Bit error rate performance of free space optical (FSO) communication systems based on differential detection with zero decision threshold (DDTZ) under moderate and strong atmospheric turbulence is investigated. Computational expressions of average bit error rate of the DDTZ FSO communication system and the differential detection system with optimal threshold are respectively derived when the two transmission lights are completely correlated or uncorrelated. Simulation results show that the problem of the error floor which is presented in single detection with fixed threshold (SDTF) dose not exist in DDTZ. The correlation of two receive signals has no effect on bit error rate of DDTZ. The bit error rate performance of DDTZ is worse than that of optimal differential detection, but better than that of SDTF. Therefore, considering of realizability and bit error rate performance, the DDTZ has more practical application value.

The optical pseudo random signals produced by pseudo random signal generator and electro-optic modulator in traditional photonic-assisted compression sampling method are replaced by optical chaotic signals generated by photoelectric oscillator. The optoelectronic oscillator simulation system is set, and produces optical chaotic signal, whose bandwidth reaches 30 GHz. Based on 1.25 GHz low-speed analog-digital converter, five frequency-random and amplitude-random sparse signals in frequency domain distributed in the 0 to 10 GHz frequency band are compressed, sampled and reconstructed, successfully. At last, a detail comparison on the reconstruction performance between the chaotic photonic compression sampling and traditional methods is shown through numerical simulation. The simulation results show that the former is better than the latter and the chaotic photonic compression sampling method is feasible.

In order to solve problem of the strain measurement limitation under high temperature, the temperature and strain characteristics of the type II pure-quartz-core fiber Bragg grating (FBG) written by femtosecond pulse laser are studied. Experimental results show that when the temperature is ranging from 20 ℃ to 1000 ℃, the pure-quartz-core FBG exhibits good linearity with the correlation coefficient of 0.9996 and the temperature sensitivity of 14.07 pm/℃. When the temperature is under 400 ℃, the pure-quartz-core FBG exhibits good wavelength stability under the uniform strain. When the temperature is above 500 ℃, the strain loading leads to fiber elongation and the red shift of the center wavelength.

The generation of vortex light in the fiber has an important application value in improving the performance and reducing the cost of orbital angular momentum communication system. Few-mode fiber is a kind of optical fiber with fundamental mode and low order modes. According to the coupling mode theory and the generation principle of vortex light, the effect of the incident angle on the excitation efficiency of the first order mode in the few-mode fiber is simulated. The first order modes of TM01, TE01 and HEeven21 are generated in the few-mode fiber, and the first order vector beams with HEeven21 and HEodd21 modes are superimposed to produce vortex light. The results of polarization detection and triangular diffraction show that the vortex light produced by the few-mode fiber is circularly polarized light and the topological charge (l) is 1. The use of few-mode fiber in the experiment provides a simple and low-cost method for the producing of vortex light.

When a Cassegrain telescope system is taken as optical antenna, the error of annular facula position detection on the photosensitive surface of four-quadrant photoelectric detector in acquisition, pointing and tracking system for atmospheric laser communication is analyzed. Based on the equivalent effects of the facula center shelter and dead zone induction light energy, mathematical models of relationships among facula center coordinate, dead zone width of detector, inner and outer circle radii of annular facula and incident annular facula offset are theoretically deduced. Numerical simulation and experimental results show that the detection linear range of annular spot is smaller than that of complete Gauss facula, and the detection sensitivity is lower. The appropriate Cassegrain optical antenna and facula radius are selected according to the experimental conditions, so that the detection linear range of detector is the largest when the shading ratio is 30%, and nonlinear error will not occur. An annular facula error compensation algorithm is proposed to overcome the position detection error caused by the facula center shelter, and the detection accuracy of the detector can reach 0.0015 mm.

The noise of repeaterless remote demodulation systems of fiber-optic hydrophone primarily comes from amplified spontaneous emission (ASE) noise and double Rayleigh scattering (DRS) noise. To optimize the noise and improve the performance of the system, the effects of ASE noise and DRS noise on phase noise of the system are separated experimentally by noise fitting. The results show that the ASE noise is the main noise source of the experimental system, while DRS noise also is the limiting factor of the phase noise reduction. The noise suppression effects of the illuminant phase modulation scheme on both ASE noise and DRS noise are theoretically analyzed and experimentally confirmed. Experimental results show that the total phase noise of 100 km remote demodulation system is suppressed by 5.2 dB when the sinusoidal phase modulation with amplitude of 2.2 rad and frequency of 40 MHz is applied by lithium niobate phase modulator, while ASE noise power is reduced by 5.2 dB and DRS noise power is reduced by 6.2 dB.

