Because laser diode ceilometer′s backscattering signal is weak and easily disturbed by various noises at the same time, the most important task and difficult point for the signal detection of laser diode ceilometer is how to take effective measures to remove the noise in the backscattering signal. In view of the redundancy reduction capability of the independent component analysis (ICA), fast ICA is proposed to eliminate noise of laser diode ceilometer′s return signals. Since fast ICA requires multi-channel signals, the continuous multiple groups of laser diode ceilometer return signals are used to construct the multi-channel signals, and then the blind source separation (BSS) of fast ICA is applied to the signals. Thus, the virtual sources are extracted one by one, and the noise embedded in the observed signal is removed. The experimental results demonstrate that the method has good effect on removing the noise from laser diode ceilometer′s return signal. Such a fast ICA algorithm has the practical value in processing laser diode ceilometer′s return signals.

Three-dimensional (3D) distribution of two-dimensional (2D) Mie scattering phase function is presented in the spherical coordinate system with the linearly and circularly polarized incident light. By using the program of Monte Carlo simulation of polarized light propagation, 2D distribution models of elements of backscattering Mueller matrix and degree of polarization (DOP) from bubbles film of ship wakes are simulated. The relation between scattering coefficient and the thickness of bubbles film is studied. The results show that spatial distributions of DOP have the properties of azimuth selection, and the polarization-maintaining characteristic of circularly polarized light is better than that of linearly polarized light. With the thickness and scattering coefficient of bubbles film increasing, the DOP of linearly polarized light gradually decreases, while the DOP of circularly polarized light first rapidly increases to a maximum and then slowly decreases.

A polarization sounding scheme of airborne lidar is proposed, in which the polarization sounding “bottle-neck” channel i.e., the perpendicular sounding channel in the traditional scheme is obliterated. Return signal differences between 532 nm depolarization sounding channel and 532 nm polarization parallel sounding channel can be minished in the polarization sounding courses. The energy ratio of two channels, return signals can be adjusted. This scheme strengthens the polarization sounding capacity when it has the same energy as first scheme. It can reduce the photomultiplier (PMT) saturation probability when cirrus is sounded by 532 nm polarization channel. This scheme also can reduce laser energy and actualize genuine 532 nm and 1064 nm dual-wavelength sounding.

Aiming at the requirements of high nonlinearity with low confinement loss of photonic crystal fiber (PCF), we design an octagonal circular-air-holes structure of PCF. Based on full vector finite element method with the boundary condition of perfectly matched layers, its effective index, nonlinear coefficient and confinement loss are numerically investigated. The numerical results indicate that the proposed fiber shows higher nonlinearity, lower confinement loss and stronger confinement ability of mode-field profile. A better result can be gotten when adjusting the parameters of PCF with d1=0.77 μm, d2=0.86 μm. The high nonlinear coefficient of 37.6 km-1·W-1 and low confinement loss of 0.7×10-17 dB/km are found at 1.55 μm wavelength.

Based on Kummer model in nonlocal nonlinear medium, we study transmission characteristics of Kummer soliton. The results show that there is a group of two-dimensional Kummer-Gaussian soliton clusters, such as ring solitons, necklace solitons and lune solitons. Numerical simulation shows that Gaussian solitons and ring solitons are stable, while other solitons are not stable. Nonlinear modulation coefficient and modulation depth parameters have an important influence on the stability of the soliton, with their increase, the stability of the soliton improves.

It has important and practical significance to establish a complete set of health monitoring system for massive project structure. Damage detection is one of the core technologies for structural health identification. Although a variety of damage identification methods have been developed, accurately measuring the response of the structural information is the premise of the effectiveness of damage identification. Damage inside the structure cannot be predicted, so it is not advisable for health monitoring by means of strain gauges. We use quasi-distributed long-gage optical fiber Bragg grating based on glass-fiber reinforced composite material package (GFRP-FBG) and combine it with the damage detection application in simply supported steel beam to verify the performance of the quasi-distributed long-gage GFRP-FBG strain sensor. The test results show that using quasi-distributed long-gage GFRP-FBG strain sensor can effectively perform damage fore-warning and damage location, and estimate the damage degree of bending stiffness.

on-axis Fourier digital holography, the conventional way for image reconstruction is inverse fast Fourier transform (IFFT), but the Shannon′s sampling theory must be satisfied in the sampling process, which causes the data redundancy and greatly increases the cost of storage and transmission. A reconstruction method of phase-shifting on-axis Fourier digital holography based on compressed sensing (CS) theory is put forward. Firstly, on-axis hologram is collected in the Mach-Zehnder interferometer light path. Then the collected data are partially sampled and measured. Lastly the image is numerically reconstructed by using the minimum total variation method. The numerical simulation result shows that the reconstruction method based on CS, which takes the sampling and compression of the hologram data to one step, is superior to that based on the conventional reconstruction method. The amount of sampling data based on CS is less than that based on IFFT, but the original image can also be accurately reconstructed from just about 8% hologram data.

