Abstracts:This paper aims to investigate the effect of laser solder jet bonding parameters to the solder joints in Head Gimbal Assembly. Laser solder jet bonding utilizes the fiber laser to melt solder ball in capillary. The molten solder is transferred to two bonding pads by nitrogen gas. The response surface methodology have been used to investigate the effects of laser energy, wait time, nitrogen gas pressure, and focal position on the shear strength of solder joints and the change of pitch static attitude (PSA). The response surface methodology is employed to establish the reliable mathematical relationships between the laser soldering parameters and desired responses. Then, multi-objective optimization is conducted to determine the optimal process parameters that can enhance the joint shear strength and minimize the change of PSA. The validation test confirms that the predicted value has good agreement with the actual value.

Abstracts:Epsilon-near-zero (ENZ) materials, including artificial metamaterials, have been advanced to mold laser beams and antenna-mediated radiated waves. Here we propose an efficient method to control Ohmic losses inherent to natural ENZ materials by the assembly of subwavelength structures in a nonperiodic matrix constituting an ENZ metacoating. Implemented over plano-concave transparent substrates whose radius can be of only a few wavelengths, ENZ surface-relief elements demonstrate to adequately shape a plane wave into highly localized fields. Furthermore, our proposal provides an energy efficiency even higher than an ideally-lossless all-ENZ plano-concave lens. Our procedure is satisfactory to generate aberration-free nonparaxial focused waves and accelerating beams in miniaturized spaces.

Abstracts:Integration of infrared polarization and intensity images has been a new topic in infrared image understanding and interpretation. The abundant infrared details and target from infrared image and the salient edge and shape information from polarization image should be preserved or even enhanced in the fused result. In this paper, a new fusion method is proposed for infrared polarization and intensity images based on the improved multi-scale toggle operator with spatial scale, which can effectively extract the feature information of source images and heavily reduce redundancy among different scale. Firstly, the multi-scale image features of infrared polarization and intensity images are respectively extracted at different scale levels by the improved multi-scale toggle operator. Secondly, the redundancy of the features among different scales is reduced by using spatial scale. Thirdly, the final image features are combined by simply adding all scalesof feature images together, and a base image is calculated by performing mean value weighted method on smoothed source images. Finally, the fusion image is obtained by importing the combined image features into the base image with a suitable strategy. Both objective assessment and subjective vision of the experimental results indicate that the proposed method obtains better performance in preserving the details and edge information as well as improving the image contrast.

Abstracts:A new type of graphene oxide (GO) is successfully prepared using an improved modified Hummers method. The Raman shift, X-ray diffraction (XRD), and scanning electron microscope (SEM) measurement techniques are used to characterize the GO. An efficient and compact Q-switched green laser based on Nd:YVO4/PPLN is demonstrated with a few-layered GO as the saturable absorber. Our experimental results show that such a few-layered GO saturable absorber allows for the generation of a stable Q-switched laser pulse centered at 532.1nm with a 3dB spectral bandwidth of 2.78nm, a repetition rate of 71.4kHz, and a pulse duration of 98ns. The maximum average output power of 536mW is obtained at the absorbed pump power of 5.16W, corresponding to an optical conversion efficiency of 10.3%.

Abstracts:In the 3D laser forming process, developing an appropriate laser scan pattern for producing specimens with high quality and uniformity is critical. This study presents certain principles for developing scan paths. Seven scan path parameters are considered, including: (1) combined linear or curved path; (2) type of combined linear path; (3) order of scan sequences; (4) the position of the start point in each scan; (5) continuous or discontinuous scan path; (6) direction of scan path; and (7) angular arrangement of combined linear scan paths. Regarding these path parameters, ten combined linear scan patterns are presented. Numerical simulations show continuous hexagonal, scan pattern, scanning from outer to inner path, is the optimized. In addition, it is observed the position of the start point and the angular arrangement of scan paths is the most effective path parameters. Also, further experimentations show four sequences due to creat symmetric condition enhance the height of the bowl-shaped products and uniformity. Finally, the optimized hexagonal pattern was compared with the similar circular one. In the hexagonal scan path, distortion value and standard deviation rather to edge height of formed specimen is very low, and the edge height despite of decreasing length of scan path increases significantly compared to the circular scan path. As a result, four-sequence hexagonal scan pattern is proposed as the optimized perimeter scan path to produce bowl-shaped product.

