In order to realize the compound tactile sensing of mechanical finger, a pressure sensor and a temperature sensor are packaged in the same polymer sensing unit, and a fiber Bragg grating (FBG) is used as a sensing element. The characteristics of the pressure sensor disturbed by temperature of target object are analyzed. A back propagation neural network is used to process the tactile sensing signal of FBG, and thus the recognition of the positive pressure applied on the surface of sensing unit is achieved accurately. The simulation and experimental results show that this method eliminates the effect of the target object′s temperature on the strain sensor, and the uncertainty error of strain sensor is reduced. The compensation improves the stability of the pressure measurement and the measurement accuracy. The temperature drift rate of pressure sensor is 1.2×10-4 nm/℃ after compensation. The research can be applied to the FBG tactile sensing array installed on the mechanical finger. The temperature interference to the strain sensing can be suppressed, so that the tactile and sliding measurement system of flexible mechanical fingers have a broad application prospect.

Mode coupling in few-mode fiber may cause the transmission performance deterioration of a mode division multiplexing (MDM) system, which is one of the major factors limiting MDM technology to be applied in practice on a large scale. Precise measurement of mode coupling coefficient in few-mode fiber and quantitative analysis on the relationship between mode coupling and the performance of MDM system can provide reliable basis for the system-damage compensation. The advantages and disadvantages of the present measuring methods for mode coupling in few-mode fiber are analyzed, and a measurement system of mode coupling in few-mode fiber with the structure of mode transverter/demultiplexer and an optical fiber circulator based on the Rayleigh backscattering theory is built. By compared with the measurement results of multiple-input-multiple-output power analysis, the measurement performance of the proposed system has been verified. The experimental results show that the proposed system can realize the measurement of the mode coupling distribution in few-mode fiber with the fiber length of 9.8 km, and the measurement results are stable.

To evaluate the effect of multipath channel accurately, a modeling method for indoor multipath channel in visible light communication (VLC) system with single light source is proposed. The impulse response of line-of-sight (LOS) and reflection transmission is calculated by recursive methods. Inter-symbol-interference (ISI) is defined after the analysis on the relationship between sampling period of receiver and modulation bandwidth of light emitting diode (LED). Considering the delay time of LOS channel as the modeling origin, the gain of multipath channel is regarded as the sum of all the impulse response in adjacent sampling intervals of the receiver. Because the orthogonal frequency division multiplex (OFDM) technique can effectively resist the ISI, the bit-error-rate (BER) of asymmetrically-clipped optical OFDM (ACO-OFDM) system and direct current-biased optical OFDM (DCO-OFDM) system are derived and the Monte Carlo simulation models are built when the nonlinear clipping noise is considered in indoor multipath channel. The BER performance is studied for different locations of photoelectric detector (PD), semi-angles at half power of LED, fields of view (FOV) of PD, and direct current biases. The simulation results indicate that BER performance is best and the multipath interference is smallest when the PD is located at the center of the room. When PD moves towards the room corner, the BER performance becomes worse and the multipath interference become larger. As the FOV and the semi-angle at half power of LED increase, BER performance degrades due to the increased received power and multipath interference. Moreover, BER performance of DCO-OFDM system is more worse when DC biasing is larger.

On the basis of presenting structure, control principle and control algorithm of acquisition, tracking and pointing (ATP) fine tracking subsystem, the semi physical model is built to analyze the tracking performance of digital to analog converters with different resolution, and the tracking contrast experiments are carried out on the same beam position and the beam after disturbance. Combined with the signal transmission of fine tracking control system, the effects of digital to analog converters with different resolution on the tracking accuracy of ATP system are analyzed. The experimental results show that the higher the resolution of digital to analog converter is, the better the tracking performance of the ATP system is. However, when a 14 bit digital to analog converter is used, there is little contribution to improve tracking accuracy even continue to increase the resolution. By analyzing the spectral component of spot centroid signal after tracking, we find that the resolution of digital to analog converter within frequency band and outside the disturbance suppression bandwidth is proportional to the corresponding spectral component, so it is necessary to improve the disturbance suppression bandwidth of fine tracking system to achieve high accuracy tracking.

