In order to study the influence of ice crystal particles on the performance parameters of quantum interference radar, based on the Van de Hulst approximation theory of ice crystal particles, standard gamma distribution, and Henyey-Greenstein phase function, the polarization changes of radar detection photons in the background of ice crystal particles are studied. The influence model of different parameters of ice particles on transmission distance, resolution, and bit error rate of quantum interference radar detection photons is established. Simulation results show that increasing the effective scale of ice crystal particles will increase the energy dissipation of the detected photons, resulting in a decrease in the transmission distance of the detected photons. The resolution of the quantum interference radar decreases as the optical thickness of the ice crystal grains increases when the number of transmitted beam photons is fixed. Particularly, when the concentration of ice crystal particles is constant, the quantum bit error rate of the link increases with the increase of effective size of the ice crystal particles and the asymmetric factor. In addition, different types of ice crystal particles have different effects on the quantum bit error rate. Meanwhile, in the case of high polarization ratio, reducing the ellipticity angle within a certain range will accordingly bring down the quantum bit error rate.

Atmospheric refraction is one of the important factors affecting the optical measurement of the target's external trajectory parameters. Atmospheric refraction correction is necessary under the condition of higher measurement accuracy for optical equipment. aiming at the problem that the theoretical derivation process of standard method is not precise enough and repeated iterations are needed in the calculation process, based on atmospheric sphere sublayer and optical equipment features, an atmospheric refraction correction method based on angular intersection is proposed. Simulations and unmanned aerial vehicle flight test show that proposed method is faster and more accurate than the standard method.

Airborne light laser detection and ranging (LiDAR) can obtain three-dimensional point cloud data with high accuracy, can reach the ground surface through forest leaves, and reflect the continuous terrain features of the study area quickly and accurately, which is conducive to the establishment of a high-resolution digital elevation model (DEM). In this paper, cloth simulation filtering (CSF) algorithm is applied to filter the airborne LiDAR data. By setting the number of particles generated in the algorithm and the threshold of ground point classification, the ground point cloud is extracted from six groups of point cloud data under different terrain conditions, and the Kappa coefficient of classification is between 0.851 and 0.954. The DEM of 1 m×1 m is generated from the ground points extracted by the CSF algorithm, and the DEM provided by the research area is linearly fitted. Experimental results show that the regression line fitting goodness factor R2 is larger than 0.99 and the root mean square error is between 0.10451 and 0.30387. The cloth simulation algorithm has few parameters for extracting ground points of the point cloud and is suitable for a wide range of terrain. The high-resolution DEM generated by the proposed algorithm can well express the continuous undulating surface changes and terrain features of the region.

In view of the problem that visible light communication (VLC) is interfered by strong background light in outdoor transmission, this paper analyzes the visible light channel in outdoor strong background light environment, and proposes a method for suppressing low-frequency outdoor shot noise based on hardware filtering, according to the characteristic that the main interference source is low-frequency sunlight in outdoor environment. We realize the point-to-point reliable communication based on white-light LED with low bit error rate (BER) under strong background light interference. Experimental results show that the noise suppression method has a BER of less than 10 -5and a data transmission rate up to 8 Mbit/s.

In order to explore the applicability of fiber Bragg grating (FBG) sensing technology in the experimental study of the penetration characteristics of open pipe pile, a sensitized miniature FBG strain sensor is used to monitor the stress state of the open pipe pile during the pile sinking process in the indoor model test. A detachable double-walled open model pipe pile is made, the FBG sensors are mounted on the model pipe pile by grooving and gluing the pile wall. The stress distribution and variation law of the model pipe pile during penetration are measured. The results indicate that the sensors with the special model pipe pile can better meet the requirements for testing the penetration characteristics of the open pipe pile. The sensors are easy to install and have a high survival rate. With the increase of the penetration depth of the model pipe pile, the bearing characteristic is similar to the friction end-bearing piles, and the axial forces of the inner and outer walls of the pile increase, but the growth rate of each point is different. The lateral frictional resistance of the inner and outer wall of the pile increases as a whole, and the unit side frictional resistance shows different degrees of “degradation effect”.

