A 2 μm pulsed laser damage threshold testing apparatus is set up according to the international standard ISO 21254, the surface laser damage threshold of infrared nonlinear optical crystal ZnGeP2 with different surface quality are measured, meanwhile, the influence of different laser parameters, such as pulse frequency, pulse width, etc, on the surface laser damage threshold testing results are analyzed. These testing results provide an important experimental reference to avoid laser damage to ZnGeP2 in practical use.

A new optical component named linear radial gradient-index lens (LRGIL) for generating Bessel beams with long non-diffracting distance and high beam quality is proposed. Based on the geometrical optics and the diffraction integral theory, the principle of LRGIL generating Bessel beams is analyzed. Using Math CAD to simulate the beam propagation process, LRGIL has the function of traditional axicons and the diffraction-free distance of the Bessel beam is variable with the thickness and the gradient index of LRGIL. A long diffraction-free distance up to 3 m is also obtained in the simulation. Besides, LRGIL has other advantages such as more durable and flexible, it has great potential applications in experiment and production.

The whole-process transient radiative transfer model of Gaussian pulse laser in anisotropic scattering medium is established using Monte Carlo method, then the probabilistic model of scattering direction is constructed and the process of coordinate system transformation is deduced. On the basis above, the temporal distribution and differences of Gaussian pulse laser echo characteristic is calculated and analyzed. Research result shows that pulsed increase/decrease of temporal echo signal is from the conversion of other signal categories and ahead or lag of itself; with the forward scattering enhancing, target-echo signal intensity increases, peak time forwards and temporal broadening weakens, while scatter- echo signal responses are in contrast and change weakly; target- echo characteristic associates with [0°, 90°] forward scattering region directly, as well as scatter-echo characteristic associating with [90° , 180° ] backward scattering region. The conclusion can provide theoretical guidance for performance improvement of active detection systems by pulse laser and anti-stealth detection of ground objects.

High average power linearly- polarized nanosecond- pulsed, modulated diode seeded thuliumdoped fiber laser based on master oscillator power amplifier (MOPA) system is reported. The modulated seed laser delivers 20 ns pulses with tunable repetition rate from 200 kHz to 1 MHz. The MOPA yields 100 W average output power at 200 kHz repetition rate. The pulse duration reduces to 6 ns during amplification due to gain reshaping effect, which lead to a higher peak power of 83 kW with pulse energy of 0.5 mJ. To the best of our knowledge, this is the first demonstration of average output power exceeding 100 W from a linear polarization, thulium doped fiber laser using modulated diode as a seed.

ooe, oeo, eoo, eeo, eoe and oee types phase matching angle calculation formulas in uniaxial crystals are provided. The formulas used for ooe, oeo and eoo types can be applied to both collinear and non-collinear configurations. The formulas used for eeo, eoe, and oee only can be applied to collinear configuration. The numerical methods are provided for non-collinear configuration for eeo, eoe and oee types. The relationship of refractive index between uniaxial crystal and biaxial crystal in principal plane is given. Using this relationship, one can use the method for uniaxial crystal to calculate the phase matching angle in biaxial crystals through replacing the refractive index. The phase matching angles in some common nonlinear crystals are calculated for researchers′ reference.

In order to obtain an optical beat source for THz generation, a dual- wavelength distributed Bragg reflection (DBR) semiconductor laser with high order Bragg gratings (HOBGs) is designed. The DBR laser is fabricated by ultraviolet lithography technology with strip width of 100 μm, grating period of 9.5 μm and grating groove width of 1.36 mm. High power continuous-wave dual-wavelength lasing is obtained at injection current from 0.9 A to 1.2 A and the side mode suppression ratios of short wavelength mode and long wavelength mode are larger than 35 dB and 39 dB, respectively. The 3 dB spectrum full width at half maximum of the two wavelength modes are both 0.04 nm. The wavelength difference of two lasing modes is larger than 0.58 nm, which is appropriate for an optical beat source for THz generation. When the injection current is 1.2 A, the output power of HOBGs DBR laser is up to 88 mW from one cavity facet. A kind of high power dual-wavelength HOBGs DBR laser is propsed, which provides a new solution for dual-wavelength semiconductor laser to mass production.

To improve the simulation accuracy of scattering process in Monte Carlo radiative transfer model, a phase function sectional-weighted sampling method is put forward based on the characteristics of scattering phase functions, and its accuracy and feasibility are validated subsequently. Transmissivity and reflectivity of infrared laser (1.06 μm) in non-spherical sand aerosol are calculated using Monte Carlo method. Its results are compared with those of Henyey- Greenstein (H- G) phase function sampling method and phase function uniformly- sampling method. Simulation results show that, phase function sectional- weighted sampling method can improve the calculation accuracy of scattering angles obviously and reduce the sampling error of phase function. Compared with H-G phase function sampling method, transmissivity calculated by H-G formula is underestimated, while reflectivity calculated by H-G formula is overestimated, and the deviation of two methods increases with the increasing of propagation distance. Compared with phase function uniformly sampling method, the relative error of transmissivity increases with the propagation distance increasing, while the relative error of reflectivity changes oppositely.

