The intensity and scintillation index of vortex beams propagating in the oceanic turbulence are simulated by using a step-by-step phase screen method. We find that the vortex beam spot diffuses gradually and the central dark spot gradually disappears with increase in the propagation distance. By changing the parameters of the turbulent phase screen to simulate the oceanic turbulence with different strengths, we find that the on-axis scintillation index of the vortex beam increases with increase of the mean-square temperature dissipation rate, increase of the relative strength of temperature and salinity fluctuations, or decrease of turbulent kinetic energy dissipation rate per unit mass of fluid. The scintillation index of the vortex beam is lower than that of the Gaussian beam when the propagation distance reaches a certain value, and the larger the topological charge is, the more rapidly the scintillation index descends.

A numerical simulation model of active illumination beacon considering surface roughness is established. Based on this model, the effect of roughness on intensity uniformity and wavefront mean square root of scattered light is discussed, and the difference between wavefronts detected by an active illumination beacon and a point source beacon and the correction effect of an adaptive optical system are analyzed. Moreover, as the surface roughness of a target is decreasing, the wavefront mean square root of scattered light and the difference between wavefronts detected by the active illumination beacon and point source beacon are increasing, but the correction effect of the adaptive optical system is decreasing. In addition, increasing the number of illuminator will suppress the influence of uplink turbulence on wavefront sensing.

In order to mitigate the performance fading of satellite-to-ground laser communication system caused by atmospheric turbulence, a multi-aperture receiving scheme based on fiber coherent beam combining (CBC) is used. A typical satellite-to-ground coherent laser communication model is considered in this paper, and the numerical simulation results of the variations in sensitivity and bit error rate of the communication system with turbulence compensation effect are given. Based on an existing beam combining method, a set of CBC optical communication receiver with four apertures is constructed, and the phase-locked bandwidth of the system under two and four apertures are measured. Then we use the rotating phase screen to simulate the influence of atmospheric turbulence on the wavefront at different Greenwood frequencies. Meanwhile, we ensure the incoherence of the received light intensity. On this basis, the relative fluctuation variances of light intensity in optical fiber before and after CBC are given. The results show that the system can effectively mitigate intensity scintillation in the weak turbulence.

In order to solve the defect of the proportional-integral control algorithm in adaptive optical correction performance, a linear quadratic Gaussian (LQG) control method is proposed to improve the correction performance of the adaptive optical system. Experimental verification in the actual system is performed in this paper. Compared with the proportional-integral control, the LQG control method can improve the peak intensity of the far-field spot from 3000 ADU to 3700 ADU, and decrease the root mean square value of the residual wavefront from 0.039 μm to 0.026 μm. The LQG control method can also suppress the violent jitter of the far-field optical field after closed-loop and improve the convergence speed of the deformed mirror voltage, further improving the stability and response speed of the adaptive optical system.

This study uses the extensively applied particle swarm algorithm to investigate the influence of the key parameters on the demodulation error using numerical simulation. The simulation results illustrate that the available range of key parameters reduces with the increase of the multiplexing number of the fiber Bragg grating (FBG) and the overlapping degree of spectral shape. Furthermore, with the maximum demodulation error as an evaluation index, we obtain a reasonable setting range of key parameters using a quantitative analysis. Under the optimal conditions, the performance of the spectral shape multiplexing demodulation of the FBG is improved, which is confirmed by the corresponding experiment.

Based on the performance evaluation method of traditional imaging optical systems, this study reveals that the autocorrelation function of the point hologram can be used to evaluate the imaging performance of incoherent digital holographic adaptive optics (IDHAO) system. Inspired by the fact that the autocorrelation function of the ideal white noise function is approximately a Dirac δ function, we propose that increasing the randomness of the point hologram can make its autocorrelation function close to the Dirac δ function and improve the imaging resolution of the IDHAO system. Accordingly, a practical method which introduces a random phase plate into the IDHAO system, is proposed and implemented to increase the randomness of the point hologram. The proposed method is evaluated through numerical simulations and effects of the pixel number and the standard deviation of phase in the random phase plate on the imaging resolution of the IDHAO system are investigated. Finally, an optical experiment is performed in the laboratory to evaluate the proposed method and experimental results demonstrate that the random phase plate can effectively improve the IDHAO system's imaging resolution.