Based on the nonparaxial vectorial beam propagation theory, the far-field characteristics of Laguerre-Gaussian beams are studied. By using the angular-spectrum diffraction formula and the stationary-phase method, the analytic expression of the vectorial electrical field distribution for a Laguerre-Gaussian beam with an initial linear polarization state after some propagation distances is obtained. The electric field components along different directions and the spatial distribution of the equiphase surface are numerically calculated for a Laguerre-Gaussian beam which propagates along the z axis and is initially polarized in the x direction. The results show that, after some propagation distances, the electric field component which is parallel to the propagation direction appears and its intensity distribution shows a double-peak pattern. The value of this component is much lesser than that of the perpendicular component. With the increase of the topological charge, this parallel component increases and the light spot divergence degree enhances. This beam has a helical equiphase surface.

Based on the diffraction theory and the definition of Airy function, a trajectory expression of the intensity peak of Airy beam is deduced theoretically when the central position of cubic phase mask deviates from optical axis of Fourier transform lens, and the influence of the initial launch angle on the acceleration trajectory of Airy beam is discussed. We find that when the lateral acceleration is a constant, the larger the initial launch angle is, the larger the initial launch angle changing is. In order to increase the initial launch angle, we manufacture cubic phase mask with big size using computer-generated hologram microfilming printing system. Accelerating Airy beams are generated with the phase mask, and the propagation trajectory of Airy beam can be controlled within a large range when the dislocation between the center of phase mask and optical axis of Fourier transform lens is changed.

With the rapid development of underwater optical communication, sensing and ladar, it is important to deeply understand the effect of oceanic turbulence on beam characteristics. The characteristics of coma beam propagating through the oceanic turbulence are studied by numerical simulation. It is shown that the comet-like beam shape disappears due to the oceanic turbulence. The position of mass center dose not coincide with the position of the maximum light intensity. The beam width calculated on the condition that the position of mass center is regarded as the center is smaller than the result calculated on the condition that the position of maximum light intensity is regarded as the center, but it suffers more from the oceanic turbulence. It should be mentioned that, when the energy Strehl ratio is chosen as the characteristic parameter, the larger the coma aberration coefficient is, the less the influence of the oceanic turbulence on the beam energy concentration is. If we choose β parameter as the characteristic parameter, the energy concentration suffers most from the oceanic turbulence when certain value of the coma aberration coefficient is adopted, which should be avoided in practice. Moreover, the physical meaning of the energy Strehl ratio is different from that of the β parameter. The influence of oceanic turbulence on the energy concentration defined by the energy within a given bucket radius (i.e., energy Strehl ratio) is different from that defined by the certain power percentage (i.e., β parameter), which should be paid much attention in practice.

The diffuse reflectance of single-fiber reflectance probe is studied with the Monte Carlo simulation, and we find that the sub-diffuse scattering light is sensitive to the scattering phase function (SPF) related to tissue microstructure. A semi-empirical diffuse reflection model for small aperture measurement is studied, and the influences of second-order and third-order optic parameters on this model are analyzed. It shows that the two parameters have contrary effects on diffuse reflectance, and both effects are non-negligible for optically anisotropic biological tissues. A simplified semi-empirical model and its application condition are given, which provides potentially applicable support for measurement of tissue scattering properties and associated microstructure.

A method to improve the sensitivity of swept source optical coherence tomography (SSOCT) system is proposed. In the SSOCT system, when the splitting ratio of the coupler before the balanced detector, is not 50%∶50%, the DC bias in the detected interference signal will affect the sensitivity of the system. In this study, the influence of the splitting ratio of the coupler on the sensitivity is theoretically analyzed when the DC bias is introduced into interference signal, and it is proved that the sensitivity can be improved by the method of adjusting the splitting ratio and increasing the reference arm′s energy. Based on the parameters of the devices of the SSOCT system in the experiment, the sensitivity of the system is numerically simulated. The numerical simulation results prove the effectiveness of the proposed method, and the experimental results show that the sensitivity is improved by 2.3 dB after the proposed method is applied.

Studying the transmission of light in biological tissues requires more accurate scattering phase function. It is necessary to study the effect of nucleus on the phase function. In this study, the Mie phase function, asymmetric factor g and second order parameter γ of monodisperse nucleated cells are modified based on the geometric scattering approximation theory, the effects of the morphological and optical parameters on the angular distribution of the Mie phase function and number of Airy peaks are analyzed. The variations of g and γ with wavelength, cell size, nucleus ratio and refractive index are numerically simulated. The results show that the distribution of the Mie phase function, number of Airy peaks, g and γ are not only related to the cell size, but also to the nucleus proportion and refractive index. The effect of intracellular optical structure cannot be ignored. Compared with HG phase function, the Mie phase function can describe the side-backscattering characteristics and calculate g and γ more accurately. The Mie phase function provides further theoretical support for studying label free cell detection methods and transmission characteristics of laser in biological tissues.

