Nonstoichiometric laser materials: Designer wavelengths in neodymium-doped garnets

The tunable nature of lasers provides for a wide range of applications. Most applications rely on finding available laser wavelengths to meet the needs of the research. This article presents the concept of compositional tuning, whereby the laser wavelength is designed by exploiting nonstoichiometry. For research where precise wavelengths are required, such as remote sensing, this is highly advantageous. A theoretical basis for the concept is presented and experimental results in spectroscopic measurements support the theoretical basis. Laser operation nicely demonstrates the validity of the concept of designer lasers.     

Design Consideration for a Two-Distributed-Junction Tuning Circuit

We describe a novel method of designing a tuning circuit with two half-wave distributed junctions separated by a half-wavelength microstripline, which analytically determines the circuit parameters such as the minimum current density of the junctions and the characteristic impedances of the distributed junctions and the microstripline. The tuning circuit was approximated by simple transmission theory and then simplified with ideal circuit components for analysis. We applied Chebyshevs band-pass filter theory, in part, to optimize the circuit design. The analytical results revealed that a high characteristic-impedance ratio between the distributed junctions and the microstripline is necessary to obtain broadband matching using low-current-density junctions. The experimental results for all-NbN SIS mixers we designed with this method demonstrated double-sideband (DSB) receiver-noise temperatures of 6–10 quanta from 710 to 810 GHz for a mixer with a current density of only 4 kA/cm² (estimated C_JR_N product of 37 at 750 GHz). The RF bandwidth was broader than that of a conventional full-wave distributed SIS mixer with the same current density.     

Surface modification of several carbon-based materials: comparison between CF4 rf plasma and direct F2-gas fluorination routes

Due to their extreme reactivity, fluorine and fluorinated gases may be used to modify the surface properties of numerous materials. In the following, the surface fluorination of some carbon-based compounds (graphite, graphitised carbon fibres, carbon blacks and elastomers) using CF₄ rf plasma technique and direct F₂-gas fluorination is proposed. From XPS studies, the different types of CF bonding obtained in the materials after treatment have been correlated either to the physico-chemical characteristics of the pristine material or to the experimental parameters of the fluorination. Reaction mechanisms are proposed.     

非线性一维光子晶体特性的动态调制

对含有非线性材料的一维光子晶体带隙结构进行了数值计算.在外部入射光强调制下,非线性缺陷层折射率的改变会引起禁带内缺陷模的移动,而光子晶体禁带位置与宽度基本保持不变；若基本周期层取非线性材料,随入射光强的改变,禁带内部缺陷模发生相同的移动,同时,禁带位置和禁带宽度也会发生移动.利用这一性质可以对光子晶体进行动态外部调制,在此基础上对非线性一维光子晶体动态滤波选频进行了实验设计.     

Tuning ranges of an injection-locked excimer laser

The advantages and the practical limitations of injection locking are discussed. Experimental results for a system working in the regime between ideal injection locking and regenerative amplification are presented.     

全固态激光器抽运的PPLN光参变振荡

用全固态1064nm调Q激光输出，抽运多周期PPLN，实现了宽调谐的准相位匹配光参变振荡，振荡阈值10．3μJ（脉宽22ns)，信号光最高输出平均功率为42．5mW，斜率效率为12．5％。     

Physical aspects of dust–plasma interactions

Low-pressure gas discharge plasmas are known to be strongly affected by the presence of small dust particles. This issue plays a role in the investigations of dust particle-forming plasmas, where the dust-induced instabilities may affect the properties of synthesized dust particles. Also, gas discharges with large amounts of microparticles are used in microgravity experiments, where strongly coupled subsystems of charged microparticles represent particle-resolved models of liquids and solids. In this field, deep understanding of dust–plasma interactions is required to construct the discharge configurations which would be able to model the desired generic condensed matter physics as well as, in the interpretation of experiments, to distinguish the plasma phenomena from the generic condensed matter physics phenomena. In this review, we address only physical aspects of dust–plasma interactions, that is, we always imply constant chemical composition of the plasma as well as constant size of the dust particles. We also restrict the review to two discharge types: dc discharge and capacitively coupled rf discharge. We describe the experimental methods used in the investigations of dust–plasma interactions and show the approaches to numerical modelling of the gas discharge plasmas with large amounts of dust. Starting from the basic physical principles governing the dust–plasma interactions, we discuss the state-of-the-art understanding of such complicated, discharge-type-specific phenomena as dust-induced stratification and transverse instability in a dc discharge or void formation and heartbeat instability in an rf discharge.     

退火对TiO2薄膜形貌、结构及光学特性影响

利用射频磁控溅射技术在熔融石英基片上制备TiO<,2>薄膜,采用X射线衍射、扫描电子显微镜(SEM)、拉曼光谱以及透过谱研究了退火温度和退火气氛对TiO<,2>薄膜的结构、形貌和光学特性的影响.实验结果表明:在大气环境下退火,退火温度越.高,薄膜晶化越好,晶粒明显长大,温度高于700℃退火的薄膜,金红石相已明显形成.实验还发现,退火气氛对金红石相的形成是非常重要的,拉曼光谱反应出Ar气氛退火,抑制了金红石晶相的发育,薄膜仍以锐钛矿相为主.Ar气氛退火的薄膜在可见光范围内的透过率比大气退火的要低,并且由透过率曲线推知:金红石的光学带隙约为2.8 eV,比锐钛矿的光学带隙小0.2 eV.     

Variable selection using penalized empirical likelihood

This paper considers variable selection for moment restriction models.We propose a penalized empirical likelihood(PEL) approach that has desirable asymptotic properties comparable to the penalized likelihood approach,which relies on a correct parametric likelihood specification.In addition to being consistent and having the oracle property,PEL admits inference on parameter without having to estimate its estimator's covariance.An approximate algorithm,along with a consistent BIC-type criterion for selecting ...