Beam spreading is an important effect when a beam propagates in atmospheric turbulence. The collimated Gaussian beam spreading experiments are carried out with beam dynamic change test system under the sea surface environment in Yantai region, and the beam spreading characteristics are analyzed based on data including beam spreading, temperature, relative humidity and atmospheric refractive index structure parameter in different distances and different time periods experiments. Results show that the correlation between beam spreading and refractive index structure parameter is better in sunny weather than in stormy waves weather. But in stormy waves weather the correlation between beam spreading and temperature and relative humidity is good at certain time. In the condition of the same link distance, the beam spreading is obviously smaller at night than in day, and the amplitude fluctuation of beam spreading has the same results.

Gradient algorithm is very important for the Hartmann-Shack sensor. The Hartmann-Shack sensor based on the normalized cross correlation (NCC) gradient algorithm shows strong noise immunity. In addition, it can detect both point source and extended target. A multi- core CPU (central processing unit) is used to implement NCC gradient algorithm to get better portability compared to the existing processor. The NCC algorithm is optimized and programmed. The program is improved by multi-core parallelization and advanced vector extension. When the template resolution is 9 pixel×9 pixel, the optimized program running on a 4-core computer, Intel (TM) Core (R) i7-3770k, spends about 340 μs to calculate the slope of 400 sub-apertures with 15 pixel×15 pixel. An adaptive optics system using optimized gradient program is built and experiences closed-loop test. The experimental results show that the CPU- based Hartmann- Shack adaptive optics system using NCC gradient algorithm can correct wavefront distortions effectively, even in strong noise environment.

Overlap joint of the FeSiB amorphous ribbon with thickness about 25 μm is successfully fabricated by micro pulsed laser. Effect of main process parameters including pulse power P, pulse width T, pulse frequency F on the weld forming is studied, and then the variation trend of mechanical properties is analyzed. The results indicate that the perfect weld forming and excellent mechanical properties can be obtained when P and T are matched appropriately, i.e. P is 4.8~7.2 W, T is 1.5~1.9 ms, and corresponding energy E is 0.9~1.2 J. With the increase of T, the microhardness of heat affected zone and weld zone decreases gradually. However, with the increase of P, the microhardness increases first and then decreases. With the increase of P and T, tensile strength of joint increases first and then decreases. The highest average microhardness of about 1300 Hv and 1000 Hv in the heat affected zone and weld zone is obtained, respectively, and the tensile strength exceeds 363 MPa, when P is 7.2 W, T is 1.7 ms, and F is 1.5 Hz.

Advancing direction of massive laser shock peening (LSP) impacts often generates different residual stress distribution at the surface and along depth direction of metallic sheet. To investigate the effect of advancing direction of massive LSP impacts on the induced residual stress fields of AM50 Mg alloy tensile samples, a 3D analysis model is developed by using ABAQUS software. At the same time, the difference between the double- sided simultaneous LSP and double-sided non-simultaneous LSP impacts is also presented. Results show that advancing direction plays an important role in the generated residual stresses, and simultaneous LSP impacts can induce a better simulation results than non-simultaneous LSP.

To promote the mechanical properties of marine high strength steels joints, fiber laser butt welding on 8 mm thick 10CrSiNiCu steel is performed by using filler wire. The microstructures, hardness, tensile strength, bending property and impact energy (at sub-zero temperature) of the welded joints are analyzed. Also, the effects of welding heat input on microstructures, hardness and fracture behavior of the welded joints are also studied. The results show that the microstructure of the weldment mainly consists of martensite + ferrite + bainite, and its hardness is the highest among the welded joint zones. When heat input decreases from 5.00 kJ/cm to 3.64 kJ/cm, the average hardness of weldment increases from 346 HV to 396 HV. Tensile specimens are all broken in base metal. A bending angle of 113° can be reached at room temperature, which is 60° lower than base metal. At the heat input of E=4.20 kJ/cm, the impact energy at fusion line and weld seam reaches its highest value, 95 J and 101 J, respectively.

