组装L-B膜光学二次谐波的实验研究

一种分子形成的多层L-B膜由于相邻层的分子取向相反而使非线性极化抵消,总的X~(2)=0.本文用光学二次谐波方法确定了带有不同极性基团的L-B单分子层的有效非线性系数的大小和符号,对有效非线性系数符号相反的两种单分子层交替组装,使相邻单分子层的非线性极化相互叠加,得到了具有较大二阶非线性系数的组装L-B膜.     

Theory of the rotational structure of resonant Raman scattering by diatomic molecules

The apparatus of irreducible tensor operators is used to calculate the rotational structure of resonant Raman light scattering by freely rotating diatomic molecules. It is shown that solution of the problem reduces to the calculation of certain special coefficients. Their relation to the Placzek-Teller factors (which are well known in the theory of polarizability) is established. The nonzero coefficients are computed for the case when resonant rotational scattering is due to the¹ terms of the diatomic molecule.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 54–58, October, 1987.The author thanks T. N. Popov for interest in the work.     

Cavity ring-down spectroscopy of metallic gold nanoparticles

The optical properties of supported gold nanoparticles with sizes of 1.3 nm, 1.6 nm, 2.5 nm, and 2.9 nm have been studies by using cavity ring-down spectroscopy in the photon energy range between 1.8 eV and 3.0 eV. The obtained results show the possibility to obtain optical information of nanoassembled materials with high sensitivity. The experimental findings are compared to calculations using Mie-Drude theory. Whereas the broadening of the surface plasmon resonance with decreasing size is well described by this model, the observed blue-shift of the surface plasmon resonance contradicts the predictions of the Mie-Drude theory. The latter effect can be explained by the presence of a skin region with decreased polarizability typical for coinage metal particles. Furthermore, it is found that the supported gold nanoparticles are robust under ambient conditions, an important issue when using these materials for optical applications.     

Inclusion of non-orthogonality on the valence bond charge-transfer model for nonlinear optical properties of push—pull molecules

In models based on valence bond theory for predicting nonlinear optical properties of push-pull molecules, the wave functions representing resonance structures are assumed to be orthogonal. We have extended the two-state valence bond charge-transfer model to include non-zero overlap integrals. The resulting model leads to analytic formulae for the polarizability and hyperpolarizabilities, which are related to the overlap and other molecular parameters. In particular we report, as a function of the overlap: (i) relatively weak dependence of the first-order polarizability; (ii) significant variations in both the magnitude and the shape of the response curves corresponding to the second- and third-order polarizabilities. This result may be of relevance in the context of optical switching effects induced by chemical changes (related to the overlap) rather than the more conventional field-induced effect.     

Nonlinear optical properties of stilbene and azobenzene derivatives containing azaphosphane groups

We have studied the nonlinear optical (NLO) properties of some donor–acceptor molecules with stilbene and azobenzene molecules as backbone. We have used the nitro group as the acceptor and azaphosphane (R₃P=N–) as the donor group. To study the effect of variation of NLO properties, we have replaced the substituents (Rs) connected to the phosphorus atom by methyl, amine and phenyl groups. We find that both first-order polarizability and hyperpolarizabilities are larger for stilbene derivatives and is maximum for the phenyl substitution. Second-order polarizability is higher for methyl substitution. We have also obtained the two-photon absorption cross-section for these molecules. We find that both one-photon and two-photon absorption cross-sections are maximum for the same excited state (first excited state in the case of stilbene and second excited state in the case of azobenzene derivatives).     

Probability density function of the intensity scattered by Rayleigh-particle aggregates. Evolution with optical properties

We study the probability density function of the statistical fluctuations of the intensity scattered by an aggregate freely floating in space and constituted by Rayleigh particles under the dipole approximation. Its evolution as a function of the optical properties of the particles (polarizability) and their separation distance is analyzed. Aggregate geometries with two and three particles will be considered. The influence of the multiple scattering effect on the statistics of the scattered intensity is especially studied.     

Optical polarizabilities of large molecules measured in near-field interferometry

We discuss a novel application of matter wave interferometry to characterize the scalar optical polarizability of molecules at 532 nm. The interferometer presented here consists of two material absorptive gratings and one central optical phase grating. The interaction of the molecules with the standing light wave is determined by the optical dipole force and is therefore directly dependent on the molecular polarizability at the wavelength of the diffracting laser light. By comparing the observed matter-wave interference contrast with a theoretical model for several intensities of the standing light wave and molecular velocities, we can infer the polarizability in this first proof-of-principle experiment for the fullerenes C₆₀ and C₇₀, and we find a good agreement with literature values. PACS 03.75.Dg; 03.65.-w; 33.15.Kr     

Approche théorique par ellipsométrie des constantes optiques de couches monoatomiques physisorbées

Ellipsometric measurements on the adsorption system xenon on graphite [5] have been confronted with partly Drude's macroscopic theory, partly Sivukhin's microscopic theory. The optical constants necessary for the theory have been calculated for each monolayer, using two experimentally known quantities, the polarizability of a free xenon atom, and the nearest-neighbour distance Xe-Xe. The ellipsometric signals calculated for each of the five monolayers are in excellent agreement with experiment, the macroscopic theory giving the best quantitative agreement. For the first incomplete monolayer the results do not grant a statement in favour of one theory or the other.     