The synchronization technology used in low-speed information protection transmission systems cannot be directly applied to high-speed information protection transmission systems. To correctly extract the ciphertext in high-speed information protection transmission systems, both communication parties must be synchronized so that the receiving end can accurately define the data transmission process, as well as the start and end positions of valid data. For a high-speed information protection transmission system encrypted using optical quantum noise, an effective key synchronization scheme is proposed herein. The synchronization frame structure and synchronization process are designed, the channel transmission delay is periodically measured, and the difference is iteratively estimated to correct the arrival time of the decryption key to complete the synchronization of the decryption key and the ciphertext under high-speed information transmission. This study analyzes the important parameters that affect the key synchronization, verifies the feasibility of the scheme, and analyzes the key performance indicators such as the success rate and bit error rate of the synchronization scheme based on the experimentally-obtained data.

To suppress the Banding phenomenon generated when the laser beam scanning (LBS) and grating optical waveguide are directly coupled in the head-mounted augmented reality display system and improve the final imaging effect of the system, the Banding phenomenon is first introduced, and the Banding phenomenon is analyzed and discussed. Then, a beam expanding suppression method with a diffuser is proposed, and its feasibility is verified by the beam expanding optical path structure. Aiming at the suppression scheme, the design optimization for the small-size and large-field-of-view relay optical path is carried out to meet its applications in the head-mounted augmented reality display system. The total length of the designed system is less than 25 mm. At the cut-off frequency of 43 lp/mm, the modulation transfer function values of the front-end and back-end fields-of-view are greater than 0.3, and the distortion is less than ±2.2%, which meets the requirements of various indicators of the design. The proposed method can effectively suppress the Banding phenomenon in the process of coupling between LBS and grating optical waveguide. Therefore, this work provides a certain reference value for the research of the head-mounted augmented reality display systems based on LBS and has potential application prospects.

According to the current situation of three-dimensional reconstruction and deformation analysis technology of large-scale surface, a dynamic measurement method of surface based on binocular structured light system is proposed. In the process of surface reconstruction, the system can move freely, and the movement path of the system can be restored through the visual positioning method. In order to ensure the accuracy of the surface reconstruction, a global optimization method is used to unify the structured light point clouds extracted from each position under the global coordinate system, which effectively avoids the accumulation of errors in the pose calculation process and obtains a high-precision surface morphology. The two-position global coordinate system poses are unified, and the high-precision attitude sensor and static reference point are used to calculate the relative pose between the global coordinate systems during the two measurements. Experimental results show that this method is fast and has high precision, and the relative error of deformation measurement is within 0.12%.

In this paper, the opto-mechanical structure design and passive athermalization design for the visible-light zoom lens of space-based photoelectric countermeasure platform are carried out. According to the working temperature index requirement of -20-50 ℃, an integrated opto-mechanical-thermal analysis of the zoom lens is carried out. Patran software is used to load the temperature stress on the lens, and calculate the thermoelastic deformation of the optical structure. Nastran software is used to calculate the rigid body displacement of the mirror nodes of optical components after thermal deformation. The Zernike coefficient of each lens surface after deformation is analyzed by Sigfit optical interface software, and the results are imported into Zemax to predict the effect of lens surface change and rigid body displacement change on modulation transfer function (MTF) and wavefront difference. Experimental results show that under the temperature load of -20-50 ℃, the maximum axial displacement of posterior fixation group can reach 6.107×10 -3 mm, which seriously affects the imaging quality. In order to reduce the influence of temperature load, flexible pressure ring is used to realize the design of axial displacement controllable heat difference dissipation. Integrated opto-mechanical-thermal analysis show that the MTF values of the optical system under temperature load are all greater than 0.3, meeting the technical requirements. Finally, the temperature adaptability of the zoom lens and the accuracy of integrated opto-mechanical-thermal analysis are tested by temperature reliability experiment, which provides a set of efficient, accurate, and wide-ranging integrated opto-mechanical-thermal analysis process.