Nanosecond pulsed laser is used to blacken the surface of copper, and the reflectance and roughness of the samples are measured by a spectrophotometer and an optical surface profiler. The micro-nanostructure is observed by a scanning electron microscope (SEM), and the effect of scanning distance on blackening under unidirectional filling scan is investigated. The results show that different micro-nanostructures are formed after different scanning distances (grating-like, approximately grating-like, and coral-like, and so on), and the decrease of scanning distance can enhance light absorption obviously. When the scanning distance is 10 μm, the absorption of blackened area is over 97% in the wavelength band ranged from 200 nm to 760 nm, over 90% ranged from 760 nm to 1110 nm, and over 85% ranged from 1110 nm to 2500 nm. In addition, the effect of different filling directions at the second time under different scanning distances is also investigated. A certain enhanced absorption value is found after the second blackening compared to the first time, and the difference in absorption among different filling directions is diminished with the decrease in scanning distance.

To study the effects of the ultrasonic vibration on femtosecond laser micromachining, an ultrasonic aided device is designed, and the laser micromachining experiments of fiber optic materials are carried out. The effects of the ultrasonic vibration with different powers on surface quality and the drilling depth are investigated. And the mechanism of the ultrasonic vibration aided laser machining is analyzed. After introducing the ultrasonic vibration, the inner surface of the ablated trench is cleaner, the residue debris on surface is significantly reduced, and the drilling depth is increased. When the ultrasonic power is 30 W, the taper of the hole is reduced from 7.34° to 4.17°. The results show that, ultrasonic vibrations can effectively improve the surface quality of materials, increase the depth of the drilled hole, improve the efficiency of the femtosecond laser processing. It is also confirmed that, the ultrasonic vibration has significant effect on improving femtosecond laser processing performance.

TheCr3Si/γ multi-phase intermetallic coating on a substrate of austenitic stainless steel 1Cr18Ni9Ti is in situ synthesized by laser cladding technique to investigate the microstructure and surface properties. Electrochemical corrosion resistance is examined by anodic polarization in the 3.5% (mass fraction) NaCl solution. Wear resistance is evaluated through mass loss of specimens in room-temperature dry sliding wear experiments. The micro failure mechanisms are investigated by optical microscope (OM), scanning electron microscope (SEM) and other test measurements. Results indicate that the laser cladding coating has a multi-phase microstructure. The hard phase Cr3Si is distributed in the Ni- base solid solution (γ) matrix, contributing to the higher microhardness. In the 3.5% NaCl solution, the passive film forms spontaneously on the surface of the coating exhibiting excellent pitting corrosion resistance. The laser cladding coating exhibits better wear resistance for the less mass loss and the lower friction coefficient.

Cobalt chromium alloy is a commonly used dental restorative material, the study of hardness variation trend is very important for the friction and wear analysis of artificial cobalt chromium alloy denture fabricated via selective laser melting (SLM). The influence rule of hardness of SLM formed cobalt chromium alloy from technological parameter is studied and a Vickers hardness model is established. Experimental results indicate that laser power is the mostly significant factor influencing the Vickers hardness of SLM cobalt- chromium alloy specimen, followed by scanning speed, and the minimal is scanning interval. The microstructure shows that along the building direction, grains grow in the shape of columnar with consistent direction and there is an obvious layer stack between the grains. The grain is grid-shaped and arranged uniformly and tightly in the perpendicular direction. As the laser energy density increases, the grain size and hardness of forming parts increase, but both of the microtexture density and hole-defect decrease significantly. Based on the experimental results comparison between the Vickers hardness, the rationality and validity of the Vickers hardness prediction model is verified.

The part with an incline angle changing from 0° to 60°and the part with multi-angle are formed by normal direction slices. They are generated by the single point deposition and the intermittent processing based on inside laser powder feeding technology and KUKA robot. The optimized loading time is got from the ANSYS thermo dynamics simulation and corresponding experiments. The experimental results indicate that the forming slender structure part has a high precision and uniform section size. The biggest relative error is 1.6% and the surface roughness is 1.98~2.47 mm. The microstructures of the part at different incline angles are similar without apparent defect.

