A method is proposed to analyze the influence of the aerosol particles on the backscattering echo from a microscopic point of view. Based on the Mie scattering theory, a Monte Carlo simulation model is established to simulate and analyze the aerosol backscattering echo by the transmitting and receiving coaxial lidar. The influence law of the aerosol particle size, real part and imaginary part of the complex refractive index on the peak intensity, signal delay and waveform broadening of backscattering echoes is obtained. The effect of the simultaneous action of multiple macroscopic properties caused by the microscopic properties on the backscattering echoes is analyzed as well. The results show that the backscattering signal intensity mainly depends on the scattering coefficient and the asymmetry factor. The echo delay and pulse width are related to the scattering coefficient. As the real part of the complex refractive index increases, the backscattering echo intensity increases, while the echo delay and pulse width decrease first and then increase, but the influence is relatively small. With the increase of the imaginary part of the complex refractive index, the backscattering echo intensity decreases first and then increases, but the imaginary part has no obvious influence on echo delay and pulse width.

A kind of circular array Airy vortex beam (CAAVB) is theoretically proposed and experimentally generated, which consists of multiple Airy beams arranged in an annular array and has the self-focusing performance. By increasing the number of Airy beam arrays, the self-focusing intensity can be effectively increased. The simulation results show that under the same conditions, the self-focusing characteristics of a CAAVB can be greatly improved by loading an optical vortex. In addition, by adjusting the radius of the annular airy beam array, the focusing position of the beam can be controlled and the non-mechanical adjustment of focus distance can be realized.

The wavefront sensorless adaptive optics (WFSless AO) system under noise is established using an 88-element deformable mirror and a charge coupled device imaging device and with an extended object as a correction object. The linear relationship between the masked detector signal and the mean-square wavefront gradient of the extended object imaging under noise is verified. The algorithm based on this linear relationship is used as the control algorithm of the WFSless AO system. The simulation experiment is carried out to check the correction ability of the model-based WFSless AO system for extended object imaging under noise. The results show that the correction effects are very close under the same turbulence condition but different signal-to-noise ratios. According to the order of turbulence conditions from small to large, the averaged root mean square relative errors after correction under a signal-to-noise ratio of 5 dB are 3.71%, 2.94% and 2.42%, respectively, if compared with the results under a signal-to-noise ratio of 20 dB. The above results indicate that the model-based control algorithm with this linear relationship has a relatively good anti-noise capability.

By using a 4f (f is the focal length) optical setup and a charge coupled device camera, the sample position is tracked. The mechanical drift is compensated by the nano-translation table which ensures the sample always at the beam waist of the light sheet and thus an optimal image is obtained. With the proposed method, the mechanical drift of several nanometers can be compensated. By using the home-made light sheet fluorescence microscopy, the long-time imaging of fluorescent microspheres with diameters of several micrometers is acquired, which confirms the feasibility of the proposed method.

The system model of visible light communication in coal mine working face is analyzed. Two optimization methods of LED light source distribution in coal mine working face are designed. One is be used to optimize the two-dimensional position of each LED light source on the top of working space, and the other is used to co-optimize the two-dimensional position and its power weight of each LED light source. The fireworks algorithm is adopted and the signal-to-noise ratio (SNR) factor of the receiving plane is set as the target function of the group optimization algorithm as well as the indicator for evaluating the uniformity of signals in the receiving plane. The research results show that after optimization with these two methods, the SNR factors of signals in the receiving plane are reduced by 16.6% and 24.6%, respectively, compared with that under the uniform array distribution of LED light sources with equal powers. The SNR fluctuation is significantly improved, the optical signal uniformity is also improved, and thus the same communication quality among different users is ensured.

A novel timing synchronization algorithm is proposed based on constant amplitude zero auto-correlation (CAZAC) sequence. In the proposed algorithm, the training sequence consists of four CAZAC sequences, which are divided into six timing windows. The correlation operation is carried out by use of the characteristics of conjugate symmetry and even symmetry of the sequences, and the timing metric function is obtained by multiplying these six timing windows. The simulation results show that the proposed algorithm can be used to obtain the timing metric function curve with the unique pulse peak and eliminate the disturbance of timing plateaus and side lobes. Meanwhile, the proposed algorithm has good timing stability within a large range of optical signal-to-noise ratio and chromatic dispersion.

