A method based on Mach-Zehnder interferometer (MZI) to generate arbitrary vectorial vortex beams in a higher-order Poincare sphere is proposed. The combination of half-wave plate and polarization beam splitter prism is used to adjust the amplitude of branch beam, and the two common half-wave plates are used to adjust the phase of the composite beam in order to generate and transform the vector vortex beam. The traditional experimental optical path is optimized, the energy loss of the beam is reduced, and the transformation of the vector vortex beam on the different high-order Poincare spheres is realized by the quarter-wave plate. Compared with the existing Mach-Zehnder interferometer-based vector beam generation method, the optical path structure is simple and the beam conversion efficiency is improved. Theoretically, the polarization state of each vector vortex beam on Poincare sphere with topological charge m=±1 is obtained by Jones matrix calculation. According to this method, a set of experimental light path of vector vortex beam is set up. The experimental results agree well with the theoretical analysis, which proves the practicability of this method.

Aimed at the application of smoothing of multi-color spectral dispersion in inertial confinement fusion facilities, an independent design and optimization method for main unit components, including electro-optic modulators, dispersion gratings and continuous phase plates (CPP) and so forth, is proposed. The effects of parameters of electro-optic phase modulators, dispersion gratings and the CPP on the laser-quad irradiation characteristics are simulated and analyzed. The parameters of optimized smoothing of multi-color spectral dispersion are proposed, and the effect of the smoothing parameters on the characteristics of longitudinal filaments of lasers is simulated. Results indicate that the irradiation uniformity on the target surface can be further improved when we optimize the parameters of electro-optical modulator and dispersion grating of different sub-beams. When different CPPs are implemented for different sub-beams in the laser-quad, the focal-spot uniformity can be improved effectively and the proportion of hot spots can be decreased significantly. Moreover, the beam quality of the laser beam is analyzed by the power spectral density. The simulation results show that the smoothing of multi-color spectral dispersion can effectively decrease the peak intensity and make the light intensity distribution more uniform, which is benefit to suppress filaments of laser beams.

The principle and design method of optical super-oscillation are introduced. A superoscillatory optical field with a local superresolution is experimentally obtained by pure amplitude-modulated spatial light modulator (SLM) and digital micro-mirror device (DMD). The experimental results show that the characteristic size of the superoscillatory field in the generated superresolution optical field is sixty percent of diffraction limit. The analysis of the spatial spectra used to validate the experimental results shows that the superoscillatory optical field does not generate spatial high frequency components beyond the diffraction limit.

Based on the chaos synchronization, a security-enhanced bidirectional long-distance chaos secure communication system is proposed. The results show that, under suitable parameters of dual-path injection conditions, low time-delay signature (TDS) and broadband chaotic signals can be generated from driving laser (DL). The chaos signals from DL are injected into two response lasers (RLs). By optimization of injection strength and detuning frequency, the optimized chaos signals with lower TDS and wider bandwidth can be generated and high-quality chaos synchronization between two RLs can be obtained. Meanwhile, the maximal synchronization coefficient between DL and RLs is lower than 0.1. Based on the high-quality chaos synchronization between two RLs, a security-enhanced bidirectional long-distance chaos communication can be achieved. Q factor of 20 Gbit/s decoded messages is more than 6 after a propagation over 120 km under dispersion shifted fiber used as channel, and Q factor of 1 Gbit/s decoded messages is more than 8 after a propagation over 140 km under normal single-mode fiber used as channel.

In order to improve measurement accuracy in the polarization mode dispersion (PMD) measurement system by the fixed analyzer method, the noise in the link should be eliminated. Here, a polarization mode dispersion measurement scheme based on empirical mode decomposition (EMD) adaptive filtering to mitigate noise is proposed. According to signal spectral characteristics, it is decomposed into a finite number of intrinsic mode functions (IMFs), which are arranged by frequency from large to small. The consecutive mean square error (CMSE) criterion is used for noise filtering and signal reconstruction, which effectively eliminates the noise impacting on the measurement results. The experiments compare results based on the EMD adaptive filtering method, Wiener filtering method and commercial instruments. The results show that this scheme is suitable for different types and lengths of fibers, and the maximum relative error between the measured result and the reference value is 0.74%. The measurement accuracy is improved obviously.