The main obstacles of metallurgical bonding and reliable joining of Mg/Ti dissimilar joint are their nonreactive and immiscible characteristics. To overcome those problems and expand their application, laser lap joining of Mg/Ti with Al-rich Mg based wire is carried out. Mg/Ti interface is observed with scanning electron microscope, and the role of Al element in interfacial diffusion and bonding mechanism is investigated based on the result of calculation of Miedema binary and Toop ternary thermodynamic model. The results demonstrate that an ultra-thin reaction layer is observed at the Mg/Ti interface with the help of Al elements from filler. The element line scan results show that enrichment of Al element is evidenced at the interface, indicating metallurgical bonding of Mg and Ti. Thermodynamic calculation result reveals Al- Ti intermetallic compound has more driving force than other compounds, which indicates that it is the compound firstly precipitated from the liquid. In addition, Al chemical potential near the Ti side is lower than that at other places. Al segregation at the interface further causes the decrease of Al chemical potential, indicating the behavior of Al element from Mg fusion zone to the interface is uphill diffusion.

A tunable multi-wavelength random fiber laser, with single-mode fiber and ring structure forming halfopen cavity, has been proposed. Tunable Brillouin pump laser is used to achieve tunable random lasing. The results show that the proposed laser has random lasing with four wavelengths, which can be accurately controlled by the output power of erbium-doped fiber amplifier when Brillouin pump wavelength is 1550.01 nm. The threshold power of the proposed laser from the first Stokes line to the fourth Stokes line are 12, 31.6, 73 and 610 mW, respectively. The slope efficiency of the first stokes wave is 12.5%. For fixed output power of erbium-doped fiber amplifier of 631 mW, the output power of the proposed laser decreases exponentially with lengths of optical fibers as random distributed feedback media. The output wavelength of the random fiber laser can be tuned between 1528 nm and 1580 nm. The scheme of half-open cavity can effectively avoid the peak power difference of odd-order and evenorder Stokes lines.

In high power laser device, near- field beam quality is evaluated through the intensity distribution. However, the measured distribution is a steady state, which can not reflect the evolution features of intensity modulation caused by noise disturbances. Some area encountering serious intensity modulation may be ignored in transmission process. Near-field transmission characteristics of the beam disturbed by noise disturbance are studied. Meanwhile, deeper understanding of the limitations of the measured near-field intensity distribution is obtained. To simplify the analysis of the near-field intensity distribution at different distance under the influence of single local defect, the characteristics of near-field intensity modulation is represented by equivalent Fresnel number. The results show that once a weak modulated information appears in the distribution of measured nearfield intensity, there may be a more serious modulation area before the measurement position. A highest modulation can be up to nine times for a phase type defects with π delay corresponding to incident intensity.

A high-power single-frequency 461 nm light by intracavity doubling of Ti:sapphire laser is designed and built. An astigmatically compensated double-folded resonator with six mirrors is employed to give two tight-focus regions, where Ti:sapphire and doubling crystals are located respectively. A type-I critical phase-matched LBO, an optical diode composed with a TGG crystal and a broadband half wave plate (HWP) are placed inside the resonator for the intracavity frequency doubler and forcing the laser to operate unidirectionally. Three birefringent filters with different thicknesses of 1, 2, 4 mm and a temperature controlled etalon with thickness of 0.25 mm are inserted in the cavity to tune the fundamental wavelength of 461 nm Ti∶sapphire laser. With the pump power of 14 W and an optimized LBO crystal with the length of 7.3 mm, the tunable single-frequency second harmonic output of 1.02 W at 460.86 nm is obtained. The peak-to-peak fluctuation of the power is less than ± 1.3% within 3 h. The measured beam quality of M2 and the tuning range of blue laser are better than 1.59 and 20 nm, respectively.

