This study describes the spatial light to single-mode fiber coupling principle, designs a nutation coupling algorithm based on a combination of fast mirror and fiber photodetector, and simulates the dynamic tracking process of the fiber end surface using LabVIEW. According to the simulation, the coupling experiments of laser nutation system are conducted, resulting in a coupling efficiency of 59.63% under static conditions and a video transmission demonstration with 1.65-GHz code rate. Further, the validity and feasibility of the nutation coupling algorithm are verified. Based on the experimental and simulation results, the study analyzes the influences of the nutation parameters, including the nutation radius, convergence step length, and number of nutation sampling points, on the coupling performance. The results denote that when the nutation radius increases from 0.1 μm to 2.5 μm, the coupling efficiency and stability decrease, whereas the coupling rate does not exhibit a significant change. However, when the nutation radius is considerably small, the convergence angle recognition error will increase, whereas the coupling speed will decrease. When the convergence step increases from 0.1 μm to 2.5 μm, the coupling efficiency and coupling stability decrease,and the coupling rate increases. When the number of nutation sampling points is reduced from 100 to 5, the coupling efficiency and stability have no obvious change. However, due to too few sampling points, the convergence angle resolution decreases and the coupling rate decreases significantly.

Because the intersatellite optical communication system is unable to perform optical relay amplification, optical receivers with high bit rate and high communication sensitivity are desirable. In this study, we first theoretically analyze a high-sensitivity homodyne coherent receiver when an erbium-doped optical fiber amplifier (EDFA) is used as the optical preamplifier. A homodyne coherent receiver based on EDFA is developed, and the performance of BPSK communication system is experimentally analyzed at a communication rate of 8-10 Gbit/s. Experimental results show that the coherent receiver achieves a sensitivity of -48 dBm when the uncoded BER is 10 -3 for the 10 Gbit/s BPSK signal. The receiver performance shows only 7 dB penalty compared with quantum noise limit; this value is better than the published test results for the 10 Gbit/s homodyne coherent communication system.

To fabricate a high-sensitivity fiber magnetic field sensing probe based on a Fabry- Pérot interferometer, an arc magnetic polymer thin film was integrated on the end face of a single-mode fiber using the UV curing method. Strip magnet was used as the field source to modulate the cavity length and refractive index of the interferometer. By monitoring the wavelength position of the interference peak, the magnetic field intensity was detected. The magnets were placed vertical and parallel to the sensing probe, and the corresponding sensitivities of the sensing structures were 46.77 pm·mT -1 and 56.37 pm·mT -1. The sensor has high sensitivity, good stability, and wide application prospects in the various fields, including biological medicine and information technology. Further, the sensor is inexpensive and can be conveniently manufactured.

We propose an improved cascade all-optical quantizing scheme for the resolution enhancement of all-optical analog-to-digital converter. Employing an additional intensity-modulated label channel, remarkable quantization resolution over 8 bit is feasible for an ultra-wideband signal. Simulation results show that a 20 GHz radio frequency signal is digitalized using the proposed scheme with the spur-free dynamic range of 53.76 dBc and effective-number-of-bits of 8.18 bit.

A two-stage action-candidate regional proposal network is designed herein for a temporal action detection task. The first stage applies a modified watershed algorithm to an one-dimensional temporal signal to form candidate regions with different lengths by immersion clustering, which obtains a rough localization of action temporal boundary. Then, a temporal pyramid structural method is introduced to model the structure of action instances and their contextual information, generating an enhanced global feature. The second stage performs a temporal-coordinate regression algorithm to local the action boundary, and simultaneously a classifier for the action and boundary is added to filter the candidate regions of background for obtaining a more accurate temporal boundary. Furthermore, an unit-level feature extracted by a three-dimensional convolution neural network (C3D) is used to train the entire two-stage proposal algorithm, which contains both spatial and temporal information and considerably improves training efficiency while improving the accuracy of the algorithm. Experiments on two large-scale benchmark datasets, Thumos 14 and ActivityNet, show that the proposed approach achieves the optimal average recall rate over other state-of-the-art methods, indicating that this method can efficiently improve the precision of an action localization task.

