Efficient Ultraviolet Nanosources Based on Third-Harmonic Generation in Dielectric–Metal Composite Nanodisks

Dielectric materials with high indices have recently attracted much attention in the community of nanophotonics. Severe optical losses in visible–ultraviolet (UV) region, however, limit their applications. This article proposes dielectric–metal nanocomposites as alternative high-index materials for Mie-resonance-based applications. Such composite materials have high indices in the range of wavelength longer than plasmon resonance of inclusion metal nanoparticles, while they have much lower losses in the range from blue-violet down to near-UV compared with commonly used high-index materials such as silicon, enabling near-UV generation with high efficiency based on third-harmonic generation (THG). The numerical results show that ZnO nanodisk containing silver nanoparticles can generate near-UV radiation at 351.3 nm via THG with an efficiency about 20 times higher compared with silicon nanodisk under same pumping condition. Significantly high THG efficiency of 0.015% has been predicted with such a composite nanodisk supported by aluminum substrate under pumping with a peak intensity of 20 GW cm⁻², a spot size of 0.8 $\mu \mathrm{m}$, a duration of 50 fs at 1054 nm, respectively.     

带沟槽结构的平板流动中的熵产分析

基于大涡模拟，采用Fluent软件对带沟槽结构的平板流动过程进行熵产分析，探究沟槽结构引起的熵产变化规律.结果表明：沟槽结构能减少流动过程中的熵产，在30 m·s^-1时（Re≈20 000），近壁区总熵产减少约25%，40 m·s^-1时（Re≈27 000）减少约19%，但其结构对后续流动没有持续性影响，且随着法向高度的增加，影响逐渐变小；熵产在沟槽顶端部分的数值远大于其他区域，湍流作用引起的熵产起主要作用.所得结论为优化沟槽结构减阻提供了理论依据.     

Offense Control Taking into Account Heterogeneity of Age

This paper studies the optimal tradeoff between the benefits and costs of preventing offenses and treating offenders. Based on a flexible age-structured epidemiological framework, a two-state compartment model is analyzed to reduce the prevalence of offending such as illicit drug consumption or violence. It turns out that, even in this highly simplified model, multiple stationary states exist. In particular, three different kinds of equilibria are identified, i.e., law and order, conservative, and liberal. The optimal mix of the control instruments is calculated providing interesting insight into the structure of the paths minimizing the discounted stream of social costs and expenditures for prevention and treatment.It can happen that a Skiba point exists. This implies that, for an initially small number of offenders, saddle-point convergence to a law-and-order equilibrium (boundary solution with no offenders) or to a conservative equilibrium (with few offenders) occurs, while if the number of offenders is large, the effects of prevention and treatment are too low or too expensive so that a liberal equilibrium (with many offenders) occurs.     

Ionization and Harmonic Generation of Diatomic Molecular Ion

l.IntroductionRecentexPerimentshavcdemonstratedthehigh-orderharmonicgenerationinraregasandmoleculargas[1~'j.TherearemanytheoreticalpaPersdealingwithharmonicgen-erationofatom[6~8j,comparativelysPeaking,theoreticalworksabouttheharmonicgen-erationofmolecuIeareless[9j,esPeciallyabouttheevolutionofionizationandharmonicgenerationwiththeinternuclearseparation,andtherelationbetweenionizationandhar-monicgeneration.InthispaPerwegivesomenumericalresultsofdiatomicmolecularionirradiatedbyalinearlyPOlari…     

Generation of Degenerate Linear Programming Problems

We present a method for constructing linear programming problems with randomly generated data. Besides the number of variables and constraints, the dimensions of the primal and dual faces are given. We show that, for problems in which the constraint matrix is carelessly constructed with random entries, with probability one only one between primal degeneracy and dual degeneracy appears.     