To adapt to the development trend of combining high precision fiber time-frequency transfer with optical fiber communication network, the time-frequency transfer performance of wavelength selection switch (WSS) which is commonly used in optical fiber communication network is studied. A system with high precision fiber time-frequency transfer is established based on the wavelength division multiplexing, bidirectional return and optical real time delay compensation scheme. The effects of output ports, output loss and variation of polarization state of input optical signal on the time-frequency transfer performance of the system are discussed. In addition, the open-loop and closed-loop performance of time-frequency transfer system including WSS and the influence of dynamic switching performance of WSS under closed-loop on the time-frequency transfer system are studied. The experimental results show that the effect of WSS on the fiber time-frequency transfer performance can be controlled, and it is proved that the high precision time-frequency transfer in the commercial optical fiber communication network with WSS is feasible.

A hybrid optimization algorithm based on shuffled frog leaping algorithm (SFLA) and least squares support vector machine (LSSVM) algorithm is proposed and applied to the feature extraction of multi-peak Brillouin scattering spectra. The penalty factor C and kernel width σ of kernel function in LSSVM algorithm are optimized by SFLA, which reduces the Brillouin frequency shift error caused by the local optimization. Multi-peak Brillouin scattering spectra in the same signal-to-noise with different line width and the same line width with different signal-to-noise ratio are presented by simulation analysis and experimental verification. The fitting fitness of the experimental data is 0.0067, the fitting degree is 99.99%, and the Brillouin frequency shift error is 0.18 MHz. The results show that the SFLA-LSSVM algorithm can precisely fit the multi-peak Brillouin scattering spectrum. The proposed algorithm has the advantages of high fitting precision, small mean square error and fast running speed. The SFLA-LSSVM algorithm is an effective fitting method in the feature extraction of multi-peak Brillouin scattering spectrum.

To solve the problems of depth location of underwater targets and complex underwater imaging environment during underwater teleoperation, an information acquisition system based on the camera array and an integral imaging three-dimensional reconstruction algorithm based on depth and sum modulus difference evaluation function are used to achieve the target depth estimation and clear imaging with occlusion simultaneously. A CCD camera automatic scanning array imaging system is established by the programming of LabVIEW software. Imaging and depth reconstruction experiments of occluded underwater targets are carried out. Errors of three independent targets′ reconstruction depths and the actual depths at different depth are 0.21%, 1.26% and 1.34% respectively. Experimental results show that this method can remove the occlusion and obtain the depth value of target simultaneously after only one reconstruction.

High repetition rate, large energy and narrow pulse width laser is widely used in the frontier fields of laser imaging, laser machining and precision measurement. Using the technology of electro-optical cavity-dumped and double rod series structure, which reduces the thermal lens effect and ensures the good matching mode of oscillation light and the pump light, the 1064 nm linearly polarized laser output with high efficiency, large energy and narrow pulse width is realized. Using the barium boron oxide (BBO) Pockels cell as electro-optical switch, and the 914 nm fiber-coupled semiconductor laser with low absorption coefficient is used to pump the Nd∶YVO4 crystal. Thus the thermal stability of the laser is improved. At the repetition rate of 7 kHz and the crystal absorption power of 79.6 W, a stable pulse laser output with a pulse width of 5 ns, maximum average output power of 35 W, and a single pulse energy of 5 mJ is obtained, and the corresponding optical conversion efficiency is 44%.

Femtosecond laser has important applications in such fields as industrial processing, laser sensing, military defense, and scientific research. A femtosecond fiber chirped pulse amplification (FCPA) system operating at 1 μm is reported. This system consists of a 1.5 μm all-fiber passive mode-locked laser source, a 1 μm nonlinear frequency converter, a two-stage Yb-doped amplifier, and a transmission diffraction grating pulse compressor. The center wavelength of the erbium-doped mode light source is 1.55 μm, the spectral bandwidth of 3 dB is 12.9 nm and the repetition frequency is 17.5 MHz. After power amplification, a 9.5 cm high nonlinear fiber is injected to generate 1 μm band dispersion wave with center wavelength of 1070 nm and 3 dB spectral bandwidth of 33 nm. Moreover, using this dispersion wave pulse as the seed source, the pulse output with repetition rate of 1.09 MHz is achieved by using a frequency selector of acousto-optic modulator. After that, the power is amplified to 11.4 W, and with the femtosecond pulse laser output with average power of 7.7 W, spectral bandwidth of 21.4 nm at 10 dB, pulse duration of 270 fs, and peak power of 26 MW is achieved after compression.