In order to identify the quality of medical materials in current market of traditional Chinese medicine (TCM), a grating spectrum imaging device based on sweeping-style spectrum imaging technology is designed. It can use electrically-controlled displacement platform to scan the sample and form an image in the one-dimensional spatial direction by taking the advantage of prismatic grating. Then, the TCM′s spectrum cube is obtained through image joining together. This device has a low cost and can realize nondestructive detection of TCM rapidly without particular laboratory environment. The detected parameters are as follows: the response range of system′s spectrum, spectral resolving rate, spatial resolving rate and the stability of the whole system. We take Panax quinquefolium as an example to detect and then combine its spectral images to form the spectrum cube. Its spectral characteristics and spatial distribution of its total saponins are obtained by describing the characteristic spectrum curve and spatial distribution imaging of fluorescence intensity.

The main method of the attitude measurement is to get series of graphs for analyzing the changing attitude of the projectile by utilizing multiple shadowgraph-taking camera stations. However, the premise of accurate results is that feature points on graphs must match their spatial coordinates in a certain spatial coordinate. Aiming at this problem, we propose a method of calibrating the spatial coordinate coherence for the long distance and multiple shadowgraph-taking camera stations with position sensitive detector (PSD), and analyze the measurement accuracy and repeatability of this method. A system is developed to do some regular experiments. According to the results, the accuracy of this calibration method is superior to 0.1 mm.

The fluid flow and heat transfer characteristics of rectangular, triangular and trapezoidal micro-channels are analyzed. The influence of height-width radio and channel types on these characteristics is simulated. The results show that the coefficient of friction resistance decreases with the increase of Reynolds number but increases with the rise of aspect ratio in micro-channels. At the same Reynolds number and aspect ratio, the maximal coefficient of friction resistance appears in the rectangular structure, and the minimal one in the triangular micro-channel. When the channel type and the aspect ratio are fixed, the Nusselt number increases with the Reynolds number, but the increasing trend is slow. General empirical formulas are proposed to evaluate the heat transfer performance of different micro-channels with consideration of inlet effect and height-width ratio.

A auging head of atomic force microscopy (AFM) based on interference of polarized light is designed for high resolution and capacity of resisting disturbance. This AFM head detects the tip displacement based on interference, in order to increase the sensitivity. In the process of design, the feasibility of focal spot on the cantilever is analyzed, and verified with experiment. The experimental result shows that two Wollastton prisms can effectively change the optical-path difference between reference beam and measurement beam, and reduce the size of AFM head. The design of common-path Nomarski interferometer can reduce noise, keep the structure of head compact and make this system useful. The axial resolution of the system can reach up to 1 nm. It can support the research of AFM technology.

In order to increase the surface hardness and wear resistance of the GCr15 steel, as well as reduce the energy consumption and improve the traditional quenching environment, laser quenching is carried out on GCr15 steel with a 400 W fundamental-mode fiber laser. The effects of scanning speed and defocusing amount on the quenching layer are analyzed. The microstructure of the hardened region consists of fine martensite and a few spheroidal carbide. The microhardness increases with the increase of scanning speed and then decreases, and the same for the defocusing amount. The microhardness of GCr15 steel is 960 Hv after being quenched with fiber laser power of 400 W, scanning speed of 0.6 mm/s and defocusing amount of 0, which is 4.4 times of that of the matrix. The wear resistance of GCr15 steel quenched by fiber laser is significantly improved. The wear mechanism is mainly oxidation wear, mechanical wear and abrasive wear.

A numerical simulation of laser cladding process on the surface of nickel-based superalloy GH4169 with coaxial powder feeding system is carried out by Marc software. The influence of different repair cross sections on the distribution of temperature and residual stress field is studied through a directly coupled thermo-mechanical analysis. The results show that for single-path laser surface reparation, different repair cross sections lead to different distribution characteristics of temperature and residual stress field in the bonding zone. The parallel component of residual stress is evidently larger than vertical component in the direction of the scanning path when it is repairing on a plane. The vertical component of residual stress is relatively increased due to the constraints from two sides of the crater when it is repairing a crater of a long strip with rectangular or arc-shaped cross section. As the aspect ratio of the section increases, the ratio of vertical component of residual stress to parallel component also increases. However, the ratio of vertical component of residual stress to parallel component for arc-shaped cross section is smaller for the same aspect ratio. In order to avoid the deformation of the thin-walled parts, an arc-shaped cross section with small aspect ratio is recommended.

