Informations about the optical and hygroscopic properties are important for understanding the haze formation mechanism. In order to detect the optical properties and hygroscopic behavior of atmospheric aerosol in fog and haze days under the background of environmental relative humidity change, two cases of typical fog and haze days in Hefei area are studied as examples, and aerosol extinction coefficient, visibility, the Angstrom wavelength index and extinction coefficient hygroscopic growth factor are obtained by using horizontal detection of dual-wavelength lidar. Case study results show that the lidar, with the advantage of detecting unperturbed and ambient atmospheric conditions, can effectively gain the change rule of fog aerosol optical parameters of the hygroscopic absorption and growth factor varying with relative humidity.

The influence of laser irradiation on enzyme activity depends on the wavelength and energy of the light. The influence of wavelength and energy on enzyme activity is studied systematically, and whether laser and LED light sources have the same effect on enzyme activity is examined. Phospholipase C is exposed at 0~810 J/cm2 of lasers at the wavelength of 532, 808, 1064, 1342 nm and two LED sources at the wavelength of 640 nm and 810 nm respectively, and enzyme responses are evaluated by measuring ceramide concentration using high performance thin-layer chromatography (HPTLC) after irradiation of 0.5, 1, 2, 3, 4, 6, 17, 24 h. The duration of effect is evaluated from the experimental data. The enzyme activity can be increased by using either laser or LED source whose wavelength is located within a certain range, and the effect depends on the energy and wavelength of the light. The increase in enzyme activity continues for about 4 h after irradiation. The result shows that the duration of enzyme activity change should be included as one of the main laser parameters while reporting the effect of laser irradiation on enzymes. Besides, laser sources and LED sources have the same effect on enzyme activity with the same wavelength and absorbed energy.

In order to build right focus window for optical measure equipment in shooting range, a novel method combined with visual perception is proposed. It can cut down compute time and overcome disturbance of background during auto-focus procedure based on image. The image is separated into several sub-images by using pyramid structure. The function and principle of cells in human visual cortex are simulated by Gabor filter and difference of Gaussian (DoG) model. Feature maps from the sub-images are extracted and combined together to get final feature map based on visual perception. The threshold is used to denoise disturbance in the feature map and build regular rectangle focus window area by spreading boundary. After plenty of experiments，the results show that this method can build focus window rapidly with exact size and right position for the target in image. And it is available for every kinds of focus states, especially for deep-defocus state. To deal with the image of 720 pixel×576 pixel, the compute time is less than 130 ms. The proposed method can construct steady and exact focus window during the whole focus procedure, which satisfies the practical demand of shooting range and is of great and wide value for engineering application.

High cycle fatigue is one of the main failures of aero-engine. The improvement of HCF properties by laser shock processing (LSP) with multiple impacts is researched. Vibration fatigue tests of different 1Cr11Ni2W2MoV stainless steel samples are conducted at room temperature. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and metallography microscope are used to investigate the influence on microstructure and mechanical performances with different impacts. The results show that with the laser impact times increasing, the residual stress and the roughness increase, while the depth of microstructure refining layer doesn′t change. The surface compressive residual stress is driven to saturation and the saturation value is up to -100%σ0.2. The depth of compressive stress has a wider increase with the impact times increaseing. Vibration tests show that the fatigue properties improve with the impact times increasing. By the superimposed effect of shock waves in multi-impact processing, the shock wave can translate into deeper materials, which make a great contribution to the greater depth of compressive residual stress and deformation microstructure, and to the further improvement of fatigue properties with multiple impacts at room temperature.

To understand the material removal mechanism better in laser cutting, the shape and characteristic parameter distribution of removal melt particles are obtained through image processing with imagine-pro plus (IPP) software. Laser cutting of 1000 series aluminum alloy sheets with thickness of 0.85 mm, is carried out based on the vapour-melt ratio controlled. The removal melt particles are classified three kinds of shape through the metric rule, including the rounded particle, the quasi-rounded particle and the tadpole-shape particle. The results show the percentage of rounded particles increases in removal melt particles with vapour-melt ratio increasing, but the percentage of quasi-rounded and tadpole-shape decreases, and the average size of particles reduces with vapour-melt ratio increasing. Also the cutting quality improves with the increase of vapour-melt ratio in test. A removal model is established, which indicates that the cutting quality has a significant relationship with removal melt. Finally the high quality cutting and the slot array antenna sheet are obtained.

