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We used 1030-nm femtosecond-laser pulses focused above/at/below the interface of two fused-silica glass substrates in optical and partial-optical contact to successfully weld them at a moderately high repetition rate of 600 kHz. Variation in the laser focal position for these two gap-distance regimes (optical and partial-optical contact) yields different bonding strengths (BSs) and machining mechanisms. The maximum bonding strength (58.2 MPa) can be achieved for a gap distance $$ {\le}\lambda /4 $$ for optical-contact welding when laser focused below the interface, and the corresponding height of the welding seam was 23 μm. In addition, our results demonstrated that the 'filamentation welding technique' is critical to the femtosecond-laser direct welding of glasses. Furthermore, line welding is significantly easier to realize when the femtosecond laser focuses at the interface in partial-optical-contact welding applications due to the combined effects of filamentation welding and ablation. [ABSTRACT FROM AUTHOR]

In this paper, it demonstrated one-step femtosecond laser welding and internal machining of three fused silica substrates in the optical- and non-optical-contact regimes by focusing 1030-nm laser pulses at the middle of the second substrate. Focusing laser pulses within the second glass in optical-contact and non-optical-contact samples induces permanent internal structural modification, leading to the three glass substrates bonding together simultaneously. The bonding mechanism is based on the internal modification of glass, and this mechanism is different from that of ordinary glass welding at the interface. Welding-spot size is affected by not only the gap distance (ablation effect) and heat transmission, but also by gravity through examining the sizes of the welding spots on the four contact welding surfaces. The maximum bonding strength of the lower interface (56.2 MPa) in the optical-contact regime is more than double that (27.6 MPa) in the non-optical-contact regime. [ABSTRACT FROM AUTHOR]

With the alignment of the fiber core systems containing dual-CCDs and high-precision electric displacement platform, twisted long period fiber gratings (T-LPFGs) were fabricated in two different twisted SMF-28 fibers by femtosecond laser. The torsion characteristics of the T-LPFGs were experimentally and theoretical investigated and demonstrated in this study. The achieved torsion sensitivity is 117.4 pm/(rad/m) in the torsion range −105–0 rad/m with a linearity of 0.9995. Experimental results show that compared with the ordinary long period fiber gratings, the resonance wavelength of the gratings presents an opposite symmetrical shift depending on the twisting direction after the applied torsion is removed. In addition, high sensitivity could be obtained, which is very suitable for the applications in the torsion sensor. These results are important for the design of new torsion sensors based on T-LPFGs fabricated by femtosecond laser. [ABSTRACT FROM AUTHOR]

In this study, an effective approach is presented for the fabrication of line-patterned superwetting surface on sapphire by using a femtosecond laser. The fabricated surface shows a powerful capillary action by which water could be rapidly sucked into the as-prepared surface structures and spread even on the vertical surface against gravitation. In addition, the effects of the period and the dimensions of the microgrooves on surface wettability are investigated. It is demonstrated that the wettability can be significantly enhanced in the case when the sizable line-patterned nanostructures exist. This work could provide a facile and promising strategy for enhancing the performance of heat dissipation in the electronic devices substrate. [ABSTRACT FROM AUTHOR]

Infrared antireflection of a zinc sulfide (ZnS) surface is important to improve performance of infrared detector systems. In this paper, double-pulse femtosecond laser micro-machining is proposed to fabricate a subwavelength quasi-periodic array (SQA) on ZnS substrate for infrared antireflection. The SQA consisting of approximately 30 million holes within a 2 × 2 cm2 area is uniformly formed in a short time. The double-pulse beam can effectively suppress the surface plasma shielding effect, resulting in obtaining a larger array depth. Further, the SQA depth is tunable by changing pulse energy and pulse delay, and can be used to readily regulate the infrared transmittance spectra as well as hydrophobicity. Additionally, the optical field intensity distributions of the SQA simulated by the rigorous coupled-wave analysis method indicate the modulation effect by the array depth. Finally, the infrared imaging quality captured through an infrared window embedded SQA is evaluated by a self-built infrared detection system. [ABSTRACT FROM AUTHOR]

In water jet guided laser processing technology, the stability of the water jet directly affects the processing quality. In order to investigate the flow characteristics of water jets, a numerical model of the flow field inside the water beam fiber is established, and the influence of different jet speeds and nozzle diameters on the formation of a stable water jet beam length with a flat cylindrical nozzle structure is analyzed. Computational fluid dynamics simulations show that a 120 μm diameter cylindrical nozzle structure with a length of 1 mm and no chamfered inlet has a maximum stabilized water jet length of 60 mm at a jet velocity of 70 m/s. The smaller the nozzle diameter, the more prone to water jet turbulence, and increasing the nozzle diameter can increase the stable length of the water jet to a certain extent. Finally, by conducting the water jet stable length experiment with different jet velocities, the maximum stable length of 65 mm is obtained and the accuracy of the simulation is verified, which provided a strong theoretical basis for the subsequent processing experiments. [ABSTRACT FROM AUTHOR]

Fiber pump lasers are widely used in a variety of fields, such as optical fiber communication, national defense, and medical beauty due to their high beam quality and intense laser energy. However, the alignment errors of optical parameters can influence the beam quality in the packaging of the fiber pump lasers. It is necessary to analyze the reflector, focusing lens, fiber, and the laser diode on the coupling influence between for guiding the fiber pump laser packaging. Firstly, we establish the optical path between the laser diode, focusing lens and reflector based on the physical ray-tracing method. On the other hand, the high coupling efficiency of whole system is achieved by optimize the parameters of each optical element. The simulation result shows that the highest coupling efficiency is 98.6% based on optimizing the parameters of the optical path while the experimental result of coupling efficiency is 90.36%. Also, the effects of refractive index, wavelength and fiber diameter on coupling efficiency are further investigated. The experimental results show that the radial displacement has the greatest influence on the coupling efficiency. The simulation results show that increasing the fiber core diameter can effectively improve the coupling efficiency. The results of rigorous analysis will provide an effective reference for manufacturing compact, high coupling efficiency fiber pumped laser. [ABSTRACT FROM AUTHOR]