Laser spallation technique, as a new micro-forming processing technique, is discussed, because several disadvantages exist in current micro-forming processing including size effect, unevenness in forming, low efficiency, high cost and high pollution. A theoretical analysis model is established to investigate the influential factors of thin films and substrate spallation under laser driven flyer. Laser energy, film thickness and type of film are investigated in experiment as they may affect the outcome of laser spallation micro-forming. The experiments show that the technique can achieve microstructure forming of thin films, and laser energy and film type are deciding factors in interfacial spallation. Film thickness within a certain range is less important, but it has significant influence on thin films micro-forming when it is out of the certain range. Therefore, laser spallation has the potential to become a controllable thin films micro-forming technique for commercial applications.

It is important that the light beam is focused into fiber core precisely with a small size when low-order fiber Bragg grating (FBG) is inscribed point-by-point with infrared femtosecond laser. The beam-spot size in fiber core is analyzed theoretically and simulated with Zemax software in the cases of focusing with an objective lens and focusing with an objective lens combined with a cylindrical lens separately when the optical fiber is thought as a cylindrical lens. The beam size is 0.67 μm×84 μm theoretically and 2.6 μm×76 μm simulatively separately when focusing using an objective lens, and the beam size is 3.76 μm×0.67 μm theoretically and 4.1 μm×2.2 μm simulatively separately when focusing using an objective lens combined with a cylindrical lens. It is found that the beam-spot size in the core can become very small when focusing using an objective lens combined with a cylindrical lens. This conclusion will provide possibility and basis for the fabrication of low-order FBG.

In order to study the effect of laser peening on the properties of titanium alloy, a TC4 titanium alloy sample is processed using YAG laser with the wavelength of 1064 nm, pulse energy of 0～6 J and pulse width of 6～14 ns, and its micro-hardness and residual stress are examined and analyzed. The experimental results show that the satisfying laser peening appearance can be achieved when the pulse energy is 6 J, pulse width is 12 ns and tamping layer thickness of water is 1.8 mm, the surface micro-hardness increases up to 33.5% and the compressive residual stress on the surface of laser shocked area reaches -323 MPa. Laser peening improves the hardness and residual stress of titanium alloy significantly. The experimental results show that the effect of laser peening evidently strengthens the titanium alloy.

The instability of semiconductor laser with external light injection is studied by solving dynamical equations of the system and analyzing its linear stability. It is shown that the injection coefficient and the linewidth enhancement factor play important roles in the stability of system, and the larger the injection coefficient and linewidth enhancement factor are, the more unstable the system becomes. The corresponding time-series diagrams and phase diagrams obtained by numerical simulation verify this conclusion.

In view of the need for secondary optical design of LED as the stage light, a design for reflecting stage light with high-power LED is proposed to achieve the asymmetric uniform illumination on stage backdrop, according to the principle of extended light source. By creating a reflecting surface model in a two-dimensional coordinate system and controlling the two marginal rays of a certain point on the target surface, the light cone formed by the two marginal rays can sweep point by point. Combined with the laws of reflection, the edge ray principle and the étendue conservation theory, the coordinates of each point on the generatrix are obtained and then the reflection surface is generated after stretching the generatrix. The ray-tracing simulations with TracePro software show that by superposition of several stage lights, in the illuminated region of 20 m width and 11 m height within a distance range of 1.5~2.0 m, the luminous uniformity is able to reach 80%. Hence, this structure enables LED light source to be applied in wide-range lighting system to get uniform illumination.

Tunable polymer microlens has been widely applied in many fields such as imaging, microfluidic sensing and adaptive optics. The physical model for controllable polymer microlens caused by thermal effect is established. Then, the finite element method (FEM) is used to analyze the spatial distribution of the microlens temperature, thermal deformation and focal length variation. The simulation results show that the thermo-optic effect has a strong influence on the optical performance of polymer microlens with large thermo-optic coefficient when the variation scope of temperature is relatively large. As a result, both thermal expansion effect and thermo-optic effect should be taken into account for the design and fabrication of such devices.

As a result of the big difference in the required space between automation machine vision system and assembly line, the traditional fixed-focus lens cannot meet the practical requirements. There is a need for the big span working distance of optical imaging system. Based on the influence of changes in the object surface position on the primary aberration, with multiple structure function of Zemax software, the wide working distance lens is designed. The results show that the focusing range is from 146 mm to infinity, and the maximum aperture is F2.8. At the center field-of-view (FOV), the modulation transfet function (MTF) is greater than 0.3 at the spatial frequency of 100 lp/mm and the MTF at the 0.7 FOV is greater than 0.3 at the spatial frequency of 72 lp/mm. Such a system can replace the manual work to observe the whole assembly line and thus can improve the degree of automation.

