Blood flow is the vital indicator to measure the body′s physiological functions and pathological condition. Blood flow testing requires an effective, live, unmarked, capillary level three-dimensional blood flow perfusion weighted imaging approach. Optical coherence tomography angiography (OCTA) technique uses the relative motion of red blood cells and the surrounding tissue as an endogenous marker of blood flow to replace conventional exogenous fluorescent markers. The spatial scattering signal acquisition capability of the optical low-coherence and the motion recognition capabilities of the dynamic optical scattering technology are comprehensively utilized to identify dynamic blood flow area in three-dimensional space, exclude the static surrounding tissue, achieve a living, unmarked, three-dimensional optical blood flow angiography, and obtain capillary blood flow perfusion morphology structure and physiological function information of the capillary level rapidly. This paper systematically reviews the mass sample OCTA technique that primarily includes the motion contrast mechanism of unmarked blood flow angiography, a detection method for high-sensitive tiny blood flow motion, an effective strategy for parallel acquisition of independent mass samples, and the application research of this technique on cortex blood flow imaging.

In view of the current clinical practice, the detection of pathogenic bacteria mainly depends on bacterial culture methods. The methods have disadvantages of long cycle and low accuracy, and are prone to cross contamination and human infection. We propose the microfluidic chip based isothermal nucleic acid amplification for molecular diagnostics. An air-insulated microfluidic chip is designed for the automatic centrifugal distribution of samples to test cells. The confocal optical imaging, rotation scanning signal acquisition, thin layer air bath heating proportion-integral-derivative temperature control, etc. are developed. A microfluidic chip based nucleic acid analyzer is also developed. We detect the pathogens of respiratory tract using the proposed system, whose sensitivity can reach 10 copies. The sample reagent consumption is reduced to 0.94 μL, and the results can be obtained in 45 min. In a blinded experiment of 100 clinical patient sputum samples, the total coincidence rate of results of our system and the traditional polymerase chain reaction is over 98%. This novel nucleic acid analyzer is suitable for low cost and accurate medical applications in hospital, community care and township health clinic, etc.

New methods based on nanomaterials, such as biomolecular detection, photothermal therapy, photodynamic therapy and nanoparticle drug delivery, are gradually becoming important measures for diagnosis and treatment. However, due to the shortcoming of conventional nanomaterials or the defects in diagnosis and treatment, current nanomedicine technologies have many challenges, including low drug utilization rate, great toxic side effect and low treatment effect. The combination of nanotechnology and photonic technologies offers precise control over light-matter interaction, which improves the accuracy and stability of the technology for biomedicine diagnosis and treatment on nanometer scale. Domestic and oversea development status of multifunctional nanophotonics technology oriented to precise biomedicine in recent years is summarized from four aspects: to enhance the stability of nanomedicine with optical technologies; to accurately monitor the process of tumor nano-treatment by using optical technologies; to acquire the physical insights of the mechanism of nanomedicine with optical technologies; to develop new methods for refinement of the frontier biomedicine research with novel optical technologies.

Photo-responsive nano-carriers for gene can realize the release of gene at a given time and a given position by external light, and have attracted much interest as non-viral gene carriers. According to different response wavelengths, photo-responsive nano-carriers for gene can be divided into ultraviolet-visible light responsive nano-carrier for gene and near infrared light responsive nano-carrier for gene. We review the recent advances of the two nano-carriers for gene and discuss the responsive mechanisms and release processes. At last, we summarize the problems to be solved in the construction progress of photo-responsive nano-carriers for gene.

Fluorescence molecular tomography (FMT) is a depth-resolved macroscopic optical imaging technique, and it can locate and quantify the fluorescent molecular probes inside biological tissue; it has a great potential in studying the protein interaction, analyzing the mechanism of drug action, and evaluating the therapeutic effect of tumor. However, one of the key challenges in FMT is that the inverse problem is highly ill-conditioned, which means that image reconstruction is sensitive to the measurement noise and the numerical errors. To improve results of image reconstruction, we should improve the performance of the imaging system as much as possible to reduce measurement noise, improve the accuracy of the forward problem of FMT to reduce the numerical error, and meanwhile alleviate and overcome the ill-condition of the inverse problem to strengthen the anti-noise ability. We introduce the research progress of FMT in image reconstruction on the last two aspects.

