the air sample, the instability of laser-induced breakdown spectroscopy signal of the aluminum alloy sample is mainly due to the change of the light-matter interaction region. The stability can be effectively improved by multi-pulse averaging for the laser-induced breakdown spectroscopy signals with normal distribution characteristics.

On the basis of extracting all the characteristic peaks of laser-induced breakdown spectroscopy (LIBS), an effective tea classification model is established based on support vector machine. The effective LIBS spectral data (190-720 nm) of fifteen tea samples are collected, and the spectra are preprocessed by window translation smoothing and peak shift function correction. Combined with principal component analysis for dimensionality reduction, the recognition rate of green tea, black tea and white tea is 98.3%. Different varieties of tea in the same species also achieve good recognition. The research results show that LIBS has a good prospect in the rapid identification of tea varieties.

The Gaussian laser beam is shaped into a flattop laser beam with uniform energy distribution by a diffractive optical element. The Cu plasma characteristics induced by two lasers are compared, and the improvement of the beam shape modification on the stability of laser-induced breakdown spectrum is studied. The research results show that the uniformity of beam energy distribution causes the difference in the morphology of the ablation crater and single-shot ablation amount. The relative standard deviations of the Gaussian laser and the flattop laser induced spectra intensity, plasma temperature and electron density are 12.33% and 6.37%, 2.10% and 1.32%, 5.31% and 0.65%, respectively. The stability of the laser-induced breakdown spectrum after beam shaping is significantly improved, and the two laser-induced plasmas are all in the local thermodynamic equilibrium state.

Potassium thiocyanate (KSCN) is used as the internal standard. And principal component analysis (PCA) is utilized to reduce the dimension. Quantitative analysis model, that is, support vector regression (SVR), is established by support vector machine (SVM) algorithm. Meanwhile, three parameter optimization methods, that is grid search (GS), genetic algorithm (GA) and particle swarm optimization (PSO), are used to fulfill quantitative analysis of single and mixed solutions of pyrene and phenanthrene. The research results show that the use of KSCN as the internal standard improves the accuracy of the quantitative mensuration results. The modeling speed is improved by PCA dimensionality reduction. The average relative errors (AREs) of pyrene solution predicted by three optimized models are within 7.6%. The AREs of phenanthrene solution prediction are within 11.3%. The three parameter optimization methods have similar prediction results for the same sample, but the operating rate of GS is the fastest. Considering the errors and analysis speed, the best results of phenanthrene and anthracene mixed solution are obtained by GS-SVR model. Surface-enhanced Raman spectroscopy (SERS) technology combined with SVM algorithm is expected to actualize quantitative analysis of polycyclic aromatic hydrocarbons.

Silver nanoparticles are prepared by redox reduction of phytic acid (IP6), trisodium citrate and silver nitrate, and IP6 terminated gold nanoparticles are synthesized by displacement reaction of silver nanoparticles with chloroauric acid. The particle size distribution and composition are studied, and it is found that the uniformity of the nanoparticles is favorable. By synthesizing surface enhanced Raman scattering (SERS) substrate, Raman probes can be accurately and efficiently detected, and the detection limit can reach 10-8 mol·L-1. When a proper amount of Fe3+ (mass fraction from 0.28×10-6 to 0.56×10-6) is added, IP6 forms a chelate with Fe3+, which increases the number of hot spots and further enhances the SERS enhancement effect and detection sensitivity.