The heat dissipating performance of high-power laser diodes packaged by silicon carbide (SiC) ceramic submounts is investigated, comparing with the commonly-used aluminum nitride (AlN) ceramic submounts. The thermal resistance of SiC and AlN submounts packaged F-mount devices are measured by the thermal resistance instrument based on the structure function method. The thermal resistance of SiC devices is about 3.0 ℃·W-1, and the AlN ones is about 3.4 ℃·W-1. The measured thermal resistance of SiC devices is about 14.7% less than that of the AlN. The experimental data shows better heat-dissipating performance of SiC submounts. In addition, the output characteristics of devices packaged by two kinds of submounts are further tested. The output power of 915 nm single emitter of SiC device achieves 15.9 W at the continuous injection of 16 A, while for AlN device, the value is only 15 W. Test results demonstrate that the SiC packaged laser diode achieves higher power output.

The factors that influence the amplification efficiency of diode end-pumped Nd∶YAG slab laser amplifier are theoretically analyzed, and a master oscillator power amplifier continuous wave laser system is designed. A narrow linewidth 1064 nm fiber laser is used as the seeder, and series and then double pass on two Nd∶YAG slab laser amplifier is followed. The two Nd∶YAG slab laser amplifiers have the same configuration, with the slab of 150.2 mm×2.5 mm×30 mm, which are pumped in double end by diode laser array (DLA). The continuous laser is output when the amplifier is pumped at 21.6 kW, with output power of 5.4 kW, optical to optical efficiency of 24.8%, and beam quality β of 3.5. Furthermore, the beam quality could be improved to 2.5 with the help of spatial filter.

Aiming at the observability of the fixed position alignment of a strapdown inertial navigation system (SINS), the observability of each state variable of the system is analyzed by the method of singular value decomposition (SVD), in which the ten-state error equation of SINS is taken as the object of study. The results show that the state variables of the system are not completely observable and the azimuth misalignment angle has a low observability. In order to improve the observability of the alignment system, the state vector is reduced according to the results of observability analysis and the application characteristics of SINS, and the seven-order Kalman filtering model is obtained. Experimental results indicate that the seven-order model is more tolerant to the filter parameter and the navigation accuracy is higher than the original model．

A new approach to generate frequency doubled triangular waveform signals is proposed and verified through the combination of carrier suppression modulation and semiconductor laser injection locking. In the scheme, the continuous wave emitted by the external cavity tunable laser is modulated by a sinusoidal signal through Mach-Zehnder modulator to suppress the optical carrier. The modulated signal is divided into two branches. One signal remains unchanged and the other is launched into a distributed feedback laser to select and amplify higher-order harmonic components for six-fold signal generation. After controlling the relative phase and power ratio of the two signals, we achieve frequency doubled triangular waveform by overlapping the signals in the photodetector. In the experiment, sinusoidal modulation signals at the frequencies of 3 GHz and 4 GHz are applied to generate full duty frequency doubled triangular waveform with a frequencies of 6 GHz and 8 GHz successfully. Both theoretical analysis and experimental results prove that the scheme is feasible. It is a simpler and more efficient way to avoid the complex spectral line operation. Moreover, it has a distinct advantage in high-frequency triangular waveform generation.

This paper reports a laser diode (LD) end-pumped Yb∶YAG slab dual-wavelength laser amplifier with high power working at room temperature. The dual-wavelength stably operates at 1029.6, 1031.5 nm. Based on the broadband fluorescence characteristic of Yb∶YAG, the dual-wavelength amplification model is built and corresponding numerical simulation is taken to study the laser spectrum amplification output properties under different pump conditions. 940 nm laser diodes is used to pump the Yb∶YAG crystal at two ends. The seed laser with the dual-wavelength spectrum is injected from one end of the crystal and amplified. Experimental results show that continuous-wave (CW) dual-wavelength laser output power of 6.56 kW is acquired when the seed injection is 1.18 kW, which matches the simulation results. These theoretical and experimental researches of dual-wavelength laser amplification can lay the foundation for the applications such as high-power spectral combination, etc.

