SHG intensity

Table 58. SHG intensity values (hdho, (SiO2)) °f some tantalum and niobium fluorides and oxyfluorides after normalization by alpha-quartz signal fu (SiO]). Measurements were taken before and after thermal treatment, up to extinction of signal.

FIGURE 27.34 SHG-intensity recorded on Au(lll) under /7-polarisation vs. azimuthal angle cp for three electrode potentials E= —0.7 V, -0.1 V, and +0.3 V. Electrolyte was IM NaC104 + 0.002M NaBr. (From Pettinger et al., 1995, with permission from Elsevier.)... 

FIG. 4 SHG intensity from the dye eosin B adsorbed at the air-water interface as a function of the pH of the bulk aqueous solution. The aqueous dye concentration is 30 /xM and the fundamental wavelength is 532 nm. 

FIG. 5 Time-resolved SHG intensity from the doubly charged eosin B at the air-water interface after randomization of the orientation distribution, (a) Square root of the SH signal recorded for the s-polarized SHG output intensity and the fundamental beam 45°-polarized. (b) Square root of the SH signal recorded for the p-polarized SHG output intensity and the fundamental beam s-polarized. (From Ref 96, copyright Elsevier Science BV.)... 

FIG. 6 SHG intensity as a function of time (ON) with and (OFF) without illumination of the interface by a probe ETV pulse. The increased SHG intensity during illumination arises from the production of the species I at the interface by photoinduced electron transfer, see text for more details. (From Ref. 103, copyright American Chemical Society.)... 

FIG. 8 SHG intensity as a function of time for a solution of DOPG and DPPG liposomes in presence of the dye malachite green in the solution and adsorbed at the liposome surface. The effect of transport across the bilayer is observed through the decay of the SHG intensity at short times. (From Ref. 117, copyright Elsevier Science BV.)... 

The measurement of SHG intensities thus provides information on the concentration N, the molecular orientation T), and the polarization a of SHG active species at the interface. 

The SHG measuring system is shown in Fig. 1. The dependence of the SHG intensity, /(2a,), of a membrane incorporated with ionophore 2 (membrane 2, see Fig. 2) in contact with 0.18 M aqueous KCl on the power of the irradiation light beam, /(a,), is shown in Fig. 3. A linear relationship is seen between the input power, /(a,), and the square root of the SHG intensity, I(2co)- This relation satisfies the principle of SHG [see Eq. (1)] and thus confirms that the light detected in this system is indeed arising from SHG. 

A nearly linear relation was in fact found between the reciprocal of the square root of the SHG intensity and the reciprocal of the bulk cation concentration for membrane 1,... 

FIG. 3 Dependence of the square root of the SHG intensity on the power of the irradiated fundamental light, as obtained with membrane 2 with an ionophore concentration of 3.0 x 10 M. The adjacent aqueous solution was 1.8 x 10 M KCl. Inset dependence of the SHG intensity on the input optical power. (From Ref 15.)... 

FIG. 6 Dependence of the square root of the SHG intensity ( I(2a>)) for membrane 2 without KTpCIPB (a) with KTpCIPB (b) on K+ ion concentrations in the adjacent aqueous solution containing KCl (O) and KSCN ( ), respectively. Inset The corresponding observed EMF to KCl and KSCN. The concentrations of ionophore 2 and KTpCIPB were 3.0 X 10 M and 1.0 x 10 M, respectively for both SHG and EMF measurements. The data points present averages for three sets of measurements. Error bars show standard deviations. (From Ref. 15.)... 

The determination of the number of the SHG active complex cations from the corresponding SHG intensity and thus the surface charge density, a°, is not possible because the values of the molecular second-order nonlinear electrical polarizability, a , and molecular orientation, T), of the SHG active complex cation and its distribution at the membrane surface are not known [see Eq. (3)]. Although the formation of an SHG active monolayer seems not to be the only possible explanation, we used the following method to estimate the surface charge density from the SHG results since the square root of the SHG intensity, is proportional to the number of SHG active cation com-... 

To determine the influence of ionic sites on the charge separation at the membrane interface, we have measured in this study SHG with ionophore-free and ionophore-incorporated liquid membranes in absence and presence of ionic sites. The dependence of the SHG intensity on the activity of the primary ion in the aqueous solution is presented and compared to the corresponding EMF. 

The EMF and SHG responses for nitrobenzene as solvent were qualitatively identical to those for l,k2-dichloroethane [Fig, 17(b)]. The only difference between the results for the two solvents was that the SHG response to KCl of nitrobenzene membranes with ionic sites was more sensitive than for 1,2-dichloroethane membranes with ionic sites, where an increase in the SHG intensity was observed at KCl activities above 10 " M KCl. 

X-ray structural analysis of the methylsulfate compound indicates the orthorhombic crystal unit cell contains two translationally inequivalent cations positioned on mirror planes and tilted at 3 ° relative to the two-fold screw (c) axis (23). This is a compromise orientation for simultaneously, rather than individually, maximizing x ccc and x /> bbc in this polar structure. This structure is therefore consistent with the extremely large SHG intensity reported in Table 1 while, also consistently, preliminary x-ray data show the perrhenate and tetrafluoroborate salts to be isostructural (23.). Details of the packing... 

Figure 5 shows a logarithmic plot of the steady state value of the SHG intensity versus applied voltage. The nearly quadratic response expected for a parabola is evident. A 20% variation from quadratic behavior would result in points within the limits indicated in Figure 5. 

Figure 4. Plot of SHG intensity vs. electric field under various conditions. See text for explanation. (Reproducedfrom Ref. 13. Copyright 1983, American Chemical Society.)...

It must be borne in mind that the signal is caused by the interference of all three terms so an increase in a(u>) does not necessarily lead to a corresponding increase in the SHG intensity. Nevertheless, a strong change in a uj) will always show up in the SHG signal. 

Fig. 1 Potential-dependent SHG response of a thin silver film (45 nm) in contact with a solution of 0.1 M NaCl04 (solid circles), 0.1 M NaCl04 -1-50 mM urea (solid squares), and 0.1 M sodium acetate - -5 mM lead acetate (open triangles). Most of the crystallites of the pc-Ag film were oriented with the (111) face parallel to the surface. The minimum of the curve occurs at around —0.75 V, which is close to the PZC for Ag(l 11) surface. Adsorption of urea causes a little shift in PZC and a significant decrease of the SHG intensity negative of PZC point, whereas the deposition of a monolayer of Pb causes a dramatic increase in the SHG intensity [6, 9].

Figure 22. (a) Square root of the SHG intensity (V/(2w)) and (b) observed membrane potential as a function of the concentration of K ion in the adjacent aqueous solution containing KCI (o) and KSCN ( ), respectively. The composition of the PVC matrix liquid membrane containing ionophore 80 is the same as in Figure 21 b (reprinted with permission from Ana/. Chem. 1995, 67, 574. Copyright 1995 American Chemical Society). 

It was indicated numerous times that the SHG intensity is dependent on both the magnitude of x<2) tensor elements as well as the phase relationships between fundamental and harmonic fields in the crystal. Under certain circumstances, it is possible to achieve phase matched propagation of the fundamental and harmonic beams. Under these conditions, power is continually transferred from the fundamental to harmonic beam over a path length, which is only limited by the ability... 

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