With the progress of science, the research objects of life science change from single organ to tissue, in vitro tissue slice, and live embryonic during development. The appearance of fluorescent-specific markers provides a means for tracking the process of the substance transfer within a single cell, tissue, organ, and even the entire embryo. In order to track the whole process, it is necessary to make nondestructive, non-invasive imaging of living embryos with sub-cellular level resolution, which poses higher requirements for fluorescence microscopy. We develop light-sheet fluorescence microscope and super-resolution fluorescence microscopy on the basis of traditional fluorescence microscopy. Light-sheet fluorescence microscope only excites the sample near the objective′s focal plane. Because of its high penetration depth, low photo-toxicity and photobleaching, and high imaging speed, light-sheet fluorescence microscope can be widely used in three-dimensional in vivo large scale biological imaging. Super-resolution fluorescence microscopy uses special light control means to improve the resolution of the microscope to nanometer level, which becomes a powerful weapon for exploring sub-cellular life activities. We introduce the development, integration, and the current problems encountered in the two technologies, and try to explore an imaging technique suitable for observing the subcellular structure and life process of three-dimensional large scale′s samples.

Raman spectroscopy is an analytical tool for chemical compositions and structures of molecules. Because it is a non-invasive technique with rich biochemical information, minimal sample preparation and little interference of water, Raman spectroscopy has been widely used in the field of biomedicine. Raman spectroscopic imaging is the combination of Raman spectroscopy and imaging, which collects Raman spectrum at each pixel for the entire region. Thus, both spatial and spectral information can be captured for positioning analysis of material molecules qualitatively and quantificationally. Compared with traditional Raman spectroscopy, Raman imaging can provide additional spatial information about the sample, which is extremely important for biomedical applications. Therefore, Raman spectroscopic imaging technique with both biochemical and spatial information shows significant values in the field of biomedicine, such as biological sample examination, clinical diagnosis, and treatment. The Raman spectroscopy technique and its development are introduced based on the principle of Raman spectroscopy. The application of Raman spectroscopy technique in the field of biomedicine in recent years is summarized. Finally, the summary and prospects of Raman spectroscopic imaging technology are discussed.

Photoacoustic microscopy is a fast-developing imaging technology, which depends on the optical absorption differences and inherits high contrast of optical imaging and deeper depth of ultrasound imaging. Thus, photoacoustic microscopy presents more merit than optical microscopy. Photoacoustic microscopy realizes multiscale imaging from acoustical resolution to the optical resolution, which provides multi-parameters imaging from simple absorption structure to its function, multi-contrast imaging from endogenous contrast agents to exogenous contrast agent, and imaging from ultrasound-transducer-based to all-optical excitation and detection, and multimodality imaging combined with optical coherence tomography, fluorescence imaging, two-photon imaging, second harmonic imaging, etc. Photoacoustic microscopy is widely applied in the field of biomedicine, such as vascular biology, oncology, neurology, ophthalmology, dermatology, and so on.

Fluorescence fluctuation-based super-resolution nanoscopy has the imaging advantages of fast imaging, high spatial resolution, low system cost and low phototoxicity, and exhibits broad prospects in imaging and monitoring of biological subcellular structures and dynamics. In recent years, based on fluorescence intermittency of fluorophores, a variety of image reconstruction algorithms have been developed to realize fluorescence fluctuation-based super-resolution imaging. These algorithms can achieve significant resolution enhancement of optical imaging without any hardware modification of conventional fluorescence microscope, and can break the optical diffraction limit. From the perspectives of reconstruction algorithms, imaging speed, resolution improvement and image quality, we analyze and compare the differences and application scopes of multiple types of fluctuation-based nanoscopy, which provides reference on optimal super-resolution techniques selection for researchers in life sciences to investigate specific biological issues.