This study proposes a novel semiconductor laser parameter inverse design method based on artificial neural network (ANN) and particle swarm optimization (PSO) algorithm. The ANN is trained using a laser output power as sampling data, which can be calculated by applying the traditional numerical simulation method. The network can be used to predict the power spectrum of the laser for any new values of the selected parameters. The mean square error can be as low as 0.5 mW and the CPU time as low as 0.07 s, which is about 1800 times more efficient than that of the numerical algorithm, which takes 125.57 s CPU time in the same environment. To obtain the design parameters for any target power spectrum, the inverse design can be achieved by combining this network with the PSO algorithm. It is clear from the calculation that the inverse design parameters are not unique, which proves that the semiconductor laser has a nonlinear multi-parameter problem. The combination of ANN and PSO inverse algorithm (with a mean square error of less than 0.4 mW and a CPU time of 39.45 s) demonstrates greater performance based on the same condition when compared with the traditional numerical simulation inverse method (with a mean square error of less than 0.89 mW and CPU time of 192 h). The accuracy and speed of the proposed method are improved by 22.25 times and about 17500 times, respectively.

An asymmetric large optical cavity waveguide structure is designed and fabricated, and a stable output of a 980 nm high power semiconductor laser is realized by combining distributed Bragg reflection (DBR) technology. The experiments use electron beam lithography technology and an inductive coupled plasma etching process with SiO2 as a hard mask. By reducing the Ar beam current, the consumption of the SiO2 hard mask due to physical bombardment is reduced. A DBR grating with good morphology, period of 890 nm, and duty cycle of 50% is fabricated. Combined with ridge waveguide laser fabrication technology, the DBR laser is successfully fabricated. Finally, when the device injection current is 15 A, the output power is up to 10.7 W, slope efficiency is 0.73 W/A, device threshold current is 0.95 A, and central wavelength is 979.3 nm. This study presents a new approach for the fabrication and research of GaAs-based DBR semiconductor lasers.

In order to evaluate the imaging quality of a high-repetition-rate system in each gated slice and provide fundamental elements for the study of pulse allocation strategy, a theoretical model describing the signal transmission process of the high-repetition-rate system is established based on the Jaffe-McGlamery model, and the factors of image degradation are analyzed. Specifically, an image quality evaluation model of the high-repetition-rate system is proposed herein. Experimentally, a pulsed laser having a repetition rate of 4 kHz is used to image a black-and-white stripe target. Results show that measured values of the experimental image fit well with the calculated values of the model on a linear range from the beginning of the target imaging to the occurrence of saturation, with an estimated error not exceeding 10%.

Nd, Gd∶CaF2 is a disordered crystal, and has advantages of broadband spectrum, high thermal conductivity, wide transmission range, and low phonon energy. Using a 0.5%Nd, 8%Gd∶CaF2 disordered crystal as laser-gain medium, in which 0.5% and 8% are both atomic fractions, a diode-pumped tunable laser is realized for the first time herein, to the best of our knowledge. A continuous tuning range of approximately 28.5 nm (1045.7-1074.2 nm) is obtained. Using a semiconductor saturable absorber mirror as mode locker, a dual-wavelength mode-locked laser is demonstrated. The central wavelengths of the mode-locked laser are 1065.45 nm and 1066.48 nm. The maximum output power of the mode-locked laser is approximately 394 mW, and the minimum pulse width is 8.37 ps.

This study demonstrates an all-solid-state acousto-optic Q-switch Nd∶YAG laser with a high repetition rate and high pulse energy. A master oscillator power amplifier system with a thermal-compensation cavity of connecting two Nd∶YAG rods in series and an amplifier containing a two-slab gain medium is selected for the experiment. Fused silica is used as the acousto-optic Q-switch crystal with an adjustable repetition rate of 10-100 kHz. At the repetition rate of 10 kHz, the linearly polarized laser with an output power of 14 W is injected into the two-slab gain medium for amplification after beam expanding and sharping. When the pump power is 22.7 kW, a laser output power of 4256 W is obtained with a pulse energy, pulse width, and peak power of 425.6 mJ, 133 ns, and 3.2 MW, respectively. The laser beam quality β is 3.8 times of the diffraction limit. The output power and pulse width at different repetition rates are kept constant during the experiment.