Abstracts:A novel structure of segment cladding fiber (SCF) with characteristics of bend-resistance and large-mode-area (LMA) is proposed. In this new structure, the high refractive index (RI) core is periodically surrounded by high RI fan-segmented claddings. Numerical investigations show that effective single-mode operation of the proposed fiber with mode field area of 700μm² can be achieved when the bending radius is 15cm. Besides, this fiber is insensitive to the bending orientation at the ranging of [−180°, 180°]. The proposed design shows great potential in high power fiber lasers and amplifiers with compact structure.

Abstracts:In this study, a double-layer Ti (C, N) film was successfully prepared on Ti-6Al-4V alloy by a series of YAG laser irradiation in nitrogen atmosphere, aiming at improving the wear resistance. The effects of laser irradiation pass upon surface chemical composition, microstructures and hardness were investigated. The results showed that the surface chemicals were independent from laser irradiation pass, which the up layer of film was a mixture of TiN and TiC0.3N0.7, and the down layer was nitrogen-rich α-Ti. Both the surface roughness and hardness increased as raising the irradiation passes. However, surface deformation and cracks happened in the case above 3 passes’ irradiation. The wear resistance of laser modified sample by 3 passes was improved approximately by 37 times compared to the as received substrate. Moreover, the cytotoxic V ion released from laser modified sample was less than that of as received Ti-6Al-4V alloy in SBF, suggesting the potentiality of a new try to modify the sliding part of Ti-based hard tissue implants in future biomedical application.

Abstracts:With the aim to explore the formation mechanisms of surface underfill, full penetration laser welding of thick stainless steel was conducted, with the use of a 10kW fiber laser. A modified “sandwich” specimen was used, so as to directly observe the dynamic behaviors of the keyhole, vapor plume, and melt pool with the formation of underfills. On the basis of the experimental investigations, the formation mechanisms of the underfills at the top surface and bottom surface were analyzed. The results show that the downward flow of the molten metal caused by the recoil momentum is a crucial driver for formation of the underfill on the top surface. At full penetration of the melt, a deep underfill with a periodic wide–narrow–wide serrated pattern is formed on the top surface of the weld owing to the periodic fluctuation of the rear keyhole wall. At full penetration of the keyhole, the formation of a deep underfill on the top surface of the weld and undercut on the bottom surface of the weld is presented with massive direct melt loss from the weld pool.

Abstracts:In this study the structure and properties of PA12 (Polyamide 12) and PBT (polybutylene terephthalate) blend specimens manufactured by SLS using a CO2 laser were investigated. The microstructures of PA12/PBT blend specimens were found to be dependent on the PBT content. The higher values for the flexural modulus and ultimate strength presented by 90/10 PA12/PBT specimens indicated the hardening effect of low quantities of PBT particles in the PA12 matrix, which provides higher stiffness. The visco-elastic and fatigue test results for the PA12/PBT 90/10 blend also suggest an elastic characteristic for this blend composition. The potential application in the manufacturing of blend parts with a composition of 90/10 PA12/PBT with high stiffness and fatigue resistance using SLS was verified.

Abstracts:Third-order nonlinear response of synthesized polyethylene glycol coated Fe3O4 nanoparticles dispersed in a suitable solvent, polyethylene glycol has been studied. The structural characterization of the synthesized magnetite nanoparticles were carried out. The linear optical property of the synthesized magnetite nanoparticles was investigated using UV-visible technique. Both closed and open aperture Z-scan techniques have been performed at 532nm with pulse width 5ns and repetition rate 10Hz. It was found that polyethylene glycol coated magnetite exhibits reverse saturable absorption, with significant nonlinear absorption coefficient. Two-photon absorption intensity dependent positive nonlinear refraction coefficients indicate self focusing phenomena. Results show that higher concentration gives better nonlinear and optical limiting properties.