Transversal hypergraphs to perfect matchings in bipartite graphs: Characterization and generation algorithms

A minimal blocker in a bipartite graph G is a minimal set of edges the removal of which leaves no perfect matching in G. We give an explicit characterization of the minimal blockers of a bipartite graph G. This result allows us to obtain a polynomial delay algorithm for finding all minimal blockers of a given bipartite graph. Equivalently, we obtain a polynomial delay algorithm for listing the anti‐vertices of the perfect matching polytope of G. We also provide generation algorithms for other related problems, including d‐factors in bipartite graphs, and perfect 2‐matchings in general graphs. © 2006 Wiley Periodicals, Inc. J Graph Theory 53: 209–232, 2006     

Crystal growth and characterisation of new organic nonlinear optical materials: 6-cyano and 6-nitro-2,2-dimethyl-3,4-epoxychroman

Two chiral organic nonlinear optical materials, (3S,4S)-(−)-6-cyano-2,2-dimethyl-3,4-epoxychroman (1) and (3R,4R)-(+)-6-nitro-2,2-dimethyl-3,4-epoxychroman (2), have been grown into single crystals of cm³-size. Although both compounds crystallise in the orthorhombic P2₁2₁2₁ space group, they are not isomorphous and their crystal packings are quite different. Angle tuned type II phase-matched second harmonic generation between 0.8 and 1.064 μm has been evidenced, with effective nonlinear coefficients d_eff of 1 and 5 pm/V at 0.96 μm for 1 and 2, respectively. These values are in agreement with those estimated in the oriented gas model approximation using EFISH first order hyperpolarisability values (β₀=2.6 and 4.0×10⁻³⁰ esu for 1 and 2, respectively).     

Theoretical Study on Intra-Cavity Distributed-Bragg-Reflection Quasi-Phase-Matched Second-Harmonic Lasers

The characteristics of intra-cavity distributed Bragg reflector (DBR) quasi-phase-matched (IDQPM) second-harmonic-generation (SHG) lasers are theoretically studied. In the IDQPM-SHG laser, a QPM device and a DBR for feedback are separately fabricated on the same substrate with the QPM device placed between the DBR and a semiconductor laser. The threshold current of the IDQPM-SHG laser depends on the coupling efficiency between the laser diode and the QPM waveguide and the reflectivity of the DBR. The SH output of the IDQPM-SHG laser is strongly dependent on the generalized SHG conversion efficiency, x. This laser has the potential to attain an SH output over a 30-mW using a currently available 50-mW semiconductor laser for the fundamental light source, when highly efficient QPM device (x=2.2 W⁻¹) is used. Its tolerance for various deviations from the initial design and the problems to develop a commercially available IDQPM-SHG laser are also discussed.     

Single axial mode Q-switched pulse generation at 1.052 μm by self seeding in a Nd: YAG oscillator

Single axial mode Q-switched pulse generation at 1.052 μm in Nd:YAG by self seeding with free running spikes is discussed. The Nd:YAG, having plane parallel faces without anti-reflection coatings, exhibits modulation-free spikes in the free running regime. By allowing the Q-switching to take place, when the radiation field of any of these pulses is present in the resonator, very reliable and reproducible modulation-free Q-switched pulses are obtained.     

The analysis of inorganic and organometallic antimony,arsenic and tin compounds using an on-column hydride generation method

A novel method of analysis of inorganic and organometallic compounds is reported. Essentially this utilizes the well-documented hydride generation technique, but in the present method the hydrides are generated from their involatile precursors (e.g. chlorides) on a GC column and separated from each other and from extraneous materials on the same GC column in a single process. Using the method, a solution of butyltin chlorides can be directly injected into a GC AA system to yield the volatile hydrides for separation, detection and quantification. To date, species analysed by this method include inorganic As(III), Me₂AsOOH, inorganic Sb(III) and Sb(V), MeSnCl₃, Me₂SnCl₂, Me₃SnCl, Et₂SnCl₂, Et₃SnCl, BuSnCl₃, Bu₂SnCl₂, Bu₃SnCl and Pr₃SnCl. With the use of the internal standard Pr₃SnCl and with the almost complete hydridization afforded by the technique, the procedure is shown to eliminate errors and to reduce the time involved in the analysis. The use of on-column derivatization also allows for the possibility that, in some cases, organotin hydrides reported to be found in the natural environment may, in fact, be organotin chlorides being reported as hydrides owing to inadvertent hydride production on the column. Some reports of successful gas chromatography for organotin halides could also conceivably be due to on-column hydride generation.