In this study, we propose a straight-line-segment feature-extraction method for the building-fa ade point-cloud data based on slicing to improve the existing method of detecting and extracting the straight-line-segment features from the building-fa ade point-cloud data, which exhibits problems of missed detection and less-than-optimal accuracy. Further, the point cloud is sliced along the three coordinate axes after adjusting the point-cloud attitude of the building to ensure that its orientation is consistent with the Y-coordinate axis. Then, the feature points on each slice are extracted, and straight-line-segment clustering is applied to the extracted feature points based on the cylinder growth method. Finally, the straight-line-segment fitting of the feature points is performed using the 1-norm minimum residual algorithm, and the endpoints of the straight line segment are adjusted and refined. Subsequently, we validate the proposed method by applying it to several sets of experimental data; the experimental results exhibit improved accuracy, precision, and recall. The extraction accuracy of the straight line segment is half the average point spacing in the point cloud. The precision of the proposed method for extracting straight line segments is increased by 2.4% on average than that of the plane segmentation and image detection methods, whereas the recall is increased by 48.1% on average. Thus, our proposed method can accurately and effectively extract straight line segments from the building-facade point-cloud data.

The effective detection of high repetition rate interference lasers depends on the accurate performance of laser seekers. Therefore, we use computational analysis to investigate the laser-seeker detection performance and false-alarm probability. By applying this method, we reach the conclusions that when the threshold-to-noise ratio TNR=3.5, the approximate false-alarm probability Pf=0.02%; when TNR=3.5 and the power density of the detected signal at the seeker entrance is 1.9 times the seeker-detector threshold, the approximate detection probability Pp=99.92%. Considering such detection probability, we study the high repetition rate interference laser to obtain the relationship among the laser-seeker detection probability Pp,parameters of the high-frequency interference laser (average power P1, pulse-transmission frequency f, and pulse width τ), laser-seeker parameters (detector threshold Pth and threshold-to-noise ratio TNR),and action distance R. During this process, we use MATLAB for simulation analysis in combination with the application background.

The separated final optics assembly (FOA) with high power has too many optical elements and complicated ghost distribution,which cause difficulty in ghost analysis of FOA. By using the Zemax software and Ghost software designed by ourselves, we analyze the ghost distribution of the FOA, establish the model to analyze the effects of the angle between the vacuum window and debris shield and the distance from the focusing lens to vacuum window or debris shield on the ghost distribution, use the model to analyze two ghost distribution schemes for the separated FOA, contrast the two designs, and get the final ghost distribution of the separated FOA.

To improve the signal-to-noise ratio of an alcohol vapor detection system, the technical parameters of a dual-pass narrow-band filter are determined according to the Beer-Lambert's law. The narrow-band filter is designed via double-sided splitting on a Si substrate according to technical parameters to establish the refractive index gradient model, realizing accurate control of films. The vacuum chamber in-situ annealing method is used to increase the density and reduce the stress of the film layer, thereby improving its adhesion and stabilizing its spectral properties. Of the prepared film layers, over 90% can satisfy transmittance at wavelengths of (1392±10) nm and 1530-1570 nm; less than 1% can satisfy 400-1350-nm and 1600-1800-nm band transmittances; the transmittance is less than 30% in the 1410-1515-nm band.

In this study, we design a high-power compact solid-state picosecond pulse laser amplifier. We design a conducting-cooled end-pumped slab laser amplifier for which the gain medium is Nd∶YAG. We achieve the four-pass amplification of the picosecond pulsed laser through the slab multi-angle magnification technology. The influences of the selection of cutting angles of slat end face and laser incident angles on the filling factor and laser power amplification are analyzed. The output power of a mode-locked laser with 9.6-ps pulse duration and 100-kHz repetition rate respectively, is amplified up to 103 W; the single-pulse energy is 1.03 mJ.

Since the existing telescope pointing error correction model cannot satisfy the needs of laser ranging systems for accurately detecting space debris, a back propagation neural network model optimized by genetic and Levenberg-Marquardt algorithms is proposed for correcting the telescope pointing error. A total of 102 stars are observed in the station's hemispherical sky area, which are divided into zones covering equal azimuth and altitude angle intervals. These observation data are used for modeling. Additionally, 12 stars are observed the following day to evaluate the model's accuracy, and the results show that its accuracies in terms of azimuth and pitch are 1.94″ and 1.12″, respectively. Finally, the proposed model is used in experiments to detect space debris and cooperative space targets. Results show that, when we use the laser ranging technique, the telescope's orientation accuracies in terms of azimuth and pitch for space debris are 1.89″ and 1.21″ respectively, and that for cooperative space targets are 2.06″ and 1.46″ respectively, showing a significant improvement over the traditional model. These results are also significant from the viewpoint of improving the detection success rate of space debris.

