Herein, we proposed a dynamic target scattering imaging method. First, we measured the optical transmission matrix by using a four-step phase-shifting interferometry method. Then, we performed numerical simulations of tracking and reconstruction for different dynamic targets through the scattering medium based on phase conjugation, Tikhnov regularization, and total variation minimization algorithms. The feasibility of this method was experimentally verified, and the properties of the three algorithms were compared. The results show that the antinoise ability of the total variation minimization algorithm is the best. The proposed method provides a new idea for dynamic target imaging through scattering media in the biomedical field.

As for deep tissues, the field of view of a single correction in the widely used adaptive optics is limited and the refresh rate of a spatial light modulator or a deformable mirror is also limited. Therefore it is difficult for them to satisfy the requirement of large field-of-view (FOV) rapid correction of wavefront distortion and thus that of high-speed imaging. A parallel wavefront correction method is proposed based on the conjugate adaptive optical correction system and the coherent optical adaptive technique. In this method, without increasing the number of refresh times of spatial light modulator, the large FOV of one-time correction can be realized by means of the parallel measurement of wavefront distortion of multiple guide stars, which provides a feasible reference solution for the high-speed and high-resolution imaging of deep tissues. The simulation results show that when 9 guiding stars are used, the effective FOV of a single correction by the proposed method is about 4.7 times than that of the conventional method for a thin scattering medium composed of 5 layers of random phase masks, and 4.6 times than that of the conventional method for 120-μm thick mouse brain tissue. Moreover, the proposed method can further improve the FOV of one-time correction by increasing the number of guide stars while the correction time does not significantly increase, which has broad application prospect in the large FOV imaging of in vivo biological tissues.

This study proposes a novel large mode area fiber structure with bend-resistant and single-mode operation, known as trench-assisted segmented cladding fiber. In this structure, a low refractive index (RI) trench is added to the fiber core and the core is surrounded periodically with high RI fan-segmented claddings. COMSOL software is used to calculate the mode leakage loss and mode area. Numerical analysis indicates that when the indicates bending radius of the fiber is 15 cm, the mode field area of the fiber can achieve 700 μm 2. Meanwhile, the loss ratio between the high-order mode (HOM) and fundamental mode (FM) is >100, which ensures effective single-mode operation. In addition, the fiber performance is stable within the bending orientation from -180° to 180°. Based on the results of this study, the proposed fiber has the potential to play an important role in developing high-power fiber lasers and amplifiers.

Based on cascaded phase modulators (PM), a scheme to generate a optical frequency comb (OFC) with adjustable comb number and comb spacing is proposed and experimentally demonstrated. The sinusoidal radio frequency (RF) signal and its double-frequency signal are used to drive the two cascaded PMs, respectively, simultaneously a small frequency offset is introduced in the second RF signal, and finally a phase-insensitive and high flatness OFC is obtained. The comb number and flatness are regulated by the modulation index of these two cascaded PMs. When the frequency offset is 10-5 times the frequency of the second RF signal, the flatness of this OFC is less than 3 dB. The experimental results show that the comb numbers are 7, 9, and 11, the comb spacing is 5.5 GHz and 7.5 GHz, and the flatness is smaller than 2.4 dB for the generated OFC.

The photosensitivity of a low-loss As2S3 chalcogenide glass fiber core under 532 nm near-bandgap light irradiation is experimentally investigated. The experimental results show that at the beginning of light irradiation, the photo-induced refractive index change of the fiber core first decreases rapidly towards the negative direction, and then recovers and increases gradually towards the positive direction with the extension of irradiation time. As for these two processes, the time duration and the refraction index change value are determined by light irradiation power. As the irradiation power increases to a certain threshold value, the photo-induced refractive index change shows a positive increment in the recovery process, and the refractive index change can be increased to about 3×10-3 with the further increases of irradiation power and exposure time. In addition, the As2S3 fiber Bragg grating is experimentally fabricated and its central wavelength occurs blue shift-recovery-red shift during exposure. At the same time, the experimental results also disclose that the optical stopping phenomenon with a cut-off efficiency of about 55% is observed in the As2S3 fiber under near-bandgap light irradiation.

An error diffusion algorithm based on the angular-spectral diffraction theory is proposed. The complex amplitude hologram of a three-dimensional object is calculated by the layered angular-spectral algorithm. The error diffusion method is used to obtain the phase-only hologram. The clear reconstructed image is reconstructed and the speckle noise of the phase-only holographic reconstructed image for a three-dimensional object is suppressed. The simulation experimental results verify the feasibility and superiority of this algorithm. This proposed algorithm can significantly improve the quality of reconstructed images.

