We investigate the phase coherence of bosons in a double-well trap with a random energy mismatch that is used to mimic disorder in the presence of effective three-body interaction. It is found that, in such a double-well disordered Bose-Hubbard model, the renormalized three-body interaction can enhance the phase coherence of the bosonic system in the presence of disorder. The dependence of the average phase coherence on the effective three-body interaction in the situation of strong disorder is also studied. To our best knowledge, it is the first time that the effective three-body interaction is investigated in the context of disordered quantum gases.

A method to compensate the hysteresis nonlinearity of piezoelectric steering mirror (tip/tilt mirror, TTM) based on neural network models is presented, which may improve the steering mirror control accuracy in adaptive optics system. The hysteresis of TTM is modeled by using back propagation (BP) neural network via the response data of TTM. We simulate the process of hysteresis response and compute the voltage applied to TTM in real time, so as to achieve the forward compensation control of TTM. In order to meet the real time intention, we use the function form of BP neural network instead of time-consuming simulation operation, which increases the computing speed and insures the operation precision. The results show that by using this compensation approach the hysteresis nonlinearity is reduced by about 70%. Moreover, the global linearity and the controlling accuracy are obviously improved.

This paper describes a low noise optical coherence tomography (OCT) technology based on curvelet algorithm and a demarcating arm to decrease the speckle noise in OCT. The demarcating arm in the Michelson interferometer makes the precise positioning of A-scans possible and diminishes the displacement error caused by tissue moving. Besides, each A-scan is curvelet transformed and adaptive filtered, the curvelet coefficients are weighted, averaged and reconstructed to reduce speckle noise. Compared with traditional A-scans average method, the application of curvelet algorithm and demarcating arm in low noise OCT provides 18.35% increase in signal to noise ratio.

To suppress speckle noise efficiently and achieve less time consuming in laser active imaging, a denoising method based on spectrum-domain constraint in signal subspace is proposed. Homomorphic transform is performed to convert the multiplicative noise to additive noise. The noisy image is decomposed using singular value decomposing to estimate the dimension of signal subspace. Based on the dimension, the covariance matrix of the noisy image is decomposed using eigenvalue decomposing to estimate the covariance of speckle noise with the eigenvector in noise subspace. After that the denoising estimating matrix is computed with the eigenvector in signal subspace and is convolved with the noisy image. Inverse homomorphic transform is carried out and the denoised image is obtained. In order to eliminate the effect of backscatter and background radiation, a laser active imaging system based on range gating ICCD is constructed. The experiment is performed using images with speckle noise in different levels and the results show that compared with classical Lee, Frost and Kuan filters, the proposed method has advanced denoising performance and the computing time is in millisecond level, which meets the requirement of real-time operation for laser active imaging.

The construction of an appropriate observation matrix is the key issue for compressed sensing practical application in embedded system. However, the matrix usually used, like Gaussian matrix, Bernoulli matrix etc, is difficult to realize for hardware. Aiming at the feasibility and the real-time of compressive sensing for embedded vision system, a simple deterministic 0-1 observation matrix is proposed, which is based on the related work of sparse transform vectorization, the characteristic of wavelet sparsity, and the pseudo-random sequence observation matrix construction. For N×N image, when the observation matrix dimension is M×N, the matrix is consist of M base vectors and the vector size is N. The base vector has only one element of 1 and the other elements are 0. So the formed observation matrix is simple and the integral circuit can be omitted in the real measurement. Base vectors are arranged according to the position of element 1 in vector from 1 to M to form a deterministic observation matrix, which is easy to remember and store the matrix, and also helpful for reconstruction.

In order to correct the distortion introduced in the null testing with computer generated hologram (CGH) for off-axis aspheric, a mapping distortion method is proposed based on affine transformation of the test ray. The distortion mapping function is solved by ray tracing. The high alignment accuracy between the calibration result and the mirror surface is realized with feature points on the mirror, and calibration points are utilized to test the correction error. An off-axis asphere with size of 800 mm×600 mm is tested. After mapping distortion correction, the position error between the test result and the prototype′s profile is reduced from 80 mm to less than 1 mm. The corrected output is applied to polish the mirror by ion beam and its accuracy [represented by root-mean-square (RMS) error] is 0.0162λ (λ=0.6328 μm).