All man-made flying objects in the sky, ships in the ocean can be regarded as small infrared targets, and the method of tracking them has been received widespread attention in recent years. In search of a further efficient method for infrared small target recognition, we propose a hierarchical attention-guided multiscale aggregation network (HAMANet) in this thesis. The proposed HAMANet mainly consists of a compound guide multilayer perceptron (CG-MLP) block embedded in the backbone net, a spatial-interactive attention module (SiAM), a pixel-interactive attention module (PiAM) and a contextual fusion module (CFM). The CG-MLP marked the width-axis, height-axis, and channel-axis, which can result in a better segmentation effect while reducing computational complexity. SiAM improves global semantic information exchange by increasing the connections between different channels, while PiAM changes the extraction of local key information features by enhancing information exchange at the pixel level. CFM fuses low-level positional information and high-level channel information of the target through coding to improve network stability and target feature utilization. Compared with other state-of-the-art methods on public infrared small target datasets, the results show that our proposed HAMANet has high detection accuracy and a low false-alarm rate. [ABSTRACT FROM AUTHOR]

Laser welding–brazing of 5A06 aluminum to Ti6Al4V titanium in a butt configuration was carried out to discuss the influences of welding parameters on dissimilar joint properties. The effects of laser offset, welding speed, and laser power on the spreading length of the molten aluminum liquid, interface fracture zone width (IFZW), fracture roughness, intermetallic compounds (IMCs) thickness, and tensile strength were also investigated. The microstructure and fracture of the joint were also studied. The results show that the tensile strength of the joint is not only influenced by the thickness and type of IMCs, but also influenced by the spreading ability of the aluminum liquid, the fracture area broken at the Ti/fusing zone (FZ) interface, and the relative area of the brittle and ductile fracture in FZ. A dissimilar butt joint with an IMC thickness of 2.79 μm was obtained by adjusting the laser offset, welding speed, and laser power to 500 μm, 11 mm/s and 1130 W, respectively. The maximum tensile strength of the joint was up to 183 MPa, which is equivalent to 83% of the tensile strength of the 5A06 aluminum alloy. [ABSTRACT FROM AUTHOR]

• Size regulation of fs-LDW grooves on ZnS is realized by wet chemical etching. • Surface roughness of microgroove sidewalls is reduced. • Emerging of microcracks is observed during etching process. In this paper, wet chemical etching is employed to treat femtosecond (fs) laser fabricated surface microstructure on zinc sulfide (ZnS) to improve its surface quality (surface roughness) and regulate its size (depth/width ratio). Dilute nitric acid (HNO 3) solution is selected as the etchant. First, the surface morphology of microgrooves before and after etching is observed as a function of etching time. Surface microcracks are also observed. Then, under different etchant concentrations, the size evolution of the microgrooves is measured for different etching time. Finally, an explanation for the changes in surface quality and size caused by etching is provided. [ABSTRACT FROM AUTHOR]

The preparation of bulk-fused silica glass using stimuli-responsive silica nanoparticle (SiNP) aggregation methods is a promising research topic. For instance, the use of a SiNP/polyethylene glycol (PEG)/polyvinyl butyral (PVB) system for thermoplastic nanocomposite preparation, followed by heat-treatment sintering, has emerged as a highly precise and scalable method for obtaining fused silica glass with a short processing time. In this study, transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and rheological analysis were used to investigate the dispersion of SiNPs in water, ethanol, water/ethanol, and water/ethanol/PEG mixtures. Furthermore, we investigated the effect of the different solvents on regulating external stimuli in the preparation of a SiNP slurry. Our results indicate that water/ethanol mixtures have a greater ability to obtain dispersed and thin slurries than water or ethanol alone, while the inclusion of PEG can further enhance this effect.The feedstocks obtained by this method is favorable for obtaining defect-free fused silica glass. In addition, agglomerates formed by SiNPs in a liquid environment can be rearranged and partially disassembled under the action of mechanical (shear) forces. Finally, optical profilometry tests showed that the sintered fused silica glass exhibited good surface quality replication, with a roughness Sa of only 148 nm. The finding in this study provides an idea for the preparation of commercial slurry for sintering fused silica glass. [ABSTRACT FROM AUTHOR]

The preparation of bulk-fused silica glass using stimuli-responsive silica nanoparticle (SiNP) aggregation methods is a promising research topic. For instance, the use of a SiNP/polyethylene glycol (PEG)/polyvinyl butyral (PVB) system for thermoplastic nanocomposite preparation, followed by heat-treatment sintering, has emerged as a highly precise and scalable method for obtaining fused silica glass with a short processing time. In this study, transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and rheological analysis were used to investigate the dispersion of SiNPs in water, ethanol, water/ethanol, and water/ethanol/PEG mixtures. Furthermore, we investigated the effect of the different solvents on regulating external stimuli in the preparation of a SiNP slurry. Our results indicate that water/ethanol mixtures have a greater ability to obtain dispersed and thin slurries than water or ethanol alone, while the inclusion of PEG can further enhance this effect.The feedstocks obtained by this method is favorable for obtaining defect-free fused silica glass. In addition, agglomerates formed by SiNPs in a liquid environment can be rearranged and partially disassembled under the action of mechanical (shear) forces. Finally, optical profilometry tests showed that the sintered fused silica glass exhibited good surface quality replication, with a roughness Sa of only 148 nm. The finding in this study provides an idea for the preparation of commercial slurry for sintering fused silica glass. [ABSTRACT FROM AUTHOR]

• A new hole identification algorithm for unorganized point cloud is proposed. • Multiple types of holes in the point cloud are identified and segmented accurately. • Holes are repaired by a fuzzy system with geometry and feature information. • The quality and efficiency of the hole repairing algorithm are taken into account. During scanning, reflection and occlusion of objects, produce holes in the acquired point clouds, causing problems to functions such as map building and target detection. In this paper, a new method for identifying and repairing such holes is proposed. First, the density and the 2D projection points of the point cloud are calculated. Based on the Euclidean distance, the hole boundary points of the original point cloud are obtained. Following, a novel preprocessing segmentation algorithm is used to obtain the boundary points of holes. Next, even if the boundary points are not fully identified, the total 2D repairing points are obtained by the proposed algorithm. Finally, a new hole repairing model, based on fuzzy inference system, is proposed, integrating geometry and curvature information of boundary points, while it can fast and accurately estimate the height coordinates of the repairing points. The experimental results show that the proposed algorithm is efficient. [ABSTRACT FROM AUTHOR]