This study presents a microwave photonic down-conversion system based on the stimulated Brillouin scattering. In this system, a local oscillator signal and radio frequency signal are introduced into two sub-Mach-Zehnder modulators of the dual-parallel Mach-Zehnder modulator to convert a high-frequency radio frequency signal to a intermediate frequency signal. Further, the gain spectrum of the stimulated Brillouin scattering effect is used to retain the two +1-order sidebands generated by the radio frequency and local oscillator signals. These two sidebands are then transmitted to a photodetector for beating, and an intermediate frequency signal is produced. Simultaneously, the phase of the intermediate frequency signal can be changed by adjusting the bias voltage of the parent Mach-Zehnder modulator in the dual-parallel Mach-Zehnder modulator. The frequency of the down-converted radio frequency signal is 10.73 GHz, which can be converted to a signal having any frequency in the range of 20-40 MHz and whose phase can be linearly transformed from 0° to 360°.

An L-band switchable dual-wavelength passively mode-locked fiber laser based on a carbon-nanotube saturable absorber is reported herein. The central wavelength of the fiber laser spectrum can switch between 1572.9 nm and 1596.6 nm with a pulse width of 1.80 ps by tuning the pump power; the corresponding 3-dB spectral widths of the two wavelengths are 3.68 nm and 2.34 nm, respectively. Additionally, the dual-wavelength mode-locked fiber laser has a wavelength separation of ~24.8 nm, with two central wavelengths of 1572.3 nm and 1597.1 nm, respectively. A numerical study is conducted on the formation and evolution of the L-band switchable dual-wavelength mode-locked fiber laser. The numerical results are in good agreement with the experimental observations, indicating that the switchable dual-wavelength mode-lock can be attributed to the change in the transmission spectrum of the gain fiber.

An underwater pulsed-laser-sound-signal detection technique is introduced by combining the frequency-domain characteristics of the laser acoustic signal. The different attenuation characteristics of the laser acoustic signal at different frequencies are analyzed. To ameliorate the serious attenuation of high frequency components at long distances, a pre-compensation filter is added to the front end of the frequency-domain energy detector; the results of Monto-Carlo simulation show that the frequency domain energy detector with pre-compensation filter can effectively improve the detection performance of laser acoustic signal at a long distance.

This study uses the self-homodyne detection and analysis cavity conversion method to compare the quadrature component noises of all-solid-state single-frequency laser and fiber laser suitable for the preparation of the squeezed-state light field in audio-band frequencies. The results show that the quadrature amplitude and quadrature phase noises of the all-solid-state, single-frequency, 1064 nm laser reach the shot-noise limitation after analysis frequencies of 1.5 MHz and 5 MHz, respectively. Moreover, the measurement bandwidth of the fiber laser is higher than that of the shot-noise limitation. With the semiconductor optical amplifier (SOA) noise-reduction system, the low-frequency-bandwidth (<620 kHz) quadrature amplitude noise of the fiber laser is smaller than that of the all-solid-state single-frequency laser. This result provides a single-frequency source-selection scheme for the study of the low-frequency-bandwidth squeezed-state light field. The SOA noise-reduction system can effectively suppress the quadrature component noise of the low-frequency-bandwidth laser and provide an evidence for the preparation of the squeezed-state light field in audio-band frequencies.

In this study, a pure iron (Fe)-based alloy cladding layer and Fe-based alloy cladding layers containing tungsten carbide (WC) particles with mass fractions of 3%, 6%, and 9% are fabricated on an AISI H13 hot-working die steel surface, and the WC is used as reinforcing phase particle. The WC particle distribution, microstructure, phase, and wear behaviors of the cladding layers are studied based on the optimized parameters of the laser cladding layers. Results reveal the existence of a good metallurgical bond between the substrate and cladding layer. The cladding layer is mainly composed of dendrites and eutectic. Upon adding WC particles, the structure around the WC particles gets refined. The Fe-based cladding layer becomes hard because of the hard-phase formation, and its wear resistance considerably improves compared to the substrate. Hardness and wear resistance of the layer are further improved when the WC mass fraction reaches 3%, 6%, and 9%. The wear mechanism of the cladding layer is mainly abrasive wear, accompanied by different degrees of adhesion wear. The oxidation wear gradually deepens when the WC mass fraction increases.

