The lock of double resonance frequency and spatial separation of two lights with frequency difference of 9.2 GHz in a three-mirror ring cavity and Mach-Zehnder (M-Z) interferometer are designed and confirmed. The double resonance for the two lights is accomplished when cavity length is 391.3 mm, and frequency difference is 9.2 GHz. And then, the two beams are spatial separated with unbalanced M-Z interferometer whose two arms optical path difference is 81.5 mm and phase differenceis π/2. The device lays an experimental foundation for the realization of the optical quantum exchange with a coherent atomic medium in an optical cavity.

Laser welding high strength steel 907A sandwich structure by IPG YLS-5000 laser welding system in this experiment. Tensile properties, microstructure, fracture morphology and microhardness of T-joints are measured by universal testing machine, microhardness tester, super depth of field three-dimensional digital microscope and scanning electron microscope. The results show that, the microhardnesses of welding seams and heat affected zone are higher than that of base metal. The microhardness of weld seam is between 330 HV0.2 and 360 HV0.2. Microstructures of weld seams are lathy martensites, and microstructures of heat affected zone mostly are martensites, residual austenite and a small amount of carbides. T-joint fracture is a composite fracture, which both have ductile fracture and cleavage fracture. In the case that welding speed and coke are certain, weld width and depth increase with higher laser power. Mechanical performance of T-joint mainly depends on the weld width. Under the conditions of this test process, it needs 3 times single laser welding, to ensure that the web and panel joint strength is bigger than the strength of the base metal.

The horizontal propagation characteristics of supercontinuum source in non-Kolmogorov turbulence is investigated. A superposition of narrow-band spectral components is used to simulate supercontinuum. The beam width of supercontinuum source and propagation efficiency are calculated with different inner and outer scales of turbulence and parameters α, as well as with various turbulence levels and different beam qualities for the spectral parts of supercontinuum source. The method of cross-spectral density is introduced here, and the atmospheric extinction is considered. It is shown that the change of parameter α, the outer scale and inner scale of turbulence, bring about different numerical results. It is also shown that turbulence can influence the beam width and induce deterioration of propagation efficiency, especially for the situation that all the spectral parts of supercontinuum source are Gaussian fundamental modes. When the spectral parts are higher-order modes, the factor affecting propagation of supercontinuum source dominantly is diffraction.

In order to realize the image stabilization and provide theory basis for the damping device design of camera platform, the impact of los jitter on image quality is analyzed. The reason how the los jitter produces and the characteristics of los jitter are analyzed. Based on the analysis, a new algorithm of the analysis of vibration blurred images based on the image gray-scale is proposed. The simulation results of blurred image caused by los jitter are obtained according to the simulation model. A set of vibration imaging device is built to verify the simulation results, and the device can get a blurred image by loading a vibration. Using mean square error (MSE) to measure image quality, the results show that in the range of permitted errors, the results of the impact of los jitter on image quality between simulation and experiment remain the same, which indicates the correctness of the simulation analysis. In practical applications, this method can effectively simulate the impact of los jitter on image quality.

A digital micro-holographic (DMH) system is designed for the observation of the micro-structure and mechanism of magneto rhedogical (MR) fluids. To obtain the actual magnification of ferromagnetism micro-particles in the MR fluids, the experimental method using calibration target is employed. The overall-sharpness (OS) method and the constrained least squares (CLS) filter are introduced to enhance the precision of focal plane of ferromagnetism micro-particles determination in digital holography. Based on the digital holography system and these numerical methods, the three-dimensional (3D) distribution of ferromagnetism micro-particles in MR fluids without an applied magnetic field and the micro-structure of MR fluids with an applied magnetic field are investigated. The transformation process of micro-structure of MR fluids under an applied magnetic field is monitored in real-time, the chaining structure, chaining speed and responding time of MR effect are obtained, and the responding time of MR fluids to be millisecond level is verified. The experimental results of MR fluids measured by DMH are contrasted with electron microscope, which indicates DMH is a high-efficiency, simple and real-time measuring system for measurement of behaviors of MR fluids.

In order to improve the resolution of reconstruction image in digital holography, the traditional resolution enhancement methods are studied. Here, a resolution improvement method based on extrapolation add with interpolation is proposed. The recorded hologram is interpolated and extra-padded using image algorithm. An iterative process is applied by diffracting the wave-field between hologram plane and object plane. The interpolated and extrapolated hologram can be retrieved by this method. The interpolation process can increase the special sample frequency while the extrapolation can enlarge the numerical aperture. Simultaneously, limiting factors of interpolation and extrapolation are also discussed. We have compared the new method with interpolation or extrapolartion, respectively. The simulation and experimental results show that the resolution of reconstructed image is improved significantly by using this proposed method.

