Electric-field-induced second harmonic generation experiment

Both theoretical analysis and dipole moment measurements indicated that sulfonyl-substituted compounds may have ft coefficients similar in magnitude to their nitro analogues. Therefore, we have measured p for several sulfonyl- and nitro-substituted compounds using electric-field-induced second-harmonic generation method (EFISH) (11,25). In this experiment, one measures an effective third-order nonlinearity rEFISH for a solution containing the compound of interest, given by... 

TDDFT methods have also been applied successfully to the description of the linear and nonlinear optical properties of heteroleptic sandwich complexes. The optical spectrum and the hyperpolarizability of Zr(OEP)(OEPz,) for which large first hyperpolarizabilities, /JSHG (SHG=second-harmonic generation) were measured in an electric field induced second-harmonic generation (EFISH) experiment [182], have been investigated by TDDFT methods [134]. The excitation energies and oscillator strengths calculated... 

The susceptibility x —2w,o),w,0) is determined in the EFISHG experiment [electric-field-induced second harmonic generation see below (Levine and Bethea, 1974, 1975)]. In order to measure the two independent components and x cxz of this susceptibility, the experiment can be performed under two polarization conditions, the incident IR photons being polarized parallel and perpendicular to the externally applied field (Wortmann et al., 1993). For theoretical treatments see also Andrews and Sherborne (1986), Wagniere (1986) and Andrews (1993). A concentration series finally yields the molar polarizabilities (Kleinman symmetry assumed) through (109),... 

Ever since HRS has been developed as an experimental technique to determine the first hyperpolarizability p of molecules in solution, it has been realized that multiphoton fluorescence is a competing nonlinear process, contributing to the HRS signal [26]. For the classical dipolar and neutral molecules that may exhibit multiphoton fluorescence, electric-field-induced second-harmonic generation (EFISHG) experiments are possible. However, for ionic and non-dipolar compounds, no electric field can be applied over the solution. Hence, no EFISHG measurements are possible. Then it is very tempting to rely on the HRS measurement only. When there is, however, a multi-photon fluorescence (MPF) contribution, an overestimation of the first hyperpolarizability value results [27]. 

Another effect sensitive to optically induced change is the electric field induced second harmonic generation (EFISH) experiment. In the presence of external electric static field, an isotropic medium becomes noncentrosymmet-rical and the second harmonic generation becomes possible ... 

The lack of a permanent dipole moment in the cryptand-based molecules makes the classical electric field-induced second harmonic generation (EFISH) experiment (154) unsuitable for the determination of molecular nonlinearity p which, however, can be obtained in solution employing the hyper-Rayleigh scattering (HRS) technique (155). The powder SHG measurements were carried... 

Most of the studies on push-pull phthalocyanines have been carried out by means of Electric Field Induced Second Harmonic (EFISH) Generation experiments in solution. Since only one experimental condition is favorable for EFISH, namely, parallel polarizations for all optical and static fields, these experiments lead to only one observable the vector component along the charge transfer axis assuming that the dipole moment vector and the vector part of the third-rank tensor along tlie molecular z-axis are collinear). 

Many of the different susceptibilities in Equations (2.165)-(2.167) correspond to important experiments in linear and nonlinear optics. x<(>> describes a possible zero-order (permanent) polarization of the medium j(1)(0 0) is the first-order static susceptibility which is related to the permittivity at zero frequency, e(0), while ft> o>) is the linear optical susceptibility related to the refractive index n" at frequency to. Turning to nonlinear effects, the Pockels susceptibility j(2)(- to, 0) and the Kerr susceptibility X(3 —to to, 0,0) describe the change of the refractive index induced by an externally applied static field. The susceptibility j(2)(—2to to, to) describes frequency doubling usually called second harmonic generation (SHG) and j(3)(-2 to, to, 0) describes the influence of an external field on the SHG process which is of great importance for the characterization of second-order NLO properties in solution in electric field second harmonic generation (EFISHG). 

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