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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]

Sintering pressed nanocomposites to obtain fused silica glasses was a simple and efficient method, while the binder plays an essential role in this process. This paper studied the influence of binder polyethylene glycol (PEG) with different molecular weights on sintering quality. The pH, viscosity, and thermal analysis of nanocomposites were analyzed. PEG of different molecular weights affects the size r of aggregated silica particles by influencing the viscosity of the suspension system and the interaction f of PEG-SiO2, which affects the specific heat capacity (Cp) and initial fusing temperature (Ti) finally. It was found that the pressed part with PEG-6000 could be densified completely after vacuum sintering for 30 min, comparing the optical images and SEM images. However, the rest pressed parts to have suboptimal optical quality since seam defects. The sintering quality of pressed parts was closely related to the trend of initial fusing temperature Ti with PEG molecular weight, and in the event of lower temperature Ti, the better sintering quality. Highlights: Transparent fused silica glass was prepared with the binder of PEG and PVB. PEG molecular weights affect the quality of sintered parts owing to the suspension viscosity as well as the specific heat capacity (Cp) and initial fusing temperature (Ti) with different. The PEG-6000 has the best performance according to the optical and sintering quality. [ABSTRACT FROM AUTHOR]

In this paper, the nano-silver paste-based femtosecond laser-assisted copper interconnection process was optimized by pickling modification of the copper surface and preheating treatment of the silver paste, which significantly improved the copper interconnection strength. Meanwhile, the effect of the height and consistency of the copper surface array microstructure prepared by femtosecond laser on the copper interconnection strength was investigated. The results demonstrated that the copper interconnection strength is mainly influenced by the high consistency of the surface array microstructure. In addition, for the pickling modification treatment process of the copper surface, the strength of copper interconnection under the modification of a weak acid (8% acetic acid) and a strong acid (3% hydrochloric acid) was studied. The shear strength of sintered joint could reach 41.64 MPa under weak acid corrosion conditions, about 2 times higher than the strong acid corrosion conditions. Finally, the temperature and stress distribution of copper interconnection in service were analyzed by finite element simulation, and the lifetimes were predicted under temperature cycling conditions (− 50 °C to 250 °C). The results proved that the reliability of sintered structure could meet the operational requirements.Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary.The authors and their respective affiliations are correct [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]

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]

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]

In this study, a highly reliable and effective method for copper bonding using femtosecond laser-fabricated microscale tapers array and Ag–Zn–Cu intermetallic compounds as assistants is proposed. By the growth of intermetallic compounds among the microscale tapers array, the copper interfaces were firmly sintered. The cross section after shearing test was marked for analysis of sintering quality. Also, the shearing strength of interconnected copper interfaces under different bonding temperature, and holding times was investigated. The results show that the shearing strength can reach up to 120.1 MPa under 300 °C bonding temperature and 30 min holding time. According to the interconnected cross section and shearing strength test, the mechanism of increased shearing strength is explained. The experimental results show that the shearing strength of interconnected interface is greatly enhanced by the increase of contact area caused by microscale tapers array and the mechanical locking caused by the growth of intermetallic compounds. More possibilities could be provided by this technology in the field of electronic packaging interconnection and three-dimensional integrated circuits. [ABSTRACT FROM AUTHOR]

A novel fiber inline Mach-Zehnder interferometer (MZI) is proposed for simultaneous measurement of curvature and temperature. The sensor composes of single mode-multimode-dispersion compensation-multimode-single mode fiber (MMF-DCF-MMF) structure, using the direct fusion technology. The experimental results show curvature sensitivities of −12.82 nm/m−1 and −14.42 nm/m−1 in the range of 0–0.65 m−1 for two resonant dips, as well as temperature sensitivities of 57.6 pm/°C and 74.3 pm/°C within the range of 20 °C–150 °C. In addition, the sensor has unique advantages of easy fabrication, low cost, high fringe visibility of 24dB, and high sensitivity, which shows a good application prospect in dual-parameters of sensing of curvature and temperature. [ABSTRACT FROM AUTHOR]

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]