激发态分子内质子转移有机分子HBT的三阶非线性光学特性

以532nm皮秒脉冲作抽运光,采用单光束Z-扫描技术对具有激发态分子内质子转移效应的有机分子2-(2′-羟基苯基)苯并噻唑(HBT)在其双光子吸收区的非线性光学特性进行了研究.实验结果表明,对532nm波长的光,HBT分子存在明显的双光子吸收.通过拟合开孔Z-扫描实验数据,求解了HBT分子在其双光子吸收区的非线性吸收系数,并探讨了抽运光强度对介质双光子吸收效应的影响.采用高斯分解法,通过拟合闭孔Z-扫描除以开孔Z-扫描数据,理论推导并计算了在介质对抽运光存在非线性吸收的情况下HBT分子的非线性折射率,以及不同入射光强度时HBT分子的三阶非线性极化率实部和虚部的值.计算结果表明,理论分析与实验结果较好地符合,这些结果为进一步研究和开发此类材料的应用提供了理论与实验依据.     

An ab initio study of vibrational corrections to the electrical properties of ethane

SCF quartic property hypersurfaces have been computed for the energy, quadrupole moment and polarizability tensor of ethane via finite differences of analytical derivatives to obtain zeropoint vibrational corrections to the properties. Coupled with accurate electrical properties computed at a correlated r _e geometry, using a range of correlated methods, especially BD and BD(T), excellent estimates of these properties have been obtained that incorporate the effects of vibrational averaging. The effect of deuterium substitution on the properties has been investigated, including the first known theoretical prediction of the dipole moment of CH₃CD₃, and the frequency dependence of the polarizability tensor and Rayleigh depolarization ratio have been examined. Careful attention has been paid to a critical comparison between these theoretical estimates and experimental measurements. Although the vibrational corrections are limited to SCF theory, and basis sets not as extensive as used in some studies of this kind, nevertheless the results can be compared quantitatively with experiment, and the agreement is found to be excellent. The results underline the necessity to allow for the effects of zero-point vibrational averaging when comparing theory with experiment, and suggest a viable approach for studies on larger molecules.     

Optimal trapping wavelengths of Cs2 molecules in an optical lattice

The present paper aims at finding optimal parameters for trapping of Cs₂ molecules in optical lattices, with the perspective of creating a quantum degenerate gas of ground-state molecules. We have calculated dynamic polarizabilities of Cs₂ molecules subject to an oscillating electric field, using accurate potential curves and electronic transition dipole moments. We show that for some particular wavelengths of the optical lattice, called “magic wavelengths”, the polarizability of the ground-state molecules is equal to the one of a Feshbach molecule. As the creation of the sample of ground-state molecules relies on an adiabatic population transfer from weakly-bound molecules created on a Feshbach resonance, such a coincidence ensures that both the initial and final states are favorably trapped by the lattice light, allowing optimized transfer in agreement with the experimental observation.     

Cavity cooling of internal molecular motion

We predict that it is possible to cool rotational, vibrational, and translational degrees of freedom of molecules by coupling a molecular dipole transition to an optical cavity. The dynamics is numerically simulated for a realistic set of experimental parameters using OH molecules. The results show that the translational motion is cooled to a few muK and the internal state is prepared in one of the two ground states of the two decoupled rotational ladders in a few seconds. Shorter cooling times are expected for molecules with larger polarizability.     

Spectra of direct excitation of phosphorescence in an isotopic mixed naphthalene crystal

Distributed polarizabilities of a series of n-alkanes C _n H_2n+2 (n = 2-7) in various conformations have been determined using Bader's topological theory of atoms in molecules. Using an appropriate localization scheme, a simple distributed model is constructed, where the methyl and methylene groups are characterized by their dipole polarizability tensors in local frames, and all charge flow polarizabilities between them are retained. A set of average polarizability parameters is proposed that takes into account the local environment of the methyl and methylene groups, and that not only reproduces the polarizability tensor for any member of the n-alkane series in an arbitrary conformation, but also is suitable for the calculation of induction energies.     