Sheet thickness is an important factor affecting shock effect when metal sheet is treated by two-sided simultaneous laser shock processing (LSP). AM50 Mg alloy sheets with different thicknesses are treated by two-sided simultaneous LSP, residual stress fields of all AM50 Mg alloy sheets are simulated by ABAQUS software. Influence mechanism of two-sided simultaneous LSP on metal sheet as a function of sheet thickness is systematically investigated, then residual stress distributions in the axial and radial direction are analyzed. Results show that under the same laser spot diameter, pulse width and peak pressure, with sheet thickness increasing, compressive residual stress in the model becomes more uniform and regular, and the influence depth turns deeper. When the sheet thickness reaches a threshold, both of them reach saturation. The appropriate thickness of AM50 Mg alloy sheet treated by two-sided simultaneous LSP should be 4 mm and more, when peak pressure is 1600 MPa, pulse width is 57 ns and laser spot diameter is 3 mm.

SUS301L stainless steel sheet with thickness of 2 mm is welded using CO2 laser-metal inert gas arc (MIG) hybrid welding. The microstructure and phase composition of joint are analyzed in detail. Furthermore, the influence of assembly gap on weld microstructures and performance is investigated. Results indicate that the joint is composed of fine dendritic structure in the weld center and columnar crystals far away from the center zone. And the columnar crystals are found growing perpendicularly to the fusion line. Grain size increases with the distance from the center of weld. Phase composition in the joint is identified as γ austenite and a little δ ferrite. The solidification type of weld is dominated by ferrite-austenite (FA) mode and the transformation from δ to γ is dominated by massive transformation and short range free diffusion. With the increase of assembly gap, residual δ content and tensile strength of weld decrease gradually. The fracture occurs at the area of coarse columnar grain near the fusion line.

Thin wall samples from Ti2AlNb-based alloy are deposited on TA15 titanium alloy plate by laser melting deposition of coaxially fed Ti-22Al-25Nb metallic powders. The microstructure, phase constitution for as-deposited and heat treated materials are investigated. The tensile properties along longitude direction at room temperature and 750 ℃ high temperature are tested for materials after heat treatment. The results show that laser direct deposited Ti2AlNb-based alloy is full dense. Both as-deposited and heat treated materials are composed of B2, α2 and O phases. For the deposited Ti2AlNb-based alloy after heat treatment, the tensile strength at room temperature and 750 ℃ are 1012 MPa and 702 MPa, with elongations of 1.8% and 2.2%, respectively.

Aero-engine combustion chamber is a round thin-walled part comprised of outward, upright and inward walls. For the characteristic of the round thin-walled parts, the mathematical models are developed based on the critical condition of offset melting powder without support and the cladding height of single-layer. Both inward and outward thin-walled parts are investigated for the offset value, forming height and angle of inclination. The results show that, due to the difference of geometry the inward thin-walled parts have longer offset, higher forming height and bigger slope angle than those of outward thin-walled parts under equal offset condition. The simulated parts of aero-engine combustion chamber are formed in the experiment. The results provide further understanding for laser forming round thin-walled parts both in theory and application.

Aluminum-lithium alloys are considered to be one of the most ideal light-weight materials for aerospace applications. 2198-T851 with thickness of 1.76 mm is welded with filler wire ER4047 by using a high power fiber laser. The effects of the laser power, welding speed and wire feeding velocity on solidification cracking susceptibility and microstructures are investigated, as well as the joint microstructure and mechanical properties under the optimal welding process. The results indicate that a joint with good surface appearance and no hot crack is obtained with the optimal welding parameters of 4 kW laser power, 4 m/min welding speed and 4 m/min wire feeding velocity. The average tensile strength of joints is 342 MPa, and reaches 65.4% of the tensile strength of base metal. The bond is the weakness region of the joint.

A fiber-coupled laser diode (LD) end-pumped Tm:YAG laser operated under cryogenic condition is studied. The central wavelength of the fiber-coupled LD is 785 nm at 15 ℃, with fiber core diameter of 400 μm and numerical aperture of 0.22. The Tm:YAG crystal, with the dimension of 3 mm×3 mm×8 mm, is doped with Tm3+ with atomic fraction of 3%. Pulse tube cryocooler used to cool the crystal in the experiment is a new type of micro-cryocooler with the advantages of no vibration in the cold end, simple structure and long lifetime. The copper heat embedded with Tm:YAG crystal is attached to the cold head of the cryocooler and then fixed in a vacuum chamber to prevent frost. By adjusting the crystal temperature, the dependence of threshold and output power of Tm:YAG laser on crystal temperature in the range of 80～290 K is investigated. When the crystal temperature is 80 K, the highest continuous wave output power of 3.78 W at 2.013 μm under the pumping power of 9 W is achieved, corresponding to optical-optical conversion efficiency of 42%, and slope efficiency of 44.9%.