Holographic stereogram printing technology is a widely used holographic technology. In recent years, our project team has proposed a new method to preprocess the perspective images and print the holographic stereograms, called as the effective perspective image segmentation and mosaicking (EPISM) method, in which the holographic printing effect can be achieved via one-step recording beyond the traditional two-step recording, and thus it possesses high research value. In order to predict the printing results of holographic stereograms based on the EPISM method before optical experiments, a numerical algorithm for the reconstruction of holographic stereograms after EPISM is proposed. This algorithm performs a numerical reconstruction of synthetic perspective images processed by the EPISM method and the reproduced images seen at different viewing angles and viewing positions prior to optical printing can be pre-obtained. Through the comparison among the original sampling images, the numerically reconstructed images and the experimentally reproduced images, it is found that the proposed algorithm can be used to simulate the optical experimental results of holographic stereogram printing with the EPISM method.

Aiming at the problems of large cross-talk noise and small multiplexing capacity in the optical multi-image encryption system, an optical multi-image encryption method based on joint power spectral (JPS) partition multiplexing is proposed. First, the phase retrieval algorithm is utilized for the optimal design of phase masks and the single-channel JPS area is thus compressed. Then, the corresponding linear phases are superimposed on the optimized phase masks and so that the each-channel JPS is shifted differently in its spectral plane. After the window filtering operation, the superposition without crosstalk is realized. In addition, the key content planning is carried out in the form of “key phase kernel plus deflection angle packet”. While the security of encryption method and the large enough key space are ensured, the key data needed to be transferred is compressed. The numerical simulation results show that, when nine gray-scale images are encrypted, the correlation coefficients between the decrypted images and the original images are over 0.94 and the decryption effect is obvious. When the evaluation threshold of decryption quality is set as 0.95, the maximum compression efficiency factors of gray-scale and binary images reach 12 and 32, respectively. The cipher-text compression ability is remarkable. Finally, an optical experiment system is built and the feasibility of this method is further verified.

A 2294 nm Raman laser using ZnWO4 crystal as Raman crystal is reported. The Tm∶YLF crystal is used to generate the fundamental laser at 1899 nm, and the intracavity pumping on ZnWO4 crystal is adopted to obtain the first-order Stokes laser at wavelength of 2294 nm. The maximum power, shortest pulse width, and corresponding peak power are 173 mW, 2.280 ns, and 25.292 kW, respectively. The feasibility of ZnWO4 as infrared Raman crystal is verified experimentally.

Based on the principle of distance measurement of laser frequency modulated continuous wave (FMCW), a distance measurement system of dual optical path FMCW is set up, which replaces the traditional linear frequency modulation with sinusoid frequency modulation so as to improve the sweep frequency. The principle of distance measurement of FMCW under sinusoid frequency modulation is also studied, the resampling formulas of sine sweep is derived, and the signal synthesis method to increase the sweep bandwidth and the quadrature modulation method to eliminate the stitching error are put forward. The experimental result shows that after the quadrature modulation method is used to splice the equal-light frequency resampling correction signal, the frequency resolution reaches to 127 μm, very close to the theoretical resolution. It is no more than 203 μm of the error and less than 194 μm of the standard deviation compared with the reference interferometer within the range between 3.3 and 4 meters.

A 348.9 nm intra-cavity frequency-doubling ultraviolet laser in blue laser diode pumped Pr∶YLF crystal is designed, in which a Z-folded cavity structure is adopted. A 444 nm blue laser diode with pump power of 1.4 W and a 469 nm blue laser diode with pump power of 1.5 W obtained are combined by a 45° combiner film as a pump laser for the Pr∶YLF crystal which has a length of 5 mm and a doping concentration (mass fraction) of 0.5%. In addition, the type I phase-matched LBO crystal is chosen for frequency-doubling. By optimizing the resonator mirror coating and structural design, we achieve a continuous ultraviolet laser output with a maximum power of 132.2 mW, a central wavelength of 348.9 nm, and an optical-to-optical conversion efficiency of 4.5% when pump power is the maximum.

