Stray light of transmission type Mie scattering lidar system is analyzed by ZEMAX software, and the reflection of optical lens surface in the lidar system and multiple reflection and scattering of the tube wall system are simulated.The power of multiple reflection light imaging on the detector surface source reaches 3×10-8 W, and the power of lens barrel light scattering imaging on the detector surface source reaches 2.8×10-9 W. Under the same measurement conditions, we analyze the continuous observation results of two kinds of laser lidars, and conclude that the echo signal strength converted from near-field stray light in the transmission type Mie scattering lidar can reach 1000 mV, which is nearly 17 times that of the reflection type lidar system. Attenuation piece is used to attenuate the two lidar signals respectively. The results show that when the signal attenuation is 80%, the near field signal of the transmission type lidar system is turned up. It can be seen from the results of nonlinear signal processing that the reflection type lidar system is better than the transmission type lidar system.

In view of the complexity of underwater laser transmission channel caused by oceanic suspended particles, the effect of oceanic suspended particles on the underwater optical communication link is studied based on equivalent spherical particle Mie scattering theory and Monte Carlo simulation method. The characteristics of suspended particles and the relationship between the incident wavelength and the optical coefficients are analyzed. The effects of particle size and complex refractive index on the received normalized energy, received light intensity, channel transmission length and channel delay are investigated. Theoretical analysis and simulation results indicate that optical coefficients of the particles increase with the increase of particle size, thus the received normalized energy under same channel length decreases, received light intensity decreases, and the channel time delay increases. The smaller the imaginary part of the complex refractive index of the particles is, the stronger the received normalized energy and the greater the peak intensity of the received light are. However, when the imaginary part of the complex refractive index is the same but the real part is different, the magnitude of the received intensity peak depends on the albedo. The larger the albedo is, the stronger the received intensity is.

The generating process of self-accelerating Airy beams is researched from the viewpoint of geometric optics, and the relationship between the phase distribution on the incident plane and the self-accelerating trajectory of Airy beams is analyzed based on the concept of tangent clusters. A iterated algorithm for calculating the phase distribution of the airy beam incidence surface based on the self-acceleration trajectory distribution function is proposed, and the formation principle of the self-healing property of Airy beams is also discussed. Two-dimensional Airy beams are generated by collimated laser modulated with spatial light modulator, and the features of these beams such as non-diffraction, self-healing and self-accelerating are verified. In addition, the one-dimensional Airy beams are modulated to generate autofocusing beams and Bessel-like beams.

The Raman spectra detection of human skin fibroblasts is studied by the growth of human skin fibroblasts on the surface of tapered fiber probe with surface enhanced Raman scattering (SERS) substrates. The tapered fiber probe is prepared by melt-pulling and chemical-etching method. The gold nanoparticles are cured by chemical self-assembly on the surface of the probe to prepare a tapered SERS fiber probe. The human skin fibroblasts are cultured on the surface of the SERS fiber probe inside the mixture of gold sol and culture medium. Then, using a micro-Raman spectrometer, we obtain the surface-enhanced Raman spectra of the human skin fibroblasts with remote detection method, meanwhile, we obtain the SERS spectra of the human skin fibroblasts with and without swallowing gold nanoparticles with direct measurement method. Based on the results of remote and direct detections, we analyze the Raman peak attribution of human skin fibroblasts, and the internal components information corresponding to the Raman characteristic peaks. The use of the tapered fiber probe allows the remote detection going deep inside the tissue, which may help the application of on-line SERS measurements in biomedical research and diagnosis. While Raman spectrum measurement of the human skin fibroblasts also provides means for the in vivo study on the mechanism of low power laser exposure in delaying wound healing.