Two-frame phase shift extraction algorithm is characterized by small number of fringe patterns and fast processing speed. However, there are many challenges related to the design of this algorithm because of the pathological problems associated with the two-frame phase shift technology. In this study, a phase shift extraction algorithm is proposed for a two-frame random time-domain phase-shifted fringe pattern. First, the background term of the fringe pattern was eliminated using high-pass filtering. Subsequently, the minimum square root of the amplitude was searched using the gradient descent algorithm in combination with the square root distribution law of amplitude. Then, the introduced phase shift was extracted. Finally, the two-step phase shift algorithm was used to obtain the measured phase. The simulation and experimental results show that compared with other classical algorithms, the proposed algorithm exhibits various features, including small recovery phase error and noise insensitivity. Furthermore, the proposed algorithm is simple, flexible, and easy to apply.

In order to improve the acquisition speed and accuracy of global positioning system (GPS) software receiver, an improved orthogonal search precise acquisition method is proposed. Firstly, the correlation acquisition results of GPS signals are used to remove the code phase, and an alternative set of functions is constructed. Then, based on signal decomposition theory, the precise acquisition of signals is realized by orthogonal search. The orthogonal search method is improved, and the iterative search strategy is adopted to improve the acquisition speed. The theoretical analysis and experimental results show that this method can achieve high precision estimation of precise acquisition frequency of GPS signal, and the convergence speed of precise acquisition is very fast, which can effectively reduce the resource consumption of GPS equipment.

A metal-dielectric-metal waveguide structure comprising a semi-circular resonant cavity, baffle, and straight waveguide based on surface plasmon polaritons is proposed. When the incident light wave entered the waveguide structure, the semi-circular resonant cavity and metal baffle formed two narrow discrete states and a wide continuous state, respectively. Consequently, the interference effect was observed, which can form two sharp asymmetric resonance spectra, that is, two modes of Fano resonance. To conduct numerical simulation analysis on the transmission spectrum characteristics of the structure, the coupled-mode theory and finite element analysis method were used. Moreover, the effects of structural and medium refractive index parameters on the transmission quality factor and sensitivity characteristics were elucidated. By analyzing the optimization of the structural parameters, the system performance can be flexibly adjusted and optimized by modifying the structural parameters. Furthermore, the transmission quality factors in the two modes are 3.05×10 5 and 4.59×10 5, and their corresponding sensitivities are 800 nm/RIU and 1160 nm/RIU, espectively. The proposed flexible dual Fano resonance structure has certain application values in the study of nanobiosensors, nonlinear optics, and slow light.

Aiming at the shortcomings of low optical trap stiffness and poor axial stability in dual-beam optical trap, a four-beam optical trap is proposed to capture and manipulate particles. Using ray optics model, the differences in mechanical characteristics between the dual-beam optical trap and the four-beam optical trap are compared and analyzed, and a four-beam optical trap chip is designed and fabricated. Polystyrene microspheres with radius of 5 μm are captured and the axial optical trap stiffness is calibrated by mean square displacement method. Both simulations and experimental results show that the stiffness of the axial light trap in the four-beam optical trap is comparable to that of the transverse optical trap in the dual-beam optical trap, and is much larger than that of the axial light trap in dual-beam optical trap. While maintaining the lateral capture stability of dual-beam optical trap, the four-beam optical trap improves the axial capture stability, and is of great significance for stable manipulation of micro-particles.

In this study, the Nd∶YAG pulsed laser is used for performing micro-modeling on the surface of a high-silicon aluminum alloy cylinder liner and the influence of typical laser parameters on its micro-dimple geometry is studied. When the energy density increases, the diameters of the micro-dimples initially increase and subsequently remain constant (the maximum diameter is 100 μm); the laser energy density only slightly affects the depths of the dimples. The diameters and depths of the dimples initially increase and then decrease with the increasing number of pulses. The maximum diameter and depth of the dimple are 140 μm after 20 pulses. Further, the ablation threshold φth of the high-silicon aluminum alloy is 2.08 J/cm 2 in case of one pulse, which decrease with an increase in the number of pulses owing to energy accumulation. In addition, the effect of microtextures on the wear reduction of the cylinder liner surface can be observed at a fixed depth and diameter of the micropits, and the samples with area fractions of 10% and 20% exhibite better wear properties than those with an area fraction of 5%.