Based on the liquid crystal/polymer grating and with MDMO-PPV as the gain medium, the emission wavelengths at different positions of the gain medium layer can be roughly modulated and then precisely tuned by applying an external electric field. A continuous fine-tuning organic semiconductor laser with a tuning range of 18 nm is finally obtained based on the liquid crystal/polymer grating. This study provides some new ideas for the improvement of a tunable distributed feedback (DFB) organic semiconductor laser.

By the use of a semiconductor gain chip with InGaAs multiple quantum wells as materials in the active region and the AlGaAs/AlAs, transparent to the pump light, as distributed Bragg reflectors, along with the end-pump geometry to simplify the device structure and an inserted etalon as the tuning element, an optically-pumped compact tunable external-cavity surface-emitting green laser is realized by the intra-cavity frequency doubling technology. The employed etalon narrows the laser linewidth as a tuning element. To prevent the second harmonic from returning to the gain chip, the etalon is coated with a high-reflectivity film at the wavelength of the second harmonic. The tuning range of the fundamental wave is over 10 nm and that of the second harmonic is 4 nm centering at 559 nm. The spectral linewidth of the second harmonic is 1.0 nm and the maximum output power is 65 mW.

We demonstrate the laser performances of Er-doped YAP crystals with the atom fraction of Er3+ of 10% pumped by an xenon lamp in the region of 2.7-3 μm. The output mirrors with three different transmissivities are adopted, and the maximum single pulse energies of 1173 mJ @1 Hz, 1284 mJ @5 Hz, 495 mJ @10 Hz, and 104 mJ @20 Hz with the corresponding slope efficiencies of 0.80%, 0.99%, 0.84% and 0.44% are achieved, respectively. Under the conditions of a repetition rate of 5 Hz and output mirror transmission of 15%, the highest laser output energy and laser efficiency can be obtained in the Er∶YAP crystals and the corresponding average output power is 6.42 W, which is about four times the existing best result reported by literatures. In addition, the laser beam quality of the Er∶YAP solid-state laser with different input powers is measured, which decreases with the increase of input power. Moreover, the four laser spectral lines at 2710, 2728, 2795, and 2918 nm are observed. Therefore, the excellent multi-wavelength mid-infrared laser output can be realized with Er∶YAP crystals.

A kind of all-solid-state Nd∶YVO4-LBO dual-wavelength laser with low noise and continuous wave (CW) single frequency is developed. By optimizing the matching temperature of LBO crystals, a CW single-frequency dual-wavelength laser with 1.06 μm output power of 3.8 W and 532 nm output power of 7.8 W is realized. The intensity and phase noises of this dual-wavelength laser are also reduced. The measured intensity noises of the 1.06 μm and 532 nm lasers reach the shot noise limit (SNL) when the analysis frequency is above 3.5 MHz, and the measured phase noises reach the SNL when the analysis frequency is above 5 MHz. When the Pound-Drever-Hall cavity-locking technique is used for the stabilization of laser cavity length, the frequency drift of 1.06 μm laser is less than ±0.8 MHz. The measured power fluctuations of the 1.06 μm and 532 nm lasers within 5 hours are less than ±0.63% and ±0.47%, and the beam quality factors are 1.04 and 1.12, respectively.

Single-pulse separated ablation and multi-pulse cumulative ablation experiments are performed on single crystal diamond by femtosecond laser with different powers. The single-pulse ablation threshold and multi-pulse cumulative ablation threshold of single-crystal diamond materials are calculated, and the variation characteristics of ablation threshold of single-crystal diamond at multi-pulse are studied. The results show that the threshold of femtosecond laser ablation of single crystal diamond is 8.80 J/cm2. The ablation threshold of single crystal diamond materials decreases with the increase of effective pulse number. When the effective pulse number is less than 124, the ablation threshold decreases sharply with the increase of the effective pulse number. When the effective pulse number increases to 486, the decreasing trend of ablation threshold tends to be gentle. The optimum laser processing parameters are as follows: the effective pulse number is 486, and the laser average power is 10.7 W.

Continue laser or pulse laser is combined with the pulse gas metal arc welding (GMAW) to study the dynamic interaction behavior of laser plasma and arc plasma at different hybrid welding modes. The study results show that the pulse laser+pulse GMAW hybrid welding mode can achieve a higher penetration than continuum laser+pulse GMAW hybrid welding under a low average power condition. It is found that if the peak time of the laser pulse has a phase shift with the arc current pulse rise period, the phenomenon of rapid expansion of the plasma at this transient moment can be suppressed, thus improve the transmission of laser energy.

