Pulse-front matched ultra-broadband optical parametric chirped pulse amplifier for sub-12 fs pulse generation

We propose a LBO-based ultra-broadband chirped pulse optical parametric amplifier employing pulse-front-matching to yield transform-limited sub-12-fs pulses. Measurement of the maximum possible gain bandwidth for the LBO-based OPCPA demonstrates more than 60nm gain bandwidth FWHM. For the generation of TL pulses by the use of this OPCPA, a suitable combination of OPCPA and PFM is first presented. The PFM pump geometry realizes tilt-free signal amplification, and permits this OPCPA to generate TL sub-12-fs pulses.

Two-dimensional photonic lattices in polymer-dispersed liquid crystal composites

The relationship between liquid crystal orientational ordering and optical diffraction properties is investigated for a two-dimensional square photonic lattice fabricated in a polymer-dispersed liquid crystal (PDLC) composite. Modifications of the nematic director field in the liquid crystal domains were induced by an external applied voltage and by heating over the nematic-isotropic (N-I) phase transition. They were studied by optical polarization microscopy and by analysing far-field optical diffraction patterns. The intensities of various diffraction orders (from the zeroth up to the eighth diffraction order) were monitored with a CCD camera, and their variations were correlated with the modifications of the director field.

Pub/Sub系统中分布式复合事件检测技术研究

随着信息技术的发展，Pub/Sub系统由于具有异步和松耦合的特点，被越来越广泛的应用到金融、供应链管理、物流等领域。在这些应用中，用户对具有各种特定逻辑或时序关系的复合事件的订阅需求越来越迫切，这使得Pub/Sub系统中的分布式复合事件检测技术成为研究的热点，分布式复合事件检测技术包括复合订阅语言、复合匹配算法、以及订阅和事件的路由算法。 目前已有的Pub/Sub系统提供的复合订阅语言比较简单，对时序支持较弱，不能满足实际应用的需要，已有的复合匹配算法也不能有效的支持具有丰富时序关系的复合事件的检测。在路由方面，基于内容的Pub/Sub系统大都是在树结构或者无环图结构的覆盖网络上，采用基于过滤的原子路由方法，该路由方法需要将原子订阅传遍几乎整个网络，以减少订阅匹配的延迟，但这种路由方法很难适应网络的拓扑变化。而目前基于事件空间划分的路由方法不支持事件空间的动态划分和事件空间在不同服务器之间的移动，并且没有提供专门针对事件空间划分的复合事件检测方法。 本文在调研了各种应用需求的基础上，提出了能够表达事件丰富的时序关系、逻辑关系和事件实例关系的复合订阅语言，并且定义了两种事件排序方式。在消费语义采用配对模式的情况下，给出了该语言在两种事件排序方式下的检测结果集的定义。针对该复合订阅语言提出并实现了图结构和时间事件发生器相结合的复合匹配算法，该匹配算法使图结构可以有效的支持时序关系和非触发式事件的检测。在路由方面，首先实现了基于过滤的逆向路径转发的原子路由方法，并在此基础上，实现了就近检测协议，该协议优化了复合订阅匹配结构在网络中的部署。最后，设计和实现了基于事件空间划分的原子路由方法，该路由方法实现了事件空间的动态划分，并可以根据系统中服务器的负载情况实现事件空间的移动，从而有效的平衡服务器的负载。在此基础上，通过对复合订阅的拆分，并利用可移动的复合事件检测器实现了复合订阅的分布式部署和复合事件的分布式检测，同时通过对复合事件检测器的复用，进一步减少了网络负载和服务器的匹配负载。本文还通过实验验证了匹配算法和两种路由方法的性能和开销。

Isolated sub-30-as pulse generation of an He+ ion by an intense few-cycle chirped laser and its high-order harmonic pulses

We present an efficient method to generate a ultrashort attosecond (as) pulse when a model He+ ion is exposed to the combination of an intense few-cycle chirped laser pulse and its 27th harmonics. By solving the time-dependent Schroumldinger equation, we found that high-order harmonic generation (HHG) from He+ ion is enhanced by seven orders of magnitude due to the presence of the harmonic pulse. After optimizing the chirp of the fundamental pulse, we show that the cut-off energy of the generated harmonics is extended effectively to I-p+25.5U(p). As a result, an isolated 26-as pulse with a bandwidth of 170.5 eV can be obtained directly from the supercontinuum around the cut-off of HHG. To better understand the physical origin of HHG enhancement and attosecond pulse emission, we perform semiclassical simulations and analyze the time-frequency characteristics of attosecond pulse.

Asymmetric heat conduction in nonlinear lattices

In this Letter, we conduct an extensive study of the two-segment Frenkel-Kontorova model. We show that the rectification effect of the heat flux reported in recent literature is possible only in the weak interfacial coupling limit. The rectification effect will be reversed when the properties of the interface and the system size change. These two types of asymmetric heat conduction are governed by different mechanisms though both are induced by nonlinearity. An intuitive physical picture is proposed to interpret the reversal of the rectification effect. Since asymmetric heat conduction depends critically on the properties of the interface and the system size, it is probably not an easy task to fabricate a thermal rectifier or thermal diode in practice.

Large-scale, rapid synthesis and application in surface-enhanced Raman spectroscopy of sub-micrometer polyhedral gold nanocrystals

Macromolecule-protected sub-micrometer polyhedral gold nanocrystals have been facilely prepared by heating an aqueous solution containing poly (N-vinyl-2-pyrrolidone) (PVP) and HAuCl4 without adding other reducing agents. Scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), ultraviolet-visible-near-infrared spectroscopy (UV-vis-NIR), and x-ray diffraction (XRD) were employed to characterize the obtained polyhedral gold nanocrystals. It is found that the 10:1 molar ratio of PVP to gold is a key factor for obtaining quasi-monodisperse polyhedral gold nanocrystals. Furthermore, the application of polyhedral gold nanocrystals in surface-enhanced Raman scattering (SERS) was investigated by using 4-aminothiophenol (4-ATP) as a probe molecule. The results indicated that the sub-micrometer polyhedral gold nanocrystals modified on the ITO substrate exhibited higher SERS activity compared to the traditional gold nanoparticle modified film. The enhancement factor (EF) on polyhedral gold nanocrystals was about six times larger than that obtained on aggregated gold nanoparticles (similar to 25 nm).

White light emission from Eu3+ in CaIn2O4 host lattices

CaIn2O4:xEu(3+) (x=0.5%,1.0%,1.5%) phosphors were prepared by the Pechini sol-gel process [U.S. Patent No. 3,330,697 (1967)] and characterized by x-ray diffraction and photoluminescence and cathodoluminescence spectra as well as lifetimes. Under the excitation of 397 nm ultraviolet light and low voltage electron beams, these phosphors show the emission lines of Eu3+ corresponding to D-5(0,1,2,3)-F-7(J) (J=0,1,2,3,4) transitions from 400 to 700 nm (whole visible spectral region) with comparable intensity, resulting in a white light emission with a quantum efficiency near 10%. The luminescence mechanism for Eu3+ in CaIn2O4 has been elucidated.