An all-fiber double-cladding photonic crystal fiber amplifier is designed and built, and the Yb-doped double-cladding photonic crystal fiber (DC-PCF) is used as the gain fiber. In the experiment, a (6+1)×1 end-pump coupler is fabricated to match the DC-PCF with six multi-mode fibers as pump fibers and ordinary single-mode fiber SMF-28 as the signal fiber. The cladding diameter and the core diameter is 105 μm and 125 μm respectively, and the numerical aperture is 0.22. An end-pump coupler is fabricated by the capillary tube method and directly spliced with DC-PCF. At last, the DC-PCF is spliced with a tapered end-cap. The end-cap is plated with 1000-1100 nm anti-reflective coating film to prevent the entire amplification system from the effect of laser feedback. The designed amplifier is tested with pump light at the wavelength of 976 nm and continuous signal of 2 W at 1064 nm. When the pump power reaches the maximum of 151.83 W, the maximum output power is 108.1 W and the slope efficiency is 72.7%. The output spot is a good fundamental mode spot. It indicates the excellent characteristics of the photonic crystal fiber, which can simultaneously maintain the large mode field and the fundamental mode transmission.

A parallel cycle shift comparison method of frame synchronization is designed and implemented. The method is applied to atmospheric laser communication system with transmission rate of 2.5 Gbit·s-1 and pulse position modulation (PPM). The operation principle and the performance of the frame synchronization are studied. The fault-tolerant ability of frame synchronization in atmospheric channel is improved with the special frame head synchronous sequence. The system can maintain high synchronization probability when the channel condition becomes worse with decreasing of the detection threshold. Analysis and simulation results show that the frame synchronization scheme can realize the frame synchronization in the high-speed PPM optical communication, and the detection threshold values are 14, 7-9, 10-13 corresponding to three different atmosphere conditions to maintain good performance of the system.

A 3×3 mode division multiplexing communication experimental system is built based on the pattern selectivity of photonic lantern pattern mode multiplexer/demultiplexer. The structural diagram and the operating principle of the system are given. With an intensity modulation and direct detection system, the transmission of 3×4.25 Gbit/s pseudo-random signal in 10 km few-mode fiber is achieved when we use the transmission channels of LP01, LP11a and LP11b modes as the separate channels. The waveforms, eye diagrams and bit error ratio of the received signal are measured. Results show that when the received signal power is -19.1 dBm, -15.8 dBm, -16.6 dBm respectively, the bit error rate of LP01, LP11a and LP11b modes can reach 10-3.

A phase noise compensation algorithm, which carries out unscented Kalman filter (UKF) in time domain, is proposed based on high-order quadrature amplitude modulation (QAM) and large linewidth coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. The algorithm realizes channel equalization based on the training symbol frequency domain Kalman filter at the receiver, and less frequency domain pilot data overhead is used to carry out frequency domain extended Kalman filter. The common phase error (CPE) noise is compensated first. Then, inter-carrier interference (ICI) phase noise coarse compensation is carried out on the data after CPE noise compensation in time domain. Initial pre-decision is performed on the frequency domain data after phase noise coarse compensation. Combining with the primary time domain data at the receiver, UKF is applied to the decision data in time domain to achieve fine compensation of ICI phase noise. Phase noise coarse compensation is performed for frequency domain data after fine compensation, and iterative operation is carried out, which greatly improves the compensation effect of phase noise. Simulations with transmission distance of 100 km are carried out based on 50 Gbit·s-1 CO-OFDM system. Compared with other algorithms, the proposed algorithm has higher spectral efficiency and better compensation effect. After two iterations of the transmission signal with laser linewidth of 700 kHz and modulation format of 32QAM, the bit error rate performance of proposed phase noise compensation algorithm can still reach the upper limit of forward error correction. The proposed algorithm promotes the application of large linewidth CO-OFDM systems in long distance access networks and metropolitan area networks.