Aiming at the case of target missing in a short time occurring frequently in target tracking with a single theodolite, Chebyshev polynomial is used to fit and extrapolate the trajectory of the target with the data observed by theodolite. Chebyshev polynomial has a better accuracy than the traditional method of interpolation by comparison. The results of residuals and standard deviation calculated through the least square method show that six-order polynomial has the best fitting accuracy with the error of about 8.226 μm. When the missing distance of theodolite is invalid or the target speed features suddenly changes, the theodolite is able to follow the trajectory of the predicted movement. Experimental results show that this method can be used to fulfill stable target tracking when the theodolite loses the targets within a short scope of time (3~4 s). Recently, this problem is still under theoretical study and cannot be put into engineering practice in the near future.

We investigate the GaN-LED epitaxial wafers whose central wavelength is 650 nm and propose a kind of bottom-emitting surface-plasmon-enhanced LED to improve its emission efficiency. This LED includes a SiO2 layer of low refractive index and a silver film coated on the sinusoidal wavy-patterned p-GaN layer in sequence. The Ag film is used to enhance the internal quantum efficiency and the SiO2 layer is employed to further improve the reflectivity of the upper surface of GaN-layer. And the transmissivity through the sapphire substrate whose thickness is optimized is very high. The emission efficiency of this structure is raised greatly.

Radar in terahertz regime has great advantages compared with microwave radar and infrared detector, such as high range resolution, strong penetrating ability, low intercept probability and strong anti-interference ability, etc. On the basis of analysis of characteristics and advantages of terahertz radar, research progress of terahertz radar systems reported recently is introduced first. Then, study of target scattering characteristics and radar imaging technologies in terahertz regime is reviewed and commented. Some of the key technologies and main research directions related to the terahertz radar are pointed out correspondingly. Key parameters of terahertz radar system are analyzed and simulated concerned with military applications of space target detecting and radar seeker, which helps to provide reference for the application development of terahertz radar.

Inner defects of object are cracks, impurity, fatigue damage and corrosion under surface. The defects are secluded so that they deteriorate the quality of product and safety of operation seriously. Taking optical components and aircraft blades as examples, we analyze the forming mechanism and the characteristic of inner defects. Non-destructive detection of inner defects is categorized into energizing and unenergizing non-destructive detection. This paper focuses introducing the principles and research achievements of thermal excitation non-destructive detection and magnetic pumping non-destructive detection.

Titanium-doped sapphire, as one of the three basic laser crystals, has prompted the laser development into a new era of ultrafast and ultraintense lasers. We review the most recent progress of the ultrafast ultraintense lasers based on Tisapphire. The application areas of ultrafast ultraintense lasers are introduced briefly.

The principle and advantages of free-space optical communication technology based on modulating retro-reflector are introduced. The principles of corner cube modulating retro-reflector and cat-eye modulating retro-reflector are introduced. Different types of both modulating retro-reflectors and the characteristics of them are introduced, and then the technology of modulating retro-reflector in free-space optical communication is summarized. The applicaitons of modulating retro-reflector free-space optical communication are presented. The key technology and difficulty of modulating retro-reflector free-space optical communication are discussed, and the future applications of modulating retro-reflector free-space optical communication are prospected.

Photoacoustic tomography imaging (PAT) is a novel, non-ionizing and non-invasive imaging technology which is based on photoacoustic effect. PAT is a hybrid imaging technology combining pure optical imaging technology with ultrasonic detection technology, so it possesses high optical absorption contrast and ultrasound resolution. This emerging imaging technology has very broad application prospects in biomedical detection. The theory of photoacoustic tomography imaging is introduced. Comparison is made among different system structures and their advantages and disadvantages. Furthermore, the main detection objects of the various system, are introduced. Finally, we predict the trend of photoacoustic tomography imaging systems, and discuss the method to improve system performance parameters of PAT.

To determine the tea polyphenols content in Puerh tea by near infrared spectroscopy, genetic algorithm combined with partial least square (GA-PLS) is used to select those wave-numbers carrying information that are highly related to the tea polyphenols of Puerh tea. As a result, 40 wave numbers are selected from the spectral range of 10001～4000 cm-1. Then principal component analysis is applied for these selected wave numbers, and the first two principal components are achieved to input into the extreme learning machine (ELM). Using sigmoidal function as active function, the ELM is trained with the number of hidden-layer neurons varying from 1 to 50. Result shows that it will reach the minimum root mean square error of prediction (RMSEP) set and get the optimal ELM model when there are 13 hidden-layer neurons. The optimal ELM model gives the correlation coefficient of prediction set R2 of 0.9705, with root mean square error of cross-validation (RMSECV) of 1.0109 and RMSEP of 1.6686. This model uses only 40 wave numbers and 2 input-layer neurons, but obtains better performance, compared with the global PLS model with 1557 wave numbers and GA-PLS model with 40 wave numbers. Results show that the tea polyphenols content in Puerh tea can be determined with high precision by using near-infrared spectroscopy combined with genetic algorithm and ELM.