To produce a high-performance microwave frequency comb (MFC), a tunable MFC generating scheme using optical comb heterodyning is proposed based on a cascaded Mach-Zehnder modulator (MZM) optical loop system. Continuous light injected through the coupler into the cascade MZM optical loop for modulation can generate an optical frequency comb (OFC), which beats in the photoelectric detector to produce MFC. A theoretical model is created to simulate the system. The influences of the light source power, light source line width, radio frequency driving signal (RF) frequency, and other parameters on the final MFC performance are studied with the optical communication system design software Optisystem. Results show that the output MFC generated by properly adjusting the parameters of the light source, RF, and other devices has a 300-GHz bandwidth, with flatness of 0.12 dB and power reaching up to 22.49 dBm. The scheme is structurally simple and easy to implement, while additionally obtaining a comb-tunable MFC when the RF signal frequency is adjusted.

This study reports a laser diode array (LDA) double-pass double-end pumped Yb∶YAG slab laser. Pump distribution models of double- and single-pass double-end pump structures are created based on the absorption characteristics of the pump in the medium. The advantages of a double-pass double-end pump are theoretically analyzed. Under the pump frequency of 400 Hz, pulse width of 1 ms, and single pump energy of 12 J, the polarization multiplexing technology is used to realize the double-pass and double-end pump slab laser. The output laser energy is about 6.13 J with an optical-optical conversion of 50%. In comparison with a single-pass double-end pump mode with the same doping concentration and absorption efficiency of the pump light, the double-pass double-end structure demonstrates the advantages of higher laser energy, higher optical conversion efficiency, and greater stability. The theoretical analysis and experimental results prove that the utilization of the double-pass double-end pump can further improve laser output energy and efficiency.

A YAG crystal exhibiting high phonon energy is used as the doping matrix to accelerate the depopulation of the 6H13/2 energy level by multi-phonon relaxation and improve the population inversion velocities of the laser upper and lower energy levels. Simultaneously, an energy transfer between Dy 3+∶ 6H13/2 and Tb 3+∶ 7F4 is achieved by introducing Tb 3+ ions exhibiting an energy level similar to that exhibited by the laser lower level; thus, the energy lifetime of 6H13/2 is successfully reduced and the yellow laser output of 582.1 nm is obtained for the very first time. Furthermore, the effects of the Tb 3+ ions on the lifetime of the laser upper energy levels are analyzed by comparing the Dy:YAG and Dy-Tb:YAG fluorescence spectra.

To meet the pre-stage light source requirement for a distributed fiber Raman temperature sensor (RDTS), an all-fiber pulsed laser with a central wavelength of 1550 nm is developed based on the main oscillator power amplification (MOPA) technology. The laser's fiber amplifier is a two-stage structure with a forward pumping mode. The fiber pulse laser has a peak power output in the adjustable range of 0-10 W, linewidth of 0.32 nm, signal-to-noise ratio of above 25 dB, and adjustable output pulse width and frequency. An experimental temperature measurement is conducted based on Raman scattering for 2 km using a self-made fiber laser. Measurement results show that the temperature demodulation accuracy is less than ±1 ℃, and the shortest temperature measurement period reaches 1.31 s. Experimental results prove that the self-made fiber laser satisfies the requirements of actual applications.

Gain-loss ratio is an essential parameter of gas lasers and has a substantial effect on the design and performance of ring laser gyroscopes. Small ring gas lasers have wide mode spacing; therefore, it is convenient to measure the gain-loss ratio. A simple formula for calculating the gain-loss ratio is derived theoretically. Then, an experimental method is proposed to measure this parameter, and experiments are conducted for a large number of lasers. Results show that by taking advantage of precise optical machining and cavity alignment, the average gain-loss ratio of a ring laser can reach up to 3.55.