The radially polarized light can be tightly focused and then forms a strong longitudinal electric field. The longitudinal electric field which follows the form of zero order Bessel function in cross section is calculated based on the Kirchhoff diffraction theory when radially polarized light is reflected and focused by a conical mirror. The relationships among spot size of incident light, cone-apex angle, radius of the exit end of conical mirror and coherent length and lateral width of the optical field of convergence region are analyzed. With these results, a hybrid structure consisting of a conical mirror and a cylindrical reflection mirror is proposed. When the appropriate parameters of conical mirror and the cylindrical reflection mirror are designed, the cascaded and periodic distribution longitudinal electric field is formed, and then the dependence of the related parameters (including lateral width, period and duty circle) of cascaded longitudinal electric field on parameters of cylindrical reflection mirror is discussed. Results show that a cascaded longitudinal electric field with periodic length of 1154λ and duty circle of 1 is formed when the conical mirror has an cone-apex angle of 60° and the radius of the exit end and the inner diameter of cylindrical reflection mirror are both 999.682λ (λ is the wavelength). This simulation suggests that the acceleration zone length can even reach the meter level when it is used for electronic acceleration. The design of this cascaded longitudinal electric field will further increase the length of the electron acceleration region to a significant extent, which could accelerate the electronics to higher energy.

Heat effect of laser medium can cause the aberration of the laser in the process of operation, resulting in the decrease of the laser beam quality, and seriously affecting the development and application of the solid-laser. A three-dimensional physical model of a double-side fluid cooling system with microchannel structure is established in the present work. Flow, temperature and Nd∶YAG crystal slices′s stress fields of the cooling system are simulated, and effects of Reynolds number and heat flux inside crystal slice on thermal deformation of the slice are investigated with fluid-solid coupling method. Results show that the flow field significantly influences temperature and stress fields of the crystal slice. The maximum Von Mises equivalent stress decreases with the increase of the Reynolds number, and its maximum value is located at the edge of the slice. There are different distributions of the thermal deformation under different flow conditions. The heat flux is found to only affect the extent of the thermal deformation, the higher the heat flux, the more obvious the thermal deformation.

A direct-liquid-cooling side-pumped Nd∶YAG multi-disk laser resonator works in quasi-continuous state is presented, in which twenty Nd∶YAG thin disks side-pumped by laser diode arrays are directly cooled by flowing siloxane solution at the end surfaces, while oscillating laser propagates through multiple thin disks and cooling flow layers in Brewster angle. The laminar flow cooling flow field is designed to cool the thin disk. The dissipation capability of the inhomogeneity of the incoming flow is verified by numerical simulation. According to the experiment reported before, a numerical model based on laminar flow is built to measure the cooling ability of the flow field. The experimental result verifies the reliability of numerical model, the thermal safety of the thin disk in laser device is evaluated based on the model. The maximum pulse energy output of 15.7 J is obtained at the pump energy of 49.9 J, corresponding to an optical-optical efficiency of 31.4% and a slope efficiency of 39.2%. The average output power of 1440 W is achieved at the pump pulse width of 250 μs, repetition frequency of 100 Hz, and average pumping energy of 5 kW.

An injection-seeded, doubly resonant ring cavity optical parametric oscillator based on PPMgLN crystal is presented. The pump beam polarization matches the e→e+e interaction in PPMgLN crystal (doped MgO with mole fraction of 5%), and thus makes the maximal nonlinear coefficient d33 (25 pm·V-1) effective. Using single-frequency pulsed laser with repetition frequency of 400 Hz , wavelength of 1064 nm and output power of 556 mW as pumping source, we obtain an average output power of 79 mW at the wavelength of 1.57 μm and output power of 38.5 mW at the wavelength of 3.3 μm when the crystal grating period is 30.5 μm and temperature is 110 ℃, corresponding to a total conversion efficiency of 22%. By using the seed laser injection technology, we obtain single-frequency narrow linewidth laser output, the linewidth of the signal laser with wavelength of 1.57 μm is less than 100 MHz, and the frequency drift is less than 141 MHz in 10 minutes.

