Photobleaching induced by excitation light limits the application of confocal microscopy for long-time observation of biological samples. A new imaging approach, controllable light exposure-confocal microscopy (CLE-CM), is proposed. CLE-CM has two thresholds decided through pre-experiments and detects the feedback of sample pixel value at set intervals. The feedback is compared with upper and lower thresholds. By spatially controlling the light-exposure time of objective pixel according to the results of comparison, CLE-CM exploits fluorescent information in a more efficient way and reduces photobleaching without decreasing image quality. Two scan series of 11 successive CLE-CM images and standard confocal images show that, CLE-CM reduces 52.62% of photobleaching in bovine pulmonary artery endothelial (BPAE) cells compared with standard confocal at the 11th image. The effect of bleaching attenuation depends on the fluorophore distribution. CLE-CM decreases photobleaching markedly through the reduction of excitation-light dose, and increases the number of good-quality images that can be captured continuously by confocal microscope.

We propose a hand-held frequency sweeping optical coherence tomography system, which can image microvasculature in human skin. We get the cross-section and en-face images using power intensity differential (PID), speckle variance (SV), and differential standard deviation of log-scale intensity (DSDLI) algorithms, and compare the practical imaging resolutions. The results show that, compared with images reconstructed by PID and SV algorithms, the image reconstructed by DSDLI algorithm is clearer and shows more blood vessels and detailed vascular information.

Compared with the traditional beam-splitting elements, the noncollinear acousto-optic tunable filter (AOTF) has many special merits, such as small size, high stability, flexible and easy to tune, convenient for signal reception and processing. It has high application value in spectral imaging field. In this study, the noncollinear AOTF is connected with the converted microscope, and a hyperspectral microscopy imaging system is built. With the system, the rapid microscopic spectral imaging for lung cancer tissue is studied in the visible range. In the experiments, the relationship between the acoustic frequency and the diffracted optical wavelength loaded on AOTF is got, and the theoretical results coincide well with the experimental data. A series of microscopy images and corresponding narrow band spectra of lung cancer tissue are received at central wavelength. The results indicate that the system keeps a well spectral resolution performance in the working waveband. By comparing the lung cancer tissue images under different wavelengths, it is found that obvious image drift is not observed, which indicates that the image has high stability. Lung cancer tissue images of each central wavelength all present good clarity. The comparison of lung cancer tissue image and the analysis results of luminance curve and transmissivity curve show that the best contrast and clarity performance of the images are in the range of 503.45-590.12 nm. It is mainly because the different intrinsic constituents and structures in different areas induce different absorptivities of the signals with different optical wavelengths in lung cancer tissues.

The vitro photodynamic therapy(PDT) inactivation efficiency of HL60 cells based on cadmium selenide-doped titanium dioxide nanoparticles modified by folic acid (FA-CdSe-TiO2) is investigated and the mechanism of folic acid modification to enhance the PDT effect of CdSe-TiO2 nanoparticles is discussed. The CdSe-TiO2 nanoparticles are prepared by hydrolysis deposition method, and FA-CdSe-TiO2 nanoparticles are prepared by surface modification method. The structure and optical properties of the nanoparticles are characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet visible absorption spectrum and so on. The cell viability is measured by CCK-8 method. The intracellular reactive oxygen species (ROS) levels are analyzed by fluorescence probe labeling technique, and the ultrastructure of the cells is observed by scanning electron microscopy. The results show that FA-CdSe-TiO2 nanoparticles have no significant change in cytotoxicity compared with CdSe-TiO2 nanoparticles in the darkroom condition. However，under the light condition, FA-CdSe-TiO2 has a great increase in cell growth inhibition rate. When the ratio of folic acid is 1.0, the PDT efficiency is 84% at 18 J/cm2 light irradiation. Folic acid surface modification increases the uptake efficiency of HL60 cells to the nanoparticles, and the level of ROS in the cells is increased, thereby the PDT inactivation efficiency of HL60 cells is enhanced.

