A measurementof beat-length in low-birefringence fibers based on wavelength modulation is shown. It measures the beat- length by wavelength modulation. Phase detection is chosen to reduce the error from environment influence. Phase compensation plate isused to ensure the testing system always sensitive to the change of phase.The optical path consistes of an amplified spontaneous emission (ASE) light source, a fiber Fabry-Perot tunable filter, two linear polarizes, the measured fiber and a phase compensation plate. The testing system is set up and tested in reality.The system performes well in the repeated test. It is simple and has no strict demand on these equipments. There is no limitation on the configuration and the length of the testing fiber in the measurement.It is reliable for fibers whose beat- length is up to 20 m. The beat- length precision of the measurement is less than 1%.

The short time Fourier transform (STFT) and continuous wavelet transform (CWT) cannot resolve slowly varying velocity at low velocity stage in most photonic Doppler velocimetry (PDV) data. A new analysis method based on Fourier transform is presented to overcome this shortcoming. Instead of extracting the frequency of interference signal for velocity analysis, the new method uses a modified Fourier transform to analysis the phase of signal, and converts phase to displacement or velocity. The validity of the proposed method is examined in experimental data of a plate- impact experiment, which distinguishes the elastic- plastic properties of Fe sample. The method not only uses all sampling points of the raw data, but also has a higher velocity resolutions especially for low velocity stage. The method is a supplement to STFT and CWT method.

In order to analyze the threshold characteristics of forward- pumped fiber Raman amplifier (FRA), signal power distribution along a fiber for forward- pumped FRA is provided with Runge- Kutta method based on the coupling equations. Then, the theoretical expression of forward- pumped FRA′ s threshold is obtained with considering the practical factors, and the effects of these parameters on threshold of FRA are investigated detailedly. It is found that: the threshold will decrease when the initial signal power, the effective fiber length, Raman gain coefficient or the pump and signal frequency ratio increase, and the threshold will increase when the fiber efficient area increases.

A 45° tilted fiber grating working at 1064 nm is fabricated successfully in photosensitive fiber by ultraviolet (UV) inscription technique. A phase mask with a period of 1070 nm is rotated by 32.7° to the fiber axis to produce tilted fringes of 45° in the fiber core. The length of the 45° tilted fiber grating is about 24 mm. The polarization dependent loss (PDL) characteristics of the tilted grating are experimentally researched. The PDL value of the 45° TFG is about 11.8 dB at 1064 nm and it keeps higher than 9 dB over a wavelength range of 50 nm from 1150 nm to 1110 nm. According to the theoretical analysis, the main causes of the relatively smaller PDL value of the tilted grating are that the period of the phase mask is not the optimum value and the length is not enough.

Target disc images are widely used in camera calibration and target location for unmanned (UAV) scout task, so a method of automatically extracting feature point coordinates is proposed for the color on the two- dimensional (2D) center of the disc to solve the problems of present corner detection algorithms. The operation of color separation for the red and blue discs is completed with the method of hue- saturation- value (HSV) volor space in order to get a gray image which has obvious symmetry and strong contrast. According to the corner points of the candidate red and blue pixels in the neighborhood with the distance less than a threshold number, the exact value of the corner is determined, and the response value of extracted large corner point is applied as a candidate by using a new type of symmetric operator. Experiment results of Matlab simulation and hardware implementation based on the field programmable gate array (FPGA) platform show that the proposed method is easy to implement in hardware technology, real- time and has good anti- noise ability. Also it has a good robustness to image rotation, stretching and scale transformation.

An experiment is designed to validate the visible imaging system′ s performance through analyzing the effects of resolution, contrast and the illumination. The effective targets at a distance of about 4.5 km are tested instead of 20 km. Under conditions of 11 km visibility, the equivalent detection range is figured out by means of contrast and illumination. If the target′ s illumination is not less than 300 lux, the system can identify the target with 0.253 contrast, but it is not sure when the contrast is between 0.2 and 0.253. With special image processing, the result is significantly improved. Experimental results show that the system′ s performance can meet the special requirements.

