基于MgO:APLN的1.57μm/3.84μm连续波内腔多光参量振荡器研究

报道了一种基于MgO:APLN实现1.57 μm和3.84 μm跨周期参量光连续输出的内腔抽运多光参量振荡器. 采用1064 nm谐振腔与多光参量振荡腔折叠型复合结构, 综合考虑高功率抽运下谐振腔的热稳定性及多光参量振荡过程的光斑模式匹配, 通过对两个子腔谐振结构的数值模拟分析, 确定了最佳腔型参数. 在此基础上, 进一步研究了谐振参量光透过率对振荡阈值、抽运光下转换效率、输出功率稳定性的影响, 最终实现了3.13 W的1.57 μm和0.85 W的3.84 μm参量光输出, 对应斜效率为6.8%和1.9%, 输出功率稳定性分别达到了1.8%和3%.     

参数不确定统一混沌系统的鲁棒分数阶比例-微分控制

针对含参数不确定的整数阶统一混沌系统, 提出一种鲁棒分数阶比例-微分(PD^μ)控制. 通过变换将受控统一混沌系统转换成等效被控对象及其等效控制器. 针对等效被控对象, 基于一种改进Monje-Vinagre方法并考虑到求解性能约束方程组的复杂度, 设计了鲁棒PD^μ控制器. 通过基于最小相角边界传递函数和最大增益边界传递函数的设计约束来保证受控统一混沌系统对参数不确定性的鲁棒性能. 数值仿真验证了所提出方法的有效性.     

基于MgO:QPLN的多光参量振荡器电场调谐特性理论与实验研究

报道了基于掺氧化镁准周期极化铌酸锂(MgO:QPLN)的多光参量振荡器电场调谐特性理论与实验研究. 通过对电场调谐能力与极化结构参数间关联性的理论分析, 确定了高正负晶畴比MgO:QPLN电场调谐的可行性, 并模拟得到跨周期参量光输出波长与加载电压的关系曲线. 实验中通过对MgO:QPLN有效的电场加载, 实现了3.84 μm波段参量光的电场调谐, 频谱调谐带宽约6 nm, 调谐速率接近1 nm/kV, 进一步结合温度调谐, 实现了参量光宽谱段高精度的连续调谐. 所获得实验结果与理论模拟结果基本符合, 电场调谐在精度控制、快速响应方面相比于传统温度调谐更具技术优势.     

Towards a new type of energy trap: Classical analog of quantum Landau-Zener tunneling

We present a novel type of an energy trap providing targeted energy transfer in a system of weakly coupled pendulums. Our approach is based on the analogy we revealed between the behavior of two weakly coupled classical parametric pendulums (in linear approximation) and the nonadiabatic Landau-Zener tunneling in a two-state quantum system. This analogy leads us to the prediction of an efficient irreversible transfer of vibration energy from one subsystem to another, when the eigenfrequency of at least one of them changes in time, so that the coupled subsystems pass through an internal resonance. The existence of such a phenomenon is not restricted to coupled pendulums, but is inherent to a wide class of both linear and nonlinear parametric oscillatory systems. This opens up the possibility of designing new types of energy traps and absorbers for the dynamic protection of various mechanical systems.     

轴向变速粘弹性Rayleigh梁参数共振稳定性

运用近似解析方法和数值方法研究轴向变速运动黏弹性Rayleigh梁的次谐波共振和组合共振的稳定性区域。基于变分原理,考虑梁断面旋转惯性的影响,推导轴向速度有周期波动的微变形梁横向振动的数学模型;采用多尺度方法建立前两阶次谐波共振和组合共振范围内的参数振动的可解性条件;进而确定梁两端简支边界条件下,因共振而产生的失稳区域;通过微分求积方法求解表征细长Rayleigh梁横向振动的运动微分方程。数值算例分析了黏弹性系数和扭转系数对梁振动失稳区域的影响,将数值仿真结果与近似解析方法的结论进行比较。算例表明:近似解析解的精度较高,第一、第二阶主共振的最大误差分别为3.206%、4.213%。     

从几何意义看洛必达法则

把0／0型未定式极限看作是一个参变量函数的割线的极限,就能在几何意义上观察到其实质是参变量方程曲线在原点的切线斜率,从而能更好地理解其含义;从参变量方程的角度,也可证明洛必达法则的正确性．     

含参弱向量均衡问题的适定性

在实Hausdorff拓扑线性空间中研究了含参弱向量均衡问题的适定性.证明了在适当条件下由近似网定义的含参适定性等价于近似解映射的上半连续性,并给出了所研究问题各种适定的充分性条件.     

High-power tunable terahertz generation from a surface-emitted THz-wave parametric oscillator based on two MgO:LiNbO3 crystals

A high-powered tunable terahertz wave (THz-wave) has been parametrically generated via a surface-emitted THz-wave parametric oscillator (TPO) pumped by a multi-longitudinal-mode Q-switched Nd:YAG laser. The effective parametric gain length was enlarged by employing two MgO:LiNbO₃ crystals. The tunable THz-wave radiation from 0.8 to 2.8 THz was realized via varying phase-matching angle between the pump wave and the Stokes wave. The maximum THz-wave radiation was 173.9 nJ/pulse at 1.7 THz as the pump energy was 82 mJ, corresponding to an energy conversion efficiency of about 2.12 × 10⁻⁶ and a photon conversion efficiency of about 0.035%. The first-order, the second-order and the third-order Stokes waves were observed during the experiments.     

周期参数扰动的T混沌系统同宿轨道分析

针对一类周期参数扰动的T混沌系统, 通过变换将系统转化为具有广义Hamilton结构的周期参数扰动的慢变系统, 运用Melnikov方法对系统的同宿轨道进行了分析计算, 并给出了系统的同宿轨道参数分支条件. 同时, 通过数值实验, 对周期参数扰动控制策略及同宿轨道进行了仿真, 验证了文中理论分析的正确性. 关键词： Hamilton系统 Melnikov方法 同宿轨道 周期参数扰动     

Holographic Storage Parametric Optimization of the Crystal LiNbO3∶Fe Based on One-center Model

Based on one-center model, the effects of the doping amount and the degrees of reduction and oxidation on the dynamic range M, the response time and the photorefractive sensitivity in the crystal LiNbO3∶Fe are analyzed in detail. The principle of material optimization is discussed. The best crystal thickness (about 1.4～2.6 mm) for the maximum dynamic range M is calculated for the different doping amounts. The results show that the more the doping amount, the lighter the reduction of the crystal should be chosen, and that the heavier the reduction of the crystal, the less effect the doping amount has on the response time. The dynamic range M is in conflict with the response time. Due to the difficulty of processing crystals, the thickness is increased to 5 mm at the cost of decreasing the dynamic range M by 0.3～0.5.