The laser welding with wire is respectively carried out with 6016 and 5182 aluminum alloy plates to study the microstructure and texture under same welding process based on the electron backscattered diffraction (EBSD) technique. The results show that the weld seams of 6016 and 5182 alloys consist of columnar dendrites and equiaxed dendrites, and strong texture along the crystallographic direction is observed in columnar dendrite area. The constitutional supercooling and heterogeneous nucleation have common effect on welded joints. Because the heterogeneous nucleation has large effect on the 6016 aluminum alloy joint, the ratio of the equiaxed dendrites in 6016 aluminum alloy is relatively large, the grain orientation randomly distributes, and the main texture of the columnar dendrites is cube texture ({001}). While the heterogeneous nucleation has little effect on the 5182 aluminum alloy joint, the texture of the equiaxed dendrites distributes along direction, the 5182 aluminum alloy joint is mainly consisted of the columnar dendrites, and the textures of the columnar dendrites are the fiber texture (∥RD), cube texture ({001}) and Goss texture ({011}).

Partial penetration laser welding experiment of DC01 galvanized steel plate and SUS304 austenite stainless steel as well as pre-deformation experiment are conducted by fiber laser. The deflection and deformation profile of SUS304 steel plate (lower plate) are measured and the mechanism of the micro bulging distortion of SUS304 steel plate surface after partial penetration laser welding. The results show that angular distortion is an important reason that lead to the micro bulging distortion of austenite stainless steel surface. Pre-deformation can decrease the maximum deformation height significantly. However, the plastic bulging distortion still occurs in micro bulging distortion area. It is concluded that the main reason of micro bulging distortion of SUS304 steel plate at weldless side in partial penetration laser welding is the combination of angular distortion and plastic deformation caused by thermal expansion during welding.

Laser welding is used to weld 10Ni5CrMoV high strength steel at vacuum. The effects of ambient pressure on the microstructure of weld bead and mechanical properties are studied. The results show that laser welding at vacuum can improve the weld formation quality and increase penetration depth. The ambient pressure has little effect on microstructure of weld bead, while had obvious influence on the microstructure of heat-affected zone. Weld beads obtained at different ambient pressures are all composed of martensite. With the decrease of ambient pressure, carbides precipitate out in heat-affected zone gradually, the microstructure transforms from martensite to martensite with carbide and very few granular bainite, and a small amount of ferrite are obtained. The decrease of martensite content is the main factor of the microhardness decrease in vacuum environment. When the ambient pressure is 10 Pa, the weld hardness decreased by 6.2% compared with the atmosphere. The tensile samples are all broken at the base metal with obvious necking, and the fracture mode is ductile fracture.

The T2 copper and 1060 aluminum alloy foil are spiral spot welded by a nanosecond laser and the galvanometer system. The weld formation and the microstructures under different overlapping combination modes are analyzed. The results show that for the overlapping combination mode in which aluminum is on the top of copper, the metal on the aluminum side is completely melted, and in some areas, aluminum penetrates into the copper substrate and the “V” shaped tiny welds are formed. In contrast for the overlapping combination mode in which copper is on the top of aluminum, the weld is composed of tiny welds with high aspect ratios. Under these two overlapping combination modes, there exist four typical areas of γ2-Cu9Al4, hypereutectic structure, eutectic structure, and hypo eutectic structure within the microstructure of welds. The CuAl2 intermetallic compound layer is thin and no obvious cracks are found at the joint interface. The brittleness of joints is obviously improved.

Surface images of aluminum alloy after laser cleaning are obtained in real-time with a high speed coupled device and light emitting diode light sources. We design an on-line detection system based on machine vision and propose a dynamic threshold fast position coupling algorithm for laser cleaning aluminum alloy. The proposed algorithm solves the problem of uneven light in laser high-speed cleaning process, realizes the accurate segmentation and the quick positioning of qualified and unqualified areas. The proposed system can detect the quality of the laser cleaning aluminum alloy in real-time. The detection time is reduced, and the recognition accuracy is improved. The system can ensure the cleaning quality.

