A patent pending open-loop liquid crystal based variable optical attenuator is introduced. The temperature dependent performance is compensated through electric monitoring and adjustment utilizing liquid crystal's...A patent pending open-loop liquid crystal based variable optical attenuator is introduced. The temperature dependent performance is compensated through electric monitoring and adjustment utilizing liquid crystal's opto-electronic properties.展开更多
High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechani...High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechanical properties of these alloys remain poorly understood. Here, we systemically investigate the mechanical behaviors and properties of Al_(1.2)CrFeCoNi(comprising a body-centered cubic phase) and Al_(0.3)CrFeCoNi(comprising a face-centered cubic phase) single-crystal micropillars with three orientations([100], [110], and [111]) at temperatures varying from 300 to 675 K by using in situ compression of micropillars inside a scanning electron microscope. The results show that the yield stresses of Al_(1.2)CrFeCoNi micropillars are insensitive to temperature changes, and their flow stresses and work hardening rates increase slightly with increasing temperature from 300 to550 K, which differs from the typical temperature dependence of yield/flow stresses in metals and alloys. In contrast,Al_(0.3)CrFeCoNi micropillars exhibit typical thermal softening. Furthermore, it is found that the Al_(1.2)CrFeCoNi micropillars exhibit a transition from homogenous deformation to localized deformation at a critical temperature, while the Al_(0.3)CrFeCoNi micropillars always maintain a well-distributed and fine slip deformation. Detailed transmission electron microscopy analyses reveal that dynamic recrystallization(involving dislocation tangles, and formation of dislocation cell structures and sub-grains)plays a key role in the observed temperature insensitivity of the yield stress and increasing flow stress(and work hardening rate)with increasing temperature in the Al_(1.2)CrFeCoNi micropillars, and that thermally activated dislocation slip leads to thermal softening of the Al_(0.3)CrFeCoNi micropillars. The differences in deformation modes and temperature dependence of the mechanical properties between Al_(1.2)CrFeCoNi and Al_(0.3)CrFeCoNi essentially originate from the differences in dislocation activities and slip systems since the two alloys adopt different phases. Our findings provide key insights in the temperature dependence of mechanical properties and deformation behaviors of high-entropy alloys with body-centered cubic and face-centered cubic phases.展开更多
A high-birefringence fiber,Tb:YAG crystal-derived silica fiber(TYDSF),was fabricated by CO_(2)laser-heating drawing technique.Its linear birefringence was 2.99×10^(-5),and it was used to fabricate an all-fiber qu...A high-birefringence fiber,Tb:YAG crystal-derived silica fiber(TYDSF),was fabricated by CO_(2)laser-heating drawing technique.Its linear birefringence was 2.99×10^(-5),and it was used to fabricate an all-fiber quarter-wave plate(QWP)device.The polarization extinction ratio(PER)of the device was 0.29 dB,and its ellipticity was 44.26°at 25℃.In the temperature range of-5℃to 200℃,its PER was always less than 0.80 dB,and the fluctuation of PER and ellipticity was also small.Compared with QWPs fabricated with PANDA-type polarization-maintaining fiber(PMF)and elliptical-core PMF,the performance of TYDSF QWP was least sensitive to temperature.Furthermore,the TYDSF QWP was used in a high-power laser system,still maintaining good circular polarization state,and the nonlinear effects were suppressed in the system.The experimental results are of great significance to high-power lasers,fiber-optic current sensors,etc.,in harsh environments.展开更多
文摘A patent pending open-loop liquid crystal based variable optical attenuator is introduced. The temperature dependent performance is compensated through electric monitoring and adjustment utilizing liquid crystal's opto-electronic properties.
基金financial support from the National Natural Science Foundation of China (Grant Nos. 11522218, 11720101002)the Beijing Natural Science Foundation (Grant No. Z180014)+1 种基金the National Science and Technology Major Project (Grant No. 2017-VI-0003-0073)financial support from the National Science Foundation (Grant No. DMR-1709318)。
文摘High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechanical properties of these alloys remain poorly understood. Here, we systemically investigate the mechanical behaviors and properties of Al_(1.2)CrFeCoNi(comprising a body-centered cubic phase) and Al_(0.3)CrFeCoNi(comprising a face-centered cubic phase) single-crystal micropillars with three orientations([100], [110], and [111]) at temperatures varying from 300 to 675 K by using in situ compression of micropillars inside a scanning electron microscope. The results show that the yield stresses of Al_(1.2)CrFeCoNi micropillars are insensitive to temperature changes, and their flow stresses and work hardening rates increase slightly with increasing temperature from 300 to550 K, which differs from the typical temperature dependence of yield/flow stresses in metals and alloys. In contrast,Al_(0.3)CrFeCoNi micropillars exhibit typical thermal softening. Furthermore, it is found that the Al_(1.2)CrFeCoNi micropillars exhibit a transition from homogenous deformation to localized deformation at a critical temperature, while the Al_(0.3)CrFeCoNi micropillars always maintain a well-distributed and fine slip deformation. Detailed transmission electron microscopy analyses reveal that dynamic recrystallization(involving dislocation tangles, and formation of dislocation cell structures and sub-grains)plays a key role in the observed temperature insensitivity of the yield stress and increasing flow stress(and work hardening rate)with increasing temperature in the Al_(1.2)CrFeCoNi micropillars, and that thermally activated dislocation slip leads to thermal softening of the Al_(0.3)CrFeCoNi micropillars. The differences in deformation modes and temperature dependence of the mechanical properties between Al_(1.2)CrFeCoNi and Al_(0.3)CrFeCoNi essentially originate from the differences in dislocation activities and slip systems since the two alloys adopt different phases. Our findings provide key insights in the temperature dependence of mechanical properties and deformation behaviors of high-entropy alloys with body-centered cubic and face-centered cubic phases.
基金supported by the National Natural Science Foundation of China(Nos.61935002,61975113,and 62275148)111 Project(No.D20031)+1 种基金the Shanghai Professional Technical Public Service Platform of Advanced Optical Waveguide Intelligent Manufacturing and Testing(No.19DZ2294000)the Jiangsu Province’s Industry Outlook and Key Core Technologies–Key Projects(No.BE2022055-4)。
文摘A high-birefringence fiber,Tb:YAG crystal-derived silica fiber(TYDSF),was fabricated by CO_(2)laser-heating drawing technique.Its linear birefringence was 2.99×10^(-5),and it was used to fabricate an all-fiber quarter-wave plate(QWP)device.The polarization extinction ratio(PER)of the device was 0.29 dB,and its ellipticity was 44.26°at 25℃.In the temperature range of-5℃to 200℃,its PER was always less than 0.80 dB,and the fluctuation of PER and ellipticity was also small.Compared with QWPs fabricated with PANDA-type polarization-maintaining fiber(PMF)and elliptical-core PMF,the performance of TYDSF QWP was least sensitive to temperature.Furthermore,the TYDSF QWP was used in a high-power laser system,still maintaining good circular polarization state,and the nonlinear effects were suppressed in the system.The experimental results are of great significance to high-power lasers,fiber-optic current sensors,etc.,in harsh environments.