Phase-shifting digital holography based on circular polarized light interference is proposed. It generates the object beam with right-rotated circular polarization and the reference beam with left-rotated circular polarization by quarter wave plate, successively changing the phase difference between the object beam and the reference beam by accurately rotating the polarizer located in front of the CCD and acquiring four digital holograms with corresponding phase changes. Numerical simulation and analysis and optical experimental results demonstrate that the method presented above can effectively remove the zero-order and conjugated images and has good-quality reconstructed image.

Laser melting deposited (LMD) TC17 titanium alloy has a vast application prospect in aerospace industries. The mechanical properties of LMD TC17 as-deposited alloy exhibits excellent strength yet lower ductility. Therefore, in an attempt to improve the mechanical properties, anneal treatment for LMD TC17 alloy is firstly studied. The volume fraction of primary α phase (αP) decreases and α lath coarsens with rising temperature, which is good for ductility but harmful for strength. Anneal treated LMD TC17 alloy cannot obtain optimistical combination of strength and ductility to conform to disk technical standard. The effect of solution-aging treatment on microstructure and mechanical properties of LMD TC17 alloy is further studied. The volume fraction of αP increases and α lath coarsens with solution temperature rising, and αS coarsens obviously when aged at high temperature. The mechanical properties are sensitive to volume fraction of αP and αS, as well as width of α lath. The ultra fine αS precipitation in β matrix results in high strength. Coarsening α lath and increasing volume fraction of αP are helpful for ductility. After 800 ℃/4 h, annealing and water quenching, then 630 ℃/8 h air cool treated, LMD TC17 alloy can obtain optimistical combination of strength and ductility, which conform to the disk technical standard.

AZ31 magnesium alloy is processed by Ndglass laser with the wavelength of 1064 nm and pulse width of 23 ns. Optical microscope (OM) and transmission electron microscope (TEM) show that ultrahigh strain rate plastic deformation induced by laser shock wave takes place at the surface layer and results in extensive formation of dislocations and twins. High density dislocations tangle and intersect with twins lead to the refinement of grains. The micro-hardness of surface layer induced by laser shock processing increases by up to 58 % and the compressive residual stress on the surface of laser shocked area reaches up to 120 MPa. The corrosion behavior of AZ31 in 3.5% NaCl solution is investigated using potentiodynamic scanning technique and the slow strain rate test (strain rate up to 1×10-6). The experimental results show that the corrosion resistance of AZ31 magnesium alloy by laser shock processing reduces due to the rise of the corrosion potential and the increment of corrosion current. However, the stress corrosion resistance of magnesium alloy after laser shock is improved greatly.

Laser-driven flyer micro-punching technology is a micro-holes manufacturing process. When an intense laser pulse irradiates onto the ablative layer, a flyer with high speed will impact the thin metal workpiece thus punching is completed. In this experiment, a short pulse Nd-YAG laser (INNOLAS Spitlight 2000) is employed, and Al foils with thickness of 20 μm are employed as flayers. AISI 1095 high-carbon steel is used as material of die, whose hardness is 58 HRC. The sheet used to make punching die is 0.5 mm in thickness and the through die-openings array in the center position are fabricated by picosecond laser. Three plum-like micro holes with 500 μm in diameter are punched simultaneously on the 20 μm thick Al foils. Under the KEYENCE VHX-1000C digital microscope, it can be found that the quality of sheared edges is good, there is an appropriate rollover zone between upper surface and punched fracture, burrs are also reduced a lot. In addition, simulations are conducted by ANSYS/LS-DYNA. The methods of finite element mesh (FEM) and smoothed particle hydrodynamics (SPH) are used. In the simulation, formation process of fracture, equivalent stress distribution, equivalent plastic strain distribution and evolution of displacement of specified particles are studied to analyze basic characteristics of laser-driven flyer micro-punching technology.