Quantum dot as spin filter and spin memory

We present the first measurement of the polarizability and the permanent dipole moment of isolated KC60 molecules by molecular beam deflection technique. We have obtained a value of 2506+/-250 A(3) for the polarizability at room temperature. The addition of a potassium atom enhances by more than a factor of 20 the polarizability of a pure C60 molecule. This very high polarizability and the lack of observed permanent dipole show that the apparent polarizability of KC60 is induced by the free skating of the potassium atom on the C60 surface, resulting in a statistical orientation of the dipole. The results are interpreted with a simple model similar to the Langevin theory for paramagnetic systems.     

Optical and structural anisotropy of a uniaxial nematic consisting of biaxial molecules with internal rotation

A relation is established between the refractive indices of a uniaxial nematic liquid crystal (LC) consisting of biaxial molecules with internal rotation and the properties of molecules and their structural ordering. It is shown that the correlation between the conformation degree of freedom associated with internal rotation of π-conjugate molecular fragments and the orientation degrees of freedom of the molecules as a whole leads to the existence of two mixed parameters of orientation-conformation order, which contribute to the optical anisotropy of the LC along with the parameters of the conformation and orientation order of the molecules. The effect of the correlation of the molecular degrees of freedom on the values of these order parameters and the properties of molecular polarizability is analyzed. The dependence of the polarizability of molecules on their orientation ordering in the LC is explained.     

太赫兹波段液晶分子极化率的理论研究

近年来,太赫兹(THz)波段电磁辐射的研究引起科学技术界广泛的关注.液晶(LC)材料具有宽带可调的特性且拥有成熟的工业技术基础,在基于液晶设计的太赫兹可调器件研究中显示了巨大的应用潜力.因此,为了快速发展实用的LC-THz调制器件,对液晶材料在太赫兹频率范围内的光电特性进行系统的了解是至关重要的.分子极化率是表征分子中电荷分布的重要物理量.采用密度泛函理论方法对液晶分子PCH5,5CB和5OCB在太赫兹波段的极化率性质进行计算研究,从电子结构的角度,利用极化率密度分析方法考察了分子不同区域对极化率数值的贡献,详细探讨了尾链、核心结构和极性取代基等不同基团对极化率及其各向异性的影响.     

Electro-optical parameters and Raman intensities of CH4, CH3D,CH2D2, CHD3 and CD4

The absolute Raman intensities and the depolarization ratios of the vibrational bands of gaseous CH₄, CH₃D, CH₂D₂, CHD₃ and CD₄ have been computed here using a compact formulation of the bond polarizability theory, in its zero and first-order approximations. The agreement with experimental values taken from the literature is very good for the first-order approximation, although the difference between both approximations is not very large for these molecules. The derivatives of the polarizability with respect to the symmetry coordinates of methane are given with signs that are physically meaningful.     

On the application of the theory of the brownian movement in a periodic potential to the study of inertial effects and dipole coupling

For a series of ten electron molecules (HF, H₂O, NH₃, CH₄) the molecular polarizability tensor and the derivatives with respect to the symmetry coordinates have been calculated from ab initio SCF wavefunctions using the finite field method as well as perturbation theory approaches. Raman intensities and degrees of depolarization derived from the finite field results agree well with the available experimental data.

The zeroth order bond polarizability model and the atom dipole interaction model have been analysed. Both models can be used to describe the computed static polarizabilities and the derivatives with respect to bond stretching, but fail for the derivatives with respect to the bending coordinates.     

A Tensorial Formalism Adapted to the Rovibronic Couplings in the Colored Hexafluorides: Application to the nu(5)(F(2g)) and nu(3)(F(1u)) Modes

A tensorial formalism adapted to the case of transition-metal hexafluorides in a degenerate electronic state has been developed on the basis of preceding works about spherical-top molecules in a nondegenerate electronic state. We have introduced electronic operators constructed using group theory features and some physical considerations. Vibronic couplings (Jahn-Teller effect, etc.) have been reviewed for the triply degenerate vibrational modes nu(5)(F(2g)) and nu(3)(F(1u)) leading to the identification of the main vibronic parameters. For the first time, an effective rovibronic Hamiltonian as well as the effective transition moment operators (dipole moment and polarizability) for rovibronic transitions have been studied qualitatively thanks to the tensorial algebra properties. Copyright 2000 Academic Press.     

Polarizability of gyrotropic sphere

The polarizability of gyrotropic spheres is studied in this short article. Gyrotropic media are anisotropic in two respects: the symmetric part of the permittivity dyadic is uniaxial, and furthermore, there is also antisymmetric part in the permittivity. The polarizability is also dyadic with its components depending on the relations of the permittivity components of the material.