Excition dynamics in the J-aggregates of a carbocyanine dye

We report on the exciton dynamics in the J-aggregating dye 5,5, 6,6-tetrachloro-1,1-diethyl-3,3-di(4-sulfobutyl)-benzimidazolocarbocyanine which is known readily to form J-aggregates, even at room temperature and at a low concentration. We performed a series of time-correlated singlephoton-counting experiments at different emission wavelengths and at different temperatures in the range between 1.5 and 125 K. Additionally, the temperature dependence of the relative fluorescence quantum yield was determined.     

Computational study of energy transfer in two-dimensional J-aggregates

We perform a computational analysis of the intra- and interband energy transfer in two-dimensional J-aggregates. Each aggregate is represented as a two-dimensional array (LB-film or self-assembled film) of two kinds of cyanine dyes. We consider the J-aggregate whose J-band is located at a shorter wavelength to be a donor and an aggregate or a small impurity with longer wavelength to be an acceptor. Light absorption in the blue wing of the donor aggregate gives rise to the population of its excitonic states. The depopulation of these states is possible by (a) radiative transfer to the ground state, (b) intraband energy transfer, and (c) interband energy transfer to the acceptor. We study the dependence of energy transfer on properties such as the energy gap, the diagonal disorder, and the exciton–phonon interaction strength. Experimentally observable parameters, such as the position and form of luminescence spectrum, and results of the kinetic spectroscopy measurements strongly depend upon the density of states in excitonic bands, rates of energy exchange between states and oscillator strengths for luminescent transitions originating from these states.     

Formation of pseudoisocyanine J-aggregates during thin-film formation

Thin-film formation of J-aggregated pseudoisocyanine iodide with long alkyl substituents C₁₈H₃₇ (PIC 2-18) and C₁₀H₂₁ (PIC 2-10) and ethyl substituents (PIC 2-2) with added anion was studied by spectrophotometry directly during spin-coating of its solutions. It is found that a bathochromic shift of the monomer dye absorption band maximum and extensive growth of a J-peak that is not compensated by the monomer decrease take place as the dye film forms. The refractive index and absorption coefficient of a solid dye thin film in monomeric (n _max = 2.1) and J-aggregated (n _max = 3.05) forms were measured as functions of the dispersion by spectral ellipsometry. The influence of a change in the local field factor on the spectral properties of the pseudoisocyanine dye solution in the course of both spin-coating and solid J-aggregated thin-film formation is considered. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 76–83, January–February, 2009.     

Temperature dependence of the exchange coupling in CO/SI(or Ge)/Fe trilayers

The temperature dependences of interfacial exchange coupling in Co/semiconductor (SM)/Fe trilayers (SM≡Si or Ge) with different spacer thicknesses are investigated. Only one step is found in the third (not in the first) quadrant of the hysteresis loop of the trilayers with different SM thicknesses, which is ascribed to a larger interfacial coupling strength of Co/CoGe (or Co/CoSi) than of Fe/FeGe (or Fe/FeSi). Furthermore, in comparison with Co/Ge/Fe, a smaller exchange bias field H_E and no clear step are observed in Co/Si/Fe, which may originate from the weaker interfacial coupling in this trilayer. The variation of coercivity H_C with spacer thickness at low temperatures in Co/Ge/Fe is different from that in Co/Si/Fe, indicating again the important effect of the SM layer in the trilayers.     

Relative-thickness dependence of exchange bias in bilayers and trilayers

We consider the models of ferromagnetic (FM)/antiferromagnetic (AFM) bilayers and trilayers and perform a modified Monte Carlo method to study their exchange bias (EB) properties at low temperature after field cooling on increasing one component thickness at the expense of the other one. The results indicate that EB is insensitive to the thickness variations as the FM layer is thicker than the AFM one. Otherwise, it has a steep increase with the decrease of FM thickness, but the purely inverse proportion is no longer valid due to the dual influences of FM and AFM thicknesses. EB in trilayers should be approximately twice larger than that in bilayers because there is a double interfacial area in the trilayers compared with the bilayers, but the dispersed FM/AFM distributions may break this relation as a result of thermal destabilization. Moreover, EB is independent of FM/AFM stacking sequences probably because of the ideal interface between them. It has been clarified unambiguously that such control of EB through varying the FM/AFM dimensions in heterostructures is attractive for spintronics applications.     

