Three-photon-induced fluorescence of diphenylhexatriene in solvents and lipid bilayers

We observed the emission of l,6-diphenyl-l,3,5-hexatriene (DPH) when excited with the fundamental output of a fs Ti:sapphire laser at 860 nm. The emission spectra of DPH were identical to that observed for one-photon excitation at 287 nm. The dependence of the DPH emission intensity on laser power was cubic, indicating three-photon excitation of DPH at 860 nm. At a shorter wavelength of 810 nm, the dependence on laser power was quadratic, indicating a two-photon process. At an intermediate wavelength of 830 nm the mode of excitation was a mixture of two- and three-photon excitation. At 830 nm the anisotropy is no longer a molecular parameter, and the mode of excitation and anisotropy of DPH depends on laser power. Frequency-domain anisotropy decays of DPH in triacetin revealed the same rotational correlation times for two- and three-photon excitation. However, the time 0 anisotropy of DPH was larger for three-photon excitation than for two-photon excitation. Steady-state anisotropy data for DPH-labeled membranes revealed the same transition temperature for one- and three-photon excitation. These anisotropy data indicate that membrane heating was not significant with three-photon excitation and that three-photon excitation may thus be of practical usefulness in fluorescence spectroscopy and microscopy of membranes.     

H2O和HLi分子的双光子激发

用全相对论量子力学计算H2O和HLi的双光子偶极激发。为对比起见,同时用非相对论的对称匹配团族-组态相互作用法(SAC-CI)计算其单光子激发。对于无对称中心的H2O和HLi,符合相应群的对称选择原则。双光子跃迁几率一般比单光子跃迁的小3～5个数量级。在计算双光子偶极激发时,应采用同时包含了空间的对称性和时间反转对称性的全相对论。     

The luminescence properties of AlN with manganese and rare earth activators under ultraviolet and cathode-ray excitation

The emission spectra of self-, Mn-, Eu- and Sm-activated AlN luminophores under ultraviolet and cathode ray excitation as well as the excitation spectra for Mn and self-activated phosphors are measured. Basic information about the kinetics, excitation density dependence and energy transfer mechanism is given. The possibility of the direct excitation mechanism of Eu centres is discussed.The authors are indebted to Mr. J. Hejduk for the preparation of the initial material and to Mr. Veselý for the activation experiments. They thank Prof. Trlifaj for his continuous interest.     

Chatter suppression by parametric excitation: Model and experiments

Chatter vibration leads to challenges in precise machining due to its harmful effect on productivity and surface quality. In this study, a chatter suppression method based on parametric excitation was developed. The effect of parametric excitation on self-excited vibration was investigated based on a model of a van der Pol-Mathieu-Duffing oscillator with a time delay. It reveals that there can be a zero solution for the oscillator under the effect of parametric excitation, while it is impossible to have a stable zero equation without parametric excitation. The stability of a parametrically excited vibration system regarding the regenerative effect in the cutting processes was studied by the averaging method. The stability analysis shows that parametric excitation with an appropriate frequency and large amplitude has a chatter suppression effect no matter whether the waveform is a sinusoidal wave, square wave or triangular wave. To validate the effect of parametric excitation for chatter suppression, experiments were conducted based on a magnetorheological (MR) fluid-controlled boring bar, which can generate high-frequency parametric excitation based on the quick response of the MR fluid. Cutting experiments with an excitation current of different waveforms and diverse frequencies show that chatter can be significantly suppressed by the effect of parametric excitation.     

Rectification of space-charge waves upon optical and electrical excitation

A comparative analysis is performed for three optical and electrical methods of exciting space-charge waves in photosemiconductors: (i) excitation by an external ac electric field combined with a static interference pattern, (ii) excitation by a moving interference grating, and (iii) excitation by an oscillating interference grating. It is shown that, in the case when space-charge waves are excited using a combination of all three methods, the dependence of the direct current passing through a sample on the excitation frequency exhibits two peaks that correspond to the resonant excitation of two modes of space-charge oscillations, namely, drift waves and trap recharging waves. It is noted that experimental observation of the peak attributed to the excitation of trap recharging waves should not pose any problems, whereas observation of the second peak associated with the excitation of drift waves is significantly complicated because of the small magnitude of the effect, especially for materials with a low electrical conductivity (or a long Maxwell relaxation time).     