In this study, the removal mechanism of polyacrylate-based paint is studied by fiber lasers. In addition, the effects of energy density on the quality of laser paint removal are investigated by scanning electron microscopy (SEM), and the relationship between the energy density and surface shape is studied. The mechanism of laser paint removal is studied using SEM, X-ray energy dispersive spectrometer (EDS), and X-ray photoelectron spectrometer (XPS). The results show that the quality of laser paint removal is considerably influenced by the energy density. When laser cleaning was performed once, the quality of laser paint removal improves with the increasing energy density. However, this quality slightly decreases because of the plasma shielding effect when the energy density is 12.56 J/cm 2 and 13.60 J/cm 2, respectively. When laser cleaning is performed twice, the quality of laser paint removal continuously improves with the increasing energy density. The combustion on the cleaning surface is weak owing to the enhanced laser-plasma-induced shock. The content of C on the cleaning surface increases, whereas that of O decreases. The morphology, element content, and chemical bonding of the cleaning surface indicates three types of cleaning mechanisms, including thermal combustion, pyrolysis, and plasma shock. Various coupling mechanisms are used to remove the polyacrylate-based paint from the surface of an aluminum alloy.

Herein, the effect of parameters on the longitudinal flexure deformation in laser welding Hastelloy C-276 using the filler wire process is evaluated by combining bending stiffness and load analyses. Results show that the linear heat input and relative wire speed can affect the longitudinal flexure deformation through the bending stiffness and equivalent load. As the linear heat input increases, the equivalent load also gradually increases, and the bending stiffness shows a decreasing→increasing→decreasing trend. Moreover, the equivalent load and bending stiffness will simultaneously increase when the linear heat input increases in a certain range, resulting in a relatively small change in flexure deformation. By increasing the relative wire speed, the bending stiffness of sample is improved, thereby causing a significant reduction in the welding deformation. By selecting small linear heat input and large relative wire speed within reasonable parameters, welding deformation can be restrained.

3.0 mm thick BTi6431S high temperature titanium alloy was welded by fiber laser beam welding. The effect of welding parameters on welding quality and stability was studied from the aspects of weld formation, porosity, and characteristics of metal vapor/plasma. The results indicate that the laser power has an effect on the weld width, residual height, underfill, and porosity. The welding speed mainly affects the weld width and weld width ratio. The effect of welding process on weld quality is closely related to the characteristics, and stability of metal vapor/plasma. At lower laser power (1.5-2.5 kW) or higher welding speed (3.5-4.5 m/min), the metal vapor/plasma area is large and area fluctuation is obvious, the weld is not penetrated, and the porosity is high. Under moderate laser power (3.0-3.5 kW), and welding speed matching (2.5 m/min), the area and periodic fluctuation of metal vapor/plasma are small, the weld is fully penetrated, and the forming quality is good.

On the basis of all-normal-dispersion fiber laser, the influences of different pumping schemes on the generation of parabolic pulses are numerically investigated. By establishing the mode of all-normal-dispersion fiber lasers, we have studied the effects of gain saturation energy and gain bandwidth on the fitting factor, pulse width, spectrum width, and pulse energy of the output parabolic pulses. The results show that in backward pumping mode, the laser can output parabolic pulses with higher energy, and can generate parabolic pulses with lower gain saturation energy. The backward pumped all-normal-dispersion fiber laser can maintain the output of the parabolic pulses in a larger gain and saturation energy range. The gain bandwidth of gain fiber has a small influence on the output characteristics of the parabolic pulses in different pumping schemes.

The time-delay characteristic and effective bandwidth of three chaotic laser systems including optical feedback, optical phase modulation, and external laser injection systems are studied. The intensity, periodic characteristic, and bandwidth of the time-delay characteristic peak are analyzed and compared. The advantages and disadvantages of the three systems applied to the confidential optical communication system are discussed. Based on practical applications, the influences of several physical parameters of the optical injection chaotic laser system on the delay characteristic peak and effective bandwidth are studied in depth. We find that it is feasible to expand the parameter space of the confidential system by adjusting the external cavity delay and injection delay of the driving laser. By matching the appropriate feedback intensity and injection intensity, the time-delay characteristic peaks can be effectively suppressed, and the effective bandwidth can be enlarged.