An imaging detection system is designed to achieve quantitative measurement of the concentration of fluorescent immune-chromatographic test strip. Using 365 nm ultraviolet light emitting diode (LED) as the excitation light, we capture the clear image of fluorescent immune-chromatographic test strip by the hand-held zoom microscope camera. Genetic algorithm on the base of Otsu is used to segment the image according to the characteristic of relatively fixed position of the detection line and the quality control line. Then, the background noise is removed by the fluorescence region localization method. The segmented fluorescence image background is filtered out and the gray values of the detection line and the quality control line are calculated. Finally, the eigenvalues of the fluorescence region are calculated to realize the quantitative analysis for the concentration of the fluorescence test strip. The experimental results show that the fluorescence detection system has good repeatability. Five different concentrations of fluorescent test strips are tested for ten times. The variable coefficients of the results are less than 0.5%. The fitting degree of the standard curve reaches 0.99944, and the rapid quantitative detection is realized.

Bioluminescence tomography (BLT) is a promising optical imaging modality, which has the advantages of low cost and high sensitivity. Efficient and stable inverse algorithm is the key to push it into application. To overcome the high ill-posedness of the inverse problem of BLT, we propose a nonconvex L1-2 regularization based on reconstruction method. A convex difference algorithm is used to solve the involved nonconvex functional minimization problem. In each iteration, an alternating direction method of multiplier with adaptive penalty is adopted to solve the problem efficiently. Phantom experiments of single-source and double-source on a digital mouse model are designed to assess the effectiveness and robustness of the proposed method. Comparison study with three typical reconstruction algorithms is also conducted. Simulation results show that the reconstruction results using L1-2 regularization have the optimal location accuracy under different experimental settings.

An axial adjustable common-path interferometric phase imaging system with simple structure is proposed based on the theory of interference imaging. In this design, making full use of the reversibility of the optical path and the reflection and refraction characteristics of the splitter prism, the incident beam is split into two parallel beams by a prism. One beam is incident on the sample and reflected by the reflecting stage as object light, and the other beam is directly reflected as reference light. The interferograms can be captured by combining object beam with reference beam through the same beam splitter. The interferometer can achieve different types of interference by adjusting the angle between the layer of the beam splitter prism and the optic axis. Taking Fourier transform and three steps phase shift norm method as examples, the phase of the interference fringe is recovered, and the performance of the system is evaluated by the analysis of the results. The feasibility of the proposed design for biological cells phase imaging is demonstrated. The system has the characteristics of simple structure, easy operation and low system error, which can provide an easy and simple method for label-free morphological detection of homogeneous cell.

In this paper, we present a dual-hop transmission system composed of underlay cognitive radio frequency(RF)network cascaded with multiple input multiple output (MIMO) free-space optical communications (FSO) links, and analyze the outage probability. For the RF link, we use the Rayleigh fading distribution model and analyze an underlay cognitive radio network where the secondary users share the spectrum with licensed primary users. For the FSO link, we use the unified Gamma-Gamma turbulence distribution model to establish the MIMO FSO channel model derived with the equal gained diversity combined technique considering the effects of atmospheric attenuation and turbulence. We derive a new exact closed-form expression for the outage probability under fixed amplify-and-forward relay scheme. The influences of various weather conditions and turbulence strength on the cascade link are verified via computer simulations. The results indicate that the performance of the mixed underlay cognitive radio network and MIMO FSO system is increased and the atmospheric effect is decreased gradually with the increase of the peak transmission power of secondary user transmitters and the number of transmitting aperture and receiving aperture.

A measurement system of temperature field under vacuum condition is established based on fiber Bragg grating (FBG). A 304 stainless steel frame, which is similar to the support structure of the vacuum chamber in Tokamak devices, is used as the research object to conduct steady-state thermal analysis under both vacuum and normal pressure conditions. Specifically, an aluminum alloy heating plate is adopted to heat the stainless steel frame under either vacuum and normal pressure conditions. As packaged with micro steel capillary, four FBG temperature sensors are placed into measurement points to detect temperature. The experimental results show that the temperatures of four measurement points under vacuum condition are higher than those under normal pressure condition. Meanwhile, the temperature of four measurement points reach stability costs 4900 s and 6150 s, respectively, under vacuum and normal pressure conditions. It is shown that heat transmits by the way of both thermal conduction and thermal radiation under vacuum and normal pressure conditions. As the stainless steel frame contacts with air under normal pressure condition, which leads to thermal losses via thermal convection, the heat loss of stainless steel frame is smaller, and the heat transmission efficiency is higher under vacuum condition.