Palpation and elastography are common diagnosis methods that detect tissue hardenability and reflect pathological status. Ultrasonic elastography is one of the existing highly developed tissue elastographies. Photoacoustic imaging uses photoacoustic signals generated by tissues that absorb pulsed light for imaging, combining the advantages of optical imaging with high selectivity and pure ultrasound imaging with high imaging depth. Elastic imaging transforms the elastic information of the material into images, which is divided into several steps such as induced deformation, deformation measurement and image formation. The mechanism and technique of elasticity detection and imaging based on photoacoustic technology have been reported, and the research results of current photoacoustic elasticity detection are reviewed. On this basis, the photoacoustic signal itself is generated by tissue thermoelastic deformation of the ultrasound, that is, the transmission of ultrasound is related to tissue elastic properties. Photoacoustic signal analysis of tissue elasticity analysis is proposed. Which combines photoacoustic function to realize multi-function imaging of function and elasticity. The proposed method can provide more accurate information for the diagnosis and treatment of diseases, especially tumors.

Surface-enhanced Raman scattering (SERS) spectroscopy, a technique with high sensitivity and high resolution, can provide the fingerprint vibration spectrum of the analyzed molecule and realize the nondestructive measurement of the sample, which has very important applications in field of spectrum analysis. The sensitivity, stability, and reproducibility of SERS spectrum depend on the performance of SERS substrate. The common SERS rigid substrates have the defects of complex preparation process, poor flexibility, inconvenience to carry, and fragility. Paper-based SERS substrate, which uses paper as support material, can effectively overcome the shortcomings of rigid substrates and meet the commands of fast, handy, and personized analysis and measurement in the future. In this review, we summarize the main methods (direct dipping/dropping, inkjet printing, chemical reaction, and physical spray coating) for the preparation of paper-based SERS substrates, and discuss the applications in biomedical analysis and sensing, environmental monitoring, and food safety.

Optical projection tomography (OPT) technique, is a new mesoscopic (from millimeter to centimetre level) three-dimensional fluorescence imaging technique with the advantages of low cost, high speed, high resolution and large imaging depth, and is regarded as a hot spot in biomedical photonics research. We review the principles, research progress, and wide applications of OPT, and present the performances of different OPT techniques. The development of OPT technique is introduced from the view of improvement of OPT system (e.g. focal plane scanning, angular multiplexing, angular filtering), improvement of reconstruction algorithms, and incorporation of multi-dimensional fluorescence imaging techniques. Through the developments, OPT has been widely used in various research fields such as biomedical, morphology, histopathology, in vivo imaging, and fluorescence tracking.

In order to solve the problem of the adhesion segmentation in fluorescent microspheres image and the classification with limited labeled samples, we propose a fluorescent microsphere segmentation and classification method based on improved watershed and semi-supervised minor reconstruction error classifier (SSMREC). Firstly, we use improved watershed method to segment the fluorescent microspheres adhesion image, and effectively separate the adhesion fluorescent microspheres into independent objects. Then we use the non-uniform quantization of Hue-Saturation-Value (HSV) color space for the microsphere objects to remove the redundant information and extract the discriminant features. Finally, the microsphere objects are classified by a semi-supervised reconstruction error classifier. We compare the proposed method with linear discriminant analysis classifier (LDA), random forest classifier (RFC), sparse representation-based classifier (SRC), K- nearest neighbor classifier (KNN), and support vector machine (SVM). The results show that the overall classification accuracy of the proposed method can be improved by 3.5%-14.3% compared with other classification methods in the case of randomly selecting 2, 4, 6, and 8 labeled samples in each class. It means that the proposed method is more effective in small number of labeled samples.

In order to improve the time resolution of super-resolution fluorescent microscopy, the methods of high-density molecule localization have been proposed. Three algorithms based on compressed sensing models, including the interior-point method in the CVX toolbox, the homotopy method, and the orthogonal matching pursuit (OMP) algorithm, are investigated. We compare the identified density, localization precision, and execution time by using these algorithms in the simulations and experiments. Simulation results show that the CVX and homotopy methods can accurately locate in the high molecule density, but the CVX method has the longest running time among these methods. The OMP method has low localization precision in the high density. The experimental results show that these algorithms can realize the localization of high molecule density. The CVX and homotopy methods get better results than OMP method in the localization precision. For the localization of 500 images, the homotopy and OMP methods are 14.9-fold and 21.2-fold faster than CVX method, which can greatly shorten the reconstruction time.