The problem of large spectral linewidth of ultrashort pulse laser is studied. The pulse evolution process in the laser cavity is simulated by RP Fiber software. The effects of different saturable absorber versus the pulse width and spectral linewidth on the laser are studied, and the cavity length and fiber Bragg grating (FBG) parameters of the laser are optimized. Finally, a passively mode-locked picosecond pulse erbium-doped ring fiber laser based on WS2 saturable absorber is designed according to the optimization results. The spectral linewidth of the output pulse is compressed by the narrowband FBG, and a narrow linewidth ultrashort-pulse output with center wavelength of 1549.4 nm, pulse width of 171 ps and 3 dB spectral linewidth of 0.02 nm is obtained.

In order to replace multi-stage fiber pre-amplification structure in a master oscillator power amplification structure, a grazing incidence slab laser amplifier with small signal and high gain is simulated and studied experimentally. The thermal conversion coefficient of the slab crystal is measured by an axicon structure caused by the linear temperature gradient in the slab. The results show that the thermal conversion coefficient are 0.37 and 0.28 for 0.1 mW and 1 W seed laser extraction, respectively. When the pump light power is 55 W, the maximum temperature rise difference of the slab between two cases is 16 K. Under small signal extraction, the temperature rise in the slab crystal becomes the main constraint on the gain increasing. The laser output power of 1.8 W is obtained when the power of seed laser is 0.1 mW and the pump light power is 50 W. The gain is as high as 43 dB, the horizontal beam quality factor M2x is 1.30 and the vertical beam quality factor M2y is 1.28.

Anti-Stokes scattering is the four-wave mixing effect of the frequency up conversion. Generally, the conversion efficiency of the anti-Stokes laser is lower. Therefore, it is particularly important for improving the performance of the laser through guiding experiment of theoretical optimization. In this paper, the rate equations of intracavity anti-Stokes lasers under plane wave approximation are normalized. By numerically solving the normalized rate equations, a group of universal theoretical curves are obtained to describe the operation of the intracavity anti-Stokes lasers. The influences of the compound normalized variables on the performance of the intracavity anti-Stokes lasers are analyzed. The normalized theory is verified with actual experimental data. The result indicates that the single pulse energy, pulse peak power and pulse width of the intracavity anti-Stokes laser estimated from the normalized theory are consistent with the measured data. The proposed normalized rate-equation model is proved correct and feasible.

To solve the problem of strayed light introduced by the shield in an inertial confinement fusion system, we establish a three-dimentional honeycomb structural model and propose a strayed light analysis method of shield. We also analyze the influences of the honeycomb curvature and central distance of two honeycombs on the strayed light. The results show that the laser is reflected through the shield, and there is always an area with the highest light intensity of the reflected light. The peak-to-valley of the reflected light intensity and total power of the light back to system increase with the increasing honeycomb diameter and honeycomb spacing of the shield. Based on this, the diameter and spacing of honeycomb should be controlled strictly when we design shield, so that to make the terminal optical system keep away from the area of highest reflected light intensity and let the strayed light distribute evenly in solid space.

As one of the most promising mid-infrared laser mediums in 3-5 μm wavelength region, Fe2+∶ZnSe crystal has many advantages in material property and conversion efficiency. The absorption characteristic of Fe2+∶ZnSe is investigated. A Fe2+∶ZnSe crystal with size of 10 mm×10 mm×5 mm and Fe2+ doping concentration of 4×1018 cm-3 is excited by a non-chain electric-discharge pulsed HF laser at room temperature. The maximum output energy reaches 65 mJ and the optical to optical conversion efficiency is 31%. The slope efficiency respecting to the absorbed pump energy is 37%.