Aiming at the problem of poor real-time performance of Brillouin optical time domain analysis (BOTDA) distributed optical fiber sensing system, we propose a extraction method of Brillouin scattering spectrum feature based on the cross-correlation convolution and high-order centroid calculation to reduce measuring time. Firstly, the sweep data of the Brillouin scattering spectrum along the optical fiber is convoluted with the ideal Lorentz curve, and the convolution result has a nearly ideal Lorentzian distribution around its peak. Then we carry out high-order centroid extraction, and take the extracted result as an estimated value of Brillouin frequency shift (BFS). A 1.5 km Rayleigh BOTDA temperature sensing experiment is designed to verify the feasibility of the proposed algorithm. The results show that the proposed algorithm is different from the conventional Lorentz curve fitting (LCF), it avoids extension of measuring time caused by the complex iterative process, and has good real-time performance and measurement accuracy. The proper selection of data point numbers and calculation orders can control the error within 1 MHz. When the sweep interval has to be increased to reduce the measurement time in long-range and high-resolution dynamic measurement, the proposed algorithm has a smaller measurement error than the LCF based on the Levenberg-Marquardt (LM) algorithm.

The spatial mode-matching problem of Gaussian beams in the preparation of squeezed field with a high compressibility is studied. The study results show that, for a small target spot, the allowed deviation ranges of the waist position and size of the injected beam are small, and the mode-matching efficiency is more sensitive to the deviation of the waist position, while for a large target spot, the situation just reverses. In addition, the ellipticity and astigmatism of the laser spot and the thermal effect of the nonlinear crystal can lead to the decrease of the mode-matching efficiency. An asymmetric cavity can expand the allowed deviation range of the waist position which matches with optical parametric oscillators, which is easier to obtain a higher mode-matching efficiency.

By using the spatial filtering method and the oceanic turbulence power spectra, the numerical simulation program of imaging by diffuse reflection light from extended objects in oceanic turbulence is designed. The dependence of the imaging quality on the oceanic turbulence parameters and the receiver size is studied. It is found that, with the increases of the ratio of seawater refractive index change caused by temperature to that caused by salinity in the oceanic turbulence power spectra and the dissipation rate of seawater temperature variance, and with the decrease of the dissipation rate of kinetic energy per unit fluid mass, the seeing parameter in oceanic turbulence decreases and the imaging quality degrades. The proposed numerical simulation method provides a feasible and correct approach for the study of imaging by diffuse reflection light from extended objects in oceanic turbulence.

Based on the coupling effect of inhomogeneous media on laser transverse modes in resonant cavities, a matrix algorithm for calculating the stable oscillation modes in resonant cavities is proposed. Energy coupling happens between transverse modes during their propagation process in the resonant cavity under the action of inhomogeneous media, and the incoherent transverse modes are coherent gradually. After a few round-trips, the transverse modes are superimposed with each other linearly by a certain energy proportion and form a stable oscillation mode. A coupling matrix of coupling effect for inhomogeneous media is given and the round-trip laser-field is expressed as a vector form. Optical field variations before and after passing through the media are calculated by the matrix calculation algorithm. A stable plane-concave cavity model is built, which is used to study the propagation of the laser field in the resonant cavity with the matrix calculation algorithm. Several stable oscillation modes are obtained under different conditions, which have a good agreement with the ideal modes. The study proves the existence of the coupling effect of inhomogeneous media and provides a new method for fast calculation of stable oscillation modes in resonant cavities.

A real-time monitoring system for center frequency of pulse laser is designed and built based on the optical heterodyne method. The single-frequency nanosecond pulse laser to be measured is mixed with a frequency-shifted continuous reference beam whose spectrum characteristics are known, and a light intensity signal is generated, which is then recorded by a photodetector and a data acquisition card. The center frequency information of the pulse laser can be calculated according to the spectrum of the beat signal. Measurement rate and precision of this system are evaluated through the method of frequency shifting, chopping and self-heterodyne, which uses a 1.57 μm continuous single-frequency laser as a reference beam. Experimental results show that the response time of the system is 6 ms, and the root-mean-square error is less than 0.07 MHz when the width of laser pulse is around 30 ns and the sampling rate is 2 GSa·s-1.