Ground-borne vibration due to static and dynamic axle loads of InterCity and high-speed trains

In predictions of railway-induced vibrations, a distinction is generally made between the quasi-static and dynamic excitation. The quasi-static excitation is related to the static component of the axle loads. The dynamic excitation is due to dynamic train–track interaction, which is generated by a large number of excitation mechanisms, such as the spatial variation of the support stiffness and the wheel and track unevenness. In the present paper, the quasi-static excitation and the dynamic excitation due to random track unevenness are evaluated by means of numerical predictions. A solution strategy is presented that allows for the evaluation of the second-order statistics of the response due to dynamic excitation based on the power spectral density function of the track unevenness. Due to the motion of the train, the second-order statistics of the response at a fixed point in the free field are non-stationary and an appropriate solution procedure is required. The quasi-static and dynamic contribution to the track and free-field response are analysed for the case of InterCity and high-speed trains running at a subcritical train speed. It is shown how the train speed affects the quasi-static and dynamic contribution. Finally, results of numerical predictions for different train speeds are compared with field measurements that have been performed at a site along the high-speed line L2 Brussels–Köln within the frame of homologation tests.     

The time dependence and efficiency of excitation of three-quantum coherence in proton spectroscopy of proteins

The time dependence and efficiency of excitation of three-quantum (3Q) coherence is examined for the peaks that are commonly observed in 'H NMR 3Q spectra of proteins. The algebraic expressions for the various contributions to each 3Q coherence are tabulated. Plots of the excitation efficiency versus the length of the excitation period are shown. These results provide guidelines for optimizing the length of the 3Q excitation period to obtain either a wide range of 3Q signals in the spectrum or the excitation of specific 3Q signals with maximum efficiency.     

Stationary States and Modulational Instability of Coupled Two-Component Bose-Einstein Condensates in a Ring Trap

We investigate modulational instability (MI) of a coupled two-component Bose-Einstein condensates in a rotating ring trap. The excitation spectrum and the MI condition of the system are presented analytically. We find that the coupling between the two components strongly modifies the MI condition, and the MI condition is phase-dependent. Furthermore, we discuss the effect of MI on both density excitation and spin excitation. If the inter- and intra-component interaction strengths are all equal, the MI causes density excitation but not spin excitation, and if the inter- and intra-component interaction strengths are different, the MI causes both density excitation and spin excitation. Our results provide a promising approach for controlling the stability and excitation of a rotating two-component Bose-Einstein condensates by modulating its coupling strength and interaction strength.     

LSO-Ce fluorescence spectra and kinetics for UV,VUV and X-ray excitation

Abstract

LSO-Ce fluorescence emission and excitation spectra and decay kinetics have been measured for UV, VUV and X-ray excitation at RT and 80 K. The features of the fluorescence excitation spectra of two types of cerium centres in the region 3 to 6 eV are analysed in the assumption of competitative absorption between them. It is shown that the centres can have similar absorption bands. Forbidden energy bandgap for LSO is evaluated to be not less than 6.5 eV.     

Strong-excitation and weak-excitation photodisintegration of DODCI

The disintegration yield of the organic dye DODCI dissolved in ethylene glycol and methanol due to cw excitation to the S1-state and due to intense picosecond pulse excitation to higher excited singlet states is determined. In the S1-state DODCI molecules disintegrate after about 5×104 excitation cycles while rhodamine 6G molecules in ethanol survive about 13×106 excitation cycles. In higher excited singlet states the DODCI molecules disintegrate on average after about 10 to 30 excitation cycles, while rhodamine 6G gets destroyed after about 140 excitation cycles.     

Quinary excitation method for pulse compression ultrasound measurements

A novel switched excitation method for linear frequency modulated excitation of ultrasonic transducers in pulse compression systems is presented that is simple to realise, yet provides reduced signal sidelobes at the output of the matched filter compared to bipolar pseudo-chirp excitation. Pulse compression signal sidelobes are reduced through the use of simple amplitude tapering at the beginning and end of the excitation duration. Amplitude tapering using switched excitation is realised through the use of intermediate voltage switching levels, half that of the main excitation voltages. In total five excitation voltages are used creating a quinary excitation system. The absence of analogue signal generation and power amplifiers renders the excitation method attractive for applications with requirements such as a high channel count or low cost per channel. A systematic study of switched linear frequency modulated excitation methods with simulated and laboratory based experimental verification is presented for 2.25 MHz non-destructive testing immersion transducers. The signal to sidelobe noise level of compressed waveforms generated using quinary and bipolar pseudo-chirp excitation are investigated for transmission through a 0.5 m water and kaolin slurry channel. Quinary linear frequency modulated excitation consistently reduces signal sidelobe power compared to bipolar excitation methods. Experimental results for transmission between two 2.25 MHz transducers separated by a 0.5 m channel of water and 5% kaolin suspension shows improvements in signal to sidelobe noise power in the order of 7–8 dB. The reported quinary switched method for linear frequency modulated excitation provides improved performance compared to pseudo-chirp excitation without the need for high performance excitation amplifiers.     