The tolerance of Lycium barbarum polysaccharide with a variety of biological activities is poor in the environment of gastric acid or intestinal canal, which leads the great weakening of to its biological activities. This defect can be modified by nano- encapsulation. Wolfberry polysaccharide nanocapsules are prepared by microemulsion technique and compound- agglomeration method. The particle sizes and distributions of these nanocapsules in liquid phase are measured by dynamic light scattering, which can analyze the stability of wolfberry polysaccharide nanocapsules in different simulation environments of gastric acid (pH=3.5), store (pH=5.5), dodecadactylon (pH=6.8) and large intestine (pH=7.4). The results show that, the polysaccharide nanocapsules can exist steadily in the environments of gastric acid, store, dodecadactylon and large intestine without standing time and in the environments of gastric acid and store within standing time of 5 h. However, the wolfberry polysaccharide nanocapsules become unstable in dodecadactylon with standing time of 2 h or in large intestine with standing time of 1 h. The above conclusions reveal that the prepared wolfberry polysaccharide nanocapsules have the effect of pH-controlled release.

Characteristics of the luminous intensity spatial distribution (LISD) of light emitting diodes (LEDs) are capable of determining whether these devices can be applied on specific occasions. The absolute LISD of high power LED can be accurately measured only when LED is fixed at a specific heat- sink temperature because of the LED′s large heat-generating capacity. In this study, an automatic test system based on LEDGON-100 goniophotometer and the meter′ s high- precision two- dimensional (2D) revolving platform, is designed. In addition, it comprises of a test adapter, a temperature controller, a photometer head, a Keithley 2400 source meter, and an in- house- developed software package. This assembly can both control heat- sink temperatures and measure the LISD characteristics rapidly for high- power LEDs. The software is developed using Delphi programming language. The test system is stable and reliable. The test time is greatly reduced and measurements are instantly displayed.Two general types of LEDs, Lambertian type and batwing type, are measured by the system to obtain their 2D and three- dimensional (3D) LISDs. Experimental results show that the absolute luminous intensity decreases as the heat- sink temperature increases. However, the relative LISDs are the same under different heat-sink temperatures.

The way of encoded fringe projection is taken through projecting six binary fringe patterns after gray coding and four sinusoidal fringe patterns with the cycle of 2N - 1 into the object to unpack phase. This method achieved a measurement of object with steep edge, and improved the accuracy of phase unwrapping at the same time. Compared with traditional methods, this method can measure the step characteristics of object, and the measurement accuracy can be improved when high frequency fringe is projected.

It developed a method to calibrate the foci- meter based on Talbot- Moiré interferometer, the calibration range of focal length up to 100 meters. Moreover, it introduced a foci-meter based on Talbot-Moiré interferometer. It includes a lens group and a laser source to generate laser beams with steady focal length and wavefronts which used to calibrate the foci- meter. The focal length of the lens group is measured by experiments taking advantage of a traceable lens.The following conclusions can be derived from experimental results: the uncertainty of this calibration method is acceptable.

The edge- based vector finite element method is introduced to calculate the field patterns in four types of dielectric- loaded double- ridge waveguides of the ridge on theshort side, including double- rectangleridge waveguide, double- V- ridge waveguide, double- elliptical- ridge waveguideand double- trapezoidal- ridge waveguide. The changes of the field patterns of various modes by changing ridge dimensions are analyzed. The figures are considered to be helpful in the design of many microwave components.