Temperature dependence of the giant magnetoresistance in Fe-Cr multilayers—Intralayer and interlayer exchange energies

We present field and temperature dependence data on giant magnetoresistive (GMR) ion-beam sputtered Fe-Cr multilayers of varying Cr thickness. We show that the decrease in GMR with temperature is related to the decrease in sublattice magnetization due to thermal excitation of magnons in the antiferromagnetic configuration. The intralayer and the interlayer exchange energies thus obtained vary systematically as the Cr thickness increases. The corresponding decrease in the measured saturation field further supports our interpretation leading to a better understanding of the physics of GMR.     

在时域实验研究扩散诱导的Ramsey压窄

基于Duan-Lukin-Cirac-Zoller(DLCZ)方案,在时域上研究了扩散诱导的Ramsey压窄. 以⁸⁷Rb热原子系综为研究对象,观测到缓冲气体,激光束尺寸和镀石蜡Rb池均可以导致Ramsey压窄现象. 实验结果和文献中重复相互作用模型预期的一致.     

在时域实验研究扩散诱导的Ramsey压窄

基于Duan-Lukin-Cirac-Zoller(DLCZ)方案,在时域上研究了扩散诱导的Ramsey压窄.以87Rb热原子系综为研究对象,观测到缓冲气体,激光束尺寸和镀石蜡Rb池均可以导致Ramsey压窄现象.实验结果和文献中重复相互作用模型预期的一致.     

Spectral narrowing in a dye laser with non-resonant feedback

The temporal development of the spectral output of a flashlamp pumped dye laser, having non-resonant feedback achieved by means of fibre optics, has been studied using a streak camera. Spectral narrowing from 40 nm (the bandwidth of the spontaneous fluorescence of the system) to 2.5 nm has been observed, with the degree of spectral narrowing depending upon the output power.     

Thickness dependence of exchange anisotropy in NiFe/IrMn bilayers studied by Planar Hall Effect

Planar Hall Effect (PHE) in NiFe(t)/IrMn(10.0 nm) thin film structures has been experimentally investigated as a function of NiFe thickness in the range from 3 to 20 nm, under the applied magnetic field perpendicular to the easy axis. The PHE voltage change and its field sensitivity increase with NiFe thickness, but the field interval of two voltage maxima decreases with the thickness. There are good agreements between measured and calculated PHE voltage profiles, where the parameters of exchange-biased and effective anisotropy fields have been characterized to decrease with NiFe thickness. However, an anisotropic resistivity change increases as the NiFe thickness increases. These analyses suggest that PHE is the effective method, inferred to single domain, to determine the electrical and magnetic parameters in magnetic devices.     

Thickness dependence of positive exchange bias in ferromagnetic/antiferromagnetic bilayers

For the ferromagnetic (FM)/antiferromagnetic (AFM) bilayers, both negative and positive exchange bias H_E have been observed for low and high cooling field H_CF, respectively. The thickness dependence of H_E and coercivity H_C have been investigated for the cases of negative and positive H_E. It is found that the negative H_E and the positive one have similar FM thickness dependence that is attributed to the interfacial nature of exchange bias. However, the AFM thickness dependence of positive H_E is completely contrary to that of the negative one, which clearly demonstrates that the AFM spins play different roles for the cases of positive and negative H_E. In particular, the AFM thickness of positive H_E was first highlighted by an AFM spin canting model. These results should be attributed to the interfacial spin configuration after field cooling procedure.     

用于补偿增益窄化效应的Rugate滤波器设计

采用Rugate膜系理论,分别根据钛宝石和钕玻璃介质增益窄化的特点,合理选择补偿增益窄化的调制函数,优化设计出了分别用于补偿钛宝石系统和钕玻璃系统增益窄化效应的Rugate滤波器.由普通均匀多层膜的特征矩阵方法近似分析了设计出的Rugate滤波器的光谱响应,数值模拟了Rugate滤波器的光谱补偿效果.结果显示,能比较好的符合光谱补偿的要求,可以用作补偿增益窄化效应的光谱调制滤波器. 关键词： 超短脉冲 增益窄化 光谱补偿 Rugate滤波器     

Motional narrowing under diffusion of two spin sub-lattices in LiNaSO4

An expression for the dipolar correlation function characterizing the fluctuations of the Hamiltonian under uncorrelated diffusion of two cationic sub-lattices in a solid has been obtained. A corresponding formula, which can be used for fitting the two-step temperature dependencies of the NMR line width, has been deduced. We also considered the case of a distribution of correlation times and deduced a corresponding analytical fitting function. Elaborated expressions have been applied to the NMR line width analysis of LiNaSO₄ in the temperature range 295–788 K.     

