Background noise from SO2, NO2 and other interfering gases in flue gas is corrected by the transverse Zeeman effect. The mercury concentration in flue gas is determined by Zeeman atomic absorption spectrometry. The average concentrations of element Hg (Hg0) in flue gas before and after wet flue gas desulfurization (WFGD) are 0.36 μg·m-3 and 11.08 μg·m-3. The concentration of Hg0 in flue gas increases significantly after desulfurization system. The monitoring results show that about 99% of SO2 in the flue gas is absorbed by the desulfurization slurry, and produces enough sulphite which reacts chemically with Hg2+ to release Hg0. The change of pH value in the desulfurization slurry also accelerates reduction reaction and release of Hg0. The use of WFGD system to remove mercury can lead to the increase of element mercury concentration. The monitoring results of element mercury have certain correlations with concentrations of other components in the flue gas, which is consistent with the theoretical analysis. The monitoring results show that transverse Zeeman atomic absorption spectrometry can effectively overcome interference caused by SO2, NOx and other gases. The results confirm the accuracy and feasibility of transverse Zeeman atomic absorption spectrometry applied in the detection of mercury content in flue gas.

The non-sequential double ionization of magnesium atom in elliptically polarized strong laser field is investigated with the classical ensemble method. The non-sequential double ionization occurs in elliptically polarized strong laser field for magnesium atom, and the ionization rate decreases a little with the increase of ellipticity. Back analysis of the non-sequential double ionization trajectories shows that the decrease of the number of returning electrons results in the decrease of ionization rate. In addition, the distributions of the correlated two-electron transverse momentum and counts of electron with different energies demonstrate the kinetic energy of ionized electrons rises with the increase of ellipticity, so the second electron can be ionized easily with the recollision of the returning electron, which can compensate the reduced ionization rate, and thus the ionization rate does not decrease too much.

Structural parameters of interdigitated back contact (IBC) crystalline silicon solar cell are investigated systematically by numerical simulation. The influences of the Si wafer thickness, the area ratio of emitter, gap and back surface field, and the distribution and linewidth of metal contact lines in emitting region on the open-circuit voltage, short-circuit current density, filling factor and conversion efficiency of solar cell are analyzed in detail. Results show that the conversion efficiency of solar cell increases with the increasing of area ratio and the decreasing of metal contact′s linewidth. When the bulk thickness of Si is 220 μm, the area ratio of emitting region, gap and back surface field is 8∶1∶1, the total linewidth of two metal contact lines in emitting region is 10 μm, and an optimum photoelectric conversion efficiency of 24.19% can be achieved for IBC solar cell.

Microfluidic systems based on laser induced fluorescence (LIF) detection technology have been widely used in the field of biochemistry detection. Aiming at the problem of weak fluorescence intensity induced by a few detection samples in the microfluidic system, a microfluidic chip integrating a microlens array (MLA) is designed and fabricated to improve the intensity of the detected fluorescence. An 8×8 photoresist MLA mold with the diameter variation coefficient of 0.36% is obtained by the hot melt technology. Then, a cover plate integrating a polydimethylsiloxane MLA is produced by the soft-lithography technology, and the focal length uniformity error is 7%. Afterwards, a micro-channel substrate is made. The substrate and the cover plate are packaged by the oxygen plasma bonding technology. Finally, the fluorescence intensity of the chip is detected by a fluorescence microscope, and the chip is injected by fluorescein isothiocyanate fluorescent dye solution with concentration of 10 μmol·L-1. The result shows that the fluorescence intensity with the microlens is improved about 2.2 times as much as the fluorescence intensity without the microlens.

The avalanche voltage of the Si avalanche photodiode (Si-APD) is temperature sensitive, which greatly limits the practical application of the single-photon detector based on Si-APD for the all-weather operation in field. A technology is developed to guarantee stable working of the Si-APD single-photon detector with a wide-range environmental temperature tolerance. The digital bias voltage auto-compensation technique is combined with the refrigeration, which can automatically compensate the operation temperature drift and maintain a stable avalanche gain of the Si-APD. The experiment proves that the single-photon detector with this technology can work stably in the temperature range from -40 ℃ to 45 ℃. The experimental result indicates that by using the proposed auto-compensation technique, the Si-APD single-photon detector has the ability of stable working in the outfield with great change of temperature. The single-photon detection technology with high stability can be provided for the photon counting laser measurement of the airborne and satellite-borne.