Dynein, tubulin, and chromosome play important roles in oocyte meiosis. However, the traditional fluorescence microscopy is limited by the diffraction limit and has low resolution, which cannot meet the imaging requirements of oocyte meiosis. Firstly, the normal maturation system of oocyte in vitro and abnormal maturation system under the action of sodium orthovanadate (SOV) are established. Then the confocal fluorescence microscopy and stochastic optical reconstruction microscopy (STORM) are applied to study the localization of the two important proteins of dynein and tubulin and the morphology and structure of chromosome during the oocyte meiosis. The fluorescence imaging results show that the co-localization of dynein, spindle assembled by tubulin, and the morphology and structure of chromosome can correctly reflect the different stages of oocyte meiosis in the normal system. In the SOV treated groups, the abnormality rate of spindle structure increases, and there are typical spindle structures such as barrel, slender, regiment, disorderly, piriform, and multipolar. The abnormality rate of chromosome structure also increases. The STORM results clearly present the structural information of the spindle, and the 3D STORM results reveal the disorder level of abnormal spindle. This method provides an imaging approach with higher resolution for the research of the oocyte meiosis.

We change feedback phases of two coupled chaotic lasers to achieve bidirectional simultaneous transmission of signals between the two lasers. The partial transparent mirror between the lasers can induce delay and the chaotic dynamics. Numerical simulation of laser rate equation considering delay proves that the two lasers can achieve high-quality synchronization. The encoding and decoding process starts with the change of the feedback phases of the two lasers induced by signals. And then the difference in the optical power of the chaotic carrier in the two lasers is detected and compared with the difference with the local signal, finally, the digital messages sent by sender are recovered. Based on the eye diagram of recovered signal, it reveals that this system has a high transmission quality. In this scheme, the eavesdroppers cannot know the local signal even if he can get the difference of the transmitted signals. So the security of transmission performance of this system can be guaranteed as the eavesdroppers are unable to demodulate the sender's information.

The traditional LED layout has the problem of uneven illumination in indoor visible light communication(VLC) system, which brings blind effect with communication. To solve these problems, we propose a light source LED optimization scheme that considers wall reflections and analyze LED layout by using the mean square error of illumination as evaluation criterion. Then, the expressions of received illumination and power are deduced by integrating, which are used to build optimization model function F(l,x,y) of rectangular layout and optimization model function F(r,x,y) of circular layout. The relationships between the mean square error of illumination and the room size, and between the optimal layout and field of view ψFOV are researched based on optimization model function. It is clear from the results that the F(l,x,y) can reach the minimum value when l=1.6 m and ψFOV=80°, and the illumination uniformity is increased from 80.5% of traditional layout to 84.3%; the F(r,x,y) could also obtain the minimum value when r=2 m and ψFOV=80°, and the illumination uniformity is increased from 85.2% to 89.2% with the increase of the number of LED.

To slove the problem of unbalanced communication performance due to uneven distribution of received optical power in indoor visible light communication, we propose an independent uniform distribution of LED arrays and an improved adaptive genetic algorithm, which is used to optimize the distance between LED arrays and LED half-power angle.The selection operator in genetic algorithm is improved, and the crossover and mutation operations in the algorithm are redesigned. The improved adaptive genetic algorithm is used to optimize the LED half-power angle and the distance between LED arrays.The simulation results show that the received power variance of the receiving plane is reduced from 3.02 dBm to 1.16 dBm and the range of illumination intensity is improved from 374~862 lx to 417~765 lx. Compared with the existing methods of optimizing received optical power, the performance and convergence speed of the algorithm are improved.

In order to reduce the influence of oceanic turbulence on link performance of underwater optical communication system, an optical soliton is used to underwater optical communication. On-off key modulation is used in the underwater communication system. We use the Lognormal channel model that describes the weak oceanic turbulence to deduce the specific expression of the oceanic scintillation and the communication bit error rate expression containing the form shape factor and scintillation, analyze and compare communication bit error rates of solitonic, rectangular, Gaussian pulses under different turbulence intensities and oceanic turbulence parameters in pulse time domain. The results show that the bit error rate of the solitonic pulses is lower than that of the Gaussian and rectangular pulses at least 3 orders of magnitude with the change of the turbulence intensity when the signal-noise ratio is 5 dB. The aperture diamiter and the ratio of oceanic turbulences induced by temperature and salinity are sensitive factors in the underwater communication. Under different influencing factors of oceanic turbulence, the soliton pulses have better anti-interference ability and lower bit error rate than Gaussian and rectangular pulses. The broadening of the soliton pulses is smaller than that of the Gaussian and the rectangular pulses, but as the distance increases, three pulses broadening tends to be consistent. The simulation results verify the advantages of the solitonic pulse for underwater communication, and could provide the theoretical reference for further research.

