Due to their atomic-level thickness and unique optoelectronic properties, the transition metal dichalcogenides (TMDs) have been received widespread attention and research. The controllable preparation, novel optoelectronic properties and optoelectronic applications in many fields, such as photodetection, light emission, spin and energy valley electronics of TMD, have been reported widely. From the three perspectives of material preparation, optoelectronic properties and applications of TMD, these works are reviewed.

Two-dimensional (2D) materials possess unique structures and optical/electric properties, thus have important applications in the fields of energy, environment, and high-performance optoelectronic sensing, etc. The research on nonlinear optical properties of 2D materials has drawn extensive interest globally. Here, we simply reviews the researches on 2D materials from the aspects of their preparation methods, crystalline/energy band structure, and nonlinear optical properties, etc. The self-assembled or composite films of optical nonlinear nanocrystals are another kind of important optical nonlinear materials. Considering their macroscopic two-dimensional nature, and to make this review more comprehensive, here we categorize this kind of material to quasi-2D material, and make a brief introduction to the researches mainly on their nonlinear optical properties and corresponding applications, as a complimentary review on the research of nonlinear optical materials.

Vector solitons play important roles in modern communication and nonlinear optics. Mode-locked fiber laser provides an important platform for investigation of vector solitons. Processing of vector soliton in a carbon nanotube mode-locked erbium fiber laser is reviewed. Various types of polarization processing trajectories have been identified. The experiment results show the presence of polarization processing of vector soliton which is as a nonlinear attractor, and indicate the possibility of a new type of mode-locked fiber laser. The application and development of the new type of mode-locked fiber laser are prospected.

Thanks to the unique two dimensional quantum confinement effect and elimination of coupling perturbation between layers in two-dimensional (2D) materials, graphene, transition metal chalcogenides (TMDs) MX2(M=Mo, W, Ti, Nb, et al.; X=S, Se, Te, et al.) and black phosphorous (BP) exhibit unique performances in electronics and photonics (compared to their bulk materials). This review mainly introduces the research progress on 2D materials including synthesis, physical properties, and ultrafast nonlinear optical performance and the devices based on the research results in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, and the prospect also is discussed.

Due to the ability of local control of light by breaking through the limit of light diffraction, nanostrucrures with localized surface plasmon resonance (LSPR) have gained plenty of attention from the photonic community since its origin. LSPR has played important roles ranging from localized field enhancement effects to the realization of metamaterials. This paper briefly summarizes ultrafast nonlinear optics of nanostructures with LSPR and its applications, with an emphasis on saturable absorption effect of unconventional surface plasmon nanomaterials and their applications in ultrafast lasers. Finally, a prospect for its potential developments is given.

Two-dimensional (2D) layered materials possess unique electron structures and quantum size effects, and have received extensive attention in the fields like optoelectronics devices. Among them, the 2D group IV-VI semiconductors have become one of the research focuses recently due to the advantages as low-cost, earth-abundant, and environment-friendly characteristics. The unique crystal structures of the 2D group IV-VI semiconductors are introduced, and the research progress on their preparation methods including mechanical exfoliation, liquid phase method and vapor deposition is reviewed. The research status of 2D group IV-VI semiconductors in the fields of effect transistors and optoelectronic devices is discussed. The suggestions are presented aiming at the current issues in the preparation and device applications and the future research directions.

As a new kind of 2D carbon nanomaterial, graphene has wide application prospect in many fields such as energy storage device, electronic device and composites, due to its excellent physical, chemical and mechanical properties. Industrialized production of graphene is one of the researching hotspots in materials science all over the world. Among the variant methods for preparing graphene, electrochemical exfoliation owns advantages such as fast, efficient, and environment friendly, etc., and it provides a probability to realize industrialization. Firstly, this paper reviews the latest research processes in preparation of graphene and graphene-like (BN and MoS2) material from electrochemical exfoliation at home and abroad. And the reaction mechanisms are discussed. Then, the research status and applications of graphene in the field of optoelectronic device are briefly introduced. Finally, the further expectation of graphene is proposed.

