Ordering susceptibility

For each EA spectrum, the transmission T was measured with the mechanical chopper in place and the electric field off. The differential transmission AT was subsequently measured without the chopper, with the electric field on, and with the lock-in amplifier set to detect signals at twice the electric-field modulation frequency. The 2/ dependency of the EA signal is due to the quadratic nature of EA in materials with definite parity. AT was then normalized to AT/T, which was free of the spectral response function. To a good approximation [18], the EA signal is related to the imaginary part of the optical third-order susceptibility ... 

G2, to G3, and to G4, the effective enhancement was 10%, 36%, and 35% larger than the value estimated by the simple addition of monomeric values. The enhancement included the local field effect due to the screening electric field generated by neighboring molecules. Assuming the chromophore-solvent effect on the second-order susceptibility is independent of the number of chro-mophore units in the dendrimers, p enhancement can be attributed to the inter-molecular dipole-dipole interaction of the chromophore units. Hence, such an intermolecular coupling for the p enhancement should be more effective with the dendrimers composed of the NLO chromophore, whose dipole moment and the charge transfer are unidirectional parallel to the molecular axis. 

If we introduce A = N/s ( a ), the description of macroscopic resonant second-order susceptibility,, is given by... 

Sum-frequency (SF) spectroscopy [1] has been used to achive vertical resolutions much better than the wavelength. Sum-frequency light is generated at an interface irradiated with infrared (IR) and visible light. The probability of sum-frequency generation is governed by a second-order susceptibility to be zero in any medium... 

The term nonlinear optical property refers to an optical property, which can be modified by exposing the material to intense light irradiation. In this section, we focus on the cascaded first- (/ 1 ) and third-order ( / ) susceptibilities describing nonlinear absorption (ESA and 2PA) and nonlinear refraction (n2) processes. Z-scan, pump-probe, and two-photon upconverted fluorescence techniques are among the most used experimental methods for determining optical nonlinearities. 

The situation is drastically different with the second order susceptibility which is non-vanishing only in materials without inversion symmetry. Its expression is (22)... 

Three Wave Mixing. A number of resonances are possible in the third-order susceptibility, These resonances may be due to... 

The large values of the hyperpolarizability in these molecules imply large susceptibilities for more concentrated solutions or solid-state films. This large third-order susceptibility can... 

Quantitative Determination of Electric and Magnetic Second-Order Susceptibility Tensors of Chiral Surfaces... 

The proportionality constants a and (> are the linear polarizability and the second-order polarizability (or first hyperpolarizability), and x(1) and x<2) are the first- and second-order susceptibility. The quadratic terms (> and x<2) are related by x(2) = (V/(P) and are responsible for second-order nonlinear optical (NLO) effects such as frequency doubling (or second-harmonic generation), frequency mixing, and the electro-optic effect (or Pockels effect). These effects are schematically illustrated in Figure 9.3. In the remainder of this chapter, we will primarily focus on the process of second-harmonic generation (SHG). 

Nonvanishing Components of Second-Order Susceptibility Tensor for Second-Harmonic Generation in Electric-Dipole Approximation for Achiral and Chiral Isotropic (i.e. isotropic in the plane of the film) Films0... 

To fit the experimental results, it is necessary to fix the overall phase. This can be done, for example, by defining h as a real quantity (/ / = 0). The values found for the coefficients /, g, and h can then subsequently be used to calculate the values of the components of the second-order susceptibility, X(2). This is done in detail for a Langmuir-Blodgett film of a poly(isocyanide) in the following section. Note that both phase and magnitude of all tensor components are relative values. The absolute phase cannot be determined... 

In this section, the experimental techniques described in the previous section are applied to the study of thin Langmuir-Blodgett films of chiral molecules and polymers. We will show in detail how the second-order susceptibility of chiral thin films can be analyzed and discuss the influence of chirality on the nonlinear optical response of these films. 

Absolute Values of Second-Order Susceptibility Components of Helical Polymer Shown in Figure 9.21, Classification of Components as Chiral or Achiral... 

Second-Order Susceptibility Component Xijk Absolute Value (pm/V) Classification... 

To analyze the second-order susceptibility, the symmetry of the films was first analyzed by measuring the intensities of the second-harmonic light. The sample was irradiated with polarized light from a Nd YAG laser incident at 45°, and the second-harmonic light emanating from the sample was detected while the sample was rotated around its surface normal. No variation in the second-harmonic intensity was observed as the sample was rotated, indicating... 

---