High power,continuous wave,singly resonant OPO based on MgO:PPLN

A continuous wave (CW), extra-cavity singly resonant optical parametric oscillator (SRO) has been demonstrated. The SRO was based on 5% Magnesium-Oxide doped periodically-poled Lithium Nio-bate (MgO:PPLN) pumped by a Yb fiber laser centered at 1064.7 nm. The SRO was able to generate light with idler wavelengths ranging from 2.9 to 4.1 μm. For a pump power of 15 W, the idler output power varied from 7.54 W at 3.03 μm to 1.04 W at 4.05 μm. The oscillation thresholds were 2.0 W at idler wavelength 3.03 μm and 7.0 W at 4.05 μm.     

Experimental simulation of the Unruh effect on an NMR quantum simulator

A triad mode resonance, or three-wave resonance, is typical of dynamical systems with quadratic nonlinearities. Suspended cables are found to be rich in triad mode resonant dynamics. In this paper, modulation equations for cable’s triad resonance are formulated by the multiple scale method. Dynamic conservative quantities, i.e., mode energy and Manley-Rowe relations, are then constructed. Equilibrium/dynamic solutions of the modulation equations are obtained, and full investigations into their stability and bifurcation characteristics are presented. Various bifurcation behaviors are detected in cable’s triad resonant responses, such as saddle-node, Hopf, pitchfork and period-doubling bifurcations. Nonlinear behaviors, like jump and saturation phenomena, are also found in cable’s responses. Based upon the bifurcation analysis, two interesting properties associated with activation of cable’s triad resonance are also proposed, i.e., energy barrier and directional dependence. The first gives the critical amplitude of high-frequency mode to activate cable’s triad resonance, and the second characterizes the degree of difficulty for activating cable’s triad resonance in two opposite directions, i.e., with positive or negative internal detuning parameter.     

Laboratory vacuum spectrometer for the soft x‐ray region

A laboratory surface x‐ray absorption near edge structure ((S)XANES) spectrometer used for measurements in the soft x‐ray region is described. The x‐ray beam path of the spectrometer is enclosed in a vacuum chamber directly connected to the x‐ray generator output port. With this setup, the absorption of the x‐rays in the air is avoided. The developed spectrometer uses a monochromator equipped with cylindrically bent PET(002), KAP(001), and Ge(111) crystals of different Rowland radii working in the Johann focusing geometry. Nine stepping motors are used to control the positions of the monochromator, receiving slit, sample, and detectors. An x‐ray photon energy available in experiment ranges from about 1 keV to 5 keV. A registration of the photoelectrons emitted from the sample with the channeltron is used to carry out surface‐sensitive measurements. The performance of the developed spectrometer is illustrated by spectra measured at the absorption K‐edges of several elements from the Na‐Ti set. Copyright © 2008 John Wiley & Sons, Ltd.     

端面抽运Tm，Ho：YLF激光器双稳特性的理论分析与实验研究

报道了波长为792nm激光二极管端面抽运Tm,Ho：YLF连续激光器的双稳输出特性.在考虑能量传递上转换和基态对2μm激光重吸收的前提下,建立了Tm,Ho：YLF双稳激光器准三能级速率方程理论模型.通过对Tm,Ho：YLF激光器速率方程的求解,理论预见了Tm,Ho：YLF激光器双稳输出的特性,并分析了其产生的机理.进行了激光二极管端面抽运Tm,Ho：YLF激光器双稳输出的实验研究,当激光晶体温度为253K时,双稳区的宽度可达1.6W,跃变点输出功率的跃变量可达82.5mW.通过对比发现理论结果与实验结果比 关键词： 端面抽运 Tm Ho：YLF晶体 连续输出 光学双稳     

Search for solar <Emphasis Type="Italic">pp</Emphasis> neutrinos with an upgrade of CTF detector

The possibility of using ultrapure liquid organic scintillator as a low-energy solar neutrino detector is discussed. The detector with an active volume of 10 t and 4π coverage will count 1.8 pp neutrinos and 5.4 ⁷Be neutrinos per day with an energy threshold of 170 keV for the recoil electrons. The evaluation of the detector sensitivity and backgrounds is based on the results obtained by the Borexino collaboration with the Counting Test Facility (CTF). The detector can be build at the LNGS underground laboratory as an upgrade of the CTF detector using already developed technologies.     

基于固定校正板和透镜阵列的机载共形窗口像差校正

为了校正大扫描视场机载共形窗口引入的像差,提出一种基于固定校正板和透镜阵列的静态校正方法。首先使用固定校正板校正静态像差;然后在像面前安置固定的透镜阵列,利用透镜阵列中的各个透镜单元分别校正不同扫描角度的动态像差;最后基于所提方法设计应用在机载共形光学系统中的像差校正器。设计结果表明,所提方法在±42°的扫描视场范围内能够良好地校正共形窗口引入的像差。与其他动态或静态校正方法相比,所提方法可以实现大扫描视场机载共形光学系统像差的校正,同时降低机载共形光学系统的质量,提高系统的稳定性。     

Understanding cool flames and warm flames

Low-temperature flames such as cool flames, warm flames, double flames, and auto-ignition assisted flames play a critical role in the performance of advanced engines and fuel design. In this paper, an overview of the recent progresses in understanding low-temperature flames and dynamics as well as their impacts on combustion, advanced engines, and fuel development will be presented. Specifically, at first, a brief review of the history of cool flames is made. Then, the recent experimental studies and computational modeling of the flame structures, dynamics, and burning limits of non-premixed and premixed cool flames, warm flames, and double flames are presented. The flammability limit diagram and the temperature-dependent chain-branching reaction pathways, respectively, for hot, warm, and cool flames at elevated temperature and pressure will be discussed and analyzed. After that, the effect of low temperature auto-ignition of auto-igniting mixtures at high ignition Damköhler numbers at engine conditions on the propagation of cool flames, warm flames, and double flames as well as turbulent flames will be discussed. Finally, a new platform using low temperature flames for the development and validation of chemical kinetic models of alternative fuels will be presented. Discussions of future research of the dynamics and control of low temperature flames under engine conditions will be made.