光纤模式混合器在差分吸收光谱系统中的应用研究

差分吸收光谱技术(DOAS)已经发展为监测对流层痕量气体的重要技术，一般采用光电倍增管(PMT)作为探测器.由于光电二极管阵列(PDA)在多道探测及像元灵敏性方面的优势，采用PDA代替扫描探测装置将能改善系统剩余噪声，提高系统性能.但实际应用中由于使用收发一体Cassegrain望远镜造成灯谱与大气谱结构不统一，在消除PDA像元间差异的过程中给系统带来误差，从而导致剩余噪声的标准偏差达到1.4×10^-3.根据光纤扰模原理在系统中加入自制光纤模式混合器很好的解决了上述难题，在实际应用中起到良好的作用，系统剩余噪声的标准偏差为3.4×10^-4. 关键词： 差分吸收光谱 扰模 模式混合器 剩余噪声     

A Stabilized Finite Element Method for Non-Stationary Conduction-Convection Problems

This paper is concerned with a stabilized finite element method based on two local Gauss integrations for the two-dimensional non-stationary conduction-convection equations by using the lowest equal-order pairs of finite elements. This method only offsets the discrete pressure space by the residual of the simple and symmetry term at element level in order to circumvent the inf-sup condition. The stability of the discrete scheme is derived under some regularity assumptions. Optimal error estimates are obtained by applying the standard Galerkin techniques. Finally, the numerical illustrations agree completely with the theoretical expectations.     

Coupled-resonator-induced transparency with a squeezed vacuum

We present the first experimental observation of quantum fluctuation spectra in two coupled optical cavities with an injected squeezed vacuum light. The quadrature components of the reflected squeezed vacuum spectra are measured by phase-sensitive homodyne detector. The experimental results demonstrate coupled-resonator-induced transparency in the quantum regime, in which the electromagnetically-induced-transparency-like characteristic of the absorption and dispersion properties of the coupled optical cavities determines the line shape of the reflected quantum noise spectra.     

Synthesis of Blue‐, Green‐, Yellow‐, and Red‐Emitting Graphene‐Quantum‐Dot‐Based Nanomaterials with Excitation‐Independent Emission

A one‐pot method is described for the preparation of graphene quantum dots/graphene oxide (GQDs/GO) hybrid composites with emission in the visible region, through heteroatom doping and hydroxyl‐radical‐induced decomposition of GO. The NH₄OH‐ and thiourea‐mediated dissociation of H₂O₂ produces hydroxyl radicals. Treatment of GO with hydroxyl radicals results in the production of small‐sized GO sheets and GQDs, which self‐assemble to form GQDs/GO through strong π–π interactions. For example, the reaction of GO with a mixture of NH₄OH and H₂O₂ for 40, 120, and 270 min generates yellow‐emitting GQDs/GO (Y‐GQDs/GO), green‐emitting GQDs/GO, and blue‐emitting GQDs, while red‐emitting GQDs/GO (R‐GQDs/GO) are prepared by incubating GO with a mixture of thiourea and H₂O₂. From the analysis of these four GQD‐based nanomaterials by transmission electron microscopy, atomic force microscopy, and fluorescence lifetime spectroscopy, it is found that this tunable fluorescence wavelength results from the differences in particle size. All four GQD‐based nanomaterials exhibit moderate quantum yields (1–10%), nanosecond fluorescence lifetimes, and excitation‐independent emissions. Except for R‐GQDs/GO, the other three GQD‐based nanomaterials are stable in a high‐concentration salt solution (e.g., 1.6 m NaCl) and under high‐power irradiation, enabling the sensitive (high‐temperature resolution and large activation energy) and reversible detection of temperature change. It is further demonstrated that Y‐GQD/GO can be used to image HeLa cells.     

Determining the η−η′ mixing by the newly measured \mathit{BR}(D(D_{s})\to\eta(\eta')+\bar{l}+\nu_{l}

The mixing of η?η′ or η?η′?G is of a great theoretical interest, because it concerns many aspects of the underlying dynamics and hadronic structure of pseudoscalar mesons and glueball. Determining the mixing parameters by fitting data is by no means trivial. In order to extract the mixing parameters from the available processes where hadrons are involved, theoretical evaluation of hadronic matrix elements is necessary. Therefore model dependence is somehow unavoidable. In fact, it is impossible to extract the mixing angle from a unique experiment because the model parameters must be obtained by fitting other experiments. Recently $\mathit{BR}(D\to\eta+\bar{l}+\nu_{l})$ and $\mathit{BR}(D_{s}\to\eta(\eta')+\bar{l}+\nu_{l})$ have been measured, thus we are able to determine the η?η′ mixing solely from the semileptonic decays of D-mesons where contamination from the final state interactions is absent. Thus we hope that the model dependence of the extraction can be somehow alleviated. Once $\mathit{BR}(D\to\eta'+\bar{l}+\nu_{l})$ is measured, we can further determine all the mixing parameters for η?η′?G. As more data are accumulated, the determination will be more accurate. In this work, we obtain the transition matrix elements of D _(s)→η ^(′) using the light-front quark model whose feasibility and reasonability for such processes have been tested.     

Q-switched operation of an in-band-pumped Ho:LuAG laser with kilohertz pulse repetition frequency

We report continuous-wave (CW) and repetitively Q-switched operation of an in-band-pumped Ho:LuAG laser at room temperature. End-pumped by a Tm:YLF solid-state laser with emission wavelength of 1.91 μm, the CW Ho:LuAG laser generated 5.4-W output at 2100.7 nm with beam quality factor of M ²～1.03 for an incident pump power of 14.1 W, corresponding to slope efficiency of 67% with respect to absorbed pump power. Up to 1.5-mJ energy per pulse at pulse repetition frequency (PRF) of 3 kHz and 4.5-W average power with FWHM pulse width of 28 ns at 5 kHz were demonstrated in repetitively Q-switched operation.     

脉冲偏压占空比对多孔氧化硅薄膜性质的影响

采用由脉冲负偏压调节的等离子体增强化学气相沉积方法,以硅烷为源气体,在玻璃基片上沉积得到了多孔二氧化硅薄膜。将反应过程中加在沉积区域的脉冲偏压固定在-350V,当占空比从0.162增大到0.864时,薄膜样品的形貌、成份和结构均不相同。扫描电镜照片表明,组成多孔氧化硅薄膜的颗粒在占空比增大时变得细腻,并且薄膜整体变得多孔且蓬松。拉曼光谱和红外光谱结果显示,薄膜样品中的非晶硅和Si-H键在较高的占空比下减弱甚至消失。占空比升高时氧化硅桥键所占比例持续增加。     

Microstructure and strain films using in-plane grazing analysis of GaN epitaxial incidence x-ray diffraction

This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of （100） reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa.     

Coordinated Control of Multi-Agent Systems with a Varying-Velocity Leader and Input Saturation

In this paper, we investigate a leader-following tracking problem for multi-agent systems with bounded inputs. We propose a distributed bounded protocol for each follower to track a leader whose states may not be completely measured. We theoretically prove that each agent can follow the leader with estimable track errors. Finally, some numerical simulations are presented to illustrate our theoretical results.     

热处理和紫外辐射对DNA影响的拉曼光谱研究

检测了鲕鱼精ＤＮＡ纤维和经过４０℃，９１℃，２００℃加热处理的拉曼光谱。研究结果表明，在熔融温度以下热处理对ＤＮＡ构象的影响是轻微的，在熔融温度以上则随温度的升高，对ＤＮＡ分子结构的影响有破坏也逐渐加剧，首先受影响的是腺嘌呤和脱氧核糖。