A novel high-power direct-liquid-cooled thin-disk solid-state laser is designed, in which the distributed gain system is composed of tens or hundreds transmission disks by intensive stacking. A special kind of laser cooling liquid flows in the planar micro-channels between gain media, and thus the direct cooling of disks is realized. The thermal stress, the reflective surface deformation and so on caused by the soldering between gain media and the heat-sink in the traditional high power solid-state laser are successfully avoided. In addition, the parameters such as intra-cavity loss and aberration are optimized. The key factors influencing the optical-to-optical conversion efficiency are analyzed, and the methods for controlling laser beam quality are introduced according to the thermal aberration characteristics. A gain module is composed of 20 disks by intensive stacking with a special angle. With these gain modules, a quasi-continuous-wave (QCW) polarized laser with an output power of larger than 9 kW is obtained in both stable and unstable cavities. Moreover, the whole volume of this laser source in laboratory is smaller than 0.4 m3.

A novel technique, for the fabrication of large size Yb3+ doped silica glass rod with a diameter of 3 mm and a length of 270 mm and thus a large-core double-clad fiber with a diameter of 80 μm and an outer cladding layer diameter of 400 μm by the glass phase-separation technology, is reported. The refractive index profile, Yb 3+ absorption spectrum and background loss are experimentally tested, and the laser performances are also demonstrated. The results show that the refractive index distributes uniformly within the active fiber core of this fiber and the the numerical aperture is about 0.065. The doping concentration of Yb3+ (mass fraction) is 1.22%, the absorption coefficient at 976 nm is 6.5 dB/m, and the background loss at 793 nm is 0.03 dB/m. Based on the power amplifier structure of the master oscillator, the lasing output at 1080 nm is realized for this fiber when pumped by a diode laser at 976 nm, where the fiber length is 2.5 m, the slope efficiency is 78%, and the maximum laser output power is 300 W. The glass phase-separation technique provides a novel technique route to fabricate the active silica glass core rods with large size and high uniformity, which has a high potential in the fabrication of heavily doped extra-large-core fibers and active fibers with a complex core structure.

The hydrophilic surfaces of PA2200 three-dimensional (3D) printing parts are prepared quickly through 248 nm KrF excimer laser irradiation, whose contact angles decrease from 121° to 70° and phase structures do not change after irradiation. With the calibration tools of X-ray diffractometer, Raman spectroscopy, scanning electron microscope, X-ray photoelectron spectroscopy and so on, the surface morphologies and microstructures of printing parts, number and types of polar functional groups are analyzed. The Cassie-Baxter model is also studied. The experimental results show that KrF excimer laser irradiation can not only make PA2200 3D printing part surfaces smooth, but also simultaneously generate C=O double hydrophilic groups, and thus the surface wettability of PA2200 3D printing parts are improved and controlled.

The observability analysis of the initial alignment problem of the vehicle-based-laser strapdown inertial navigation system (SINS) aided by odometer is carried out. First, the system equation is established by considering the system error items including the odometer scale factor error, inertial measurement unit zero bias, SINS misalignment error angle, etc. Then, starting from system equation, the system observability problem is transformed to the determination of whether there is a unique solution to the state variables of the system. The observability analysis of the system state is conducted by the global observability analysis method, and requirements for maneuvering is given to ensure that the system is observable. Finally, the initial alignment algorithm method and on-track incentive mode are designed according to the results of observable analysis. The simulation of odometer aided laser SINS in-motion initial alignment is conducted by extended Kalman filter, and the simulation results verify the validity of the theoretical analysis.

In order to obtain a dual frequency pulsed laser with high peak power, good coherence and large frequency difference, a diode-pumped passively Q-switched two-cavity dual-frequency Nd∶YAG laser is designed, which adopts a structure composed of two T-shaped standing-wave cavities sharing a common gain medium. An intracavity polarizing beam-splitter and a half wave-plate are combined to form a birefringent filter acting as the laser longitudinal mode selector, a piece of Cr 4+∶YAG crystal is chosen as a passive Q-switch, and thus the p-component and s-component of this 1064 nm laser are forced to oscillate simultaneously in a single longitudinal mode within the linear and right angle cavities, respectively. The output of orthogonally and linearly polarized dual-frequency pulsed laser at 1064 nm is realized. In addition, the rate equation group of a passively Q-switched two-cavity Nd∶YAG laser is established and the output characteristics of two-cavity pulsed laser are analyzed theoretically. Moreover, both the oscillation and output characteristics of this two-cavity dual-frequency pulsed laser are investigated experimentally. The experimental results show that, when the pump power of laser diode is 2.7 W, as for the p-polarization single-frequency pulsed laser output from the linear cavity, the repetition frequency, pulse width and peak power are 5.8 kHz, 42 ns and 126.4 W, respectively. In contrast, as for the s-polarization single-frequency pulsed laser output from the right angle cavity, those are 5.8 kHz, 40 ns and 133.6 W, respectively. The frequency-difference of this dual-frequency pulsed laser is approximately 10 GHz. This dual-frequency pulsed solid-state laser has a wide application prospect in the fields of laser interferometry, lidar coherent detection, and so on.