A melting and solidification mathematical model under stationary or moving laser beams at various laser powers P and scan speeds V is established to simulate the selective laser melting of copper-tungsten powder system. The transient temperature and velocity field as well as the forces acting on tungsten particles are obtained, and the metallurgy behavior in the laser-powder interaction zone is analyzed. The results indicate that when the laser power P ranges from 600 W to 900 W, the value of velocity field angle θ decreases from 50° to 0°, implying the enhancement of heat transfer from laser center to edge of molten pool. Under the condition of a stationary laser beam, P≥800 W, or for a moving laser beam, linear energy density η=16 kJ/m, there exists the second flow around the tungsten particles, leading to the formation of pressure acting on the tungsten particle induced by the pressure difference. As the included angle of attractive force and pressure is acute angle, tungsten particles tend to form small-scaled rim structure and the rearrangement rate is limited, accordingly tending to form segregation structure. Otherwise, tungsten particles tend to form large-scaled rim structure and the rearrangement is efficient, contributing to the formation of homogeneously distributed structure.

An austenite NiTi shape memory alloy is processed by laser shock peening (LSP), and the mechanical properties is investigated. It is found that the thickness of shock affected layer is about 300 μm. The surface hardness of the specimen is increased by approximately 10% after LSP. The strain of the specimen is extracted from the images recorded in the tension by the digital image correlation technique in order to obtain the stress-strain curves. The superelastic stress-strain curves of the fully LSP processed NiTi material show no change in phase transition stress, the martensite yield stress decreases to about 100 MPa, and a loss of maximum transition strain about 13% after LSP. The ultrahigh-strain-rate plastic deformation by LSP results in dense dislocation underneath the surface which is responsible for the hardness increase and superelastic strain loss.

Ti6Al4V-CoCrMo gradient multi-pass wall is fabricated by laser metal direct forming, with the CoCrMo volume fraction of 10%, 20%, 30%, respectively. The part of 10% CoCrMo volume fraction is crackles, while 20%, 30% parts crack seriously. Advanced investigations are made on the cracking of 20%, 30% CoCrMo volume fraction parts from three aspects: fracture morphology, microstructure and residual stress. The results show that the cracking of gradient material is a kind of cold cracking. The fracture displays the features of quasi-cleavage and transgranular. Reasons of the cracking mainly include of Ti6Al4V and CoCrMo form limited solid solution, increasing the brittle of the material. With the content of CoCrMo increasing, the microstructure of the Ti6Al4V-CoCrMo gradient material changes. Around the Ti6Al4V-CoCrMo limited solid solution network CoCrMo precipitated, not only the possibility of stress concentration improves, leading to crack source appearing in some cases, but also the stress due to the differences of thermal physcial parameters of two materials increases.

The influence of welding parameters on weld depth and porosity is investigated in partial penetration fiber laser welding using 7 kW fiber laser, and the relationship between weld and keyhole depthes is discussed. The suppression of porosity is also investigated using triangular wave power modulation. The results indicate that the keyhole depth coincides approximately with the weld depth in laser welding. The weld depth and the porosity reduce with the welding speed increasing. When the defocus distance is 0, the weld depth and porosity ratio reach the maximums, whereas both of them decrease as the laser focus position is off the sample surface. In a wide range of pulse frequency (20~125 Hz), the porosity is effectively suppressed by triangular wave power modulation for fiber laser welding, and the optimal frequency is 60 Hz. The keyhole behavior is analyzed by X-ray transmission imaging system to find that the stabilization of keyhole is promoted by power modulation, which results in the suppression of porosity.

The surface of 40CrNiMo high strength steel is quenched with CO2 laser, and the fatigue limits of 40CrNiMo before and after laser quenching are obtained through the tension-tension fatigue experiments based on Locati theory. The fracture morphologies of 40CrNiMo before and after laser quenching are investigated by scanning electron microscope. The mechanism of laser quenching on 40CrNiMo′s fatigue strength is analyzed. The results show that a layer of hardened zone, martensite and compressive residual stress after laser quenching is formed on the sample surface, and the fatigue strength of 40CrNiMo is increased significantly from 626 MPa to 715 MPa, increasing by 14.2%. The fatigue crack sources of the sample in quenching and tempering state are produced in the surface, while that are transferred to the subsurface after laser quenching. The fatigue crack sources expand slowly to be fracture. Grain refinement and compressive residual stress by laser quenching are the main mechanism.