Fluorescence of horse liver alcohol dehydrogenase using one- and two-photon excitation

We examined the steady-state and time-resolved emission of liver alcohol dehydrogenase resulting from one-photon and two-photon excitation. Previous studies with one-photon excitation revealed that the two nonidentical tryptophan residues display different emission spectra and decay times. The use of two-photon excitation resulted in similar emission spectra, multiexponential intensity decays, time-resolved emission spectra, and anisotropy decays as was observed for one-photon excitation. These results suggest that both nonidentical tryptophan residues are excited to a similar extent for one- and two-photon excitation. However, the limiting anisotropy (r ₀) with two-photon excitation from 585 to 610 nm is below 0.1 and appears distinct from that observed previously forN-acetyl-l-tryptophanamide.Abbreviations LADH liver alcohol dehydrogenase - -NAD⁺ -nicotinamide adenine dinucleotide - OPE one-photon excitation - OPIF one-photon induced fluorescence - TPE two-photon excitation - TCSPC time-correlated single photon counting - TPIF two-photon induced fluorescence     

Piezoelectric surface excitation and detection of GHz-sound waves using planar structures: Hertzian- and H-slot resonators

We report on experiments with two new kinds of microwave resonators for piezoelectric surface excitation of GHz-sound waves. These resonators consist of planar metal structures simply made by photolithography and especially suitable for the higher frequency range where the usual reentrant cavities can be applied no more due to mechanical fabrication difficulties. Moreover, by choosing an appropriate resonator geometry, an electric excitation field with preferred orientation can be generated which allows to enhance or to supress wanted sound modes simply by turning the crystal relative to the excitation structure into an optimum orientation.Supported by Deutsche Forschungsgemeinschaft     

水溶性CdTe量子点的稳态和纳秒时间分辨光致发光光谱

报道了以飞秒脉冲激光为激发光源的水溶性CdTe量子点(QDs)的稳态荧光光谱和纳秒时间分辨荧光光谱.实验发现CdTe量子点的荧光光谱峰值位置随激发波长变化发生明显移动，激发脉冲波长越长，荧光峰位红移越大.荧光动力学实验数据显示，在400nm和800nm脉冲激光激发下，水溶性CdTe量子点的荧光光谱中均含有激子态和诱捕态两个衰减成分，两者的发射峰相距很近，诱捕态的发射峰波长较长.在800nm脉冲激光激发下的诱捕态成分占总荧光强度的比重比400nm激发下的约高3倍，其相对强度的这种变化导致了稳态荧光发射峰位的红移. 关键词： CdTe 量子点 时间分辨 荧光光谱 上转换荧光     

Interference between electric and magnetic amplitudes for K shell excitation of high-Z H-like projectiles

We report an investigation of projectile K shell excitation for high-Z ions in relativistic ion-atom collisions. For the case of H-like Bi, the excitation process is unambiguously identified by observing the radiative decay of the excited levels to the vacant 1s shell, in coincidence with ions that did not undergo any charge exchange in the reaction target. The results are compared with detailed relativistic calculations, showing that the magnetic interaction is of considerable importance for the K shell excitation process in high-Z ions. For excitation to the L shell sublevels, the experimental data confirm that the magnetic part of the Liénard-Wiechert interaction must be added coherently with the electric part leading to a significant reduction of the K shell excitation cross section.     

振动和转动激发对N2在Fe(111)表面解离吸附的影响

N₂的解离化学吸附是工业合成氨的速控步骤. 基于最近构建的六维势能面,本文研究了N₂的初始振动激发和转动激发在Fe(111)表面的反应性的作用. 由于该反应具有重要的量子效应,通过六维量子动力学计算研究了入射能量低于1.6 eV 时振动激发的效应. 并采用准经典轨线计算揭示了高入射能量下的振动和转动激发的影响. 通过这些研究发现增加平动能量在一定程度上能提高解离几率,振动激发或转动激发能更有效地促进解离. 这项研究为重原子分子-表面反应的模式特异性动力学提供了有价值的见解.     

光/电激发方式对AlGaInP及GaN基LED电学特性的影响

采用光激励与电激励的方式对AlGaInP与InGaN/GaN基LED的电学特性进行了表征,并重点比较分析了两种激励方式的下理想因子这一重要参数的差异.探讨了影响LED理想因子的因素,确定理想因子的适宜注入强度范围.研究结果表明:结温与注入强度是影响LED理想因子的重要因素;对于特定类型的发光二极管,空间电荷区起主导作用...     

Rabi oscillations and excitation trapping in the coherent excitation of a mesoscopic frozen Rydberg gas

We demonstrate the coherent excitation of a mesoscopic ensemble of about 100 ultracold atoms to Rydberg states by driving Rabi oscillations from the atomic ground state. We employ a dedicated beam shaping and optical pumping scheme to compensate for the small transition matrix element. We study the excitation in a weakly interacting regime and in the regime of strong interactions. When increasing the interaction strength by pair state resonances, we observe an increased excitation rate through coupling to high angular momentum states. This effect is in contrast to the proposed and previously observed interaction-induced suppression of excitation, the so-called dipole blockade.