A new type of micro-structured optical fiber (MOF) is designed. The fiber cladding has two pairs of elliptical air holes that are perpendicular to each other. The larger holes are filled with air and the smaller holes are filled with magnetic fluid. The four holes form a rectangular core. The finite element method is utilized to simulate and analyze the birefringence and confinement loss of the fiber at 2 μm wavelength band, and the best fiber structure is obtained by the structure parameters optimization. The simulation results show that the optical fiber model birefringence can reach to 10-3, while the loss is less than 10-11 dB·m-1, thus, double standards of high birefringence and low confinement loss are achieved simultaneously. The refractive index of the magnetic fluid material can be changed by change of the external magnetic field, and then the effective refractive index of the fiber is changed. Consequently, the transmission of polarized light in the fiber can be tuned continuously.

The frequency modulation phase response of single section distributed feedback (DFB) semiconductor laser has a 180° phase reversal in 0.1-5 MHz, which makes it difficult for phase locking of optical phase-locked loop (OPLL) when single section DFB semiconductor lasers act as slave lasers. To solve the problem of phase locking in single section DFB semiconductor lasers, we add the adjustable lead phase shift functional circuit and adjustable gain function unit in the single feedback loop, and optimize parameters of phase shift to accomplish phase locking of DFB laser with MHz level linewidth. The residual phase noise of improved OPLL is 0.012 rad2, and the linewidth of DFB laser is compressed from 2 MHz in free-running state to 10 kHz in phase-locked state. In addition, we research the influence of loop gain of the feedback loop on the phase locking performance of OPLL and give the optimized loop gain parameter.

Based on the spin-flip model, the output laser circular polarization switching (PS) and polarization bistability (PB) characteristics of 1300 nm spin vertical-cavity surface-emitting lasers (Spin-VCSEL) under optical pumping are investigated numerically. The results show that, for a certain polarization ellipticity PP of the pump light, the pump power Pout can control the polarization ellipticity of the output light at a certain extent, and its absolute value increases with the increase of pump power. For a certain normalized pump power η, the PS can occur between the left circularly polarized light and the right circularly polarized light of the spin-VCSEL and the PB phenomenon can be observed when PP is scanned forward (gradually increasing) or backward (gradually decreasing). For the small η, the bistability loop width increases to a maximum, and then decreases to 0 with the increasing η. For a large η, the bistability loop width shows a decreasing trend with the increasing η on the whole. Moreover, the internal parameters such as linewidth enhancement factor α of the laser and birefringence coefficient γp of the source medium have a great influence on the PS and PB characteristics induced through the changing of PP. In addition, the distribution of the bistability loop width is also given in the parameter space of some key internal parameters of the laser and η.

We design a single fiber quasi-single mode all-fiber laser oscillator based on single-end 915 nm semiconductor laser forward-pumping, which produces 2.02 kW output power at 1080 nm. We study the relationship among the gain fiber length, stimulated Raman scattering (SRS), and the output power theoretically and experimentally. We optimize the length of the gain fiber to achieve a laser with a high SRS suppression ratio of 0.8 %, which has an output power of more than 2 kW. The optical to optical conversion efficiency of the laser oscillator is about 70%, and the power fluctuation is less than ±1% within 180 min running. The fiber coiling technique is adopted to effectively depress the high-order laser modes to obtain a quasi-single-mode laser (beam quality factor M2≈1.5) at the maximum output power. What is more, the application of the laser in laser cutting is investigated.

Color proportion and color temperature in RGB laser display are studied based on CIE1931 and CIE1964 standard colormetric observers to realize the automatic white balance of laser projection. Firstly, the color coordinates and color temperature of white color generated by RGB colors are described based on Grassmann′s laws of color mixture. Secondly, the laser power ratios of red laser (638 nm), green laser (532 nm, 525 nm) and blue laser (445 nm) are calculated at 6500 K and 9300 K, and the change of power ratio is analyzed with continuously adjustable temperature of 6500-9300 K. Then, the influence of green wavelength change on color temperature and luminance, and the change of color temperature caused by power degradation are gained. Finally, an experimental system for measuring color temperature of laser display source is set up, and the experimental result of color temperature is lower about 15% than the theoretical color temperature according to the standard power ratio.

There are many reflected and refracted points in prism ring cavity. The angle of work plane, pyramidal error and cavity adjustment are strictly required in order to ensure the stability of gyroscopes. We set the angle error of prisms and sphere eccentricity as the perturbation terms in meridian and sagittal planes, and amend the transmission matrices of light reflecting and refracting in prism surfaces. We establish physical models of light geometric deflection loss and light path non-coplanar loss in prism ring cavity, and analyze the rate of deviation from the design position by the revised transmission matrices. Based on the assorted screen and resonant loss controlled, we design a new way for cavity adjustment. The experimental results show that the new cavity adjustment method makes once pass rate rise to above 90% from 75%.

