Beam Recombination Characteristics in Array Laser Amplification Using Stimulated Brillouin Scattering Phase Conjugation

Beam recombination characteristics were numerically investigated in array laser amplification using stimulated Brillouin scattering phase conjugation. To clarify the effect of piston errors due to imperfect phase locking, spatial intensity profiles of the beam recombination output were calculated in both the near and the far field on the basis of Rayleigh-Sommerfeld diffraction theory. The analyses indicate that piston errors are seriously detrimental to the quality of a beam recombination output and should be eliminated by a proper phase locking. It is also found that the gap between the beam splitting-combining wedges has a negligible effect.Presented at 1996 International Workshop on Interferometry (IWI ‘96), August 27-29, Saitama, Japan.     

Gain evaluation of compact designing on Er/Yb codoped germanate glass channel waveguide

Bent waveguide structures (U- and F-bend) based on UV-sensitive Er³⁺/Yb³⁺ codoped germanate glass substrates have been designed to achieve high-gain C-band amplification. Using simulated-bend method, the optimal radius for curved structure is offered to be 1.90 cm with loss coefficient of 0.0015 dB/cm, as the substrate size is minimally schemed. In the wavelength range of 1528–1559 nm, obvious gain enhancement for the bent structure waveguides is anticipated, while, for the F-bend waveguide, the internal gain at 1533.8 nm wavelength is derived to be 22.55 dB, which is much higher than the value of 14.06 dB in the U-bend waveguide, and over three times higher than that of the straight one, after compensating both the bend loss and the transition loss. The simulation results indicate that the bent structure designing is beneficial in attaining high optical gain in Er³⁺/Yb³⁺ codoped germanate glass substrates, which assures that long-period grating can be applied to implement practical C-band gain-flattened amplification.     

Electromagnetically induced transparency and evolution of a two-level system under chaotic field of arbitrary intensity

The electromagnetically induced transparency (EIT) with a (near-)resonant chaotic (amplitude-phase fluctuating, Gaussian-Markovian) coupling field is studied theoretically. The Fourier transform of the steady-state EIT spectrum, which determines a nonstationary probe absorption, is also considered. This quantity equals the average diagonal element of the (reduced) evolution operator of the coupled transition (the evolution function). The exact solution in the form of a continued fraction is obtained and used to perform numerical calculations. Moreover, a number of approximate analytical results are obtained, which, together with the results of previous publications, describe the EIT and the evolution function in all possible regimes. In particular, in the constructive-interference case the EIT increases with the coupling-field bandwidth ν at sufficiently small ν. For a strong field, the maximum of the transparency as a function of ν is less than that for a monochromatic field of the same average intensity. In contrast, for a weak field, there is a range of ν values, where the field fluctuations do not affect the EIT. The latter result is shown to hold for a broad class of stochastic fields. Received 31 December 2000 and Received in final form 14 May 2001     

Dielectric and structural relaxation phenomena in Na0.5Bi0.5TiO3 single crystal

Abstract

Dielectric permittivity studies of Na_0.5Bi_0.5TiO₃ single crystals in a broad range of frequency up to 10 MHz and temperature 300—823 K are reported. In this temperature range dielectric dispersion below 1 MHz has been found. The obtained data were fitted to the Cole-Cole relation. The mean relaxation time τ is strongly temperature dependent (0.04 ? 2.6 × 10^?5 s). A remarkable hysteresis effect in the values of τ on cooling and heating took place. The Δε(T) dependence (the maximal value of Δε ～ 400) is similar to the global ε′(T) response at low frequency. An isothermal structural transformation in Na_0.5Bi_0.5TiO₃ was observed by X-ray measurements. The order of the time in which the transformation takes place (～300 minutes) corresponds to the time in which the strongest time evolution of electric permittivity and time changes of dielectric dispersion were detected.     

第三讲 非线性原子光学

随着玻色-爱因斯坦凝聚（BEC）的实现及其非线性效应研究的快速发展,原子光学的一门新兴分支学科——“非线性原子光学”已初步形成,并取得了一系列重大的实验进展.文章重点介绍了非线性原子光学的研究内容、实验结果及其最新进展,主要包括原子孤子、原子物质波中的四波混频、光速减慢与负群速现象、超流及涡流（vortex）、Josephson效应和物质波的相位相干放大等.     