A compact and robust, passively air cooled picosecond 1064 nm Nd:YVO4 oscillator mode-locked by semiconductor saturable absorber mirror (SESAM) is demonstrated. Based on the theoretical analysis and experimental verification of the passive mode locking method, a more precise formula describing the pulse width of a mode locked laser is proposed. The laser operates at pulse duration of 15.5 ps and a repetition rate of 100 MHz with output power of 210 mW. It is proven to be TEM00 mode according to measured beam quality factor of M2=1.15. The root mean square (RMS) power fluctuation is less than 1% . The footprint of the laser is only 350 mm × 150 mm × 50 mm. Thus, this laser can be a reliable seed source to be amplified for more applications in research and industrial fields.

A high-power picosecond mode-locked Nd∶YVO4 laser system with high repetition-rate of 80 MHz is reported. When the pump power is 22.4 W, the oscillator provides the output power of 5.1 W with signal-tonoise ratio more than 60 dB and a pulse duration of 23.7 ps. The semiconductor saturable- absorber mirror (SESAM) of oscillator can work for more than 500 h without any damage by selecting reasonable SESAM parameters and suitable cavity. The power is amplified to 44 W by two stages of power amplifier end-pumped by a continuous- wave 888 nm laser diode (LD). Optical- optical conversion efficiency of amplified system is more than 25%. The beam quality factor M2 after amplification is less than 1.5.

Photovoltaic cell performance determined by its parameters is of vital importance for laser wireless power transmission system. The output characteristics of single crystal silicon photovoltaic cell illuminated by diode laser operating at 940 nm are investigated. The relationship between output characteristics and two factors, i.e. laser intensity and temperature, are studied. The results indicate that with the increasing of laser intensity, short-circuit current increases linearly in low intensity levels and then begins to saturate. Both open-circuit voltage and efficiency has a maximum value with increasing laser intensity. The experimental maximum efficiency of photovoltaic cell at 293 K is 29.49%. In the range of 283 K~308 K, short-circuit current is independent of temperature in low intensity levels and decreases linearly in high intensity levels. Open-circuit voltage and efficiency decrease linearly with increasing temperature. However, their temperature coefficients vary with the variation in laser intensity. The relationship between series resistance and efficiency is also simulated. It shows that small series resistance and the reduction of recombination for photovoltaic cell are essential for efficient energy conversion under high intensity laser illumination.

The principle and experimental results of laser frequency noise suppression by all- fiber ring resonator is provided. A saturated absorption spectroscopy and fiber ring resonator double-loop-stabilization for laser frequency is realized by Pound- Drever- Hall technique. The frequency noise of stabilized laser is measured by a heterodyne Mach- Zehnder interferometer and obtain the frequency noise suppression larger than 40 dB when Fourier frequency f < 100 Hz . At 1 Hz offset, the frequency noise power spectral density of stabilized laser is less than 100 dB Hz2 /Hz and the frequency noise suppression is 60 dB.

Passive harmonic mode-locking of erbium-doped fiber laser with graphene as a saturable absorber is proposed. Graphene saturable absorber is obtained via mechanical exfoliation method by peeling highly oriented pyrolytic graphite repeatedly. When the pump power is 135 mW, the laser operates at fundamental repetition rate of 1.646 MHz with pulse duration of 1.82 ps and 3 dB bandwidth of 1.7 nm. With the pump power and adjusting polarization in the cavity appropriately increasing, the laser operates at several harmonics of fundamental repetition rate and the highest repetition rate achieved is 77.36 MHz, which corresponds to the 47th harmonic. The output power, pulse duration and single pulse energy for different harmonics have been studied.

With good machine performance and spectrum characteristic, Ho:YAG crystal has become one of the choices for high-repetition-frequency 2 μm laser. In order to acquire high efficiency and high power 2 μm Ho:YAG laser with high-repetition-frequency, radiation mechanism of singly-doped Ho3 + laser are analyzed. And the calculation model of conversion efficiency in high-repetition-frequency Ho:YAG laser is established through rate equation. The effects of the parameters such as output coupler transmittance, laser mode size, ratio of pump-laser mode and Ho-doping atomic number fraction, on the conversion efficiency in high-repetition-frequency Ho:YAG laser are analyzed by this calculation model. The design scope of those parameters is also put forward. The theoretical simulation results are verified through experiments.

WC/Co- Y2O3 alloying layers are prepared by laser alloying on 38CrMoAl steel substrate. The influences of Y2O3 mass fraction on microstructure and properties of the layers are investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness tester, and friction wear testing machine. The results show that the layers with different mass fractions of Y2O3 are mainly consist of austenite, martensite, Fe3W3C and WC phases. With the increase of the Y2O3 addition, the contents of the Fe3W3C, nano- WC, and austenite gradually increase, whereas the content of martensite gradually decreases. But when the mass fraction of Y2O3 is more than 1.0% , the content of the nano- WC begins to decrease, the solidified microstructure is slightly coarsened. Because of these changes in the microstructure, the hardness and wear resistance of the layers first increase and then decrease, that is, the layer has the highest hardenss and the better wear resistance as the Y2O3 mass fraction is 1.0%.