In order to obtain high efficiency diode pumped alkali metal vapor laser, a gain cell with Brewster angle structure is used. The one-trip transmittance of the laser is improved effectively and the one-trip transmittance of the laser in p-polarization is 97%. A gain cell with length of 1 nm is used. It is filled with alkali metal rubidium vapor as gain medium and methane with pressure of 79.99 kPa as buffer gas. A diode laser is used as the pump source when the power is 48 W, the central wavelength is 780 nm and the line width is 0.1 nm. In order to reduce the thermal effect of gain cell, a chopper is used to change the continuous pump laser to pulse output with pulse width of 1.85 ms , repetition frequency of 15 Hz and duty ratio of 2.77%. The experiment is optimized by using 12 cm flat concave resonator and the output mirrors with output coupling rate of 41%, 58%, 76%. When the temperature of the cell is 160 ℃, using the output mirror of 76%, the rubidium laser with wavelength of 795 nm and highest peak power of 16.8 W is obtained. The optical to optical efficiency is about 35%, and the slope efficiency is 44.2%.

A high power self-similar fiber laser based on the Yb-doped large mode area photonic crystal fiber (LMAPCF) is studied by simulation and experiment. The laser is operated in an all-normal-dispersion region. To obtain higher power, the laser is performed by Yb-doped LMA-PCF without dispersion map with length of 1.9 m, which operates in the all normal dispersion. A ring cavity is employed and the stable mode-locking is achieved through nonlinear polarization rotation with a grating filter. The laser directly outputs the self-similar pulses with average power of 5 W at repetition rate of 72 MHz with pulse duration of 1.699 ps, corresponding to pulse energy of 69 nJ. The dechirped pulse is 84 fs which is compressed by a pair of 1200 line/mm transmission gratings. The laser shows good self-starting property with the beam quality factor M2 of 1.41.

The integration-test-bed (ITB) device is established for research on inertial confinement fusion(ICF) in China. The single-beam output energy reaches 19.6 kJ successfully when the fundamental frequency emission wavelength is 1053 nm and the pulsewidth is 5 ns. Experimental results of thermal effect of 400 mm × 400 mm aperture slab amplifiers in ITB devices show that the peak-to-valley value dPV of pump-induced wave-distortion of the whole laser chain is about 5.3 l, in the revise extension of deformable mirror, when the gain coefficient is 5.28% cm-1. Combined with the optimizations of heat management, the thermal recovery time is about 2.5 h, which can satisfy the requirement of 4 h/shot.

Fabrication and characteristic research of electrically controlled holographic polymer dispersed liquid crystal (H-PDLC) gratings which are simultaneously sensitive to red, green and blue laser beams are reported. Two different systems with photoinitiator and coinitiator, rose Bengal and N-phenylglycine, methylene blue and ptoluenesulfonic acid, as well as silver nanoparticles are employed in pre-polymer and liquid crystal mixture to record volume gratings formed under three laser beams (632.8, 532, 441.6 nm). The diffraction efficiency and electro-optical characteristics of the gratings are experimentally measured and studied. In addition, diffraction of the three primary colors is used to display image to demonstrate the image splitter function of left and right eyes for autostereoscopic display. The experimental results show that the tri-color excited gratings have high diffraction efficiency and good electro-optical characteristics under red, green and blue laser beams, and they have potential application prospect in autostereoscopic display and some other related fields.

A method of obtaining graphene coated bimetallic nanoparticles used as surface enhanced Raman scattering (SERS) substrates is put forward, by which graphene grows on two-layer metal films in-situ by chemical vapor deposition (CVD) method. The morphology, Raman spectra and probe moleculars of substrate are characterized, and the stability and enhancement factor are analyzed. The experiment results indicate that the substrate shows a well-distributed morphology characteristic and remains SERS-active with a long lifetime. The enhanced factor is estimated to be 107. Graphene plays a role in preventing the surface oxidation of Ag and Cu nanoparticles after exposured to ambient air and dramatically suppress fluorescence of the probe molecules. The chemical enhancement of graphene can also help to improve the enhanced factor of substrate.

The temporal profile of frequency tripled beam of the high power laser facility is measured using the distortionless sampling by the diffraction of the beam sampling grating, transient photodiode,high-speed digital oscillograph and the multiplexing technology of multichannel. The high resolution and dynamic range of the temporal profiles of frequency tripled beam is obtained. The detailed measurement technology and methods are important for the precision diagnosis of the temporal profile measurement system of frequency tripled beam of the high power laser facility.