Bracket bonding technology is widely applied in clinical orthodontic practice. However, orthodontic bracket sheds off frequently due to various reasons which results in the advocating of recycling utilization of the brackets by refurbishing. In this study, the refurbishing of Mini Sprint stainless bracket by picosecond laser (wavelengths of 532 nm and 1064 nm, pulse width: <20 ps) is studied. High clean quality without any resin adhesive is achieved which overcome the limitation of edge diffraction effect during conventional laser cleaning technique. There is an evidence that the diffusion of the stress vibration due to the elastic waves generated by ultra-short pulse shots with high frequency is the picosecond laser cleaning mechanism. It is observed that there are differences between the microstructure on the top of columnar bracket base refurbished by picosecond lasers with different wavelengths. It is suggested that localized surface polaritons (LSPs) induced by the original point defects on bracket base surface under the irradiation of 532 nm picosecond laser enhance the energy distribution of laser input, which results in the formation of micro-pit structures on the bracket surface beneficial for the rebonding.

In the biomedical field, the implants need to be welded with biocompatible materials to adapt different environments in the human body. Laser transmission welding (LTW) is a new method which can be used to connect biomedical materials. However, using the experimental way to get the optimum process parameters of biomedical materials is a time-consuming and high cost project. A numerical simulation-driven experiment design modeling and optimization approach is presented. The LTW of biomedical materials is systematically investigated. Firstly, finite element modeling (FEM) is used to simulate the LTW process and the simulated results is confirmed with welding experiments. Then, an experiment design based on the FEM results is conducted and the artificial neural network (ANN) is used to establish the mathematical models between the process parameters and welding results. The predicted results of the ANN models are tested by FEM. Finally, desirability function (DF) integrated with developed non-dominating sorting genetic algorithm-II (NSGA-II) is used to carry out the multi-objective optimization of the process parameters. It demonstrates that the predicted results of the optimization are in good agreement with the simulated results and experimental results each other, so this approach provides a new way to guide the welding experiments, enhance the welding quality and reduce production cost in the biomedical sector.

During nanosecond pulse laser drilling, recast layer will form along the hole wall, which has a great effect on the quality of nickel-based high-temperature alloy. By considering the heat convection, the heat conduction, and the influence of recoil pressure, surface tension and thermal capillary force, a three dimensional mathematical model of nanosecond pulse laser drilling on nickel-based high-temperature alloy is established. Different pulse parameters of nanosecond pulse laser drilling are simulated when the pulse energy is 24 mJ. The simulated results agree with experimental results. The research shows that the thermal and mechanical effect are all very important to the formation of recast layer. During the drilling process, the temperature of keyhole wall is very high, the maximum of which can reach over 3200 K, and temperature distribution of keyhole wall is not uniform. Besides, recoil pressure is an important factor to cause the melt flow, and the velocity of melt flow caused by recoil pressure is very large, which can come to 60 m/s at peak. Due to the convection of melt in the keyhole′s opening , recast layer in this place is the thickest. Laser width has a great effect on the formation of recast layer, the greater pulse width makes the bigger recast layer thickness, and the greater melt velocity.

With advantages of low heat input, high feeding efficiency and low penetration ratio, laser hot wire welding is fit for surfacing and joining thick plate. How to obtain the stable wire transfer is the key problem for laser hot wire welding. High speed imaging is used to observe wire transfer behavior under different welding parameters, which are divided into four kinds: drop transfer, fusing transfer, continuous transfer and wire hit transfer. The continuous transfer is the stable wire transfer and it is the assurance of good weld formation. The differences among the four wire transfer kinds show that the different wire fusion positions are decided by the wire heat. Therefore, the control principles to obtain the stable wire transfer are that wire fusion heat is larger than the resistance heat, and smaller than the total of the resistance heat and the conduct heat from the molten pool to the wire. The temperature of the wire outside the molten pool is calculated. It is found that it is beneficial to obtain the stable wire transfer when the wire temperature is close to the wire fusion point.

The laser processing parameters of the sample guideway are optimized through orthogonal experiment. The microstructure analysis and hardness test of the laser-treated sample are carried out by optical microscopy, scanning electron microscope (SEM) and microhardness tester, and a contrast test of wear-resistance between the laser-treated and normally treated samples is conducted in oil-lubricated conditions. The results show that hardening depth is influenced most strongly by current, followed successively by scanning speed, pulse width and frequency. The optimized laser processing parameters are as follows: 0.25 mm/s for scanning speed, 150 A for current, 10 ms for pulse width, and 7 Hz for frequency. The spheroidal graphite is observed in the melted region of the laser-treated sample. The grain size in the phase transformation region is much smaller than that in the melted region and the grain is more evenly distributed. Compared with the normal treatment, laser processing produces a dramatic improvement in hardness without variation of gradient in distribution. When the cycle number reaches 38000, the wear-resistance of the laser-treated sample is almost one time higher than that of the normally treated one.