Via numerical simulation and experiment, a two-dimensional transient model of laser polishing (LP) is established to simulate the surface-morphological evolution of materials during LP. A moving laser-beam heat source with the combined effects of capillary and thermocapillary forces is adopted, and the flow and temperature fields are also coupled. The simulated-model surface and the actual examined material surface are constructed by performing spectrum analysis. The simulated results show that under the effects of capillary and thermocapillary forces, the peak material flows to the trough and fills the contour hollow on the polished material surface, achieving the polishing effect. The laser power and scanning speed significantly affect the polishing results. A low-heat input leads to a small molten pool, resulting in a poor polishing effect with insufficient flow time; excessive heat input results in a molten pool with a long duration of time, which increases the LP surface roughness. Compared with the experimental results, the simulated surface roughness and the depth of the molten pool have an error of less than 8%, reaching a high simulation accuracy.

We investigate dry and liquid film-assisted laser cleaning methods and elucidate the influence of laser power on the state of a specimen surface. We also compare the derusting mechanisms of the two methods. The results denote that both the aforementioned methods can effectively eliminate the rusting layer on a sample surface,and the effect of liquid film-assisted laser cleaning at low power is better than that of the dry laser cleaning. The optimized liquid film-assisted laser cleaning process parameters include a laser power of 400 W, pulse frequency of 10 kHz, and pulse width of 30 ns. Under these conditions, the oxygen content of the sample surface is reduced to 3.38%,and the surface roughness is observed to be 3.04 μm.

To understand the low-temperature fracture behavior of the laser-MAG(metal active gas) hybrid welding joint of weather-resistant steel for high-speed trains, the integral values Jm of fracture toughness of the welding metal, heat-affected zone, and base material are obtained through a low-temperature fracture toughness test. The relationship between fracture toughness and temperature is fitted by the Boltzmann function, and the ductile-to-brittle transition temperature of each zone is obtained. The results demonstrate that the variation trend of the fracture toughness of each zone is reduced as temperature decreases. The base material has higher low-temperature toughness compared with the welding metal. The ductile-to-brittle transition temperatures of the welding metal and heat-affected zone are -65.9 ℃ and -70.4 ℃ respectively, both of which are higher than that of the base material (-81.9 ℃). The micro-fracture mechanism of each zone of the laser-MAG hybrid welding joint is explained based on the observation of the microstructure and fracture morphology. The poor low-temperature fracture toughness of the welding metal is primarily due to the large-size coarse grain and proeutectoid ferrite in the microstructure.

Metal parts with textured bumps are widely used in engineering, and controlling their morphology precisely is critical to control the performance of related parts accurately. In this paper, the 45 steel is taken as the research object, and a two-dimensional axisymmetric model is used to simulate to explore the evolution of the temperature field and the direction and velocity of fluid flow in the molten pool irradiated by the pulsed laser. Therefore, the microscopic mechanism and dynamic process of the formation of the textured morphology can be studied. The results show that during the heating period and while the temperature of the surface is below the critical temperature, the tangential stress is negative, and the melt flows to the center of the molten pool. If the surface temperature is above the critical temperature, the tangential stress is positive, and the melt flows to the edge of the molten pool, finally forming a convection-free location at the junction of the two circulations. For the same circulation, the greater the tangential stress is, the greater the peak velocity is. If the new circulation velocity is small when the surface temperature exceeds the critical temperature, it will weaken the deformation of the morphology at the last moment. Otherwise, an abnormal shape will be produced at the convection-free position.

In this paper, we introduce the laser stir welding method to reduce the welding defect of laser heating to aluminum alloy during the laser welding of carbon fiber reinforced thermal polymers (CFRTP)/aluminum alloy and improve the mechanical properties of welded joints during the jointing process. With the same laser power and welding speed, the jointing strength of this method is 3.25 times of that of the traditional linear welding method. Moreover, the bubble defect in laser stir welding is significantly reduced, and a good welding morphology is obtained. Further, the temperature field in the laser stir welding of the CFRTP/aluminum alloy is simulated to study the mechanism of laser stir welding in CFRTP/aluminum alloy. The results show that the temperature on the surface of aluminum alloy changes in the form of a non-equal amplitude oscillation. Two peaks are observed, and laser stir welding can reduce the welding defect owing to these peaks, amongst other reasons. The weld depth and width are calculated, and the error is within 9.87%.