By using the model of multi- photon nonlinear Compton scattering and the transverse dielectric constant formula of electron- positron plasma，the transverse dielectric in the un- magnetized, non- collision, isotropic and ultra- relativistic electron- positron plasma is studied by using the analytic and numerical computing methods. The relativistic Fermi′s distribution under the Compton scattering，the expression of linear dispersion, and the numerical analytic and numerical of the transverse dispersion are given. The results show that the curve length of the short wave in the analytic transverse dispersion is increased in comparison with that before scattering, the curve length of the long wave is decreased, and their positions move to left and upward. The key causesare that frequency of the electron-positron plasma is increased by the scattering, the short wave and long wave components are increased and decreased, respectively. The two discontinuous analytic curves areabsolutely connected by the numerical transverse dispersion curve, so that a smooth curve is formed. The key causes are that the ultra- relativistic probabilities resulting from Compton scattering in the electronpositron plasma are greatly increased, the coupling density and temperature are increased，the high frequency component is decreased，and the whole dispersion composition is increased.

The laser-induced cavitation bubble collapse noise spectrum in the liquid are studied experimentally by using a piezoelectric transducer (PTZ) hydrophone. Experimental methods and a cavitation detection system are designed to investigate bubble collapse noise. The wavelet transformation, fast Fourier transform (FFT) and other signal analysis methods are used to monitor the cavitation noise and reduce wavelet noise, analyze power spectrum. The result shows that application of wavelet denoising in cavitation bubble collapse noise spectrum analysis is an effective method. In addition, the designed software can quickly analyze the spectral characteristics of bubble noise signal, and it can detect and monitor cavitation on-line. The results have certain significance on the warning and researching of turbine cavitation, propeller cavitation and other water conservancy machineries.

In order to compare the welding characteristics of fiber laser and CO2 laser, a 2 kW fiber laser and a 2.4 kW CO2 laser are used to weld 590 MPa high strength steel plates. By changing the defocusing distance and the welding speed, the penetration depth is investigated. The results show that with the same welding speed and the same output power, the fiber laser welding gets more penetration depth compared with CO2 laser welding. With a negative defocusing distance, the penetration depth becomes greater when the defocusing distance is within the range of focal depth; the penetration depth increases with the decrease of welding speed when the power is constant, and the penetration depth using the CO2 laser welding decreases faster with the increase of welding speed than fiber laser welding.

As 2 mm laser is in eye-safe areas and weak atmospheric absorption band, thulium-doped fiber laser attracts a lot of attentions. The lasers output power characteristics of thulium- doped double- clad fiber under laser diode (LD) backward pumping using a plane mirror and concave mirror are compared. Experiments and theories suggest that the laser cavity losses increase because the gap, tilt, and fiber end face defects between the fiber end face and the plane mirror and mirror thermal damage and other factors, and the laser output performance is severely affected. The cavity insertion loss properties are analyzed after using a plane mirror and concave mirror respectively at the end of the fiber based on the wave theory, which suggests that using a concave mirror cavity the loss is smaller than that using a plane mirror. When using the concave mirror cavity structure after fiber end, the maximum output power of 22 W is obtained, corresponding to the center wavelength of 1998.6 nm and the slope efficiency of 43% relative to the incident pump power. Comparing to the use of plane mirror cavity the laser slope efficiency increases of 10% , and the thermal damage of mirror is alleviated obviously.

A general analysis of the influence of two- photon or three- photon absorption on terahertz (THz) generation via optical- difference frequency generation from the nonlinear optical material is presented. We calculate the best length of crystal and the corresponding THz quantum conversion efficiency for different values of the pump peak power under phase-mismatched condition and compare the results with that in phasematched condition. From the results we know that multi- photon absorption influence difference frequency generation slightly at low pump power and the impact will be strong with the increase of pump power. Because of the effect of two- photon or three- photon absorption, difference frequency generation at high pump power requires longer crystal to achieve the maximum photon conversion efficiency for both phase- matched and phase-mismatched situations. The maximum photon conversion decreases when pump power increases.We also present approaches to reduce this adverse effect.