A quantitative phase imaging system capable of revealing three-dimensional changes of microstructure and light scattering properties of cancer tissues is developed based on the transport-of-intensity equation using the differential interference contrast (DIC) microscope. The DIC images of unstained paraffin embedded tissue sections of 257 patients with invasive ductal carcinoma are acquired with the quantitative phase imaging system. The corresponding two-dimensional phase maps are obtained with the calculation of the transport-of-intensity equation. The spatially resolved optical properties of the tissues are computed from the two-dimensional phase maps using the scattering-phase theorem afterwards. The results show that the grade of invasive ductal carcinoma has strong correlation with reduced scattering coefficients and anisotropy of tissues. When the grade of invasive ductal carcinoma increases, the reduced scattering coefficient of invasive ductal carcinoma tissues increases significantly, while the anisotropy decreases significantly. The retrieved optical parameters are shown to distinguish invasive ductal carcinoma with different grades with a high accuracy of 88%. Owing to the label-free and high-contrast characteristics of DIC microscope, the proposed approach is also applicable for fresh or frozen tissues, and may have promising applications in real-time and rapid cancer diagnosis.

In the process of fluorescence molecular tomography reconstruction, there are different optical parameters in the reconstructed image for the fluorescent targets with the same optical parameters, the same embedded depth, but different volumes in the tissues. To solve this problem, we propose a novel fluorescence molecular tomography reconstruction algorithm based on volume compensation. We use an improved iterative self-organized data analysis techniques algorithm (ISODATA) to decide the center and the expectation number of the initial clusters and to make a cluster analysis of the pre-iterative reconstruction image. According to the sizes of different fluorophores clustered by the improved ISODATA, we design an operational method with volume weight coefficient based on logarithm to compensate nonlinearly the reconstructed optical parameters of different fluorophores. The simulation results show that our compensation method can effectively amend the reconstruction error resulted from the volume difference of the fluorophore.

One major challenge of the life-science research is to study the subcellular structure and the interactions among organelles and molecules or different molecules in vivo. To develop a single molecule detection and tracking technology, which can real-time detect multiple biomolecules in living cells, is significant to the study on the molecular mechanism of the life process. We design and establish a microscopy imaging system based on the distorted grating and the double helix point spread function technologies, which can extend the depth of field and reach nano-positioning in three-dimensional space. The simulational results show that the system can achieve dynamic detection the 12 μm-depth sample with high localization accuracy. And the real-time positioning and tracking of dynamic biomolecules in living cells is achieved experimentally.

Photoacoustic imaging, which combines the advantages of optical imaging and acoustic imaging, is a non-invasive imaging technique with high spatial resolution and high contrast ratio. Therefore, photoacoustic imaging is one of the research hot spots in biomedical imaging. However, the reconstruction of photoacoustic image is a typically ill-posed inverse problem. Aiming at the ill-posedness of photoacoustic imaging and the slow velocity of the reconstruction owing to the large size of the system matrix, we present a fast exponential-filtering reconstruction method based on Lanczos double diagonalization and the effectiveness of the proposed method is proved by numerical simulation. The simulation results show that the proposed method can increase the reconstruction velocity greatly, while preserving the high quality of reconstructed images. The reconstruction time is 1/67-1/47 of those using exponential-filtering method and back projection method.

