Unlike a traditional fiber laser with a defined resonant cavity, a random fiber laser(RFL), whose operation is based on distributed feedback and gain via Rayleigh scattering(RS) and stimulated Raman scattering in a lo...Unlike a traditional fiber laser with a defined resonant cavity, a random fiber laser(RFL), whose operation is based on distributed feedback and gain via Rayleigh scattering(RS) and stimulated Raman scattering in a long passive fiber, has fundamental scientific challenges in pulsing operation for its remarkable cavity-free feature. For the time being, stable pulsed RFL utilizing a passive method has not been reported. Here, we propose and experimentally realize the passive spatiotemporal gain-modulation-induced stable pulsing operation of counterpumped RFL. Thanks to the good temporal stability of an employed pumping amplified spontaneous emission source and the superiority of this pulse generation scheme, a stable and regular pulse train can be obtained.Furthermore, the pump hysteresis and bistability phenomena with the generation of high-order Stokes light is presented, and the dynamics of pulsing operation is discussed after the theoretical investigation of the counterpumped RFL. This work extends our comprehension of temporal property of RFL and paves an effective novel avenue for the exploration of pulsed RFL with structural simplicity, low cost, and stable output.展开更多
A new type of commercial reactor is first built up in China.This paper briefly describesits performances,working foundamentals and various possible uses.The reactor uses urani-um-zirconium hydride as fuel element and ...A new type of commercial reactor is first built up in China.This paper briefly describesits performances,working foundamentals and various possible uses.The reactor uses urani-um-zirconium hydride as fuel element and has a large prompt negative temperature coefficientof reactivity,featuring inherent safety and a fairly high pulsed-power capacity.展开更多
Stimulated Raman scattering （SRS） of picosecond pulses is investigated in a new crystal SrWO4. The second harmonic generation of a mode-locked Nd：YAG laser system is used as the pump source. In an external singlepa...Stimulated Raman scattering （SRS） of picosecond pulses is investigated in a new crystal SrWO4. The second harmonic generation of a mode-locked Nd：YAG laser system is used as the pump source. In an external singlepass configuration, the SRS thresholds for the first to the fourth Stokes lines are measured. For the first Stokes line, the steady-state gain coefficient of the SrWO4 crystal is calculated to be 15.96cm//GW. In our experiment, as many as five Stokes lines （559.23 nm, 589.61 nm, 623.49 nm, 661.50 nm, 704.44 nm） and three anti-Stokes lines （506.97nm, 484.34 nm, 463.65nm） are observed, and the total conversion efficiency is as high as 62%.展开更多
The behavior of a RF-excited waveguide CO2 laser in the pulse regime is studied theoretically. The output pulse evolution is studied by applying three types of pulses namely the square, sine and the triangular ones as...The behavior of a RF-excited waveguide CO2 laser in the pulse regime is studied theoretically. The output pulse evolution is studied by applying three types of pulses namely the square, sine and the triangular ones as the excitation pulses. The frequency dependence behavior of the output pulse is also presented.展开更多
Dielectric elastomer actuators(DEAs)are a class of artificial muscles capable of large linear strains(well over 100%),and with high energy density,and low cost and weight.One of the most prominent failure modes of a D...Dielectric elastomer actuators(DEAs)are a class of artificial muscles capable of large linear strains(well over 100%),and with high energy density,and low cost and weight.One of the most prominent failure modes of a DEA is electrical breakdown,which can damage the device permanently,limiting its deformation capability.Breakdown is also common,since to maximize energy output,devices often operate near the breakdown limit.Elucidating breakdown mechanisms,as well as finding ways to prevent it,are of intense research interest.We show that by applying short electrical pulses,one could minimize the exposure of the DEAs to high leakage current,which is one of the main mechanisms for electrical breakdown.This allows one to operate at significantly higher potentials than the DC breakdown voltage.By applying pulses,we demonstrate up to 81.7%area strain repeatedly,at voltages more than twice the DC breakdown limit,without the risk of failure.The pulsed operation mode of DEAs accommodating higher voltages than possible with DC represents an opportunity for potential applications,safer and simpler device designs,and a technique for further study of DEA breakdown mechanisms.展开更多