In this paper, a composite scanning method combining high energy density contour carbonization with high energy density contour bonding is proposed, and the proposed method and ordinary scanning method are used to implement sintering experiment. The tensile fracture, tensile strength, forming accuracy and deformation are studied. The results show that the composite scanning method can effectively remove the secondary sinter, improve the precision and initial sintering strength of the sinter, and reduce the deformation in the process of post-treatment heating strengthening. At lase, sintered parts with high precision and high performance are obtained.

Laser deposition technology and weld additive manufacturing technology are used to repair the laser deposition manufactured TC4 titanium alloy with defects, and then different heat treatments are carried out. Microstructures and mechanical properties of two kinds of repaired specimens are analyzed before and after heat treatments. The results show that there is dense metallurgical bonding between repaired zone and the substrate, and there is no obvious heat affected zone. In the laser repaired zone, prior columnar beta grain extends from the substrate to the top of repaired zone and the whole structure is almost same. In the weld repaired zone, there are huge equiaxed beta grains, the transgranular alpha phases are longer than alpha phases in the substrate. The strength and plasticity of laser repaired specimen are higher than those of TC4 forging standard. The strength of the weld repaired specimen is similar to that of the laser repaired specimen, but the reduction of area of the former is lower than that of the latter. The annealing heat treatment has little effects on microstructure and mechanical. The solution and aging treatment can coarse the alpha phase obviously and promote the plastic sharply of the specimen, and it has slight effect on strength, so the specimen can obtain good strength and plasticity. The two kinds of repaired specimen in heat treatment state have different tensile fracture mechanisms. The fracture surface of laser repaired specimen is covered with big and deep dimples, and the fracture shows ductile characteristics. The weld repaired specimen exhibits quasi-cleavage fracture with slight necking fracture, and shallow and flat dimples.

The elastic-plastic deformation evolution, stress distribution and tensile fracture behavior during the tensile process of laser non-penetrating lap welded joints of the 301L stainless steel plates with different thicknesses are studied by the numerical analysis methods. The finite element model of laser welded joints is established and the simulated tensile curves of welded joints are in a relatively good agreement with the experimental results. With the increase of tensile load, the plastic deformation of welded specimens extends from the base metal near the weld interface to both of the weld interface and the base metal. In contrast, with the increase of the ratio of weld width to plate thickness, the plastic strain zone of welded specimens extends gradually from the vicinity of weld interface to the base metal. The tensile fracture displacement increases with the increase of plastic deformation zone. Moreover, when the ratio of weld width to plate thickness is higher than 0.75 and the fracture displacement of welded specimens is larger than 5 mm, the fracture strength is relatively high and the shear fracture strength of laser weld is about 794 MPa.

The effect of ultrasonic vibration on the microstructures and mechanical properties of the as-deposited and the solution-aging treated forming parts is investigated during the laser cladding deposition of Ti6Al4V alloys. The research results show that, the ultrasonic vibration during deposition can reduce the surface roughness and residual stress of forming parts, which makes the β columnar grains refined, and the strength and elongation of the forming part increase slightly. As for the forming parts after solution-aging treatment, a mixed structure composed of equiaxed α phase, basket-shaped flaky α phase and converted β phase is formed. However, the grains are still small, the elongation is relatively high, the plasticity increases significantly, and the strength decreases little. The comprehensive mechanical properties overpass the forged part standard.

The influences of the He-Ar mixed shielding gas on the droplet transition behaviors and the weld porosity defects are investigated in the laser-MIG hybrid welding of aluminum alloys. According to the dynamic characteristics of the keyholes in the welding process, the reason for the suppression of porosity defects is analyzed. The results show that, the He-Ar mixed shielding gas can enhance the stability of the keyholes and reduce the weld porosity effectively. When the volume fraction of He in the He-Ar mixed shielding gas is 50%, the droplet transition mode changes from “one drop per pulse” to “short-circuit” transition and the weld porosity is about 1.0%, reduced by 80% if compared with that for the pure argon shielding gas. The further increase of the He content is not helpful to the suppression of the porosity. When the shielding gas is the pure He gas, the big spatter and the bad welding seam occur.