Considering the serious oxidation of titanium alloy induced by laser cladding in air, a coaxial nozzle with shielding gas is designed to protect the molten pool. A three-dimensional numerical model of the coaxial cladding nozzle with inside-laser powder feeding is established using FLUENT software, and the influences of the inlet number, angle, and flow rate of shielding gas on the mass fraction of argon are analyzed. The results demonstrate that the inlet number of the shielding gas is related to the symmetry of argon distribution. The inlet angle has little effect on the mass distribution of argon; however, increasing the flow rate of the shielding gas will greatly improve the effective protection domain. According to the optimized parameters of the coaxial shielding gas nozzle, the laser cladding of the Ti-6Al-4V alloy in an open environment is conducted by using argon as the shielding gas. The surface of the molten track presents silvery white and the cladding layer is fine, indicating that the coaxial gas nozzle can effectively protect the molten pool from oxidation.

In this study, TC4 titanium alloy bulk specimens are prepared using the laser three-dimensional(3D)printing technology. The effect of normalizing temperature on the laser 3D-printed TC4 titanium alloy microstructure, phase composition, and tensile properties at room temperature is studied via an optical microscope, scanning electron microscopy (SEM), X-ray diffractometer (XRD), and electronic universal testing machine. Experimental results reveal that the α-Ti phase recrystallizes and the length and width of the α-Ti phase increase after being normalized at the α-Ti phase zone. The microstructures mainly comprise α-Ti phase and a small amount (or trace amount) of the β-Ti phase. The tensile property at room temperature is general. After being normalized at the α+β phase zone, the slender primary α-Ti phase in the as-deposited state thrusts each other because of the β-Ti phase precipitation, transforming into a short rod-shaped primary α-Ti phase. The β-Ti phase not only coexists with the secondary α-Ti phase between the short rod-shaped primary α-Ti phases, but also precipitates and is distributed as networks inside the short rod-shaped primary α-Ti phase. After 990 ℃/2 h/AC treatment, the room-temperature tensile strength, yield strength, and elongation are 960 MPa, 835 MPa, and 17%, which satisfy the national standard for forging. The fracture morphology of the tensile specimens is covered with dimples, all of which are ductile fractures.

This study obtains W-Cu materials suitable for the electronic packaging by fabricating W-Cu composites with different W contents (such as 60W-40Cu, 70W-30Cu, 75W-25Cu, and 80W-5Ni-15Cu) through selective laser melting. The effect of W content on the microstructure, density, thermal conductivity, coefficient of thermal expansion, roughness, and hardness is evaluated. The results show that the balling phenomenon is common in such four composites. When the W mass fraction is less than 70%, the densification mechanism is rearrangement; connection and contiguity are hardly observed between W phases; heat conduction is preferred in the Cu phases. In addition, when the W mass fraction is higher than 75%, solid sintering is the main densification mechanism, and the heat conduction path contains the constitutional unit of Cu occupying the unit edges and W occupying the unit center. The deviation between the thermal conductivity/coefficient of thermal expansion of W-Cu composites and the theoretical values increases with increasing W content, which also occurs in the cases of roughness and hardness. The obtained densities of 60W-40Cu, 70W-30Cu, 75W-25Cu, and 80W-5Ni-15Cu are 97.9%, 94.5%, 91.6%, and 91.9%, respectively. The thermal conductivities of the four composites are 210.4, 176.8, 152.7, and 121.3 W·K-1·m-1, respectively. Furthermore, the thermal expansion coefficients of the four composites are 11.05×10-6, 9.33×10-6, 8.17×10-6, and 7.02×10-6 ℃-1, respectively. The surface roughnesses of the four composites are 9.2, 13.7, 15.2, and 15.4 μm, and the microhardnesses are 183, 324, 567, and 729 HV, respectively.