The design of the direct-liquid-cooled thin-disk laser is detailedly discussed. It includes the choosing of crystal and coolant in the gain module as well as the design of the channel structure. Moreover, the advantages and disadvantages of two kinds of combination modes are analyzed. In the first mode, the incident angle of the beam and the cutting angle of the crystal should be controlled strictly. The theory calculations and analysis are given. In the second mode, the angles do not need to be specially selected, while the refractive index of the coolant should be close to that of the crystal. In the aspect of pump mode selection, the energy storage and aberration effects both in end-pumped and side-pumped lasers are analyzed. Theoretically, with the use of 10 pieces of Nd∶YLF thin-disks as the gain media and the refractive index matched liquid as the coolant, an average output power larger than 1 kW is achieved at the pump power of 5 kW, corresponding to an optical-optical efficiency larger than 20%. The theoretical analysis is basically consistent with the experimental results.

The catastrophic optical damage of the high power laser is studied, and the damage mechanism of the laser facet coating is analyzed. In order to increase the output power of the laser, the TiO2 is used to replace the Si as the high refractive index materials, the nonstandard film is set up to reduce the intensity of electric field. Meanwhile, the roughness of the film materials is optimized, and the ion source is used to clean and flux. The threshold of the catastrophic optical damage is effectively improved. The results show that the proposed laser has a maximum continuous output power of 13.6 W.

WC/SS316L composite depositon layer was successfully prepared on the 316L substrates by the supersonic laser deposition (SLD) technique. The deposition behavior, interfacial bonding, microstructural characteristics and electrochemical failure mechanism of the particles in these prepared composite depostion layers are analyzed. The results show that, due to the softening effect of laser irradiation, the SS316L particles show an excellent plasticity deformation ability in the high-speed impact process and can be effectively deposited. Under the combined actions of laser irradiation and plasticity deformation of high-speed particles, the SLD layer has a better interfacial bonding behavior than the deposition layer prepared by the cold spray (CS) technique. The micro-hardness of SS316L particles in deposition layers is obviously higher than that of the original powder, which is attributed to the working-hardening produced within plasticity deformation of high-speed particles. Moreover, the WC/SS316L interface is prone to electrochemical failure.

Single channel laser cladding layer is prepared on Ti811 titanium alloy surface using synchronous powder feeding laser cladding technology. Microstructure and phase composition of the layer are analyzed with utilization of X-ray diffractometer, scanning electron microscope and energy dispersive spectrometer. The microhardness of the layer is measured with utilization of micro-sclerometer, and friction and wear properties are measured with utilization of the friction wear testing machine and the white-light interferometry profilometer. The results show that the typical Widmanstatten structure is found in the layer. α′-Ti, α″-Ti, and β′-Ti are distributed in the crystal boundary surrounded by α-Ti, and the nano-Ti3Al particles are dispersively distributed in the layer. The highest microhardness of the layer is 480 HV, which is higher than that of the substrate. A large number of nano-Ti3Al particles are dispersively distributed in the layer. Under the action of particles, the friction coefficient decreases and the friction and wear properties increase.

The three-dimensional transient laser welding heat-flow coupling model for the filler metal feeding process and the combined heat source model are established, in which the welding driving forces, such as recoil pressure, surface tension, thermal buoyancy and gravity, are introduced. The volume-of-fluid method is used to track the gas-liquid interfaces of keyholes, and the effect of filler metal on the three-dimensional shape of keyholes and the flow behavior of molten pools is studied. The influence mechanism of the filler metal filling on the keyhole stability is analyzed. The research results show that the filler metal filling is unfavorable to the stability of keyholes and the keyhole bottom is prone to close. In the autogenous laser welding process, a flow from inside to outside and from bottom to top appears on the keyhole walls, which is favorable to the stable opening of keyholes.

The center overlap welding experiments of aluminum alloy and magnesium alloy sheets are carried out by the nanosecond laser technology, and the effects of nanosecond laser process parameters on the formation and mechanical property of Al/Mg welds are analyzed. The results show that the Al/Mg joints are successfully welded by the nanosecond laser and their shear tensile strength can reach to 86 MPa under the conditions of low energy input, high power density and high welding speed. In the laser power range of 5-10 kW, the penetration depth of welds possesses a linear relationship with the nanosecond laser power density, however a logarithmic relationship with the laser duration and the laser point energy.