Nano-silicon slurry with heavily doped boron is used as the source of boron, and nanosecond laser cladding process is used to form a heavily doped boron silicon cladding layer on the back of passivated emitter rear contact (PERC) solar cells. The finite element simulation model of three-dimensional transient temperature field is established. Based on this model and single factor simulation experiments, the influence rules of laser process parameters on temperature field are obtained and reasonable range of laser process parameters is preliminarily determined. Through range analysis, the interaction law between laser processing parameters and temperature field distribution of laser cladding is obtained. Laser cladding process is compatible with PERC solar cells preparation experiment. The experimental results show that the simulation model is consistent with the experimental results, and the average photoelectric conversion efficiency of the solar cell is improved by 0.27%.

The residual stress, equiaxed crystal grain size and surface roughness of laser cladding deposition TC4 samples after micro forging treatment are tested, and room-temperature tensile properties and anisotropy of samples in deposition state, solution state and micro forging-solution aging state are analyzed. The results show that the columnar crystal grains transform into equiaxed grain with size variation from 70 μm to 140 μm after micro forging treatment. After micro forging treatment, the plasticity of the formed parts in horizontal direction is significantly improved, the tensile properties in all directions are higher than those of the forging parts, and the anisotropy of the formed parts is less than 10%.

A self-developed laser processing system consisting of discrete designed transformation module and reflected ring focusing module is employed to re-melt the inner face of small-bore tube, and the macro appearances and microstructures of remelted layers are analyzed in details. The results show that the processing system can re-melt the inner face of the small-bore tube with diameter below 30 mm without a rotating mechanism. The quality of remelted layer is good without spiral overlapping edges and ripples under the optimum processing parameters. The molten pool is ring-shape and the cracking tendency is remedied obviously. The penetration of remelted layer increases first and then decreases with the increase of the number of laser scanning, and the penetration and surface toughness reduce with the increase of scanning speed.

The cracking characteristics and the liquation cracking mechanism of laser additive repaired K452 superalloys are explored. The low-heat input pulsed laser process is used to control the generation of liquation cracks, and the microstructures and the mechanical properties of the repaired zones are analyzed. The results show that liquation cracks tend to be generated during laser additive repairing of K452 superalloys, which originate from the heat affected zone and extend to the repaired zone and the substrate along the grain boundaries. Under the action of tensile stress, the liquid films on the grain boundaries of the heat-affected zone become liquation cracks. The low-heat input pulsed laser process can effectively control the generation of liquation cracks. The average microhardness of the repaired zone of the pulsed laser repaired sample is 267.9 HV. The tensile strength and the yield strength are 814.3 MPa and 685.8 MPa, respectively, slightly larger than those of the as-cast substrate. The elongation is 4.87%, slightly smaller than 6.25% of the as-cast substrate. The low-heat input pulse laser process achieves crack-free slotting repair. The strength of the as-cast repair specimen reaches the strength standard of the as-cast substrate, and the elongation is slightly lower than that of the as-cast substrate.

The propagation law of laser-induced particles in three-dimensional space is studied. The interaction of single pulse laser with fused silica can produce particles with diameter form 0.3 μm to 10.0 μm when the spot area is 0.8 mm 2, laser splitting ratio is 25.4 and average energy is 8 mJ. Most of these particles are sprayed along the neutral surface with a large scattering angle, while their concentrations are lessened from top to bottom. The proportion of particle sediments located at substrate is monotonically decreasing along the longitudinal (reverse direction of incident light) and horizontal (vertical to direction of incident light) direction except for a local growth occurring at 120 mm and 360 mm in longitudinal direction. The distances of movement of particles are inversely proportional to their diameters, and the particles with diameter of 0.3 μm can achieve the distance no more than 622 mm.

The effects of annealing temperature on the photoelectric properties of Al-doped ZnO (AZO) film grown with atomic layer deposition (ALD) technique are investigated. It is found that the full width at half maximum of X-ray diffraction peaks of the AZO thin film decreases from 0.609° before annealing to 0.454° after annealing at 600 ℃, and the crystal quality is improved. The surface roughness of thin film reduces from 0.841 nm before annealing to 0.738 nm after annealing at 600 ℃. The carrier concentration and mobility ratio of the thin film annealed at 400 ℃ are the largest, and they are 1.9×1019 cm-3 and 4.2 cm2·V-1·s-1, respectively. However, as the annealing temperature continues to increase, the carrier concentration and mobility ratio decrease. With the annealing temperature increases from 300 ℃ to 600 ℃, the absorption edge of the thin film shows blue-shift at first and then red-shift.