Metal halide perovskites possess excellent photoelectrical properties and have extensive applications in the fields like solar cells and photoelectric detection. They also show wonderful emission properties and full band emission in the visible range can be realized by adjusting the type and ratio of halide atoms. In addition, the full width at half maximum of the emission light is narrow, which makes this kind of materials widely used in the fields like display. These properties make metal halide perovskites very suitable as laser gain materials. Moreover, the low-dimensional metal halide perovskites themselves can be used as a natural optical cavity, which makes lasing possible. Much significant progress has been made on the related research.

Pulse fiber lasers operating at 3 μm mid-infrared spectral region have numerous applications in defense, military, biomedicine and atmospheric communication. The graphene two-dimensional materials have drawn great attentions as saturable absorbers in the mid-infrared spectral region owing to their highlighted advantages such as convenient integration and compact all-fiber structure. We introduce the atomic structures and the optical properties of two-dimensional materials including graphene, black phosphorus, topological insulators, and transition metal sulfide. The mechanism and characteristics of the pulse mid-infrared fiber lasers based on these two-dimensional materials are introduced. Recent experimental achievements in the area of mid-infrared pulse fiber lasers utilizing two-dimensional materials are summarized. The future prospects of two-dimensional materials based pulse fiber lasers are also discussed.

Using the saturated absorption properties of vanadium dioxide (VO2), we achieve picosecond pulse laser output by adjusting waveguide laser via evanescent-field absorption mode. The pulse duration, repetition frequency and energy of output laser can be adjusted by controlling the temperature of VO2. VO2 membrane on neodymium-doped yttrium aluminum garnet (Nd∶YAG) waveguides can be used as the saturable absorber, whose saturable absorption is directly observed during the transition from the insulator to the metallic phase. Through the evanescent-field interaction of VO2 membrane with waveguide mode, the optical absorption of VO2 increases significantly. Benefiting from the unique thermal-driven optical properties of VO2, the waveguide lasing at 1064 nm exhibits effective switching of operation between the picosecond pulses and the continuous-wave (CW) regime. Due to the thermal hysteresis feature of the saturable absorption of VO2 membrane, the CW and picosecond pulse laser can be generated at the same temperature by either cooling or heating treatments. This work opens a way to achieve thermally controlled active integrated light sources in a chip-scale platform.

Organic-inorganic heterojunctions are formed by combining 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA) with molybdenum disulfide (MoS2) monolayer or graphene and their fluorescence properties are studied, respectively. In the MoS2/PTCDA system, the fluorescence intensity is greatly enhanced, because the MoS2 surface promotes the epitaxial growth of PTCDA. However, in the graphene/PTCDA system, the fluorescence intensity is obviously reduced due to the transfer transition of photo-induced electrons in the heterojunction.

We report a switchable dual-wavelength soliton fiber laser based on graphene ternary composite, that is, graphene/SnO2/PANI film. The graphene composite is synthesized by the liquid-phase ultrasonic method, the composite is transferred into the laser cavity by the polymer-film method. The as-prepared graphene device not only can act as an excellent saturable absorber for mode-locking, but also induces a highly third-order nonlinear optical effect to form a filter for dual-wavelength pulse generation in the laser. By exploiting the dual-function of this device, the switchable dual-wavelength soliton operation of the fiber laser is stably initiated with a minimum pulse width of 1.25 ps, a fundamental repetition rate of 2.13 MHz, a pulse energy of 1.51 nJ and peak power of 1.2 kW.

Due to their unique optoelectronic properties, recently the black phosphorus quantum dots (BPQDs) has attracted considerable attention. By introducing the microfiber-based BPQDs photonics device into the erbium-doped fiber laser cavity, the single and dual-wavelength pulse cluster phenomena are achieved because of the characteristics of saturable absorption and high nonlinear effect of BPQDs. In the case of single wavelength pulse cluster, each pulse cluster contains 9 pulses, which has different time intervals. While in the case of dual-wavelength pulse cluster, each wavelength corresponds to one sequence of pulse cluster, which has different amplitudes and time intervals. These results help to deepen the understanding of multi-wavelength fiber laser and pulse cluster dynamics, and further demonstrate that the BPQDs can act as the saturable absorber with excellent performance into many fields, such as ultrafast optics.

