Second harmonic measurements

Detailed information about the components of the second-order susceptibility y2)(-2w to, w) can be obtained from second harmonic measurements on well-defined samples such as single crystals or oriented thin films, the latter obtained by procedures such as the asymmetric Langmuir-Blodgett deposition technique or electric-field poling of NLO chromophore-doped polymers.31 In the case of single-crystal samples, the second harmonic is... 

For these classes of conjugated molecular and polymer structures, the principal property is that their nonreson-ant, nonlinear optical responses are dominated by ultrafast, virtual excitations of the ir-electron states. This was directly demonstrated by MNA (2-methyl-4-nitroaniline) single crystal measurements of macroscopic second order susceptibilities at do (j 3) and optical frequencies (13-1 ) and combined second harmonic measurements and theo-... 

This high glass transition temperature polymer exhibits large electrooptic coefficients, -14-35 pm fV. The second harmonic measurements indicate long-term stability of the dipole orientation (> 800h at 100 °C). 

Rasing Th, Shen Y R, Kim M W, Valint P Jr and Bock J 1985 Orientation of surfactant molecules at a liquid-air interface measured by optical second-harmonic generation Phys. Rev. A 31 537-9... 

Lantz J M and Corn R M 1994 Time-resolved optical second harmonic generation measurements of picosecond band flattening processes at single crystal TiO, electrodes J. Phys. Chem. 98 9387-90... 

Dadap J I, Shan J, Weling A S, Misewich J A, Nahata A and Heinz T F 1999 Measurement of the vector character of electric fields by optical second-harmonic generation Opt. Lett. 24 1059-61... 

In a second kind of infrared ellipsometer a dynamic retarder, consisting of a photoelastic modulator (PEM), replaces the static one. The PEM produces a sinusoidal phase shift of approximately 40 kHz and supplies the detector exit with signals of the ground frequency and the second harmonic. From these two frequencies and two settings of the polarizer and PEM the ellipsometric spectra are determined [4.316]. This ellipsometer system is mainly used for rapid and relative measurements. 

CB04. The spontaneous polarisation was measured by the pulse pyroelectric technique (Ps = 46 nC/cm ). The piezoelectric coefficient evaluated for CB04 was dsi = 1.6 pC/N. The estimation of the efficiency of the second harmonic generation for compound CB04 gives the value three times more than for quartz. 

Deslouis C, Maurin G, Pebere N, Tribollet B (1988) Investigation of tellurium electrocrystal-Uzation by EHD impedance technique. J Appl Electrochem 18 745-750 Yagi I, Nakabayashi S, Uosaki K (1998) In situ optical second harmonic rotational anisotropy measurements of an Au(l 11) electrode during electrochemical deposition of tellurium. J Phys Chem B 102 2677-2683... 

Because the second harmonic response is sensitive to the polarizability of the interface, it is sensitive to the adsorption and desorption of surface species and is capable of quantifying surface species concentrations. Furthermore, SHG can be used to quantify surface order and determine surface symmetry by measuring the anisotropic polarization dependence of the second harmonic response. SHG can also be used to determine important molecular-level and electrochemical quantities such as molecular orientation and surface charge density. 

Lantz, J. M. and Corn, R. M. (1994) Electrostatic field measurements and hand fiattening during electron-transfer processes at single-crystal Ti02 electrodes by electric field-induced optical second harmonic generation. J. Phys. Chem., 98, 4899-4905. 

The development of hydrodynamic techniques which allow the direct measurement of interfacial fluxes and interfacial concentrations is likely to be a key trend of future work in this area. Suitable detectors for local interfacial or near-interfacial measurements include spectroscopic probes, such as total internal reflection fluorometry [88-90], surface second-harmonic generation [91], probe beam deflection [92], and spatially resolved UV-visible absorption spectroscopy [93]. Additionally, building on the ideas in MEMED, submicrometer or nanometer scale electrodes may prove to be relatively noninvasive probes of interfacial concentrations in other hydrodynamic systems. The construction and application of electrodes of this size is now becoming more widespread and general [94-96]. 

Recently, Eisenthal and coworkers have developed time-resolved surface second harmonic techniques to probe dynamics of polar solvation and isomerization reactions occurring at liquid liquid, liquid air, and liquid solid interfaces [22]. As these experiments afford subpicosecond time resolution, they are analogous to ultrafast pump probe measurements. Specifically, they excite a dye molecule residing at the interface and follow its dynamics via the resonance enhance second harmonic signal. 

To further corroborate these potentiometric results, we again used optical second harmonic generation (SHG). The SHG measurement system was essentially the same as used in the study described in Section II, except the laser beam was first reflected by a mirror and then totally reflected by the liquid-liquid interface. 

Figure I. Comparative quantities for selected tensor components of second harmonic generation (left) and the linear electro-optic effect (right) (measured at 1.06 pm wavelength). (The strain free quantity, f, was measured at 0.633 pm wavelength except in the case of GaAs which was measured at - 0.9 pm). (Reproduced with permission from Ref. 8. Copyright 1982, Laser Focus.)...

The value of 3 and its dispersion for a molecule, or polymer chain, can be experimentally determined by DC induced second harmonic generation (DCSHG) measurements of liquid solutions -1 2). The experimental arrangement requiring an applied DC field E° to remove the natural center of inversion symmetry of the solution is described in Figure 4. The second harmonic polarization of the solution is expressed as... 

The fundamentally important case p-nitroaniline (PNA), the high symmetry parent molecular unit of MNA, presents an excellent example for both experimental methodology and theoretical analysis. In the C 2 v symmetry for PNA and second harmonic generation, the measured principal component 3X is given by... 

---