A dual-wavelength 1.0 μm Q-switched and 1.5 μm gain-switched pulsed fiber laser is demonstrated by using a single Er/Yb co-doped gain fiber. Experimental setup consists of two loop resonators with one common branch including the Er/Yb co-doped fiber. The 1.0 μm Q-switched pulses are generated via the saturable absorption effect of the unpumped Er/Yb co-doped fiber, whereas a reabsorption of 1.0 μm Q-switched pulses from the Yb ions modulates the population inversion of Er ions periodically to generate 1.5 μm gain-switched pulses at the same repetition rate of 1.0 μm Q-switched pulses. With the increasing of pump power, the repetition rates of both pulses vary from 5.4 kHz to 11.7 kHz. However, the 1.5 μm pulses have a delay relative to 1.0 μm pulses, and the delay decreases with the increasing of pump power. At the maximum pump power, the pulse duration, single pulse energy and average output power for 1.0 μm pulses are 5.3 μs, 402.6 nJ and 4.7 mW respectively, whereas they are 4.6 μs, 374.4 nJ and 4.4 mW respectively for 1.5 μm pulses.

A nanosecond Tm-doped all-fiber dual-cavity laser with fiber-based saturable absorber is reported. The laser oscillator is constructed in a linear dual-cavity. The system uses a 1550 nm continuous-wave fiber laser as the pump source and fiber Bragg gratings as the wavelength-selective devices. Based on the saturable absorption characteristics of the Tm-doped fiber and the unique design of dual-cavity, the stable nanosecond operation is achieved. Meanwhile, the effect of the single-cladding Ho-Tm co-doped fiber and double-cladding Tm-doped fiber as the gain media on the laser output performance is studied. The maximum output power of the system is 256.3 mW, and the minimum pulse duration is 87 ns with the central wavelength of 1993 nm. The sequential nanosecond pulses can be obtained at the repetition rate of 20.0-33.3 kHz.

In order to improve the operation security of Shenguang II 5 PW (SGII-5 PW) ultrashort pulse laser system, the near-field distribution uniformity of large energy optical parametric chirped pulse amplification (OPCPA) beam is numerically simulated, and the simulation results are compared with experimental results. In the 1 PW amplifier, based on the measurement data of the preamplifier and the SGII high energy pump pulse, the evolution of the near field fill factor and the fluence beam contrast in optical parametric amplification process are presented by numerical simulation of parametric coupling wave equations. The conversion efficiency and the amplification stability are also discussed. The optimal range of nonlinear crystal length, in which high beam quality, high conversion efficiency and high stability can be achieved simultaneously, is obtained. The results also indicate that the pump light greatly affects the amplified beam uniformity. Enhancement of the SGII 7th beam quality is a practical way to improve the beam uniformity of second stage OPCPA.

A high peak power Nd∶YAG laser system with moderate repetition rate is demonstrated. The laser system contains three main components, the all-fiber-based seed, LD-pumped Nd∶YAG regenerative amplifier and flashlamp-pumped two-pass Nd∶YAG amplifier. The average power is 12 W, the repetition rate is 10 Hz, the single pulse energy of the laser system is up to 1.2 J, and the pulse width is 3 ns. With the wavelength of 1064 nm, the diameter of the output beam is 10 mm. More than 95% pulse energy is focused in the range of 600 μrad.The beam intensity distribution is near top-hat in the near filed and the intensity modulation is less than 1.2. The temporal pulse shape is square-pulse. The root mean square value of the pulse energy is less than 1.4%.

A mid-infrared Ho-doped fiber laser localized at 3 μm band is achieved using the all-fiber 1150 nm fiber laser oscillator as the pump source. The Ho-doped fiber adopts a linear cavity structure which consists of a high-reflectivity golden mirror and a vertical-cutted fiber tip. A 4.5 m Ho:Pr co-doped dual cladding fiber is used as the gain media. The core diameter is 10 μm and the numerical aperture of the fiber core is 0.2. When the 1150 nm pump power is 1.43 W, the mid-infrared fiber laser output is 115 mW. The optical-to-optical conversion efficiency of the Ho-doped fiber laser is 8.0%. The central wavelength is 2868.4 nm under the maximum output power and the full width at half maximum is 1.3 nm. The research results can make a contribution to the further development of mid-infrared Ho-doped fiber laser.