The temperature characteristics of emission-cross section spectra of Nd∶GdVO4 and Nd∶YVO4 crystals are studied experimentally. According to the relationship between the emission cross section spectra and the laser wavelength, the influence of temperature on the output spectra of Nd∶GdVO4 and Nd∶YVO4 dual-frequency microchip laser wavelengths is further investigated. The experimental results show that, in the studied temperature range, the central wavelength of the emission-cross section spectra of Nd∶GdVO4 and Nd∶YVO4 crystals shows red-shift and the peak decline. Both of them are linearly related to the temperature. The wavelength of the corresponding dual-frequency microchip laser also shows a linear red shift with temperature increasing, but the double frequency difference remains unchanged. The power balance of the dual-frequency laser changes with the common red-shift of the crystal emission cross section spectrum and the laser wavelength.

The thermal effect of gain medium is an important factor to control the high power and high beam quality of the grazing incidence slab laser. The Nd∶YAG and sapphire crystal bonding method is used to study the thermal effect of grazing incidence slab laser. The temperature field distribution and thermal focal length of gain media of Nd∶YAG and sapphire bonding crystal are simulated theoretically. The output characteristics of gain media of Nd∶YAG and sapphire bonding crystal and single Nd∶YAG crystal are compared experimentally. The maximum stable output power of the bonding crystal is 26% higher than that of the single Nd∶YAG crystal, under the same condition of cavity length and pump free oscillation. When the pump power is 44 W, the thermal focal length of bonding crystal increased by 69% with respect to the single Nd∶YAG crystal. The beam quality factors along the width and thickness direction of bonding crystal are M2x=1.84 and M2y=2.29, respectively. The beam quality factors along the width and thickness direction of single Nd∶YAG crystal are M2x=2.92 and M2y=4.38, respectively. The theoretical analysis and experimental results show that the Nd∶YAG and sapphire bonding crystals can reduce the thermal effect of gain medium in grazing incidence slab laser, which is beneficial to improve the output power and beam quality.

Because of the large difference in beam quality between the fast axis and slow axis directions of the diode laser, a prism stack is used for beam shaping to complete fiber coupling of the diode laser stack. A beam shaping technology of filling the dark areas in the fast axis direction before rotating rearrangement is proposed. The technology is based on the total internal reflection of prism stack and the deviation effect of the parallel plate, and it can complete the whole beam shaping process without using prism stack. By the proposed technology, the laser from stack which is equipped with 8 bars is coupled into a fiber with a core diameter of 200 μm and numerical aperture of 0.22. The output power can reach 544.47 W and optical-to-optical conversion efficiency of the system can reach up to 85%.

To research the electro-optic effect of lead magnesium niobate-lead titanate (PMN-PT) transparent electro-optic ceramic at different temperatures from 275 K to 325 K, ferroelectric domains with different sizes are observed, and electro-optic coefficient of the ceramics with different ferroelectric domain sizes are measured. The influence of temperature on the electro-optic effect is explained from the viewpoint of ferroelectricity. The electro-optic effect the electro-optic ceramic at different wavelengths is characterized. The results show that the electro-optic coefficient of the ceramic is larger at low temperature. The electro-optic coefficient decreases with the increase of the temperature, but the trend varies slightly with different bands, which explains in microcosmic view that the dielectric property variation of the ceramics is the reason of electro-optic characteristic variation due to temperature variation.

Aiming at the problem that the surface shape of polishing pad in continuous polishing is difficult to control precisely, the basic model of optical element polishing is established based on Preston equation and Winkler assumption. Through theoretical analysis, computer simulation and experiment, system characteristics of the continuous polishing is studied further. The result shows that the system has a state that can keep the surface shape of the disk unchanged. The state of this situation is the equilibrium state of the system. It is possible to obtain the high precision plane continuously without adjusting the position of conditioning plate when the workpiece is polished in the equilibrium state. Under different working conditions, the position of the conditioning plate is different in the equilibrium state of the system. The relationship between the position of the conditioning plate and the size of the workpiece in the equilibrium state is quantitively studied by using established model. The experiments prove that the accuracy of workpiece surface shape and processing efficiency are improved when the workpiece is polished in equilibrium state.