The mechanisms of pore formation in the remelting zone under different protective atmosphere conditions are investigated by the laser remelting experiments of HT250 gray cast irons. The study results show that the pores in the remelting zone are dissolved pores under the argon shielding atmosphere, and the pores are dissolved pores and reactive pores under the open atmosphere. With the same process parameters, there are more pores in the melting zone under the open atmosphere than those under the argon shielding atmosphere at a low scanning speed, however, at a high scanning speed, the pores are basically the same under these two protective atmosphere conditions. When the laser energy density is relatively low, the main reason of pore formation in the remelting zone is the dissolving out of gasses from the gray cast irons.

The nitrogen passivation of GaSb by etching method layer by layer is conducted based on the plasma enhanced atomic layer deposition (PEALD) system, and the influence of etching cycle in the passivation process on the passivation effect of GaSb is discussed. The study results show that, the passivation effect is the best when the etching cycle number is 200. When the etching cycle number is smaller than 100, the passivation effect is the weakest. When the etching cycle is relatively higher (300-400), the larger the etching cycle number is, the weaker the passivation effect is.

In order to achieve the imaging resolution of 45 nm with a numerical aperture of 1.35 and a wavelength of 193 nm in the lithography exposure system of ultra-large scale integrated circuits, a novel optical variable attenuator is designed. The device cannot only control the light transmittance, but also adjust the exposure energy. The average transmittance of the attenuation surface decreases from 95% to 8% linearly when the light incidence angle changes from 20° to 40° , and light energy loss of the other three faces are less than 1% in this system. Optical films are designed and fabricated with fused silica as substrate, and LaF3 as well as AlF3 as optical films. Experiments are performed to investigate the attenuator performance, and the results show that the light transmittance is continuously tunable in the range from 8% to 90%, which satisfies the requirements of the system. Compared with traditional optical variable attenuators, the device is with wider attenuation modulation range and more stable attenuation, and it has potential applications.

By the plasma enhanced atomic layer deposition (PEALD) technique, the N δ-doped Cu2O films are prepared with NH3 as the doping source. The effects of N-doping on the surface morphology, optical and electrical properties of Cu2O films are studied. The study results show that the N-doping causes the lattice distortion and the surface roughness of the N δ-doped Cu2O thin films increases. The bandgap width of the N δ-doped Cu2O thin films increases from 2.70 eV to 3.20 eV, and the absorption edge becomes steep. The carrier concentration of the doped sample is 6.32×1019 cm-3, enhanced by one order of magnitude comparing with that of the un-doped samples (5.77×1018 cm-3).

In order to study the classification of ancient porcelains based on the physical structures of glaze layer, optical coherence tomography (OCT) technology combined with X-ray fluorescence spectroscopy (XRF) technology, scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) technology and laser Raman spectroscopy (LRS) technology are used to analyze the Celadon and Jun porcelains which are dated to the Jin and Yuan dynasties and excavated from the Qingliangsi site in Baofeng County, Henan Province, China. The glaze layers are classified qualitatively according to the characteristics of OCT images of glaze layers. The image texture analysis technique is used to characterize the OCT images of glaze layers quantitatively, and principal component analysis is performed based on the image texture parameters determined by the image texture analysis. The classification results of the enamel according to the OCT image are compared with the classification results of the chemical composition of the glaze obtained from XRF. The relationship between the chemical compositions of glaze layers and the OCT image feature are discussed based on the results of SEM-EDS and LRS.

A method to measure the laser damage threshold of optical component surface based on Gaussian pulsed laser spatial resolution is proposed. The energy density partition is performed on the Gaussian spot by setting the laser energy density difference. By analyzing the energy distribution of the Gaussian pulse laser spot and the distribution of the damage point, a laser energy density with zero damage density is obtained as the laser damage threshold of the measured element. At the same time, the international standard 1-on-1 laser damage threshold test method will be used to measure the surface damage threshold at the same sample. And the damage thresholds obtained by the two methods are compared and analyzed. It is proved that the laser damage threshold method based on Gaussian pulsed laser spatial resolution is used to solve the problem that the energy density of the space in the Gaussian spot and the inhomogeneous distribution of the damage point are regarded as uniform distribution in the international standard 1-on-1 laser damage threshold test.