To avoid the angular deformation of T joint in high-strength aluminum alloy plate of large aircraft, a method that equips skin back with auxiliary heat source (AHS) is proposed to prevent angular deformation effectively. A welding model applicable to this welding method is developed based on finite element software ABAQUS, the material and geometrical nonlinear finite element methods and the thermal-elastic-plastic finite element method for moving heat source are applied to simulate the thermodynamic coupling behavior as well as to analyze the temperature field, residual stress and welding deformation in welding process. The deformation of the weld joint before and after the addition of the AHS is measured by experimental method. The findings show that the flexural deflection and angular deformation achieved through numerical computation completely consist with the experimental result, which has proved the effectiveness of the finite element methods developed.

Laser cladding technology is based on horizontal or small-angle reference plane at present. The poor powder converging characteristic when the nozzle is inclined is solved by adopting the technology of“hollow laser beam and internal powder feeding”. The variable postures moving of nozzle with larger inclined angle are realized by controlling laser processing robot. The axis direction of powder feeding nozzle is always coincident with curved surface normal direction. The uniform coating on the curved surface with large inclined angle are accomplished. The forces of molten pool on the curved surface are analyzed. The influences of different inclined angles on molten pool size and scanning path on cladding layer are also analyzed. The width of cladding layer keep stable by controlling the collimating gas rate, and the morphology and performance of curved surface cladding layer with different inclined angles are investigated detailedly. The results show that the thickness of cladding layer is uniform, the section microstructure is dense without obvious cracks and pores and the cladding layer is combined well with substrate. A new method for repairing complex metal parts is provided.

In computer-assisted surgery (CAS), the surgical instruments in patient need to locate. To avoid the line of sight (LOS) problem in the optical tracking (OPT), magnetic tracking (MT) technology is usually adopted. A new multi- dipole model of cylindrical magnets, which can avoid limited tracking range and lower tracking accuracy problems that appear in signal magnetic dipole model of cylindrical permanent magnet, is proposed. This model approximates cylindrical magnetic dipole as multiple dipoles ranging along the magnet′s axis, and tracking results are obtained through adaptive particle swarm optimization (APSO). Compared with classical method, the proposed model can ensure its validity in near magnets region. Experiments show that, the solution can decrease positioning error by 15.5%~31.6%, and decrease orientation error by 10.5%~24.4%.

To build the system of computer- aided diagnosis for coronary heart disease and provide some parameters for lesion detection, a new method for coronary artery lumen segmentation based on the coronary artery centerline is proposed, which is the result of the algorithm of improved minimal cost path with second order Hessian vessel filter. The method uses the centerline as the tracking path to get every cross section of the vessel, and then ray casting is used for locating the coronary artery lumen along every ray. The disperse coordinates of the lumen location in every ray can be fitted to an outline of the coronary lumen in every cross section by piecewise spline fitting. As a result of all the outlines of coronary artery lumen in cross section reconstruction, a 3D coronary artery lumen can be built by marching cubes algorithm. The result of the method, which has high computing performance, has nice visualization of vessel lumen and can be the basis of the vessel parameter calculation.

Nondestructive investigation and analysis of the internal structure of three-dimensional (3D) bio-printed hydrogel scaffolds is very important for the design, fabrication, and biological functions of engineered tissue scaffolds. Swept- source optical coherence tomography (SS- OCT) is applied to nondestructive imaging and quantitative analysis of 3D bio- printed hydrogel scaffolds. 3D bio- printing technique is used to produce four representative designed geometries of hydrogel scaffolds. High-resolution SS-OCT visualizes the three-dimensional internal structure of the scaffolds, identifies the difference between the designed model and as- produced construction, and detects the printed defects such as fused pores, deformation of pores, breakages of flow channels. The automatic imaging analysis algorithms are developed to quantitatively characterize the pore size (PS) and its distribution, strut size (StS), volume porosity (VP), and pore interconnectivity (PC). It concludes that OCT may be a key tool for the design optimization, process refinement, function realization of 3D bio- printed hydrogel scaffolds.

The method of combined multiple phase screens and split-step Fourier to simulate the drift behavior of circular-Airy beams in atomspheric turbulence is proposed. The propagation of circular-Airy beams in turbulence is simulated theoretically and experimentally. Through comparing the drift behavior of Airy beams with related Gaussian beam, it is found that the drift distances of circular-Airy beams are less than that of reference beams. Therefore, employing the circular-Airy beams as information carrier has potential application for long-distance transmission.

