Third-order susceptibility magnitude

As expected, the third order susceptibilities vary significantly with polymer orientation. It seems unlikely however that this feature alone will ever increase the values by more than an order of magnitude and further significant improvements will probably require more highly polarizable substituents, the introduction of... 

Laser lights with short wavelengths are important in optical data processing, and conjugated polymers are expected to be useful materials for their generation. Optical third-harmonic generation measurements have been performed for poly(phenylacetylenes) " The magnitudes of the third-order susceptibility were 7 x 10 esu for poly(phenylacetylene) and in the order of 10 -10" esu for its derivatives . ... 

With their extensively delocalized-electron systems along their backbones, PBX polymers have emerged as ideal candidates for NLO applications. We are particularly interested in their third-ordered susceptibility characteristics. Indeed, it has been shown " that PBZT film processed from polyphosphoric acid (PPA) solution had a relatively high value of about 3 x 10"" e.s.u. Further improvement in the optical quality of the PBZT film by coagulation of a methanesulfonic acid (MSA) solution in water had increased the x (3) value by an order of magnitude (3.3-4.5 x 10 e.s.u.). Since the three-fused-ring... 

Several of the third-order nonlinear effects described in section 4.1.3 can be used to characterize bulk materials. Degenerate four-wave mixing (DFWM) is used for measuring third-order properties of films and solutions [43-45], and though this experiment is complex to set up and interpret, it can give valuable information on the magnitude, sign and speed of the nlo process, as well as an indication of the nature of the excitation process. Results from DFWM can be found in section 4.3. Optical Kerr effect (OKE) [46] and electrical Kerr effect (EKE) [47] measurements have also been used to characterize third-order properties of nlo polymers. It is important to note that THG, DFWM, OKE and EKE all measure different parts of the third-order susceptibility, and... 

In electrostatic units, this corresponds to a third-order susceptibility on the order of 9.54 X 5 X 10 -5 X 10 esu (see Chapter 11 on unit equivalence). This nonlinear coefficient is about eight orders of magnitude larger than that of CS2 and about seven orders of magnitude larger than the isotropic phase liquid crystal reorienta-tional nonlinearity discussed in Section 8.2.3. 

The third type of experiment was performed to show that inhibition by the products is insufficient to account for the observed difference in rate. The substrate consisted of a 50 50 mixture (in terms of optical density) of native DNA and oligonucleotides. With this mixture the rate of hydrolysis decreased to about one-half of that for native DNA. This result agrees with the previously established (52) competitive-type inhibition by the products. It also shows that the inhibition by products accounts for changes in rate within one order of magnitude, whereas the decreasing affinity toward the newly formed substrates accounts for more than three orders of magnitude. With so pronounced a difference in susceptibility of substrate in the very early and in the very late phases of the reaction, the two phases must be considered independently. 

The presence of L-histidine as the third amino acid residue in tripeptide complexes of Cu(II) drastically decreases their susceptibility to both nucleophilic attack and acid attack (11, 12). Thus, the doubly deprotonated complex of glycylglycyl-L-histidine (Cu(H 2gly-gly-his) shown in Structure I is relatively slow to react with the nucleophilic tri-ethylenetetramine (trien) since this reaction is seven orders of magnitude slower than the corresponding reaction with Cu(H 2gly-gly-gly). The... 

The photoinduced susceptibility shown in Equation 11.14a is the sum of two terms one with exp(-2Dt) (relaxation of the first-order parameter A ) decay and the second with exp(-12D ) (relaxation of the third-order pammeter A3) decay. Hence, the first very rapid decay may contain the fast exp(-12D ) contribution. However, as can be seen from Figure 11.14, the relative magnitude of this initial very fast decay does not depend on the optimization of the intensity ratio between the writing beams. So, this first rapid decay may not be due to the decay of the third-order parameter A3. In addition, because the hyperpolarizability P of DRl is different in the ds and in the trans state, the first very rapid decay also contains a contribution connected with the hferime of the metastable ds form, which is due to molecules coming back to the trans form without any net orientation. A better model would have to account for a distribution of diffusion constants for molecules embedded with various free volumes, which may explain the multiexponential behavior of the decay. 

Sinclair and coworkersmeasured the third-order nonlinear optical susceptibility of rm 5 -polyacetylene. The measured susceptibility was 5 x 10 esu, which is comparable to the magnitude of the large nonlinear susceptibilities measured in the polydiacetylenes. 

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