Utilizing the method of light- induced photonic lattices，we fabricate multiple rotational symmetry two- dimensional photonic lattices in LiNbO3:Fe crystal by masks with 3, 4, 5, 8 and 12 holes. Based on the interference principle, the multiple- beam interference pattern is obtained by numerical simulation. We observe the 3, 4, 5, 8 and 12 holes Brillouin- zone spectra and far- field diffraction patterns, and analyze the relationship between them. Experimental results are quite consistent with the simulation results. Traditional methods of observing Brillouin-zone spectra need rotating diffuser, using different optical paths to induce superlattices and observe Brillouin zone. We use attenuator only, so that the proposed method is simpler, more stable, and easier to adjust.

InGaN/GaN superlattice (SL) barrier near p- GaN and n- GaN are designed to replace the conventional GaN barrier of InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs). The lightvoltage performance curves, electroluminescence (EL) characteristics, energy band diagrams, electron concentration and radiative recombination rate of LEDs with SL barrier near p- GaN and n- GaN have been studied numerically. The results indicate that the InGaN/GaN LED with SL barrier near n- GaN improves light output performance mane than that near p- GaN. The improved performance is due to the enhanced injection efficiency of electrons and radiative recombination rate.

An optimization design method of collimating lens is proposed. The quadratic B-spline theory, Scheme language and optimization engine are used in combination to achieve the optimization of freeform surface lens. The Lambert emission of 1 mm × 1 mm LED is used as light source, and the lens material is polymethyl methacrylate (PMMA). The collimating lenses of different structures are optimized by this way. The energy efficiency can be up to 90% . Compared with the current methods, it has the advantages of less dependence on the initial model, simple design process and high versatility.

Using the Collins formula, we deduce the analytical expression of hollow Gaussian beams propagating in a gradient-index medium and analyze the corresponding propagation properties of hollow Gaussian beams. The influence of the gradient-index medium on the propagation properties of hollow Gaussian beams is also discussed. The results show that propagation properties of hollow Gaussian beams are largely influenced by the medium′s gradient-index.

As an active optical compensation technology, adaptive optics (AO) is used to correct wavefront distortion extensively because of its advantages such as simplicity, instantaneity and validity. In recent years, AO technology is increasingly used in high- energy laser system. We review the basic principles of the AO system, and discuss the research progress of solid- state AO correction technology at home and aboard. Introduction to two categories is presented according to if there is a wavefront sensor in an AO system to correct the wavefront distortion in solid state lasers, and the key technologies are introduced. Finally, theexisting technical difficulties are summarized, and the application prospect is presented.

The principle and main characteristics of lidar detection technologies for biological/chemical warfare agents are described. The foreign developments of the primary lidar detection technologies such as differential laser radar technology, Raman spectroscopy and laser- induced fluorescence technique are analyzed. Some newest technologies are introduced such as photo- acoustic spectroscopy, Raman fluorescence detection, quantum cascade lasers and infrared focal planar array to detect biological/chemical warfare agents. Finally, the review points out the development trend of lidar detection technology for biological/chemical warfare agents.

Surface- enhanced Raman Scattering (SERS), with high sensitivity and selectivity , has been used in many areas of scientific research and production practice. The developme- nt of SERS technology in detecting environmental pollutants of heavy metal ions, polycyclic aromatic hydrocarbons, pathogenic microorganisms and pesticide in recent years is presented in this paper .And the advantages and disadvantages of SERS in these applications was analyzed. The development tendency of SERS was predicted in the end.

To increase the operation temperature and service life of superalloy, thermal barrier coatings are widely employed in the surface protective field of high- temperature components of aircraft engine. In this paper, the research progress on materials and preparation techniques of thermal barrier coatings is reviewed. The main issues are analyzed and the method of the functionally graded thermal barrier coatings by laserinduction hybrid cladding (LIHC) is put forward. Namely, the substrate is preheated meanwhile laser cladding is carried out to form LIHC heat source, which is combined with the design of functionally graded structure. As a result, the crack- free and high- property thermal barrier coatings can be obtained under the condition of high efficiency.

