Polarization static electric fields

Expressions for the sixth- through tenth-order coefficients are given in the Appendix. In ESHG experiments with the optical field polarized perpendicular to the static electric field, the measured second hyperpolarizability is [13]... 

The general problem of the orienting effect of a static electric field (orientation of polar molecules) was first considered by Debye [6, 7], Frolich [8], and more recently Bottcher [9,10]. 

When a strong static electric field is applied across a medium, its dielectric and optical properties become anisotropic. When a low frequency analyzing electric field is used to probe the anisotropy, it is called the nonlinear dielectric effect (NLDE) or dielectric saturation (17). It is the low frequency analogue of the Kerr effect. The interactions which cause the NLDE are similar to those of EFLS. For a single flexible polar molecule, the external field will influence the molecule in two ways firstly, it will interact with the total dipole moment and orient it, secondly, it will perturb the equilibrium conformation of the molecule to favor the conformations with the larger dipole moment. Thus, the orientation by the field will cause a decrease while the polarization of the molecule will cause an... 

A steady current does not flow in a perfect insulator in a static electric field, but energy is stored in the sample as a result of dielectric polarization. Thus, the insulator acts as a device to store energy. In reality, some leakage of current occurs even for the best insulators. 

The return to equilibrium of a polarized region is quite different in the Debye and Lorentz models. Suppose that a material composed of Lorentz oscillators is electrically polarized and the static electric field is suddenly removed. The charges equilibrate by executing damped harmonic motion about their equilibrium positions. This can be seen by setting the right side of (9.3) equal to zero and solving the homogeneous differential equation with the initial conditions x = x0 and x = 0 at t = 0 the result is the damped harmonic oscillator equation ... 

If a material of polar molecules, such as water, is exposed to a fixed or static electric field, the molecules will all rotate in an attempt to orient themselves in the direction of the field. The magnitude of separated charges of a polar molecule is defined as the dipole moment, and determines the strength of interaction with the field. The dipole moment is also a measure of the dielectric constant e. A symmetrical molecule, with no dipole moment, is said to be non-polar and does not react with an electric field. If an electric field impinging upon a polar molecule is alternating, the molecules will rotate, following reversals of field. 

The application of a static electric field polarizes the electronic charge distribution and leads to changes in molecular magnetic susceptibility and nuclear... 

There are at least two ways to obtain information by t.s.c. The first is that for the global spectra where the polymeric film is polarized by a static electric field at the polarization temperature Tp and then quenching down to the freezing temperature. With the field turned off and the sample short circuited the depolarization current due to dipolar reorientation is measured as the temperature increases from T0 to the final temperature Tf > Tp. 

Because a ceramic is composed of a large number of randomly oriented crystallites it would normally be expected to be isotropic in its properties. The possibility of altering the direction of the polarization in the crystallites of a ferroelectric ceramic (a process called poling ) makes it capable of piezoelectric, pyroelectric and electro-optic behaviour. The poling process - the application of a static electric field under appropriate conditions of temperature and time -aligns the polar axis as near to the field direction as the local environment and the crystal structure allow. 

In this section, a simple description of the dielectric polarization process is provided, and later to describe dielectric relaxation processes, the polarization mechanisms of materials produced by macroscopic static electric fields are analyzed. The relation between the macroscopic electric response and microscopic properties such as electronic, ionic, orientational, and hopping charge polarizabilities is very complex and is out of the scope of this book. This problem was successfully treated by Lorentz. He established that a remarkable improvement of the obtained results can be obtained at all frequencies by proposing the existence of a local field, which diverges from the macroscopic electric field by a correction factor, the Lorentz local-field factor [27],... 

The application of a strong static electric field modifies the quadrupole coupling constant as an effect of the sample polarization. The phenomenon has been reviewed by Lucken s) who mentions some results concerning halogens. 

LFnder the influence of a static electric field liquid crystalline solutions of PBLG become uniaxially oriented and show both linear and circular birefringence and linear and circular dichroism. Accordingly, the measured CD shows a dependence of the microscopic angle, a, that the fast optical axis of the oriented solution makes with respect to the plane of polarization of the polarizer in the CD instrument. When the film is reasonably thin (0.01-0.1 mm thick) or/and only partially oriented (less than 5% orientation), the apparent CD of oriented film of deoxyribonucleic acid is expressed by the equation (50) ... 

Figure 11 To the medium under investigation is rigidly attached the laboratory Cartesian reference system x, y, z, whereas to the molecule under consideration is attached the Cartesian system of axes x, Xj, Xj. The static electric field E, which polarizes the medium non-linearly, acts along the z-axis. The light wave which serves for analysing the induced non-linearity propagates along y...

---