Nonlinear second-harmonic signal

Nonlinear Optical Devices. A transparent, optically active, sol—gel-derived organic—inorganic glass has been synthesized (68). This hybrid consists of a 2,4-dinitroaminophenylpropyl-triethoxysilane covalently bound to a siUcon alkoxide-derived siUca network. This hybrid exhibits a strong electric field-induced second harmonic signal and showed no signs of crystallization. 

The nonlinearity of the sample was analyzed using the experimental procedure described in Section 3.3 The polarization of the fundamental beam of a YAG laser was continuously varied by means of a quarter waveplate, and the intensity of the second-harmonic signal was measured as a function of the rotation angle of the quarter waveplate. The obtained polarization pattern were then fitted to Eq. (42), which yields the relative values of the expansion coefficients /, g, and h. The experimental results for the transmitted, glass-side-incidence, s-polarizcd signal are shown in Figure 9.20. 

Although use of the second harmonic signal from metal surfaces as an indirect probe of chemisorption lacks structural specificity, the utility of the technique is clearly demonstrated by the experiments reported here. The next step in our studies will be to demonstrate how one can directly monitor chemisorption with some degree of molecular specificity via the resonant second harmonic signal from the nonlinear susceptibility of adsorbed species. 

The Maker fringe method is one of the most used methods for determining the second-order nonlinear susceptibility x /t of a crystal [27]. It is a relative method and is only useful when the second-harmonic signal is compared with the signal from a crystal with known values. The experiment is designed as follows. 

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