Mode instability has become the major limitation for power scaling of fiber lasers with nearly diffraction-limited beam quality. Based on mode coupling theory, we establish a semi-analytical model to simulate mode instability effect. Compared with co-pumped fiber laser, counter-pumped and bi-pumped fiber lasers reveal mode instability threshold enhancement in our theoretical model. Compared with that of the co-pumped scheme, the experimental mode instability threshold of the counter-pumped fiber laser is enhanced by at least 50%. Moreover, we demonstrate a 2 kW high power narrow-linewidth counter-pumped fiber laser with high beam quality.

A section of graphene film is transferred on the tapered fiber and the light interacts with graphene by the evanescent field so as to generate the mode-locked pulse. When the pump power is transferred to the threshold of 230 mW, the self-staring mode-locked pulse can be realized. Fixing the pump power at 300 mW, soliton bundles with controlled 2-6 sub-pulses are generated by adjusting the polarization controller. Fixing the pump power at 450 mW, different order harmonic mode-locked pulses can be achieved by adjusting the polarization controller. The highest order of harmonic mode-locked pulse is 117, and the corresponding pulse repetition frequency is 2.412 GHz.

A pulsed single-longitude-mode laser which uses a Fabry-Perot (F-P) etalon to select mode has advantages of simple compact structure and tunable wavelength. However, the output energy of the laser is sensitive to the change of cavity length, and the long-term stability is poor. To solve these problem, the main factors affecting the stability of output energy are analyzed based on the principle of single-longitude-mode laser with F-P etalon. The relationship among frequency, resonant cavity length and energy of output laser is obtained. An energy stability control method of dynamic feedback control cavity length is proposed. A high-speed digital circuit energy stabilization system based on field programmable gate array (FPGA) is designed. The length of resonant cavity is controlled periodically with the proposed method, and the intensity of the nanosecond pulsed laser signal is detected by photodiode. The frequency variation of longitudinal caused by the cavity length modulation directly affects the intensity of the output laser signal. The information of laser intensity change is analyzed, and the cavity length detuning is calculated. Based on this, the cavity length compensation is realized and a closed-loop control system is formed. Finally, the long-term stable output of the single-longitude-mode laser is achieved. Experimental results show that energy stability of the nanosecond pulsed single-longitude-mode laser is significantly improved with the proposed control system. The energy instability of continuous working for 3 h is 1.3%.

The gradient coating with the nickel-aluminum (KF-6) as a transition layer and with the TiB2 reinforced Ni-based composite coating as a strengthened layer is fabricated by laser cladding on copper alloy (Cr-Zr-Cu) surface with KF-6 and TiB2 as cladding materials. The study results show that the microstructural morphology of TiB2 is obviously different in the strengthened layer when the TiB2 content is different in laser cladding powders. The average microhardness of the strengthened layer is between 1150 HV and 1450 HV. The gradient coating has the lowest wear rate when the mass fraction of TiB2 is 10%. When the mass fraction of TiB2 is 30%, the coefficient friction of the gradient coating is stable (about 0.4). The transition layer between the strengthened layer and the substrate can effectively reduce the abrupt changes of the composition and microhardness between the strengthened layer and the substrate, which makes the transitions of the composition and microhardness smooth in the gradient coating.

The WC/Co50/Al cemented carbide coated tools with good macro morphology, uniform and dense microstructure, no pores and cracks are prepared by the laser cladding additive manufacturing technique. The study results show that the laser cladding layer of tools mainly consists of WC, W2C, Al2O3, Co3W3C, solid solution CoCr and (Co, Ni, Fe, Cr)2Si phases. The large hard WC particles on the laser cladding coating surface is coated in the Co50 bonding phase. The solid solution is formed by small WC particles with partial melting and decomposition. The axial and the radial cutting force are relatively stable in the cutting process, while the tangential cutting force fluctuates greatly. The tangential cutting force and the cutting heat of the laser-cladding cemented carbide tools are higher than those of YG8 cemented carbide cutting tools. However, the friction coefficient and the surface roughness of the work piece treated by the former are less than those by the latter.

The cryogenic laser peening (CLP) of 2024-T351 aluminum alloys is performed. The results show that the effective grain refinement on the surface of 2024-T351 aluminum alloys is induced by the CLP, the grain size in the severe plastic deformation layer is mostly smaller than 10 μm, and the second-phase distribution is more homogeneous. Compared with those of untreated samples, the surface hardness, the tensile strength and the yield strength of samples treated by the CLP increase by 34.1%, 21.6% and 28.9%, respectively, and the elongation of materials increases slightly. The simultaneous improvement of strength and ductility is realized. The tensile fracture morphology indicates that the fracture form of 2024-T351 aluminum alloys strengthened by the CLP is a ductile fracture which is beneficial to improve the tensile property of aluminum alloys.