The ignition threshold of laser supported detonation wave (LSDW) of aluminum generated by 1064 nm and 355 nm laser pulses is studied using acoustic method. The relation between the pressure of laser-induced plasma acoustic wave and the expansion velocity of shock wave is analyzed theoretically. Then the experimental research of aluminum target irradiated by the laser with the wavelength of 1064 nm and 355 nm is developed. The experimental results show that the lifetime of plasma acoustic wave is on the millisecond order, and the peak intensity of plasma acoustic wave decays exponentially. It is found in the experiment that the signal amplitude of plasma acoustic wave generated by the laser irradiation on aluminum target increases with laser power density increasing. However, the peak intensity of plasma acoustic wave appears jump stage twice while laser power density increases. From this it can be determined that the ignition threshold range of LSDW is (3.95～13.05)×108 W/cm2 for 1064 nm and (3.14～10.07)×108 W/cm2 for 355 nm laser pulse. Furthermore, the wavelength effect on the ignition threshold of LSDW is analyzed.

In view of problems of laser spot welding of aluminum, a precise control wire filler is built, and the feasibility of laser spot welding of aluminum alloy with filler wire and the influences of filler wire angle, wire feed volume, delay time are analyzed. Experimental results show that the filler wire method can improve the defects of laser spot welding of aluminum. The angle of the filler wire is the key factor which influences the stability of the process of the melt wire into the pool. When the wire is feed at an angle of 30° or so, the feed process is most stable. The delay time is one of the main factors which determine the pool size. When the delay time is too short, the filler wire can be easily accumulated on the surface of the specimen. The volume of the wire feed into the pool is directly related to the improved effect of collapse.

Coaxial powder feeding laser cladding of the Ni60A-B4C-TiN-CeO2 mixed powders on an aviation material TA15-2 titanium alloy substrate can form a hard wear resistance composite coating. Such coating is investigated by means of a scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM). Experimental results indicate that a large amount of nanocrystals-amorphous phases are produced in such composite coating. The nanocrystalline/amorphous interface owns a high bonding energy, which retards the growth of the nanocrystals in a certain extent; and the production of the nanocrystals lead the enhancement of free energy on the crystal boundary, which increases the density of point defect, causing the lattice distortions of the coating. Amorphous, nanocrystals and the other crystalline phases coexist in such coating. Such coating exhibits a better wear resistance than that of a TA15-2 substrate, and the main wear mechanisms of the coating are abrasive grain wear and the adhere wear.

Laser repair contrast experiments by using nickel-based superalloy material FGH95 powder are performed on the GH4169 that is commonly used in aero-engine filed under different laser linear energy densities q. By testing the flexural property and analyzing the metallic phase, the influence of the laser linear energy density on flexural properties of repaired samples and microscopic mechanism of flexural property change are studied. The results indicate that the flexural strength of repaired samples is close to that of original sample and basically achieves flexural property of original sample. When q=120.0 J/mm2, the flexural strength of 827.16 MPa is maximum and has a 0.5 percent larger than that of original sample. With laser linear energy increasing, the flexural strength of repaired samples first increases and then decreases. The flexural property decreases at a higher laser energy density of 154.3 J/mm2 due to the coarsening of repaired area dendrites.

The ablation resistance of composite material is usually characterized by ablation heat that laser energy is consumed per unit ablation mass. Whereas the characterization ignores the effects of laser parameters. Taking C/SiC composite material as an example, by using a program for the numerical simulation of laser ablation of composite material, the ablation heat of C/SiC composite material is computed for different laser parameters. Effects of intensity, repetitive frequency and duty radio are analyzed. The result indicates that ablation heat is mainly correlated with intensity and duty cycle of the irradiating laser beams. More intensive laser beam causes more severe ablation. Ablation of unit mass requires more than average incident energy if duty cycle of the laser pulses decreases. In addition, it is realized that the repetitive frequency rate of laser has minor effect on ablation as long as average beam intensity and duty cycle are fixed. For C/SiC material, introducing of some instabilities into laser beams would enhance the ablation process, which leads to low ablation heat.