Novel multi-wavelength passively mode-locked erbium-doped fiber laser based on single-walled carbon nanotube/polyimide film and Mach-Zehnder filter is proposed. A 3.2-m length of erbium-doped fiber acts as a gain medium. It is forward pumped by a 980-nm laser diode. The single-walled carbon nanotubes acts as mode locking devices. When pump power adds to 24 mW, the laser produces a stable pulse train with central wavelength of 1559.3 nm, 3 dB spectral width of 1.4 nm and average power of 0.8 mW. Then the Mach-Zehnder filter is introduced in the ring cavity as a comb filter. When the pump power is 25 mW, a stable 15-wavelength laser pulse is obtained by adjusting the polarization controller at the room temperature. The wavelength interval is 0.1 nm. The fiber laser can obtain stable multi-wavelength pulse train after continuous observation over 0.5 h.

An effective radially polarized beam can be generated by coherently combined beams, each one with an appropriately oriented linear polarization, named radially polarized coherent beams array. However, the characteristic of the effective radially polarized beam is different from that of an ideal one. Based on the Richards-Wolf vector diffraction theory, numerical calculation is performed to analyze the intensity distribution at focal plane of a tightly focused radially polarized coherent beams array. The parameter, such as the full-width at half-maximum (FWHM) of the longitudinal and total field, the purity parameter and the generation efficiency of the longitudinal field are used to characterize the intensity distribution at focal plane. The results show that the azimuthally polarized field exists at focal plane for a tightly focused radially polarized coherent beams array, in contrast with an ideal radially polarized beam. To generate a radially polarized beam with better beam quality, the beamlets should be placed in one single ring and close to the pupil edge of the objective lens. When increasing the number of beams in the single-ring-shaped array, the FWHM of the longitudinal and total field and the purity parameter remain almost unchanged, but the generation efficiency of the longitudinal field is improved.

By employing positive branch confocal unstable resonator, design of cavity parameters and experimental research on non-chain pulsed DF laser are carried out. The advantages of suppressing divergence angle and improving beam quality are shown by comparing plano-concave stable resonator with unstable resonator. To estimate the beam quality, diffraction limit magnification β is chosen as evaluating criterion, which can incarnate both the energy focusing degree and divergence angle excursion. 86.5% enveloping energy is used to define spot size, and 90-10 knife edge method is adopted to measure it. Nine sets of mirrors with different magnifications and mode volumes are tested and compared, and optimization method of unstable cavity parameters is concluded. Taking energy, divergence and diffraction limit magnification into account, the optimal parameters are M=1.89, D=40 mm. Laser beam with divergence angle of 0.74 mrad, β=1.35, laser energy of 1.86 J, and peak power of 16.4 MW is obtained at these parameters.

In order to solve the problem that high fill factor and accurate surface shape of the refractive lens are difficult to realize, a new approach for homogenization of semiconductor laser planar array by using diffractive micro-lens array is proposed. Diffractive micro-lens array with phase steps based on the theory of scalar diffraction is designed. The equations of intensity distribution from the input plane to the output plane are derived. The numerical simulation and experiment of the non-imaging homogenization system of diffractive micro-lens array are carried out successfully. When the diameter of the micro-lens is 0.125 mm, relative aperture is 0.1 and phase step number is 8, in fast axis, the non-homogeneity is 12.34% and the energy efficiency is 96.6%; in slow axis, the non-homogeneity is 5.42% and the energy efficiency is 95.74%. The result of the experiment agrees well with the simulated result, proving the feasibility of the system of the diffractive micro-lens array for beam homogenization.

A mode-locked radially polarized laser is generated based on the difference of thermal focal length in side-pumped Nd:YAG and the condition of mode-locking by the semiconductor saturable absorption mirror (SESAM). The spot size of radial polarization and azimuthal polarization with different pumping currents, and the parameters of the LD side-pumped Nd:YAG four-mirror-folded passively mode-locked cavity are analyzed. The maximum output power of 13 W with the frequency of 59 MHz and the wavelength of 1064 nm is acquired. We demonstrate that the purity of the radially polarized beam is more than 92%.