The random phase screens in anisotropic non-Kolmogorov turbulence are generated by the non-uniform sampling and power spectral inversion method, and the spatial optical modulator is adopted to simulate the drift characteristics and the changes of the orbital angular momentum of ring Airy Gaussian vortex beams in atmospheric turbulence. Numerical simulation and optical experiment results show that the drift values of ring Airy Gaussian vortex beams increase with the increasing beam attenuation coefficients, radius of the primary ring, outer scale of the atmospheric turbulence, and transmission distance, and decrease with the increasing turbulent anisotropic coefficients and topological charge of the beams. There exists a maximum drift value near the turbulent power-law value of 3.3. Moreover, comparing the interference fringe patterns of ring Airy Gaussian bortex beams before and after propagating through the atmospheric turbulence, we find that the smaller the topological charge is, the better the stability of topological charge after beam propagating in the turbulence is.

To solve error propagation problem in combination of pulse position modulation (PPM) and multilevel coding, we propose an iterative demodulation and decoding method based on "chain rule" of multistage decoding principle and give the hard decision iterative algorithm of 8-PPM multilevel coded modulation. The simulation results show that the error propagation is improved and the bit error ratio (BER) is decreased effectively by the hard decision iterative method. The larger the channel attenuation is, the more obvious the gain gets with the same iterations. Considering both improvement and cost, the iterations should be less than M times for M-order coded modulation system.

Based on received signal strength indicator (RSSI), which has wide serviceability, simple and easy-to-construct structure, and good portability, we study a visible light communication positioning method with high accuracy. Due to the interference from background resources, the measurement error of RSSI-based positioning method is difficult to control below centimeters. We use wavelet analysis to significantly reduce the noise mixed with received signal, use the correlation test method to extract the source signal in noise, and use the least square method to estimate location coordinate. We verify the reliability of the method by the simulations under different signal-to-noise ratios (SNRs). It is found that the error of the RSSI-based visible light positioning is less than 1 cm and is insensitive with noise, which is dozens of times better than the theoretical accuracy without processing based on error analysis.

Based on multi-scattering model，we design an LED transmission system based Monte-Carol simulation model, and study the influence of arriving angle of the received signal and field of view (FOV) of the receiver on the received signal power and the received signal-to-noise ratio (SNR) under different water environments. Under pure water and clear ocean water environments, the received power is mainly distributed at the arriving angle range of 0°-3°, and when the receiver with small FOV (1°), the maximum received SNR can be achieved. While under harbor and coastal water environments, the received power distribution obviously spread, especially for harbor water, the distribution expands from 0° to 90°. Under coastal water environment, when the receiver FOV is set at 8°, the maximum SNR is achieved. Under harbor water environment, when the receiver FOV increases to 30°, the maximum SNR is achieved.

Aiming at the problem that high density data results in challenge for data transmission and storage in fibber Bragg grating (FBG) sensing system, we propose a segmented adaptive sampling compressed sensing and improved orthogonal matching pursuit (SASCS-IOMP) algorithm. Firstly, we design the Gabor filter with specific parameters to extract frequency points of the upper sideband with the largest slope in the FBG spectral signal, and adaptively segment the FBG spectrum according to the coarse positioning of the FBG central wavelength achieved by the Hilbert transform. Then, we set different signal to noise ratio (SNR) thresholds in different segmented regions to reduce the overall compression ratio. To speed up algorithm speed, we design an adaptive step growth mechanism based on proportional-integral-derivative control algorithm in the process of adaptive sampling. Finally, we use IOMP algorithm to reconstruct the spectrum. The simulation result shows that the SASCS-IOMP algorithm can reduce the total number of observations in both the single-peak and multi-peak spectra. The reconstructed root mean square error is less than 0.7% within 3 dB bandwidth of FBG spectrum.

The transmission functions and the characteristics of transmission spectra of phase-shifted fiber gratings are analyzed based on the transmission matrix method and the coupled mode theory. The results show that the phase-shifted fiber gratings have superior integral property, and the integral order is proportional to the number of inserted phase-shifted points. The pulse shaping structure is designed based on the first-order integral characteristic of phase-shifted fiber grating, which can shape the Gaussian ultrashort optical pulse into a flat-topped pulse or a symmetrical triangular light pulse. The system can output asymmetric triangular light pulses by further adjusting the weighting coefficients in the proposed structure. When the pulse width of the input Gaussian light pulse fluctuates ±10%, the flat-topped pulse and triangular light pulse with high quality can be obtained, which proves that the designed pulse shaping system has high stability.