The structural characteristics and the key influencing factors of self-assembled nanogratings within GeO2 glass are investigated by using an ultrafast laser system with tunable repetition rate and pulse duration. The formation threshold of nanogratings in GeO2 glass is experimentally determined, which is dependent on material bandgap and laser pulse duration. In addition, based on the optimization of process parameters and the use of birefringence of nanogratings, the micro-optical components are fabricated within GeO2 glass and their functions are demonstrated. Moreover, the influence of repetition rate of femtosecond laser on the formation and structural properties of nanogratings is also analyzed. It is found that the birefringence strength of nanograting in GeO2 glass has an anomalous polarization dependence, and the corresponding origin is speculated.

The 3 mm thick high-strength steels are taken as test materials and the technique of fiber laser-arc hybrid welding assisted by metal inert gas is chosen. The effects of laser power and arc voltage at welding speed of 5 m·min-1 on weld appearances are investigated. The comparison with those weld appearances generated in low speed welding of thick plates is conducted. The research results show that the increases of laser power and arc voltage can ensure the improvement of welding stability and the obtainment of good weld formation. There exist different shallow and deep Y-type weld appearances at different heat source positions. The high-speed photography indicates that the droplet size is relatively large in the laser leading mode. In addition, it is prone to vaporization and explosion in the transfer process. Thus, the impact on molten pool are relatively strong. In contrast, in the arc leading mode, the keyholes are stable. The liquid metal flows down along the keyhole walls and thus the bottom area of molten pool increases. As for the low speed welding of thick plates, the weld appearances are not consistent with those for high speed welding of thin plates due to the differences in welding line energy and surface tension of workpieces.

The copper-containing stainless steels formed by adding a suitable amount of supersaturated copper ions in medical stainless steels have a nice biological function. The laser alloying method instead of the traditional heat treatment alloying method is adopted to form a Cu-Co alloyed layer on the stainless steel surface in order to explore the possibility of more than one alloying element simultaneously existing in the alloyed layer. Scanning electron microscopy and X-ray diffractometer are used to analyze the structural characteristics of the microstructures of the alloyed layer. The antibacterial function of this alloyed layer is verified via the E. coli experiment and the brine corrosion test is used to analyze the corrosion resistance property of this alloyed layer. The results show that the fabricated alloy has a stable surface metallography and good antibacterial ability and corrosion resistance when the laser power is 600 W, the scanning speed is 400 mm/s, the preset thickness is 500 μm, the overlap ratio is 35%, and the mass ratio of Cu to Co in the mixed powder is 1∶1. In addition, the hardness of the alloyed layer is higher by 20% than that of the base. It is proved that the laser alloying method is able to replace the traditional alloying method for the preparation of bio-functionalized medical metals.

The as-deposited and solution-treated Inconel 718 superalloy samples are fabricated by laser solid forming, and the influences of aging temperature and aging time on the size, morphology, and volume fraction of δ phases are investigated. The results show that as for the aging treatment of as-deposited samples, the δ phases precipitate around the interdendritic Laves phases with a short needle pattern, and there are no δ phases throughout grains with a long needle pattern. In contrast, as for a long time δ aging treatment of solution-treated samples, there occur δ phases throughout grains with a long needle pattern at 890 ℃, while for the aging treatment at 950 ℃, only the short-bar-like δ phases precipitate at grain boundaries. In addition, the incubation time of δ phase precipitation elongates, while the volume fraction of δ phases formed after aging treatment decreases. The apparent activation energies of δ phase precipitation for the as-deposited and solution-treated samples are 1917 kJ·mol -1 and 1867 kJ·mol-1, respectively.