The cross-rolled AZ31 sheet and the cold-rolled molybdenum strip are shocked by the Thales Laser with the maximum output pulse energy of 12.5 J. Properties of these two laser shock forming (LSF) are compared and then fracture behavior and microstructure are analyzed and discussed. The results show that cold forming of AZ31 sheet and molybdenum strip with high strain rate is realized after continuously repeat laser shock under different energy densities. The LSF fracture behavior of AZ31 sheet and molybdenum strip both perform thickness thinning while a spallation phenomenon is observed during LSF of molybdenum strip. The fracture of AZ31 sheet is a mixture of ductile and brittle fracture, while that of molybdenum strip is the brittle fracture. In addition, the effect of these two metal sheet anisotropy and strain rate on the LSF formability with high energy, high strain rate and fracture behavior is discussed.

In order to study the influence of laser processing parameters on the resulting color and a possible connection of laser parameters, the heating process of the stainless steel in laser marking are simulated based on the analytical results of temperature fields generated by nanosecond laser pulse marking on the surface of stainless steel. Experimental results indicate the reasonability of the heat analysis in this study. It is found that the influence of laser process parameters on the resulting color are based on heat treatment, so the same color can be produced by different sets of parameters. Besides, different types of heat input are changed by various laser parameters, which produce different heat treatments. Accordingly, some colors can be marked only by specific sets of laser parameters.

A passively Q-switched mode-locked fiber laser based on graphene saturable absorber mirror is reported. A large-mode-area double-cladding Yb-doped photonic crystal fiber is adopted as a gain medium and a linear cavity is used. At pump power of 12 W, the maximum output power of 115 mW is obtained and the spectrum is centered at 1039 nm with full width of half maximum of 6 nm. The experimental results and the phenomenon are discussed and analyzed.

In high power excimer laser system, due to high gain and nonstorage medium, amplified spontaneous emission (ASE) is the key factor impacting on the signal contrast of the system output. In angular multiplexing master oscillator power amplifier (MOPA) laser amplifier chain, combination of the electro-optical switch and gain control method is used to suppress ASE. An electro-optical (E-O) switch is plugged after the first amplifier, and the other polarizer component of the analyzer is used for controlling the light beam and as gain controlling beam of the next amplifier. The optical path is constructed, principle experiments are carried out, and signal contrast up to 403001 is obtained in the second pre-amplifier. The advantages of this method are less energy loss and lower damage threshold request. The combination of E-O switch and gain control method gives a good solution to the ASE suppression of the first two pre-amplifiers.

In order to improve the output power and wall plug efficiency (WPE) of the broad area 940 nm semiconductor laser diode (LD), we design and fabricate a new type quantum well LD with a step graded index (GRIN) structure. By using a two-dimensional self-consistent software, the energy band structures of step GRIN structure laser and traditional separate confinement heterojunction (SCH) laser are simulated and compared. The result shows the significant elimination of band offset between heterojunctions in step GRIN structure. High quality laser materials are obtained by using low-pressure metal organic chemical vapor deposition (LP-MOCVD) method. Broad area laser devices with 100 μm wide stripe and 2000 μm long cavity are fabricated and tested under 25 ℃ continuous wave (CW) operation condition. The new step GRIN structure laser diode shows a drop down voltage of 0.07 V at 10 A operation current than the SCH structure laser. By optimizing the design and growth method, the internal loss of step GRIN structure laser is reduced from 0.52 cm-1 to 0.43 cm-1 and the wall plug efficiency is increased from 69% to 76%. The LD chip yields a slope efficiency of 1.24 W/A and 10.0 W at 10 A operation current at 25 ℃ room temperature.

A variety of water cooling designs for conduction cooling end pumped slab (CCEPS) laser are simulated with computational fluid dynamics (CFD) methods. The difference between fluid-solid coupled method and mere heat conduction simulation in gain media is comparatively investigated. The influences of the size, number of the cooling channels and flow rate of the cooling water to the temperature distribution of the slab and the flow resistance characteristics of the heat sink are studied. In general, decreasing of characteristic size, increasing of channel numbers and the flow rate of the cooling water can reduce the thermal resistance between the solid and fluid interface. Thus total heat transfer coefficient is extended to a very high level. That is, total thermal resistance of heat sink can be remarkably reduced with micro-channels cooling structure compared to cavity or mini-channels structure. The temperature level of gain media can be apparently lowered down. However, the pressure loss in heat sink increases significantly.