In the process of autogenously welding of SUS 304 stainless steel plate with 12-mm thickness using high power fiber laser, because the welding pool can not maintain homeostasis in the combined action of gravity, surface tension and vapor recoil, the flow of the liquid metal in the molten pool is drastic and the poor formation is easy to cause welding defects of its surface such as spatters, surface undercut and root hump. With certain welding power and top protection gas with certain flow rate, the influences of the welding speeding, defocus, butt joint gap and the flow rate of bottom shielding gas on welding quality by changing the single variable are discussed. The results show that adopting some reasonable technology measures can efficiently improve the welding quality, make the welding surface smooth and well-distributed, and reduce following machining amount after being welded. Tensile test shows that ductile fracture happens in parent metal place, far away from the weld. The maximum tensile stress is 809 MPa, and the mechanical performance of the weld is good.

Two laser systems that can be used in coherent manipulation of the ground states of cesium (Cs) atoms with the frequency difference of 9.2 GHz are studied. The advantages and disadvantages of two laser systems are analyzed. The frequency difference of the two lasers is approved by saturated absorption spectroscopy or Fabry-Perot cavity, and the relative frequency stabilization of coherent laser beams is also analyzed by the beat-note signal. Using the temperature controlled etalon with free spectral range of 18.4 GHz, the laser can be locked to about 10 GHz negative detuning from the D2 transmission line of cesium atoms, which realizes a large frequency difference lock of phase coherent light. The single cesium atom trapped in the magneto-optcial trap (MOT) and the far-off-resonance optcial dipole trap (FORT) is already prepared and dectected in the hyperfine states experimentally. Raman laser system can be applied to the single atom to realize the coherent manipulation of the ground state of single cesium atom.

The theoretical model of laser-induced acoustic signals is analyzed. The experimental platform is built to research characteristic of laser-induced acoustic signals. With the increase of water depth in 0~100 m, the time interval of adjacent peak pressures of laser-induced acoustic signals decreases. Peak pressures of acoustic signals induced by laser-plasma decreases. Peak pressures of acoustic signals induced by bubble collapse first increase in 0~20 m, then decrease in 20~100 m. Number of acoustic signals induced by bubble collapse decreases.

The sources of cavity stress in total reflection prisms laser gyro are complex, and strong stress may seriously affect the gyro′s accuracy. Based on the prism material dielectric constant change under stress, the effect of stress-birefringence on the gyro output is analyzed systematically by using Jones matrix and the elastic-optic effect theory. The energy distributions of the reflected and transmitted light are obtained at Brewster angle, and the explanation of the reflected interference speckle is given. The reflected light intensity is simulated corresponding to uniform gradient, point concentration and complex stresses fields between the prism and cavity. The related experimental results agree with the simulation. An engineered equipment for prism and other correlates stress detection is designed.

Temperature characteristics of 980 nm semiconductor laser facet are analyzed. Catastrophic optical damage (COD) of semiconductor laser facet is the main reason which limits the lifetime and output power of laser. Through analyzing the heat source produced by facet, the model of facet temperature distribution is established and facet temperature field distribution is analyzed. Antireflection film and high reflection film with diamond passivation film are designed to simulate and contrast facet temperature characteristics of 980 nm semiconductor lasers with and without diamond passivation film. Simulation results show that the temperature of the former is lower than the latter of 9.0626 ℃. It can effectively reduce the facet temperature and improve the COD threshold of 980 nm semiconductor laser when coated with diamond passivation film.

The utilization of supersonic nozzles to accelerate and cool the flow in the chemical oxygen-iodine laser is a significant progress in laser research. However, there are complex three-dimensional structures in the supersonic flow field. The relationships between flow structures and laser outputs are important criterions on the design of pneumatic components. The simulation system presented in the paper contains three blocks: the chemical flow calculation block, the optical calculation block and thermal structure calculation block. With the numerical platform, the analysis of the performance of laser under different flow conditions is carried out and the focus is the influence of the shock waves in the flow field on the near field laser output. According to the analysis, optimal methods are proposed. It makes an increase of the beam quality (F factor) of 45%.

In experiment of semiconductor optical amplifier based laser, the phenomenon of self-mode locking is observed. Pulse duration of 30 ns and 50 ns are achieved with repetition frequencies of 19.34 MHz and 9.67 MHz, respectively. The laser adopts a ring cavity configuration, with semiconductor optical amplifier used as key device of the self-mode locking. When the pump current adds to 200 mA, self-mode locking pulse is observed after adjusting the polarization controller. In addition, the phenomenon of dimidiate frequency is abserved, that is the repetition frequency of the pulses is equal to half of the cavity fundamental frequency. The effect of polarization rotation caused by the semiconductor optical amplifier leads to the change in output power, which is, the alternation of pulses with high power and low power, which is called the phenomenon of dimidiate frequency.