A model of optical Kerr effect time gate is built. The CS2 Kerr signal curve obtained through the pump-probe experiment is acted as optical gate response function. The beam propagation is divided through time slicing and space distribution, and the temporal and spatial variation of the optical gate is given through the simulation. The width of the time gate and the spatial distribution of the beam are studied under different angles between the pump beam and the probe beam and different spatial distributions of the pulses. The results indicate that, for the pump beam and probe beam with Gaussian distribution, the time gate width becomes narrow with the intersection angle increasing between the pump beam and the probe beam, and the spatial distribution changes from roundness to ellipse. The bigger the intersection angle is, the bigger the ellipse degree is. If the spatial distributions of input pump beam and probe beam are super-Gaussian distribution, the rise edge of the temporal distribution becomes slow with increasing intersection angle between the pump beam and the probe beam, while the spatial distribution is unchanged, and the ellipse degree is about 1/3. The results provide reference for parameter design of experiments such as pump probe and time gated ballistic imaging.

High peak power and high beam quality laser is vitally valuable for applications in laser machining and other fields. A fiber laser with repetition frequency of 50 kHz, pulse width of 3.9 ps, and average power of 10.9 mW is used as the seed source. The average output power of 27.65 W is obtained in double-passing amplifier of two stages, with the pulse peak power of 65 MW. The first amplifier stage is end-pumped Nd∶YVO4 solid amplifier, and the second is side-pumped Nd∶YAG solid amplifier. The beam quality is preserved by a double-passing configuration for spherical-aberration compensation. By optimizing the beam filling factor in each solid amplifier, the M2 factor of the output beam reaches 1.30 finally.

Laser spot echo imaging detection experiment is carried out on a 1 km transmission path in turbulent atmosphere under typical weather conditions using a red laser, a 3M microcrystalline prism array reflector, and a telephoto high speed CCD. Scintilloscope and atmospheric coherence meter are used for real-time monitoring of turbulence parameters. Intensity of the laser spot image is statistically analyzed. Spatial correlation coefficients of the scintillation index and the light intensity fluctuation in different positions and different aperture ranges are obtained, and the ideal point scintillation index of the center point of the spot is obtained with the fitting method. The turbulent refractive index struture constant calculated by scintillation index is compared with the real-time monitoring data, and the results show that the turbulent refractive index structure constant obtained by this method is in good agreement with the measured value of the laser scintillator. The laser imaging detection method of the reentry path can easily ensure the paraxial approximation conditions, which is theoretically more realistic. This system can be used not only to observe the complete far-field laser spot affected by atmospheric turbulence, but also to develop a new detection technology of single-ended atmospheric optical turbulence parameter imaging through quantitative modeling.

A high peak power, sub-nanosecond passively Q-switched Nd∶GdVO4 laser with wide temperature stability is presented. The oscillator adopts a flat-concave cavity structure with pigtail coupling of semiconductor laser diode, and takes Cr4+∶YAG as saturable absorber. When the pump absorption energy is 5.9 mJ, the output peak power of the oscillation is 1.5 MW, with pulse width of 600 ps and pulse energy of 0.9 mJ. The efficiency of light to light conversion is 15.4%. The divergence angle is 1.2 mrad. An end pumped double pass amplifier is used and the output peak power of 3.5 MW with pulse energy of 2.1 mJ is achieved. The output laser energies at different temperatures are measured. The results show that the jitter of laser output energy (root-mean-square) is 5% when the temperature is in the range of 20-36 ℃. The laser has compact structure and low power consumption, which can be used as light source for future space laser applications.

Picosecond pulse fiber laser oscillator with narrow linewidth and multistage fiber amplifier which are used in the fiber-solid picosecond laser source are optimally designed. Spontaneous emission and nonlinear effect in the fiber are fully suppressed by fiber link, so that when the system operates at 1 kHz repetition rate, the spectral signal to noise ratio is still better than 20 dB and the spectral bandwidth is narrower than 0.5 nm. Furthermore, picosecond pulse generated from the fiber link is further amplified by a three-stage double-pass Nd∶YVO4 solid amplifier. The average output powers of the laser system are as high as 2.34, 4.30, 10.30 W, corresponding to 2.34, 0.43, 0.10 mJ single pulse energies at 1, 10, 100 kHz repetition rates. With only passively cooling on the Nd∶YVO4 crystals, beam quality M2 is less than 1.3 and beam roundness is more than 90% when the output power of system doesn′t exceed 7 W.