In order to suppress the four wave mixing (FWM) effect, two improved schemes aiming at traditional wavelength division multiplexing (WDM) systems with equal frequency intervals are proposed according to the formation mechanism and main influence factors of FWM effect. One scheme is to design a channel spacing which is broad in the middle and narrows toward each end. Another scheme is to design the channel spacing with unequal intervals. A seven-channel WDM system is established and simulated with OptiSystem. The two schemes can suppress the FWM effect and the second one is better than the first one.

Most of the displacement and vibration testing methods based on vision require artificial marker on structure surface, which makes vision-based testing and monitoring for real-life more complicated. Aiming at the disadvantages of the existing machine vision technology in vibration modal testing for thin-walled components, a vibration modal testing method of thin-walled components based on curvature scale space (CSS) corner detecting and matching is proposed. The virtual corner is set to replace traditional physical targets, and the key point of vibration image sequence of thin-walled components is oriented by the improved CSS corner detection algorithm, which is matched by using. Thus, the vibration information is obtained and modal parameters are identified. Eventually, the vibration modal testing experiments for thin-walled beam and thin-walled cylinder is carried out. By analyzing measurement results and verifying with finite element simulation and accelerometer, the results show that the proposed method can effectively and accurately obtain modal parameters, and the measurement error is less than 5%.

The full spatial information cannot be obtained by single filter in characteristics extraction of hyperspectral image. We propose a classification method which combines two kinds of information extracted by non-local means filter and guided filter. This method advances a fusion of spatial information for hyperspectral image classification. One kind of spatial information for all bands of hyperspectral image is extracted by the non-local means algorithm, and another kind of spatial information is obtained by guided filter for the same image after reducing dimensionality with principal component analysis (PCA). Two kinds of spatial information are combined, and the classification is done by support vector machine (SVM). Experimental results show that the proposed algorithm is better than the spectrum information, PCA dimensionality reduction, spatial-spectral SVM, edge-preserving filtering and recursive filtering methods, and the classification accuracy of hyperspectral image is effectively improved.

Pedestrian detection is one of the most important tasks of robots and unmanned vehicles at nighttime. Faster region convolution neural network framework is used to realize the pedestrian detection of infrared image at nighttime. This framework uses region proposal network to generate region proposals. Therefore, it is unnecessary to generate region proposals separately from the image. The parameter sharing mechanism is adopted in the convolutional layers in region proposal network and convolutional network for classification and bounding box regression, which makes the framework an end-to-end advantage. Thus, the pedestrian detection can be implemented from the input image to the detection result directly and it is unnecessary to manually select the features of the target. Experimental results show that the proposed method increases the recognition accuracy from 68.2% and 73.4% to 90.9% and shortens the recognition time from 3.6 s/frame and 2.3 s/frame to 0.04 s/frame compared with the traditional method and fast region convolution neural network, respectively, which reaches the required real-time level in practical applications.

In order to optimize the insufficient ability for complex multi-target remote sensing image detection using the reported saliency algorithms, an extraction algorithm of salient object based on similarity measurement for superpixel regions is proposed. The original image is segmented into certain superpixel regions using simple linear iterative clustering method, and some high saliency regions are extracted correctly using graph-based visual saliency method. Meanwhile, parts of the edge superpixels need to be amended and the rest of salient superpixels are used as training samples. By calculating the similarity of all superpixels and training samples hierarchically, a reasonable membership value of each superpixel is established to separate the goal superpixel regions with high saliency. Finally, all the superpixels salient objects from the original images are extracted successfully using the membership values. The experimental results show that the proposed algorithm has higher precision and recall rates than the other saliency detection methods, thus it can be effectively applied to complicated multi-objective in target information extraction of remote sensing images significantly.

