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To achieve a damage-controllable and earthquake-resilient steel frame with more feasible and simple dissipative devices, an innovative steel moment-resisting connection with bolted ductile double T-stub fuses is developed in this work. These T-stubs with appropriate free deformation length in the stems, made of Low-Yield-Point (LYP) steels instead of ordinary steels, simultaneously behave as connectors, bearing elements, and replaceable dissipative fuses that benefit from the inherent excellent ductility, dissipation capacity, and fatigue performance of the LYP materials. The cyclic responses of the connections with LYP T-stubs subjected to different weakening strategies are explored and compared via extensive nonlinear numerical parametric analyses. Subsequently, the influences of the free deformation length and the weakened degree of the T-stub stem on the seismic performance and the structural fuse effect are evaluated. Finally, optimal design suggestions for this connection are proposed, which provide a reference for engineering applications. Analytical results demonstrate that properly designed LYP T-stubs with various weakened parameters can act as structural fuses by dissipating more than 90% of the system energy and concentrating most of the plasticity and damage, which effectively protect the main structural members from damage while being subjected to seismic excitations. Besides, due to low yield strengths, to achieve an identical weakened degree, the T-stubs made of LYP steels are stockier than the ones made of traditional or high-strength steels. This feature is able to avoid serious local buckling of stem plates and significant strength degradation, thus is conducive to the improvement of the ductility. By comprehensively considering the construction advantages, ductility, dissipation capacity, structural fuse performance, and material efficiency, LYP T-stub with a relatively thin stem is a more promising solution. The method of increasing the free deformation length of the stem effectively controls the damage within the LYP T-stubs, adequately improves the effect of structural fuses, and further lowers the required weakened degree; thus, the protection of primary frame members is achieved without excessively reducing the strength of the connection. Nevertheless, the T-stub fuses with overly-large free deformation lengths and thin stem plates tend to buckle substantially, resulting in significant strength deterioration that adversely decreases the ductility of the connections. As a result, an optimal solution with a satisfactory weakened degree and an appropriate free deformation length (α d = 0.8 and l e = 1.0 b ts) is suggested as a good compromise among the material efficiency, dissipation and ductility capacities, and structural fuse performance. • An innovative connection with ductile and dissipative T-stub fuses is developed. • Cyclic responses of connections with LYP T-stubs having different weakening strategies are explored. • Optimal suggestions are proposed through evaluating the influence of key parameters. [ABSTRACT FROM AUTHOR]

• Laser performance of LD side-pumped Er:LuYSGG bonding crystal was demonstrated. • Maximum output power of 20.76 W is achieved and improved effectively by bonding. • M 2 factors of 6.80/6.74 of the bonding crystal are better than that of un-bonding one. • Er:LuYSGG bonding crystal is a promising 2.8 μm gain element operated at high power. We demonstrate the laser performance of 970 nm LD side-pumped LuYSGG/Er:LuYSGG/LuYSGG bonding crystal in a frequency range of 50–800 Hz. The thermal distribution simulation implies that the bonded Er:LuYSGG crystal possesses a higher cooling efficiency compared with the un-bonded one. The maximum average power of 20.76 W is realized at a frequency of 150 Hz and a pulse width of 200 μs, corresponding to a slope efficiency of 23.94 % and optical-to-optical conversion efficiency of 19.22 %. A single laser wavelength of 2797.5 nm is observed. The M 2 factors of the bonding rod are 6.80/6.74, indicating a relatively high beam quality. Therefore, the LuYSGG/Er:LuYSGG/LuYSGG bonding crystal exhibits an improvement of laser performance operated at 2.8 μm due to excellent heat dissipation ability, which is a promising gain element and can be applied to the harsh radiation environment. [ABSTRACT FROM AUTHOR]