Wavefront distortion affects the compressibility and the far-field focal spot quality of the output laser pulse of parallel grating pair compressor. We establish a theoretical model of parallel grating pair compressor based on ray-tracing method and principle of Fraunhofer far-field diffraction, and analyze the effects of wavefront error of input pulse, the deformation and wave aberration of grating diffraction surface on the spatial-temporal property of the far-field focal plane of the compressor output pulse. The corresponding error tolerances are presented based on Monte-Carlo simulation. The results provide a theoretical reference of wavefront distortion correction and grating quality control for parallel grating pair compressor in high-power laser facilities.

Linewidth narrowing module is an important component of excimer laser for lithography. The installation angles of prisms and gratings affect the system output characteristics directly. In order to improve installation and debugging technique of linewidth narrowing module, we study the influence of the angle deviation of the prism in the prism expander on the energy and linewidth of the system. Through the theoretical derivation and experimental verification, we analyze the influence of individual prism angle deflection on the energy and linewidth of the excimer laser system, and determine the alignment error of each prism. The experimental results are in good agreement with the theoretical analysis results. The alignment method for optimizing the linewidth narrowing module design according to the alignment error has guiding significance for the spectrum control engineering.

We propose a hybrid surface plasmonic waveguide structure containing a metal ridge with rounded corners and a special triangular air gap layer. The combination of this particular triangular structure and other materials effectively improves the performance of nano-lasers. We apply the finite element method and use COMSOL Multiphysics software to construct the two-dimensional and three-dimensional models, and use the modal analysis module to analyze the waveguide characteristics of the waveguide structure and the parameters of the laser. The results indicate that the optical field confinement of the designed waveguide can reach a better deep-subwavelength level while maintaining a long propagation length at the 1550 nm operating wavelength. The waveguide structure enables super strong coupling between the surface plasmon polariton mode and the cylindrical mode. The maximum coupling strength is 0.96 and the propagation length is 28047 nm. When this structure is applied to nano-lasers, we adjust the waveguide design parameters to obtain the higher quality factor, lower energy loss, threshold limit, and ultra-small effective mode size. Compared to the previously reported structure with a single triangular air gap, this structure has stronger capacity of field confinement and microcavity bound with the same geometric parameters. So this structure is expected to be applied in the fields of on-chip interconnects, photonic integrated circuits, optical storage, and optical signal process.

While the disk amplifier is operated, the aerosols originating from the decomposition of organic material exposed to flash lamp light is inevitable, which can cause the disk contamination and damage consequently. The nitrogen gas purging is routinely employed to re-achieve the slab cavity cleanliness, which is fundamentally required for disk amplifier reliable performance. The influence on aerosol dissipation by swirl is measured, demonstrating that the desirable cleanliness can not be achieved simply by prolonging the purging time or adjusting the flowing rate as plenty of aerosol is slaved in swirl. So we propose the aerosol dissipation by intermittent purging. The decaying of aerosol concentration is achieved rapidly by repeated dilution as the swirl is destructed time after time. The comparative experiment is carried out at a Φ130 mm disk amplifier specially. After intermittent purging, the residual aerosol concentration in slab cavity is 1/100 of that after a continuous but longer purging. The slab cavity environment cleanliness remains lower than level 40 in the following 15 h, which is much more desirable to prevent neodymium glass from contamination and damage.

A 31 kW narrow-linewidth linearly polarized nanosecond all-fiber laser is proposed. The single-frequency continuous laser generated by the seed-source laser is modulated by an electro-optic intensity modulator. To suppress stimulated Brillouin scattering (SBS), the pulse width is set to 2.8 ns, and the repetition rate is 1.59 MHz. After two levels of pre-amplification, and primary power amplification for amplification, the maximum average output power of laser can reach 139 W while the peak power is 31 kW. As stimulated Raman scattering (SRS) is not found during the experiment , the increase in power is limited by SBS. The laser beam quality is less than 1.3 at the maximum output power. The polarization extinction ratio is 14.5 dB, which is limited by the polarization-maintaining (6+1)×1 fiber combiner.