In order to analyze the drought of maize plants and aiming at the difficulty and broad in recognizing agricultural drought, we propose a method to identify the drought of maize plants based on the multi-features fusion. The images of normal and seriously drought plants are taken as samples. The K-means algorithm is used to extract the interesting areas of maize plant images. And, the features of the pictures are extracted after image segmentation, including colors, singular value decomposition (SVD) and textures, a total of 20 dimensional features. The genetic algorithm is used to select a effective features subset of 20 dimensional features. Finally, the discrimination model based on least squares support vector machine is established for the effective features subset and images of maize plant drought are obtained. The single feature (color、SVD、texture) after directly fusion and using principal component analysis for feature selection are performed as comparative experiments, the average recognition accuracies are 0.9503, 0.9627, 0.9771, 0.9460, 0.9745, respectively. The genetic algorithm is used to select the features, and finally finds 9 dimensional features as the optimal solution. The average recognition accuracy is 0.9903. The result shows that this image processing technology can identify the drought situation of the maize plants effectively and efficiently. And it also provides a new idea for the drought identification of maize plants.

In order to get a better detection result of crack regions on pictorial stone, a crack detection algorithm based on editing distance is proposed. The pictorial carved stone image is separated into many patches with identical sizes. For separating the crack regions from the background, the editing distances between each patch are calculated and the mask image is generated simultaneously. The blank area on mask image is filled by dilation operation which belongs to morphology. The crack detection is finished by setting a threshold to the mask image. Experimental results show that this algorithm can detect the crack regions on pictorial carved stone accurately.

According to the features of laser active imaging, a new edge detection algorithm combining fractional differential and Sobel operator is proposed. The image preprocessing is completed by constructing a denoising algorithm based on the combination of wavelet soft threshold denoising and non-local means filtering. The deficiency of traditional Sobel operator is analyzed. Then the Sobel edge detection operator is improved by fractional differential, and a four-direction edge detection model based on the fractional differential and Sobel operator is proposed to complete image gradient operation. The maximum interclass differential method is used to automatically select the threshold, so as to achieve the binarization to complete edge detection. Experimental results show that compared with the traditional edge detection algorithms, the proposed algorithm can detect more image edge details and has better matching parameters.

Excellent auto-focusing technology is necessary for measuring the diameter of the optical fiber accurately, stably, efficiently and real-time, especially the coating layer peeled optical fiber by microimaging. Focusing window selection is the premise of auto focusing. In order to avoid the influence of the intermediate transmission or the diffraction light band on the optical fiber side imaging, an improved method to select the localized elliptical window is proposed. At the same time, the effects of different window shapes on the clearness evaluation and calculation speed are also compared. By applying the method to the measurement of 125 μm standard optical fiber, we find that the standard error is within 0.3 μm and the measurement accuracy is increased by an order of magnitude compared to the micron scale of the VM2.22 precision measurement software. The method is practical, fast and versatile, and can be used as an effective method for automatic focusing window selection.

An algorithm to improve the positioning accuracy of spot centroid for Shack-Hartmann wavefront sensor is proposed. The detection errors of spot centroid are analyzed. The image resolution is improved by utilizing the detection window whose size is matched with that of spot and using the interpolation method. The centroid position is calculated by the two-order moment algorithm. The proposed algorithm is used to process and calculate the spot images with noise and the wavefront reconstruction diagram of the test component is also presented. The results show that, compared with the traditional algorithm, the proposed algorithm improves the detection accuracy of centroid by about 0.8 times.

The chiral isomers D- and DL-tartaric acid are measured by terahertz time-domain spectroscopy (THz-TDS), and characteristic absorption peaks of two isomers in the range of THz are obtained. The differences between them are obvious. The single molecular and unit cell of two isomers of tartaric acid are calculated by density functional theory in quantum chemistry software. The absorption peaks of two isomers of tartaric acid are obtained and identified. The results of the experiment are basically consistent with the calculated results at absorption peak. Through the identification of the absorption peak, the formation mechanism of the absorption peaks of such isomers in the range of THz is deeply analyzed. The results show that THz-TDS technology can identify small differences between tartaric acid chiral isomer and its racemate.

A scheme for high precision time synchronization measurement of laser pulses is presented. The time to digital conversion technology is used to measure the relative time delay of laser pulses accurately, and the measurement accuracy is less than 10 ps (the peak-valley value). In order to meet the requirements of the input pulse width of the measuring circuit, an electric pulse broadening module is designed for short laser pulse. An electric pulse signal can be broaden from hundred picoseconds to nanoseconds, with the root mean square of the additional jitter less than 2 ps. This scheme can realize the real-time high precision time synchronization measurement, and can be used for real-time monitoring of a time synchronization feedback compensation system.