Hexametaphosphate‐Capped Silica Mesoporous Nanoparticles Containing CuII Complexes for the Selective and Sensitive Optical Detection of Hydrogen Sulfide in Water

Cu^II‐macrocycle functionalized hexametaphosphate‐capped silica mesoporous nanoparticles have been prepared and used for the selective and sensitive detection of hydrogen sulfide in aqueous environments. The possibility of using different metal complexes combined with different capping anions and choice of different dyes or other sensing molecules as indicators makes this new protocol highly appealing for the preparation of new sensing systems for sulfide detection in different environments.     

Elucidating the Structure of Chiral Molecules by using Amplified Vibrational Circular Dichroism: From Theory to Experimental Realization

Recent experimental observations of enhanced vibrational circular dichroism (VCD) in molecular systems with low‐lying electronically excited states suggest interesting new applications of VCD spectroscopy. The theory describing VCD enhancement through vibronic coupling schemes was derived by Nafie in 1983, but only recently experimental evidence of VCD amplification has demonstrated the extent to which this effect can be exploited as a structure elucidation tool to probe local structure. In this Concept paper, we give an overview of the physics behind vibrational circular dichroism, in particular the equations governing the VCD amplification effect, and review the latest experimental developments with a prospective view on the application of amplified VCD to locally probe biomolecular structure.     

多孔物质气固反应动力学研究

利用自主研制的微型流化床反应分析仪（MFBRA）在等温条件下测试了高比表面活性炭氧化反应,并根据基于固体转化的热分析动力学方法及考虑气体在微孔内扩散与反应的应用化工动力学方法求算了动力学参数．在内外扩散抑制最小化的实验条件下,粒径小于5μm的活性炭在700-1000℃的燃烧反应动力学研究表明,根据微型流化床中实验数据,采用等温热分析动力学方法求算得内扩散控制区活化能约为95kJ／mol;弓l入化工动力学方法中的随机孔模型对低温区等温燃烧数据拟合,可得孔结构参数在0．17m^-3左右,反应活化能为178kJ／mol,约为内扩散反应活化能的两倍,最为接近本征的碳燃烧反应活化能．     

ZIF-8材料中CH4/H2吸附与扩散的分子模拟

采用平衡分子动力学和巨正则系综蒙特卡洛模拟方法对多孔沸石咪唑酯骨架材料(ZIF-8)中CH4和H2分子的吸附与扩散特性进行了比较研究.结果表明,采用柔性力场能够很好地复制ZIF-8在不同压力或温度条件下的晶体结构,也能准确地计算不同温度下CH4和H2分子在ZIF-8中的扩散系数,特别是高温下CH4分子因能够摆脱ZIF-8骨架笼口的空间限制而使其扩散系数出现大幅提升.同时,该力场也能粗略地模拟CH4和H2分子在ZIF-8中的等温吸附曲线,通过自编程序得到吸附和扩散平衡时CH4和H2分子在ZIF-8单元晶胞内的几率密度分布数据,并利用VMD软件可视化.结果显示CH4和H2分子在ZIF-8中的优先吸附位置均在大孔中心靠近咪唑环的区域,但CH4分子的优先吸附位置有两个不同层次,而H2分子的优先吸附位置只有一个层次,说明CH4和H2分子在ZIF-8中存在着不同的吸附机理.     

数字核酸扩增检测技术的研究与应用进展

近年来,微纳尺度流体控制技术由于具备实现多相、多步和平行反应的优势,已成为传统分析手段的首选的补充和替代方法.其与核酸扩增方法的完美结合,有效推动了数字核酸扩增检测(Digital nucleic acid detection,dNAD)技术的建立与发展.作为可实现单分子水平检测的分析方法,dNAD技术已成为分子诊断领域重要的组成部分.本文回顾了dNAD技术的发展历程,阐述了其检测原理,以及相比于传统方法的优势,对其最新研究与应用进展进行了综述,并对其未来的发展进行了展望.