According to the reversible principle of optical path, a computer generated half-circle view-able color rainbow holographic algorithm based on frequency domain synthesis is proposed. Firstly, the principle of half-circle view-able color rainbow hologram is analyzed, and the corresponding relationship between observation window and frequency domain is summarized. It is pointed out that the frequency spectrum of half-circle view-able color rainbow hologram object light is composed of the half-ring frequency spectrum of three primary colors. A plurality of projection images in a specific direction of a color three-dimensional object are used to separately perform color separation and interpolation, and perform a two-dimensional Fourier transform. The object light frequency spectrum of the half-circle view-able color rainbow hologram in the frequency domain is synthesized. And the synthesis object light frequency spectrum is transformed by two-dimensional inverse Fourier transform. Half-circle view-able color rainbow hologram is got by taking the real part and adding a bias component. Using this algorithm, a hologram with the area of 47 mm×47 mm and a resolution of 84000 pixel×84000 pixel is calculated and output by the holographic output system. Then it is followed by development, fixation and bleaching. Half-circle view-able color rainbow hologram with white light reconstruction is realized. The hologram shows vivid three-dimensional effect, brilliant colors, and can be watched by many people at the same time.

We demonstrate a stable, low threshold, passive Q-switched mode-locked Tm, Ho∶LiLuF4 solid-state laser with the graphene oxide (GO) prepared by vertical growth method as a saturable absorber and the special designed low threshold resonant cavity. The output power of the laser is as low as 73 mW, the stable mode-locked threshold power is 663 mW, and the corresponding power density of the GO saturable absorber is 76.4 μJ·cm-2. Typical Q-switched pulse envelope has a repetition frequency of 104.2 kHz and a pulse width of 30 μs. The repetition frequency of mode-locked pulse sequence is 178.6 MHz, and the modulation depth is close to 100%.

The 6061-T6 aluminium alloys are welded by the laser-TIG hybrid heat source at a high speed. The influences of process parameters such as arc current, laser pulse duration and laser frequency on pore formation are studied. The results show that, in the process of laser-TIG hybrid welding of 6061-T6 aluminum alloys at a high speed, the increase of welding speed makes the cooling speed of molten pool increase, there exist thin isometric crystals in the weld microstructure, and the width of softening zone in the heat affected zone decreases. The change of the cooling state of the molten pool results in the reduction of keyhole stability, the easy collapse of keyholes, and the easy formation of pores in welds. With the increase of laser pulse duration, the number of pores decreases, and the diameter also decreases. With the increase of laser pulse frequency, the number of pores first decreases and then increases. When the arc current increases from 180 A to 200 A, the number of pores in welds significantly reduces.

By using the hybrid welding technology of fiber-laser and VPTIG (variable-polarity tungsten inert gas arc welding), the A7204 aluminum alloys are welded with different filler wires. The microstructures and mechanical properties of these joints by this hybrid welding are analyzed, and the softening behavior and mechanism of these joints are also investigated. The results show that the upper part of the weld with ER5087 filler wires presents the finest microstructure with narrow dendrite arms. After the natural aging of 90 days, the mechanical properties of joints welded with three kinds of filler wires are similar, and the tensile specimens fracture basically in the heat-affected zone which is close to the base metal. The microhardness of these joints welded with three kinds of filler wires in the heat-affected zone, 1.6-2 mm away from the fusion line, is the highest, in contrast, the softening zone obviously occurs in the heat-affected zone, 3-7 mm away from the weld center. In the heat-affected zone, there exist the obvious aging hardening zone and recrystallization softening zone, and the natural aging has an obvious effect on the softening of heat-affected zone.

