Spectro-streak picosecond studies of intramolecular charge-transfer fluorescence

A spectro-streak photometer, an instrument for simultaneously measuring fluorescence intensity, time, and wavelength,I(t, ), with a single picosecond excitation pulse, has been constructed. Two typical and currently highly topical examples of mesurements are discussed. (1) the temporal development of the fluorescence form the intramolecular charge-transfer (ICT) state of the rigid aromatic compound 4,5-(1-methylindolino)3,4-naphthanthracene is studied in the protic solvent hexanol. (2) Propyl chain-linked pyrene/N,N-dimethylaniline is used as the model compound to study conformational changes associated with the transition from a contact ion pair to a sandwich exciplex.     

Triplet states of humic acids studied by laser flash photolysis using different excitation wavelengths

The spectra and kinetics of short-lived intermediates formed from aqueous (0.1 N NaOH) solutions of the natural mixture of humic and fulvic acids (HFA) were studied by laser flash photolysis using excitation wavelengths of 337, 390, 470, and 520 nm. Laser photolysis of HFA with light of 520 and 470 nm results in the formation of triplet excited states (T_HFA) characterized by the broad absorption spectrum with a maximum near 630 nm and lifetimes of 0.15 ms in deoxygenated solutions. The formation of two types of T_HFA with lifetimes of 0.1 and 2 ms and absorption spectra with maxima at 570 nm is observed under photolysis with light of 337 and 390 nm. The estimation of quantum yields of T_HFA gives 1 and 0.3% under photolysis with excitation wavelengths of 337 and 520 nm, respectively. The rate constants of T_HFA quenching by molecular oxygen are equal to (7—8)·10⁸ L mol^–1 s^–1.     

Quantum model of selective multiphoton processes: The role of external (field) and internal (anharmonic coupling) detunings

Quantum equations of motion describing the energy transfer dynamics via intramolecular anharmonic coupling are presented and solved numerically. Dynamical features of the average excitations of a homogeneous system (SF₆) and a heterogeneous system (H/W) are quantitatively discussed in terms of the intramolecular vibrational relaxation (IVR) rates. Possible mechanisms of surface-enhanced desorption via low-power laser radiation are proposed.This work was supported in part by the Office of Naval Research, the Air Force Office of Scientific Research (AFSC), United States Air Force, under Grant AFOSR-82-0046 and the National Science Foundation under Grant No. CHE-8022874Camille and Henry Dreyfus Teacher-Scholar (1975–82)     

次级源和误差传感器布放对带弹性障板的充液直管声振复合有源控制的影响*

针对充液管路系统噪声有源控制问题,研究了次级源和误差传感器布放对带弹性障板的充液直管管路系统有源消声与有源消振复合控制效果的影响。基于声固耦合方法建立了带弹性障板的充液直管管路系统的有限元模型,在声激励下对比了次级声源布放对系统有源消声性能的影响,并在组合激励下分析了次级力源、次级声源和误差传感器布放对系统复合有源控制的影响。结果表明,非对称分布的次级声源容易激起管壁振动,进而带动障板振动,导致有源消声效果不佳;采用对称分布的次级声源可使低频段的降噪量提高10 dB以上。复合有源控制可进一步提升全频段的控制效果。通过增加振动误差传感器数量,可使绝大多数频点的降噪量提高1~20 dB不等。此外,在管壁上布放的两圈次级力源的间距小于管壁振动波长的1/4,且都不位于管壁振动节点附近时控制效果更好。     

任意信源随机和的一类随机Shannon-McMillan定理

采用构造相容分布与非负上鞅的方法研究任意信源随机和相对熵密度的强极限定理,并由此得出若干任意信源,m阶马氏信源,无记忆信源的随机Shannon-Mcmillan定理.将已有的关于离散信源的结果加以推广.     