The saturable absorber Bismuth Telluride nanosheets are synthesized via optical self-assembly method, and the nonlinear optical response characteristics are obtained. By introducing the saturable absorber into the Er-doped fiber laser, the Q-switched fiber laser can deliver the pulse laser with pulse duration of 2.91 μs , wavelength of 1564.94 nm with the pump power of 170 mW. With the modulation of continuous wave laser on nonlinear absorption devices, the pulse duration and repetition frequency tunable Q-switched fiber laser is realized.

Tungsten disulfide (WS2) is widely used in the fabrication of optoelectronic devices due to its remarkable saturable absorption characteristics. All-fiber passively Q-switched Er-doped fiber lasers based on WS2 saturable absorber (WS2 SA) are studied. With pulse laser deposition method, WS2 is uniformly grown on the tapered fiber surface. The gold film is deposited on the surface of WS2 to avoid WS2 being oxidized, and this method increases anti-interference capability of WS2 SA. With the balanced twin-detector method, the modulation depth of 15.2%, saturation intensity of 2.84 MW/cm2 and unsaturated loss of 78% of WS2 SA are measured. Stable Q-switched output pulse sequences of fiber laser with different pump powers are obtained when we rotate the polarization controller. When pump power ranges from 300 mW to 630 mW, the laser repetition rate can be tuned from 174 kHz to 250 kHz. Experimental results show that the narrowest pulse width is 780 ns, the maximum output power is 18 mW, the single pulse energy is 23.5 nJ, and the signal-to-noise ratio is 85 dB. The proposed Q-switched fiber lasers have good stability.

The feasibility of γ-PGA/MoS2 nanocluster synthesized with the assistance of γ-poly glutamic acid (γ-PGA) is discussed. Thermal conversion performance of γ-PGA/MoS2 nanocluster under near-infrared laser is analyzed. γ-PGA and (NH4)2MoS4 which is the precursor of MoS2 nanosheet are dissolved into distilled water, and γ-PGA modified MoS2 nanocluster is synthesized from bottom to top with hydrothermal method. The diameter of nanocluster is (197.3±26.6) nm. Nanocluster configuration may be relevant to the coordination between Mo4+ ion and oxygen atom belonging to the carboxyl group of γ-PGA. During the hydrothermal reaction process, generated MoS2 nanosheets may form clusters due to the existence of coordination, and the oxygen atoms in γ-PGA molecular chain are the center. Nanoclusters show excellent colloidal stability, photothermal conversion performance (with mass extinction coefficient of 11.23 L·g-1·cm-1) and admirable cytocompatibility, and they are expected to be applied to the field of photothermal therapy for tumor.

n-butyl mercaptan modified molybdenum disulfide nanosheets (MoS2-C4) are synthesized by simple one-pot method. The structure, component, morphology and electrical bistable properties of the samples are investigated. In the reaction process, n-butyl mercaptan is not only used as a sulfur source but also used as the surfactant. X-ray diffraction (XRD) test indicate that the obtained sample is MoS2 with hexagonal system. The sheet-like morphology is confirmed by the transmission electron microscopy (TEM) and atomic force micros (AFM). And the bigger nanosheets are self-assembled by the lesser nanosheets. The absorption spectrum of the sample is tested and the location of absorption peak reveals that the sample is 2H-MoS2. Electrical bistable device is fabricated by the mixture of prepared nanosheets and polyvinylcarbazole (PVK). And the device exhibits obvious electrical bistability by I-V test.

In this paper, we fabricated thin-film saturable absorber by mixing 2D material tungsten diselenide (WSe2) and polymer polyvinyl alcohol (PVA). The WSe2-PVA saturable absorber (SA) was incorporated in an erbium-doped polarization maintaining (PM) fiber laser, and stable Q-switched operation was realized. An all PM cavity can reduce environmental perturbation on the cavity birefringence. Based on this PM cavity, we investigated the stability of WSe2-PVA SA in the Q-switched operation. It is found that when the heat accumulation reached a certain threshold in the SA, the polymer substrate firstly melted and more heat accumulateed quickly. As a result, WSe2 was damaged, showing a significant increase of SA loss.