Based on semiconductor lasers, the zero-expansion coefficient material is employed to build an ultra-stable cavity which is used to realize a narrow linewidth laser output. A laser diode and a grating are combined to form a Littrow structural external-cavity. After the first order diffraction, a small part of the output beam is used to lock the ultra-stable cavity which realizes the linewidth narrowing, and most of the output beam is injected into a tapered amplifier to achieve an amplification of optical power. A laser output with the wavelength of 1064 nm, output power of 290 mW and linewidth of 10 kHz is finally acquired. This technique can be applied in the area of atomic and molecular precision spectroscopy.

A process model of the bending angle in laser-bending shaping of tubes is built by using the response surface method and its reliability is demonstrated with the designed experiment. The interactive influences of the process parameters such as the distance from free edge, the irradiation length, the scanning angle and the number of scanning on the bending angle are analyzed based on this model. The results show that the distance from free edge, the number of scanning and the irradiation length have significant influences on the bending angle, but the scanning angle has little influence. The irradiation length has a weak interaction with the number of scanning, but a strong one with the distance from free edge.

An all-fiber based polarization output mode-locked laser is proposed. Without a band-pass filter in the oscillator, stable mode-locked pulse train in the all-normal dispersion region is obtained when the polarization output of fiber polarization splitter and the birefringence filtering effect of fiber are used. The repetition rate of pulse is 2.2 MHz and the single pulse energy is 100 nJ. The single-wavelength and dual-wavelength mode-locked output are experimentally obtained when we adjust the intra-cavity polarization by an in-line polarization controller, and the stable dark soliton pulse is observed at 1 μm. The evolution of the intra-cavity polarization is the key to obtain different mode-locked states. Under the dual-wavelength mode-locked state, the wavelength tunable width can reach 12 nm. The system transmission function is used to theoretically analysis the principle of wavelength tuning based on intra-cavity polarization controlling.

The selective laser sintering (SLS) technology is applied to the molding of the graphite/phenolic resin mixed powders, the change rule of the dimensional precision of the graphite prototype is studied experimentally, and its internal cause is revealed. It is found that the dimensional deviations in both the X and Y directions of the graphite prototype increase with the increase of the laser energy density, and decrease with the increase of the layer thickness. The dimensional deviation in the Z direction shows a tendency to decrease first and then increase with the increase of the laser energy density and the layer thickness. Compared with the dimensions in the X and Y directions, the dimension in the Z direction is more obviously affected by the process parameters. The main reasons for the large dimensional deviation of the graphite prototype are the secondary sintering and the Z-axis bonus, which are produced in the SLS process. The orthogonal experimental results show that the factors affecting the relative dimension error in the Z direction are sorted by the order of influence degree from large to small as the scanning interval, the layer thickness, the laser power and the scanning speed. The optimal combination of process parameters which makes the relative error in the Z direction smallest is: laser power of 23 W, scanning speed of 1000 mm·s-1, scanning interval of 0.18 mm and layer thickness of 0.14 mm.

Erbium-doped fiber lasers have wide applications in fiber communication, fiber sensors, coherent detection and combination because of its narrow linewidth and low noise. An erbium-doped fiber laser with ring cavity is constructed by a self-designed π phase-shifted fiber grating and a high-reflective fiber Bragg grating (FBG), which can achieve narrow linewidth erbium-doped fiber laser output in 1.5 μm-band by utilizing the π phase-shifted fiber grating as a narrowband filter. When the pump power of 980 nm diode laser is 5 W, the laser output power is 1.006 W, the optical to optical efficiency is more than 20%, and the central wavelength is 1549.45 nm with laser linewidth of 5.32 pm. The output light is without residual pump, which indicates that the laser power can be further increased by increasing pump power. High-efficiency, high power, single-longitudinal-mode laser can be achieved by optimizing the bandwidth of transmission peak of π phase-shifted fiber grating, the reflectance spectrum of FBG, and the structure of the laser cavity.