Based on the original computer-generated hologram (CGH) of an object, a zooming algorithm of the reconstructed image of CGH is presented based on the Gerchberg-Saxton iterative algorithm. Based on the principle of object-image relationships and the setting of appropriate parameters, this algorithm achieves reproduction at any given zooming factor in the specified reproduction position, which can effectively avoid the problems such as uneven lighting caused by excessive enlargement zooming. Numerical simulation is operated on MATLAB platform a holographic reconstruction optical path based on liquid crystal on silicon spatial light modulator with pure phase is built to verify the algorithm. Reconstructed images of a binary picture with zoom factors of 0.5, 2 and 3 are obtained respectively at a specified diffraction position. A grayscale picture is enlarged to analyze the imaging effect of this algorithm. The experimental results show that the expected image zooming is obtained and the quality of reconstructed images is effectively improved.

The structure of active mirror Nd∶glass laser amplifier is presented, which is pumped by Xe-lamps. The gain characteristics and energy extraction of the active mirror Nd∶glass laser amplifier are experimentally studied. The size of Nd∶glass is 380 mm×160 mm×30 mm, and the doping concentration of Nd:glass is 2.2%(mass fraction). Experimental results show that when the charging voltage is 23 kV, the small signal gain coefficient of the system is 0.056 cm-1, and the energy storage efficiency is 2.0%. The spot size of the output laser is 126 mm×126 mm and the pulse width is 5 ns when the charging voltage is 22 kV. The laser amplifier obtains the maximum output energy of 349 J when the injected energy is 6.67 J. The peak to valley (PV) value of the static wavefront of the system is 8.38λ.

The high power 660 nm semiconductor laser is fabricated with non-absorbing window structure by Zn diffusion method. The photoluminescence wavelength of the active layer near the window region blue shifts by 61 nm with the selective Zn diffusion in the window region of the chips, which effectively reduces the optical absorption of the cavity facets. The stripe width is 150 μm and the cavity length is 1000 μm. The chips are sintered with AuSn solder by p-side down onto the AlN heat sink. The packaged device shows the highest output power of 4.2 W without catastrophic optical damage. The horizontal divergence angle of the semiconductor laser is 6° and the vertical divergence angle is 39°. The emission peak wavelength of the laser is 659 nm at room temperature and the current of 1.5 A. The 10 semiconductor lasers are aged at the current of 1.5 A in continuous-wave mode with the simple air-cooled heat dissipation condition, and no failure has ever occurred for 4000 h. Therefore, the 660 nm semiconductor laser with watt-level output power has the advantage of high reliability and low operating cost.

Double optical feedback and double light injection are two important schemes to suppress the delay time signature peak of optical feedback chaotic lasers. In essence, the delay time signature peak is suppressed by the Mach-Zehnder interferometer. We summarize the suppression law for the delay time signature peak in the two schemes, and systematically analyze the function and mechanism of the interferometer in the suppression of the delay time signature peak. When the arms of the interferometer are close to each other, the electric field intensity and phase of the two chaotic lasers are strongly correlated. The superposition of light is dominated by coherent superposition, and the delay time signature peak of chaotic laser changes periodically with τd (delay time corresponding to the optical path difference in the interferometer). When the arms of the interferometer are obviously unequal and out of proportion, the correlation between the electric field intensity and phase of the two chaotic lasers decreases or even disappears, the superposition of light is a non-coherent superposition, but the suppression of the delay time signature peak is mainly determined by the interference term, and the main delay time signature peak does not change with τd, while generating the new delay time signature peaks.

A compact high-energy solid-state Nd∶YAG master-oscillator power amplification system side-pumped by laser diode is presented. We use the thermoelectric cooler in the whole system, and a compact and miniaturized laser system is achieved. A Nd∶YAG crystal rod with diameter of 7 mm, length of 100 mm and doping concentration (atomic number fraction) of 1.1% is used in the master oscillator. We obtain a laser pulse with maximum pulse energy of 350 mJ, pulse width of 9.7 ns under repetition rate of 10 Hz. A Nd∶YAG crystal rod with diameter of 7.5 mm, length of 134 mm and doping concentration of 1.1% is used as gain medium in power amplification stage. Finally, we obtain the laser pulse with energy of 700 mJ and pulse width of 10 ns.