Colored conical emission (CCE) is an attractive nonlinear phenomenon, which is induced during intense ultra-short pulses propagating in nonlinear medium. A detailed experimental study on the generation of CCE in type-Ⅰ β-barium borate (BBO) crystal pumped by femtosecond pulses is reported. A physical model based on CCE is constructed, it numerically calculates the conical angle with different wavelengths and the spectral characteristics of CCE is analyzed. The influence of parametrics on the characteristics of CCE is discussed in details. With the pumped intensity decreasing and the pulse incident angle increasing, the central wavelength of the CCE spectrum has a red shift based on the numerically simulation. The observation shows that the CCE is originated from spontaneous parametric down conversion of second harmonic pulses.

High average power linearly-polorized picosecond pulsed laser sources have a wide range of applications in the fields of industrial material processing, coherent beam combination and nonlinear optics. A high power linearly polarized picosecond pulse ytterbium-doped all-fiber laser based on a seed of mode-locked fiber laser with a semiconductor saturable absorber mirror is reported. The fiber laser is constructed with a two-stage master oscillator power amplifier (MOPA) configuration. Stable mode-locked pulse train occurs when the incident pump power increasing and the pulse repetition rate is 40 MHz in a ring cavity configuration. Increasing the incident pump power to 200 mW, the maximum output average power is 12 mW. The pulse width is measured to be 20 ps. The center wavelength and the spectrum bandwidth are 1038.2 nm and 1.7 nm, respectively. The steep edge in the optical spectrum is a clear indication of the dissipative solitons (DSs) in this all-normal-dispersion mode-locked fiber laser. After two-stage fiber amplifier with the polarization maintaining double-cladding ytterbium-doped fiber as the gain medium, 5 W average output power is achieved, corresponding to a single pulse energy of 125 nJ and a peak power of 6.25 kW, respectively. No undesirable nonlinear processes such as stimulated Raman scattering are observed. At this high output power, the spectrum bandwidth and the pulse width are measured to be 3.1 nm and 20 ps, respectively, and the polarization extinction ratio is 20 dB.

The configuration and principle of the temporal profile measurement system are introduced, which are used for multi-beam infrared laser of the high power laser facility. The system is composed of sampling and coupling, fiber transmission, multiplexing coupler, photoelectric conversion and data acquisition unit. The reduced beam and optics imaging method are adopted in sampling of optical fiber in order to solve the problem of the great drift of beams. Because of the laser beam of sinusoidal frequency modulation, the influence of the temporal profile on measurement is systematically evaluated. Optical aberration caused by diagnostic system, the temporal characteristic of different regions, and the bandwidth of sensor are analyzed experimentally and theoretically. The experimental results show that the measurement system of temporal profile based on optical fiber can provide the profile of integral entirely beam of frequency modulation, and monitor the profile reliability.

A double-layered cylindrical microcavity is fabricated by filling Rh6G dye solution into a fused capillary. By pumping with s- and p- polarized laser light respectively, whispering-gallery mode lasing emission with transverse magnetic and transverse electric polarization is observed. The interference modulation effect in the whispering-gallery-mode lasing spectra is found when pumped by s- polarized light. And the modulation period increases with the refractive index of dye solution, but decreases with the ratio of the external to internal diameter of a capillary. By applying the interference modulation theory on the reflective and refractive waves in the double-layered cylindrical microcavity, the observed phenomenon can be explained successfully. The interference modulation effect provides a certain reference for mode selection in a multimode whispering-gallery-mode laser.

An asymmetric super large optical cavity waveguide is designed to realize the high output power semiconductor laser, in which the super large optical cavity is used to raise the catastrophic optical mirror damage (COMD) limit, and the asymmetric waveguide is used to inhibit the lasing of higher order modes. Meanwhile, the optimized thickness of the asymmetric waveguide is analyzed. By optimizing the process condition of metal organic chemical vapor disposition (MOCVD) epitaxy for the active layer, and combining with the electrode fabrication and facet coating, a 4-mm cavity length semiconductor laser die with 2 μm super large optical cavity waveguide at 980 nm wavelength is fabricated. Without any active cooling process, an output power of 23.6 W is reached with injection current of 30 A without COMD at room temperature. Because of the introducing of the super large optical cavity waveguide, the far field test shows that only the transverse fundamental mode is lased with a vertical far field angle of 24°. The results show that the asymmetric super large optical cavity structure is an effective way to get the high output power of semiconductor laser.