In order to accurately control the exposure dose, it is necessary to measure optical transmittance of lithography system accurately. A double-contrast method of optical transmittance measurement is introduced. It effectively eliminates the measurement error caused by an excimer laser energy fluctuation. In order to eliminate the measurement errors caused by diversification of excimer laser polarization, a polarizer is used in this equipment. The experimental setup is designed to measure the transmittance of an optical sample whose transmittance can be calculated accurately. The experimental results show that measurement results are consistent with theoretical calculations and the repeatability of measurement is less than 0.3%. The transmittance of optical sample is measured by the spectrophotometer, and the difference between the two kinds of equipment is 0.28% . Furthermore, the equipment has flexible application for transmittance measurement of optical system and advantage for not influenced by optical sample sizes.

For the issue of structure- light auto- scanning measurement system parameters calibration, a high precision calibration method based on coplanarity is proposed, and the internal and external parameters of the system are calibrated simultaneously. The camera model and the system model are established. The intrinsic and extrinsic parameters of camera and the planar chessboard target are calibrated with the Zhang method. In view of the system calibration requirements, the target location planning is completed, and the position and orientation of the target is changed in the same light plane to obtain coplanar light stripe center points. The light plane equations are solved separately in several light stripe center point data groups. Considering that cross lines of several light planes are more than one, an optimized objective function is defined to solve and optimize the galvanometer shaft expression in the camera coordinate system. The transformation matrix from galvanometer coordinate system to camera coordinate system is obtained. The calibration process is simple, and computation of the algorithm is small. It′s suitable for calibration on spot. Results show that the high precision calibration method is able to meet the requirement.

Refractive index is an important parameter in the method of particle measurement, which is based on forward light scattering with Mie theory. In order to minimize the errors of the particle size measurement, the effects caused by relative refractive index are studied with Mie theory and its Debye series expansion as well as the Fraunhofer diffraction approximation. Numerical calculation reveals that the width of distribution of the scattered light energy shows oscillating properties periodically along with variation of the relative refractive index, which can be described with the empirical expressions. The cause of the scattered light energy distribution changing with relative refractive index is introduced as well. Experimental results show that the forward scattered light energy behaves in a periodical oscillating way along with variation of the relative refractive index and the period of oscillation is π. The inversion results, which are related to the minimum points of oscillating curve, are closer to the nominal value. So, it is necessary to make the width of the distribution of the scattered light energy correspond to the minimum points on scattering light signal oscillation curve by choosing dispersion with proper refractive index in practice.

The wind speed measurement technology based on laser stripe image is studied. According to the Fizeau interferometer transmittance function and atmospheric scattering spectrum function of molecular scattering spectral characteristics for its optimization design, We obtain a set of Fizeau interferometer system parameters based on any incident light beam. The cavity length is 12 mm, the reflectivity is 0.65 from plate and the apex is 10 μrad. At last，under the condition of 20 mJ、repetition frequency of 100 Hz and receiving diameter of 200 mm, the simulating results indicate that when wind velocity error is 1 m/s, the detection ability is 17.8 km above ground.

The three-dimensional profilometry based on structured light triangulation can achieve relatively high precision, but the offset angle formed by the optical axis of projection system and observation system can cause shadow and occlusion. The measurements from two directions and image stitching technology are needed. Different from the triangulation methods, the modulation measuring profilometry is based on vertical measurement theory. In its measuring system, the optical axes of projection and observation are coaxial, which avoid the shadow and occlusion problem in the triangulation methods. A modulation measuring profilometry with auto-synchronous phase shifting and vertical scanning and the reconstruct algorithm are studied. The features of scanning fringes are analyzed, and the features of several algorithms about modulation extraction and 3D shape reconstruction are introduced and compared. Experiments indicate that choosing the proper algorithm can achieve better measuring accuracy of 0.19 mm standard deviation in the measuring range of 115 mm while measuring a 120 mm×120 mm testing plane, under vertical measuring mode.

