Periodic poling is a formation of layers with alternate orientation in a
birefringent
Birefringence, also called double refraction, is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are described as birefring ...
material. The domains are regularly spaced, with period in a multiple of the desired
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of operation. The structure is designed to achieve
quasi-phase-matching (QPM) in the material.
Periodically poled
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s are frequently used as
nonlinear optical
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. The non-linearity is typicall ...
materials. They are more efficient at
second-harmonic generation
Second-harmonic generation (SHG), also known as frequency doubling, is the lowest-order wave-wave nonlinear interaction that occurs in various systems, including optical, radio, atmospheric, and magnetohydrodynamic systems. As a prototype behav ...
than crystals of the same material without
periodic structure. The material for the crystals is usually a wide-
bandgap
In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to the ...
inorganic
An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bondsthat is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''.
Inor ...
crystal, or in some cases a suitable
organic polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
. Some popular materials in current use are
potassium titanyl phosphate
Potassium titanyl phosphate (KTP) is an inorganic compound with the formula . It is a white solid. KTP is an important nonlinear optics, nonlinear optical material that is commonly used for second-harmonic generation, frequency-doubling diode-pum ...
(KTP),
lithium niobate
Lithium niobate () is a synthetic salt consisting of niobium, lithium
Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperatur ...
, and
lithium tantalate
Lithium tantalate is the inorganic compound with the formula Li Ta O3. It is a white, diamagnetic, water-insoluble solid. The compound has the perovskite structure. It has optical, piezoelectric, and pyroelectric properties. Considerable infor ...
.
The periodic structure is created in the crystal using a range of techniques. Pulsed electric field, electron bombardment, thermal pulsing, or other methods can be used to reposition the
atom
Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
s in the
lattice, creating oriented domains. This can be achieved either during the growth of the crystal or subsequently.
[M. Houe and P. D. Townsend]
"An introduction to methods of periodic poling for second-harmonic generation"
Journal of Physics D: Applied Physics, volume 28 (1995), number 9.
See also
*
Glass poling
References
External links
Encyclopedia of laser physics and technology
Nonlinear optics
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