Multiwavelength Brillouin erbium-doped fiber lasers with wavelength spacing of double and triple Brillouin frequency shifts are reported, and the multiwavelength tunable lasers are realized through changing the Brillouin pump wavelength. The experimental results show that eight Brillouin wavelengths with wavelength spacing 0.17 nm of double Brillouin frequency shifts are generated, and the wavelength can be tuned in a range of 110 nm (1528-1638 nm). Meanwhile, five Brillouin wavelengths with wavelength spacing 0.26 nm of triple Brillouin frequency shifts are obtained, and the wavelength can be tuned in a range of 60 nm (1535-1595 nm). Additionally, the experimental results also indicate that the Brillouin wavelength number can reach the maximum when the wavelength of the Brillouin pump laser is in the range of the self-excited oscillation. This tunable multiwavelength Brillouin fiber laser with multiple Brillouin frequency shift interval has important applications in many fields, including dense wavelength division multiplex optical fiber communication system, microwave signal generation, optical fiber sensing, and spectrum measurement.

The 1064 nm distributed Bragg reflector (DBR) semiconductor laser has the characteristics of narrow linewidth and stable output, and it has a broad application prospect in the field of free space laser communication used as seed light source. A single mode and narrow linewidth 1064 nm DBR semiconductor laser is designed． Metalorganic chemical vapor deposition (MOCVD) technique is used to grow InGaAs strained quantum well laser material, and a ridge waveguide 1064 nm DBR semiconductor laser with the cavity length of 1200 μm is fabricated. When injection current is 70 mA, the continuous output power of the laser can reach 7 mW, and 3 dB spectral linewidth of the laser is 0.12 nm at room temperature.

The Al-Li alloys are fabricated by the laser additive manufacturing technique, and the microstructures of the as-deposited Al-Li alloys are analyzed. The processing parameters for double-stage homogenization annealing and solution heat treatment are optimized, and the TB phase precipitation behavior is explored. The results show that, after the double-stage homogenization annealing and solution heat treatment, the amount of copper-rich phase with a low melting point precipitated on the grain boundary and within grains is reduced, and thus the uniformity of Al-Li alloy compositions is improved. The amount of the precipitated TB phase reaches the maximum at an aging temperature of 400 ℃, and with the further increment of the aging temperature, the amount of TB phase gradually decreases. In addition, the micro-hardness decreases first and then increases with the increase of the aging temperature.

Composite coatings including TiC particles are fabricated on the TC21 titanium alloy surface by the laser cladding process. The effects of SiC particle size on the phase compositions, microstructures, hardness, friction and wear properties of the cladding coatings are investigated. The results show that the main phases of the cladding coatings are Ti2Ni, TiNi, Ti5Si3 and TiC and the TiC particles refine the grain size. The addition of micro-SiC particles makes the hardness and the wear resistance of the cladding coating surface increase to 2.1 and 2.082 times that of the matrix, respectively, in contrast, the addition of nano-SiC makes them increase to 2.4 times and 1.475 times, respectively.

Pulsed laser shocks are adopted to conduct a shock penning processing on the surface of 7050-T7451 aluminum alloys, and the diffraction pattern and microstructure of specimen surface are obtained by the X-ray diffractometer (XRD) and the field emission transmission electron microscope (TEM). A microstructure response model of the laser shock processed 7050-T7451 aluminum alloy surface is established. The results indicate that, when the laser power density is 1.83 GW·cm-2, the destabilization decomposition of supersaturated solid solution occurs; when the laser power density is 2.34 GW·cm-2, the grain size increases; when the laser power density is 2.85 GW·cm-2, nanocrystals are produced on the specimen surface. The XRD pattern and the TEM analysis results of laser shock processed 7050-T7451 aluminum alloy surface are of consistency.