The scattering characteristics simulation of microsphere defects in sapphire wafers is implemented based on the generalized Lorenz-Mie theory, the influences of the receiving position of scattered light, defect size, the wavelength of incident light on the scattering light intensity are analyzed. The results show that the spatial scattering light intensity in the front scattering direction contains the largest amount of information, so the test results are the most accurate. The defect size has significant effect on the scattering light intensity distribution, therefore, it is possible that the characteristics of the scattering light intensity distribution curves can be used as the basis to estimate the defect size. The smaller the wavelength of the incident light, the more accurate the detection results.

A parallel-plane cavity Fabry-Perot interferometer is designed and made to narrow the linewidth of the pulsed dye laser from 4 GHz to 340 MHz. The Fabry-Perot etalon photographing method is used to monitor the laser line type in real time, and the synchronous scanning of the pulse laser line type is realized. With the iodine absorption spectrum measurement, we built a fine-wavelength tuning and calibration system on the 100 MHz scale of the linewidth narrow pulsed dye laser. The laser system is used in the laser-induced fluorescence diagnostic of oxide-coated cathode discharge argon plasma. The feasibility of the linewidth narrowing system is verified, and the velocity resolution of the ion velocity distribution function is up to 200 m/s.

In order to solve the problem of high feature dimension in the feature construction of airborne light detection and ranging (LiDAR) and hyperspectral images for the classification of ground objects, we propose a feature selection algorithm based on extreme gradient boosting (XGBoost) combined with Pearson correlation coefficients (PCCS), named XGB-PCCS. Meanwhile, another feature selection algorithm based on XGBoost combined with sequential backward selection (SBS), named XGB-SBS, is designed to compare with XGB-PCCS. The real data is used to verify the two algorithms designed above. The results show that both algorithms can effectively reduce the dimension of feature sets on the basis that the accuracy of classification results is ensured. As for the XGB-SBS algorithm, the retained feature dimension is 33, the overall classification accuracy is 95.63%, and the Kappa coefficient is 0.943. In contrast, as for the XGB-PCCS algorithm, the retained feature dimension is 25, the overall classification accuracy is 95.55%, and the Kappa coefficient is 0.942. The XGB-PCCS algorithm has low degree of human intervention and short running time, and the retained feature set is compact. In addition, the feature subsets obtained by the two algorithms are compared, and 24 kinds of features with high importance in the multi-modal feature construction of LiDAR point cloud and hyperspectral images are summarized.

The echo characteristics of the atmospheric ozone detection laser lidar in the event of hardware failure are analyzed. According to the echo shape and intensity of the radar, we use the fuzzy logic-based quality control method to identify and test the lidar hardware failure data. The recognition rate reaches 93%, which means that the method can better realize the quality control of hardware failure data. The mean values of ozone concentration and signal-to-noise ratio (SNR) at the height of 300-500 m of hardware failure data and misjudged normal are compared. The statistical characteristics are found and the false positive rate for data without hardware failure is reduced.

An in-situ calibration method based on the autocollimator is proposed. Based on the principle of circumferential closure and the nature of Fourier series, this paper establishes the functional relationship between the measured value and the ideal value. Using the deviation between the ideal scribing position and the actual scribing position, we obtain the calibration curves. The calibration principle is deduced and analyzed in detail. The calibration angle measurement system is built and verified by experiments. The experimental results show that the original angle measurement error of the single readhead angle measurement sensor is 734.8″, and the error after calibration is 2.4″, and the calibration effect is better than that of the commonly used harmonic compensation method. The repeatability of the calibration system is better than 0.13″. The in-situ calibration method can effectively reduce the angle measurement error, and the method is simple and the calibration efficiency is high.

A point cloud registration algorithm based on canonical correlation analysis is proposed. We centralize the target point cloud and the point cloud to be registered, and rotate it around the coordinate origin. The two sets of point clouds can satisfy the maximum square of the correlation coefficient between the dimensions. The two sets of rotation matrices are solved by typical correlation analysis method. The rotation matrix and the translation vector of the rigid transformation between the two points of the clouds are solved by the rotation matrix, and the registration of the point cloud is realized. We use the proportional square value of the eigenvalues of the covariance matrix to scale the registration point cloud proportionally, and complete the affine registration. The simulation results show that, compared with several other algorithms, the proposed algorithm can be quickly and accurately registered with good stability, when point clouds are out of order, occluded, missing, size scaling and interrupted by noise.