Picosecond pulses have an important application in supercontinuum sources. A picosecond ytterbium-doped fiber laser passively mode-locked by an semiconductor saturable absorber mirror (SESAM) in linear cavity is constructed, and the effects of the reflectivity as well as the bandwidth of the fiber Bragg grating and the parameters of the SESAM on the characteristics of the output pulse are analyzed in detail and compared with each other. The experimental results show that a fiber Bragg grating with 10% reflectivity and 0.3 nm reflection bandwidth is more profitable for the mode-locking stability of the fiber laser, and the fiber laser has a wide working range for the parameters of the SESAM. In addition, the non-saturable loss of the SESAM has an important influence on the average output power of the fiber laser, and a smaller value of non-saturable loss results in higher output power for the laser.

High pulse energy mid-infrared laser has important applications in remote atmospheric detection and object recognition. To obtain high pulse energy mid-infrared laser radiation, a self-grown ZnGeP2 (ZGP) crystal is employed as the nonlinear crystal of optical parametric oscillator, and the cutting angle is 55° with the type Ⅰ phase matching. A self-developed 2.09 μm La3Ga5SiO14 (LGS) electro-optically Q-switched Cr, Tm, Ho:YAG laser is used to pump the ZGP optical parametric oscillator (OPO) directly. The OPO conversion efficiency can be improved with a round-trip pumping way which can reflect pump light. The 2.09 μm Q-switched holmium laser radiation with pulse width of about 35 ns is used to pump the ZGP-OPO directly. Pulse energy of 5.9 mJ at 4.8 μm with an optical-optical conversion efficiency of 13.1% and a slop efficiency of 17% is obtained by the singly resonate operation; pulse energy of 9 mJ at 3.7 μm and 4.8 μm with an optical-optical conversion efficiency of 23.9% and a slop efficiency of 26.7% is obtained by the doubly resonate operation.

In high power laser driver, frequency modulation to amplitude modulation (FM-to-AM) effect is a key parameter that could restrict fusion ignition, so qualitative investigation and evaluation are necessary. Based on acceptable bandwidth of the crystal, the physical mechanism of FM-to-AM effect in the process of frequency conversion is investigated from aspects of spectrum aberration and instantaneous frequency, respectively. Using instantaneous frequency, the correlation between phase modulation and intensity modulation is qualitatively analyzed, and the variation regularity of modulation frequency regarding the third harmonic generation (THG) intensity at the optimal phase matching angle is presented. With analytical derivation of modulation degree model, the modulation characteristics of output THG laser are quantitatively analyzed and the influences of input bandwidth and power density on THG intensity modulation are quantitatively studied as well. By numerical simulation, the reliability of the model is verified. All obtained results can give theoretical guide to suppress intensity modulation induced by FM-to-AM effects in THG process.

In order to improve the damage threshold of semiconductor laser facet film and increase the laser output power, the causes of the catastrophic optical mirror damage in the laser are discussed. The highest field intensity in the high-reflective (HR) film is moved out of the interface in view of the damage principle. The reflectance and electric field distribution are simulated with film thickness changing continuously by using optical transmission matrix to get the optimized high reflective film, and the film damage is reduced at the interface by the optimized film. LaB6 with improved higher plasma density is adopted as in situ plasma source, and the cleaning parameter of ion source is optimized. In the earlier period of preparing film, facet deoxidation is made with ion pre-cleaning in vacuum environment, and the film is fabricated with ion-assisted electron beam evaporation, and the stability of the film is tested under high temperature and high humidity environment. The laser output power is raised from 4.5 W to 7.02 W, operating current is raised from 5 A to 8 A in the case of the quasi-continuous operation with the optimized film and cleaning method.

To meet the requirements of real-time statistics of the stream of people, a head detection algorithm is presented. The method isolates the region with moving persons by the moving target detection in the binocular camera images, a rapid matching method mixed region matching and feature matching is used to this region. Using the continuity of disparity, we just need to match the strong texture points by sum of absolute differences (SAD) method and simply verify the disparity to other points, so we can get the dense disparity map, and then calculate the depth map by the triangle projection relation. As the depth distributions between people and secne are different in the depth map generated by binocular stereo imaging, we can use the mathematical morphology operations to precondition, then get many candidate contours by edge detection. The characteristics of the head are used to determine whether the contour is the head. Experiments show that this algorithm can be well adapted to head detection in complex scenarios with high precision and speed.

