SH signal intensity

For thicker DRl-MMA 35/65 copolymer samples, a sinusoidal dependence of the SH signal in function of the relative phase difference is also observed. But the contrast between the extreme values of the SH signal intensities is lower than for the 0.1 jj.m thick film. Modulation amplitude C is given by ... 

Table 2 and Table 3 give, respectively, the SHG intensity for the samples processed at 10 g and at 1 g, and measured after 10 days, 120 days and 150 days after their processings. The SH signal intensity was measured on two sides of the specimen to find out the polarization direction. The side which gave the higher signal was the correct side and the subsequent measurements were made for that side at three different points. 

Figures 6.2 and 6.3 show changes in the SH signal intensity from metal and semiconductor surfaces as the surfaces are covered by CO molecules and sodium atoms, respectively. The SH signal intensity was induced by 60 fs pulses at 570 nm (solid line, circles) and at 497 nm (dashed line) in 60° reflection geometry and in pp-orientation.

The deduced symmetries are consistent with electron diffraction (LEED) results. In contrast to LEED studies, however, which do not allow one to exclude the existence of a higher order (e.g., sixfold) symmetry, this is possible via SH measurements since at normal incidence a surface with such high symmetry would show no SH signal intensity at all. 

Via SHG it is possible to see the heat-induced increase in symmetry of the silicon surface if one observes the vanishing of the signal in a direction in which only the (2x1) surface induces SH signal intensity (Fig. 6.5). It can be seen that the phase transition from the lower to the higher symmetry has already started around 550 K surface temperature (Heinz et al. 1985). 

Frequency-dependent SH measurements at Ag(llO) have detailed different resonances in the energetic range between 1.6 eV and 2.1 eV (fundamental of the laser), which can be traced back partially to interband transitions and partially to transitions between occupied and nonoccupied surface states (Urbach et al. 1992). In the regime of interband transitions (for silver 2a = 3.8 eV) the corresponding field enhancement results in an enhancement of the SH signal intensity. A similar effect occurs if 2a corresponds to the transition between an occupied surface state below the Fermi level and an imoccupied state in the gap. Since transitions from bulk states of the same symmetry as the occupied... 

The SH signal directly scales as the square of the surface concentration of the optically active compounds, as deduced from Eqs. (3), (4), and (9). Hence, the SHG technique can be used as a determination of the surface coverage. Unfortunately, it is very difficult to obtain an absolute calibration of the SH intensity and therefore to determine the absolute number for the surface density of molecules at the interface. This determination also entails the separate measurement of the hyperpolarizability tensor jS,-, another difficult task because of local fields effects as the coverage increases [53]. However, with a proper normalization of the SH intensity with the one obtained at full monolayer coverage, the adsorption isotherm can still be extracted through the square root of the SH intensity. Such a procedure has been followed at the polarized water-DCE interface, for example, see Fig. 3 in the case of 2-( -octadecylamino)-naphthalene-6-sulfonate (ONS) [54]. The surface coverage 6 takes the form ... 

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.)... 

Figure 9.15 Second-harmonic intensity as function of rotation angle of quarter waveplate. (a) Transmitted -polarized SH signal, (b) transmitted p-polarized SH signal, (c) reflected -polarized SH signal, and (d) reflected p-polarized SH signal. Left- and right-hand circularly polarized input light is indicated with open and filled circles, respectively.

The symmetry of the LB films was determined by polarized ultraviolet-visible (UV-Vis) absorption spectroscopy, optical rotation, and second-harmonic generation. All studies showed that the constructed LB films are anisotropic in the plane of the film and that the symmetry of the film is C2 with the twofold rotation axis perpendicular to the film plane. For example, when the SH intensity is plotted as a function of the azimuthal rotation angle (rotation around an axis perpendicular to the plane of the film), the twofold symmetry becomes evident (Figure 9.23). Isotropic films generate an SH signal independent of the azimuthal rotation angle. On the other hand, the LB... 

Fig. 5.21. Transient SH response of a Cu(l 11) electrode during thallium underpotential deposition. Incident wavelength = 1064 nm. (a) Isotropic SH signal, /PjP(f). The solid line is a single exponential fit to the entire transient with time constant, t= 10.7 0.3 msec, (b) Anisotropic SH signal, /p s(f). The intensity scale is 2X more sensitive than in (a). From Ref. 117.

After several tests, it is possible to estimate approximately the optimal relative intensities needed to obtain large photoinduced nonlinearities within relatively short preparation periods. The dependence of the generated SH signal is a function of the phase difference AO between the writing beams at CD and 2co frequencies. The relative phase difference AO can be varied by tilting a BK7 plate of known thickness and refractive index dispersion. ... 

FIG. t I.IO Intensity of the generated SH signal (in arbitrary units) after 20 minutes of seeding time, in function of the relative phase difference A between the writing beams at frequencies co and 2(o/The reference (i.e. A = 0) is arbitrarily taken at normal incidence of the writing beams onto the BK7 plate.The solid line represents a theoretical fit to Equation 11.6. The curve shown in the insert shows... 

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