Tunable subnanosecond laser pulse generation using an active mirror concept

We report (theory, experimental check) an improved approach for generation of a tunable, subnanosecond pulse (0.1–0.4 ns), based on a single pulsation (“spike”) separation from the transient oscillations in a dye laser with active mirror (AMIR). A pumping by 20–50 ns pulses from Q-switched Nd:YAG laser is considered. The separation is in original, two-spectral selective channels cavity, where the forced by AMIR quenched generation at one of the wavelength stops initially started spiking generation at the other wavelength after the first spike development. The AMIR quickly starts the quenching generation at a precisely controlled moment and with necessary intensity thus assuring the desired separation. An advantage is a high reproducibility of the separation for high (~250%) pump power fluctuations combined with tuning in large range (~20 nm). To obtain such an operation we form ~1 ns leading front pump pulse by electrooptical temporal cutting of the input pump pulse and use an optical delay line. This increases also a few times the power in the separated spike (to be ~100 kW). Our approach widens the combinations of lasers for effective applications of spike separation technique (dye lasers excited by Q-switched solid-state or Cu-vapor lasers).     

Boltzmann distribution of free energies in a finite-connectivity spin-glass system and the cavity approach

At sufficiently low temperatures, the configurational phase space of a large spin-glass system breaks into many separated domains, each of which is referred to as a macroscopic state. The system is able to visit all spin configurations of the same macroscopic state, while it can not spontaneously jump between two different macroscopic states. Ergodicity of the whole configurational phase space of the system, however, can be recovered if a temperature-annealing process is repeated an infinite number of times. In a heating-annealing cycle, the environmental temperature is first elevated to a high level and then decreased extremely slowly until a final low temperature T is reached. Different macroscopic states may be reached in different rounds of the annealing experiment; while the probability of finding the system in macroscopic state α decreases exponentially with the free energy F _α (T) of this state. For finite-connectivity spin glass systems, we use this free energy Boltzmann distribution to formulate the cavity approach of Mézard and Parisi [Eur. Phys. J. B, 2001, 20: 217] in a slightly different form. For the ±J spin-glass model on a random regular graph of degree K = 6, the predictions of the present work agree with earlier simulational and theoretical results.      

Cyclic Heating-Annealing and Boltzmann Distribution of Free Energies in a Spin-Glass System

Ergodicity of a spin-glass is broken at low temperatures; the system is trapped in one of many ergodic configurational domains. Transitions between different ergodic domains are achievable through a heating-annealing procedure. If this experiment is repeated infinite times, all ergodic configurational domains will be visited with frequences that decreasing exponentially with their free energies. The mean free energy density of a spin-glass system on a random graph is calculated based on this free energy Boltzmann distribution in the present work, by means of the cavity approach.     

Schemes for Probabilistic Teleportation of a Three-Atom GHZ Class State via Cavity QED

Using a quantum channel composed of a two-atom and a three-atom nonmaximally entangled states,we present two schemes to teleport a three-atom GHZ class state via entanglement swapping in cavity QED with different success probabilities. The schemes can be respectively realized with the large-detuned vacuum cavities and with the large-detuned thermal cavities by separate atomic measurements after we choose appropriate atom-cavity-field interaction time.     

新型双间隙虚阴极振荡器的理论分析和数值模拟

 该新型双间隙虚阴极振荡器的互作用区为一带孔金属薄膜隔开的两个圆柱形谐振腔；器件采用侧向提取同轴输出的方法，具有输出效率高和输出模式纯的优点；第一阳极薄膜采用了局部薄膜结构。对互作用腔进行冷腔分析，计算得到互作用腔Ⅰ和Ⅱ的品质因子分别为6 960和71.8，共振频率为2.3 GHz。当电子束电压为515 kV、电流为10 kA时，通过参数优化，模拟得到周期平均峰值功率大于570 MW、频率约2.4 GHz的微波输出，效率达到11%。模拟还发现电子束的最佳阻抗值约为51.5 W；电子束的输入功率在较大范围内变化时，器件的输出效率保持大于10%；在一定的范围内，器件的输出效率随电子束密度的增加而增加。对器件中由于电子能量沉积而引起的阳极膜的温升进行了估算，得到膜的最高温度为434 K，远低于熔点933 K。     

端面抽运四镜折叠腔Nd∶YVO4激光器的研究

基于传输矩阵理论,针对端面抽运的z型折叠腔Nd∶YVO4固体激光器的谐振腔设计进行了数值模拟,详细分析了腔内各参量对谐振腔稳定性的影响.由模拟结果推断,z型腔激光器具有两个稳区,并且稳区的范围可通过谐振腔各分臂的臂长来调节.利用相同的光学元件在不同的稳区范围设计了两种热稳腔,指出了长短腔型各自的利弊.实验考察了输出功率随腔长改变的变化情况,在不同腔长下的不同稳区分别获得了稳定的1 342 nm激光输出,谐振腔稳区范围的变化规律与理论计算基本符合.     

斯塔克效应对两模双光子J-C模型腔场谱的影响

研究了斯塔克(Stark)效应对两模双光子Jaynes-Cummings(J-C)模型腔场谱的影响,推导计算出了腔场处于光子数态时腔场谱的计算公式和数值结果,讨论了斯塔克效应和初始场强对腔场谱的影响。发现斯塔克效应在弱场条件下对腔场谱线的频率和强度都有明显的影响,破坏了谱结构的对称性,使两模的谱线更加丰富。初始场较强时斯塔克效应对谱线的影响较弱。模Ⅰ为真空场、模Ⅱ初始场强递增时,斯塔克效应使模Ⅱ的高频峰受到较强的抑制作用,其低频峰在初始场较弱时受到抑制,初始场较强时又有强化作用,初始场更强时,模Ⅱ的谱线退化为经典的共振荧光谱,与无斯塔克效应的情况基本相同。     

恒热流加热开口腔自然对流的可视化实验和数值模拟

本文采用激光全息干涉和激光片光照射烟可视化方法获得了恒热流加热的二维开口腔自然对流问题的温度场和流场,并进行了数值分析.实验结果与数值模拟结果吻合.数值计算表明方腔内流体的流通量与Ra*和深高比B有关,当Ra*＞104时随深高比B增加流通量增加;B×Nu与深高比B呈线性关系.利用B×Nu与深高比B的线性关系,通过引入当量导热系数λc,本文还给出了加热壁面的平均温度的简单计算方法.     

用于全光缓存的光阈值门理论和实验研究

提出了一种基于光阈值门的全光缓存方案,采用两个非对称的SOA环形腔激光器耦合构成光阈值门,其输出光可以在两种波长上切换,可控制波长转换器实现光包路由,从而将需缓存的数据包路由到缓存端口,避免了复杂的包头处理.建立了光阈值门的理论模型,对10 Gbit/s的光阈值门的动态特性进行了数值模拟和实验研究,实验结果和理论计算结果相符合,实验也表明光阈值门两种输出状态的消光比可达30dB.     

温度效应对F-P腔光纤液位传感器系统的影响及自补偿

分析了温度效应对F-P腔光纤液位传感器系统的影响,提出相应的解决方案以实现对温度效应的自补偿.在26℃-28℃环境温度条件下,实验结果表明,在1.87 m（水）量程内经过优化的传感系统参考光动态稳定性可达到0.059 9%,准确度误差为1.122 mm.自补偿措施对获得高准确度、长期稳定性的光纤液位传感器具有重要意义.