A significant yet not widely realized topic is analyzed when the field-widened Michelson interferometer (FWMI) is used as a spectroscopic filter in high spectral resolution lidar (HSRL), that is, tolerance evaluation for anti-reflection (AR) coating reflectivity of the FWMI. Since AR coatings on the interface of different materials in the FWMI cannot be with 100% transmittance, a part of the radiation would be reflected back once the light passes through these surfaces, and these reflected lights would be further reflected many times in the interferometer as stray lights. The influence mechanism on the FWMI performance due to the multi-reflection caused by AR coating reflectivity is analyzed, and an iterative algorithm is proposed to estimate the relationship between the performance of the FWMI and the reflectivity of the AR coating quantitatively, using the spectral discrimination ratio (SDR) as the performance metric. Results show that the reflection induced by AR coating will degrade the suppression ability of the FWMI to the aerosol scattering while it imposes no effect on the molecular transmittance. The overall consequence is to make the SDR of the FWMI decrease. This method can provide considerable reference for the tolerance evaluation of AR coating reflectivity in FWMI, and is one of the important aspects that can guarantee good design performance of the FWMI.

Molecular beam epitaxy conditions of resonant tunneling diode photodetector (RTD-PD) are researched. The structure of the detector with In0.53Ga0.47As absorption layer and In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As double barrier structure is designed. The growth quality of In0.52Al0.48As material under different Al flux and growth temperature is tested and the optimal growth conditions are determined through X-ray diffraction and atomic force microscope test. The growth quality of In0.53Ga0.47As material under different Ga flux is researched. As there are punctate embossments on In0.53Ga0.47As surface grown under constant temperature, the In0.53Ga0.47As material is grown under varying temperature and the punctate embossments are eliminated. Two RTD-PD samples grown under constant temperature and varying temperature are fabricated. The current-voltage and photo response test show that the sample grown under varying temperature reaches higher peak current and photo response.

The laser and pulse positon modulation (PPM) modulation technology as a whole is studied. The concept based on PPM characteristics of fiber laser is proposed. Theoretical research of single pulse energy, peak power, pulse width of the Q-switched fiber laser is studied, and characteristic curves between the pulse peak power of Q-switched fiber laser and the laser parameters are obtained through simulation. Combined with three PPM signal model analysises, the relationships between the transmission rate, the required power, the required bandwidth of the three PPM modes and laser parameters N are obtained. From the experiment modulation, the influences of the pumped current, the initial transmittance and the cavity length of the optical laser on the transmission rate and required bandwidth of the three PPM modes are concluded.

A fiber-optic temperature sensor based on fluorescence intensity ratiometric (FIR) method is proposed and investigated experimentally. Plastic optical fibers are employed for transmitting the excitation light and collecting the Rhodamine B (RHB) and Rhodamine110 (RH110) fluorescence signals. Given that the fluorescence intensity of RHB is temperature-dependent while that of RH110 is temperature-independent, the temperature can be measured by calculating the fluorescence intensity ratio of these two dyes. To achieve a desired performance, the optimal integration ranges of fluorescence intensities of the two dyes are identified via considerable experimental tests. Indeed, a precise measurement is achieved in experiments. The feasible range of temperatures is from 25 ℃ to 60 ℃ ; a minimum rms temperature error of 0.38 ℃ and a sensitivity of 0.0134 /℃ are achieved. Further, the proposed sensor is proved to be insensitive to fiber bending for bend radii exceeding 9 mm. Thus, the sensor can be used for in situ temperature monitoring.

In high power fiber amplifier system, stimulated Brillouin scattering (SBS) becomes the primary limiting factor to achieve high power because of its relatively lower threshold. In order to improve SBS threshold, a new method to suppress SBS is presencted, which needs to modulate the incident seed laser both in phase and intensity. A model of SBS dynamics to numerically simulate the SBS threshold is established after using this method. The simulation results show that this method using phase modulation and intensity modulation simultaneously can greatly enhance SBS threshold under the condition of narrow linewidth output. When 20 W seed laser is put into a fiber amplifier system after phase modulation of 100 MHz, 10 V and intensity modulation of 10 MHz, 4 ns, the output power of fiber amplifier can reach 1127.4 W, which is 18 times of that of the SBS threshold for single frequency laser.

To the crack monitoring of the carbon fibre reinforced plastics (CFRP) concrete composite arch, an experiment is conducted to monitor the appearance of the crack with bare fiber Bragg grating (FBG) strain sensors. The location of fiber Bragg grating (FBG) is determined via mechanic analysis, two kinds of pasting method is studied: local and distributed coupling (in the first case the measurement fiber is attached to the host structure at two points, in the second case the measurement fiber is attached along the whole active region). A comparison between the data of FBG and strain gauge is conducted to validate the precision and stability of FBG. The test results show the quantitative rule of crack initiation via K value standard deviation criterion. The initial cracking can be monitored by arranging the FBG sensors appropriately, good consistency can be achieved between FBG and strain gauge.

