Electric-field-induced second harmonic generation technique

As an example, we can consider the values of A m( 2w w, w, 0) which can be measured using Electric-Field-Induced Second-Harmonic Generation techniques. The values of A jxL( 2u> w, w, 0) in the different conventions will obey the following relationships... 

Electric Field Induced Second-Harmonic Generation. An essential aspect of the development of materials for second-order nonlinear optics is the determination of the p tensor components. The technique that has been developed to accomplish this is called electric field induced second harmonic generation (EFISH) (13,14). 

Third-Order NLO Techniques. There is a wider range of third-order techniques commonly used to characterize materials, including electric field induced second harmonic generation (EFISH) (15, 16), third harmonic generation (THG) (17) and degenerate four wave mixing (DFWM) (18). EFISH and DFWM will be discussed briefly then... 

For the experimental determination of the second-order first hyperpolarizability, some sort of non-centrosymmetry has to be present in the solution. This can be achieved by applying a static electric field over a solution of neutral molecules with dipolar chromophores. Implicitly, this description limits the applicability of this Electric-field-induced second-harmonic generation (EFISHG) technique ... 

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]. 

The first common method for molecular first hyperpolarizability determination is the electric field-induced second harmonic generation (EFISH) technique in solution [6-10]. This technique can be applied only to dipolar molecules. Under an applied external electric field, molecules in solution orient approximately in the direction of the field giving rise to second harmonic generation. The measured third-order nonlinear optical susceptibility is given by the following expression ... 

Kajzar F (1997) Electric field induced second harmonic generation in materials characterization and optical probe techniques. In Lessard R, Franke H (eds) Critical reviews of optical science and technology. SPIE, vol CR69, Bellingham, p 480... 

The Electric-Field-Induced Second-Harmonic Generation (EFISHG) technique makes it possible to measure the molecular hyperpolarizability, p, on liquids or molecular solutions. The centrosymmetry of tire solution is broken by applying a DC electric field to induce an average orientation of the molecules due to interactions of the permanent dipoles of the molecules and the electric field. The energy of a dipole with a permanent dipole fi in an electric field E is given by ... 

In order to select a particular experimental technique to measure x , it is very important to keep in mind which parameter of the third-order nonlinear response has to be characterized. For example, if one wants to determine the time-response due to molecular reorientation, one cannot choose Third-Harmonic Generation or Electric-Field-Induced Second-Harmonic Generation, since none of these techniques provide time-response information. Depending on the parameter of interest, a specific technique must be chosen. The following physical mechanisms can contribute to the third-order nonlinear response [54] ... 

Bruce and Thornton reported the first hyperpolarisability (f3) of chiral rhodium(I) and iridium(I) 4-alkoxystilbazole complexes via the technique of electric-field induced second harmonic generation (EFISH), and found values of about 24 x 10 Barbera et al. determined / ... 

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... 

Suslick et al. measured the first hyperpolarizabilities ()S) of porphyrins having electron-donor (amino) and -acceptor (nitro) groups in the para-position of 5,10,15,20-substituted tetraphenylporphyrins (Figure 25) using electric field induced second harmonic generation (EFISH) technique at 1.19 pm with chloroform solutions. The dipole moment (p) and P values were affected by the position of donor and acceptor groups. A P value of 30 x 10 esu and dipole moment of 7 x 10 esu were measured for the porphyrin having R = R = NO2, R = R = NH2 and the porphyrin... 

Experimentally, mainly two techniques - the electric field induced second harmonic generation (EFISH) and hyper-Rayleigh scattering (HRS, also termed harmonic light scattering method) - are used in order to determine in solution the experimental value of the quadratic hyperpolarizability of molecular NLO chromophores. 

P -Values can be measured by several techniques, including electric field induced second harmonic generation and solvatochromic measurements of absorption and fluorescence Moreover, quantum mechanical calculations can be used to estimate these nonlinearities For a more detailed description of the physical backgrounds of nonlinear optics we like to refer to excellent reviews and books< ° >. 

Combination with Static Fieids. A common technique, useful for optoelectronic devices, is to combine a monochromatic optical field with a DC or quasistatic field. This combination can lead to refractive index and absorption changes (linear or quadratic electrooptic effects and electroabsorption), or to electric-field induced second-harmonic generation (EFISH or DC-SHG, 2 > = > - - third-order process. In EFISH, the DC field orients the molecular dipole moments to enable or enhance the second-harmonic response of the material to the applied laser frequency. The combination of a DC field component with a single optical field is referred to as the linear electrooptic (Pockels) effect co = co + 0), or the quadratic electrooptic (Kerr) effect ( > = > - - 0 -I- 0). These electrooptic effects are discussed extensively in the article Electrooptical Applications (qv). EFISH is... 

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