A singly resonant optical parametric oscillator (SRO) is built up based on periodically poled lithium niobate (PPLN) crystal pumped by a self-made high power and continuous-wave (CW) single-frequency 1.06 μm laser. A broadly tunable and high power CW single-frequency laser source in the infrared is obtained and the signal and idler can be tuned from 1.45 μm to 1.79 μm and from 2.62 μm to 3.99 μm by controlling the polarization period and temperature of PPLN crystal, respectively. The measured maximum output powers of the signal (1.52 μm) and idler (3.53 μm) are 5.1 W and 2.1 W, respectively, at a pump power of 15.5 W. The optical conversion efficient of the SRO is 46.5%. When the SRO is free running, the power fluctuation of the signal and idler are less than ±2.77% and ±2.79% for a given 4 h, respectively, and the frequency drift of the signal is less than ±45 MHz for the given 4 h.

A passive electrical probe detection device is employed to detect the electrical signal of plasma in the process of YAG laser welding for A304 stainless steels, and a high-speed CCD camera device is synchronously triggered to record the plasma plume shape. The high-speed camera images of plasma and the electrical signal in time domain are compared and analyzed, and it is found that the fluctuation characteristic of electrical signal is basically consistent with that of the plasma plume shape. The electrical signal with a certain time length is analyzed via its power spectral density (PSD), and it is found that the frequency of the characteristic peak in the PSD plot has a good agreement with the fluctuation frequency of plasma plume shape. The results indicate that there exist strong correlations among the plasma plume shape fluctuation, the fluctuation characteristic of electrical signal and the behavior of keyhole. This kind of fluctuation characteristic is affected by welding parameters, and the fluctuation frequency decreases with the increase of laser heat input.

The microstructure change and oxidation weight increase of Ti-48Al-2Nb-2Cr intermetallic compounds prepared by laser additive manufacturing at the temperature of 850 ℃ are studied, the difference of oxidation behavior between the as-deposited and the as-casted specimens is analyzed, and their oxidation mechanisms are disclosed. The results show that, when the oxidation time is same, the oxidation weight increase rate of the as-deposited specimen is obviously smaller than that of the as-casted specimen. After oxidation of 60 h, the oxidation layer of the as-casted specimen is completely delaminated from the alloy matrix, while the oxidation layer of the as-deposited specimen is well combined locally with the matrix. The compositions of oxidation films of the as-deposited and those of as-casted specimens are different, the former is TiO2/Al2O3/matrix and the latter is TiO2/Al2O3/TiO2+Al2O3/matrix.

The magnetic-thermal-flow field coupling in the process of laser additive manufacturing of Ni45 alloys under alternative magnetic fields is numerically investigated by using the finite element and finite volume methods. The influence of the external magnetic field on the evolution trend and properties of solidification structures is investigated based on experiments. The results show that the introduction of external magnetic field enhances the compulsory convection resulted from the coupling between the surface tension gradient and the buoyant force. The convection heat transfer in the molten pool gradually enhances with the increase of magnetic field intensity, which makes the temperature gradient of the molten pool gradually decrease and the solidification rate gradually increase. As a result, the solidification structure of the alloy forming part is gradually refined, and the friction and wear performances are enhanced.

With the metal powders as the filler materials, the laser welding between the dissimilar materials of Ti3Al-based alloy and GH4169 superalloy is carried out. The microstructures at different areas of the joints are analyzed. The micro-hardness in different cross sectional regions of joints and the tensile strength at the room temperature of the joints are tested. The study results indicate that, when the filler material is only the Ti-Ni-Nb powders, the average tensile strength at the room temperature of the joints is 129 MPa. There are no reaction layers generated in both interfaces between the filler material and the two kinds of base materials, and the welds mainly consist of Ti-Ni-Nb phase, Nb-Ti solid solution and precipitated Nb. The micro-hardnesses at the interfaces between welds and base materials are higher than those of the weld center and the base materials. When the filler material is composed of Ti-Nb/Ti-Ni-Nb/Ni-Cu powders, the tensile strength of the joints increases to 180 MPa. The contents of the main elements in the joints vary gradually along the weld line with the composition variation of the filler materials. The Ti3Al/Ti-Nb interface possesses the relatively high micro-hardness, and the hardnesses in the Ti-Nb and Ti-Ni-Nb regions are higher than that in the Ni-Cu region.