The magnetic field sensitivity is the main source of errors in fiber optic gyroscope (FOG) and the optical fiber coil is a major sensitive source. In an external magnetic field, a nonreciprocal phase error will be generated in a FOG and decrease the gyro precision. Related experimental results show that the axial magnetic field sensitivity in the polarization maintaining (PM) fiber coils is more obvious than the radial magnetic field sensitivity. The axial magnetic field sensitivity is studied, including Faraday shift caused by fiber random twist, Faraday nonreciprocal phase caused by geometry twist and non-Faraday nonreciprocal phase caused by vertical component magnetic field. Theoretical results are simulated and verified by the experiments. Results show that nonreciprocal phase caused by vertical component magnetic field is the main reason for axial magnetic field sensitivity and closely related to the fiber coil′s skeleton radius. Furthermore, the smaller the skeleton radius is, the greater the axial magnetic field sensitivity will be.

Optical phase lock loop (OPLL) is an important part in the coherent laser communication system. A castas digital optical phase lock loop system is designed, which is used in the inter- orbit coherent laser communication and Doppler frequency shift tracking. The system uses field programmable gate array (FPGA) as the central processor. The local laser (LO) is 1550 nm central wavelength sideband modulation injection locking laser, which has high tuning speed and narrow linewidth. Compared with the traditional OPLL, the proposed system provides more stability and frequency acquisition speed. It can achieve phase lock in frequency deviation range of 140 MHz and the phase locked time is longer than 1 h in the experiment. It can also achieve 20 MHz/s Doppler frequency shift tracking and provide the experimental supports for followed- up inter- orbit coherent laser communications.

A semi-analytical method of rapidly estimating the maximum communication distance of an underwater laser communication system is proposed. For a given underwater optical channel, only two simulation times are needed to obtain the maximum communication distance. Once the system conditions are changed, no more simulations are needed. Two reference distances through simple mathematical operations based on the parameters of underwater optical channel are initially deduced. Than a separate simulation is conducted for each reference distance. Finally, an equation for calculating the maximum communication distance is deduced based on theoretical analysis. The simulation results are compared with experimental ones and are found to coincide well with each other. The validation of the semi-analytical method is proved.

To the problem of the peak detection that could not be adaptively solved in the multi-peak fiber Bragg grating (FBG) signal, a self-adaptive multi-peak detection algorithm is proposed. This algorithm uses the sliding mean filtering method to remove the noise in spectral signal, and combines with the Hilbert transform to adaptively segment the peak area of the multi-peak spectrum. By analyzing the asymmetric characteristic of spectral peak, a peak value is compensated by the strategy based on the asymmetric generalized Gaussian model for improving position precision of spectral peak. Experimental results show that the proposed algorithm could gain higher accuracy and better stability than the comparing algorithms, and the detection error is under 1 pm. The proposed algorithm impacts on the multi-peak detection of distributed sensor networks.

Supercontinuum generation by dual-wavelength pumping in photonic crystal fiber(PCF) with threezero dispersion wavelengths is proposed. The spectrum extended from near infrared to mid infrared. Evolutions of pulse are modeled based on the nonlinear Schrodinger equation by predictor- corrector split- step Flourier method when the pulse travels in a tellurite PCF. The impacts of the fiber length and pulse peak power on the spectrum are discussed respectively. The result reveals that a combined visible and infrared supercontinuum spectrum spanning from 690 nm to 3150 nm after 10 cm traveling distance when the fiber is pumped by two pulses centred at 1 μm and 2 μm simultaneously with pulse width of 100 fs, repetition frequency of 200 kHz and peak pulse power of 10 kW. The spectrum has good continuity and flatness.

To deal with the hale phenomenon at the image edges, image hue、tone and brightness distortion problems in the classic dark channel theory algorithm, enhancement dark channel algorithm of fog image based on the total variation (TV) model is proposed.The rough transmission image based on the dark channel theory mathematical model is smoothed by the TV model. The image is segmented by the tolerance mechanism and distinguishes sky areas, so as to solve the halo phenomenon in the image highlight area. According to the dark channel theory mathematical model, it gets a defogging enhancement image from the inverse solution. Through the subjective observation and objective evaluation, the algorithm is better than the classic dark channel algorithm in the overall and details.

The impact of cubic phase plate decenter on the imaging of wavefront coding system is analyzed, and the phase component of pupil function of wavefront coding system with the tilt and decenter parameters is calculated. It presents that decenter can also enlarge or reduce the phase factor and the amount of defocus. The simulation indicates that the decenter makes the system modulation transfer function (MTF) drop through changing the energy distribution and the sagittal or meridional length of point spread function (PSF). It also indicates that the effect of z-direction decenter is lower than that of x-direction or y-direction decenter. The experimental results show that decenter has lower influence on PSF in a certain range, and the clarity of restored images has excellent consistency in the range of depth of focus, but extension of depth of focus drops with decenter. The experimental results confirm the analysis of decenter. This study has high application value in the space optical system, microscopy system, and infrared imaging system with the wavefront coding technology.