The demand for output performance and reliability of the HPLD (high-power laser diode) has become increasingly stringent with the development of application requirements. The thermal effect of the HPLD will lead to optical components' thermal-induced misalignment, which will significantly affect the output quality and power of the laser. In this paper, the influence of the thickness and uniformity of UV-curing adhesive on the thermal-induced misalignment of the bonding module is revealed. Then the thermal stability of UV-curing adhesive is optimized by the microparticles composite modification method. Finally, the single emitter array laser is packaged with the optimized modified UV-curing adhesive, the thermal-induced misalignment of beam-shaping components can be reduced by 8 times, and the power reduction ratio of the laser is reduced from 3.8% to 0.72%. This research supports efficient control of the thermal-induced misalignment which to ensures high-performance packaging and manufacturing for HPLD. [ABSTRACT FROM AUTHOR]

With the quick development of electromagnetic propulsion systems, permanent magnet linear synchronous motors (PMLSMs) have been the focus of research for high-performance propulsion systems. Compared with traditional windings, two ring windings with novel structures and better performance for PMLSMs are proposed: the single-layer ring windings are suitable for high-power systems; the double-layer ring windings can be adopted in low fluctuation systems. This paper first analyzes the electromagnetic parameters of the ring windings based on the equivalent magnetizing current method to verify the availabilities of ring windings. The main parameters of two ring windings are compared to achieve the optimization guides. Then, the magnetic fields and thrust characteristics of ring windings and traditional lap windings are analyzed by the finite-element method, and the independent magnetic field of ring winding ends is verified. And then a prototype motor with double-layer ring windings was manufactured and experimentally tested, the measurement data were matched with the theoretical calculations. The results illustrate that the PMLSM with ring windings has higher thrust density and lower thrust ripple, ring winding structure is more suitable for electromagnetic propulsion systems. [ABSTRACT FROM PUBLISHER]

Sapphire has a potential as a new generation of electronics display. However, direct processing of sapphire surface by visible or near-IR laser light is challenging since sapphire is transparent to these wavelengths. In this study, we investigate the formation of femtosecond laser-induced periodic surface structures (LIPSSs) on sapphire coated with nanolayered gold film. We found a reduced threshold by about 25 % in generating uniform LIPSSs on sapphire due to the nanolayered gold film. Different thickness of nanolayered gold films are studied, and it is shown that the change in thickness does not significantly affect the threshold reduction. It is believed that the diffusion of hot electrons in the gold films increases interfacial carrier density and electron-phonon coupling that results in a reduced threshold and more uniform periodic surface structure generation. [ABSTRACT FROM AUTHOR]

Constant elastic alloy is widely used material with high applied performance. In order to develop the application of constant elastic alloy, laser ablation of constant elastic alloy in different ablation mediums was investigated with different femtosecond lasers. Constant elastic alloy was ablated in solution with different ethanol contents and different thicknesses of the liquid layer above the target material and for comparison, in air. Also, the effects of laser energy and laser pulses of femtosecond laser on the morphology are studied. The effects of the position of the laser focus relative to the target surface were also discussed. The experimental results indicate that larger laser-induced area and smaller depth of craters tend to be obtained in solution than in air. The laser-induced area firstly increases and then decreases, and depths of craters decrease at first and increase later with the increase in ethanol content. Furthermore, the larger were energy of laser pulses, the larger were laser-induced area and deeper craters made in all different ablation solutions. [ABSTRACT FROM AUTHOR]

Appropriate Footprints of Uncertainty (FOUs) are crucial to the ability of Interval Type-2 (IT2) Fuzzy PI Controllers (FPICs) to deal with system uncertainty; hence how to quickly and accurately determine the right FOUs is important to the designer. In this research, the effects of increasing the difference between two FOUs of IT2 FPICs, on computing the firing intervals, on switch points of KM type-reducer and on close-form solution of output, are studied. It is proven that as the difference between two FOUs increases: around the convergence point, the control laws gradually become fewer; the number of combinations of switch points is gradually decreasing (the output form of the KM type-reducer will no longer change); the variable gain of IT2 FPIC Kp decreases monotonously, and Ki increases monotonously in input space. A guideline for designing FOUs is provided, as the difference increases. The position control experiments and simulations are carried out, in order to illustrate the presented findings. [ABSTRACT FROM AUTHOR]

Tiny target recognition in automation is currently a hot research task that usually suffers from typical issues such as complex background, dim target, and slow detection speed. In the current study, a data-driven method is proposed to realize the posture recognition of micro-lens during optical device coupling to achieve accurate clamping of the gripper. First, we establish a pixel-by-pixel labeled optical micro-lens dataset named single-frame micro-lens target (SFMT), which provides data support for the subsequently proposed convolutional neural network. Subsequently, an asymmetric convolutional multi-level attention network (ACMANet) is proposed to realize accurate segmentation detection of micro-lenses by employing an embedded multi-scale asymmetric convolutional module (MACM) and a multi-level interactive attention module (MIAM). MACM achieves not only a reduction in computational complexity but also enhanced robustness for rotated image recognition through multi-scale asymmetric convolutional kernels. Furthermore, MIAM improves the accuracy of image segmentation by connecting the down-sampling and up-sampling stages and realizing the fusion of pixel position details and key channel features. Extensive experimental results based on our self-constructed image acquisition system demonstrate that the values of normalized intersection over union and dice are successively 91.41% and 95.50%, and the processing speed is 3.3 s/100 images, which shows the advance of ACMANet. [ABSTRACT FROM AUTHOR]

Tiny target recognition in automation is currently a hot research task that usually suffers from typical issues such as complex background, dim target, and slow detection speed. In the current study, a data-driven method is proposed to realize the posture recognition of micro-lens during optical device coupling to achieve accurate clamping of the gripper. First, we establish a pixel-by-pixel labeled optical micro-lens dataset named single-frame micro-lens target (SFMT), which provides data support for the subsequently proposed convolutional neural network. Subsequently, an asymmetric convolutional multi-level attention network (ACMANet) is proposed to realize accurate segmentation detection of micro-lenses by employing an embedded multi-scale asymmetric convolutional module (MACM) and a multi-level interactive attention module (MIAM). MACM achieves not only a reduction in computational complexity but also enhanced robustness for rotated image recognition through multi-scale asymmetric convolutional kernels. Furthermore, MIAM improves the accuracy of image segmentation by connecting the down-sampling and up-sampling stages and realizing the fusion of pixel position details and key channel features. Extensive experimental results based on our self-constructed image acquisition system demonstrate that the values of normalized intersection over union and dice are successively 91.41% and 95.50%, and the processing speed is 3.3 s/100 images, which shows the advance of ACMANet. [ABSTRACT FROM AUTHOR]