Based on the coating design software,a type of λ/4-λ/2-λ/2 tri-layer broadband antireflective coating was deposited on the K9 substrate via sol-gel dip coating using tetrabutylorthotitanate and tetraethoxysilane as precursors. A broadband antireflective coating with a high average transmission of 99.25% (500-900 nm) was obtained, and the transmittance gain increased with the increasing incident angle. The main absorption peak of the Nd glass could be effectively covered even at an oblique incident angle range of 0°-60°, increasing the average transmittance gain from 7.2% to 10.2%. After heat treatment at 150 ℃, the film had a certain rubbing resistance and good surface uniformity with a root mean square roughness of 4.00 nm.

Herein, the vertical aligned nematic color filter liquid crystal on silicon (VA CF-LCoS) microdisplay was studied, and the fringing field effect in micro-pixels was optimized by changing the pre-tilt angle and pixel size. To further optimize device performance, a three-dimensional (3D) optical model of the VA CF-LCoS was established using circularly polarized light as the incident light source. Results reveal that the optical reflection efficiency of VA CF-LCoS can be considerably improved when a circularly polarized light is used as the illumination source. Herein, using 3D optical analysis, a completely different conclusion has been reported compared to those reported by former researchers who use two-dimensional optical analysis: the black lines in bright sub-pixels caused by the fringing field effect can only be reduced via optimization, and not completely eliminated.

Long-distance and large-range beam translation is achieved in the optical scanning and photodetection systems by analyzing the accuracy of the beam translation system comprised of a double pentaprism and by obtaining the parallel accuracy of the system using the autocollimation method. The direction of the emergent light in the system is not parallel to that of the incident light because of the errors in the positions of two pentaprisms in an component relative to the theoretical position. The autocollimation method can be used to optically adjust the system to ensure that the direction of the emergent light is parallel to that of the incident light. The beam-translating component comprising a double pentaprism rotates around the incident optical axis by the rotating pair during operation; hence, the whole system will generate a rotational error around a certain mechanical axis, which will cause the coordinate transformation matrix of the double pentaprism system to no longer be the unit matrix and the direction of the emergent light to no longer be parallel to the direction of the incident light. Further, a mathematical model can be established by analyzing the azimuth error of the pentaprism and the nonlinear relation between the overall rotation error and the systematic error of the system. The ray-tracing simulation is used herein to verify the theoretical analysis accuracy. A solution is also proposed for reducing the systematic error, which controls the accuracy of the beam translation system comprising double pentaprisms to within 10″ and provides a good reference for the error analysis of the prism in case of the beam folding problem.

The polarization scanner (POSP) is a remote sensor which can simultaneously measure polarization and aperture. The optical-mechanical system design and index requirements of POSP are introduced. In order to ensure the measurement accuracy, the environmental adaptability design and analysis of POSP are carried out aiming at the mechanical property during the transport and launch phases and the thermal environment of in-orbit operation, and the thermal vacuum and identification level mechanical tests are carried out. The experimental results show that the fundamental frequency of the instrument is about 110 Hz, and the modes are basically consistent with the simulation results. The strength and hardness of the whole machine meet requirements. After the thermal vacuum test, the output of the instrument is normal, and each component of the optical-mechanical system works normally. The performance of the whole machine is tested before and after the thermal and mechanical tests. The results show that the coincidence degree of field of view is more than 90%, and the polarization precision is better than 0.5%. The instrument has good adaptability to the space environment, and meets the stable and reliable work requirements on the ground and in orbit.

In this paper, a new modulation measuring profilometry method based on phase-shifting and modulation ratio is proposed in order to balance the measurement speed and accuracy of the traditional methods. In the proposed method, a special projection system comprising a common projection lens and a cylindrical lens is used. Two groups of vertical and horizontal phase shifting sinusoidal grating fringes are projected onto the measurement area. The “image planes” of the two types of fringes are separated by the cylindrical lens, and the measurement area is between the two “image planes.” The modulation distributions of the two types of sinusoidal grating fringes are obtained using a phase shifting algorithm, and the mapping relationship between the modulation ratio of the fringes and the actual position is established. The three-dimensional shape of the object can be reconstructed according to the mapping relationship between modulation ratio of the fringes and the actual position. In addition, the experiments are conducted to evaluate the feasibility of the proposed method.