A high-precision time-synchronization fiducial system is necessary when using high-power laser drivers in physical experiments. To meet the demands of physical experiments, a time division multiplexing scheme based on an arbitrary waveform generator and high-speed electrooptic modulation is proposed. The time-synchronization fiducial system based on this scheme can generate multichannel signals, such as main laser, optic time fiducial lasers, electric time fiducial signals, and high-precision triggers. The proposed system can output 10 comb-shaped optic time fiducial lasers at three wavelengths, i.e., 532, 355, and 266 nm, 8 comb-shaped electric time fiducial signals, and two high-precision triggers with fast rise time and large amplitude. The peak-to-peak synchronization jitter value between the optic time fiducial laser and main laser is measured to be 12.80 ps, and the peak jitter of the optic time fiducial laser's period is 6.40 ps, which is close to the limit of the measurement system currently in use. A demonstration experiment of this system in a high-power laser driver is implemented to confirm that the system meets diagnostics requirements. Additionally, the time reference calibration of the streak camera's different scanning strokes is processed to effectively calibrate the time error of the camera in large sweeps.

In high-power laser systems, traditional small-tool polishing results in significant mid-spatial-frequency errors, which reduce the stability and reliability of such systems. In this study, we propose a polishing method that uses the compound swing trajectory (CST) based on a simple harmonic motion and demonstrate a polishing system that employs the CST of a multi-link mechanism. By analyzing the basic principle of small-tool polishing, we observe that the regular and orderly trajectories of traditional translational motion (TM) polishing are important causes of the mid-spatial-frequency errors. Further, we propose a function model based on a CST, study the basic polishing process, and perform the discretization calculation for such trajectories to improve the complexity of the trajectory of the removal function. We conduct a processing experiment by selecting appropriate process parameters and trajectories for the removal functions to compare the CST with the traditional TM. Subsequently, we measure the wavefronts using interferometers and observe that the interferometric fringe patterns obtained using the CST processing method are without burrs and smoother than those obtained using TM processing method. The power-spectral-density curve obtained using the CST processing method is lower than that obtained using the TM processing method in 50 mm×50 mm, displaying a better overall processing effect. These experimental results denote that a polishing system using the CST of a multi-link mechanism exhibits a significantly greater capability in suppressing mid-spatial-frequency errors when compared with the TM method.

A flat-top thin-walled structure is formed on a special-shaped base surface using hollow laser-light internal powder-feeding technology. A method of fractal stratification is proposed to solve problems of lap defects of scanning initiating terminal and low efficiency when the traditional equal-high stratification is used on uneven special surfaces. This method uses the linear relationship among the cladding height, scanning speed, cladding layer width, and defocusing amount in a certain range. A segmented variable speed is used to achieve the segmented melting height, so that the substrate low point is raised and a flat top structure is gradually added on the top of the special-shaped base surface. Test results demonstrate that, by combining the base surface and interlayer, the top surface of the thin-walled structure is typically flat. It has a maximum absolute error of approximately 0.2 mm, with a size error within 8%; the forming region's microstructure is dense and uniform without obvious pores, cracks, or other defects;the range of microhardness is 685-720 HV.

Herein, porous scaffolds were fabricated from polylaurylamide (PA12)/hydroxyapatite (HA) composite using selective laser sintering (SLS). First, the response surface method was adopted to obtain the optimal process parameters, and the porous scaffolds of PA12/HA were manufactured employing these optimized parameters. The influences of pore type, porosity, and HA ratio on the mechanical properties of the porous scaffolds were then studied based on the L9(3 4) orthogonal test. Results show that the laser power of 27.5 W, scanning spacing of 0.12 mm, and scanning speed of 1500 mm·s -1 are the optimal combination of process parameters. Porosity has the biggest effect on the compressive strength of porous scaffolds, followed by pore type and HA ratio. The maximum compressive strength is 8.04 MPa when the porosity is 60%, the pore type is circular, and the HA ratio is 15%. The minimum strength of 0.26 MPa is obtained when the porosity is 80%, the pore type is square, and the HA ratio is 15%.