As a special kind of Bragg grating, phase-shifted fiber Bragg grating (PS-FBG) has attracted extensive attention because of its extremely narrow transmission window and excellent sensing performance. The main purpose of this manuscript is to discuss the PS-FBG with special sensing characteristics and explore the influence of different inscription technologies on the sensing characteristics of PS-FBG by comparing the existing inscription methods. The sensing characteristics, advantages and disadvantages of PS-FBG with different structures are analyzed. [ABSTRACT FROM AUTHOR]

In order to solve the problem of high measurement cost and complex operation of position-independent geometric errors (PIGEs) calibration on a five-axis motion platform, this paper first proposes a low-cost pose measurement method, based on monocular vision, which can accurately determine the pose in the environment, even with image shadow and noise. Next, an improved method, combining pose measurement and kinematic parameters identification, is proposed to calibrate a five-axis motion platform. The kinematic error model of the platform and the pose planning of automatic image acquisition are established, providing the pose data and motor position data, required for calibration. Combined with the kinematic loop method, the kinematic parameters of the five-axis motion platform are identified, while the geometric structure parameters are accurately calibrated. Before and after calibration, a circular trajectory of the target coordinate system (TCS) origin, relative to the camera coordinate system (CCS), is used to test the comprehensive accuracy evolution of the five-axis motion platform, by comparing the position and orientation errors of the theoretical circle trajectory to the actual one. The experimental data show that, before and after calibration, the average position error of the five-axis motion platform is reduced by 79.46%, while the average direction error is reduced by 86.53%. The experimental results clearly demonstrate that the proposed calibration method significantly improves the comprehensive motion accuracy of the five-axis motion platform, and they verify the practical value and effectiveness of the calibration scheme. [ABSTRACT FROM AUTHOR]

• Laser diode, graded-index lens, and fiber constitute coupling system. • Component misalignment with various parameters for calculating coupling efficiency. • The results can guide manufacture of fiber-coupled diode lasers. For single emitter fiber coupling module, miniaturization and high stability have always been the goal in the field of industry and medical. Based on the beam propagation principle, a compact, flexible, and simple coupling optical system between laser diode (LD) and multimode fiber (MMF) by graded refractive index (GRIN) lens is proposed, which shows a coupling structure with relatively loose optical tolerance. The coupling efficiency is explored under all kinds of optical coupling system parameters, such as the working distance between the GRIN lens and MMF, incident wavelength, slow axis divergence angle of the LD, fiber diameter, and GRIN lens length. The results show that the maximum coupling efficiency reaches 97.55% in the simulation when not considering the lens refraction loss and fiber end face loss, and the maximum coupling efficiency reaches 90.8% in the experiment, which indicating the rationality and applicability of the designed model. The optimized model allows the fiber and GRIN lens to coaxially assemble, and the axial deviations and transverse displacements for influencing coupling efficiency are also discussed in detail. These results provide an important reference point for the design and manufacture of fiber-coupled diode lasers. [ABSTRACT FROM AUTHOR]

• Copper-coated fiber Bragg grating was developed. • Multilayer FBG with nickel, gold, copper showed high strength and sensitivity. • Multilayer FBG can be applied in extremely high-temperature environments. In this study, a copper coating was deposited on the surface of a fiber Bragg grating (FBG) via electroplating. We compared the temperature responses of the uncoated and copper-coated FBGs from 20 °C to 1000 °C. Under high-temperature conditions, copper diffused into the FBG to form copper crystals, and the copper coating gradually underwent high-temperature oxidation. This reduced the sensitivity and spectral consistency of the copper-coated FBG. A multilayer metal-coated FBG was prepared with an inner layer of nickel, outer layer of gold, and copper layer in the middle. The multilayer FBG exhibited a temperature sensitivity of 23.1–23.53 pm/°C. Furthermore, it showed the coating-enhancement effect and good linearity after multiple thermal cycles. The multilayer metal-coated FBG not only shows high-temperature sensitization but also solves the problem of bare FBGs being extremely fragile after experiencing high temperatures. This study provides a feasible solution for the application of FBGs in extremely high-temperature environments. [ABSTRACT FROM AUTHOR]

This paper investigated the thermal stress distribution in laser welding of Ti6Al4V and 2024-T4 alloys using the coupled thermal–mechanical model based on the thermo-elastoplastic theory. The microstructure and hardness of the dissimilar joint were analyzed based on the simulated results. The asymmetry of temperature and stress distribution indicated that the great difference of material properties had significant effects on the uniformity of thermal stress distribution. The combination of experiment and simulation demonstrated that the growth of grains in heat-affected zone and fusion zone was closely related to the thermal cycle process. The good agreement between the simulated and experimental results verified the rationality of the combined heat source model of double ellipsoid and rotating Gaussian body. The coupled model and simulated results could offer the instructive information in laser welding for other dissimilar alloys. [ABSTRACT FROM AUTHOR]