In order to measure flue gas velocity and particulate concentration by optical non-intrusive method, a system is developed with double light paths structure, and is tested on industrial stack. The transmitting and collecting units locate at bilateral of the stack. The gas flow in stack is very complex and changes quickly, thus an inverse cascade model is proposed to describe the developing process of gas flow, and the data processing method for calculating flue gas velocity is improved. Analytical results indicate that, the difference of statistical mean value of flue gas velocities calculated by the new method and those measured by pitot tube at a single point is 0.7 m/s, which is larger than the expectation value, but the ensemble average velocities obtained by these two kinds of measurement are almost the same and are all about 7.6 m/s. When signals collected by our optical measuring system are perfect, the new method will not change the value of velocity and its trend is explicitly acquired after simple filter. There is clearly linear relationship between light intensity fluctuation measured by flue gas velocity measuring system and particulate concentration in stack measured by optical particle counter, and the correlation coefficient can reach 0.97.

A lateral shearing interfeometer for the wavefront test of small beam is proposed. The interferometer is composed of a polarization beam splitter, a crystal plate, a quarter-wave plate, a mirror and a CCD detector. The polarization beam splitter is used both as a polarizer and an analyzer. The interferometer can test wavefront of low coherent light for its equal optical path length. Small shearing amount can be obtained by the crystal plate whose optical axis is parallel to its surface, thus it′s suitable for the wavefront test of small beam. The shearing amount can be continuously adjusted by rotating the crystal plate. Using ASAP software, the lateral shearing interferometer is simulated. The simulation result is well coincident with the theoretical derivation. In the experiments, the interferometer is built to obtain interferogram by rotating the crystal plate. The experimental result is well coincident with the simulation result. The usefulness of the interferometer is verified.

According to the measurement of oil film thickness on the sea, an oil film thickness sensor based on buoy is developed using vertical incidence differential laser trigonometry. The composition and principle of sensor is introduced and the process of the system integration and debugging is presented. Ceramic grade 0 gauge block is measured as a standard thickness and high order curve is fitted based on least square method for the calibration of the sensor. 1.4~9.4 mm gauge blocks are measured to verify the precision. The results show that the measurement relative error is less than 1%.

Display screen is an integral part of laser projection system. The surface roughness of screen directly affects speckle suppression based on angle diversity. The relation between speckle correlation and the surface roughness of measured screen is established by analyzing the speckle suppression method based on angle diversity. In the experiment, the incident angle is fixed to 1° and the angle increment is set to 0.0038°, which is a compromise between the sensitivities of surface roughness of the measured screen to those two factors. To avoid the effects of external perturbation and surface flatness on measured results, nine sub-regions are chosen in 5 cm×5 cm measured screen areas and measured results from these sub-regions are averaged, which effectively improves the measurement accuracy. The surface roughness for four screens determined by the proposed method are 235.80, 209.57, 132.24 and 137.60 μm, respectively, which provides a basis to design a projection display screen applied to effectively reduce laser speckle.

The three-dimensional (3D) coordinate measuring system based on laser multi-lateration can realize the non-target self-calibration. Its measurement accuracy is influenced by the self-calibration accuracy. However, the layout of the system is one of main impact factors on the self-calibration accuracy. By theoretical analysis of the non-target self-calibration model, the result of the system layout optimization is the tri-rectangular pyramid layout. Simulation results show that the tri-rectangular pyramid layout can improve the self-calibration accuracy, thus can ensure the system accuracy.

A simultaneous line imaging and plane framing imaging velocity interferometer system for any reflector (VISAR) for spatial and temporal resolution measurement of velocity field of laser driven flyer is developed. Different from the conventional point VISAR, imaging VISAR uses streak camera and framing camera to record the movement of comb fringe, and provides a one-dimensional velocity history versus time along a line and a two-dimensional velocity map of the whole surface at different time. In addition, the instrument measures velocity field at spatial resolution of 10 μm and velocity resolution of 15 m/s. The technique is employed to measure temporal and spatial velocity field of Al foils flyer driven by a pulse laser, and to reveal the continuous evolution of flyers. These results demonstrate that the simultaneous line imaging and plane framing imaging VISAR can be a valuable diagnostics for shock physics.