The periodic hole array is fabricated on GaAs substrate by holographic lithography and wet etching. The double exposure in holographic lithography is adopted with optimized exposure time of 60 s. Wet etching solution with 1∶1∶10 volume ratio of H3PO4, H2O2 and H2O is adopted to etch the hole array for 30 s. Images of scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the hole array has a period of 528 nm, etching depth of 124 nm, with perfect surface morphology, good fringe continuity and uniformity.

Yb:KGW laser material is well suited to build diode-pumped pulse lasers in watt region because of its broad gain bandwidth of 24 nm, large emission cross section of 2.8×10- 20 cm2 and good thermal conductivity of 3.3 W/(m·K). A passively Q- switched Yb:KGW laser is obtained using a transmission- type topological insulator Bi2Se3 as a saturable absorber. The achieved maximum pulse energy is 4.7 μJ and the peak power is 3.13 W for a pulse duration of 1.5 μs.

Novel Ga-Sb-S chalcogenide glasses doped with Dy3 + ions are synthesized. Their thermal stability, optical property, structure and mid-infrared (MIR) emission property are studied. The glass thermal stability against crystallization is significantly improved by slightly adjusting the glass composition, and therefore the fibers with good optical quality are drawn. The Dy3 +-doped Ga-Sb-S glasses show good thermal stability, excellent infrared transparency, low phonon energy, and intense emissions around 2.95, 3.59, 4.17 and 4.40 μm. The substitution of a small amount of Sb with As reduces the crystallization tendency of the glass during the fiber drawing without making remarkable effects on the emission property. Spectral analyses indicate that the quantum efficiencies of the 2.95 mm and 4.17 mm emissions of Dy3 + ion in the Ga-Sb-S glass are 88.1% and 75.9%, respectively; and the respective stimulated emission cross sections are 1.1×10-20 cm2 and 0.38×10-20 cm2. The high quantum efficiencies and large stimulated emission cross sections of the MIR emissions in the Dy3 +- doped Ga-Sb-S glasses make them promising gain materials for the MIR lasers.

A short pulse(6 ns)laser with wavelength of 532 nm is employed to mill Y-TZP ceramic. The relationship between power and groove width by single-pass machining is explored, and the relationship between threshold and pulse number is analyzed to make sure the threshold of Y-TZP. Also the variation of removal rate and quality with different parameters is analyzed to determine the optimal process parameters further. the micron-sized twodimension structure is conducted further. The results show that the square of groove width is proportional to logarithmic peak pulse laser power, and the calculated laser spot radius is matched with measured value. The material threshold decreases with the increase in the number of pulses. The removal rate is up to the maximum, 1.35 mm3/min, in the optimum combination of scanning speed, power and repetition rate. The blind hole of diameter 500 mm and steps in square cavity structure of width 200 mm and depth 100 mm are obtained by optimizing laser processing parameters. The two-dimension structures are no crack and better processing quality and the surface roughness Ra is 3.746 mm.

A composite method combining the laser cladding and plasma spraying is adopted to prepare the fluorinated bio-ceramic composite hydroxyapatite (HA) coating. The mixed powder of HA, calcium fluoride (CaF2) and titanium (Ti) is laser cladded on the Ti-6Al-4V substrates to produce the transition layer, on which HA·CaF2 powder is plasma sprayed as Ca10 (PO4) 6Fx (OH)2-x rich ceramic layer. The influence of F content on the phase composition, bonding strength, surface morphology and biological activity of the composite coating is studied by tensile test, simulated body fluid (SBF) immersion test and X-ray diffraction (XRD)、scanning electron microscope and energy dispersive spectrometer (SEM/EDS) analysis. It is shown that the bonding strength of the above composite coating increases up to 20.1 MPa and reaches its maximum value of 28.4 MPa when x=1.5, the crystallinity and the biological activity of the coating as well as the number of the cracks in the coating surface increases with x, the coating with optimal comprehensive performance is obtained when x=1.0~1.5.

Using the first-principles plane-wave ultrasoft pseudopotential method based on density functional theory (DFT) system, the study on titanium dioxide surface adsorption hydrogen halide gas (HX, X=F, Cl, Br) and oxygen vacancy oxidation characteristics is carried out. The calculation results show that: 1) The surface containing oxygen vacancy adsorbed hydrogen halide gas easier, whose adsorption method is chemical adsorption, among them, HF and HCl reduced by surface oxygen vacancy while HBr oxidized by surface oxygen vacancy, and the stable level of adsorption is HF>HBr>HCl; 2) adsorption hydrogen halide gas molecules can improve optical properties including dielectric constant, absorption coefficient and reflectivity of the TiO2 (110) surface, and the order of improvement ability is HF>HBr>HCl.