ICESat-2 satellite data are collected by a multi-beam photon-counting system, which greatly improves data coverage density and data accuracy. The forward-scattering effect caused by clouds and aerosols in the atmosphere significantly influences data accuracy. In this paper, an apparent surface reflectance-based cloud-detection algorithm using the pulse-folding characteristics of the ATLAS photon-counting system is proposed. The ICESat-2 cloud-detection process and its related algorithm are described in detail, which will be helpful for the application and expansion of ICESat-2 data in studies of the atmosphere. The results will provide reference that will be of significance for the correction of subsequent atmospheric effects in laser altimetry acquired by Chinese satellites.

In this study, the transfer matrix method is used to enhance and regulate Goos-H?nchen (GH) shift based on graphene/hexagonal boron nitride (hBN) heterostructure in the infrared band. Theoretical research demonstrates that when the transverse magnetic polarized light with 12.20 μm wavelength is incident, hBN heterostructure GH shift can be effectively improved by adjusting the Fermi level of graphene or the number of graphene layer. This phenomenon is attributed to the Lorentz resonance phenomenon in the infrared band of hBN. For 0.2 eV Fermi energy, GH shift of 80.97λ can be achieved using a single layer of graphene as the heterostructure. Moreover, the law of GH shift varying with the hBN thickness exhibits the same as that with the hBN dielectric constant. Notably, when the hBN thickness changes around 1.53 μm, the positive and negative variations in GH shift can be flexibly switched in the range of -150λ-150λ. Furthermore, these findings are helpful in designing new high-sensitivity infrared optical sensors.

In this study, we first derive the light field distribution for the spatial interference with quasi-coherent or broadband light illumination, so as to obtain a four-step phase shift corrected method for such an illumination. Second, we construct a spatial interference microscope system that uses green light and diluted 6-μm polystyrene microsphere into the microscopic objective oil to simulate microenvironment of a cell. Finally, using four of the spatial-interference images, we reconstruct the phase distribution of the oil-immersed microspheres. The relative error in the microsphere radius is 6.5%, and the relative error of optical path difference volume of the oil-immersed microsphere is 8.4%. By comparing these results with those achieved by the traditional four-step phase shift method, the improvement can be neglected. Therefore, in situations where the imaging speed is important and the observed cell is sufficiently thin, it is not necessary to use the corrected four-step phase-shift method to increase the imaging speed.

The influence of adverse factors such as tilting of the movable mirror and mechanical vibration in the Fourier transform infrared spectrometer on the performance of the spectrometer is analyzed. Aiming at these influencing factors, a dynamic calibration technology with fixed mirror is used on the Fourier transform infrared spectrometer. Based on this technology, the key performance index parameters of the spectrometer are tested. Experimental results show that the performance indexes are good, which has a good reference for the design and development of the spectrometer.

In this study, the symplectic multi-resolution time-domain (S-MRTD) algorithm is introduced in numerical simulation calculations of photonic crystals to address the problems of low calculation accuracy and large dispersion error in the traditional finite-difference time-domain (FDTD) method. First, the symplectic sub-technology and approximate difference of wavelet scale function were introduced into the S-MRTD algorithm in time and space, respectively. Next, based on the time-reversible constraints and growth factors, a set of optimized symplectic operators was solved. Further, the stability and numerical dispersion of the traditional FDTD method and S-MRTD algorithm were discussed. Finally, based on the S-MRTD algorithm, the transmission and reflection coefficients of photonic crystals were analyzed. Numerical calculation and simulation results verify the feasibility and accuracy of the S-MRTD algorithm. The successful application of the S-MRTD algorithm facilitates a new numerical calculation technique with high accuracy and efficiency for elucidating the transmission characteristics of photonic crystals.

We design an automatic test system based on a digital supermode distributed Bragg reflector laser, electro-optical modulation polarization controller, InGaAs photoelectric detector, high-speed optical switch, and a combination of high-precision control-detection algorithm and wavelength-division multiplexing technology. The proposed system is designed to automatically test performance-related indicators, such as wavelength and polarization dependent losses of passive optical components. To realize excellent control of power stability, the light source module of this system uses the OPA569AIDWP chip as the control core. Multi-grade amplification range control is used for power detection module. Further, shielding noise reduction technology and software algorithms are used to significantly suppress system noise and improve the power meter sensitivity and dynamic range. The test process of the proposed system is simple, highly accuracy, and stable, with a test deviation of less than 0.05 dB, which improves the automatic detection capability of the passive optical device production line and reduces the requirements of manual operation level for using complex instruments. The equipment practicality of the proposed system is good and it shows its broad market prospects.