A continuous annealing process is used to treat transformation-induced plasticity (TRIP) steel containing carbon, manganese, and aluminum and obtain the steel-plate samples at different temperatures and holding time of isothermal bainite transformation (IBT). Further, the microstructure, element distribution, and retained austenite of the steel treated by different processes have been characterized using scanning electron microscopy, electron probe microanalysis, electron backscattered diffraction, transmission electron microscopy, and X-ray diffraction. The stability of retained austenite under different bainite isothermal conditions and its effects on the plasticity and work hardening of experimental steel are studied. The results denote that the microstructure of experimental steel treated by different processes comprises ferrite, bainite, retained austenite, and small amounts of martensite. With increasing the temperature of IBT from 380 ℃ to 420 ℃, the volume fraction of retained austenite, mass fraction of carbon in retained austenite, and product of tensile strength and elongation increase gradually. As the temperature of IBT further increasing up to 460 ℃, those three parameters decrease gradually. At the IBT temperature of 420 ℃, the stability of retained austenite as well as the comprehensive mechanical properties are observed to be optimal. When the time for holding the temperature of IBT at 420 ℃ is 180 s, the corresponding volume fraction of retained austenite is 10.7%, mass fraction of carbon in retained austenite is 1.069%, yield strength is 455 MPa, tensile strength is 681 MPa, total elongation is 31.7%, and the product of tensile strength and elongation is 21.59 GPa·%. The extension of holding time of IBT can accelerate the bainite transformation, improve the volume fraction and stability of the retained austenite, and enhance the comprehensive mechanical properties of TRIP steel. It is necessary to ensure sufficient volume fraction of the retained austenite to induce the TRIP effect, ensure proper stability during continuous work hardening, and improve the plasticity.

A laser vision sensing three-dimensional (3D) reconstruction system has been designed to collect the surface-profile-depth point cloud information of the welded side surfaces under different welding conditions and to solve the problem of surface-form detection of the side surfaces obtained by using multi-layer single-channel arc additive manufacturing. Point cloud processing algorithms, such as RANSAC (Random Sample Consensus) and KNN (K-Nearest Neighbors), are used to extract the 3D point cloud of a deposition layer. We analyze the interlayer distribution of the multi-layer single-channel weld deposition, quantify a side-surface roughness of the deposition layer,and investigate the influence of the distance between the end of the welding wire and the plate on the 3D forming of the deposition layer. The results denote that the laser vision sensing system can accurately determine the surface-forming condition of the side surfaces obtained by using arc additive manufacturing. The 3D point cloud algorithm is used for 3D reconstruction and feature extraction of the side surfaces obtained by using arc additive manufacturing to visually describe and quantify the 3D forming features of the deposition layer, providing a novel method for performing surface-form inspection and quantitative analysis in case of arc additive manufacturing.

Laser-micro-welding based on galvanometer scanning has attracted great interest. Herein, bead-on-plate scanning micro-welding of 100-μm-thick AISI304 stainless steel foil is conducted by using a single-mode fiber laser equipped with a galvanometer scanning system. A comparative study is conducted on the laser-micro-welding processes with/without Ar-gas protection, and process windows of laser-micro-welding for the both conditions are established. Results show that an unstable transition zone exists during laser-micro-welding without gas shielding. The unstable transition zone is generated during the deep penetration welding mode alone, rather than during the alternation of thermal conductivity welding mode and deep penetration welding mode, as reported previously. The oxidation during laser-micro-welding results in an unstable deep penetration welding mode, during which a transition zone is formed. Furthermore, by applying gas shielding, we find that the unstable transition zone is eliminated, and the welding-process window is expanded.

To investigate the impacts of process parameters on the cracking behavior, porosity, and microstructure, an SRR99 nickel-based superalloy was fabricated by selective laser melting (SLM) technology. The results show that high-density samples can be prepared by setting reasonable scanning velocity, hatch spacing, and layer thickness under the fixed laser power. The laser volume energy density is the main parameter that affects crack and porosity of the SRR99 nickel-based superalloy. The number and size of cracks increase sharply as the laser volume energy density rises. It is found that most of the cracks originate in the interface of cladding layers and propagate along intergrain boundaries. At the same time, the pores are irregularly shape when the laser volume energy density is inadequate, whereas they gradually transform from irregularity to roundness with the increase of the laser volume energy density. The microstructures of the SLM deposition samples are superfine columnar dendrites. In addition, the primary dendrite spacing increases slightly with the increase of building height, and secondary dendrite arms are underdeveloped.