A novel simultaneous phase-shifting multi-wavelength interferometry based on the least-square iterative algorithm is presented. From the in-line phase-shifting interferometry system of three illumination wavelengths, a phase-shifting procedure of all illumination wavelengths can be carried out simultaneously. A sequence of phasesshifting interferograms with unknown phase-shifts at multiple wavelengths have been recorded simultaneously by a monochrome CCD. By using the least-square iterative operation, the wrapped phase at each single wavelength can be retrieved respectively, so the phase of synthetic wavelength can be obtained by multi-wavelength optical phase unwrapping and noise reduction, and then the three-dimensional topography of the measured object is got. The proposed method has been validated by both the numerical simulation and optical experiment, which shows simple optical setup, high measuring accuracy and capacity of anti-noise.

A system based on quartz enhanced photo- acoustic spectroscopy technique is investigated for trace ammonia gas detection. And hollow- core photonic band- gap fiber is introduced as reference gas cavity for high accuracy and sensitivity. The reference gas cavity is consisted with a 5 m long hollow- core photonic bandgap fiber, which filles with ammonia gas and splices with single-mode optical fibers at both ends. Modes interference is analyzed to obtain transmission spectrum with low interference noise. For improving detection accuracy, gas filling time and pressure are controlled in filling procedure. Ammonia absorption line width in ref? erence gas cavity of hollow-core photonic bandgap fiber is measured, and compared with the high-resolution transmission (HITRAN) database data. By this method, wavelength of distributed feed back (DFB) laser is locked accurately. Quartz enhanced photo- acoustic spectroscopy system is used for ammonia detection with optimal modulation parameters, which yields that a noise equivalent concentration (namely volume fraction) of ammonia is 6.74×10-6 (3 s).

In order to achieve optical wireless communication in condition of strong attenuation, the signal photons which arrive at receiver are detected by single photon avalanche detector. The principle of Geiger-mode avalanche photodiode detector (Gm-APD) operating in gated mode is analyzed. Based on the Poisson distribution, the trigger probability of Gm-APD in a gate is researched. According to the binomial distribution, the bit error rate (BER) model of single Gm-APD is built. It is researched that how BER varies with signal photons per gate, background photons per gate and the number of gates per bit. Theory and simulation results show that the best BER performance is determined by the number of gates per bit; the BER decreases exponentially with the increase of gates per bit, and the receiving sensitivity can be improved at least 3 dB under BER of 10-3 compared to BER of 10-9. Finally, the BER obtained by experiment under the given conditions is compared with simulation results, which shows the validity of the BER model.

As a transmission media of communication, optical fiber communication is widely used in people′s lives for its high transmission rate, large amount of information. Under this background, the band-pass filter film is made to satisfy the requirements for the laser communication system. Using Ta2O5 and SiO2 as coating materials, the bandpass filter which has five resonators is designed and the thickness of coupling layers are monitored by analyzing and solving the question of material stress match. The insertion loss of the filter is less than 0.3 dB at from1479 nm to 1504 nm and the transmission isolation is higher than 39 dB and 31 dB at from 1260 nm to 1450 nm and from 1530 nm to 1620 nm, which meets requirement of the system.

To study the influence of prestressing on distributed feedback (DFB) fiber laser hydrophone in underwater acoustic detection, a theoretical model of DFB fiber laser hydrophone with two diaphragms, which presents the relation between pressure sensitivity and prestressing force, is established. The relation between dynamic performance of hydrophone and prestressing force is simulated and analyzed by finite element software ANSYS. Prototypes of the DFB fiber laser hydrophones under different prestressing forces are fabricated and tested in an anechoic tank. The experimental results show that the frequency response of hydrophone becomes flatter with the increasing of prestressing force. When the wavelength variation induced by prestressing force increases to 400 pm, the acoustic pressure sensitivity of hydrophone is 136.8 dB±0.3 dB in a frequency range from 2.5 kHz to 10 kHz. However, the frequency response curve changes small when prestressing force continues to increase, which agrees well with both the theoretical analysis and simulation results.