In this study, a slot waveguide structure is designed based on the principle of external reflection. Further, this structure is optimized to limit the propagation of light in low-refractive-index materials and concentrate energy. The slot waveguide structure comprises two symmetrical high-refractive-index slabs, a middle low-refractive-index slot, and a peripheral cladding. The effects of the cladding size, the height and width of the middle low-refractive-index slot, and the width of the slab are simulated under two-dimensional conditions with an incident wavelength of 1550 nm based on the finite element analysis method. The aforementioned parameters are optimized to ensure that energy is more concentrated in the middle low-refractive-index slot. In addition, the distribution of the electric field in a three-dimensional space is studied when the optimized parameters are used to establish a three-dimensional model, proving that light can propagate in low-refractive-index materials when the proposed structure is used.

This paper proposes a phase-controllable polarization-preserving scheme by adjusting Goos-H?nchen displacement based on the optical tunneling effect. First, two dielectric films (i.e., films 1 and 2) are coated outside a corner-cube reflector's reflective plane. Then, the refractive index and thickness of the dielectric film are optimized through particle swarm optimization (PSO) method to realize the incident light, which can be totally reflected at the interface of the corner-cube reflector and the dielectric film. The evanescent wave returns to the corner-cube reflector through the film 2. The polarization preservation can be achieved using the superposition effect of the reflected beam and the evanescent wave to change the propagating beam phase. Finally, COMSOL Multiphysics simulation software is used to simulate the polarization preservation effect of the corner-cube reflector. Simulation results show that when the initial azimuth of the incident polarized light is in the range of [-40°,40°], it exhibits better preserved polarization, i.e., the azimuth angle and the ellipticity of the emitted light are varied by approximately 0.2° and 0, respectively.

Intracellular delivery is a critical step in cell engineering and cell therapy. Compared with conventional microinjection, cell fusion, and electroporation, laser-induced intracellular delivery has advantages such as high precision, high throughput, and non-invasiveness. This technology has received increasing attention in recent years. The laser induces cell membrane to produce transient micropores that increase the permeability of the cell membrane and allow the cargo to pass through the cell membrane and go into the cell. This paper mainly introduces the principles that laser uses thermal effect, chemical effect, and fluid shear force to destroy cell membrane. Their implementation methods are divided into direct laser action, and laser action on the nanoparticles, substrate material or photothermal knife to destroy the cell membrane. The advantages and disadvantages of each method are evaluated, and the prospects of the laser-induced intracellular delivery are forecasted.

Photoacoustic conversion refers to the process of using photoacoustic effect to produce sound. High frequency and wide band ultrasonic signals can be generated by stimulating photoacoustic materials with pulsed light. Metal nanostructures generate localized surface plasmon resonance and therefore have high optical absorption and controllability, so that they can be used as important photoacoustic conversion materials and can be applied to biomedical imaging and other fields. In this paper, the mechanisms and principles of the photoacoustic conversion are firstly introduced. Then the research and application progresses of photoacoustic conversion of metal nanostructures such as gold nanorods, gold nanodisks, and gold nanoarrays are summarized. Finally, the possible future development directions of metal photoacoustic nanomaterials are prospected.

Time synchronization technology based on optical fiber transmission has the advantages of high precision, high stability, and low loss. It has become the main method for high-precision time synchronization, with robust application requirements and development prospects. Bidirectional comparison technology is a widely used optical fiber time synchronization method, and relevant institutions (locally and internationally) continue to propose new methods, technologies, and applications in this field. Furthermore, by combining the research history and progress of optical fiber bidirectional alignment technologies, this paper introduces the basic principles and technical characteristics of four mainstream bidirectional comparison schemes. The uncertainties and sources of errors of the synchronization system and their impact on time synchronization results are analyzed. Accordingly, this study provides a reference to further improve the accuracy of optical fiber time synchronization and establish a high-precision, safe, and stable ground-based timing system.