Herein, Ti6Al4V/Inconel625 gradient high-temperature resistant coating with dense microstructure, no cracks, holes, and other defects is prepared via laser melting deposition. The microstructure, composition, and phase transformation of the gradient coating are studied via scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Results show the microstructure changes from a lamellar structure comprising lamellar α and β phases to an equiaxed structure with changes in the compositional gradient. Further, as the nickel-based alloy composition increases, the amount of alloying elements and concentration of solute in the liquid molten phase increase. Additionally, when the coating composition is too cold, the nucleation rate increases and the microstructure is further refined. The phase composition of the gradient high-temperature resistant coating changes as follows: α+β → α+β+Ti2Ni → Ti2Ni+β → Ti2Ni+CrNi2+γ-Ni. β-Ti and Ti2Ni exist as isolated eutectic phases in the intergranular region, in the presence of a CrNi2 phase. As the Inconel625 content increases, the hardness of the gradient coating increases. When the volume fraction of the nickel-based alloy reaches 100%, the hardness reaches a peak of 855 HV under the combined action of eutectoid strengthening and solid-solution strengthening. The hardness of the gradient coating is mainly related to the contents of β phase, Ti2Ni precipitates, CrNi2 compounds, and solute elements.

The ablation effect of the combined continuous wave (CW) and pulsed lasers on metal targets is better than that of single CW or pulsed lasers. To optimize the parameter selection of the combined action of CW and pulsed lasers, both the experimental and simulation methods are used to study the influence of irradiation time sequence on damage effectiveness of the combined lasers. The results denote that the combined laser brings the best damage effectiveness when the pulsed laser irradiates during CW laser irradiation. The combined laser considerably reduces the damage time and increases the ablation range. Furthermore, the longer the preheating time, the larger the damage range. In case of the combined lasers, wastage of laser energy is observed if the energy of the long laser pulse becomes considerably high. Therefore, it is essential to select reasonable parameters for energy matching of CW laser power and long pulsed laser.

Chemically strengthened glass is widely used in electronic device display screens; however, they are difficult to cut. With the high peak power of a picosecond laser and long focal depth of a Bessel beam, a narrow-modified plane is machined inside the chemical glass. Owing to its original stress and stress induced by the picosecond laser, chemically strengthened glass accurately self-breaks along the modified plane with cutting speed of 400 mm/s and surface roughness of 395 nm. Experimental results show that pulse energy and pulse modification spacing are the main parameters affecting cutting speed and quality.

Laser cladding deposition is used to fabricate the Ti40 (Ti-25V-15Cr-0.2Si) flame-retardant layers on the surfaces of traditional TC4 alloys. Further, the composition, microstructure, and microhardness distribution of the cladding layer are subsequently investigated. Subsequently, theoretical methods are established for predicting the dilution rate and composition of transition zone of cladding layer under different laser powers. The experimental and analysis results show that there is a transition zone with respect to the composition and microhardness at the interface between the TC4 matrix and the Ti40 laser cladding zone; in 300-350 μm of the transition zone, significant composition and microhardness changes are observed under four laser powers. Among the four laser powers, the laser power of 1800 W results in the most substantial changes with respect to the microhardness and element contents of Al, V, and Cr. With increasing laser power, the size of the transition zone gradually decreases. Furthermore, the results of composition analysis of transition zone and Mo equivalent calculation show that the direct transformation of α+β→β causes the sudden change of microhardness at the cladding interface when the heat affected zone transfers to the cladding area.

This study aims to achieve pump-free transport of droplets along an infiltrating gradient trajectory on an aluminum plate by using ultrafast lasers and further increase the speed of the droplet movement. First, a superhydrophobic surface is prepared on a 1050 aluminum plate by using a nanosecond laser. Then, a wedge-shaped superhydrophilic trajectory is prepared on this superhydrophobic surface by using a femtosecond laser. The wettability, surface topography, and chemical composition of the sample surface are measured by using a contact angle measuring instrument, an electron scanning microscope, and a Fourier infrared spectrometer, respectively. The movement of droplets on the horizontal plane and the plane with a slope of 30° is recorded by using a high-speed camera. Results show that a surface with wettability-recycling property could be prepared on an aluminum plate by using a laser method. The contact angle could change from 0° to 164.6° and then from 164.6° to 0°. The hyper hydrophilic trajectory wedge angle changes from 4° to 10°, whereas the maximum droplet velocity changes from 300 to 500 mm/s. The sample heating environment changes from air to vacuum, sample rolling angle reduces from above 30° to 3.04°, and average droplet velocity changes from 50 to 100 mm/s. Therefore, it can be concluded that increasing the trajectory wedge angle or reducing the adhesion of the superhydrophobic surface can effectively improve the movement speed of droplets along the wettability gradient trajectory.