The laser cladding of W-Cu composite powders is conducted by the coaxial powder feeding method and the influences of different process parameters on the geometrical characteristics and the particle distributions of single-track cladding layers are investigated. A concept of effective mass energy density (k) is also proposed. The results show that, in the experimental fabrication system with single-track cladding, the dissipation energy density of cladding layers is approximatively 3.5×10-3 kJ·mm-2. Under the certain fabrication conditions, there exists a critical value k′ of effective mass energy density in cladding layers. A dilution zone can be formed in the cladding layers when k＞k′. With the decrease of k, as for the W particles in cladding layers, the successive change from agglomerate to uniform distribution, distribution along the edge of cladding layer, and W-rim/Cu core structure occurs. For a single track multi-layer cladding, the value of k is significantly affected by the shape of the single-track cladding layer. The smaller the width-height ratio of cladding layer is, the smaller the actual k value and the relative density are.

A 800 nm femtosecond laser tweezer can be used to capture the silver nanoparticles dispersed in water and the silver wires are directly written on the glass substrate. The influences of laser power on the silver wire width and surface morphology are investigated by adjusting laser parameters. The direct writing of silver wires with a width of 378 nm is realized. After tests, the electrical resistivity of the fabricated silver wire is 19.88 times that of bulk silver. In addition, a two-dimensional (2D) silver grid structure is fabricated by this technique, which manifests that this technique possesses a good process ability in the field of 2D structure direct writing.

By means of selective analysis for round hole specimen, the influences of laser power, scanning line angle and number of contour scans on the forming quality of overhanging round holes are investigated. The results show that, the laser power has a significant effect on the forming quality of round holes. With the increase of laser power, the roundness of round holes increases and the dimensional accuracy decreases. At the same time, there are many thin and long melt pools on the overhanging surface, and part of them are fractured into spherical droplets; the overhanging surface quality is better when the scanning line direction is parallel to the edge lines of the overhanging surface, but there occurs a serious collapse on the top of round holes and near to the horizontal overhanging surface. Within the setting number of scans, the increase of the number of contour scans can reduce the surface roughness of the overhanging surfaces and optimize the surface quality.

A method of estimating atmospheric optical turbulence is introduced which is called support vector machine (SVM). Based on this method, the gradient of temperature, wind speed, and relative humidity are used to calculate the refractive structure parameter C2n in Chengdu, Sichuan from 2014-5-13 to 2014-5-18, which is a continuous 6-day estimated result. The estimated results agree well with the measurement results, which can basically show the characteristics of optical turbulence in Chengdu area. Compared with results of Wyngaard algorithm, the results of SVM are more consistent with the measurements, and the estimation accuracy at night is higher than that of the Wyngaard algorithm. The relative analysis demonstrates that the correlation coefficient between the estimations and observations is over 80%. Besides, mean absolute error and mean relative error prove that after training, SVM can precisely estimate C2n in Chengdu. However, deviations are found between estimations and measurements during the transition time, which should be overcome to improve the performance of the model.

How to improve the sub-aperture stitching interferometry accuracy is critical for the sub-aperture stitching system. For one-dimensional flat sub-aperture stitching system, the influence of the stitching stage positioning error, the reference surface error and random noise on the stitching accuracy is simulated and analyzed of data based on both double sub-aperture stitching algorithm and error averaging stitching algorithm. The simulation results show that, the flat stitching system is insensitive to the high order errors of reference surface and the random noise. The stitching error of the high order errors of reference surface is a little larger than that of the random noise. The low order errors (the second order errors) of the reference surface will be accumulated and enlarged during the stitching process, which is the main error source for the flat stitching interferometry. The stitching accumulation error of the low order errors of the reference surface cannot be effectively controlled by the error averaging stitching algorithm. The double sub-aperture stitching algorithm and the error averaging stitching algorithm almost get the same stitching result. A flat mirror with aperture of 450 mm×60 mm is tested by 15 sub-apertures. The deviation between the stitching result and the test result of a large aperture interferometer is reduced from λ/3 ［peak valley value (PV), λ=632.8 nm］to λ/45 (PV) after removing the low order errors of the reference surface.

Free-space optical communication (FSO) has attracted more and more attention because of its advantages of high-speed, convenience and strong ability of anti-electromagnetic interference, and has become a research hotspot in military and civilian fields. A method of 3D ship deformation measurement is proposed. A time unit is designed by FSO technology. The optical structure of system can realize the measurement of 3D ship deformation angle, the stimulation of optical imaging of receiving unit and the timing of measurement results at the same time. The structure of the system and the design of key circuit are represented. The system error is analyzed with data simulation. The results indicate that this measurement method is theoretically feasible, and not only meets the measurement precision, but also has lower hardware complexity and higher availability. It is potential to be used in practice.