The asymmetric deformation of silicon wafer alignment mark after lithography process causes an alignment error. Currently, such errors are typically calibrated via process verification; however, this method is challenged by its lack of process adaptability. Herein, we present a new calibration method which uses the differences in alignment positions of the asymmetrically deformed wafer alignment marks under illuminations with different wavelengths and polarizations to calibrate the alignment error, and the proposed method exhibits good process adaptability. Additionally, the proposed calibration method is extended to calibrate the overlay measurement error, improving the process adaptability of overlay measurement.

We propose an active method for light field depth computation with high accuracy and high robustness. Structured illumination is employed to provide encoding information so that both direction information of light rays and depth-modulated phase information are recorded in the light field. The phase information can provide intensity-insensitive matching features for constructing light field depth cues. Thus, scene depth can be computed accurately. Experimental results demonstrate that, compared with the passive method, the proposed active method can obtain higher quality depth maps and achieve light field depth computation with higher accuracy and higher robustness.

A calibration method for a rotary scanning system is proposed based on two-dimensional profile data. Firstly, key features oftwo-dimensional profile data collected by each sensor are extracted, and the accurate calibrations for relative poses of multiple sensors are achieved by establishing the matching relationship of the obtained features. Secondly, initial solution of the rotating axis is estimated based on the geometric constraint among the laser plane, target, and rotating axis. Meanwhile, the target optimization function is established based on the target radius size, and the precise pose of the rotating axis can be solved iteratively. Experimental results show that the measurement accuracy reaches 0.08 mm, and the measurement time is 20 s. The proposed method can replace the manual detection, achieve on-line measurement of wheel size, and be applied to 3D measurements for other large rotators.

A high-precision laser tracking system based on a two-dimensional galvanometer and position sensitive detector is proposed. A geometrical optics model of the tracking system is established using the ray tracing method, and error analysis is performed to simulate positioning precision and tracking performance of the proposed laser tracking system. Simulation results demonstrate that, when the target is located at a distance of 100 m, the tracking system's point position precision is 0.35 mm, angular precision is 0.72″, tracking range is -10° to 10°, and maximum tracking speed is 3.6 rad/s. These results indicate that the system can realize high precision and real-time active detection tracking for fast moving targets at long distances.

A Kalman filter spectrophotometry based on interval selection of correlation coefficient threshold method is proposed to simultaneously detect trace ions of copper, cobalt, and nickel in industrial wastewater without any separation steps. Firstly, 40 groups of mixed standard solutions of copper, cobalt, and nickel are prepared, and the absorbance coefficient matrix is solved by multiple linear regression method. Then, a correlation coefficient threshold method is proposed to select the wavelength region with high sensitivity for filtering. Finally, the filter end point is determined by the filter variance to obtain the estimated mass concentrations of copper, cobalt, and nickel. The linear detection ranges of mass concentrations of copper, cobalt, and nickel are 0.5-5.0, 0.2-2.0, and 0.3-3.0 mg/L, respectively. The average relative errors of copper, cobalt, and nickel are 2.862%, 2.464%, and 3.781%, respectively, which are all less than 5%. The predicted root mean square errors of copper, cobalt, and nickel are 0.1124, 0.0279, and 0.0663, respectively. The results show that the proposed method is simple and rapid, can filter while scanning, and is easy to analyze on-line.

In this study, the working principle of the chromatic confocal displacement sensor and the conditions of linear axial dispersion were applied for the optimal selection of three kinds of glass materials, namely N-KZFS11, N-SF66, and N-PK52A, which were combined with the theory of aberration to design the initial structure of a linear dispersive objective composed of three single lenses and two double cemented lenses. Then, the Zemax software was used to optimize the initial structure of the dispersive objective and analyze its tolerance. The results indicate that within the wavelength range from 450 nm to 650 nm, the blur spot at each wavelength is much smaller than the Airy spot. The measurement range of the dispersive objective is up to 1.05 mm, the linear determination coefficient R2 between the axial dispersion and wavelength is 0.997, and the theoretical resolution could reach 105 nm.