基于波分复用技术，通过级联方式在230 km 光纤链路中实现了频率和时间的同传。该级联系统包含了150 km 和80 km 两级链路系统，其中为了补偿150 km 光纤链路中的损耗，在链路中间放置了一个双向掺铒光纤放大器。当每一级传递系统通过光学补偿方式达到稳定后，整个级联系统的频率稳定度为3.1×10-14(平均时间1 s时)和6.3×10-18(平均时间104 s时)，时间稳定度为3.5 ps(平均时间102~104 s时)。实验结果也证明，不管是对频率信号还是时间信号，都满足误差理论，整个系统的稳定度几乎等于两级链路稳定度的标准偏差。同时通过两级系统的校准，最后得到整个级联系统的时间同步准确度为90 ps。

The principle of operation of the traditional Pound-Drever-Hall (PDH) method for laser frequency stabilization is analyzed. Based on the principle of quadrature demodulation, a scheme of PDH laser frequency stabilization is designed, in which both sine and cosine signals with the same frequency of 10 MHz are generated simultaneously by making use of a direct digital synthesizer. The sine signal is divided into two parts, one used to drive an electro-optic modulator to produce the phase sidebands, and the other together with the cosine signal used as the reference signals for the phase demodulation. The phase- modulated laser beams are coupled into the reference Fabry-Perot cavity, and the optical heterodyne interference signal is detected by a photo-detector, whose output is mixed respectively with the two orthogonal reference signals to get the two quadrature components of the error signal after low-pass filtered. By the A/D conversations, the two quadrature components are transmitted to the microprocessor to perform the algorithm of orthogonal phase sensitive detection so that the error signal of the PDH frequency- stabilized system is obtained. A system of the PDH laser frequency discrimination using quadrature demodulation method is established and investigated experimentally, and by linearly sweeping the cavity- length of the reference Fabry-Perot cavity, a curve of frequency discrimination is observed, with a sensitivity of 1.82 V/MHz and a maximum frequency change of 5.48 MHz. Experimental results show that the scheme of the PDH laser frequency stabilization system using the quadrature demodulation method is indeed feasible.

Two kinds of field rotation occur in large optical telescopes, one is caused by the coordinate transformation between horizontal coordinate system and equatorial coordinate system, the other is caused by the mutual rotation among fold mirrors in telescope. In order to get high spatial resolution and stationary image, field rotation compensation is required. Now K mirror, as a derotator, is widely applied. Using matrix can explain the principal of K mirror and achieve the requirements for derotation, which leads to two sorts of K mirror: the symmetric and asymmetric. Similar to prisms, K mirror can affect the optical axis and imaging.Considered the requirements of machining, assembly and the total optical path, the aperture, volume and base angles of K mirror have been analyzed and optimized in this paper. An example of the symmetric K mirror is designed by Zemax. The tolerance of assembly and alignment have been explained by 3D-geometric relationship and calculated by Zemax and MATLAB.

The effect of the wideband signal-to-noise ratio (RSNW) and the effective power spectral width on the Doppler frequency estimation performance using maximum likelihood (ML) estimator have been studied. The performance of the ML algorithm is applied to simulation signal. Experimental data are described by the detection probability and the standard deviation (SD), and also compare with periodogram maximum (PM) estimator. The data are acquired by 1.5 μm all fiber coherent Doppler lidar in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences. The results indicate that ML′s SD can enhance 0.5 MHz higher than PM′s under the same spectral width. ML is close to PM under the narrow spectral width. To satisfy the 90% detection probability, the required RSNW is 2 dB smaller than PM′s. In the real-process, ML′s SD can be 1.1 MHz lower than the PM, and the detection probability is 9% lower than PM. To obtain the wind speed accuracy less than 1 m/s while the detection probability is above 80%, the required RSNW is larger than -14 dB.

The imaging mechanism of ghost imaging determines that it needs a large number of measurement, measuring the more the better imaging quality, but the longer imaging time. Therefore, multi-wavelength ghost imaging system is proposed, it can reduce imaging time through changing system composition, since different detectors measure different wavelength intensities simultaneously. Experimental results indicate that when light source with three wavelengths is used to imaging the target at the same time, the contrast ratio improves by 36% and the carrier noise ratio improves by 66% , comparing with conventional ghost imaging system with single wavelength.