真空界面是脉冲功率装置的薄弱环节,对于重频运行的系统,该问题更为突出.介绍了-种应用于重频脉冲驱动源的陶瓷绝缘子真空界面.首先依据真空沿面闪络设计原则给出了一种改进型同轴馈电陶瓷真空界面绝缘结构,该结构采用陶瓷-金属钎焊连...真空界面是脉冲功率装置的薄弱环节,对于重频运行的系统,该问题更为突出.介绍了-种应用于重频脉冲驱动源的陶瓷绝缘子真空界面.首先依据真空沿面闪络设计原则给出了一种改进型同轴馈电陶瓷真空界面绝缘结构,该结构采用陶瓷-金属钎焊连接形式;通过采取均压、屏蔽措施,静电场模拟结果显示,陶瓷沿面电场分布均勻,总场强小于1 0 0 k V /c m ,沿面分量小于70k V /c m ,阴、阳极三结合点场强均小于4 0 k V /c m ;在输出幅值600 k V 、脉宽80 n s、重复频率1-5 H z 可调的脉冲功率驱动源上进行了实验测试,陶瓷真空界面平均绝缘场强达到4 4 k V /c m ,运行稳定;采取（0-1）分布对实验结果进行了统计分析,置信度取为0. 9 时,陶瓷真空界面的可靠度大于9 7 % .最后,还探讨了表面处理工艺对闪络电压的影响,实验发现,增加表面粗糙度可有效提高陶瓷绝缘子的闪络电压.展开更多
基金National Natural Science Foundation of China(NSFC)(61322505,61635005)Hunan Provincial Innovation Foundation for Postgraduate Student(CX2017B030)
文摘Unlike a traditional fiber laser with a defined resonant cavity, a random fiber laser(RFL), whose operation is based on distributed feedback and gain via Rayleigh scattering(RS) and stimulated Raman scattering in a long passive fiber, has fundamental scientific challenges in pulsing operation for its remarkable cavity-free feature. For the time being, stable pulsed RFL utilizing a passive method has not been reported. Here, we propose and experimentally realize the passive spatiotemporal gain-modulation-induced stable pulsing operation of counterpumped RFL. Thanks to the good temporal stability of an employed pumping amplified spontaneous emission source and the superiority of this pulse generation scheme, a stable and regular pulse train can be obtained.Furthermore, the pump hysteresis and bistability phenomena with the generation of high-order Stokes light is presented, and the dynamics of pulsing operation is discussed after the theoretical investigation of the counterpumped RFL. This work extends our comprehension of temporal property of RFL and paves an effective novel avenue for the exploration of pulsed RFL with structural simplicity, low cost, and stable output.
基金the Commission of Science,Technology and Industry for National Defence
文摘A new type of commercial reactor is first built up in China.This paper briefly describesits performances,working foundamentals and various possible uses.The reactor uses urani-um-zirconium hydride as fuel element and has a large prompt negative temperature coefficientof reactivity,featuring inherent safety and a fairly high pulsed-power capacity.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50590401 and 60508010.
文摘Stimulated Raman scattering （SRS） of picosecond pulses is investigated in a new crystal SrWO4. The second harmonic generation of a mode-locked Nd：YAG laser system is used as the pump source. In an external singlepass configuration, the SRS thresholds for the first to the fourth Stokes lines are measured. For the first Stokes line, the steady-state gain coefficient of the SrWO4 crystal is calculated to be 15.96cm//GW. In our experiment, as many as five Stokes lines （559.23 nm, 589.61 nm, 623.49 nm, 661.50 nm, 704.44 nm） and three anti-Stokes lines （506.97nm, 484.34 nm, 463.65nm） are observed, and the total conversion efficiency is as high as 62%.
文摘The behavior of a RF-excited waveguide CO2 laser in the pulse regime is studied theoretically. The output pulse evolution is studied by applying three types of pulses namely the square, sine and the triangular ones as the excitation pulses. The frequency dependence behavior of the output pulse is also presented.
基金funding support from the European Research Council(ERC)grant EMATTER[#280078]the ESNAM COST action(MP 1003)support for attending the DEA workshop in Darmstadt,Germany.
文摘Dielectric elastomer actuators(DEAs)are a class of artificial muscles capable of large linear strains(well over 100%),and with high energy density,and low cost and weight.One of the most prominent failure modes of a DEA is electrical breakdown,which can damage the device permanently,limiting its deformation capability.Breakdown is also common,since to maximize energy output,devices often operate near the breakdown limit.Elucidating breakdown mechanisms,as well as finding ways to prevent it,are of intense research interest.We show that by applying short electrical pulses,one could minimize the exposure of the DEAs to high leakage current,which is one of the main mechanisms for electrical breakdown.This allows one to operate at significantly higher potentials than the DC breakdown voltage.By applying pulses,we demonstrate up to 81.7%area strain repeatedly,at voltages more than twice the DC breakdown limit,without the risk of failure.The pulsed operation mode of DEAs accommodating higher voltages than possible with DC represents an opportunity for potential applications,safer and simpler device designs,and a technique for further study of DEA breakdown mechanisms.
文摘真空界面是脉冲功率装置的薄弱环节,对于重频运行的系统,该问题更为突出.介绍了-种应用于重频脉冲驱动源的陶瓷绝缘子真空界面.首先依据真空沿面闪络设计原则给出了一种改进型同轴馈电陶瓷真空界面绝缘结构,该结构采用陶瓷-金属钎焊连接形式;通过采取均压、屏蔽措施,静电场模拟结果显示,陶瓷沿面电场分布均勻,总场强小于1 0 0 k V /c m ,沿面分量小于70k V /c m ,阴、阳极三结合点场强均小于4 0 k V /c m ;在输出幅值600 k V 、脉宽80 n s、重复频率1-5 H z 可调的脉冲功率驱动源上进行了实验测试,陶瓷真空界面平均绝缘场强达到4 4 k V /c m ,运行稳定;采取（0-1）分布对实验结果进行了统计分析,置信度取为0. 9 时,陶瓷真空界面的可靠度大于9 7 % .最后,还探讨了表面处理工艺对闪络电压的影响,实验发现,增加表面粗糙度可有效提高陶瓷绝缘子的闪络电压.