According to the on-orbit working state and imaging characteristics of cameras for space exploration, the lunar-edge method is used to detect its on-orbit modulation transfer function (MTF), combined with the commonly used test method of MTF. This method uses the high-contrast linear edge image formed by the lunar edge and the deep space background as the test target. The simulation is used to analyze the calculation precision and running speed of various processing methods in each link, forming an optimized process of on-orbit MIT detection based on the lunar-edge method. In the link of edge spread function (ESF) processing, a modified Savitsky-Golay filter combined with double Gaussian fitting method is used to obtain an accurate ESF while effectively suppressing the noise. The simulation and experimental results show that the proposed method has an accuracy of 0.02 for images with a signal-to-noise ratio higher than 30 dB, which can achieve accurate calibration of camera focal plane position and MTF.

Grassberger entropy is improved, and the improved Grassberger entropy is used to compute information gain. The random forest classifier is trained by selecting the optimal split parameters of the split node. The trained random forest classifier predicts whether the proposal windows generated by selective search contain object. For each of training samples and proposal windows, one normalized gradient magnitude, three LUV color channels, and six histograms of oriented gradients are extracted. The algorithm performance is tested on SenseAndAvoid dataset, and the average detection precision of 73.2% is achieved. Results show that the average detection precision is more than 98% in the range of safety envelope. The improved Grassberger entropy computing information gain can promote precision of object detection.

Point cloud target segmentation is the key to perceive targets for a smart car using three-dimensional (3D) LiDAR. Aiming at the problems of poor real-time and low accuracy of the existing in 3D LiDAR point cloud target segmentation algorithms, an approach based on a depth map is proposed in this paper to realize fast and accurate segmentation for point cloud target segmentation. The original data are transformed into a depth map, and the mapping relationship between point cloud data and a depth map is established. After removing the ground point cloud data by using the angle threshold of the LiDAR scanning line, the non-ground point cloud is clustered and segmented by the improved DBSCAN(Density-Based Spatial Clustering of Applications with Noise) algorithm combined with the depth map and the adaptive parameters. Experimental results show that the proposed method has a significant improvement in time efficiency compared with the traditional clustering algorithms. Moreover, the under-segment error rate is decreased while the segmentation accuracy is increased by 10% to 85.02%.

In this study, an accurate absorption model is established by using the wavelength modulation technology based on tunable diode laser absorption spectroscopy. The free spectral range of an etalon is calibrated by the two absorption lines whose transition line centers are known, and the frequency-time response of the laser is obtained using a description model close to the output characteristics of the laser. Along with the hybrid absorption line parameters calibrated in the laboratory and the HITEMP database, an accurate model that can be directly compared with the actual absorption is established for diagnosing the combustion flow field. Herein, H2O is the target molecule, and the transition line centers of the two selected lines are 7185.60 and 6807.83 cm-1. The flow field temperature can be obtained via the peak of the normalized second harmonic signal with background subtracted and verified in a high-temperature flow field generated by a tubular high-temperature furnace. The maximum temperature is 1500 K, and the relative measurement error is less than 3.1%. Further, the accuracy of the absorption model determines the accuracy of the measured flow field parameters. The method used to establish the model can be applied to the complex combustion flow fields for accurately measuring the flow field parameters.

Quantitative analysis of target elements Mg, Ti, Ni, and Cr in standard oil was performed using substrate-assisted laser-induced breakdown spectroscopy. Mg II 279.55 nm, Ti I 334.94 nm, Ni I 352.45 nm, and Cr I 425.44 nm were selected as the spectral lines of the target elements in the quantitative analysis. The effects of sample pretreatment time, average sample oil film thickness, detection delay, and energy of laser pulse on the spectral signal intensity and signal-to-background ratio of Mg, Ti, Ni, and Cr were investigated. Under the optimal experimental conditions, the standard curve calibration model was established using six standard oil samples. The limits of detection of Mg, Ti, Ni, and Cr were 3.10, 8.17, 18.79, and 6.10 μg·g -1, respectively. The mass ratios of Mg, Ti, Ni, and Cr in other five standard oil samples were predicted by the calibration curve, and the relative errors were 7.43%, 8.91%, 13.66%, and 10.40%, respectively.