The selective laser melting (SLM) technology is used to process the TiB2/S136 composites and the effect of laser energy density η on the densities, microstructures and mechanical properties of SLM-processed specimens is investigated. X-ray diffraction instrument, field emission scanning electron microscopy and transmission electron microscopy are used to study the phase compositions, surface morphologies and microstructures of specimens. The results show that, when η is low, the powders are not fully molten and thus a large amount of residual pores are formed. However, when η is too high, the micro-cracks are formed in the specimens because of thermal stress. When η is 66.7 J/mm3, the specimens have less surface defects, their densities are up to 97.3%, and there exist fine and uniformly-distributed equiaxed grains. As for these specimens, the average micro-hardness is up to 742.4 HV0.1, and the average friction coefficient and wear rate are 0.5593 and 0.272×10-4 mm3·N-1·m-1, respectively, indicating an excellent abrasion resistance performance. The tensile strength is 1051.3 MPa and the elongation is 5.84%, indicating a relatively good plasticity. Above all, the optimal η for the SLM-processed TiB2/S136 composites is 66.7 J/mm 3, and if η is too high or too low, the densities and mechanical properties of TiB2/S136 composites would be seriously affected. This study provides a useful theoretical basis and a process guidance for SLM-processed high-performance die steels.

With the same process parameters and the heat treatment/hot isostatic pressure technique, two batches of Hastelloy-X alloy specimens with different powder compositions are processed by selective laser melting, in which batch A is high in carbon and manganese contents and while batch B is high in silicon content. The tensile properties at room and high temperatures are tested. The microstructural characteristics and tensile fractures at room temperature are investigated. The results show that the transverse structural morphologies of forming parts from two kinds of materials are similar, but the grain morphologies and the intragranular carbides are quite different in the longitudinal structures. The microstructures of batch A materials are equiaxed grains and the intragranular carbides precipitate more, and while the microstructures of batch B materials are columnar crystals along the longitudinal direction. The tensile properties of batch A specimens at room and high temperatures reach the standard of bar forgings, and while those of batch B specimens exhibit much a more obvious anisotropy in the transverse and longitudinal directions. The longitudinal tensile properties of batch B materials are characterized by low strength and high plasticity, and are subject to the effects of carbon and silicon elements. There exist an obvious plastic deformation for the fractures of the two batches of materials at room temperature, which are cup-like intergranular dimple.

This study aims to obtain a Fe-based alloy coating with high strength, high toughness, and good corrosion resistance. Therefore, a novel low-carbon and low-alloy martensite/ferrite dual-phase stainless steel (M/Fss) powder with trace addition of boron is cladded on Q235 steel by the laser cladding technique. The research results reveal that the surface of the laser cladding coating has metallic luster, and there are no inclusions and pores in the coating. The coating is constituted of martensite, ferrite, and boron carbides M(B,C) with uniform and discontinuous distribution along the dendrite (M represents Fe, Cr, etc.). A few M23(B,C)6 particles precipitated within the dendrite. The cladding layer exhibits excellent mechanical properties, including average hardness of 431.9 HV, tensile strength of 1352 MPa, and ductility of 12.3%. Its superior corrosion resistance is better than that of 1Cr13 martensite stainless steel. This new type of M/Fss coating can be widely used for surface modification or remanufacturing of Fe-based materials in working environments requiring mechanical and corrosion resistances.

The collinear autocorrelation measurement method is adopted based on the principle of Michelson interferometer, in which the intensity autocorrelation and the two-dimensional electric field autocorrelation are simultaneously measured. A Gaussian function is used to fit the intensity autocorrelation data and the full width at half maximum of the measured laser pulse in time domain is about 96.2 fs. From the interference fringe distribution of two-dimensional electric field autocorrelation obtained by the CMOS imaging sensor, the tilt information of pulsed light spot wavefront phase can be obtained. Moreover, the Fourier series analysis tool is adopted to fit the interference fringes shifting with time delay. Within the restriction of delay stage accuracy, a weak component at 1090 nm is disclosed in the pulsed laser power spectrum.

To meet the requirements of high-precision, long-distance, and highly dynamic measurements, this article proposes a scheme for absolute distance measurement based on optical frequency combs. Cascaded phase modulators and intensity modulators are used to electro-optically generate a flat-top optical frequency comb. The system offers advantages, including direct traceability, cost efficiency, and reproducibility. Furthermore, a mathematical model is formulated and used to assess the quality of the optical frequency comb generated for use in a multi-heterodyne ranging system. The system is simpler than traditional multi-wavelength measurement systems, and realizes absolute distance measurements by extracting phase information from the synthesized wavelengths of the optical comb. The mathematical model presented herein is used to analyze the noise and uncertainty involved in the system.