An all-fiber continuous-wave thulium-doped fiber laser with narrow linear width based on a master oscillator power amplifier (MOPA) system that consists of a seed source and two-stage thulium-doped all-fiber amplifiers pumped by fiber-pigtailed multimode diodes at 793 nm is reported. The maximum output power is 120 W with a slope efficiency of 60% after the seed source amplified by a two-stage thulium-doped amplifier. The center wavelength is 1986 nm and 3 dB spectral width is only 0.48 nm. The maximum output power is currently limited by available pump power. In addition, a broadband thulium-doped superfluorescent source with average output power of 122 W based on the same MOPA configuration is reported. The center wavelength is 1990 nm and 3 dB spectral width is 25 nm.

Pulsed laser with 100 MHz repetition rate and 1 ns pulse width is obtained by intensity modulating a continous wave (CW) single frequency fiber laser with 70 kHz line width. The spectrum line width of the modulated pulsed laser is less than 0.8 GHz. A combined amplification setup with a fiber amplifier and two solid-state amplifiers is used to achieve power amplification of the pulsed laser. The output average powers are 13 W and 32.9 W after first and second solid-state laser amplifier, respectively. The small signal of the modulated pulsed laser is firstly amplified up to 2 W by a fiber pre-amplifier. The pre-amplified laser transmits the two solid-state main amplifiers for further power amplification. The combined amplification setup effectively weakens the stimulated scattering and amplified spontaneous emission (ASE) in the fiber amplifier. After amplification, the output laser preserves line width of 0.8 GHz with pulse width of 1 ns and repetition rate of 100 MHz. Such a laser output with single frequency, narrow pulse width and high repletion rate is required in many special applications.

By means of the diffraction loss sensitivity of the diaphragm, the anti-alignment capability of ring laser gyro (RLG) is analyzed numerically. Deriving from the condition of mode suppression of RLG, the lower limit of mode suppression ratio (MSR), which is defined as the ratio of the loss of a higher order transverse mode to that of the primary transverse mode, is calculated to obtain the optimal diaphragm diffraction loss sensitivity. The dependence of the lower limit of MSR (LLMSR) for a RLG on its gain level as well as its total mirror loss is investigated both numerically and experimentally, with the results showing that the higher the gain level, the higher the LLMSR, while the higher the total mirror loss, the lower the LLMSR. These results will be of great significance for the MSR optimizing control during the resonator alignment of RLG.

For side lobes caused by the high spatial frequency oscillations in the output beam of off-axis negative-branch unstable-waveguide hybrid resonator of 2 kW radio frequency slab CO2 laser, the near-field distributions of the hybrid resonator are investigated by numerical simulation and experimental method. The eigenvector method and the analytical expression of the rectangular waveguide resonator are used for the numerical simulation. The variations of intensity profiles of the output beam in the beam shaping system and the spatial filter design of beam shaping system are also studied with Collins integral expression. The results show that the laser emits a simple astigmatic beam with a rectangular intensity distribution. The unshaped beam has severe high spatial frequency oscillations in the unstable direction. The side lobes of the unshaped beam are eliminated and the unshaped beam is changed into an approximately circular, nearly Gaussian-shaped beam beam by a beam shaping system with a spatial filter. The shaped beam propagation factor M2 is 1.10 in the unstable direction and M2 is 1.08 in the waveguide direction.

Passively Q-switching of dual-wavelength lasers at 1064 nm and 1342 nm is realized in a laser doide (LD) end-pumped three-mirror compound resonator Nd:YVO4 laser using graphene dispersion as the saturable absorber, by setting the cavity lengths and the output mirror transmissivities of two branch cavity appropriatly. When the transmissivity of 1064 nm branch cavity is 20%, both 1064 nm pulse with 10.8 ns duration and 1342 nm pulse with 12.5 ns duration are achieved, and the 1064 nm pulse is in the front, the time interval between two pulses is 16 ns. Both 1064nm pulse with 11.3 ns duration and 1342 nm pulse with 14.2 ns duration are achieved when the transmissivity of 1064 nm branch cavity is 25%, and 1342 nm pulse is in the front, the time interval between two pulses is 19 ns. A reasonable theoretical explanation is given to the above-mentioned experiment according to dual-wavelength line competition and the saturable absorption of grephene in 1064 nm and 1342 nm lasers.