A systematic design method of the laser welding process is proposed. A simplified finite element simulation model for the single-fiber bidirectional optical subassembly (BOSA) is established by using the ANSYS software. The numerical simulation method of the indirect welding stress field is adopted to study the parameters which render the minimum offset under the single beam laser welding. By combining the optimized parameters, the optical power losses after welding are analyzed under different laser welding machine parameters. The results show that when the single beam laser power is 100 W, the pulse width is 0.2 ms, and the spot radius is about 0.18 mm, the optical assembly has the minimum offset and the optical power loss ratio after optimization is decreased by 7.1%.

A single-longitudinal-mode Tm, Ho∶YAG laser is realized by using a diode-pumped L-shaped twisted mode cavity. There mainly exist two oscillator wavebands at around 2090 nm in the output spectrum of Tm, Ho∶YAG laser under free running. The maximum output power is 483 mW under pump power of 6.12 W. The single-longitudinal-mode laser possesses a maximum output power of 202 mW at 2090.9 nm under the pump power of 5.9 W, and the corresponding slope efficiency is 6.95%. When the pump power increases to over 5.9 W, the Tm, Ho∶YAG laser runs with multi modes. The output beam radii of single-longitudinal-mode Tm, Ho∶YAG laser are measured with knife-edge method at several positions after the beams pass through a lens. The beam quality factor is about 1.17.

In order to design a wide-angle high-absorption electromagnetic wave absorption device, a cascaded stratified structure based on graphene metamaterials is designed. By means of the special attributes of metamaterials, the transfer matrix formula is derived, which is used to study the transmission characteristics of the designed structure. The research results show that, under the condition that a high-absorption rate is kept, a wide-angle absorption bandwidth can be achieved by adjusting the structural parameters. The absorption bandwidth is related to the number of cascaded layers, however the absorption bandwidth tends to saturate when the number of layers reaches a certain value.

The parasitic absorption loss in the light-injection side of HIT (heterojunction with intrinsic thin layer) structured a-Si∶H/c-Si solar cell is one of the bottlenecks to limit transfer efficiency improvement of HIT cells. A kind of bi-facial solar cell with a structure of Ag grid/SiNx/c-Si(n+)/n-c-Si/a-Si∶H(i)/a-Si∶H(p+)/ITO/Ag grid is designed and prepared. The properties of the solar cell samples with light coming from each side are analyzed by means of J-V characteristics, quantum efficiency and Suns-Voc measurement methods. The results show that higher short-circuit current density of the cells can be obtained with rear-junction installation than that with a front-junction installation, which is the reason for higher conversion efficiency with rear-junction installation. In the research, the maximum short-circuit current density of 40.3 mA·cm-2 is got in a cell with wafer thickness of 160 μm, which is higher than the maximum value of the short-circuit current density of 39.5 mA·cm-2 for the HIT cells.

The key to auto-focusing of microscopic images is to design a high sensitivity focusing function. Due to uncertainty of the details among different microscopic images, traditional gradient functions are less sensitive to less detailed images. To solve the problem, an auto-focusing function, VarGrad, combining global and local gray-scale variation, is proposed. According to the characteristics of microscopic images, VarGrad function combines the gray variance function based on global gray-scale variation with the gray gradient function based on local gray-scale variation by using focusing windows. The VarGrad function exhibits high sensitivity regardless of image detail. We carry out quantitative evaluation of the proposed VarGrad function using two different peripheral blood cell image sequences with different image details. The experimental results show that three sensitivity indices, sharpness rate, steepness, and rate of change of sharpness, are improved by over 30% for detailed images and less detailed images, compared with that of several traditional typical focusing functions.

Dynamical propagation characteristics of spatial solitons after passing a parity-time (PT) symmetric potential with a longitudinal barrier is investigated by numerical simulation．The simulation results show that a spatial soliton transversally deflects after transmitting through the barrier. The deflection angle is related to the gain/loss coefficient, the modulation depth and the longitudinal dimension of the PT symmetric potential barrier. The gain/loss coefficient shows an important influence on the dynamical propagation characteristics of spatial solitons. Besides, after passing a PT symmetric potential barrier, the spatial soliton obtains an energy gain whose value is closely related to the deflection angle. By adjusting the barrier parameters, the deflection angle can be controlled. This makes spatial solitons have a great application potential in many fields such as optical switch and optical communications.