An external cavity diode laser (ECDL) with Littman-Metcalf configuration is constructed in this paper. The ECDL adopts a compact structure with a star-flexure hinge as the tuning mechanism. Its mechanical characteristics and design are analyzed and optimized by finite element calculations. The first order resonance frequency of tuning arm is measured as 3.7 kHz. The laser cavity structure parameters are designed according to the mode-hop-free tuning condition, and the performance of the ECDL is obviously improved, showing single-mode operation with mode-hopping free tuning range over 80 GHz at 780 nm. The device has been operating stably without realignment for more than one year, indicating its good ruggedness. The frequency of ECDL can be locked at 87Rb (F=2→F′=2,3) transitions. The linewidth of 200 kHz and temperature stability of 35 MHz/℃ are measured, and the Allen deviation reaches 3.5×10-11 in 3-s integration time. Its output power is continuously monitored with fluctuation below 0.75% for 24 h, showing with good stability.

All-fiber mid-infrared supercontinuum source is obtained using ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) single-mode fiber, which has low transmission loss in this wavelength region. The supercontinuum is extended to mid-infrared wavelength. This scheme is based on multi-stage supercontinum generation in master oscillator power amplifier with nanosecond pulsed semiconductor seed laser operating at 1550 nm. The spectrum of seed laser is extended to 2.6 μm in Tm/Ho co-doped fiber, and the wavelength components lying in the gain band of Tm doped fiber are amplified in Tm doped double-clad fiber amplifier and then pump 10-m ZBLAN single-mode fiber. Spectral broadening from 1.9 μm to 4.3 μm with average output power of 185 mW is achieved resulting from the interaction between dispersion and nonlinear effects.

According to the dipole-dipole approximation of plasmon hybridization theory, the localized surface plasmon resonance (LSPR) spectra of a pair of closely spaced gold and silver nanodisks, i.e. the plasmonic scattering characteristics of the bimetallic nanodisk dimer, have been studied by using the finite element method (FEM). The results show that, the plasmonic scattering intensities of the bimetallic nanodisk dimer are affected by the polarization of incident electromagnetic field and its structure parameters, such as the disk diameter, thickness and gap distance. Moreover, the LSPR spectra of the bimetallic nanodisk dimer have considerably red-shift as the increasing of diameters, the decreasing of thicknesses and gap distance. It is significant to apply the heterodimer plasmonic systems on biological sensors and photosensitive detectors.

Aiming to manufacture high output power of high reflective mirror, the influence of O2 ion-beam assistance and annealing treatment to ZrO2 films and ZrO2/SiO2 high reflection films used for 441.6 nm He-Cd laser is studied. The effects of different deposition processes and post-treatment on the optical and roughness of the samples are characterized by ultraviolet-visible spectrophotometer and atomic force microscopy, respectively. The results show that O2 ion-beam assisted deposition increases the reflectivity and form a dense film structure, but the output power of laser is smaller due to the introduction of impurity defects to improve the absorption rate of film; the output power of annealed films has been improved significantly than films without annealing while impurity gas and water on film surface are eliminated.

The CNx films are deposited on monocrystalline silicon by direct current glow discharge assisted pulsed laser deposition (PLD) technique under various laser fluxes. The composition, microstructure, surface morphology, mechanical and tribological properties of the films are characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nano indenter and ball-on-disk tribometer, respectively. The results show that the films are of amorphous structure. The nitrogen atomic content of the CNx film increases from 27.7% to 34.1% with the increase of laser flux from 5.1 J/cm2 to 7.5 J/cm2. An increased area percentage of sp3C—N bond, sp2C—N bond, and a decreased area percentage of sp3C—C bond are observed in the film. An increased degree of carbon sp3 hybrid and a decreased degree of graphitization of the film are found. With the increasing of laser flux, the film hardness increases from 3.7 GPa to 5.3 GPa, the wear rate of the film decreases from 3.8×10-13 m3/(N·m) to 7.9×10-14 m3/(N·m), and the friction coefficient increases from 0.13 to 0.18, respectively.

