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In classical electromagnetism, polarization density (or electric polarization, or simply polarization) is the vector field that expresses the volumetric density of permanent or induced electric dipole moments in a dielectric material. When a dielectric is placed in an external electric field, its molecules gain electric dipole moment and the ...
Nonlinear optics. Structure of KTP crystal, viewed down b axis, used in second harmonic generation. Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light.
Hyperpolarizability. The hyperpolarizability, a nonlinear-optical property of a molecule, is the second order electric susceptibility per unit volume. [1] The hyperpolarizability can be calculated using quantum chemical calculations developed in several software packages. [2][3][4] See nonlinear optics.
In electromagnetism, the Clausius–Mossotti relation, named for O. F. Mossotti and Rudolf Clausius, expresses the dielectric constant (relative permittivity, εr) of a material in terms of the atomic polarizability, α, of the material's constituent atoms and/or molecules, or a homogeneous mixture thereof. It is equivalent to the Lorentz ...
Cell polarity. Cell polarity refers to spatial differences in shape, structure, and function within a cell. Almost all cell types exhibit some form of polarity, which enables them to carry out specialized functions. Classical examples of polarized cells are described below, including epithelial cells with apical-basal polarity, neurons in which ...
Refractive index. In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the medium to the speed in air or vacuum. The refractive index determines how much the path of light is bent, or refracted, when entering a material. This is described by Snell's law of refraction, n1 sin ...
The electric dipole moment is a measure of the separation of positive and negative electrical charges within a system: that is, a measure of the system's overall polarity. The SI unit for electric dipole moment is the coulomb - metre (C⋅m). The debye (D) is another unit of measurement used in atomic physics and chemistry.
Permittivity as a function of frequency can take on real or complex values. In SI units, permittivity is measured in farads per meter (F/m or A 2 ·s 4 ·kg −1 ·m −3). The displacement field D is measured in units of coulombs per square meter (C/m 2), while the electric field E is measured in volts per meter (V/m).