Body-centered-cubic porous structures of Ti6Al4V titanium alloys are prepared by the selective laser melting (SLM) technology. The effects of the linear laser energy density and the microrod diameter on the compressive property along the forming direction (Z axis) and non-forming direction (X/Y axis) of these body-centered-cubic porous structures are studied. The results show that the body-centered-cubic porous structures fabricated by the SLM technology exhibit an obvious anisotropy. With the decrease of the linear energy density, the compressive strength of these body-centered-cubic porous structures increases first and then decreases. The degree of anisotropy is the lowest under the optimal parameters. With the decrease of the microrod diameter, the degree of anisotropy gradually weakens and when the microrod diameter reaches 0.4 mm, the degree of anisotropy is only about 3%. The research indicates that, even an isotropic porous structure, after fabrication by SLM technology, shows an obvious anisotropy. Such an anisotropy is related to the forming quality and the interlayer boundary which can be weakened to a certain extent by adjusting process parameters and changing model characteristic dimensions.

Laser lap welding of 0.2 mm-thickness 304 stainless steel and 0.2 mm-thickness T2 red copper ultra-thin sheets is conducted by using a fiber laser with a wavelength of 1070 nm. With the steel-copper-steel tri-layer lap welding method, good welds and wide process windows can be obtained. Black layered patterns parallel to the weld edge are observed in the weld microstructure. Energy spectral analysis results show that the content of copper at the weld bottom is higher than that at the weld top. The microhardness test results show that the lowest hardness zone is in the heat affected zone of the copper sheet, and the unilateral width of the heat affected zone is about 1 mm. The tensile test results show that the fracture occurs in the heat affected zone of the copper sheet, and the maximum tensile strength is 213 MPa.

The numerical simulation of three-dimensional flattened laser shocking of 2024 aluminum alloy is conducted with the finite element method, and the simulation results are consistent with the experimental results obtained from literatures. The influences of different process parameters on the residual stress distribution in materials are studied. The results show that, when the spot size increases, the residual stress of materials increases while the change gradient of the surface residual stress decreases. When the shocking times increase, the residual stress increases and tends to saturate. When the overlapping rate is 10%, the change gradient of the surface residual stress is relatively small. When the overlapping rate increases, the residual stress along the depth direction increases but its increasing amplitude is small.

The influences of external longitudinal magnetic field on weld joint forming characteristics, microstructure and microhardness distribution are investigated in SUS316L austenitic stainless steels by laser-metal inert gas hybrid welding. The experimental results show that, under the action of external longitudinal magnetic field, the weld joint reinforcement decreases, the weld width increases, the forming coefficient increases, and the cross section appears wide and deep. The external magnetic field alters the thermal cycle of the weld joint, which makes the striped δ-ferrite precipitation occur in the heat affected zone and the grain growth is inhibited. The external magnetic field causes the rotation of the molten pool and the weld joint grains are refined. The uniformity of crystallization is improved and the microhardness distribution becomes stable. This effect enhances with the increase of the magnetic induction intensity but weakens with the increase of the weld joint depth.

By using the thermoelastic model, the finite element analysis of dispensing process of optical slices is performed. The process parameters which influence the surface deformation of workpieces (Δp) after dispensing are optimized. For an optical slice with a diameter of 100 mm and a thickness of 2 mm, a thin base plate with high elastic modulus and low thermal expansion coefficient is the optimal selection. Δp decreases with the decreases of radius, number and elastic modulus of glue dots. The glue dot position should avoid the high Δp zones. The thermal expansion coefficient of glue dots has little influence on Δp.

With the deepening of research on the military stealth, solar energy conversion, laser heat treatment and other technologies, the technical requirements for surface absorption films are continuously improved. In order to meet the requirements of solar spectrum absorption, a novel optical film with strong absorption in the 400-2500 nm band is developed, which is applicable to multiple kinds of substrate. The absorption structure model is established based on the absorption theory, and the design of the absorption film is realized by combination of the characteristics of the materials. The solar spectrum strong absorption film is prepared based on the vacuum ion-assisted deposition technique and the fractional deposition process optimized by the reverse inversion method. The test results show that the average absorptance of the absorption film is 98.15% in the range of 400-2500 nm. The prepared absorption films can meet the requirement of mechanical fastness and have better adhesiveness to the substrate.

