The elemental micro-segregation characteristic within the weld zone for ytterbium fiber laser welded Hastelloy C-276sheet was investigated. The analysis of segregation ratio and equilibrium distribution coefficient of...The elemental micro-segregation characteristic within the weld zone for ytterbium fiber laser welded Hastelloy C-276sheet was investigated. The analysis of segregation ratio and equilibrium distribution coefficient of elements, determined throughEDS data, indicate the reduction in micro-segregation of elements compared with the previous reported literatures for laser weldedHastelloy C-276. High melting efficiency of ytterbium fiber laser, reduction in the amount of linear heat input, and high cooling rateof the mushy zone lead to the reduction in micro-segregation. The melting efficiency of ytterbium fiber laser for welding of HastelloyC-276 of 64% is higher than that （48%） of conventional welding methods. High melting efficiency leads to the reduction in the linearheat input required for welding. Hence, in the present investigation, the same was found to substantially reduce as compared to theprevious reported literature. The cooling rate from liquidus temperature to solidus temperature at the weld centerline was found to bein the order of 10^3℃/s. Cellular dendritic substructure that constituted for lower micro-segregation was formed at the weldcenterline.展开更多
To obtain the stable operation of erbium-doped fibre laser, the simple and ideal technology is adopted by use of the erbium doped polarization maintaining fibre （EDPMF）. The design criteria of the Panda-type EDPMF a...To obtain the stable operation of erbium-doped fibre laser, the simple and ideal technology is adopted by use of the erbium doped polarization maintaining fibre （EDPMF）. The design criteria of the Panda-type EDPMF are presented, which take into account the cutoff wavelength, mode field diameter, modal birefringence and background loss. Four groups of optimum structural paramcter combinations are determined in terms of the design criteria. Two kinds of the Panda-type EDPMFs are selected to be fabricated. The fabrication process and the parameter control of the Panda-type EDPMFs are presented in detail. Their refractive index profiles, birefringence and absorption spectra are experimentally investigated. The absorption coefficient of the EDPMF, whose core is co-doped with Bi, Ga, A1 and Ge, is about 57.9dB/m at 1.53μm. Co-doping Bi, Ga and A1 can greatly increase the erbium concentration in the silica-based fibre. The high birefringence is obtained for the Panda-type EDPMF. The group birefringence of the EDPMF, whose outer cladding diameter is 125 μm, is about 4.8 × 10%^-4.展开更多
A novel structure for efficient side-coupling of high power double-cladding fiber lasers is presented. The maximum cou- pling efficiency of this structure is more than 90% for TM-polarization in the +1 and -1 order bu...A novel structure for efficient side-coupling of high power double-cladding fiber lasers is presented. The maximum cou- pling efficiency of this structure is more than 90% for TM-polarization in the +1 and -1 order but is only 40% for TE- polarization. Thus, a multi-layer stair-structure is introduced and optimized by combining transmission algorithm and genetic algorithm to obtain higher coupling efficiencyηfor TE-polarization and the maximum coupling efficiency almost reaches to 70%.展开更多
文摘The elemental micro-segregation characteristic within the weld zone for ytterbium fiber laser welded Hastelloy C-276sheet was investigated. The analysis of segregation ratio and equilibrium distribution coefficient of elements, determined throughEDS data, indicate the reduction in micro-segregation of elements compared with the previous reported literatures for laser weldedHastelloy C-276. High melting efficiency of ytterbium fiber laser, reduction in the amount of linear heat input, and high cooling rateof the mushy zone lead to the reduction in micro-segregation. The melting efficiency of ytterbium fiber laser for welding of HastelloyC-276 of 64% is higher than that （48%） of conventional welding methods. High melting efficiency leads to the reduction in the linearheat input required for welding. Hence, in the present investigation, the same was found to substantially reduce as compared to theprevious reported literature. The cooling rate from liquidus temperature to solidus temperature at the weld centerline was found to bein the order of 10^3℃/s. Cellular dendritic substructure that constituted for lower micro-segregation was formed at the weldcenterline.
文摘To obtain the stable operation of erbium-doped fibre laser, the simple and ideal technology is adopted by use of the erbium doped polarization maintaining fibre （EDPMF）. The design criteria of the Panda-type EDPMF are presented, which take into account the cutoff wavelength, mode field diameter, modal birefringence and background loss. Four groups of optimum structural paramcter combinations are determined in terms of the design criteria. Two kinds of the Panda-type EDPMFs are selected to be fabricated. The fabrication process and the parameter control of the Panda-type EDPMFs are presented in detail. Their refractive index profiles, birefringence and absorption spectra are experimentally investigated. The absorption coefficient of the EDPMF, whose core is co-doped with Bi, Ga, A1 and Ge, is about 57.9dB/m at 1.53μm. Co-doping Bi, Ga and A1 can greatly increase the erbium concentration in the silica-based fibre. The high birefringence is obtained for the Panda-type EDPMF. The group birefringence of the EDPMF, whose outer cladding diameter is 125 μm, is about 4.8 × 10%^-4.
文摘A novel structure for efficient side-coupling of high power double-cladding fiber lasers is presented. The maximum cou- pling efficiency of this structure is more than 90% for TM-polarization in the +1 and -1 order but is only 40% for TE- polarization. Thus, a multi-layer stair-structure is introduced and optimized by combining transmission algorithm and genetic algorithm to obtain higher coupling efficiencyηfor TE-polarization and the maximum coupling efficiency almost reaches to 70%.
