EFISH harmonic technique

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... 

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 ... 

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. 

The HRS technique [25-27] involves the detection of the incoherently scattered second harmonic generated by the molecule in solution under irradiation with a laser of wavelength 2, leading to the mean value of the x tensor product. By analysis of the polarization dependence of the second harmonic signal, which can be evaluated selecting the polarization of the incident and scattered radiation, it is possible to obtain information about the single components of the quadratic hyperpolarizability tensor jS. Unlike EFISH, HRS can also be used for ionic molecular species and for nondipolar molecules such as ocmpolar molecules. In this chapter, the quadratic hyperpolarizability measured with an incident wavelength 2 by the EFISH and HRS techniques will be indicated as /l i(EFISH) and / (HRS), respectively. 

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... 

In the EFISH technique (Electric Field Induced Second Harmonic) a solution of the (dipolar) chromophore under consideration is put into a uniform static electric field, obtained for example with parallel metal electrodes. In practice, instead of putting metal electrodes in the solution, the solution is put in a wedge shaped cell bounded by glass windows at which metal electrodes are applied [8]. Owing to the dipolar nature of the chromophores, they statistically orient under the electric field and the whole solution becomes a second order NLO-active polar medium. When a laser radiation crosses the solution, second harmonic radiation is generated and collected. By comparison with a standard nonlinear medium (usually a quartz slab) it is possible to extract the value of the dot product of the chromophore. As we have... 

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