Two kinds of Ni-Ti-Si composite coatings are prepared on copper alloy surfaces by the laser cladding technique. The compositions, microstructures, friction and wear properties of these coatings are measured and analyzed. The results show that the Ni-15Ti-15Si coating (coating 1) microstructure is mainly composed of the dendritic TiSi, TiSi/TiNi3 eutectic structure and the γ-Ni phase, however the Ni-35Ti-15Si coating (coating 2) is mainly composed of the black dendritic Ti2Ni3Si strengthening phase and the white band shaped Ti2Ni phase. The average microhardness of coating 2 is 1.3 times of that of coating 1 and is about 9.5 times of that of copper alloy. The coating 2 at a room temperature possesses the outstanding wear resistance with an average friction coefficient of 0.54, 35% smaller than that of the copper substrate.

The process of laser transmission welding of polycarbonate is studied. The relationship between welding quality and surface roughness is investigated from the perspectives of fracture morphology and material absorptivity. Based on the Weierstrass-Mandelbrot function and measured points data, the three-dimensional real surface model is built and the temperature field numerical simulation of single-board welding is carried out. Experimental results show that, with the increase of the specimen surface roughness, the welding quality deteriorates. Simulation results show that the rough surface reaches peak temperature faster than the smooth surface, while the peak temperature of the smooth surface is higher than that of the rough surface. With the increase of the welding rate, the welding temperature appears an overall decline, and the temperature variation curves of surfaces with different roughness overlap gradually.

By the SiC particle tracer method, the effect rule of filler wire on the surface flow of molten pool is obtained, and the effects of different welding processes, wire feeding modes and wire feeding angles on the fluctuation behavior of the molten pool surface and weld formation are analyzed. The results show that, in the autogenous laser welding process, the liquid metal on the molten pool surface flows to the back and the other side of the molten pool, the molten pool surface fluctuates remarkably, and depression defects appear on the weld surface; in the laser welding process with filler wire, the molten pool surface metal flows rapidly from forward to backward, the molten pool surface is relatively stable, and the weld surface is well formed. In the process of laser welding with filler wire, the transition modes of filler wire have significant effects on the stability of the molten pool surface, and it is beneficial to obtaining a stable liquid bridge transition and reducing the weld hole defects by reducing the wire feeding angle.

With different pure metal materials such as copper, silver, tungsten, vanadium, tantalum and molybdenum as filler metals , the experiments of laser welding of 304 stainless steel (304 SS) and niobium are carried out by using the preset interlayer method. The results show that, among all the filler metals to be selected, Cu and Ag as interlayer can be used to realize the connection between 304 SS and niobium. The joint strength with the former as interlayer is the highest which reaches up to 250 MPa, thus the optimum filler metal is Cu. The hindering effect of Cu interlayer on the formation of Fe2Nb increases with the increase of Cu interlayer thickness, and so does the strength of joints, but the Cu interlayer cannot be too thick.

By the multi-pass fiber laser welding technique with filler wire based on the ultra-narrow-gap grooves, the 50 mm thick SA508Gr.3Cl.2 nuclear power steel is welded, and the microstructures and properties of joints are tested and analyzed. The results show that there are no macro defects inside the welded joints. After heat treatment, the central organization of the welds in the middle of joints mainly consists of upper bainite and acicular lower bainite, the coarse grain area in the heat affected zone near the base material consists of high-temperature tempered martensite, and the microhardness of this area is 280 HV. The tensile fracture position of welding joints is located in the base material, which indicates that the tensile strength of joints is good. The impact toughness of the welds in the top, middle and bottom area of joints are smaller than that of the base material, but the fracture morphology of the impact specimen extracted from the welds has certain characteristics of toughness fracture.

Based on the laser melting deposition technique, the TC4-Cu duplex coating is prepared with A3 steel as the matrix, copper alloy as the transition layer and TC4 alloy as the coating. The interface structure, chemical compositions and phase compositions are analyzed. Meanwhile, the microhardness and the corrosion resistance of this coating are tested. The results show that the atom diffusion occurs at the TC4-Cu-Fe interfaces. Solid solutions, like α-Fe and α-Ti, are formed at the interfaces. The grains in the binding area have small sizes. The Ti diffusion to the Cu-Fe interface is blocked by the transition layer successfully. The average microhardness of the coating is about 500 HV, which is about 3 times of that of the matrix. The corrosion resistance of the TC4-Cu duplex coating is slightly higher than that of the commercial TC4 alloy, and far higher than that of A3 steel.