Light transmission properties of one-dimensional sinc function photonic crystals containing a dispersive defect layer with negative refractive index are studied by transfer matrix method. The results show that one-dimensional sinc function photonic crystals containing a dispersive defect layer with negative refractive index have a broader forbidden-bands than one-dimensional cosine function photonic crystals containing the same defect layer. The forbidden bandwidth of this function photonic crystals is rapidly shrunk and narrowed with the increase of the refractive index nB(0)、nA(0) or half period thickness of the dielectric layer, and defect modes are disappeared. The forbidden bandwidth of this function photonic crystals is widened with the increase of angles of incidence, the defect modes are redshift with the forbidden-bands, and the structure of forbidden bands is also sensitive to changes on the position of a dispersive defect layer with negative refractive index. But the thickness variation of defect layers can not change the position and width of the forbidden band, and defect modes move toward the center of the band gap with the increase of the defect layer thickness. These results are important for the design of one-dimensional function photonic crystals.

In the high-precision photogrammetric, binocular vision measurement method is an efficient and feasible method. In order to explore the effect of the location relationship between cameras on measurement results, the interference factors such as camera calibration, orientation and image coordinate extraction are considered as ideal values. From the perspective of mathematics model of interchange measurement the measurement results and accuracy are analyzed through combining the main factors such as the camera field angle, merging angle and radiant angle of infrared light emitting diode (LED). It ultimately gives the stations optimization strategy by analyzing the measuring results and accuracy of the infrared LED in the measurement area which are fixed as control points at various locations between the cameras.

A fast phase retrieval method for annular pupil using spot image is proposed. The analytic formula to compute point spread function for annular pupil is derived. With this formula, the point spread function is represented as linear composition of polynomials, the coefficients of which are just the annular Zernike expansion coefficients of the pupil phase. The objective function and its gradient in phase retrieval for annular pupil are computed with this formula. It can avoid the Fourier transform and finite differences, which are necessary in common phase retrieval method, and decrease the computational burden in phase retrieval. The effectiveness of the proposed fast phase retrieval for annular pupil is demonstrated using numerical simulation and phase retrieval experiment. Experimental results indicate that the proposed method can improve the speed of phase retrieval for annular pupil effectively.

A surface measurement method of convex aspherical lens with large clear aperture is proposed based on an aspherical compensation mirror. It overcomes the difficulty that multiple lenses are needed for compensating the normal aberration of convex aspherical lens. In addition, it simplifies the design and reduces the cost. Aspherical lens measurement system with large diameter is designed and implemented. Source of error is systematically analyzed, and elimination method of error is also proposed. In order to verify the feasibility of the proposed method, a convex aspherical lens with an aperture of 270 mm is inspected. The peak valley (PV) value and root mean square (RMS) of the tested aspherical surface are 0.585λ and 0.083λ, respectively. This method provides a technical reference for large aperture aspherical surface testing, and also can be used in the field of rough polishing testing.

As a super-precision and un-touched measuring system, dual-frequency laser interferometers with the advantages of high accuracy, large-scale and high measurement speed plays an important role in many fields. It is well known that environments such as temperature, air pressure and humidity play the most influence on measurement precision of dual-frequency laser interferometer. In order to improve precision, environments must be controlled and compensated. The environment compensation technologies are described and a novel wavelength tracker is developed. The test results contrasted with Edlen show that the novel wavelength tracker has good effects on environmental compensation. Moreover, the servo controlling precision of moving stage measured by dual-frequency interferometer compensated with the novel wavelength tracker is 1.61 nm.

A numerical model of time-resolved laser-induced radiation model of micro-scale carbon particulates based on non-Fourier heat diffusion is developed, through adapting thermal relaxation time to present time lag between thermal disturbance and response inside particles, as well as correcting air conductivity coefficient via Kn number to judge flux region of heated particles. Theoretical temperature and radiation signal profiles of heated carbon particulate are presented, in order to discuss the effect of radiation signals of micro-scale particles on different thermal relaxations and laser fluences. The results show non-Fourier phenomenon becomes obvious in radiation signals, in the case of high thermal relaxation, high laser fluence, and small particles. The discussion of the numerical results provides guidance for laser-induced radiation technique measuring the concentration and size of micro-scale carbon particulates in high temperature environment.

A scheme on frequency up-conversion of radio-over-fiber (RoF) signal is proposed to use dispersion-compressed short pulse rather than the tradition continuous wave carrier as carrier. By compressing pulse width based on optical fiber dispersion, harmonic component is strengthened, signal component over pulse carrier at the receiving end is converted to higher harmonic waves, and finally the up-conversion is completed at the remote antenna unit (RAU). The generation of high-frequency microwave signal with low frequency local oscillator (LO) doesn′t need any electric frequency multiplier and mixer in transmitting terminal, rather than a filter which can select the desired signal in receiving terminal, and the system is simplified. In this system only with an optical amplifier, 2 Gbit/s signal can be up-converted to 16 GHz after transmission of 60 km standard single-mode fiber (SMF), and the bit error rate (BER) is below 10-8 after 5.4 m wireless communication, no need of on-line, pre-amplification, dispersion compensation and optical filter.