In this paper, a high-precision laser tracking measurement method is proposed in order to meet the requirements of high measurement accuracy, large measurement range and real-time measurement in every filed of modern industry, which realizes precise tracking measurement of follow-up target. The laser tracking measurement system based on the four-quadrant detector can measure the incident laser spot offset that is relative to the center of the four-quadrant detector in real time. A fast response servo motor and the motion control card of programmable multi-axes controller (PMAC) are applied to build the closed-loop control system, which achieves high precision and fast laser tracking measurement. The experimental results show that the high-precision laser tracking measurement method proposed in this paper has good real-time performance and high measurement accuracy. When the tracking measurement of laser spot is within ±1000 μm away from the center of the four-quadrant detector, the error of spot offset is about 31.2 μm, and the average time of the laser spot returning the center of four-quadrant detector is 0.259 ms.

In the process of laser ultrasonic visualization, the external noise and incident wave lead to lower image quality and defect identification capability. In this paper, local statistic filtering is used to reduce the interference of speckle noise, and average gradient and entropy are investigated in order to evaluate denoising results. Two-order differential operator is applied to the enhancement of denoised image, and the image enhancement effects with different differential operators are compared. The penalty function is used to restrain the interference of incident wave on defect scattering wave. The variation trend of peak signal-to-noise ratio and structural similarity are investigated by weighting factor and regularization coefficient, and the method is compared with the method of suppressing incident wave by subtraction of adjacent waves. The results show that the laser ultrasonic visual image quality can be improved by image processing method, and the defect information can be highlighted.

The grating mosaic technique is an effective method to obtain the large-aperture grating of the petawatt laser system. The five degree of freedom parallel mosaic mechanism is designed. The macro/micro dual-drive technique of ball screw and piezoelectric ceramic achieves the location precision of nanometer level in the work range of millimeter level. Based on finite element method, the displacement coupling properties analysis shows that the mechanism has high linearity and the error of displacement coupling is nanometer level. The relative angle deviation of grating mosaic mechanism is less than 0.2 μrad. The displacement deviation is less than 20 nm. Two gratings with size of 200 mm×400 mm are installed in the proposed mosaic mechanism in order to conduct experimental study. The clear image of far-field focal spot is obtained, which proves that the proposed mechanism can meet the accuracy requirement of large-aperture mosaic grating system.

Extending temperature acceptance bandwidth in second harmonic generation (SHG) by cascading nonlinear crystals is a simple and efficient method. Based on the dispersion of air, a formula describing how dispersion of air affect the conversion efficiency is derived. Based on the formula, conversion efficiency of SHG of 1064 nm in cascaded KTiOPO4 crystals versus temperature is simulated, and corresponding experiments are conducted. In the experiments, conversion efficient is cosine distribute versus the distance between two cascaded crystals, and when the phase mismatch caused by dispersion of air is integer times of 2π, the maximum conversion efficiency reaches 47.9%, which is 12.9% higher than the maximum conversion efficiency in a single KTP crystal, and the temperature acceptance bandwidth is 78 ℃, which is two times broader than that in a single KTP crystal. The theoretical analysis is in good agreement with the experimental results. The research conclusions are conducive to extending temperature acceptance bandwidth for nonlinear frequency conversion by cascading crystals.

In order to solve the stimulated Brillouin scattering (SBS) damage by reflected diffraction of fused silica grating with large aperture, we establish the design and analysis model of grating, the reflected diffraction angle, focal length and efficiency from 1 to 6 orders reflected diffraction of the grating are calculated. The gain and intensity of SBS with modulated laser and original laser are analyzed based on SBS principle, and the reliability of the analysis is verified by an engineering example. The experimental results show that the SBS intensity is large, the grating element is seriously damaged and its service life is short when the phase modulation is not applied. Moreover, when the phase modulation is applied, the SBS intensity is less than the damage threshold of fused silica and the service life of grating element increases evidently. In the actual high power laser system, phase modulation must be applied to suppress SBS damage of grating reflected diffraction.