• A non-uniform 1 × 5 PLC splitter with excellent performance is designed and manufactured. • The sensitivity of device performance to each structure size is discussed using orthogonal experimental method. • The performance of optical splitter oscillates with the increase of the length of narrow straight waveguide. The non-uniform planar lightwave circuit (PLC) splitter with one primary and multiple signal distribution function is one of the most crucial devices in Fiber-To-The-Room (FTTR) technology. Reducing the device loss and optimizing output uniformity are challenging obstacles during the design and optimization process of PLC splitters. In this paper, the design and optimization of a non-uniform 1 × 5 PLC splitter are carried out, and the device performance sensitivity analysis towards various structure dimensions was then determined using the orthogonal experimental method. The measurement results show that for an operating wavelength range from 1.27 μm to 1.63 μm, the insertion loss (IL) of the main channel is less than 1.25 dB. Whilst the IL, wavelength-dependent loss (WDL), and uniformity loss (UL) of channel 2 ∼ 5 are less than 14.06 dB, 0.18 dB, and 0.24 dB, respectively. The adopted design method has manifested convenient practicality and advanced efficiency and could considerably scale down the design and optimization cycle of PLC splitters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Broadband light absorption surface is obtained from cross-scale micro-/nanostructures fabricated by femtosecond laser. • Light absorption mechanism is numerically and experimentally studied. • Photo-thermal-electric conversion efficiency of a Seebeck device is improved with such surface integrated on. • Performance parameters and device design of a thermoelectric photodetector are explored. The limited sensitivity and inherent long response time restrict the widespread applicability of thermally-based photodetectors. Herein, a copper surface endowed with optical absorption enhancement by femtosecond laser fabrication is introduced, to improve the sensitivity and power prediction speed of thermoelectric photodetectors. Cross-scale microstructures including periodic micro-taper array and randomly dispersed particles are obtained on the surface, and their formation mechanism is elucidated. The surface exhibits an average reflectivity of 8% over the wavelength range of 200–2500 nm. This broadband absorption is mainly due to the local light field enhancement by the unevenly oxidized and size-dispersed particles, while the periodic micro-taper array further enhances the absorption by geometric light trapping effect. When integrated into a thermoelectric device, a comprehensive parameter analysis including sensitivity (45.053 mV/W), response time (5.47 s), precision of time-dependent prediction (2 s to obtain R 2 ⩾ 0.999), and precision of measuring at different points (3.97%) is performed. Our study offers a practical approach to produce cross-scale light absorption microstructure, paving the way for its promising advances in photothermal-based optoelectronic applications. [ABSTRACT FROM AUTHOR]

• A simple and robust method for fabricating patterned superhydrophobic surfaces by femtosecond laser micromachining is presented. • The wettability and the adhesion force of the patterned surface are tuned by changing the width of the linear pattern. • Based on the modified Furmidge equation, the relationship between the adhesion and the liquid-solid interface width is explained. • The patterned surface has the ability to manage fluid motion, transportation and mixing. Patterned superhydrophobic surfaces have a wide range of applications in terms of microfluidic devices. In this work, a simple and robust method is proposed to fabricate patterned superhydrophobic surfaces by two combined steps including femtosecond laser microfabrication and immersion treatment. The obtained surface exhibits contact angles of 170.0°, 167.6°, and 169.5°, and sliding angles of 5.8°, 6.0°, and 3.9° for 12 μL, 18 μL, and 30 μL water droplets, respectively. The high-adhesion hydrophobic linear pattern combined with the surrounding low-adhesion superhydrophobic surface exhibits controllable wettability and pronounced liquid-sliding anisotropy. Since the contact angle and the adhesion force can be controlled by adjusting the width of the linear pattern, the droplet motion can be directionally modulated. As the line width increases, the sliding angle in parallel direction can be regulated from 18.9° to 90°, from 15.3° to 47.6°, and from 8.6° to 25.0° for 12 μL, 18 μL, and 30 μL water droplets, respectively. Based on the modified Furmidge equation, the relationship between adhesion and liquid-solid interface width can be reasonably explained. Furthermore, the potential applications of the patterned surfaces for droplet transport and mixing are explored. The wettability of the superhydrophobic surfaces to liquids of different types and pH is also investigated. The work presented here has the potential to advance femtosecond laser scanning as a simple, precise, and controllable method for fabricating patterned superhydrophobic surfaces, and to accelerate their applications in parallel reactors, chemical micro-assays, drug delivery systems and so on. [ABSTRACT FROM AUTHOR]

• A point cloud spiral repair method with local surface interpolation is proposed. • The algorithm produces more accurate results and the threshold setting is simpler. • The proposed algorithm prevents the splitting of hole boundary points. • The geometric characteristics of repair points are consistent with the point cloud. Due to unfavorable factors, such as environmental noise, reflection, and occlusion of a scanned object, a point cloud obtained by structured light measurement equipment contains holes, which limits further application of the three-dimensional data. This study proposes a point cloud hole spiral-filling method based on the fusion of two- and three-dimensional data. The pixel coordinates corresponding to the point cloud are calculated according to the scanning system parameters. Based on a matrix-like distribution pattern of a camera's pixel coordinates, the missing pixel coordinates are used to locate the hole boundary points, and the pixel coordinates of the filled points are obtained. In addition, the pixel coordinates of the hole boundary points are used as a sampling layer, which can be used to separate the outermost pixel coordinates of the filled points. Similarly, the pixel coordinates of the filling points are helically stratified. The pixel coordinates of the filling points and their neighboring points, as well as the height coordinates of the neighboring points, are used for surface interpolation to estimate the height coordinates of the filling points. The hole filling is realized after the correction of coordinates using the four-connected domain. The experimental results demonstrate that the proposed spiral hole filling algorithm can accurately identify the hole boundary and can estimate the filling points completely while preserving the details of the repair area. [ABSTRACT FROM AUTHOR]

In this research, amplitude Fresnel zone plates (FZPs) were fabricated on fused silica glass with femtosecond laser. The focusing characteristics including focal length, diffraction efficiency, geometric concentrator ratio, spot energy uniformity, depth of focus and resolution were studied by simulations and experiments. To optimize the focusing characteristics of FZP, we proposed an optimized machining process, an extended FZP and an fractal FZP. The optimized machining process increased the diffraction efficiency of the amplitude FZP from 6.96% to 8.14%, the extended FZP broke through the limit of minimum line width in processing and improved the resolution, and the fractal FZP increased the focus depth from 4 mm to 10 mm. In addition, we wrote a FZP on the end face of multi mode fiber, the divergent annular beam converged and formed an focus ring at the focal plane. This research will provide broad applications in fiber tweezers, beam coupling and optical communication. [ABSTRACT FROM AUTHOR]

