单畴钇钡铜氧块材高Q值谐振腔研究

高性能滤波器、低相位噪声振荡器以及加速器研究的需要促进人们对更高Q值微波谐振腔的探索。X波段铜微波谐振腔在室温下的Q值只能约10^4；低温超导铌腔在X波段和4．2K温度时的Q值为106-107，在X波段和1．25K温度时Q值约10^11，用高Q值(10^9)低温超导微波谐振腔在X波段可以实现了10^-17频率稳定度。但由于需要工作在液氦温区而限制了它们的应用：因为液氦非常昂贵，并且液氦的保存系统机构复杂；在1．25K温度下的超流特性和极高的渗透性，对低温腔的真空密封提出了非常严格的要求。     

纳米技术新秀:单原子晶体管

 美国康奈尔大学的一个科学家小组研制成由一个钴原子构成的晶体管,钴原子包裹有一层复杂有机化合物,直径仅为10纳米的黄金导线被放置在硅片上,并用这种有机化合物覆盖住。然后在导线上钻一个直径约为1纳米的小孔,制成电源电极和电流电极,再将带有钴原子的有机化合物放置在小孔上,用二氧化硅作绝缘体。哈佛大学另一组科学家也用类似方法研制成单原子晶体管,他们是在黄金电极上放置钒分子,而用氧化铝作绝缘体。单原子或单分子晶体管研究表明,只有在加上一定电压时电流才会通过这类晶体管。此外,将它们放置在磁场中时,通过电流中的电子数量会增加。     

r探测器的中子灵敏度标定技术

CeF3，YaP：Ce等无机晶体分别配光电倍增管构成的探测器，对r线有较高的探测效率，被称为r测器。由于其中子灵敏度比相同能量的r敏度要低数倍，有的甚至低一个量级，因此中子辐射源与周围环境物质作用产生的散射中子和r线将严重影响其输出电流，导致中子灵敏度的标定难以实现。     

Time-Resolved Femtosecond Degenerate Four-Wave Mixing in LiNbO3：Fe,Mg Crystal

Forward degenerate four-wave mixing （DFWM） processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron （LiNbO3：Fe, Mg）. The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility x^（3） in the material is evaluated to be 4.96 × 10^-13 esu. The time-resolved DFWM process shows a response time of x^（3） shorter than 100fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast x^（3） optical nonlinearity.     

Experimental and Theoretical Evidence for the Existence of Broad Forbidden Gaps in the Three—Component Composite

The influence of localized resonance on the properties of band-gaps of the two-dimensional periodic composite are analysed numerically and experimentally by comparing the two-component phononic crystal with the three-component one. The three-component composite which exhibits localized resonance in the elastically soft coating ring is composed of a square array of coated cylinders embedded in an epoxy resin. The coated cylinders consist of a steel inner core and a rubber coating, which has much smaller wave velocity and mass density than the matrixand tile inner material. Tile measured transmission power of tile three-component composite drops to the noise level in a broad ultrasonic frequency interval in contrast to the binary composite, which is in good agreement with the calculation using the finite element method.     

Modified Photoluminescence by Silicon-Based One-Dimensional Photonic Crystal Microcavities

photoluminescence (PL) lrom one-dimensional photonic band structures is investigated. The doped photonic crystal with microcavitles are fabricated by using alternating hydrogenated amorphous silicon nitride (a-SiNx:H/a-SiNy:H) layers in a plasma enhanced chemical vapour deposition (PECVD) chamber. It is observed that microcavities strongly modify the PL spectra from active hydrogenated amorphous silicon nitride (a-SiNx:H) thin film. By comparison, the wide emission band width 208nm is strongly narrowed to 11 nm, and the resonant enhancement of the peak PL intensity is about two orders of magnitude with respect to the emission of the λ/2-thick layer of a-SiNx:H. A linewidth of Δλ=11 nm and a quality factor of Q=69 are achieved in our one-dimensional a-SiNz photonic crystal microcavities. Measurements of transmittance spectra of the as-grown samples show that the transmittance resonant peak of a cavity mode at 710nm is introduced into the band gap of one-dimensional photonic crystal distributed Bragg reflector (DBR), which further verifies the microcavity effects.     

二维NaCl晶体马德隆常数计算

通过计算机运算，给出二维ＮａＣｌ晶体马德隆常数的计算结果。     

闪光灯泵浦的Nd:KGd(WO4)2激光器

报道了用闪光灯泵浦的掺钕的钨酸钆镓(Nd³⁺:KGd(WO₄)₂激光器.在重复频率1Hz,脉宽120μs的灯泵下,测量了不同透过率下激光输出能量,获得最大输出能量384mJ,斜率效率1.0%,外推阈值0.54J.在调Q运行时,Nd:KGW晶体的斜率效率为0.16%,最大输出能量46mJ.