Gold nanoparticles are prepared in chloroauric acid trihydrate (HAuCl4·3H2O) aqueous solution by the ablation with a focused femtosecond pulse laser beam of 800 nm wavelength and 30 fs pulse duration. The effects of HAuCl4·3H2O aqueous solution concentration, laser pulse energy and dispersant polyvinyl pyrrolidone (PVP) amount on particle size and size distribution of gold nanoparticles are investigated by means of UV-Vis absorption spectrum, transmission electron microscopic morphology, X-ray diffraction spectrum, and selected area electron diffraction pattern. The results show that the surface plasma resonance absorption peak of the gold nanoparticles locates around 530 nm. Lower solution concentration, higher laser pulse energy and higher PVP amount are helpful to obtain nanoparticles with smaller average particle size, narrower particle size range and higher dispersion when other experimental parameters are fixed at certain values. The prepared particles are mostly spherical and display multi-nanocrystal surface structure. The strong X-ray diffraction peaks of (111), (200), (220) and (311) crystal planes of gold nanocrystal are observed. The growth process of gold nanoparticle includes aggregation stage and adsorption stage.

Laser Doppler velocimeter (LDV) is widely applied in the measurement of fluid velocity with the advantages of high accuracy, non-contact measurement and quick dynamic response. The fringe nonuniformity is a key factor to influence the measurement accuracy of LDV. To accurately measure fluid velocity of LDV, the interference fringe spacing and the gradient distribution in the measuring volume have to be determined exactly. The interference fringe spacing and the gradient distribution of LDV in the measuring volume are analyzed in theory. The relationship between the Gaussian beam propagation characteristics and its interference fringe distribution are revealed. The parameters influencing the interference fringe distribution are determined. The beam waist radii of the green beam and purple beam are 114 μm and 83 μm respectively, which are obtained by beam profiler. Meanwhile, the spatial location of the beam waist is determined. The interference fringe spacing and gradient distribution of green and purple beams in the measuring volume at any locations are quantified by using measured parameters. In the measuring volume of green and purple beams, normalized fringe gradient maximums can reach 0.46% and 0.60%, respectively. The interference fringe spacing results of green and purple beams measured by spinning-disk system are compared, and theoretical analysis and measuring results of the interference fringes distribution are verified. The maximum relative errors are 0.87% and 0.78%, respectively.

To obtain images with high signal-to-noise ratio (SNR), a ultraviolet imaging system is developed based on a scientific grade CCD (CCD47-20) which is sensitive on ultraviolet. The imaging system can quickly image flames of burning solid fuel at particular ultraviolet waveband. CCD47-20 has deeper potential sell, which guarantees SNR of the imaging system. However, the exposure time of these CCD is usually above 200 ms. To realize quick exposure on target, a CCD driven timing sequence with twice-frame-transfer and once-horizontal-readout is designed based on the analysis of performance and working principle of CCD47-20. The design of imaging system is finished, and the exposure time of CCD is reduced to 10 ms. The irradiation test of the system is carried out in the laboratory. The results show that when exposure time changes, the responsivity of CCD is linear, which verifies the correctness of design of timing sequence and driven circuit. SNR test results show that the SNR of the system can reach 46.8 dB. Flames of burning fuel in the specified ultraviolet waveband are imaged using the ultraviolet imaging system. Shapes of flames are captured, which validates the fast exposure performance of ultraviolet imaging system.

To improve the measurement accuracy of stereovision method, a correction method based on epipolar constraint for digital image correlation (DIC) stereo matching is proposed. The initial stereo matching result is obtained by DIC method, and then the initial results are corrected by epipolar constraint. The point on the right pole line, which is the nearest to the initial result of DIC method, is selected as the new matching point on right image. In addition, this method is also used to match the sequential images. The tensile test of 304 stainless steel specimen is conducted on a material testing machine. Compared the measurement error of the proposed method with that of stereovision method without correction, the experimental results show that the maximum error, the average error and the root mean square value of the proposed method decrease through correction by epipolar constraint, which testifies that the proposed method can improve the measurement accuracy of stereovision method.