Oxycodone is a common type of opioid used for the treatment of moderate to severe pain. Besides its analgesic effects on neuron cells, the effects of oxycodone on other cell types are yet to be elucidated. We previously demonstrated that oxycodone displayed both pro- and anti-cancer effects on bulk cancer cells. This work further investigated the effects of oxycodone on normal and malignant hematopoietic stem cells. Using hematopoietic CD34+ cells isolated from normal bone marrow (NBM) or patients with acute myeloid leukemia (AML), we showed that oxycodone activates hematopoietic cells regardless of cell development stage and malignant status. Oxycodone dose-dependently increases colony formation and self-renewal capacity of NBM and AML stem/progenitor cells, and promotes proliferation of AML bulk cells. NBM stem/progenitor cells are more sensitive to oxycodone than AML counterparts. In addition, oxycodone alleviates chemotherapy drug-induced toxicity in AML stem/progenitor cells. Mechanism studies demonstrate that oxycodone acts on hematopoietic cells in an opioid-receptor-independent manner. Oxycodone did not affect epithelial growth factor receptor (EGFR) signaling neither but stimulated Wnt/β-catenin signaling. Rescue studies via depleting β-catenin using genetic and pharmacological approaches confirmed that β-catenin was required for the activation of hematopoietic cells induced by oxycodone. Our work demonstrates 1) the protective role of oxycodone in malignant hematopoietic cells from chemotherapy; 2) stimulatory effects of oxycodone in normal hematopoietic stem cells; and 3) ability of oxycodone in Wnt signaling activation. • Oxycodone activates normal bone marrow and leukemia stem/progenitor cells. • Oxycodone alleviates chemotherapy-induced toxicity in leukemia cells. • Oxycodone acts on hematopoietic cells via activation of Wnt/β-catenin. [ABSTRACT FROM AUTHOR]

Femtosecond laser ablation is a flexible method for manufacturing gallium arsenide (GaAs) micro-optical components. However, its machining efficiency and surface quality do not satisfy industry requirements. Wet etching assisted femtosecond laser ablation is proposed to solve these problems. After corrosion, protrusions and particles are selectively corroded. X-ray diffraction and energy dispersive X-ray spectroscopy results show that oxides are formed after laser ablation, and the crystal cell size of GaAs increases. Thus the contact area between hydrofluoric acid atoms and the GaAs crystal cell increases, the ratio of modified-to-unmodified corrosion rate is as high as 10:1. A one-dimensional grating, a conventional Fresnel zone plate (FZP), and a fractal FZP are fabricated using this method. Experiments show that the GaAs micro-optical component can diffract and focus infrared light with a wavelength of 1.5 µm well. The process offers a way to achieve high efficiency and quality manufacturing of GaAs microstructures. [ABSTRACT FROM AUTHOR]

This study investigates the resonant effects on nonlinear photoionization of Li4 cluster under femtosecond laser irradiation. The real-time and real-space time-dependent density functional theory is applied to describe the optical linear response and nonlinear electron dynamics during the laser-material interactions. The calculations describe well the behaviors of the ionization process for both the off resonance and on resonance cases. For given laser intensities, the frequency dependence of electron ionization and energy absorption on multiphoton and/or tunnel ionization mechanisms is investigated. Theoretical results show that (1) the off resonance behaves as a classical oscillator whereas resonance leads to an internal excitation with subsequent emission of electrons after the laser termination; (2) when multiphoton ionization dominates, the frequency dependence of emitted electrons and absorbed energy coincides with trend of the spectral cross section for photon absorption; (3) while when tunnel ionization becomes significant, the aforementioned correlation gradually disappears, and the enhancement of resonant effect on photoionization is not manifest. [ABSTRACT FROM AUTHOR]

• Error evaluation method based on the variation of beam propagation is proposed. • The effect of the collimator offset on the light field is revealed. • The effect of the collimator offset on the coupling efficiency (CE) is obtained. • The most influential positioning error is Δ Y FAC , When Δ Y FAC = 4 μ m , CE = 21.5%. • The influence of FAC positioning error is much stronger than that in SAC. The positioning error of optical components is one of the crucial factors affecting the beam quality for high-power semiconductor laser diode and the fiber coupling efficiency. This paper, derives the evaluation equations for the influence of collimator positioning error of single emitter laser array on light intensity distribution, and explores the effect of positioning error on the shape and position of beam spot through simulation. Moreover, the effects of positioning error on the coupling efficiency are researched by the experiment and are supported by simulations. The results show that the most influential positioning error, a 4 μ m displacement error in the y-axis of the fast axis collimator will decrease the coupling efficiency by 78.5%. Besides, the sensitivity analysis of each positioning error on coupling efficiency is investigated. [ABSTRACT FROM AUTHOR]

The fuzzy operator is one of the most important elements affecting the control performance of interval type-2 (IT2) fuzzy proportional-integral (PI) controllers. At present, the most popular fuzzy operators are product fuzzy operator and min() operator. However, the influence of these two different types of fuzzy operators on the IT2 fuzzy PI controllers is not clear. In this research, by studying the derived analytical structure of an IT2 fuzzy PI controller using typical configurations, it is proved mathematically that the variable gains, i.e., proportional and integral gains of typical IT2 fuzzy PI controllers using the min() operator are smaller than those using the product operator. Moreover, the study highlights that unlike the controllers based on the product operator, the controllers based on the min() operator have a simple analytical structure but provide more control laws. Real-time control experiments on a linear motor validate the theoretical results. [ABSTRACT FROM AUTHOR]

A high coupling efficiency is required to guarantee high-output power for lasers. However, positioning errors in optical devices can lead to different degrees of attenuation for the coupling efficiency. This paper, investigates the effects of positioning errors on the coupling efficiency of optical devices. Specifically, the combining, focusing, and coupling processes of a three-wire single emitter laser array are studied through experiments and are supported by simulations. The results show that a 50 μ m position error in the Y-axis of the fiber will reduce the coupling efficiency by 44 %, and a rotation error of 0.5° in the X-axis of the reflector will reduce the coupling efficiency by 100 %. Moreover, the sensitivity of the coupling efficiency to each error is revealed. [ABSTRACT FROM AUTHOR]

Surface with oil–water separation performance has attracted more and more attention in the application of oil-containing wastewater purification. Much related work has been done by many researchers. However, there are still many difficulties in rapid manufacturing of filter membranes with special wettability. In this paper, an efficient, flexible method to fabricate microporous arrays by using a femtosecond (fs) laser combined with a spatial light modulator is proposed. The laser treated copper sheet surface shows hydrophobic and superoleophilic properties due to the microstructure. Meanwhile, the array of micro-through-holes on the surface can allow oil to penetrate through holes and prevent water from penetrating. The manufacturing process is not only extremely efficient, with a 10 × 10 focus array used in the ablation, but also it is without chemical method and the filter presents a long-term stable hydrophobic and superoleophilic performance. [ABSTRACT FROM AUTHOR]