Color holographic display is an important aim of holographic video display technology. In this paper， an overview of the issues about the methods and system design of color holographic display based on spatial light modulator (SLM) is presented. Firstly, the basic principles that three monochromatic holographic images are combined into a color image are introduced. The methods of generating holograms are analyzed and the comparison of three kinds of holograms including optical holograms, digital holograms, and computergenerated holograms (CGHs) is achieved. Secondly, the choice of SLM to design a color holographic display system and the phase modulation characteristics for multi- wavelength illumination are discussed. It is feasible to employ either red, green, and blue (RGB) lasers or light- emitting diodes (LEDs) as illumination source in practice system. Then, the configurations of color holographic display system by use of different methods including time division multiplexing, space division multiplexing, spatial division, and spatial multiplexing are described, and it is pointed out that the color holographic reconstructions are corrupted by effects arising from the discrete nature of SLM and the chromatics. Finally, the prospective development of color holographic display technology is given.

In recent years, the developments of semiconductor materials follow two directions. One is socalled the material engineering, which is focusing on continuously pursuing new semiconductor material systems. The other one is the band engineering which is used to change the band energy of known semiconductor material system by adjusting their dimensions. Quasi-zero-dimensional semiconductor quantum dot is a typical representative of band engineering by changing the size of dot. In this paper, we are mainly concentrated on introducing the bottlenecks of quasi-zero-dimensional semiconductor quantum dot lasers.

Single crystal silicon (Si) sphere method is an important scheme for precise measurement of Avogadro constant and redefinition of kilogram. The surface oxide layer thickness is related to the correction of the measured mass and diameter of the single crystal sphere, and contributes a large proportion of the relative uncertainty of the Avogadro constant. We discuss several basic problems in measuring the sphere surface by ellipsometer, i.e., the influence of the crystal- orientation- dependent optical constants and surface curvature induced ellipsometric light beam scattering. And the uncertainty components for the adopted indirect method are analyzed. The study provides both experimental and theoretical bases for the measurement research in surface layer on Si sphere.

Laser-arc hybrid welding technology is one of the research focuses in the high-energy beam welding areas, and also the optimal welding method for heavy- gauge steel (thickness not less than 5 mm). This paper systematically introduces the research progress of domestic and foreign researchers and companies in the laserarc hybrid welding of steel, and our latest research work on fiber laser- arc hybrid welding ofnew nano- scale strengthened steel (yield strength of 600~700 MPa) steel is briefly described. Finally, the heavy- gauge steel laser-arc hybrid welding technology research directions are analyzed and discussed.

Laser-induced breakdown spectroscopy(LIBS) has been used as a promising element analysis technique with the advantages of in-situ detection and remote monitoring etc. It is a relatively new task to apply LIBS to mosquito coil sample. In order to apply LIBS technique in the field related to environmental monitoring, we use time-resolved LIBS to measure and analyze mosquito coil sample. Eleven kinds of elemental composition of mosquito coil, which are Al, Mn, Mg, Sr, Zn, Ba, Na, Ca, Fe, Si and H, are identified. Based on local thermodynamic equilibrium (LTE) assumption, the plasma temperature is obtained. The relative concentrations of these elements are estimated by calibration-free method. The experimental result prove that LIBS can be applied to the rapid and effective detection on the harmful elements.

Transmission enhancement of nanohole array has very important applications and prospects in many fields. Numerical simulation on transmission enhancement of metallic nanohole array is performed with finitedifference time-domain (FDTD) method. The factors such as round hole radius, film thickness, array cycle, and different materials are analyzed, and changing trend of transmission enhancement spectrum is discussed under the conditions of different parameters. Studies show that large round hole radius and thin film are helpful to the improvement of transmission enhancement, and larger hole array cycle is not conducive to transmission enhancement. The effect of different shape of nanohole on transmission enhancement is discussed, and rectangular hole array is used for comparison. Finally by changing thin film material the corresponding transmission performance is calculated.