The 7020 aluminum alloy joints welded by laser-metal inert-gas arc (MIG) hybrid welding are obtained. The microstructure, mechanical properties, fatigue performance and fracture mechanism of these hybrid welded joints are investigated by the techniques of electron backscatter diffraction and high resolution synchrotron radiation X-ray micro-tomography. The results show that, under the influence of thermal circulation in welding, the grain morphology, size and chemical constituent in different zones of butt-welded joints after cooling show obvious changes. The static tensile strength, yield strength and welding coefficient of hybrid welded joints are 265.34 MPa, 218.85 MPa and 0.74, respectively. When the fatigue life is 2×106 cycles and the survival is 50%, the fatigue strength of hybrid welded joints is 96.13 MPa, and is about 63.14% of that of the base metal, which shows that the welding process significantly deteriorates the performance against fatigue. It is found that the fatigue cracks initiate from a notch with 103 μm depth at the surface in the fusion zone, and show a typical I mode quarter elliptical crack profile. The pores have little effect on the crack growth rate in the stable extension stage.

By using TA15 spherical powder as the raw material, the bulk specimens of TA15 titanium alloy are formed by laser deposition manufacturing. The effects of single-annealing and duplex-annealing on microstructures, tensile properties at room temperature, and anisotropy of TA15 titanium alloys are studied. The results show that, there exist significant differences in the α-phase morphologies under the two annealing methods, tensile properties at room temperature are characterized by high strength and low plasticity due to the influence of β columnar grain boundary, and the deformation in the deposition direction is relatively large. The duplex-annealing can make obvious improvements on the strength and plastic anisotropy. The micro hardness under single-annealing is hardly influenced by the increase of annealing temperature, in contrast, that under duplex-annealing increases slightly.

Based on the inside-laser powder feeding technology,the normal stratified path planning, and the high-level measurement system, the closed-loop control of laser cladding forming of fan-shaped unequal-height parts is conducted. A new method of hierarchical and segmented control is proposed, which ensures the width of forming parts consistency. The speed proportion-integration (PI) controller is established, which ensures that the actual heap reaches the desired value, and the high precision forming of structural parts is realized.

The Fe-Cr-Si-P amorphous coatings are prepared on the 304L stainless steel surface by using the broad-band laser cladding technique. The microstructures and formation mechanism of these coatings are analyzed. The mathematical and physics models of laser cladding are established, and the change rules of temperature gradient and cooling rate of molten pool along the depth direction are obtained. The results show that the microstructures of the coating are planar crystalline and epitaxial growth dendrites in the bonding zone, amorphous character in the middle zone and fine equiaxed crystalline on the surface. During the solidification process, the temperature gradient from the bottom to the surface for the molten pool decreases and the cooling rate increases gradually. Based on the rapid solidification theory, the model of the relationship between the coating microstructure character and the shape control factor as well as that between the coating microstructure character and the cooling rate is established.

Basded on the hollow laser beam internal powder feeding technology, the thickness-variable eccentric ring structure is fabricated by laser cladding forming. The scanning paths for forming the thickness-variable eccentric ring structures are planned. The layer-height control software based on machine vision is used to obtain the actual height for the each forming layer, which is compared with the desired height. The speed-correction model based on the proportion-integration (PI) controller is established. The forming eccentric ring structure has the minimum wall thickness of 2.14 mm and the maximum wall thickness of 6.38 mm. The error of actual total height with respect to the desired one of each segment is relatively small and the overall height is relatively flat, which shows the forming accuracy is high. At positions with different wall thicknesses of forming parts, the grain structure is uniform and grain size is comparable.

By means of the uniaxial isothermal compression test, the thermal deformation behaviors of laser additive manufactured TC18 titanium alloys are studied under different thermal deformation conditions. The regularity of flow stress-strain and softening mechanism are analyzed. The constitutive equation of peak stress is established. The results show that the flow stress-strain curves of laser additive manufactured TC18 titanium alloys can be characterized by two kinds of characteristics of the continuous softening and the steady rheology, and the activation energy is 476.8 kJ·mol-1. When the thermal working temperature is in the α+β two-phase region, the softening mechanism is mainly the dynamic recovery; when the thermal working temperature is in the β single phase region, the softening mechanism is the dynamic recrystallization. The ideal thermal process parameters for laser additive manufactured TC18 titanium alloys are the defomation temperature of 830-880 ℃ and the strain rate of 0.001-0.003 s-1, or the deformation temperature of 750-760 ℃ and the strain rate of 0.001-0.002 s-1.