All optical link networks of the space laser communication with high transmission rate determine their development position and direction in global space communication in the future. All optical link networks require to solve the problem of the one-point to multi-points optical link. Different ways to solve the problem require different optical antenna structures and different tracking control ways. Based on the optical principle of all optical link networks, a flat four-mirror optical antenna structure is proposed. The mathematical model is established based on the dynamic tracking principle of link network scheme. The mathematical relationship is given based on the optical parameters of communication nodes, and data are analyzed. It can be used as the guidance for space laser communication terminal ATP (acquisition, tracking, pointing) control system. A networking scheme of low earth orbit double links is proposed, the working plane of laser communication terminal four plane tracking mirrors optical antenna is placed at the satellite link orbit plane, and all optical link networks with space laser communication in low earth orbit can be realized.

π-rotation low-density parity-check (LDPC) code is applied in polarization division multiplexing differential quadrature phase shift keying (PDM-DQPSK) modulation optical fiber communication system. Performance analysis and comparison are conducted by numerical simulation, in which the same kind of codes with higher code rates are generated by employing puncturing technique and compared with primitive code in correction performance. With regard to decoding, the Chi-square statistical model of PDM-DQPSK is derived and compared with Gaussian one. The results exhibit that π-rotation LDPC codes can achieve their utmost performances when code rate is 0.5 and Chi-square statistical model is employed, which ensures bit error rate (BER) is below 10-9 while optical signal to noise ratio (OSNR) is 14.2 dB. When OSNR penalty is 2 dB, the system can tolerate 102 ps/nm chromatic dispersion, 18 ps first-order polarization mode dispersion and 4.88×10-2 rad nonlinear phase shift. The results indicate that π-rotation LDPC codes can enhance the transmitting reliability significantly.

An optical arbitrary waveform generator based on two fiber Bragg grating (FBG) arrays with independent phase control is proposed. It is composed of an amplitude controller and a phase controller. In the amplitude controller and phase controller, the controllable components are the FBG arrays. The FBG arrays comprise radial arrangement of several FBGs and fiber stretchers. The amplitude and phase of each spectral line of the output signal are controlled by only adjusting the fiber stretchers, which results in optical arbitrary waveform pulse. The amplitudes of spectral lines of the output signal are insusceptible to adjusting the fiber stretchers in the amplitude controller. Adjusting the fiber stretchers in the amplitude controller can affect the phases of spectral lines of the output signal. So the amplitude controller should precede the phase controller to be adjusted.

The theory that the magnetic field vertical to the sensing coil plane may induce nonreciprocal phase difference (NPD) in polarization maintaining fiber (PMF) optical gyroscope is put forward. The corresponding mathematical model is established. Simulated analysis and experimental verification are carried out. The magnetic field error induced by vertical magnetic field in polarization maintaining fiber optical gyroscope arises from the bending of the fiber. And the error is closely related with the diameter of the optical fiber coil, fiber′s diameter, fiber′s length and the strength of the vertical magnetic field and so on. The simulation analysis and experimental result show that, as to a fiber optical gyroscope, in which the angles of the two tail fibers between the integrated optical components (IOC) and the fiber loop are 0°, and the magnetic drift is random in some range. But in which the ones are 45°, the magnetic drift is very stable and is linear to the magnitude of the vertical magnetic field.

The change of the fiber Bragg grating (FBG) spectrum induced by intense light is caused by the nonlinear effect together with the photo-thermal effect. Based on the sensing model of FBG, the contribution of nonlinear effect and the photo-thermal effect on the FBG spectrum change is analyzed by using the nonlinear refractive index coefficient and one-dimensional steady state heat equation. By analyzing the relationship between the wavelength shift and phase change, nonlinear refractive index coefficient calculation model is built. And the photo-thermal effect on the spectrum chirp and wavelength shift is confirmed by theoretical simulation of temperature distribution. As the theoretical and experimental results show, for conventional single mode fiber, FBG spectrum change is mainly caused by the photo-thermal effect rather than the nonlinear effect when a relatively lower power pump is injected to single mode optical fiber.

In experiment it has been found that the output waveform of integrated optical waveguide electric field sensor is overlapped by interference signal with frequency of hundreds of kilohertz, which leads to a distortion of the detected electric field signal. The resonance phenomenon is analyzed theoretically based on the piezoelectric effect of LiNbO3 crystal. By comparing the resonant frequency value of theoretical calculation with that of measurement, it shows that the resonance is mainly influenced by the width of LiNbO3 substrate. For lighting impulse detecting, an integrated optical waveguide electric field sensor with 3 mm substrate width is designed and experimental results demonstrate that the resonance phenomenon has been obviously suppressed under -30 dB.