Absorptive reduction and width narrowing in Λ-type atoms confined between two dielectric walls

This paper investigates the absorptive reduction and the width narrowing of electromagnetically induced transparency （EIT） in a thin vapour film of A-type atoms confined between two dielectric walls whose thickness is comparable with the wavelength of the probe field. The absorptive lines of the weak probe field exhibit strong reductions and very narrow EIT dips, which mainly results from the velocity slow-down effects and transient behaviour of atoms in a confined system. It is also shown that the lines are modified by the strength of the coupling field and the ratio of L/λ, with L the film thickness and λthe wavelength of the probe field. A simple robust recipe for EIT in a thin medium is achievable in experiment.     

Tailored slice selection in solid-state MRI by DANTE under magic-echo line narrowing

We propose a method of slice selection in solid-state MRI by combining DANTE selective excitation with magic-echo (ME) line narrowing. The DANTE RF pulses applied at the ME peaks practically do not interfere with the ME line narrowing in the combined ME DANTE sequence. This allows straightforward tailoring of the slice profile simply by introducing an appropriate modulation, such as a sinc modulation, into the flip angles of the applied DANTE RF pulses. The utility of the method has been demonstrated by preliminary experiments performed on a test sample of adamantane.     

软X射线皮秒分幅相机的增益压窄效应

 高速行波选通的X射线皮秒分幅相机的时间分辨率受皮秒选通脉冲的宽度和幅值的非线性关系直接影响。针对微通道板(MCP)行波选通皮秒分幅相机中的“增益压窄效应”,在高斯型皮秒选通电脉冲作用下,通过计算MCP分幅管的时间分辨率和对增益压窄效应的分析,得到MCP皮秒选通分幅管的增益压窄指数约为10.0,分幅管的时间分辨率约为选通脉冲脉宽的1/3.16。并在脉冲参数（250 ps,－1 100 V）和（220 ps,－900 V）下进行了分幅相机时间分辨率理论计算和实验测试,分别得到了理论时间分辨率为78.8 ps和67.6 ps,相机实验时间分辨率为76.4 ps 和66.5 ps的结果。     

Observation of linewidth narrowing due to a spontaneously generated coherence effect

We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields.We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the latter being a system that exhibits spontaneously generated coherence and can display ultrasharp spectral lines.We find a suitable energy scheme in a 85Rb atom and experimentally observe the narrowing of the central peak in a rubidium atomic beam.The corresponding spectrum can convincingly demonstrate the existence of spontaneously generated coherence.     

Cooling-field dependence of exchange bias in Mg-diluted Ni1−xMgxO/Ni granular systems

The exchange-bias (EB) properties of Mg-diluted Ni_1−xMg_xO/Ni (0?x?0.3) granular systems have been investigated. Magnetic dilution with Mg greatly affects the EB field and the coercivity. The temperature dependence of the EB field and the coercivity can be explained in terms of formation of domain states. The value of the EB field increases and shows a maximum value with increasing cooling field, which can be explained by the competition between the field-dependent Zeeman energy and the exchange interaction at the interface.     

棱镜色散腔XeF(C-A)蓝绿激光线宽压缩

XeF(C-A)蓝绿激光的增益系数较低,仅为0.003 cm-1,要获得高能量窄线宽激光输出有一定难度。利用色散元件棱镜开展了高单脉冲能量窄线宽激光输出实验研究,结果表明:采用凹面输出镜的情况下,激光线宽可以压缩到约2.5 nm,激光输出能量最大为3.47 J;采用平面输出镜,激光线宽压缩到约0.7 nm,激光输出能量最大为2.93 J,激光光谱调谐范围最大可达到60 nm,在460～520 nm之间。