Single-photon counting is a vital technique in the field of quantum optics. It is widely used in two-photon coincidence detection and correlation control. In this study, we employ a single-photon-counting card and a router to construct a three-photon coincidence system by using two-photon coincidence and time-division multiplexing. The software control is based on LabVIEW program. The system performs coincidence detection for two or three photons, provides real-time displays, and stores the results. We obtain good results when using the system to detect three beams of light generated via the six-wave mixing process. The system can be applied to classical light sources in the field of quantum communication and to other non-classical light sources with time-frequency quantum correlations produced via nonlinear processes.

The traditional line laser scanning technology is based on machine vision, the corresponding algorithm is complex, the amount of calculation is large, and the matching efficiency is not high. In contrast, the point laser scanning technology is based on laser triangulation, the corresponding algorithm is concise, but the measurement speed is low and the reconstructed point cloud is sparse. To solve these problems, the laser-triangulation-based line laser scanning technology is proposed. The camera pinhole model and the relative position between camera and line laser are used for the establishment of an object-image relationship equation. The 3D coordinates of the scene are solved and the whole reconstruction algorithm is simplified. The calibration algorithm based on the least square method is adopted for the calibration of parameters such as the relative position between camera and line laser and the rotation center deviation of the system. Simultaneously, the theoretical precision of the system is analyzed, and the reliability and accuracy are tested by the experiments of scene reconstruction and accuracy evaluation. The experimental results show that the system possesses a high efficiency and a good precision. The error of the system is less than 2.6 mm and the precision is higher than 0.25% in the measurement range of 1000-1700 mm, which satisfies the requirements for a general scene reconstruction.

The polarization modulation ranging method uses the polarization-modulated light to transmit the measured distance phase information and the polarization response of the retroreflector as its cooperative target affects the system performance. In order to study this response, a complex signal description method of polarization-modulated light is presented. In the global coordinate system, the complex signal representation of reflected polarization-modulated light is obtained with the polarization transfer parameters. Under normal incidence, the polarization responses of uncoated solid (BK7) and hollow (Au film) retroreflectors to polarization-modulated light are analyzed, the polarization-preservation performances of three kinds of common metal coatings to the polarization-modulated light are compared, and the influence of attitude angle of the retroreflector on the polarization-preservation properties is analyzed. The calculation results show that the polarization-preservation performance of Ag film is better than those of Au film and Al film. In the global coordinate system, the amplitude ratio of polarization-modulated light is significantly affected by the deflection angle, and the phase delay is significantly affected by the pitching angle. These results can provide a theoretical guidance for the optimal design of a polarization modulation ranging system.

A highly sensitive noncryogenic rubidium magnetometer based on spin exchange relaxation free (SERF) is designed, whose sensitivity at 15 Hz is 6 fT/Hz. With this SERF magnetometer, the difference in the human brain magnetic field induced by eye opening and closing is recorded inside the shielded barrel. This SERF magnetometer is operated in double light mode with a pump-probe arrangement. Compared with single beam arrangement, this SERF magnetometer can achieve a higher sensitivity and does not require any extra magnetic modulation. Thus, the complexity of the acquisition system is reduced and the lock-in amplifier is not needed any more. Moreover, this kind of configuration is easily adapted to miniaturize the sensor array for the future whole-head magnetoencephalography equipment.

We design a tunable parity-time (PT) symmetric structure, in which magnetic microcavity is inserted. By transmission spectrum calculated by the transfer matrix method,we research the modulation effects of microcavity resonance under the applied magnetic field on PT symmetric structure. An enhanced non-reciprocal band-edge mode is obtained, which can be modulated by directions and sizes of incident angles. The modulation transforms the band-edge modes between the left and right edges of the band. Results reveal that the increase of the magnetic field causes the edge mode to move to high frequencies, and the change of magnetic field direction also causes the transformation of the band-edge modes between the left and right band edges.

The entanglement dynamic properties between two mechanical modes and nitrogen-vacancy(NV) centers in the system of second-order-magnetic-gradient induced nanodiamond NV center coupled to mechanical resonator are investigated. The influences of coherence angle, decay rate of mechanical modes and spontaneous decay rate of NV centers on entanglement are analyzed. The research results show that the maximum entangled state between mechanical modes and NV centers can be produced by the suitable choice of system parameters. In addition, the coherence angle has an important influence on the entanglement dynamics, and the coherence angle can be used to effectively adjust the resistance ability to entanglement attenuation when dissipation is considered. Moreover, compared to the spontaneous decay of NV centers, that of mechanical modes can make the system entanglement decay and disappear more quickly.