Based on the coupled-mode theory, according to the variation of effective index of cladding modes in coated long-period fiber grating (LPFG) with the film parameters, the partition and characteristics of mode transition region are pointed out. The response characteristics of refractive index in coated LPFG transmission spectrum in mode transition region and its vicinity are investigated. Further, the two kinds of sensitivity definitions are given for the different detection types of wavelength shift and amplitude change from the aspect of sensor design. The changes of sensitivity with film parameters and grating parameters are discussed. By using optimization method, the optimum design parameters and regions with high sensitivity are obtained. The results show that the sensor resolution of film refractive index can be also available to 10-7, if detected by wavelength shift and transmittance change. When the suitable film parameters and grating parameters are selected, mode transition region is fit for the sensor detected by wavelength shift, while the vicinity of mode transition region is fit for the sensor detected by transmittance.

A scheme is proposed to achieve all-optical wavelength conversion and all-optical OR-logic gate, which are two key techniques for repetition rate multiplication of pseudorandom bit sequences (PRBS) based on terahertz optical asymmetric demultiplexer (TOAD). The switch characteristics of TOAD are discussed followed by 10 Gb/s wavelength conversion and all-optical OR-logic gate with theoretical simulations and experiments. The results indicate that the wavelength conversion and all-optical OR-logic gate can be implemented at ultra-high bit rate by this TOAD scheme if the widths of control pulse and switch window are smaller. Furthermore, all-optical PRBS with higher rate can be generated by employing both of the key techniques to achieve the repetition rate multiplication of PRBS.

The photo-induced insulator-metal phase transition of VO2 nanofilms under femtosecond pulse excitation is investigated using terahertz (THz) time-domain spectroscopy. A number of VO2 films are fabricated on sapphire substrates by direct current (DC) magnetron sputtering under different conditions. The film quality is evaluated by measuring the THz transmissions of the films in which photo-induced phase transition has occured and the results show that for a fixed sputtering time of 60 min VO2 films of high quality can be prepared when the annealing time and temperature are 60 s and 560 ℃, respectively. The degree of phase transition of the film fabricated under those best conditions can be as high as 80%. The conductivity of the film in the process of photo-induced phase transition in the THz range is determined based on thin film approximation, and calculations show that the real part of the conductivity is on the order of 103 Ω-1·cm-1. The complex dielectric constant and complex refractive index of the metallic-state thin film are further calculated based on the Drude model. The VO2 films fabricated on insulator substrates have an obvious threshold for the excitation pulse power and show a high degree of phase transition, which will play an important role in THz modulation devices.

To satisfy the requirement of high-resolution hyperspectral imager with a large relative aperture and a wide spectral region, and to avoid the difficulties of fabricating the convex grating in the Offner spectral imaging system and the problems of low relative aperture in the modified Czerny-Turner spectral imaging system, a neotype Schwarzschild spectral imaging system using planar grating with a large relative aperture is proposed. Based on the Rowland circle theory of the reflective spherical surface, the astigmatism-correcting method of the Schwarzschild spectral imaging system is analyzed. The initial parameters computing program is written using Matlab software. As an example, a Schwarzschild spectral imaging system operating in 400～1000 nm waveband with relative aperture of 1/2.5 is designed. First, the initial parameters are computed using our Matlab program, and then the ray tracing and optimization for the spectral imaging system are carried out with Zemax-EE software. The analyzed results demonstrate that the size of spot diagram is less than 13 μm in the whole working waveband, aberration correction is realized, and good imaging quality is obtained in a wide spectral region with a large relative aperture, which satisfies the requirement of design specifications, and proves the feasibility of the novel Schwarzschild spectral imaging system. It has extensive application prospect in hyperspectral remote sensing field.

A virtual impactor for submicron particles is prerequisite for bio-aerosol optical online monitoring and it is a hot research topic. Based on aerodynamics and past research work, a 0.4-μm-cutpoint virtual impactor is designed with the help of a commercial computational fluid dynamics (CFD) package, Fluent. Discrete phase model (DPM) is applied to simulate and analyze the effect of nozzle-to-collection probe distance, collection probe diameter and minor-to-major flow ratio. The virtual impactor with optimum design parameters is fabricated and tested. According to the experimental results, the virtual impactor can collect 0.37 μm, 0.5 μm and 0.7 μm PSL microspheres efficiently as desired, which proves that the CFD method is practical. Cutoff diameter of the virtual impactor can reach 0.4 μm, which is fit for practical applications.