A structure based on the dielectric and graphene coating is presented to control the Goos-Hnchen shift. The influence of structural parameters on the resonance angle and the Goos-Hnchen shift near the resonance angle are studied with the transfer matrix method. The numerical simulation results show that the resonance angle increases with the increase of the dielectric layer thickness, but decreases with the increase of the graphene Fermi energy. The magnitude of the Goos-Hnchen shift increases first and then decreases with the increase of the dielectric layer thickness, while decreases monotonically with the increase of the graphene Fermi energy. The influence of the dielectric layer thickness on the resonance angle is more significant, while the influence of the graphene Fermi energy on the Goos-Hnchen shift is more significant.

The WS2 is used as a saturable absorber in 2 μm band. A low-threshold passively Q-switched Tm, Ho∶LuLiF4 laser with a typical X-type four-cavity structure is demonstrated. The experimental results show that the Q-switched operation starts at the absorbed pump power of 260 mW and becomes stable when it is over 650 mW. When the absorbed pump power is 2000 mW, the output power is 88 mW, corresponding to the typical pulse duration of 4 μs, the repetition frequency of 16.89 kHz, and the maximum single pulse energy of 5.21 μJ. The results show that the WS2 material can be used as a saturable absorber for passively Q-switched lasers in 2 μm band.

Benefiting from the surface plasmon resonance effect, the gold nanorod saturable absorber possesses the properties of tunable broadband of saturable absorption and fast nonlinear response. It can also easy integrate with a variety of laser resonators, making it a promising saturable absorber with a wide broadband. The passively Q-switched 1 μm solid-state laser using gold nanorods as saturable absorbers is demonstrated. The gold nanorods are directly spin coated on the output coupler, and introduced in the laser resonator as saturable absorbers. Passively Q-switched operation of a LD pump Nd∶YVO4 laser at 1064 nm is realized accordingly. The pulsed laser output with a maximum average output power of 540 mW, a minimum pulse width of 138 ns, and a pulse repetition rate of 602 kHz are achieved when the pump power is 7.5 W.

Argentum nanorods (ANRs) with the absorption wavelength of 2 μm are prepared and employed as a saturable absorber in a 2 μm passively Q-switched laser. A laser diode (LD) pumped by 2 μm passively Q-switched laser is designed with a compact linear cavity. When the absorbed pump power is 5.73 W, average output power of 118 mW, repetition rate of 24.32 kHz and pulse width of 1.455 μs are obtained.

Numerical simulation is used to study the effect of pump wavelength on mid-infrared supercontinuum generation when femtosecond pulse is transmitted in As2S3 suspended-core microstructure optical fiber. The transmission characteristics and evolution process of femtosecond pulse with different pump wavelengths in As2S3 suspended-core microstructure optical fiber are analyzed by using split-step Fourier method to solve the generalized nonlinear Schrdinger equation numerically. The analytical results demonstrate that the flatter and wider mid-infrared supercontinuum of 1-7 μm can be obtained when the pump wavelength is 2300 nm, locating in anomalous dispersion region and closing to zero dispersion wavelength. And the wider mid-infrared supercontinuum of 1-7.5 μm can be obtained when the pump wavelength is 2500 nm, locating in anomalous dispersion region and keeping away from zero dispersion wavelength. But the flatness of mid-infrared supercontinuum with 2500 nm is slightly worse. This study has a significant reference value for selecting pump wavelength and optimizing mid-infrared supercontinuum.

Based on patterned graphene, an ultra-thin broadband terahertz metamaterial absorber with the thickness of 33.254 μm (about 1/7 of the incident wavelength) is designed. The bandwidth with an absorptivity of above 80% can reach 1.422 THz. The simulation and analysis results show that the absorption characteristics of this absorber is polarization-independent and insensitive to the incident angle. The absorbed energy of this absorber can be adjusted effectively by changing the chemical potential of graphene. In addition, the absorption performance can be improved when the thickness of polyimide interlayer increases.