• A universal correction method for grating fringes phase is proposed. • The grating fringes pose distortion is eliminated using a single projected image. • The light intensity attenuation function is derived based on a blank image analysis. • A light intensity correction algorithm of grating fringes is presented. • The standard sinusoidal phase of grating fringes is obtained after processing. In a phase measuring profilometry system, while the camera optical axis is perpendicular to the reference plane and the projector is installed obliquely, the sinusoidal characteristic of the grating fringes is lost (i.e., non-uniform pitch and amplitude), thus affecting the measurement accuracy. In this paper, a universal correction method for grating fringes is proposed, in the case where the projector optical axis is not perpendicular to the reference plane. This method includes pose correction (i.e., uniform pitch) and light intensity correction (i.e., uniform amplitude) of grating fringes. The pose transformation model, which is used to convert the pixel coordinates from the projector coordinates system into the camera coordinates system, is established by projecting a single image. Next, the digital grating fringes pattern with pre-corrected pose can be obtained, according to the established pose transformation model and the projector resolution. Regarding the light intensity correction, after capturing a projected blank pattern with pre-corrected pose, the light intensity correction coefficients on the reference plane are quantified by iteration method, and they can be used to correct the light intensity of grating fringes. The experimental results show that the presented method can effectively realize the sinusoidal correction of grating fringes. [ABSTRACT FROM AUTHOR]

• A dynamics model is built to systematically study the mechanism of the CPL drilling. • The time–space parameter matching of the CPL drilling is revealed. • The CPL drilling is compared with conventional single laser drilling. Combined pulse laser (CPL), a hybrid laser processing technology, has proven to be a reliable method for high-quality and high-efficiency processing of the hard and brittle materials. In this paper, a fluid dynamics model is built to systematically study the effects of the temporal and/or spatial shaping on the (nanosecond laser/millisecond laser) CPL drilling of alumina ceramic. The auxiliary effect of nanosecond laser is suggested to be simulated by quantifying the recoil pressure generated by the transient heating of the nanosecond laser. In this context, the assisted nanosecond laser is spatial shaped to annular spots with different diameters (0–200 µm), and temporal shaped to 1, 2 and 4 pulses with the same total pulse energy, which are compared with the conventional Gaussian nanosecond laser in terms of the CPL drilling performance. In addition, the transient absorption, temperature evolution, melting and vaporization of the target, melt flow and micro-hole profile, sputtering of the melt by the recoil pressure, recast layer thickness and material removal rate (MRR) of the CPL are analyzed comprehensively in a systematic comparison. Finally, the optimal matching parameters of the CPL drilling was proved which can provide guidance for high-quality, high-efficiency hole processing of the hard and brittle materials. [ABSTRACT FROM AUTHOR]

Beam shaping has been widely used in laser processing. Compared with Bessel beam, Bessel-like beam has unique advantages of fabricating high-aspect-ratio holes due to its tunable and longer non-diffraction length. However, the theoretical and experimental optimization of Bessel-like beams for laser manufacture has remained to be investigated. In this paper, we established a theoretical model of the intensity distribution and peak energy density of the Bessel-like beams based on a simplified phase of arc axicon. It was found that the longer propagation length and the lower peak energy density of the Bessel-like beams, contributed to the longer ablation length and higher ablation precision in the silica glass. The ablation length of the optimized Bessel-like beams was at least 1.6 times longer than that of the Bessel beam, which furtherly improved the fabrication efficiency of microdrilling. • Bessel-like beams were generated by an arc axicon. • The intensity distribution and peak energy density of Bessel-like beams were investigated. • The optimized Bessel-like beams ablated longer length and higher precision in silica glass. • Through-microholes array showed considerable precision and uniformity. [ABSTRACT FROM AUTHOR]

The concentration of cortisol in the human body is related to health. Research has shown that the cortisol level in the body correlates with glucose. Therefore, simultaneously and sensitively measuring cortisol and glucose levels is very important for diabetic patients. A combination of biomolecules and metal nanoparticle surfaces can change the refractive index and induce a shift in the surface plasmon resonance (SPR) wavelength. Therefore, a sensor for cortisol and glucose detection is designed and fabricated. The logarithmic sensitivity of cortisol and glucose concentrations reach 5.267 nm/log(ng ml-1) and 9.878 nm/log(mM), respectively. The limits of detection (LODs) for the cortisol and glucose concentrations reach 0.0126 ng ml-1 and 1.136 × 10−3 mM respectively. The detection range covers a concentration variation range of human saliva. The proposed sensor has a compact structure. In this work, it is proven that the sensor has good specificity and selectivity through experiments, and the technical methods of the sensor can be extended to applications in medical, biological and environmental detection. [ABSTRACT FROM AUTHOR]

In this paper, one-step fabrication of fusiform hierarchical micro/nanostructures on copper surface by femtosecond laser is proposed. According to the preferential valley ablation, Marangoni effect based on melt hydrodynamics and the coupling of the incident light and surface plasmon polaritons, the formation mechanism of the fusiform hierarchical micro/nanostructures is explained. And the effect of laser parameters including the defocusing distance, laser power, and scanning speed on the surface morphology is investigated. Also, the quantitative analysis of the fusiform tapers is carried out. It is demonstrated that the three-dimensional size of the fusiform hierarchical micro/nanostructures could be controlled by adjusting laser parameters. In addition, the potential applications of the fusiform hierarchical micro/nanostructures in microliter droplet directional transportation and light absorption are explored. • One step fabrication of fusiform hierarchical micro/nanostructures on Cu by fs laser is proposed. • The formation mechanism of the micro/nanostructures is explained by Marangoni effect and surface plasmons model. • Effect of laser parameters on the three-dimensional micro/nanostructures' size is investigated. • The potential applications of the micro/nanostructures in droplet transportation and light absorption are explored. [ABSTRACT FROM AUTHOR]