In order to meet the requirements of high accuracy and rapid measurement of seawater temperature, we propose a temperature sensing scheme based on optical fiber Farby-Perot (F-P) sensor. The sensor is composed of silicon chip and fiber tail, and the silicon chip acts as the F-P cavity of the optical fiber F-P sensor. Temperature sensing is realized based on the thermal optical effect and thermal expansion effect of silicon. The demodulation algorithm of optical fiber F-P sensor is the fast cross correlation demodulation algorithm based on dichotomy, which can realize high precision and fast demodulation. The experimental results of optical fiber F-P temperature sensor show that the sensor can reach the precision of 0.15 ℃ and distinguish the temperature change at 0.001 ℃, and the temperature response time can reach 128 ms. The sensor is expected to be applied in the field of disposable measurement.

The system indexes of a space-based synthetic aperture LiDAR (SAL) system used for ground imaging are analyzed. A membrane-based diffractive optical system with a 10 m aperture is chosen to satisfy the requirement of power aperture product. Based on the synthetic aperture radar phased array antenna model, the device parameters and beam patterns in the diffractive optical system are analyzed. Aiming at the aperture transition problem existing in the diffractive optical system with a large aperture, a signal compensation and focusing method with a high range resolution is proposed based on digital signal processing. The research results show that based on this space-based SAL with a 10 m diffractive aperture, the image tracking with a high resolution and a high data rate to the specific long-distance targets is possible. Moreover, the realization of this technique can be feasible.

A fiber sensing system based on laser intracavity modulation with a low detection limit for refractive index sensing is proposed. A kind of all-fiber multimode interference structure based on single-mode-no-core-single-mode fiber is inserted in a fiber laser ring cavity as a loss-modulation device. The fiber laser intracavity modulation technology is used to obtain high-sensitivity sensing signal with high signal-to-noise ratio and narrow full width at half maximum. Depend on these characteristics, the low detection limit of the sensing system can reach up to 7.3×10-7 RIU. The sensing system with output stability and low temperature cross-sensitivity has a great potential in high-accuracy biochemical sensing and marine environmental monitoring.

Raman spectroscopy has advantages of rapid response, non-contact, less detection restrictions and high selectivity, which make it widely used in many fields of production and life. However, the actual measured Raman spectra contain varying degrees of baseline drift, which seriously affects the validity and accuracy of spectral analysis. In order to solve the issues that the final baseline is underestimated in the no peak region and the height of peaks might be overestimated in existing baseline correction methods, we propose a novel correction algorithm, which is named locally symmetric reweighted penalized least squares (LSRPLS). Based on asymmetrical least squares, the method works by iteratively adjusting weights of the difference between the fitted baseline and the original signal, introducing the idea of local symmetric weighting by a softsign function. The algorithm is applied to the simulated and the actual Raman spectra to correct the baseline drifting. The results show that the LSRPLS algorithm can not only correct different types of baselines, but also has good advantages in accuracy and stability compared with the existing baseline correction methods. In addition, after baseline correction, the distribution of samples in principal component spaces becomes concentrated, and the classification accuracy of the model is significantly improved. This indicates that the LSRPLS algorithm can retain the spectral information effectively while removing the baseline, which provides a basis for further analysis of Raman spectroscopy.

The content ratios of four elements in Cu(In, Ga)Se2 (CIGS) thin film have great impact on performance of the thin film. CIGS thin films are deposited by magnetron sputtering at different work pressures, and the laser induced breakdown spectroscopy is used to quantitatively analyze the ratio of Ga content to In and Ga contents, as well as the ratio of Cu content and In and Ga contents. The spectral intensities of elements in CIGS deposited at different working pressures are analyzed, the results show that the intensity ratio of Ga spectral line to In and Ga spectral lines is corresponding to optical band gap, and they increase initially and then reduce with the increase of the work pressure, and the maximum optical band gaps are achieved at the pressure of 2.0 Pa, the intensity ratio of Cu spectral line to In and Ga spectral lines is nearly invariable corresponding to the value obtained from energy spectroscopy. The rapid detection of element content proportion in thin film can be realized by LIBS technology, the relative ratios of different intensities of spectral lines can indirectly reflect the element content ratios in thin film, which indicates the potential of LIBS technology in thin film analysis, providing method and technical support for optimizing working parameters in CIGS preparation by magnetron sputtering.