In order to improve the temperature adaptability of vehicle-borne beam expander system, a structural optimization method is proposed to directly deal with optical wavefront aberrations. After sensitivity analysis, root mean square (RMS) value of the optical wavefront aberration can be calculated from the strain of the finite element nodes through homogeneous coordinate transformation. Taking the minimum wavefront aberration as the optimization objective, an optimized topology is obtained. According to the topology of material, the frame is divided into blocks, and optimized secondly in the form of size optimization. Finally, a manufacturable structure with good temperature flexibility is obtained. When the thermal load is -50 ℃, the wavefront aberration RMS value is reduced from 0.728 λ to 0.196 λ, λ= 632.8 nm. And in the range of ±50 ℃, the optimized wavefront aberration RMS value is about 1/4 times as large as that before optimization at the same thermal load conditions.

Based on the rigorous couple-wave analysis (RCWA) method, columned ZnSe sub-wavelength micro-structure by genetic algorithm (GA) is optimized and optimum structure parameters are obtained. The effect of structure parameter error and profile shape error of columned ZnSe structure on the anti-reflective properties in actual manufacturing process is discussed. The transmittance of the multilevel ZnSe gratings with coned profile is also presented as a function of the structure height. The results show that the columned ZnSe micro-structure can have excellent average anti-reflective properties between 8 μm and 14 μm at normal incidence when the structure period, height and filling factor are 3.3 μm, 1.7517 μm and 0.7566, respectively. The errors of filling factor, height and profile shape have a big influence on the average transmittance. The transmittance of the ZnSe microstructure with coned profile shows some regular distribution with the increase of structure height and the number of divided layers, and it has a great improvement as compared with the optimized columned ZnSe micro-structure.

Handheld Raman spectrometer probe system shares the same optical configuration for illumination and light receiving. Thus, stray light caused by multiple reflections of laser, expect for Rayleigh scattering, is a problem to be solved for this kind of probe system. By real ray tracing method, setting up reasonable stray light analysis model and theoretical calculation, we get the total stray light information, together with our actual prototype structural data, such as the size and location of focus, emergent direction, energy in the slit and so on. Then a new approach of stray light suppression for spectrometer probe system that uses black board to block the stray light is proposed. The size and location of the black board are determined according to the analysis of the stray light. The optical simulation analysis results show that the black board suppresses stray light to the level of 10-13 in Raman spectral region. This satisfies the requirements of the handheld Raman spectrometer. With black board method, almost 50% of the laser reflection with incidence angle larger than 2° on the notch filter can be filtered.

The structure of PDH technique is greatly simplified when the fiber components especially fiber electro-optic modulator (EOM) are applied to it. Since the key of this locking technique is frequency modulation, unaligned modulation process induces residual amplitude modulation (RAM), which produces a temperature dependent direct current (DC) offset and a lineshape distortion. This effect may induce the drifting of frequency locking point and shortening of locking time. A theoretical and experimental analysis of PDH error signal including RAM is given, and the symmetric PDH error signal of RAM reducing method based on Hnsch-Couillaud technique is obtained experimentally. The locking performance of the laser to the cavity is analyzed with and without RAM reducing feedback, and it is verified that the RAM reducing scheme greatly increases the stability of fiber EOM based PDH frequency locking technique.

CO2 and H2O are the important greenhouse gases in the atmosphere. On-line monitoring of CO2 and H2O concentrations in ecosystem can be used for analyzing environment and climate change. With the near-infrared absorption lines of CO2 and H2O, CO2 and H2O on-line detection instrument in open-path based on tunable diode laser absorption spectroscopy (TDLAS) technology and automatic gain adjustment technology is designed. The continuous observation experiment is carried out in Yucheng Integrated Experimental Station, Chinese Academy of Sciences with the time resolution of 20 Hz in 1238 m optical path by this instrument. The results show that the problem of large signal intensity fluctuation in open-path detection is solved by automatic gain adjustment. The CO2 concentration in site has an obvious diurnal periodicity that the concentration is low in the daytime and high at night. Comparing with LI-7500 of eddy covariance system, the data consistency is better. This technology has the characteristics of high sensitivity, fast response and without sampling, so the stable and continuous CO2 and H2O on-line detection is achieved in large-scale regional ecosystem.