The Al-Li alloy plates are fabricated by the laser additive manufacturing technique and the evolution of precipitation phase and the change of mechanical properties during the heat treatment process of Al-Li alloys are analyzed. The results show that the as-deposited microstructures of Al-Li alloys mainly consist of α(Al) matrix and TB(Al7Cu4Li) phase, and there exists a small amount of copper-rich phase in the grain boundary. After annealing, the TB phase is more evenly distributed inside the grains, where the copper-rich phase almost disappears and the Al-Cu-Fe impurity phase is rarely present in the grain boundary. After solid solution quenching, the TB phase is nearly dissolved in the matrix and a small amount of δ′(Al3Li) phase appears. After aging, numerous θ′(Al2Cu) and σ(Al5Cu6Mg2) are mainly precipitated. After heat treatment, the microhardness and tensile strength of Al-Li alloys are increased by 47.6% and 87.7%, respectively, if compared with those of as-deposited alloys.

The distribution characteristics of residual stress field along the surface and depth directions are investigated by numerical simulation when laser shocks titanium alloy parts with different thicknesses. The reflection of shock wave among different planes is investigated by dynamic analyses. The results show that, when the thickness increases but other parameters are kept constant, the front residual stress increases while the reverse residual stress increases first and then decreases. As for the front micro-hardness, it reaches the maximum at 440.2 HV when the specimen thickness is 4 mm, in contrast, the reverse micro-hardness reaches the maximum at 416.1 HV when the specimen thickness is 2 mm. The tensile and compressional waves are generated when the shock wave interacts with the acoustic impedance interface, which have obvious influences on the residual stress field distribution.

The laser-arc hybrid welding of HG785D high-strength steels is performed and the effects of laser power and wire feeding speed on the hybrid welding process under different heat source orders are investigated. The dynamic behavior of plasma in the hybrid welding process is investigated. The electron temperature and electron density in plasma under different heat source orders are obtained and the coupling mechanism of heat sources in the welding process is disclosed. The results show that, the weld penetration decreases first and then increases with the increase of laser power, and it decreases gradually with the increase of wire feeding speed. Under the laser-leading condition, the plasma possesses a large volume and a high electron temperature, and the weld penetration is large, simultaneously, the tensile strength of joints is high but the plasticity is weak, and the micro-hardness at each area of joints is high, if compared with those under the arc-leading condition.

The 20-mm-thick 316LN austenitic stainless steels are welded by the 20 kW ultra high power fiber laser, the effects of welding parameters on the macro-morphologies and weld formation are investigated, and the microstructures and mechanical properties of welded joints are analyzed. The results show that better surface appearances can be obtained via a negative defocusing. The weld microstructure is single austenite and there exist the equiaxed grains in the central areas of the top and bottom zones of welds; in contrast, there exist the coarse columnar grains in the central areas of the middle zone of welds. Under the optimal welding parameters, the tensile strength of welded joints is 645 MPa, equivalent to that of base metals. The fracture of welded joints occurs at the fusion line in a typical ductile manner. The micro-hardness of the heat-affected zone is slightly higher than those of welds and base metal.

To investigate the effect of femtosecond laser helical processing parameters on the evolution of hole formation process, we use 304 stainless steel as the target material, select main parameters of the helical drilling by femtosecond pulsed laser, and design orthogonal experiments with 5 factors and 5 levels based on L25(56) orthogonal table. The significance levels of the ablation depth affected by 5 main parameters, such as the single pulse energy, repetition frequency, rotation rate, rate of focus down, and the air-blowing pressure, are analyzed. Based on the back propagation (BP) neural network, we establish the relationship model between the 5 main parameters and the ablation depth of the laser drilling. The data obtained from the orthogonal experiment are used to train the neural network. The generalization ability is tested by additional experiments. The results show that the prediction error of the relationship model is less than 3%. Moreover, the single factor experiment is designed to analyze the influence of the rate of focus down during the helical drilling. The effect of the different rates of focus down on the hole formation during the femtosecond laser helical drilling process is obtained.

In order to make the industrial robots complete the cutting and machining processes of complicated workpieces accurately and efficiently, one algorithm for the robot cutting and machining processing paths directly generated by the three dimensional (3D) point cloud is proposed, which is combined with the point cloud technology and the robot technology. The point cloud measurement system with laser displacement sensors and industrial robots as its core units is constructed, and the extension from one-dimensional measurement to the 3D measurement is realized by the coordinate transformation. The 3D point cloud of the machined workpiece profiles is obtained by the on-line measurement, and the point cloud preprocessing algorithm and the robot path planning algorithm are adopted to generate directly the robot paths for the machined workpieces. The simulation results show that this measurement system and the algorithms can accurately extract the 3D point cloud of the workpiece profiles and quickly generate the robot processing paths.