Antireflection properties on material surfaces are of great value in many fields including solar utilization, sensing, stealth, aerospace technology, military, etc. Through the interaction of picosecond laser with metallic materials, unique micro/nano hierarchical structures are produced on Cu, Al, Ti, and H13 steel surfaces, realizing significant antireflection properties through the ultra-broad spectrum band from ultraviolet (UV) to infrared (FIR) region. Wherein the total reflectance of the micro/nano structured Al, Ti, and H13 steel surfaces in the UV-VIS-NIR region are reduced down to around 10%, 5%, and 5%, respectively. The average reflectance of the disordered porous structures covered by abundant nanoparticles on Cu surface in the UV-VIS, UV-NIR, UV-MIR, and UV-FIR regions are reduced down to around 3% , 6% , 9% , and 10% , respectively, exhibiting extraordinary ultra- broad- band antireflection property. The formation mechanisms of the ultra-broad-band antireflection property as well as its relationship with surface micro/nano structures are discussed.

Starting from the Maxwell equation and material density equation, the vector theory of simultaneous gain and loss stimulated Brillouin scattering (SBS) is developed for the first time. During the derivation, the effect of electrostriction on SBS is described through mathematical express. At the same time, it is found that the parameters (linewidth and Brillouin frequency) differ from each other in gain and loss spectrum theoretically. Moreover, the vector models in Jones space and Stokes space are concluded. It′s the most comprehensive vector theory of SBS as far as concerned. The theory complete the system of SBS, and will make numerous differences in the fields of SBS-based polarization effects, polarization pulling and birefringence measurement. Based on the vector theory, the effects of birefringence and polarization on average SBS gain are simulated and analyzed.

Measuring the thickness of metal sheets is an issue of great importance in production facilities and in other industrial applications. The conventional triangulation method is not suitable for the detection of rough surfaces and semitransparent or multi- scattering materials. Therefore, an adaptive two- wave mixing interferometer based on the photorefractive Bi12SiO20 (BSO) crystal is designed to measure the thickness of an aluminum metal sheet. A holographic grating, formed by the photorefractive effect, diffracts both the signal beam and the reference beam to demodulate the ultrasonic vibration. The system, in which the low frequency noise caused by the environmental perturbation can be filtered automatically through the dynamic holography grating, is demonstrated to be a highly sensitive, convenient, and inexpensive non- contact technique for thickness measurement and ultrasonic vibration detection on rough surfaces. The technique has the potential for the detection of hidden defects, especially when it is combined with laser ultrasonic technology.

A kind of dual-band surface plasmons (SPs) Bragg reflectors, based on metal-insulator-metal (MIM) waveguides, is proposed. By adjusting the width of the insulator layer periodically, a quasiperiodic SPs Bragg grating is achieved in the MIM waveguide structure. According to projection theory, transmission spectrum of SPs produces two band gaps, in which SPs′ propagation is prohibited under the suitable structure parameters. When inserting the defect layer of appropriate length into the structure, two SPs defect modes appear, whose center wavelengths are respectively located at around 1310 nm and 1550 nm. Because of the SPs Fabry-Perot effect, the center wavelengths of the defect modes change periodically as the change of defect layer length. The electromagnetic simulation is conducted by commercial software Comsol to verify the design.

The anti-reflection properties of silicon based solar cell with parabolic cone array structure is studied. The parameters of structure that influence the anti-reflection performance, such as the height of parabolic cone array, the period and the duty factor, are analyzed by using of the finite-difference time-domain method. The analysis shows that the reflectivity tends to reduce as the height and duty factor of structure increase. According to the simulation result, less than 3% reflectivity can be achieved in the whole response spectrum of silicon solar cell (wavelength from 300 nm to 1200 nm) for 5 groups of parameters, i.e. the base diameter of parabolic cone is 128, 160, 213, 256, 320 nm respectively, with the array’s height of 600 nm and the period of array equal to the base diameter. A novel composite structure based on parabolic cone is also proposed, which reduces the reflectivity to 1%. It provides a novel design approach for the anti-reflective surface of silicon-based solar cells.

Two-color quantum correlation between fundamental (1.56 mm) and second-harmonic (780 nm) fields is investigated by an external cavity- enhanced periodically poled lithium niobate frequency doubler. Centers wavelength of the system at 1560 nm and 780 nm are in the wave band of quantum states transmission and quantum storage, respectively. So this kind of system can be employed for researches of practical quantum information processing. When the second-harmonic power of 10 mW is obtained with the conversion efficiency of 45%, 1.2 dB quantum correlation between fundamental (1560 nm) and second-harmonic (780 nm) fields is observed.

In order to extend the dynamic range of the Lidar measurement, a signal acquisition system based on simultaneous analog and photon counting fusion method is designed. The signal acquisition system is comprised of the universal data acquisition card and universal photon counter card, a dual-channel preamplifier which is designed for the simultaneous analog and photon counting measurement by using the technique of multistage amplification. A testing system is configured with a Lidar signal simulation device. According to the plateaus characteristics of the photomultiplier tube (PMT) and the differential pulse height distributions measured by the testing system, the supply voltage of the PMT and the discriminator level are selected. The performance of the analog channel and photon counting channel of the signal acquisition system and the practicability of gluing two channels are tested. Experimental results show that the designed signal acquisition system has better performance than TR20-160, the Lidar transient recorder from LICEL. The signals from two channels are suitable for being glued together, and the dynamic range of the Lidar signal acquisition system is extended by the gluing.