Based on the laser controlled hot fracture method, a method of separating thick transparent materials with a multi-focus laser is proposed. The optical system which can support three focal points is designed by using the theoretical calculation and ZEMAX software simulation. The separation experiments of transparent materials including laminated glass, potassium dihydrogen phosphate (KDP) crystal and ultra clear glass are carried out by using this system. The results show that this method can obtain the flat and smooth cross section without sub-surface damage and with small roughness, which effectively solves the problem that the hot fracture separation method by a single laser focus is limited by the material thickness, and has great application prospects.

To solve the problem of weld defects caused by zinc vapor in the process of laser welding of galvanized steel sheets, we adopt the laminar flow above a keyhole to keep the keyhole open continuously and form a stable zinc vapor venting channel. The effects of the laminar gas flow on weld forming quality and mechanical properties of gap-free laser lap welded joint of galvanized steel sheet are studied. The influencing mechanism of the laminar flow on the effective escape of zinc vapor is analyzed with the utilization of real-time monitoring and numerical simulation of the welding process. The results show that for gap-free laser lap welding of DP590 galvanized steel sheet with thickness of 1 mm, the laminar flow can effectively promote the escape of the zinc vapor, and thus a lap joint with excellent surface quality and mechanical properties is obtained.

Precise pulsewidth measurement of petawatt laser with high energy is important to diagnosis of the focal intensity of the off-axis parabolic mirror and analysis of the gratings′ damage threshold. Two sources of error are discussed in this article, namely, the beam pointing and the periodic modulation of the near field distribution. The results show that when the stability of mirrors is within 5 μrad, the leam pointing error is 0.03%. The error decreases when the modulation period of near field increases. The error increases when the modulation depth increases. Besides, adopting mirror structure can reduce the measurement error caused by the near-field defects. When the period modulation depth of the near field is 1.5 and the modulation period is greater than 10, the comprehensive error is less than 20% and the minimum can be reduced to 10%. Total error of mirror structure is overall below 15% and the minimum can be reduced to 0. In the petawatt laser pulse width measurement experiment, the effect and improvement of the modulation of the near field on pulse width measurement is demonstrated.

The real refractive angle of light beam through the wedge-shaped absorbing medium is studied, and the relationship between the real refractive angle and the real and imaginary parts of the complex refractive index is obtained. The results show that, when the refractive index of the air, the complex refractive index and the vertex angle of the wedge-shaped absorbing medium are given, the real refractive angle can be calculated. When two light beams enter vertically into two samples with the same material but different vertex angles, respectively, the real and imaginary parts of the complex refractive index of the absorbing medium can be obtained by inversion if the real refractive angles of light exiting from the beveled edge are measured. The numerical simulation results show that, when the vertex angle is relatively small, the real refractive angle has the approximate linear relationship with the vertex angle. When the vertex angle is relatively large, the real refractive angle changes gently with the increase of vertex angle. In the case of the same real parts, the magnitude of the real refractive angle decreases as the imaginary part of the complex refractive index increases.

In order to solve the problems of complex calibration and low accuracy that exist in large-scale measurement of the present line structured light, a measurement method with large-scale and high precision based on multi-vision line structured light sensor is proposed. Multi-vision line structured light sensor is comprised of a laser and several equidistant cameras (a single master and multi-slavers) which are arrayed side by side. About 1/3 overlapped field of view (OFOV) exists between neighboring cameras. The laser beam can cover the total width of field of view of all cameras. The calibration of sensor just needs a simple chessboard target. The method of Zhang′s calibration method is used to acquire the target images and calibrate traditional parameters. In addition, considering that the perspectives of camera are invariable, the transformation matrix of images stitching in adjacent cameras can be pre-calibrated through image registration with the known feature corner points extracted from the internal calibration images in OFOV. Continuous multiplication of the transformation matrixes can finally build the perspective transformation model (PTM) which can be used to transform arbitrary slave camera image to the imaging plane of the master camera. With the proposed method, local light stripe images of large-scale object can be collected simultaneously by cameras. Then, all the local light stripe images are quickly stitched into a complete stripe image with PTM. Finally, 3D coordinates of light stripe location are obtained by the extraction and the conversion of the coordinate of the light stripe. The experimental results show that the proposed method is more accurate and convenient than the existing methods. The average texture depth of the reconstructed model is only 8.3% away from that of real model.