Highlights • A novel strain sensor based on MZI with TCF-PCF-TCF structure is • proposed. • A high strain sensitivity of −1.89 pm/µε in the range of 0–4000 µε is achieved. • The proposed MZI has exhibited good fringe visibility as high as 21 dB. • The dependence of strain sensitivity on the MZI length is investigated. • The sensor is easy to fabricate and own high sensitivity and low cost. Abstract We have demonstrated a high-sensitivity strain sensor based on a novel photonic crystal fiber (PCF) interferometer by means of splicing two sections of thin core fibers (TCF) with a piece of PCF between two single mode fibers (SMFs). The proposed MZI has exhibited an excellent fringe visibility as high as 21 dB in air. Particularly, the measurement range was up to 4 mε and a strain sensitivity of −1.89 pm/µε was achieved. It was found that the strain sensitivity of the MZI was weekly dependent on the PCF length. The measured sensitivities of the MZI with 25 mm, 30 mm and 35 mm PCF at ∼1590 nm were −1.83 pm/µε, −1.85 pm/µε and −1.77 pm/µε, respectively. Moreover, the temperature characteristics of the sensor were also investigated. Additionally, the sensor has advantages of simplicity of fabrication, low cost, compact size as well as large strain measurement range. [ABSTRACT FROM AUTHOR]

• Compared with traditional solvents, the ethanol/water system is more nontoxic and environmentally friendly. • Chain-like cluster of water and ethanol has the ability to increase the dispersion effect. • The dispersion effect of water is reflected in the increase of zeta potential, solvation layer, and viscosity. • Water as a solvent does not cause problems with crystallization and high hydroxyl content. Thermoplastic nanocomposite preparation using a silica nanopowder/polyethylene glycol (PEG) / polyvinyl butyral (PVB) system followed by heat-treatment sintering to obtain fused silica glass has high precision, scalable manufacturing processes, and short processing time. However, conventional solvents are toxic and harmful to the environment, and for this reason, the ethanol/water solvent system was proposed in this study. In this study, the effect of water content on the dispersion effect of nano-silica suspensions was investigated through particle size and zeta potential tests and FTIR spectra analysis; in addition, the study proposes a dispersion theory based on the solvation layer of the ethanol/water competitive adsorption and viscosity effect. Finally, optical photographs and SEM characterization showed that the obtained fused silica glass was transparent and had no seam defects, and the XRD and hydroxyl group tests showed that the glass had a low hydroxyl group content of only 2.55 ppm. [ABSTRACT FROM AUTHOR]

With the rapid development of communication technology, frequency selective surface (FSS) operating at higher frequencies is required and it is necessary to design and fabricate new FSS. In this paper, a broadband double-layer FSS is proposed which is composed of one layer of foam, two metal layers, and four layers of substrate. The simulation result shows that a high transmission in the band of 60.03–89.33 GHz (covering the E band) with a relative bandwidth up to 29 % is achieved. In addition, the effects of the key structural parameters, oblique incidence angle, and TE/TM polarization on the transmission performance are further explored. The results indicate that the proposed FSS has good oblique incidence angular stability and polarization insensitivity up to 60°. Finally, the proposed FSS is fabricated by the femtosecond laser and measured by the waveguide method. Experimental results show that the machined sample has high precision and the machining error is within 1 µm, and good agreement between the simulated and measured results is observed. Therefore, the proposed FSS could be used as spatial filters or sub-reflectors of multiband antennas and the corresponding processing method could be extended to other millimeter wave functional devices, such as absorbers, radomes, etc. [ABSTRACT FROM AUTHOR]

In this study, a facile and detailed strategy to fabricate superhydrophobic aluminum surfaces with controllable adhesion by femtosecond laser ablation is presented. The influences of key femtosecond laser processing parameters including the scanning speed, laser power and interval on the wetting properties of the laser-ablated surfaces are investigated. It is demonstrated that the adhesion between water and superhydrophobic surface can be effectively tuned from extremely low adhesion to high adhesion by adjusting laser processing parameters. At the same time, the mechanism is discussed for the changes of the wetting behaviors of the laser-ablated surfaces. These superhydrophobic surfaces with tunable adhesion have many potential applications, such as self-cleaning surface, oil–water separation, anti-icing surface and liquid transportation. [ABSTRACT FROM AUTHOR]

A simple and efficient technique for fabricating parabolic cylindrical microlens arrays (CMLAs) on the surface of fused silica by shaped femtosecond (fs) laser direct-writing is demonstrated. By means of spatially shaping of a Gaussian fs laser beam to a Bessel distribution, an inversed cylindrical shape laser intensity profile is formed in a specific cross-sectional plane among the shaped optical field. Applying it to experiments, large area close-packed parabolic CMLAs with line-width of 37.5 μm and array size of about 5 × 5 mm are produced. The cross-sectional outline of obtained lenslets has a satisfied parabolic profile and the numerical aperture (NA) of lenslets is more than 0.35. Furthermore, the focusing performance of the fabricated CMLA is also tested in this work and it has been demonstrated that the focusing power of the CMLA with a parabolic profile is better than that with a semi-circular one. [ABSTRACT FROM AUTHOR]

In this study, the temperature effects on hole geometry of the PMMA during micro-holes drilling by femtosecond laser has been studied under various pulse energy and number of pulse. The laser-induced hole’s diameter is considerably increased by 73% as the temperature rises from 20 °C to 90 °C. Remarkable enhancement in the removal volume of micro-hole is also observed under high temperature. The possible mechanism for such changes is discussed in detail on account of optical absorption enhancement and higher density of surface plasma. The atomic percentage of oxygen obviously increases with the increase of temperature, which is beneficial to femtosecond laser fabrication of PMMA micro-hole. The spatter area of micro-hole has been found to tremendously extend with the increase of temperature, which is due to recoil pressure effect. These results demonstrate that temperature plays a crucial role to tailor micro-hole fabrication by femtosecond laser. [ABSTRACT FROM AUTHOR]

A highly sensitive strain sensor based on a novel fiber in line Mach-Zehnder interferometer (MZI) was demonstrated experimentally. The MZI was realized by splicing a section of photonic crystal fiber (PCF) with the same length of thin core fiber (TCF) between two single mode fibers (SMFs). The fringe visibility of MZI can reach as high as 20 dB in air. In particular, the strain sensitivity of -1.95 pm/µe was achieved within a range from 0 to 4000 µe. Furthermore, the strain properties of different length of MZI was investigated. It was found that the sensitivity was weekly dependent on the length of MZI. The strain sensitivities corresponding to the MZI with 35 mm PCF, 40 mm PCF and 45 mm PCF at 1550 nm band were -1.78 pm/µe, -1.73 pm/µe and -1.63 pm/µe, respectively. Additionally, the sensor has advantages of simple fabrication, compact size and high sensitivity as well as good fringe visibility [ABSTRACT FROM AUTHOR]