Based on optical design theory of imaging illumination and non-imaging optical theory, an initial optical structure of illumination system is established according to the special requirements of Talbot self-imaging lithographic equipment. The optical design software Zemax is applied to optimize the initial structure. The software Lighttools is used to set up models and perform large-scale ray tracing. The simulation result shows that the nonuniformity of illumination approaches 1.83% in the illumination area of 60 mm×60 mm. Meanwhile, the power density is no less than 1.15 mW·mm-2. The tolerance analysis is carried out on the illumination system. The results show that the illumination system satisfies the demand of Talbot self-imaging lithography.

A kind of strain feedback type piezoelectric optical deflector is presented. The mechanical structure and internal composition principle are firstly introduced for the optical deflector. Two strain feedback type piezoelectric actuators are integrated within the optical deflector, which is used to actuate the mirror and measure its angle displacement. An autocollimator is used to calibrate the deflector, and the obtained deflection accuracy is 0.05′. And then a series of tests are conducted to validate the positioning and tracking performances for both open and closed loop operations. Experimental results show that, the value of creep reaches 12.60% within 30 min and the tracking error for the varied-amplitude triangular-wave reaches 13.70% of the full scale in open loop mode. In closed loop mode, the creep effect is basically eliminated and the tracking error reaches 4.31% of the full scale. The designed piezoelectric optical deflector has good engineering application value for its reasonable structure and stable performance.

For high pass filter in terahertz frequency range, a laboratory preparation process of subwavelength structure sample on polyethylene terephthalate film coated with aluminum layer using photolithography process is described. The influence of subwavelength rectangular metal hole array structure on the transmission properties of terahertz wave is mainly studied, and the high-pass filter characteristics of this structure are analyzed theoretically by using simulation software. The influence of hole size and metal line width of the rectangular hole structure on the high-pass filtering effect is numerically analyzed, and the corresponding mathematical model is established.

In order to improve the processing efficiency of lens in fisheye lens, traditional rigid disk and elastic disk are replaced by designed three-piece nonblocking fixture for fine grinding and polishing. The production efficiency is enhanced. In the polishing process, the effect of glues on surface form can be avoided by utilizing fused polyurethane instead of blocking glues. The stability of aperture in polishing and fine grinding processes of hem machine is enhanced by using the rubber band instead of the pressure gage in the equipment. The regulatory usage of molds in polishing and fine grinding processes is in favor of improving production efficiency. The impact of impressions and scratches on the surfaces of the parts caused by edging process are avoided effectively by adjusting the sequence of polishing and mechanical centering and edging. The production efficiency is enhanced and the labor intensity is reduced by improving the structure of fixture for smearing ink. In production, the production efficiency of three-piece nonblocking fixture is lower, and how to successfully develop multi-piece nonblocking fixture is the focus of the further work.

The contact angles of droplets are measured by using the vertical shooting-diameter measurement method instead of the traditional lateral shooting-contour extraction-function fitting method. The measuring efficiency is improved because the process of function fitting is omitted. The theoretical formula for contact angles is derived. With the combination of computer with image processing technology, the edge contours of projected images of droplets are extracted and the diameters of these edges are measured. By substituting the diameter value into the derived theoretical formula, the contact angles of droplets are obtained. The relation curves of contact angle versus applied voltage obtained by the experiment and theoretical calculation are consistent, which confirms the feasibility of this proposed method.

A method based on the superposition of oblique phase in the 3/2 phase distribution is proposed to generate the decelerating Airy beams (DABs) whose main lobes are bent toward side lobes. By adjusting the obliquity factor of the superposition phase, the DABs with different trajectories are obtained. In the circular symmetry case, the circular DABs (CDABs) are generated by the superposition of circular oblique phase. The self-focusing and tight focusing properties of CDABs are invesitigated by numerical simulation. In the self-focusing case, the generated CDABs whose side lobes are surrounded by the main lobes can be used in particle manipulation. In the tight focusing case, the CDABs can produce a spot chain or a light needle which behavior is similar to that of the accelerating Airy beams, but the focus position and distribution can be adjusted by the phase obliquity factor. These results provide a reference on obtaining new Airy beams and expanding their applications.