Based on fiber Bragg grating and Fourier heat conduction equation, a method of water-heat is used to measure the thermal diffusivity of composite cylindrical structure, with theoretical analysis and experimental research represented. When the temperature of fluid in cylindrical structure rises, the initial low-temperature equilibrium state of cylindrical structure transits to high-temperature equilibrium state, its internal fluid heat is transmitted from inside to outside, the structure exhibits different temperature characteristics due to the thermal resistance. According to this principle, the center wavelength with temperature function relationship is obtained by experiment, followed to get the relationship between the center wavelength and time functions, the cylindrical structure temperature distribution function is conclude. Based on the Fourier one dimensional heat conduction equations and boundary conditions, the structural thermal diffusivity can be obtained. Result shows that the cylindrical structure thermal diffusion coefficient in heating and cooling process is consistent, which proves the feasibility of the measurement program. Water-heat balance method is simple, stable, operable, which provides a novel and feasible method for such cylindrical structure of the thermal diffusivity measurement.

A binary spatiotemproal encoding method for structured light projection of three-dimensional measurement is proposed. Through the projection of three binary encoded fringe patterns, every discontinuities in the wrapped phase are encoded with the code values in the left and right sides of the stripe boundary. During measurement, according to the initial position of discontinuities, the gray values in the left and right sides of the discontinuities in the three encoded patterns can be got, and each discontinuities can obtain a binary code, after decoding the order of the discontinuities can be calculated, thereby the corresponding order of fringe pattern can be determined. According to the order of fringe pattern, the absolute phase can be got. The experimental results show that the encoded method effectively decreases the number of encoded patterns and improves the measurement speed under the premise of ensuring the measurement accuracy and reliability, and it is very suitable for high speed three-dimensional measurement system.

In order to improve the accuracy of projected fringe deflectometry (PFD) in measuring the free-form surface, a standard intensity insensitive five-step phase-shifting algorithm in PFD test is proposed by analyzing the change patterns of the intensity on the tested surface. Fourier techniques are used to analyze the feasibility of the algorithm. The result of the computer simulation indicates that the peak value of phase retrieve precision of the proposed algorithm is 0.0042λ and the root mean square value is 0.0014λ with 1%~5% change in standard intensity and 0.1%~0.5% stray noise. After removing defocus, the precision of phase retrieve is 0.0009λ. By comparing with other phase-shifting algorithms, the performance of the algorithm manifests the advantages. As a result, the standard intensity insensitive five-step phase-shifting algorithm has a high application value in the measurement of free-form surface in PFD.

It is necessary to calibrate the optical path length before using wavelength-tuned phase-shifting interferometer based on fixed step phase-shifting algorithm to compute the phase distribution, as the precision of measurements depends on the step value. To implement the calibration for the interferometer, a new algorithm named two-frame differential average phase-shifting algorithm (TDA) is proposed to calculate phase shift directly by using the interference figure. Simulation and theory analysis are adopted to verify the accuracy and practicability of the algorithm. Furthermore, related experiments are made. The result indicates that by handling the fixed step phase-shifting interferograms with TDA, the result which matches well with the real value can be obtained; the root mean square (RMS) repeatability is better than 0.07 nm(1.106λ/10000), which meets the design index; by comparing the measurement results for the same component with this interferometer and Zygo interferometer, the RMS of the difference is 0.742 nm.

A superresolution imaging technique based on wide-field stochastic fluorescent bleaching is studied. A stream of fluorescence images is simply acquired, and single fluorophore is detected by subtracting each frame from the previous one. After image subtractions, a superresolution image is got by fitting images of single fluorescent molecules with a point dispersion function method to localize them. Then this method is used to image the human embryonic kidney cells with the conventional fluorescent probe Alex 488. Compared with the conventional fluorescence microscope, the resolution increases about 40%, showing that it works with the sample with conventional fluorescent probes and can break the diffraction limit. Also it overcomes the weakness of conventional techniques based on the precise localization of single molecules, which needs to activate and quench the fluorescent molecules repeatedly, and can not be applied to conventional fluorescent samples.