The surface electromagnetic field enhancement in a sub-wavelength metallic groove array is studied with rigorous coupled wave analysis for surface enhanced Raman scattering. The effects of groove depth and array period on electromagnetic field enhancement at the rabbet of a groove array are simulated. The contribution of resonance effect in structure to electromagnetic field enhancement is achieved. The average enhanced effect of Raman scattering of sub-wavelength metallic groove array and the effective range of electromagnetic field enhancement out of the array are investigated. The results show that with the contribution of resonance in grooves, the Raman scattering enhancement factor of sub-wavelength metallic groove array in one period can reach 106 orders of magnitude. Obvious electromagnetic field enhancement can be obtained at vertical distance to the array surface within 1/5 wavelength, out of which enhancement factor declines rapidly to unitary magnitude. The numerical results show that the surface electromagnetic field enhancement of the sub-wavelength metallic groove array depends weakly on the type of noble metal.

Iodine value is an important index for evaluating quality of the fatty acid. In order to research the feasibility of measuring unsaturation degree of fatty acid of intact fat sample by using the Raman spectroscopy and chemometrics method, we use pork′s subcutaneous adipose tissue as research object to obtain the Raman spectra in the wavelength range of 300-2000 cm-1 with utilization of self-constructed Raman spectroscopy detection system. Both of preprocessing methods and iodine value related variables are optimized. Using the iodine value obtained by traditional Wijs titration as reference, we build the calibration model of iodine value in fat sample by partial least square algorithm. The experimental results show that the optimal preprocessing method is the 8th order polynomial fitting method. The optimal combination band, 1106-1470 cm-1, is obtained by interval partial least square method. Based on the optimized pretreatment method and selected variables, the iodine value prediction model is developed, the prediction set coefficient (Rp) and root mean square error of prediction (RMSEP) of the model are 0.9463 and 2.5391×10-2, respectively. The study results indicate that optimized variable can be used in rapid and nondestructive measurement of iodine value of intact pork fat, which provides theoretical basis for on-line, rapid, and nondestructive measurement of unsaturation degree of fatty acid in pig carcasses based on Raman spectroscopy.

The nutrient elements in the soil are quantitatively detected by laser induced breakdown spectroscopy (LIBS). The Nd∶YAG pulsed laser with output wavelength of 1064 nm and pulse width of 5.82 ns is used as light source to focus on the surface of the soil to generate laser induced plasma. The plasma emission spectra are measured with utilization of a three grating spectrometer and a gate width controlled intensified charge-coupled device (ICCD). On the basis of traditional LIBS system, beam expander system and real-time monitoring system are added to form LIBS system with cage structure. The focusing position of laser in LIBS system with cage structure is optimized, the optimum laser focusing position is 0.2 cm. The signal intensities of Mg II 279.56 nm, Mg II 280.26 nm and Mg I 285.21 nm spectral lines are tested. The results show that the LIBS system with cage structure is superior to the traditional LIBS system in signal stability. The detection limits of Cu, Mn, Mg and K elements in soils are 0.42×10-6, 13.2×10-6, 38.5×10-6, 62 ×10-6, respectively, which are better than the detection limits obtained by traditional LIBS system. The mass fractions of Cu, Mn, Mg and K elements in soils are predicted based on the calibration model, the average relative errors of the elements are 9.2%, 9.6%, 8.5%, and 10.9%, respectively.

In order to eliminate the influence of noise in laser absorption spectral signal on analysis result, we propose a threshold denoising method based on wavelet transform. The simulation experiment is implemented with the utilization of direct absorption spectroscopy signal of gas molecules combined with MATLAB software, and the effects of threshold methods, decomposition level and wavelet function type on denoising effect are analyzed in details. Finally, the optimized filtering parameters are used to analyse the spectral signal of human expired gas in experiment. The results show that the wavelet transform algorithm developed in this study has a good denoising effect for the spectral signal. In addition, real-time analysis of the other component of expired gas can be realized by selecting different tunable laser light sources at other wavelength. The quantum cascade laser (QCL) spectroscopy system can be widely used in the field of expired gas diagnosis and other fields.