The finite element model for human lumbar spinal L3-L4 is described by three-dimensional reconstruction method-marching cubes (MC). With some vital soft tissues on spine, such as anterior ligament, opisthodetic ligament, yellow ligament and fiber ring added, the complete three-dimensional finite element model of spine is rebuilt precisely. Then the finite element model is divided into mesh and the corresponding material properties of all parts are set. Finally, load and boundary conditions with different directions are defined to simulate the stress and displacement of normal model and intervertebral disc swelling degeneration model under different conditions. Which can provide biomechanical basis on the clinical diagnosis and treatment of intervertebral disc bulge and intervertebral disc protrusion by analyzing its biomechanical properties.

Resonant fiber optic gyro (RFOG) has attracted many attentions due to its advantages such as short-sensitive fiber and small size. The influences of laser linewidth, fiber ring resonator (FRR) and detection technology on the sensitivity of RFOG are analyzed. According to the detection method for RFOG signal, a formula of RFOG sensitivity limited by photoelectric detector sensitivity and a correction formula of RFOG sensitivity considering laser linewidth and 90° polarization-axis rotated splice are derived. The sensitivity influenced by error and noise of digital phase modulation voltage is studied based on multi-beam interference principle. The simulation results show that, in order to get high sensitivity, the length of FRR should be selected according to laser linewidth, and the length of two sections of fibers in both sides of 90° polarization-axis rotated splice should be set as odd times of the half-beat length of polarization maintaining fiber. Additionally, the root-mean-square of digital phase modulation voltage noise should be less than 0.22 V. The work provides theoretical guidance for the design of high precision RFOG.

The influence of spatial chirp on broadband ultrashort pulse laser system is analyzed. An experimental method for studying spatial chirp in SG-II-5 PW setup with wavefront sensor is proposed. In experiments, the wavefront feature of broadband ultrashort pulse laser is collected after the pulse passing through the stretcher and multi-stage spatial filters, and the lateral spatial chirp and the offset of the wavefront aberration centre relative to the optical axis of the system are measured. The dispersion regulator is adjusted in real-time to eliminate the spatial chirp in the laser system. The wavefront distributions before and after the spatial chirp elimination are compared, and the theoretical simulation shows that the focusing performance and the far field energy concentration of laser from SG-II-5 PW system are improved obviously.

The mathematical model of the nonreciprocity phase error generation of Sagnac fiber coil under the shock mechanical stress is established based on Hooke′s law and the elastic-optic effect theory. The influence of Young′s modulus of adhesive on the Sagnac fiber coil is discussed. The influence of Young′s modulus of the fiber adhesive on the Sagnac fiber interferometer error is verified by simulation and experiment. The results show that the higher the Young′s modulus of the adhesive is, the more stable the system is.

The high power single frequency laser at 507.4 nm is proposed based on the high efficient frequency doubling technology of a 1014.8 nm room-temperature fiber laser amplifier. High efficient frequency doubling is realized in a high gain ring cavity with a normal incidence lithium triborate crystal. The double frequency efficiency is up to 61.5% and the output power is up to 3 W. The experimental data and simulated results of the input-output characteristics of the frequency doubling are coincide. The double frequency efficiency is insensitive with the input power at the peak working point when the input power of infrared laser is more than 4 W. The power fluctuation in root mean square is 1.7% in 1.5 h. The high power single frequency laser at 507.4 nm can be both used to generate the 253.7 nm ultraviolet laser for laser cooling of neutral mercury atom by barium boron oxide crystal, and to detect the transition of ytterbium atom from 1S0 to 3P2 state, and related experiments.

The laser beams emitted from a pair of 520 nm/1.45 W green diode lasers are shaped and focused on a Ti∶sapphire laser crystal to complete the pumping process. The intracavity dispersion is compensated by using the GTI (Gires-Tournois interferometer) mirrors. The stable Kerr-lens mode locking state is achieved with an output pulse width of 91 fs, an output power of 208 mW, and a single pulse energy of 1.59 nJ. The narrowest pulse width of 82 fs is further realized after the optimization of cavity-type parameters and the maximum output power reaches 232 mW when the cavity length is shortened.

