Showing papers on "Hyperpolarizability published in 1982"

Relations between microscopic and macroscopic lowest-order optical nonlinearities of molecular crystals with one- or two-dimensional units

Abstract: Efficiency of three-wave interactions in molecular crystals depends on the conjugation of the molecular unit, which in turn is a one- or two-dimensional property. This strong anisotropy reduces the number of non-negligible molecular lowest-order hyperpolarizability coefficients to four. The lowest-order macroscopic optical nonlinearity can be expressed, in the absence of significant intermolecular effects, as the tensorial sum of molecular hyperpolarizabilities. This analysis is applied to the 17 relevant noncentrosymmetric crystal point groups, generalizing a previous analysis of nonlinear-optical properties of methyl-(2,4-dinitrophenyl)-aminopropanoate crystals. In several cases, the molecular unit anisotropy is shown to impose structural relations between coefficients of macroscopic nonlinearities, in addition to the usual relations resulting from the crystal point symmetry only. In such cases, nonlinear-optics experiments can be used for testing molecular anisotropy and molecular orientations within the unit cell in the absence of significant nonlinearity arising from intermolecular coupling. Similar relations can be derived between electro-optic coefficients, but limited to the case of weak contributions of intermolecular vibration to the electro-optic effect. We investigate for each point group the possibility of inferring hyperpolarizability coefficients from macroscopic nonlinear measurements, a complementary approach to that based on theoretical molecular calculations or electric-field-induced second-harmonic generation in solution. In the case of highly anisotropic one-dimensional charge-transfer systems (exemplified by $p$-nitroaniline), for each point group and a given molecular hyperpolarizability, the optimal orientation of the charge transfer axis, leading to the highest phase-matchable coefficient, is given. It is shown that crystal point groups 1,2,$m$, and $\mathrm{mm}2$ correspond to the highest possible value of this coefficient, while other crystal symmetry is less favorable. These considerations are applied to four available efficient molecular crystals and used either as a check of molecular orientations in a case of low crystalline symmetry or to estimate otherwise unavailable molecular nonlinear coefficients.

Structural dependence of nonlinear-optical properties of methyl-(2,4-dinitrophenyl)-aminopropanoate crystals

Abstract: We analyze the structural relationship between microscopic and macroscopic tensors which characterize the linear- and nonlinear-optical properties of molecular crystals exhibiting a strong donor-acceptor intramolecular interaction, with particular reference to methyl-(2,4-dinitrophenyl)-aminopropanoate (MAP). The quasiplanar structure of the active part of these molecules results in a strong and characteristic anisotropy of the optical hyperpolarizabilities, which can be traced up to the macroscopic level when taking into account the crystal symmetry as well as the orientation of the molecules in the unit cell. The experimental data on MAP are thoroughly analyzed on this basis, and it is found that a two-dimensional model of the lowest-order hyperpolarizability tensor results in a structural relation between the macroscopic tensor components, which is in agreement with experimental data. In addition, the principal dielectric axes of this monoclinic crystal are determined by the orientation of the aromatic plane in the unit cell. The overall analysis also enables the determination of four independent components of the molecular hyperpolarizability tensor from experimental data only, and the results have been compared to those of a semiempirical intermediate neglect of differential overlap calculation. The anisotropy of this tensor reveals that the intramolecular charge transfer responsible for the large optical nonlinearity is predominantly from the amino group to the nitro group in para position, rather than towards the nitro group in ortho position. Finally the overall analysis provides a basis for discussing what should be the best orientation of the molecules in the unit cell for maximizing the crystal nonlinearity. The result is that phase-matchable nonlinear coefficients up to six times larger than in MAP could be observed in compounds with similar molecular hyperpolarizabilities but an optimum crystal structure.

New organic molecular materials for nonlinear optics

Abstract: We present four molecular organic crystals which were recently proposed for applications in nonlinear optics (three-wave-mixing and electrooptic effects) : methyl - (2,4 - dinitrophenyl) - aminopropanoate (MAP), 2 - methyl - 4 - nitroaniline (MNA), 3 - methyl - 4 - nitropyridine - 1 - oxyde (POM) and urea. The nonlinear efficiency of molecular organic crystals is seen to depend on the molecular hyperpolarizability and on the crystalline geometry. Both features are discussed and shown to lead, for crystal point groups of lower symmetry, to new structural relations between crystalline non linear coefficients. Each of the four molecular crystals discussed here are shown to have specific properties connected to different types of applications.

Calculations of induced moments in large molecules. III. Polarizabilities and second hyperpolarizabilities of some aromatics

Abstract: We report the results of calculations of the average polarizability α and second hyperpolarizability γ for benzene, naphthalene, and three different configurations of biphenyl, phenanthrene, anthracene, and pyrene. The computations were performed employing a scheme whose main elements are McWeeny’s coupled Hartree–Fock perturbation theory, the CNDO approximations, and a small, properly optimized, extended basis. The mean error for the average polarizabilities is 7%. The error for the second hyperpolarizability of naphthalene is within the experimental uncertainty.

An SCF calculation of the derivatives of the multipole moments and polarizabilities of formaldehyde

Abstract: The components of the dipole moment 𝛍, quadrupole moment 𝛉, dipole polarizability α, dipole-quadrupole polarizability A and first hyperpolarizability β of the formaldehyde molecule have been calculated as functions of nuclear coordinates with an accurate SCF wavefunction. Calculation of derivatives of these properties subject to the Eckart conditions is discussed.

Calculations of induced moments in large molecules I. Polarizabilities and second hyperpolarizabilities in some alkanes

Abstract: We report the results of coupled Hartree-Fock computations for the average polarizability, α, and hyperpolarizability, γ, of CH4, C2H6, C3H6 and C3H8. The Hamiltonian matrices are constructed from an extended CNDO model. Small as well as large basis sets were tested. Agreement with available experimental values is within 13% for α and 31% for γ.

Electric properties of negative ions. Dipole hyperpolarizability of the fluoride ion

Abstract: Hyperpolarizability γ of the fluoride ion is calculated. The calculations were performed using GTO/CGTO basis sets3. (AIP)

The Polarizability and Hyperpolarizability Tensors

Abstract: This chapter is concerned with the properties of the polarizability and hyperpolarizability tensors with particular reference to their roles in Rayleigh and Raman scattering and in hyper Rayleigh and hyper Raman scattering, respectively. Before embarking on the detailed mathematical treatments of these tensors it seems appropriate to indicate briefly the nature of these forms of scattering and why an understanding of these tensors is necessary.

Dependences of the parameters of the liquid-crystal order on the molecular hyperpolarizability

Abstract: An anharmonic oscillator model of an anisotropic molecule is used to calculate the changes in the temperature of a nematic phase transition and in the pitch of a cholesteric helix as a function of the cubic hyperpolarizability. The results obtained are used to explain the nonmesogenic nature of anisotropic molecules with an internal (intramolecular) charge transfer.