• High-quality Ho:YAP crystal was fabricated by the Czochralski method. • The structure, spectroscopy and J-O parameters of Ho:YAP were discussed. • For the first time, ∼3 μm CW laser was realized in single Ho-doped crystal host. • Maximum power of 176 mW and slope efficiency of 3.36% was obtained. We demonstrate the spectroscopy and mid-infrared laser performance on the Ho:YAP oxide crystal grown by the Czochralski method in detail. The crystal belongs to orthorhombic system of Pnmb (62) space group and shows high crystalline quality. The lifetimes of 5I 6 and 5I 7 levels are 0.412 and 4.485 ms, respectively. Particularly, under 1150 nm Raman fiber laser pumping, a 3.01 μm CW laser with a maximum power of 181 mW and slope-efficiency of 3.35% is achieved. The M2 factor of 1.35/1.37 indicates that the yield laser has excellent beam quality. The results reveal that the Ho:YAP crystal possesses great potential for developing efficient 3.0 μm mid-infrared lasers. [ABSTRACT FROM AUTHOR]

• Cascade Er:YSGG crystal pulsed lasers near 1.6 and 2.8 μm are realized at room temperature. • The slope efficiency of MIR laser increases to 4.2 % from 1.9 % by cascade process. • Four laser wavelengths of 2.793, 2.821, ∼2.860, 2.917 μm in Er:YSGG laser are discovered. • The cascade process can improve the MIR laser performance based on the Er:YSGG crystal. We demonstrate a pulsed cascade laser on LD end-pumped Er:YSGG crystal near 1.6 and 2.8 μm at room temperature for the first time. The slope efficiency of mid-infrared laser with the assistance of cascade process is significantly improved. Under the working frequency of 100 Hz and pump pulse width of 6 ms, a maximum power of 243 mW centered at 2.79 μm is achieved with increasing slope efficiency of 4.2 %, while the slope efficiency of non-cascade is only 1.9 %. Under high pump power, four laser wavelengths of 2.793, 2.821, ∼2.860, and 2.918 μm are discovered and the phenomenon is explained according to the Boltzmann factors. This work would be conducive to the exploration of pulsed cascade laser based on the Er:YSGG crystal. [ABSTRACT FROM AUTHOR]

• Influence of 60Co gamma-ray irradiation on the Er:LuYSGG crystal was demonstrated. • Maximum average output power of 886 mW is achieved after irradiation. • Maximum output power and slope efficiency are reduced by only 2.5% and 3.7%. • Lifetime ratio between lower and upper laser levels is reduced after irradiation. • Er:LuYSGG crystal is a potential 2.79 μm radiation-resistant laser material. We demonstrate the influence of gamma-ray irradiation on the structure, spectroscopies, and laser performance of Er:LuYSGG crystal. After 100 Mrad 60Co gamma-ray irradiation, the crystal structure remains unchanged, the absorption near 968 nm and emission within 2.7 ∼ 3 μm are almost unaffected, the level lifetimes are reduced, and the maximum output power of 886 mW is achieved with a maximum slope efficiency of 20.8%. The maximum output power and slope efficiency decrease by only 2.5% and 3.7% after irradiation, respectively, and the M 2 factor is little affected by irradiation. The results indicate that the Er:LuYSGG crystal is a potential mid-infrared radiation-resistant laser material applied in radiation environments. [ABSTRACT FROM AUTHOR]

• Laser performance of LD side-pumped YSGG/Er:YSGG with concave end-faces is studied. • The laser rods with negative curvature radii of 250, 500 and 1000 mm are employed. • Highest power of 20.92 W with slope efficiency of 26.18% at 150 Hz is achieved. • 15.59 W at 500 Hz is obtained in rod with negative curvature radius of 500 mm. • Thermal bonding and concave end-faces can effectively improve laser performance. We demonstrate the laser performance of 970 nm LD side-pumped YSGG/Er:YSGG/YSGG thermal bonding crystal rods with negative curvature radii of 250, 500, and 1000 mm, respectively. The maximum average output powers of 20.04, 20.92, 17.02 W are achieved, corresponding to the slope efficiencies of 26.28%, 26.18%, 21.28%, and optical–optical efficiencies of 18.56%, 19.37%, 15.76%, respectively. The results of the laser performance and thermal focal length indicate that the negative curvature of 500 mm has an optimal effect on thermal lensing compensation. At the high repetition rate of 500 Hz, the average output power of 15.59 W is obtained. The beam quality factors of M x 2/M y 2 are calculated to be 3.37/3.34. These results can provide valuable references for promoting the development of 2.7–3 μm lasers. [ABSTRACT FROM AUTHOR]