A tapered double-cladding fiber (TDCF) temperature sensor based on surface temperature sensitive thin-film is presented. It consists of two sections of common single-mode fiber (SMF), and a TDCF is welded between them. The structure is SMF-TDCF-SMF. Because the mode field of the SMF core mode does not match that of the TDCF core mode, the light transmitted from SMF is partially coupled into the TDCF core, and the rest is coupled into the TDCF cladding in the form of a cladding mode. When the two beams reach output end SMF and interfere, the Mach-Zehnder interferometer can be obtained. The TDCF is coated with a layer of temperature-sensitive thin-film, so that the optical path difference between the TDCF core mode and the cladding mode will change with the external temperature, thus causing a change in the sensor interference spectrum. Therefore, temperature measurement can be achieved by detecting changes in the sensing spectrum. The temperature characteristics of the sensor are experimentally studied, and the results show that the free spectral range of the sensor decreases with the increase of tapered cone length. When the length of the tapered cone is 16 mm and the temperature is within the range of 32-65.3 ℃, the transmission spectrum of the sensor is blue-shifted with the increase of temperature. The temperature sensitivity is up to -1296.78 pm/℃, and it has good linearity degree. The sensor is simple, highly sensitive, and has good prospects in temperature measurement occasions of scientific research, industrial and agricultural production.

In order to research the relation between self-emission spectrum and transmittance of target at oxygen A-band, the method for fitting the baseline of oxygen A-band spectrum based on the partial least square regression (PLSR) is proposed according to the transmittance calculation method. The experimental system is set up to verify the accuracy of baseline fitting. Firstly, the calculation method of oxygen A-band average transmittance is given according to the blackbody radiation theory. The spectrum of the target to be measured is used as study object. The PLSR is used to fit the baseline of the target to be measured at oxygen A-band according to the out-of-band data. For the sake of improving the fitting accuracy, the singular point of measurement is eliminated. The baseline fitting uncertainty is used to evaluate the fitting accuracy of PLSR. In order to verify the accuracy of this method, the spectra with different distances and different resolutions at the same distance is measured in the range of ~130 m using the halogen light. These spectra are fitted and each standard deviation is analyzed. The results show that the average standard deviation is 0.23% with different resolutions at the same distance. The baseline fitting uncertainty becomes smaller and signal to noise ratio is increased with the resolution reducing. In addition, the baseline fitting uncertainty is related to the resolution of the test equipment. The higher the resolution is, the larger the uncertainty of out-of-band data baseline fitting becomes, whereas, the smaller the out-of-band baseline fitting becomes.

By measuring the surface-enhanced Raman spectra (SERS) of various low concentrations of platelet-derived growth factor-BB (PDGF-BB) aqueous solution, the Raman characteristic peak at Raman shift of 1509 cm-1 can be detected for PDGF-BB aqueous solution with mass fraction as low as 10-8. By detecting SERS of urine samples of the preoperative patient who has higher degree of atherosclerosis and is treated with percutaneous coronary intervention (PCI) and the patient who has lower degree of atherosclerosis and is not treated with PCI, as well as the Raman characteristic peak of PDGF-BB at Raman shift of 1509 cm-1, we find that the peak at 1509 cm-1 can be detected on the SERS of the patient with PCI, which reveals that the concentration of PDGF-BB in urine is correlative with the degree of atherosclerosis. The results show that the low concentration of aqueous solution of PDGF-BB can be detected by SERS technology, and the SERS of urine sample can be used to determine whether the patients with coronary heart disease need to have PCI. Hence, the technology will be a clinical diagnostic tool for non-destructive testing and screening coronary heart disease.

The ultra-narrow band spectrum filtering system based on double multi-layer dielectric (MLD) coating diffraction gratings can achieve the sub-nanometer scale ultra-narrow spectral filter width that cannot be realized by common narrow band filter. Using this system may greatly improve the signal-to-noise ratio and anti-jamming ability of laser light echo detection system. An ultra-narrow band spectral filter system based on dual MLD dispersion compensation gratings is designed, and theoretical simulation of the system aberration is made using CODE V software. The result shows that the system aberration can be ignored. Also, theoretical simulation of the filtering linewidth and effective energy transmittance of the system is made by Matlab software, which provides a relatively complete theoretical basis for choosing the optimal structure parameters to solve the actual filtering problem in actual situation. Finally, by using domestic multi-layer film dielectric gratings in the laboratory, we successfully transform the input laser with spectrum full-width at half-maxima (FWHM) of 0.3 nm into the output laser spectrum FWHM of 0.03 nm, which is at center wavelength band of 1064 nm.