Selective laser sintering (SLS) is a kind of additive manufacturing technology. A large amount of powders are not sintered during the SLS forming of polyamide 2200 (PA2200), and the reuse of the unsintered powders is important for reducing the cost. However, the high temperature during the SLS process changes the performance of unsintered powders, and the effect of powder recycling on the properties of the formed samples is not yet clear. The influences of powder recycling times on hardness and impact toughness of the sintered samples are systematically investigated with the help of EOS P110 system and EOS PA2200 powders. The results show that the melting point of the recycled powders increases with the increase of recycling times of the powders. When the recycling times exceeds two, the unmelted powders and pores inside the formed samples increase, and the toughness and hardness of the formed samples decrease. When the recycling times of powders is less than two, the impact toughness of the formed samples declines slightly and its hardness increases.

The Al-doped ZnO (AZO) films with different Al doping concentrations are fabricated on the Al2O3 substrates. The effects of Al composition on the photoelectric and surface plasma properties of AZO films are analyzed by the ultraviolet-visible (UV-Vis) absorption spectra, Hall measurement, refractive index and dielectric constant measurements. With the increase of Al composition concentration, the absorption edge is blue-shifted and the absorption intensity decreases gradually ,which means the optical loss is reduced. Meanwhile, the carrier concentration and mobility first increase and then decrease, while the electrical loss first decreases and then increases.

In order to realize rapid detection of measurement accuracy of numerical control equipments, a set of two-dimensional gimbal mount rotatory axes is designed for laser tracing measuring system. A high precision reference sphere serves as the reflection unit, and it is fixed on the base, which ensures laser tracing measuring system perform in a large tracking angle and avoids the influence on measurement accuracy caused by the movement of rotatory axes. The effect of the main geometric errors of axes on measurement accuracy of laser tracing measuring system is analyzed. The relation between run-out error of axes and measurement accuracy is studied, and the model of run-out error of axes is simplified. Experimental results show that measurement error of the laser tracing measuring system is less than 0.1 μm when the run-out error is within the range of ±5 μm, which indicates that the laser tracing measuring system can reduce the effect of run-out error.

In order to reduce the difficulties in manufacture and assembly of the spatial filter with two square windows in image plane, we propose a grating lateral shearing interferometry based on a nine step phase shifting method, which is used to calibrate the zero-order phase error. The zero-order crosstalk could be eliminated only by a variable space filter. The parameters are designed and the principle verification system is completed for a projection lithography lens with numerical aperture of 0.125. Then the wavefront aberration measurement of this lens is achieved by the restoration of shearing phase and the reconstruction of wavefront. The results show that the wavefront aberration is less than 20.32 nm. The repeatability precision of the grating lateral shearing interferometer is measured. The root-mean-square value of the repeatability precision is 0.1303 nm, which shows the performance of this system is well.

The waveguide ring resonator (WRR) is one of the key elements in the fields of integrated optical communications and optical sensors. The performance of these systems will be affected by the shape of the resonant curve. Aiming at the difference of transmission loss between the symmetric and anti-symmetric modes of the cavity coupler, and the reflection at the end face of the straight waveguide outside the resonator, the expression of the output line of the waveguide ring resonator is obtained using the principle of multi-beam interference superposition. The high aspect ratio silicon nitride WRR is tested with an optical vector network analyzer based on single-side band modulation. The results confirm the effect of the coupler mode and the reflection at waveguide end face on the resonance curve. The actual test curves can be well fitted with the theoretical simulation results.

An ultra-fast compact optical quantum random number generator (QRNG) is designed and realized by using the amplified spontaneous emission (ASE) noise of superluminescent light-emitting diodes as the quantum random entropy source. In order to reduce the influences of the classical noise and imperfect devices on the randomness and based on the minimum entropy estimation for the quantum entropy source, the exclusive OR (XOR) operation of the adjacent bits for the each collected sequence is conducted and the 12-least-significant bit is intercepted as the final random sequence in the high speed field programmable gate array in real-time. The proposed QRNG with a real-time random number generation rate of 1.4 Gb/s can directly deliver to a host computer and work stably for a long time, which possesses the practical application potential.