Sapphire, with extremely high hardness, high-temperature stability and wear resistance, often corroded in molten KOH at 300 °C after processing. The fabrication of microstructures on sapphire substrate performed by femtosecond laser irradiation combined with KOH solution chemical etching at room temperature is presented. It is found that this method reduces the harsh requirements of sapphire corrosion. After femtosecond irradiation, the sapphire has a high corrosion speed at room temperature. Through the analysis of Raman spectrum and XRD spectrum, a novel insight of femtosecond laser interaction with sapphire (α-AlO) is proposed. Results indicated that grooves on sapphire surface were formed by the lasers ablation removal, and the groove surface was modified in a certain depth. The modified area of the groove surface was changed from α-AlO to γ-AlO. In addition, the impacts of three experimental parameters, laser power, scanning velocities and etching time, on the width and depth of microstructures are investigated, respectively. The modified area dimension is about 2 μm within limits power and speed. This work could fabricate high-quality arbitrary microstructures and enhance the performance of sapphire processing. [ABSTRACT FROM AUTHOR]

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]

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]

We give a systematic experimental study of multipulse bunches in a graphene oxide saturable absorber (GOSA) passively mode-locked all-normal dispersion ytterbium-doped fiber laser (YDFL). Some special phenomena such as harmonic multipulse bunches, harmonic mode-locking, and chaotic multipulse states are also obtained. Our experiment reveals that the inserted 2.5-nm narrow bandwidth filter plays an important role in the formation of multipulse in all-normal dispersion fiber lasers. Because of the effective gain bandwidth depends on both the 2.5-nm narrow bandwidth filter and the artificial fiber birefringence filter, the multipulse operation states are sensitive to the polarization. It is the first demonstration of multipulse evolution in a GOSA passively mode-locked all-normal dispersion YDFL. [ABSTRACT FROM AUTHOR]

In this paper, a kind of bi-layered asymmetrical split ring metamaterial was proposed as a circular polarization converter. Simulations and experiments at the microwave regime showed that the proposed structures can achieve the conversions from right-handed circularly polarized electromagnetic waves to left-handed ones and the reversed conversions in the opposite propagating direction. The linear to circular polarization transmission coefficients and the surface currents were investigated to understand the mechanism of the circular polarization conversions. Moreover, we optimized the proposed metamaterials by increasing the distance between the two metal layers. The proposed circular polarization converters have applications in microwave wave plates and metamaterial antennas. [ABSTRACT FROM AUTHOR]

Femtosecond laser (fs) ablation is an effective method to processing waveguide, microfluidic channel and other functional devices in fused silica glass. The accuracy of ablation is critical for high-performance devices. In this paper, a double-pulse femtosecond laser was used to control the surface ablation threshold of fused silica. It was found that, when the delay time of the double pulses ranged from 0 to 100 ps, with the increasing of delay time, the ablation threshold first rapidly increased to the maximum value, then fell to a stable value. And the overall threshold was higher than the threshold at 0 ps, which means the processing accuracy could be significantly improved. By simulating the relationship between the maximum electron density of conduction band and the time delay, it can conclude that the modification of threshold was caused by the difference of maximum electron density. In addition, to find the more optimized processing parameters, we also studied the weights of the two sub-pulses at 10 ps. These results provide an important reference for ultra-precision machining. [ABSTRACT FROM AUTHOR]

Rear damage around cutting edge reduces its mechanical strength, which confines the application of femtosecond (fs) laser cutting thin fused silica. In this paper, we report a method by liquid-assisted cutting to minimize the damage. The surface morphology and area of damage are investigated. It is found that the damage can be decreased by altering the polarization from perpendicular (S-polarization) to be parallel (P-polarization) to the plane incidence, owing to the decrease of reflectivity on the boundary during fs laser cutting. Based on this theory, we further reduce the reflection on the rear side of the glass by adding water. Experienced twice scans, the damage area per unit length along cutting direction can be reduced from 41.84 to 1.88 μm2 by water cutting. This method can open up prospects for high precision fabrication of thin transparent material. [ABSTRACT FROM AUTHOR]