A nonlinearity model of the detector′s power-current (P-I) characteristics is established based on the theories and experiments in respect to photo-electric conversion efficiency. The model is used to analyze the detector′s photo-electric convertion ability in both linear and nonlinear cases. With the theories and experiments, the frequency response of the visible light communication (VLC) system when photodiode becomes saturated is studied. It proves that although the afterglow of fluorescent powder cannot be modulated in high speed, it can decrease the frequency response of the detector. The detector′s saturation due to the high optical power has an effect on the frequency response and the bandwidth in VLC system.

The amplification and nonlinear broadening dynamics of dissipative soliton are studied. A compact all-fiber highly coherent supercontinuum source is successfully developed. The seed laser in the experiment is a dissipative all-fiber mode-locked laser working in all-normal dispersion region. The nonlinear polarization rotation mode-locking technology is applied. The output pulse width of the dissipative soliton is 5.18 ps with a repetition rate of 24 MHz. The seed laser pulse is amplified with a 15-m double-clad ytterbium-doped fiber, then is coupled into a 10 m photonic crystal fiber. The supercontinuum generation achieves more than one octave of bandwidth (550～1750 nm) at 700 mW average power. The amplification process of dissipative soliton and the mechanism of supercontinuum generation in anomalous dispersion region of photonic crystal fiber are systematically studied.

A quasi-distributed fiber Bragg grating (FBG) demodulating system is developed by combining the wavelength tunable laser and the optical time domain reflectometry (OTDR) technique. By optimizing the optical pulse modulation and the light detection circuit, the ultra-weak reflective FBGs can be demodulated and located. In the experiment, 20 ultra-weak reflective FBGs of only 0.01% reflection with the interval space of 2 m are connected to the end of a 5.8 km long fiber. All the central wavelength and position of the FBGs can be measured simultaneously. The measured FBG center wavelength has a good linearity of 99.7%.

A polarization-selective photodetector with high performance is necessary for polarization sensitive systems. A hybrid integrated photodetector is proposed by integrating a silicon resonant waveguide grating with an InP/InGaAs PIN photodetector. The resonant waveguide grating is designed using rigorous coupled-wave analysis method. Parameters of the hybrid integrated photodetector are optimized by finite difference time domain method. The simulated results indicate that the proposed photodetector exhibits high quantum efficiency, large incident angle tolerance, and polarization selectivity in a broad spectral range, which can be used in polarization sensitive systems.

A room-temperature-operation tunable continuous-wave terahertz (THz) radiation and detection system, which consists of two external cavity semiconductor lasers and an interdigited finger bow-tie antenna on low temperature GaAs substrate, is established based on photomixing and coherent detection technology. The generation and detection of continuous-wave THz wave are realized, and the spectral purity of system is better than 1 MHz. The signal-to-noise ratio (SNR) of the system is better than 50 dB with frequency below 0.70 THz, and the maximum SNR of 64 dB is achieved at 0.50 THz. In addition, the relation between the electric field intensity of the radiated terahertz wave and the biased electrical field for the photoconductive antenna is experimentally given, and the impact of multi-longitudinal mode operation of the external cavity semiconductor laser on continuous-wave THz radiation is discussed.

The alignment method of off-axis three-mirror anastigmat combines initial positioning and computer-aided alignment. During manufacturing, due to the limit of testing methods, the off-axis fabrication and off-axis angle cannot be measured precisely. The initial positioning based on the manufacturing off-axis parameter can bring large initial aberration, which can not be converged when using computer-aided alignment. The optical path is analyzed based on the auto-collimation principle, and the mathematic relationship between the position of off-axis mirror and the reflected image is derived. A system based on the relationship is given to measure the off-axis fabrication and off-axis angle, it includes the right angle plate of high precision, linear guides of high precision, the special center orientation tool, internal focusing telescope and self-standardized micro-flat optical tube. The measurement accuracy of off-axis fabrication and off-axis angle is ±0.05mm and ±10″ respectively.