Because the spectrum of the interference optical signal in optical fiber Fabry-Pérot (F-P) sensor is sparse, the traditional fast Fourier transform (FFT) algorithm needs to calculate the spectrum components in the whole frequency range in the process of solving the cavity length, and the calculation speed is slow. While sparse fast Fourier transform (SFFT) algorithm only needs to calculate the main spectrum components of the interference optical signal. Through rearranging spectrum, filtering with window function, down sampling in frequency domain, and finally looping location and valuation, SFFT can quickly calculate the K maximal Fourier coefficients of the signal spectrum. Thus SFFT can quickly find the frequency corresponding to cavity length and demodulate the cavity length. The algorithm is simple in structure and low in time complexity. It is verified that the accuracy of the demodulation results of SFFT algorithm is better, and the efficiency is faster than that of FFT algorithm by analyzing the actual interference optical signal of optical fiber F-P sensor demodulation system. It is proved that SFFT is very suitable for on-line real-time demodulation of cavity length of optical fiber F-P sensors, so as to measure physical quantities in real time.

In order to eliminate the influence of polarization-induced fading and polarization-induced phase shift on the positioning performance in a dual Mach-Zehnder interferometry disturbance sensing system, a polarization control method based on field programmable gate array (FPGA) with simple structure and high efficiency is proposed. The method adopts polarization controller feedback technology and uses feedback values of two optical signals as control functions. In combination with the improved harmony search (IHS) algorithm, the FPGA hardware parallel structure and pipeline technology are used to rapidly implement the algorithm iteration and control the polarization controller to adjust the polarization state. The experimental results show that the method can adjust the polarization state of the system in a short time, the polarization control time is about 0.7808 s, and the positioning error of the system is improved up to within ±20 m, which effectively eliminate the polarization effect on the positioning performance. Besides, the use of FPGA instead of the computer as the control core of the system improves the data processing speed, reduces the polarization control time, and improves the integration of system, thereby facilitating the miniaturization of the polarization control instruments.

Poor coherence of local oscillator signal restricts the azimuth/lateral resolution of long-range target imaging with synthetic aperture ladar (SAL). Coherence maintenance problem of SAL signal is studied, and a method for maintaining the coherence of SAL signal based on local oscillator digital delay is proposed. By setting the local oscillator signal reference channel and using the self-heterodyne detection method, the phase introduced by the frequency instability of the local oscillator signal is extracted in the digital domain, which is used to compensate the phase in target echo signal after the delay in the digital domain. The laser signal model is established, and the error analysis of the proposed SAL signal coherence maintenance method is given. The selection principle of the fiber delay length from the self-heterodyne detection is given. Theoretical analysis and simulation experiment show that the proposed method can effectively maintain the coherence of SAL signal.

We build a panoramic spherical coordinate system using the panoramic images collected by vehicle mobile measurement system. The fusion of the laser point cloud and panoramic images is realized through a series of coordinate transformation of vehicle points based on collinear principle of center of sphere, image point and object point of spherical surface.The black hole of true color point cloud caused by the blind area of panoramic images creates the road information loss, we use the overlapping relationship of adjacent images to solve the black hole. Precision evaluation is conducted via manual information collection. We use the manual collection checkpoints to evaluate the fusion accuracy, and the results show that the fusion method is correct and precision. The road information is preserved completely after repairing the black hole by accurate collection of panoramic images and laser point cloud.

The feasibility of a spaceborne lidar system for global CO2 concentration and aerosol detection is studied. As the atmospheric backscatter signal is weak, the spaceborne lidar is very sensitive to stray light. The lidar system is composed of Ritchey-Chretien receiving telescopes, multi-band relay optical systems, and photodetection systems. Therefore, compared with conventional imaging optical systems, the analysis and suppression of stray light of the lidar system can be improved. Based on the modeling of opto-mechanical structures and the classification of stray light sources and a large number of ray traces, a stray light suppression method is proposed in the laser lidar rear-optical system rather than in the receiving telescope. The simulation results show that the baffles in the collimator lens barrels in rear-optical system largely suppresses the stray light. Therefore, the baffles in the receiving telescope should be removed.