In this study, TiN/CP-Ti composites are successfully prepared using selective laser melting (SLM), and the effect of TiN content on the microstructure, microhardness, and wear behavior of Ti-based composites is studied. Results show that diffraction peaks of the α-Ti phase shift, diffraction intensities of the TiN gradually increase, and microhardness of the composites also increases from (228±13) HV to (403±20) HV with increasing TiN content. When the mass fraction of TiN is increased to 7.5%, wear resistance of the composites increases by 29.2% compared with that of CP-Ti. It shows that the addition of TiN particles can improve the microhardness and wear resistance of SLM-produced Ti-based composites.

Thin-wall parts of 316L alloy are fabricated with different Z-increments using the powder-feeding laser metal deposition technology. The microstructure and mechanical properties such as the grain size, re-melting depth, and anisotropy of the tensile property of the thin-wall parts are explored at different positions. Moreover, the grain morphologies and growth directions of a single-pass cladding layer and the thin-wall parts are investigated. Based on the microstructure with different Z-increments, the tensile strength and elongation in different directions of the thin-wall parts are analyzed. The results demonstrate that for different Z-increments, the grain morphology of the thin-wall part is mainly columnar, which differs from that of the single-pass cladding layer. In addition, the growth direction of the columnar grain is different in different regions. There is a nonlinear relationship between the Z-increment and the grain size. The growth direction and size of the columnar grain of different Z-increments affect the anisotropy of the tensile property of the thin-wall parts.

The laser damage characteristics of calcium fluoride (CaF2) crystals with various lattice planes irradiated by 355-nm pulse laser are investigated. Further, the damage thresholds and damage morphologies of three different lattice planes, i.e., (100), (110), and (111), are measured under a 7.8-ns pulse laser irradiation. In addition, the photothermal absorption is evaluated by using the surface thermal lensing technique. The (111) CaF2 crystal exhibits the highest photothermal absorption and lowest laser damage threshold. The (111) damage morphology comprises a melt pit, which is accompanied by lamellar peeling, indicating that this plane is easily cleaved by the 355-nm laser. The (100) and (110) damage morphologies also comprise a melt pit; however, the damage threshold and photothermal absorption have no clear correlation with the two lattice planes.

Herein, amorphous silicon silver (a-Si∶Ag) thin films are prepared via magnetron co-sputtering and subjected to femtosecond laser irradiation. The scanning electron microscopy, Raman spectroscopy, integrating sphere, and semiconductor performance tester are used to characterize the surface morphology, microstructure, and photoelectric properties of thin films before and after irradiation. Results show that for an irradiation energy of 300 mJ/cm 2, no obvious etching trace is observed on the surface of the a-Si∶Ag thin film, nanocrystalline Si particles are formed in the thin film, and the size of the Ag nanocrystals in the thin film increases. For an irradiation energy of 600 mJ/cm 2, obvious etching marks appear on the surface of the thin film, and the size of the Ag nanocrystal increases; however, the nanocrystalline Si particles do not change in size. The a-Si∶Ag thin film irradiated by the femtosecond laser has low resistivity, and the irradiated film can diminish a reflection of the incident light in the visible-near-infrared band. The obtained results positively affect the performance of artificial synaptic devices based on a-Si∶Ag thin films.

The first-principles plane-wave supersoft pseudopotential method based on the density functional theory (DFT-D) is used to determine the optical CO gas-sensing properties of pure, single-doped N, single-doped Rh, and N/Rh codoped rutile TiO2 (110) surfaces. We observe that the pure and doped surfaces of rutile TiO2 exhibit certain optical CO gas-sensing characteristics that results from variations in surface oxidation performance. We find that N/Rh codoping greatly improves surface oxidation. The adsorption of CO gas on an N/Rh co-doped surface is characterized by a negligent adsorption distance, enormous adsorption energy, and unparalleled stability after adsorption; it is also easy to implement. Therefore, N/Rh co-doped surfaces are more effective at optical gas sensing when compared with pure and single-doped surfaces, and N/Rh codoping is a suitable way to improve the optical gas-sensing properties of TiO2.