We use the 1064 nm laser as pumping light to obtain the 1248 nm laser via wavelength conversion based on stimulated Raman scattering in high pressure CO2 gas. By optimizing the pressure of CO2 and focal length of lens, we obtain the maximum conversion efficiency of 36.6% and the maximum pulse energy of 82 mJ for the first order Stokes light (S1, 1248 nm).

To reduce the influences of acceleration response of distributed feedback (DFB) fiber laser hydrophone on underwater acoustic detection, we design a DFB fiber laser hydrophone with sensitivity-enhanced structure through polyurethane end surface pulling. Firstly, we establish the acceleration sensitivity model of the designed hydrophone. Secondly, we theoretically analyze the relationship between the sleeve structure and the acceleration sensitivity. Thirdly, we simulate the relationship between elastic modulus, Poisson′s ratio, and height difference and acceleration sensitivity. Fourthly, we optimize the structure and materials parameters of hydrophone. At last, we fabricate and test the prototype samples of hydrophones and towed line array samples. The experimental results show that the acceleration sensitivity is less than 1.2 dB at each frequency point in the frequency range of 20-2000 Hz, which agrees well with theoretical results. The towed line array can form stable beam pointing with high noise-signal ratio during the variable speed motion phase of dynamic drag. The anti-acceleration performance of the hydrophone is effectively predicted and experimentally verified.

In order to meet the real-time requirement of the polarized light positioning system, the polarized light positioning system based on STM32 is designed, which achieves the synchronization of polarization azimuth data acquisition, reduces the complexity of the system data bus and the complexity of personal computer data receiving, and solves the problem of double-solution of solar altitude angle and azimuth. Firstly, based on the principle of polarized light positioning, four polarization azimuth acquisition modules are designed to get the polarization azimuth of the four directions in the sky, and the error of every module is under ±0.2°. Then, the sun vector judgment module is designed to solve the problem of 180° double-solution of solar altitude angle and azimuth, which results from the polarization vector. The experiments show that the polarized light positioning system can obtain the correct solar altitude angle and azimuth, and it is suitable for daytime. The maximum errors of longitude and latitude are ±1° and ±1.5° respectively in the experiment of about 55 minutes. The polarized light positioning system meets the requirements of real-time with a stable positioning accuracy, so it can be applied to the actual positioning.

On the basis of the technological application of modulation transfer spectroscopy, absorption frequency discrimination, and dispersion frequency discrimination, according to the operating theory of passive hydrogen maser, the theoretical analysis of the process where a single frequency modulation signal carries out frequency discrimination of hydrogen transition and of the microwave cavity resonance are mathematically derived in details. The relation of frequency discrimination curves and the error signal amplitudes with different modulation depths from simulation is obtained by simulation, and the simulated results are compared with the experimental results. The simulated and experimental results verify the effectiveness of the derivation process, and the modulation depth is acquired, which endows the short-term stability of passive hydrogen maser with the best performance. The analysis procedure provides the theoretical basis of performance optimization for passive hydrogen maser based on single frequency modulation, and it provides the design principle of project improvement for electronic circuit.

A terahertz broadband polarization converter based on anisotropic metasurface is proposed, which is composed of metal-dielectric-metal three layers. The top layer is a square-shaped resonator intersecting along a diagonal line. The bottom layer is the metal plate. The top and bottom layers are separated by a dielectric layer. The reflection ratio and polarization conversion rate of the structure in the studied frequency range are calculated by simulation. The results show that the polarization converter can rotate the polarization direction of the linearly polarized terahertz wave 90° in the frequency range of 0.4-1.04 THz, and the conversion rate is more than 90%. Meanwhile, the distribution of the surface current of the structure is simulated at the frequency with high polarization conversion rate, and the mechanism of high polarization conversion rate is analyzed. Compared with the previous design, the polarization converter has a simple structure and a broad operation bandwidth, and has a potential application value in the field of terahertz polarization modulation.