When the core size of a holey microstructural fiber is close to the wavelength, the light propagation in the core is greatly enhanced and a strong evanescent field is produced around the core. A new air suspended core microstructural fiber with the core diameter of only 2 μm is reported. The air suspended core fiber fabricated by sheet-stacking method has large evanescent field and the unit structure with micrometer-size holes. The air suspended core fiber, whose loss is 0.16 dB/cm at the wavelength of 532 nm, is very suitable for sensing detection of biochemical substances. Using the air suspended core fiber as sensing probe, we establish a simple fluorescence detection system combining with laser technology, and detect the fluorescence properties of bioluminescent labeling material CdTe/CdS/ZnS quantum dots with this system. The limit of the fluorescence quantum dots detected by this system is about 1 nmol/L (corresponds to 3.78×107 quantum dots), which indicates that this system has the properties of high sensitivity and rapid detection speed. The fluorescence detection system based on the air suspended core microstructural fiber provides a new method and idea for the sensitive detection of biomaterials marked by quantum dots.

Location distribution and diameter at breast height (DBH) of trees are important indicators for studying forest ecology and managing forest areas. Lidar have great potential for obtaining tree-related data. Therefore, a fast statistics method of tree information from three-dimensional laser point clouds obtained by hand-held mobile laser is proposed. The hand-held mobile laser can collect the tree information from close distance and obtain the detailed information of a single tree facade. In view of the characteristics of the above point cloud, a method based on hierarchical clustering is proposed. A group of cross-section slices of point cloud are formed at different heights, and the segmentation process of each slice is performed by cluster analysis. We use random sample consensus algorithm to fit the circle according to the result of segmentation and complete the tree point cloud extraction by comparing the fitting results of a set of slice sections. This method of sampling and recalculating greatly improves the processing speed. The results show that the accuracy of trunk extraction is 94.4%, the average calculation error of DBH is 3.4 cm. The proposed method can quickly statistic tree information.

Laser radar can be used not only to analyze the target spectral characteristics, but also to obtain the spatial orientation, distance, three-dimensional profile and movement characteristics of the target. The conventional lidars can only measure single characteristic of the target, thus it is difficult to obtain the above measurement features of the target at the same time. To meet the multi-functional requirements, such kind of lidar with the above measurement capabilities is designed. The structure of the optical system is greatly simplified by adopting transmitting/receiving common optical system. The optical system, with a special refraction /reflective structure, can achieve 400-1400 nm wide band transmission and reception by using two kinds of optical materials. To achieve multi-spectral detection, the laser light source uses an optical parametric oscillator single pulse tunable laser, of which spectral adjustment range covers the entire detection band. The equivalent beam expansion ratio of the laser emission system reaches 12.6, and the equivalent F number of monochrome echo receiving system is 8. The radial energy within 20 μm is close to 100% with the photomultiplier tube. In order to track and finely measure the structure of the target, a visible light receiving system is adopted to the common light path. Thus, the multi-spectral laser radar has visible light imaging capabilities. The full field of view of the visible light receiving system is 1.6°, and the designed modulation transfer function is better than 0.5 at 37 lp·mm-1. The design parameters of the system meet the detection requirements.

Using a continue-wave semiconductor laser as transmitter and a charge-coupled device (CCD) with a fish-eye lens as detector, a set of polar nephelometer is designed for measuring angular distribution of light scattered by atmospheric molecular and aerosols. The device can observe the scattering image of the atmospheric sample in real time, the scattering angle observation range is 14°-162°, and the polarization angle observation range is 0°-360°. We use this device to observe pure nitrogen and water vapor in real time seperately, then obtain their scattering images. The nitrogen scattering light shows good correlation with Rayleigh scattering theory and the linear fitting R-square of sacattering intensity varied by polarization angle with calculation is 98%. The variation trend of water vapor scattering light with scattering angle is in good agreement with Mie scattering theory. The results show that the device has potential application value in quantitative observation of aerosol scattering light.