To obtain the absolute distribution of a three-dimensional surface, a method for three-sphere construction based on odd/even functions and the Fourier series is proposed. According to the traditional three-sphere method, the measurement of a test surface rotating by 90° is included in the combined experiments. Further, the surface shape distribution is decomposed into orthogonal basis functions in the odd/even form, and the functions are all solved individually. The algorithm is simulated based on the actual shape, and the root mean square (RMS) of the residual error reaches 1.5λ/1000. The proposed three-sphere method is also compared with the two-sphere method and the random ball method; the maximum residual RMS is 1.99 nm. The rotation, translation, tilt, and defocus errors of the adjustment mechanism during the experiments are quantitatively analyzed; a maximum error of 0.90 nm is revealed. The absolute distribution of the three-dimensional surface is detected in this study, enabling synchronous full-aperture detection of multiple spherical mirrors.

We establish a motion trajectory model for the principal point of a camera when it rotates with the rotating device. We also propose a calibration method based on the two-dimensional planar calibration of the camera to determine the distance between the camera's principal point and the turntable axis; the resulting translation matrix allows the calculation of the position relation between the principal point and the rotating center, providing a guidance for the camera installation. Further, the proposed motion trajectory model and calibration method are experimentally validated. The principal point of camera lens crosses the center of the rotation axis, and the standard deviation of the measured changes in translation matrix is 0.0826 mm. The results of this study can be used to support the installation of rotating measurement systems.

To conveniently, quickly, and accurately obtain three-dimensional (3D) point clouds of a complete surface, this study proposes a coarse splicing method of multi-view point clouds based on the calibrated parameters of a turntable. The proposed method uses a two-dimensional calibration target as the switching hub of coordinate systems. A nonlinear model including the turntable rotating angle and different measuring coordinate systems is established by exclusively using the coordinate system's relationship at two positions. Coarse registration of 3D point clouds under multiple measurement angles provides a good initial value for the iterative closest point (ICP) algorithm and increases the robustness of the ICP algorithm. Experimental results show that the operation of this method is convenient, fast, and easy to implement. Additionally, the obtained splicing error of point clouds is less than 0.12 mm.

The coupling of the sensing cable to the surrounding soil is essential to the application of distributed optical fiber monitoring technology for monitoring soil deformation, particularly the coordination of fiber-soil deformation under low confining pressures, which seriously affects the accuracy of the measurement data. In this study, the anchored fiber-optic cable is designed and the fiber-soil pull-out test is performed to investigate the effects of backfill material and anchoring method on fiber-soil coupling under low confining pressures. Results show that the backfill material considerably affects the fiber-soil coupling. The higher the clay content is, the better the coupling is. Under low confining pressures, the fiber-soil coupling can be effectively enhanced by adding the wafer anchor into the sensing cable. Decreasing anchor interval and increasing anchor diameter can improve the fiber-soil coupling.

A Nd∶YAG (yttrium aluminum garnet) nanosecond laser pulse is used in this study to ablate silicon for producing plasma spectroscopy. Further, the changes of the atomic and ionic spectral lines in the silicon plasma spectra are studied by changing the distance from focusing lens to sample surface (LTSD). The main lines discussed are Si(I) 390.55 nm and Si(II) 385.60 nm. The results show that the changes in the spectral intensities of Si(I) and Si(II) are strongly dependent on the LTSD. The spectral intensity initially increases and subsequently decreases with an increase in LTSD. In addition, the intensity of the Si(I) line is higher than that of the Si(II) line when the sample surface is located far from the focal point. In contrast, the intensity of the Si(II) line is higher than that of the Si(I) line when the sample surface is located near the focal point. At a high laser energy, more atoms in the produced plasma are ionized into ions, and the ionic line intensity is observed to increase accordingly. Changing the LTSD can optimize the spectral intensity of laser-induced breakdown spectroscopy and the ratio of ionic and atomic lines.

Powerful terahertz (THz) radiation is generated by the interaction between laser and plasma of a super short laser source; such THz radiation is usually single-shot. Herein, we propose a single-shot measurement strategy that involves splitting the THz beam, measuring the THz radiation in the horizontal and vertical directions using two independent spectral detection systems with chirped pulses, and finally obtaining the polarization state. We perform a proof experiment based on this strategy and measure an elliptically polarized THz waveform via the single-shot method. Experimental results agree well with the model analysis, verifying the feasibility of our strategy in addition to providing a new plan for single-shot detection of the polarization state of elliptically polarized THz radiation.