A subwavelength metal grating/dielectric/metal hybrid waveguide sensing structure is proposed. In the structure, the resonance mode of guided mode, surface plasmon polariton resonance mode and local surface plasmon polariton mode can be generated, and these modes are coupled with each other, resulting in two narrow band resonance defect peaks in the reflection spectrum. After studying the magnetic field distribution at the resonance defect peaks and the influence of structural parameters on the reflection spectrum, we analyze the resonance modes in the structure. According to the principle of mode resonance of guided mode and surface plasmon resonance, the relationships between the wavelength of resonance defect peaks and the structural parameters are established. The drifts of resonance peaks wavelengths are observed, and the dynamic real-time monitoring of the gas samples can be realized. The porous silicon is used as the sensing carrier, and the formaldehyde is used as the sample to be tested. The quality factor and sensitivity of the sensor are analyzed. The results shows that the quality factors of two narrow band resonance defect peaks are 42.3 RIU-1 and 78.5 RIU-1, and the sensitivities are 466 nm/RIU and 628 nm/RIU, respectively.

We propose a distributed fiber-optic vibration and temperature sensing system． The proposed system can obtain coupled light of two wavelengths on one sensing arm based on the structure of the dual Mach-Zehnder interferometer by employing the wavelength division multiplexing technique. The implement scheme can achieve the parallel detection of distributed fiber-optic vibration sensing based on laser interference and distributed temperature sensing based on Raman backscattering, thus the simultaneous detection of vibration and temperature is realized. The method effectively uses the sensing fiber-optic based on the dual Mach-Zehnder interferometer and realizes simultaneous detection of vibration and temperature at a distance of 10 km in the experiment. The positioning error of vibration sensing is ±30 m. The spatial resolution and temperature error of temperature sensing are 1 m and ±1.8 ℃, respectively. The advantage of the system is to combine laser interference with Raman backscattering effectively and realize simultaneous detection of vibration and temperature under the complicated condition. In addition, the proposed system effectively uses sensing fiber-optic and has great practical and economic value.

The laser scanning intensity is an attribute of point cloud. It is the optical power of echo from laser to target and can reflect the surface properties of the target. The surface properties of Phyllostachys edulis depend on its physiological growth characteristics. We analyze the information of laser scanning intensity of Phyllostachys edulis, model the relationship between trunk No. and laser scanning intensity for Phyllostachys edulis with different ages, compare the root mean square error between the fitting and measured laser scanning intensity so as to distinguish the bamboo age and verify accuracy of the constructed model. The results show that there is significant difference in laser intensity of bamboos with different ages and in different trunks, while the difference is not significant in laser intensity of bamboos in the same trunk. The distinguishing accuracy over 92.5% is realized. The polynomial model can efficiently distinguish Phyllostachys edulis age, which is helpful for estimating its biomass by three-dimensional terrestrial laser scanning.

Measurement method of two-dimensional tomography of gas temperature and H2O concentration distributions in non-uniform combustion flow field is proposed based on wavelength modulation spectroscopy (WMS). By using the measured 2f/1f signals, we measure the integrated absorbance after laser passing through the non-uniform field according to numerical simulation and iteration. Then, we realize the measurement of two-dimensional tomography of combustion flow field using the reconstructed algorithm. The numerical simulation for single Gaussian and step change distribution models is carried out with selecting two groups of spectral lines of H2O. Frequency division multiplexing technology is adopted to realize the measurement of temperature and H2O concentration distributions in the flat combustion flame. It is proved that the method based WMS has relative high reconstruction accuracy. For single Gaussian model, the reconstruction errors of temperature and H2O concentration are less than 2% and 2.5% using the lines of 7185.60 cm-1 and 7454.45 cm-1. It also can be seen that the reconstruction errors are small if the lines are sensitivity to the temperature while the reconstruction errors are big if the lines are insensitivity to the temperature. Experimental results show that the reconstruction results are agreement with the predicted values in the middle region of flame where the temperature has the tendency of continuous change, the reconstruction error is less than 3.2%. However, in the edge region of flame where the temperature has the tendency of step change, the reconstructed effect is not good because the WMS and algebraic iterative reconstruction algorithm are insensitive to field where the temperature has the tendency of step change.