With the improvement of the accuracy and efficiency of laser scanning technology, three-dimensional (3D) terrestrial laser scanning (TLS) technology, which can obtain high precise points-cloud, has been applied in the field of deformation monitoring of subway tunnels, structures building and other fields. However, the data contains many outliers, which are produced by pipe and bolt holes and should be removed for deformation analysis. Based on the 3D TLS technology, taking the subway tunnel in operation as the research object, we propose a new cross section analytical method. We use an ellipse fitting method based on 1-norm minimum residual algorithm to deal with the points which are not on the tunnel cross section. An adaptive threshold selection method is introduced to filter the points which are not on the tunnel cross section. Circular arcs model, instead of overall oval model, is adopted to analyze the deformation of subway tunnel. Deformation analysis of the extraction cross section is tested. The results indicate that this method can eliminate gross errors in the data and the cross section method using circular arcs model can more accurately reflect the tunnel deformation.

In order to reduce the influence of base station layout on the measurement result in the machine tool precision detection by multi-station and time-sharing measurement with laser tracker, the research on optimization of base station layout is conducted. The influence of location layout of base station on its calibration accuracy by multi-station and time-sharing measurement is analyzed. The positional dilution of precision (PDOP) in global positioning system (GPS) measurement is applied as an indicator to evaluate whether the layout distribution of base station is reasonable or not, and the optimization function of base station layout is established. On this basis, the optimal layout position of base station is determined according to the established base station distribution optimization function for three different motion regions (1D line, 2D plane, 3D space) of machine tool during measurement. The distribution law of PDOP at different space positions is also analyzed, which can provide a reference for the reasonable distribution of base station layout in field measurement.

A velocity azimuth display (VAD) wind retrieval method based on conjugate gradient algorithm is proposed, in which the conjugate gradient algorithm is used to replace the solution of Fourier series expansion in original VAD method by using optimization theory. In order to solve the problem that the algorithm does not converge to the optimal solution in wind retrieval, the Hessian matrix is used to modify the algorithm. At the same time, a synchronous comparison experiment had been carried out with Doppler lidar and standard wind cup anemometer in accord with IEC 61400-12-1 international standards for 43 days. The results show that, when the azimuth scanning range and radial number of lidar are 60° and 7 respectively, the correlation coefficients of wind speed and wind direction are 0.991 and 0.998, the standard deviations of wind speed and wind direction are 0.52 m/s and 5.1°, the deviations of wind speed and wind direction are -0.02 m/s and 3.6°. The results of comparison experiment prove that the VAD wind retrieval method based on conjugate gradient algorithm can guarantee the measurement accuracy to meet international standard in case of low azimuth scanning range with strong applicability. Meanwhile, the measurement performance of lidar system is confirmed, which provides a better choice for the monitoring of dynamic complex wind field.

The dual-comb spectroscopy (DCS) based on optical frequency combs (OFCs) offers a revolutionary new spectroscopic method that can combine the advantages of high spectral resolution, high detection sensitivity, broadband spectral coverage, and fast measurement in one. In the past few years, the DCS has experienced rapid development, resulting in numerous demonstrations of new measuring principles and implementation schemes, as well as the availability of new measuring technologies and applications. Therefore, it is necessary to systematically review the current development status for the DCS and predict its future trends objectively. To provide a reference for relevant scientific and technical personnel to grasp the whole development of DCS, based on the mechanism of asynchronous optical sampling and the noise properties, we begin with the OFC and provide a comprehensive review on research advances of DCS regarding measuring principles, implementation schemes, performance indexes, application technologies, and instrumentations, and predict possible development trends in the future.

One kind of antireflection (AR) coating based on terahertz metamaterial with a stand-up structure is designed, which utilizing stand-up double split ring resonators (SRRs) to suppress the reflection in the terahertz range. The minimum reflectivity of AR coating is 0.001 and the band width is 0.45 THz when the reflectivity is below 0.1. The operating mechanism of this metamaterial antireflection coating is analyzed,the effects of the distance between the two split rings and the thickness of the polymer substrate on the performances of the metamaterial AR coating are investigated, and the performance comparison with that of the single SRR AR coating is conducted. The numerical simulation and analysis results show that the designed metamaterial AR coating has an excellent broadband reflection inhibition characteristic and a large production-parameter-tolerance characteristic.