The bandwidth characteristics of fiber Bragg grating (FBG) made with femtosecond laser radiation are studied theoretically and experimentally. The simulation results show that the FBG bandwidth increases with refractive index modulation increasing, while it decreases dramatically and then saturates with grating length increasing. FBGs are fabricated in silica fiber with femtosecond laser radiation and a phase mask and then characterized by spectral analyser. FBG bandwidth remains constant when the laser power is low. However, when the laser power is large enough, FBG bandwidth increases with laser power increasing. With the exposure time increasing, FBG bandwidth increases initially and then become saturated. These results can be attributed to the change of the refractive index modulation and the grating length with femtosecond radiation.

A double cladding seven-core photonic crystal fiber (PCF) is reported with zero dispersion wavelength (ZDW) at 1036 nm and the nonlinear coefficient of 2.43 W-1·km-1 at 1060 nm. A gain-switched all polarization-maintaining fiber laser system with central wavelength of 1060 nm, pulse width of 160 ps, repetition rate of 1 MHz, beam quality M2<1.3 and average power of 4.5 W is utilized to pump a 35 m-long seven-core PCF, allowing the supercontinuum generation (SCG) with output power of 2.443 W covering wavelength from 500 nm to 1700 nm. The far field of seven-core PCF is measured, the pattern of which is in agreement with the calculated far field of in-phase supermode. The experiment can be a useful reference for the high power supercontinuum source.

The main factors affecting the stability of the process of bidirectional beam tracking in inter-satellite optical communication are investigated. The iteration convergence process of the bidirectional beam tracking is analyzed by building the model of aiming error angle which images in the array detector in the receiving terminal, with considering the influence of signal noise ratio. Steady tracking constraint conditions theoretical formula which is closer to the actual situation is deduced. The theoretical result is verified and modified by simulation and the simulation experiments on the ground with optical terminal. The above work has important significance to modify a satellite communication system.

According to the requirements of satellite optical switching network, an on-board optical switching scheduling algorithm based on data burst stream resource reservation is proposed combining the ground optical scheduling algorithm considering resource reserve and scheduling algorithm. Flow-estimation prediction is used to differentiate the data burst into single burst and burst stream according to the destination address and emergency package quality of service (QoS), and then resource reservation with different classifies is accomplished. The data channels are classified into different channels according to priorities. Different kinds of data bursts search the corresponding level channel, but high priority burst or burst stream can reave low level channels. From the comparison results of analysis and simulation, the reconfiguration time and switching time delay of optical switching matrix are not only lowed, but also the channel utility is improved. The algorithm complexity is also the same as latest available unscheduled channel with void filling in the worst condition. Packet loss rate is 10-7 on average when the load is 0.5, so the algorithm meets the requirements of optical satellite communication.

According to the theory of multi-carrier generation based on recirculating frequency shifter (RFS), a modified scheme for multi-carrier generation to improve signal to noise ratio (SNR) through noise suppression by inserting an asymmetric Mach-Zehnder interferometer (AMZI) in the RFS loop is proposed creatively. The formulas of optical signal power and amplified spontaneous emission (ASE) noise power after AMZI are deduced. According to the assumption that the AMZI arms optical path difference is much shorter than the coherence length of the laser and longer than the coherence length of the ASE noise, ASE noise is reduced by 3 dB without affecting the optical signals power simultaneously. 50 output subcarriers are generated with both simulation and experiment confirmations, respectively. The results show that carrier to noise ratio of the multi-carrier generated by the improved scheme can be as high as 37.5 dB and is up to 17.5 dB higher than the traditional structures.

In order to increase the signal-to-noise ratio and sensitivity of surface plasmon resonance (SPR) sensor, incident light should be coupled with surface plasmon polariton (SPP) as much as possible. The profile of a metal grating is studied in order to realize the highest SPR coupling efficient. The parameters of one-dimensional rectangular grating are optimized to find the highest SPR coupling efficient. Fourier expansion of the grating shape is used to analyze the contribution of each order to the excitation of SPR, which will provide analytic support to seek essence of physics of the max-coupling of SPR.

In order to detect weak absorption signal overwhelmed in noise, phase-sensitive detection technique used in wavelength modulation spectroscopy system is studied, and a design scheme for digital phase-sensitive detection is presented. An algorithm of orthogonal vector structure is analyzed, and then the extraction of harmonic component is realized by hardware circuit design and computer software programming. The experiment is carried out for the measurement of O2 in open air by scanning two absorption lines of O2 near 764 nm, and the second-harmonic signal is successfully extracted. The result shows that the detection limit for volume fraction of the system is 0.50% (with the optical path of 1 m).