A fast mosaic method of surface defects based on sparse matrix is proposed. In the method, a ring white light source is used to irradiate uniformly on the component surface under test, and thus a bright defect image is formed in a dark background by a microscopic scattering dark field imaging system. Then the sub-aperture stitching image is obtained by scanning the x and y directions of optical elements. Based on sparse matrix and image stitching, the fast stitching of sub-aperture images is carried out to obtain a full-aperture defect image. Based on the principle of minimal external rectangle, the image defects are identified and classified. Seven defects on the surface of optical components are finally obtained, in which the largest one has a length of 15.2110 mm and a width of 0.0297 mm. Simultaneously there exist five pock marks, in which the largest one has a length of 0.1089 mm and a width of 0.0967 mm. The relative error range of scratch width is -5.00%-5.50% after comparison between the measured and standard scratch widths. On this basis, the actual optical surface is detected, and the surface defect information of optical elements is obtained.

Based on the acousto-optic effect between the optical frequency comb and the ultrasonic pulse, we propose a method for direct measurement of seawater sound velocity. We measure the flight distance of the ultrasonic pulse according to the phase of the beat frequency between the optical frequency combs, and measure the flight time of the ultrasonic pulse based on the intensity variation of the zero-order light caused by the pulse acousto-optic effect. A measuring device based on Mach-Zehnder interferometer is built. The experimental results show that this method can achieve high precision seawater sound velocity measurement in lab, and the measurement uncertainty is better than 5 cm/s.

In order to obtain the boundary feature points and boundary lines quickly and efficiently in the scattered point cloud, a point cloud feature regularization algorithm is proposed by means of the fusion of improved field force and judging criterion. An improved k-d (k-dimensional) tree method is first used to search the k neighbors of a sampling point. Then this sampling point and its k neighbors are used as the reference points to fit a micro-cut plane and project to this plane. The local coordinate system is established on the micro-cut plane and the three-dimensional coordinate is transformed into the two-dimensional coordinate. The boundary feature points are identified by use of field force and judging criterion. These boundary feature points are sorted and connected according to the vector deflection angle and distance. The boundary lines are smoothed by the improved cubic B-spline fitting algorithm. The experimental results show that the proposed algorithm can used to extract the boundary feature points quickly and efficiently, and the deviations of the fitted boundary lines are in the level of 10 -5 m, indicating a relatively high precision.

A spatial carrier interferometry method is used for the thermo-optical aberration measurement of a thin-disk laser crystal, and the influence of jet impingement cooling system on the thermo-aberration of the thin-disk laser crystal is studied in detail. The experimental results show that the distortion of the thin-disk laser crystal caused by the jet impingement cooling system is mainly spherical deformation. As the pumping power increases, the thermo-aberration of the thin-disk laser crystal becomes worse. In the center of the pumping spot, the thermo-aberration is mainly spherical and the dioptric power decreases linearly with the increase of pumping power. In contrast, on the edge of the pumping spot, the thermo-aberration is mainly aspherical and the aspherical distortion becomes worse with the increase of pumping power. The wavefront distortion curve under a pumping power of 493 W is presented and the repeatable measurement precision of its root-mean-square is 1.153 nm. The experimental results show a good consistency with the results of theoretical analysis. It provides an important reference for the design of a stable resonator and the compensation of thermo-aberration for a disk solid-state laser.

A simultaneous measurement system based on the diode-laser absorption spectroscopy (DLAS) technique is developed to simultaneously measure the thickness and temperature of a dynamic liquid film with high accuracy. The measurement accuracy of this system is validated by a calibration tool and the results show that the average measurement errors of film thickness and temperature are 4.58% and 1.34%, respectively. On this basis, this system is employed to study the evaporation process of the liquid film on a horizontal quartz glass plate and the results indicate that the average evaporation rate of this liquid film is 0.34 μm/s and the evaporation rate increases with the increase of film temperature. Moreover, the results by DLAS, imaging method and thermocouple are well consistent. In addition, the system is applied to the dynamic liquid film in a flow channel and the results disclose that under different film temperatures of 308, 315 and 323 K, the average thicknesses of the liquid film are basically consistent and they fluctuates for 11 times within one second, while the film temperature is almost constant.