A method which can well distribute optical power of each component of zoom system through analysis of Matlab to bring down excessive dependence on experiences is proposed. We treat the gaps between each component as the initial configuration, and the object distance of zoom group as free parameters, then find out the optical power distribution and movement type which meet the space requirement. Matlab simulation can draw mobile trajectory of each component in the process of zooming and analyze the drift angle, field angle and other factors affect on the system complexity, which may help to achieve the reasonable allocation of optical power and initial configuration. It is a wonderful idea for the green hands. A 14× zoom optical system is designed, and its optimized optical power allocation is close to the results of calculation using Matlab, which may verify the feasibility of the scheme.

The printed circuit board (PCB), such as the high density interconnection (HDI), can be exposed by the laser direct image (LDI) lithography tool when the thickness range of the HDI substrate is from 0.025 mm to 3 mm. Accordingly, it is designed that the total track of a lithography projective lens is variable. The double telecentricity layout is used and the range of variable total track is 3 mm by reduction of double telecentricity error. The image quality of this projective lens, such as wave front error (WFE), distortion and modulation transfer function (MTF), is very good when the range of the variable total track is from 0 to 3 mm by the reasonable match between positive lenses and negative lenses. It is confirmed that a lithography projective lens with a variable total track is available by this method of reduction of double telecentricity error, and the image quality of this projective lens with the variable total track meet the actual requirements of the LDI lithography tool.

Many measurement errors affect the positioning accuracy of the laser point cloud obtained from airborne laser scanning (ALS). These error factors exist together and influence each other. Therefore, it is of practical significance to find out them, and to analysis their impact sizes and make a sorting. The working principle of conical scanning mode airborne laser scanner is analyzed, and error factors affecting the positioning accuracy of laser point cloud are determined. Furthermore, the transfer relationship between the error factors and the three-dimensional (3D) coordinate errors of the laser point cloud is established. By using multiple linear regression method, regression equations between the error factors and the 3D coordinate errors are established, and the impact significance of each error factor on the 3D coordinate errors is quantitatively evaluated and further sorted. The study provides an important theoretical basis for compensating the significant error factors, so as to effectively improve position accuracy of laser point cloud.

Light frequency shift is one of the important factors which influence the performance of the standard frequency of a coherent population trapping (CPT) atomic clock. Usually, it takes a long time to optimize the light frequency shift behavior of a CPT atomic clock. With field programmable gate array, a digital quadrature demodulation method which considerably reduces the time and amount of work to optimize light frequency shift behavior of a CPT atomic clock is developed. Applying the method to the production of the CPT atomic clocks, the debug period and workload can be reduced.

The performance of photoacoustic cell is one of the important factors which determine the trace gas detection system sensitivity based on photoacoustic spectroscopy (PAS). The photoacoustic cell design is a key part of PAS gas detection system. A first-order longitudinal length adjustable feedback resonant photoacoustic cell is designed based on PAS and acoustic theory. The resonance frequency is conveniently achieved by actual measurement, which effectively avoids the double counting process and the manufacturing error, makes the measurement easier and improves the sensitivity of detection system. The PAS trace gas detection system is built. The impacts of cavity length, photoacoustic cell length and source power on photoacoustic signal are discussed experimentally. The signal to noise ratio is 39.5 and sensitivity is 2.78×10-6.

By home-made experimental setup with aqueous jets and dual-pulse laser-induced breakdown spectroscopy (LIBS) technique, the dual-pulse and single pulse LIBS are applied to the detection of Al trace element in AlCl3 aqueous and mixed compound solution jets. The optimum parameters of dual-pulse and single pulse LIBS experiment are presented. Both the dual-pulse and single pulse LIBS detection limits of mass fraction of Al element in AlCl3 aqueous and mixed compound solutions are obtained as 26.79×10-6, 28.85×10-6 and 11.93×10-6, 14.46×10-6 respectively under the optimum experiment conditions. It is shown that detection sensitivity of dual-pulse LIBS is enhanced dramatically compared to the single pulse case.

In order to apply laser induced breakdown spectroscopy (LIBS) to the study of the features of heating surface metallic materials, 12Cr1MoV steel samples with different grain sizes (class 7, 6, 5 and 4) are selected as the objects. Under different experimental conditions (both laser energy and spot diameter), the relevance between spectral characteristics and different classes of 12Cr1MoV grain size is investigated. The results show that it makes a well correlation between Fe or Cr spectral intensities and different grain size classes in different enery conditions with the spot diameter of 206 μm. It is found that in the condition of 100.6 mJ laser energy and 206 μm spot diameter, the fitting degree is 0.987 which is better than the fitting effect directly obtained by the spectral intensity, when analyse the ratio of Fe ion line and atomic line.