Direct detection Doppler wind lidar based on Fabry-Perot interferometer has been demonstrated for its capability of atmospheric wind detection ranging from troposphere to mesosphere with high temporal and spatial resolution. However, bias would emerge while retrieving the radial velocity during the observation and an external wind reference is needed to eliminate this bias. Reasons for this bias are theoretically analyzed and results show that the ambient temperatures of Fabry-Perot interferometer (FPI) and seeder laser are main effects. Then this effect of temperature is learned by experiment. By precise control of the ambient temperature of FPI and seeder laser separately, laser transmission through calibrated FPI, which depends upon the temperature, is studied. Using the instrumental function of the FPI, the frequency bias dependence on temperature is obtained. The experimental results show that the temperature coefficient of frequency bias for seeder laser is 1650 MHz/K while the one for FPI is 799 MHz/K, which means the precision of ambient temperature should be theoretically better than 0.004 K for seeder laser and 0.007 K for FPI in 355 nm Doppler wind lidar system.

A point cloud simplification based on the information entropy of normal vector angle is proposed, in view of the difficulty to ensure the optimal of precision and speed of simplification. The principal component analysis is used to estimate the normal of each point and the angle between normal vector and reference plane is computed. The K-nearest neighbor search algorithm is used to determine K-nearest neighbor points, and the local entropy of normal vector angle is proposed according to information entropy. The local entropy represents the features of surface. The point cloud is gradually simplified according to the different local entropy, the more points of convex region are retained and more points of plane are simplified, the non-uniform simplification is realized. The experimental results show that the proposed method can achieve a balance of precision and speed of simplification.

The active laser detection technique has a broad application prospect in the antimissile and air defense. However, the aerodynamic flow field around the planes and missiles causes serious distortion effect on the detection laser beams, according to the complicate physical process of the laser propagation in the“cat-eye”lenses and aerodynamic flow field, distortion propagation calculation method is performed. The physical optics propagation equations for the incidence and reflection process are calculated using Collins formula and angular spectrum diffraction theory respectively. In addition, turbulent performance of the aerodynamic flow field is estimated according to the propagation theory through a random medium, the root mean square (RMS) optical path difference (OPD) and Strehl ratio of the turbulent optical distortion are obtained. Computational fluid mechanics and propagation distortion calculation of the detection laser beam are performed with the hemisphere-on-cylinder turret as an example.

Terahertz time- domain spectroscopy provides us a powerful tool to carry out a fast and accurate measurement of optical constants of materials in terahertz range. The thickness determination of sample has a large influence on extracting the refractive index of materials. At the same time, the thickness of sample is generally difficult to be accurately measured. In order to avoid the influence from the measurement error of sample thickness on the determined refractive index, it is useful to develop a method which simultaneously determines the thickness and refractive index of sample. Due to the roundtrip reflected signal is weaker, the method presented by Duvillaret from the aspects of calculated frequency range and iterative algorithm is improved, making the calculated results more accurate and the operation more convenient. The thickness and refractive index of polyethylene and silicon wafer are determined as an example so that to verify the effectiveness of this method.

Vanadium oxide (VOx) films are deposited by radio frequency (RF) magnetron sputtering. Effects of sputtering powers on structure, optical and mechanical properties of the vanadium oxide films are investigated. Deposition rate, crystalline structure, surface morphology are measured by the profiler, X- ray diffraction, and scanning electron microscopy, respectively. The spectrophotometer, ellipsometer and nano-indenter are employed to test the optical properties such as transmittance, reflective index, absorption, mechanical properties of hardness and elastic modulus. The results show that all of the film samples are transparent with transmittance of more than 80% within the optical range. The deposition rate, hardness and refractive indices within the visible range monotonously increase with increasing sputtering power. While surface roughness of the films increases firstly and then decreases with increasing sputtering power. It is found that the sputtering power has influence on the crystalline structure as well.

The films of nanoscale-carbonare is formed through laser exfoliation of graphite on the substrate silicon (Si) without a catalytic layer and the chamber is vacuumed to 1.33×10-4 Pa in the growth process. The femtosecond (fs) laser exfoliation process is investigated at different laser fluences and deposition time. The composition of the carbon films deposited at different pulse energies and irradiation time are detected by the visible Raman spectroscopy. Scanning electron microscope (SEM) and atomic force microscope are used to display the surface of the thin films. The results show that the deposition time influences ratio of ID/IG, microstructure, the grain size of the carbon. High-intensity femtosecond laser pulse energy can promote the crystallization of carbon particles. Some special particles (pattern-snowflake-like，cube and quadrangle), which are formed by femtosecond laser pulse ablates a graphite at a high laser fluence, particles are found on the sample surface.