In order to achieve Q-switched pulse output of the CO2 waveguide laser, a half-external cavity laser is necessary to insert the Q switch in the resonator. We study the relationship between the output power of the rectangular waveguide half-external cavity CO2 laser with the waveguide aspect ratio m=2 and the optical structural parameters of the resonator. We compare the output powers of the laser whose waveguide port clings to the plane mirror, and obtain the relationship between the loss generated by the resonant cavity mode coupling to the waveguide port and the radius of the total reflection mirror R, and the distance between the total reflection mirror and the waveguide port d. Based on the Fresnel diffraction integral theory, the relationship between the coupling efficiency of the resonator and R, d when m =2 is calculated with the Simpson algorithm variable step length theory. The results show that d=R and d=10 mm are two optical and structural parameters which are suitable for the rectangular waveguide half-external cavity CO2 laser with a high aspect ratio, where larger R will induce higher coupling efficiency.

Research on high power continuous-wave and cavity dumped Yb∶YAG thin disk lasers is conducted. Based on the plane-wave quasi-three-level laser model, the parameters of Yb∶YAG thin disk laser are optimized. The maximum output power in laser diode pumped Yb∶YAG thin disk laser at 1030 nm reaches 100 W with an optical-to-optical efficiency of 50.2% and a slope efficiency of 56.8%. By using RTP electro-optical Q-switched, the cavity-dumped Yb∶YAG thin disk laser at 1030 nm is constructed. A constant pulse duration of 20.2 ns is achieved within the repetition rate from 10 kHz to 100 kHz. The maximum output peak power at 1030 nm achieves 109.8 kW with a repetition rate of 10 kHz.

In a fiber amplifier which is based on master oscillator power amplifier structure, generating a seed source with narrow linewidth and stable temporal property is very important for suppressing nonlinear effects and obtaining multi-kilowatts power. The random fiber laser based on Rayleigh scattering and Raman gain has been widely investigated due to the superior performance on temporal stability. Taking 1018 nm fiber laser based on self-fabricated fiber grating as the pump source, a 10.6 GHz, 1067.6 nm random fiber laser as the seed source is achieved by adopting a half open cavity. A three-stage power amplifier structure boosts the seed to 42.8 W, the linewidth is maintained during the power scaling process, which shows that the light source has a great potential to be used as the seed source of multi-kilowatts fiber amplifier.

An automatically and broadly tunable Ti∶sapphire laser based on the control of LabVIEW is designed, which is implemented by feedback controlling the angle of intracavity birefringent filters (BRF). The feedback signal is generated by LabVIEW program after the laser output wavelength measured by a wavelength meter is obtained. Then the one-to-one relationship between the BRF angle and the laser output wavelength is established based on the measured wavelengths. The BRF angle corresponding to the setting wavelength is calculated and then controlled by LabVIEW procedure, so that the laser wavelength can be automatically tuned without wavelength meter, which simplifies the laser system. With the automatically tunable system, the tuning range of the designed Ti∶sapphire laser is 110 nm.

π- and σ-polarization laser emission in a-cut Nd∶YVO4 crystal are selectively realized with a polarization beam splitter (PBS). The difference of polarized fluorescence spectra of tetragonal Nd∶YVO4 crystal results in the performance difference between the π- and σ-polarization laser outputs. The π- and σ-polarization laser performances of a-cut Nd∶YVO4 crystal with 4F3/2 to 4I11/2 and 4F3/2 to 4I13/2 energy level transitions are investigated by rotating the laser crystal along the optical direction and active polarization selection of PBS reflected beam. When the pump power is 11 W, π-polarization laser at 1064.3 nm with output power of 5.5 W and σ-polarization laser at 1066.7 nm with output power of 4.4 W are obtained for the 4F3/2-4I11/2 energy level transition, respectively. While for the 4F3/2-4I13/2 energy level transition, π-polarization laser at 1341.8 nm with output power of 2.9 W and σ-polarization laser at 1341.8 nm with output power of 1.6 W are obtained, respectively. The experimental results show that the π-polarization laser has higher conversion efficiency and the σ-polarization laser owns longer laser spectrum for a-cut Nd∶YVO4 crystal.