Propagation of Light in an Ensemble of Tripod Level Atoms

We study the propagation of a quantum probe light in an ensemble of tripod level atoms when the atoms are coupled to two other classical control fields. First we calculate the dispersion properties, such as susceptibility and group velocity, of the probe light within such an atomic medium under the case of three-photon resonance via the dynamical algebra method of collective atomic excitations. Then we calculate the dispersion of the probe light in the case that two classical control fields have the different detunings to the relative atomic transitions. Our results show that in both cases the phenomenon of electromagnetically induced transparency can occur. Especially under the second case, we can find two transparency windows for the probe light.     

双光子激发荧光成像技术对小鼠植入前胚胎的实时观测

双光子激发的蓝移效应可使利用同一束超快激光同时激发多种不同荧光特性的生物荧光染料的设想得以实现。选取锁模飞秒掺钛蓝宝石(Ti-sapphire)激光器输出的730nm激光,分别激发Hoechst33342,Fluo-4,PI和Indo-1四种常用生物荧光染料,分别利用(455±15)nm,(540±15)nm,(580±16)nm和(500±15)nm四种滤光片获得特异性荧光图像。结合双光子激发荧光成像技术穿透深,光损伤小,信噪比好等优势,选取合适的荧光染料组,应用单束激光激发、双染双通道成像方法,对小鼠植入前胚胎内细胞中的钙信号和染色体进行三维、四维实时成像,为探究小鼠植入前胚胎发育规律提供一种全新的多参数观测手段。     

电子俘获材料CaS∶Eu,Sm光谱特性研究

研究了电子俘获材料CaS∶Eu,Sm多晶粉末的紫外-可见-红外吸收光谱及红外激励光谱.研究结果表明,CaS∶Eu,Sm中主激活剂Eu和辅助激活剂Sm分别以Eu2 离子和Sm3 离子的形式存在;ETM的吸收差谱及红外激励光谱所反映的光谱特性是不同的.紫外-可见光区的吸收差谱给出了ETM光谱存储灵敏度的信息,而红外光谱区的吸收差谱给出了ETM所俘获电子数量的信息及电子陷阱能级的特征(深度和宽度)信息.红外激励光谱则反映了ETM将不同波长的红外激励光的能量转换为特定波长处的红外辐射光能量的光谱转换灵敏度.二者结合起来可以更完整地描述ETM的光谱特性.     

Functional neuroimaging of inner fields-of-view with 2D-selective RF excitations

Echo-planar imaging is widely used in functional neuroimaging but suffers from its pronounced sensitivity to field inhomogeneities that cause geometric distortions and image blurring which both limit the effective in-plane resolution achievable. In this work, it is shown how inner-field-of-view techniques based on 2D-selective RF excitations (2DRF) can be applied to reduce the field-of-view in the phase-encoding direction without aliasing and increase the in-plane resolution accordingly. Free-induction-decay (FID) EPI and echo-train-shifted (T2*-weighted) and standard (T2-weighted) spin-echo (SE) EPI with in-plane resolutions of up to 0.5×1.0 mm² (slice thickness 5 mm) were acquired at 3 T. Unwanted signal contributions of 2DRF side excitations were shifted out of the object (FID-EPI) or of the refocusing plane by tilting the excitation plane (SE-EPI). Brain activation in healthy volunteers was investigated with checkerboard and finger-tapping block-design paradigms. Brain activation could be detected with all sequences and contrasts, most reliably with FID-EPI due to its higher signal amplitude and the longer 2DRF excitation that are more sensitive to magnetic field inhomogeneities. In conclusion, inner-FOV EPI based on 2DRF excitations could help to improve the spatial resolution of fMRI of focal target regions, e.g. for applications in the spinal cord.     

Efcient Multipartite Polarization Entanglement Distribution Over Arbitrary Noise Channel

We present an efcient faithful multipartite polarization entanglement distribution protocol over an arbitrary noisy channel.The spatial degree of freedom is used to carry the entanglement during the transmission.We describe the principle by distributing n-qubit Greenberge–Horne–Zeilinger state and n-qubit W state.Our scheme can be used to distribute arbitrary n-qubit entangled states to n distant locations.The remote parties can obtain maximally entangled states deterministically on the polarization of photons.Only passive linear optics are employed in our setup,which makes our scheme more feasible and efcient for practical application in long distance quantum communication.