Based on the current experimental conditions, a model of annular four-level semiconductor quantum dot electromagnetically induced transparency medium is constructed by considering the phonon-assisted transition effect in semiconductor quantum dot. Dynamical behaviors of the temporal optical soliton in this system is analytically studied by using multiple-scale method. The results show that dynamical properties such as amplitude, width and group velocity of the temporal optical soliton can be controlled by adjusting the strength of the phonon-assisted transition. The group velocity of the temporal optical soliton is much smaller than the velocity of light. And when the strength of the phonon-assisted transition increases, the group velocity of the soliton decreases continuously. So, the group velocity may slowly close to zero that it appears stagnation. The optical stagnation is helpful for light storing in quantum devices. It provides some reference values to realize optical storage in the semiconductor quantum devices.

Mode instability effect occurs when the output power of a fiber laser reaches a certain threshold, and it results in serious influence on output power and beam quality, so that the applications of high power fiber lasers are restricted. It is meaningful to study mode instability mechanism and suppression methods for the further improvement of output power of high power fiber lasers. The mechanism of mode instability is systematically introduced, and some suppression methods are summarized.

Optical fiber gratings have become one of the most important devices in the field of optical fiber sensing and optical fiber communication. Because of the novel characteristics, cascaded structures of the fiber gratings have always been the focus of research. The research progresses of cladding mode recoupling, edge filtering and independent cascading of the fiber Bragg grating-long period fiber grating (FBG-LPG) cascaded structure are summarized, and their technical difficulties are discussed. Suggestions for improvement are presented. To address the problem of the complexity of transmission type FBG-LPG optical path, a reflection type FBG-LPG independent cascaded structure which can effectively simplify the structure is proposed, and the system performance is optimized and verified by experiment. The development trend of the FBG-LPG cascaded structure is predicted.

A visible light communication (VLC) technology based on light-emitting diode (LED), which integrates the dual functions of lighting and data communication, is becoming a hot topic of wireless communication research. Deficient modulation bandwidth of commercial LED limits the development of high speed transmission of VLC system. In order to solve the problem, a hardware pre-equalization technology is proposed to extend the -3 dB modulation bandwidth of VLC system effectively, and the transmission rate of VLC system is improved. The development progress and the application status both at home and abroad of hardware pre-equalization technology used in high-speed VLC system are summarized. The comparison of equalization control strategy, equalization circuit structure and equalization effect of different pre-equalization plans is carried out. The research trend of equalization technology is made, which provides a reference for the research of high-speed VLC technology in the future.

As one of key components of powder feeding system in the technology of laser rapid prototyping for metal powder, the powder feeding efficiency of powder feeding nozzles influences directly the laser rapid prototyping efficiency and accuracy of metal powder. The in-depth studies at home and abroad are performed in this field and a variety of new powder feeding nozzles are developed in which the coaxial powder feeding nozzle can effectively improve the metal powder cladding effect and utilization. The feeding principle and the research status at home and abroad of coaxial powder feeding nozzles are introduced, the main factors influencing powder utilization and laser-powder coupling performance are analyzed and summarized, and the improvement methods are proposed. Improvement approaches for laser focusing, powder segregation and bounce, and poor cooling efficiency are proposed, and the applications of coaxial powder feeding nozzles are prospected.

Reservoir computing is a simple and effective machine learning algorithm to process time dependent signals. Compared with the software implementation in traditional electronic computer, reservoir computing implementation with optical components is more beneficial to information processing with ultrafast speed and ultralow power consumption. The basic principles of reservoir computing are presented, and the research progress in hardware implementation of reservoir computers is introduced from three aspects of input layer, reservoir and output layer. The existing problems in the development of the hardware implementation are demonstrated, and their future developing trends are discussed as well.