The distributed optical fiber vibration sensing system is a sensing system that uses optical fibers as sensing sensitive components and signal transmission media to obtain strain information. It has the characteristics of long sensing distance, real-time measurement, reversible vibration signal, and strong environmental adaptability. Distributed optical fiber vibration sensing systems based on phase-sensitive optical time domain reflectometry have been a hot spot in recent years. This paper mainly introduces the research progress of distributed optical fiber vibration sensing system based on phase sensitive optical time domain reflectometer from different detection structures and demodulation methods, and concludes the advantages and disadvantages of these methods and structures. This is of great significance for selecting the appropriate detection system in practical applications.

In recent years, terahertz spectroscopy has shown great potential in the fields of safety inspection, biomedicine, food detection, and resource detection. Among them, the detection of pesticide residues in agricultural products is one of the current research hotspots. This paper systematically expounds the latest research progress of terahertz spectroscopy in the field of pesticide detection, and combs the terahertz spectroscopy experimental instrument and theoretical calculation method. From the identification of pesticides, the establishment of pesticide fingerprint database, the quantitative and qualitative analysis of pesticides and the theoretical calculation of pesticides, this paper summarizes the research results obtained by scholars at home and abroad in recent years, and analyzes the existing problems and future research directions, which also provides prospects for the application of terahertz spectroscopy in the field of pesticide detection.

Different people exhibit different allergic reactions to various types of pollen. Therefore, this study presents a method to rapidly detect and classify the pollen particles in air. Herein, 465 Raman spectroscopic data associated with 42 pollen samples were obtained using a Raman spectrometer by considering common pollen as the research object. Subsequently, they were categorized as interfamily and intergeneric pollen according to their biological classification, and then classified and predicted. After the obtained spectral data were preprocessed, principal component analysis was used for extracting the spectral characteristic information, and a support vector machine recognition model was established. The prediction accuracy of interfamily pollen is 97.75%, and the pollen prediction accuracy of the genus Rosaceae is 90.47%, which indicates that Raman spectroscopy can be used to classify and identify pollen in a feasible manner.

To realize the rapid identification and detection of oil pollutants, a fluorescence spectrum detection system based on laser-induced fluorescence (LIF) technology is built, and the fluorescence spectra of three different oils, i.e., 0 # diesel, 95 # gasoline, and common kerosene, are obtained. Characteristic parameters are extracted from the spectral information. The standard deviation, center distance, and kurtosis coefficients of the fluorescence peak are taken as sensitive characteristic parameters for cluster analysis. Finally, the curve fitting method is used to quantitatively measure the mass concentration of samples. Experimental results show that the combination of LIF technology with the characteristic parameter extraction method and curve fitting method can be used for the qualitative and quantitative detection of different oil pollutants, which provides a new idea for their rapid identification and detection.

Taking glyphosate pesticide sold in the market as test sample and capillary glass tube with Ag nanoparticles adsorbed on the inner wall as active substrate, the surface enhanced Raman spectra (SERSs) of the glyphosate and its volatiles in the air are studied to explore a new method for determination of the pesticide residues using the pesticide volatiles. Using prepared Ag colloid substrates, the SERS detection is performed on commercially available glyphosate pesticides with different concentrations, and the detection concentration of the glyphosate can be as low as 1.8×10 -6 mol/L. Next the SERS of the volatiles of glyphosate solutions with different concentrations are studied by using the prepared capillary glass tube. When the glyphosate solution is diluted to a concentration of 1.8×10 -6 mol/L, there is still a significant characteristic absorption peak of the glyphosate, which indicates the detected concentration of the experimental method can reach 1.8×10 -6 mol/L (about 0.3 mg/kg). According to the National Food Safety Standard formulated in 2016, the maximum glyphosate residue in fruits is 0.5 mg/kg. Compared with the national standard,the concentration of the glyphosate pesticide residues in the detected water has basically reached the national maximum detection standard of pesticide residues. Therefore, this experimental method can be used as a scientific and effective method for the detection of glyphosate pesticide residues and can provide a reference for detecting other pesticide residues.