By introducing a diffraction grating into the laser feedback interference(LFI) system, we propose a laser feedback grating interferometry (LFGI) based on Littrow configuration for the measurement of one-dimensional and two-dimensional displacement. The beam emitted from the semiconductor laser is incident onto the reflective holographic grating under the condition of Littrow configuration. After the diffracted light returns to the laser cavity in the direction of the incident light, a laser feedback interference effect occurs in the cavity. The sinusoidal phase modulation and demodulation technique is introduced to obtain the one-dimensional and two-dimensional displacement with high precision. The Littrow configuration and LFGI system have the advantages of great self-collimation, compact structure, easy operation and high stability. The experimental results show that the displacement measurement accuracy of the Littrow LFGI system can reach the order of 10 nm.

Based on deep learning, one method for the intelligent detection of parking spaces is proposed. The TensorFlow deep learning platform is applied to train the car object recognition model, the optimal interval of the effective car images is extracted, the accurate recognition result of the car distribution is presented, and the order numbering of the recognition results of the car distribution and the accurate judgment of the vacancy situation of parking spaces are realized. The simulation results and the actually collected data are adopted to verify the reliability of intelligent identification of parking space distribution, intelligent numbering of parking space, and the judgement of empty parking space.

A quantum key distribution scheme based on heralded single photon sources and quantum memory is studied. The relationship between key generation rate and safe transmission distance and storage time is analyzed, and the effect of decoherence effect of quantum memory on the final key generation rate is analyzed. The influence of quantum memory on measurement-device-independent quantum key distribution scheme based on heralded single photon sources is studied. The simulation results show that under heralded single photon sources, the increase of the actual coherence time of the quantum memory makes the safe transmission distance of the system increase, and the quantum decoherence effect has a weak influence on the final key generation rate.

Based on the optical frequency domain reflection technology, we establish a strain transfer model, derive the strain transfer relationship of fiber, and analyze the influencing factors of the distributed fiber strain measurement results. Through the equal-strength beam bending experiment, we study the measurement results of the fiber-optic sensor from the aspects of the adhesion length and the shear modulus of the coating layer. The results show that the longer the adhension length, the higher the strain transfer rate. When the adhesion length reaches a certain level, the strain transfer rate in the middle of the optical fiber is 1, and those of the both ends are gradually reduced. The higher the shear modulus of the coating layer and the adhesive, the greater the strain transfer rate. Therefore, coating fibers and adhesives with high shear modulus should be used in engineering applications, and the adhesion length should be greater than the length of the area to be measured.

By changing the modulation frequency of the microwave electro-optic modulator, we achieve the optical frequency scanning. Using the variation of the interference pattern of the backward Rayleigh scattered light generated by the optical frequency shift, we can obtain the information of the sensing temperature change. Based on the cross-correlation properties of the two scanning frequency curves before and after the temperature change and their correspondence with the temperature variation, we propose an optical frequency scanning extension scheme. Theoretical analysis and experimental results show that the proposed scheme can effectively improve the temperature detection range of the system. In the experiment, the signal-to-noise ratio is improved by 2.13 dB, and the minimum detectable temperature change of the system is about 0.029 ℃.

The effects of fuel types on the soot evolution are studied using laser-induced incandescence (LII) and laser-induced fluorescence (LIF) technologies. The diffusion flames from methane, ethylene and propane are selected as research objectives, and the two-dimensional distributions of volume fraction, primary particle size, and particle number concentration of soot as well as the relative concentration of polycyclic aromatic hydrocarbon (PAH) are measured. The measurement results show that the carbon conversion factors in methane, ethylene and propane flames are 0.0058, 0.144 and 0.043; the average particle sizes of soot are 9.2, 20.8 and 14.7 nm, and the corresponding particle number concentrations are 6.9×1021, 8.7×1021 and 7.8×1021 m-3, respectively. It is found that the PAH and soot formation are fast in the flame for the fuel with the unsaturated bond or more carbon atoms. The comprehensive changes in both specific surface growth rate and growth time for the soot result in the largest soot particle size in ethylene flame and followed by the propane flame and methane flame.