The pyrolysis products and their components of pulverized coal will directly affect the combustion characteristics. In order to further study the variation of the product concentration during pyrolysis process, a group of CH4 absorption lines (2v3) near 1.65 μm are used for on-line measurement of CH4 concentration in Datong pulverized coal and Zhundong pulverized coal pyrolysis processes based on wavelength modulation technique. The pulverized coal particle with diameter of 8 mm and mass of 360 mg is hung on the quartz tube, a high power CO2 laser is applied to rapid and uniform heating of the pulverized coal particle. The tunable laser beam goes through the quartz tube cross section with triple effective reflection, and the laser beam is at 10 mm below the pulverized coal. The measurement process continues until the pyrolysis process is completely over. At the beginning of the pyrolysis process, the volume fraction of CH4 increases rapidly, then gradually decreases until the concentration is zero, and the whole pyrolysis process lasts about 60 s. The volume fraction of CH4 of Zhundong coal at maximum release rate is twice of that of Datong coal, and the pyrolytic reaction of Zhundong coal is quicker, and much more CH4 gas can be generated by Zhundong coal.

The quantitative method named moving window partial least square (MWPLS) is applied to predicting the content of Cd in navel orange by analyzing the spectral information obtained by laser induced breakdown spectroscopy (LIBS). Five methods like standard normal variate (SNV), first derivative (FD), second derivative (SD), centralization and multivariate scatter correction (MSC) are utilized to process LIBS data and acquire better spectral quality, and the window width of MWPLS is optimized to select the area of wavelength correlated with Cd element. Meanwhile, MWPLS is compared with conventional partial least square method. The results display that the model built by FD is better when moving window is 61 wavelength wide and the range of wavelength is 218.61-222.55 nm. At this condition, the determinant coefficient of validation set, root mean square error of prediction (RMSEP), principal component and average relative error are 0.9953, 15.10×10-6, 12 and 7.43%, respectively. This study shows that the LIBS area for predicting Cd in navel orange can be screened by MWPLS coupled with suitable data preprocessing, and the prediction ability can be improved effectively.

Time-of-flight mass spectrum of freon 1110 (C2Cl4) under action of 400 nm femtosecond laser pulse is obtained by time-of-flight mass spectrometry technology. Three major fragment ions, C2Cl+4, C2Cl+3 and C2Cl+2 are discovered in the mass spectrum. Based on the density functional theory, the energy changes in dissociation channels of C2Cl+4 during photodissociation process are further calculated and analyzed at the basis set of B3LYP/6-311G++(d,p). The results show that C2Cl+4 needs to absorb energy during photodissociation process, which indicates that C2Cl+4 is more stable in the ozone layer. Besides, compared with the mass spectrum of C2Cl4 obtained with 800 nm femtosecond pulse laser which has been experienced by other researchers, and through calculating the proportion of each peak to total peak area and the chlorine isotope abundance ratio of major ions in the mass spectra, it is found that C2Cl4 is more likely to dissociate under infrared light radiation. Moreover, the potential energy surfaces of C2Cl4 and C2Cl+4 about C-Cl bond are scanned via the same basis set, and the saddle points are obtained. It is found that the activity of C-Cl bond of C2Cl+4 becomes higher and the C-Cl bond is easier to break than that in C2Cl4. Infrared spectrum and Raman spectrum of C2Cl+4 are calculated and analyzed, and UV-VIS spectrum is obtained with CIS method.

The vials easily crack in the filling process of freeze-dried products. Cracks and loose assembly of the vial plugs causes air to enter the vials, and thus leads to the metamorphism or degeneration of the freeze-dried products. A measurement system based on tunable diode laser absorption spectroscopy (TDLAS) was developed for fast and non-invasive leakage detection of vials. By analyzing the mole fraction difference of water vapor between the detection light path and the reference light path (Δx) and mole fraction of water vapor (xr) of the reference light path, the threshold at different conditions is obtained. The measurement accuracy of the system is validated firstly, and it reveals that the standard deviation of the system is less than 0.007%. Then, ten vials are detected when xr is 1.29%, 1.33%, 1.89%, 2.20%, respectively. Vials No.4 and No.8 are considered as leaked vials, since Δx is larger than the corresponding threshold at various mole fractions of water vapor xr, and the results are in good agreement with the real situation.

The silver film with a periodically arrayed micro-nano structure is chosen as the research object and its transmission characteristics are numerically simulated with the finite element method. The effects of the aperture size, the film thickness, the array period and the polarization state of the incident light on the transmission spectra of this micro-nano structure are analyzed. The results show that the transmission spectra are only sensitive to the change of the array period.