A new technique on laser-shock flexible micro-forming (LSFF) of multilayer-metal composite sheets is investigated, and its feasibility is verified. It is found that there is no delamination or cracks in the formed parts under appropriate process parameters. The study results show that the forming depth of Ni/Cu/Ni metal composite sheets under LSFF is between the forming depth of copper foils and that of nickel foils, which increases with the increase of the laser energy and laser impact times. Surface roughening happens in the formed parts and the roughness increases with the increase of the laser energy.

In order to investigate the effect of laser peening (LP) on surface biological corrosion resistance of medical Ti6Al4V alloy, LP experiment was carried out on Ti6Al4V alloy and the electrochemical corrosion property of the alloy was investigated using potentiodynamic polarization curve method. The surface morphology of etched samples was observed by scanning electron microscope, and the energy spectra were measured. The results show that the self-corrosion potential of LP samples shifts positively and corrosion tendency decreases in the range of tested parameters; the passivation current density decreases while the potential range of passivation region increases, and passivation performance is more stable; the breakdown potential shifts positively and pitting susceptibility also decreases; the corrosion current density and corrosion rate all decrease. Compared with the untreated samples, the self-corrosion potential of LP samples maximally shifts 0.209 V and the passivation current density is reduced by two orders of magnitude; the maximum increases of the potential range of passivation region and breakdown potential are 86.90% and 88.31%, respectively, and the self-corrosion current density is maximally decreased by 81.75%. Therefore, LP process can effectively improve the biological corrosion resistance of the medical Ti6Al4V alloy.

In laser metal deposition (LMD), fixed process parameters are mostly used during the deposition. The actual deposition height of each layer is generally fixed and uncontrollable. In order to improve forming stability and accuracy of the forming parts, and compensate the error of deposition height, a real time closed-loop control system of deposition height with variable process parameters is development. The actual deposition height is controlled by means of the feedback of the error between actual deposition height and the set desired layer height. Both P-controller and PI-controller are designed, and scanning speed and laser power as input variables are implemented respectively to control the actual deposition height. The experimental results indicate that the variable scanning speed control is better than variable laser power control. The best fluctuation range of the actual deposition height is ±0.015 mm. The total deposition height can achieve the desired total layer height using PI-controller. If the powder feeding rate changes abruptly, the P-control system has a nice robustness. The sectional view of cladding layer texture shows the variable deposition heights, which are in accord with the step response curve of P-controller. The system provides a new method to control deposition height and to compensate deposition error.

Both temporal and spatial characteristics of air plasma induced by tightly-focused laser pulse with central wavelength of 800 nm and pulse width of 50 fs are numerically simulated on the basis of a three-dimensional spatial ionization model with rotational symmetry, and the dynamic evolution of refractive index in whole plasma area is revealed. The simulation results clearly show that, when the laser pulse begins to focus, the ionization of air firstly appears in the region near the focal point. The initially ionized air gradually grows to form a water droplet-like plasma region with saturated electron density at the center and a high refractive index gradient in the peripheral. As the laser pulse propagates through the focal plane, the plasma zone expands forwards and forms an ionization region with almost symmetrical double-oval-shape. After the laser pulse propagates out of the focal region, the intensity of air plasma decreases along the direction of transmission and varnishes finally. Focused by a 10-fold microscope objective, the whole evolution process of the air plasma induced by laser pulse with pulse energy of 500 μJ and pulse width of 50 fs lasts about 3 ps. The simulation results can fit the experimental results obtained under low air pressure of 30 kPa.

In order to obtain continuous spectral transmittance of total atmosphere with high accuracy, a sun-photometer is developed based on the combination of grating spectrometer and high precision two-dimensional rotating frame. We can use the wavelet transformation to achieve spectral denoising and baseline correction, and the design complexity of the instrument structure is reduced. A mixed calibration method which combines Langley calibration method and standard light source method is introduced in consideration of limitations of the two methods above mentioned. The base of calibration can be traced to the extra-atmospheric sun irradiance. A comparative experiment between the sun-photometer and the POM-2 photometer is carried out at the same place and time, and the subsequent comparative analysis is also made between data measured by the sun-photometer and data obtained by the MODTRAN software. The experiment indicates the reliability of instrument structure design and the high precision of the new calibration method.