Poling field

Poling Response. Application of a poling field in the isotropic case, even for very large fields and for dipoles of the magnitude of p in DANS (7D), only perturbs P (6) weakly since the jl E electrostatic energy is small compared to kT at or above 300 K. This behavior is represented in an exaggerated manner by the dashed curve I in Figure 1. A similar effect occurs in the liquid crystal when... 

Figure 3. Time dependence of harmonic generation (of polymer/guest induced polar alignment and relaxation) when the laser intensity is overly strong. The poling-field time dependence is depicted at top. (Reproducedfrom Ref. 23. Copyright 1983, American...

Makarov, A.A. Resonance Ejection From the Paul Trap A Theoretical Treatment Incorporating a Weak Octa-pole Field. Anal. Chem. 1996, 68, 4257-4263. 

Fig. 12 Pyroelectricity of STOlS-lOOx single crystals. The absolute value of the poling field is 24.8 kV/m [24]...

Fig. 22. Relation between polarities of poling field and pyroelectric current of polarized films a dipole orientation, b ion separation, and c homocharge injection...

Fig. 26. Correlation between increment of spontaneous polarization from 80° C to 15° C and piezoelectric strain constant at room temperature for /9-form polarized poly(vinylidene fluoride) films. Poling temperature = 90° C. Poling field = 700 kV/cm (Murayama, 1972)...

Pr is reasonable because the x-axis of the film is taken as the direction of the poling field. On the other hand, the spontaneous polarization of the P-form crystal of PVDF is estimated from the crystal structure as Ps= 1.3 x 10 5 coul/cm2 = 4x 104 cgsesu. Considering the incompleteness in crystallinity ami orientation, the estimated value of PJN is reasonable compared with PF However, it would still be premature to conclude that the piezoelectricity of drawn and polarized PVDF film is due to the strain dependence of spontaneous polarization. 

Figure 6. Schematic representation of molecular orientation in a polymer film with respect to die poling field in the z direction.

Figure 5. Electro-optic coefficient (r33) vs. poling field for a 20 mol%...

Since the dipoles of chromophore molecules are randomly distributed in an inert organic matrix in amorphous PR materials, the material is centrosymmet-ric and no second-order optical nonlinearity can be observed. However, in the presence of a dc external field, the dipole molecules tend to be aligned along the direction of the field and the bulk properties become asymmetric. Under the assumption that the interaction between the molecular dipoles is negligible compared to the interaction between the dipoles and the external poling field (oriented gas model), the linear anisotropy induced by the external field along Z axis at weak poling field limit (pE/ksT <[Pg.276]

Both the amplitude and the direction of the total poling field are functions of position x. The dipole chromophore will align in response to the field Et(x), and a periodic refractive index modulation will be formed due to both molecular anisotropy and the Pockels effect [37], The contribution from molecular anisotropy is an important, sometimes even dominant, mechanism. 

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