Photon induced electric field poling
Encyclopedia
In physics
, photon induced electric field poling is a phenomenon whereby a pattern of local electric field orientations can be encoded in a suitable ferroelectric material, such as perovskite
. The resulting encoded material is conceptually similar to the pattern of magnetic field orientations within the magnetic domains of a ferromagnet, and thus may be considered as a possible technology for computer storage
media. The encoded regions are optically active (have a varying index of refraction) and thus may be "read out" optically.
Patents, US 6028835 2/22/2000 US 6046973 4/4/2000
light tuned to the absorption band
associated with the transition of electrons from the valence band
to the conduction band
. During UV application, an external electric field
is used to modify the electric dipole moment
of regions of the ferroelectric material that are exposed to UV light. By this process, a pattern of local electric field orientations can be encoded.
Technically, the encoding effect proceeds by the creation of a population inversion
between the valence and conduction bands, with the resulting creation of plasmon
s. During this time, ferroelectric perovskite
materials can be forced to change geometry by the application of an electric field. The encoded regions become optically active due to the Pockels effect
.
of the ferroelectric material at wavelengths from near-infrared
through to near-ultraviolet is affected by the electric field within the material. A changing pattern of electric field domains within a ferroelectric substrate results in different regions of the substrate having different refractive indices. Under these conditions, the substrate behaves as a diffraction grating
, allowing the pattern of domains to be inferred from the interference pattern present in the transmitted readout beam.
Bo-Kuai Lai, Inna Ponomareva, Ivan Naumov, Igor Kornev, Huaxiang Fu, Laurent Bellaiche, and Greg Salamo, press release, University of Arkansas
, 16 Mar. 2006
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, photon induced electric field poling is a phenomenon whereby a pattern of local electric field orientations can be encoded in a suitable ferroelectric material, such as perovskite
Perovskite
A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide , known as the perovskite structure, or XIIA2+VIB4+X2−3 with the oxygen in the face centers. Perovskites take their name from this compound, which was first discovered in the Ural mountains of...
. The resulting encoded material is conceptually similar to the pattern of magnetic field orientations within the magnetic domains of a ferromagnet, and thus may be considered as a possible technology for computer storage
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
media. The encoded regions are optically active (have a varying index of refraction) and thus may be "read out" optically.
Patents, US 6028835 2/22/2000 US 6046973 4/4/2000
Encoding process
The encoding process proceeds by application of ultravioletUltraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light tuned to the absorption band
Absorption band
An absorption band is a range of wavelengths, frequencies or energies in the electromagnetic spectrum which are able to excite a particular transition in a substance...
associated with the transition of electrons from the valence band
Valence band
In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature....
to the conduction band
Conduction band
In the solid-state physics field of semiconductors and insulators, the conduction band is the range of electron energies, higher than that of the valence band, sufficient to free an electron from binding with its individual atom and allow it to move freely within the atomic lattice of the material...
. During UV application, an external electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
is used to modify the electric dipole moment
Electric dipole moment
In physics, the electric dipole moment is a measure of the separation of positive and negative electrical charges in a system of charges, that is, a measure of the charge system's overall polarity with SI units of Coulomb-meter...
of regions of the ferroelectric material that are exposed to UV light. By this process, a pattern of local electric field orientations can be encoded.
Technically, the encoding effect proceeds by the creation of a population inversion
Population inversion
In physics, specifically statistical mechanics, a population inversion occurs when a system exists in state with more members in an excited state than in lower energy states...
between the valence and conduction bands, with the resulting creation of plasmon
Plasmon
In physics, a plasmon is a quantum of plasma oscillation. The plasmon is a quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and mechanical vibrations, respectively...
s. During this time, ferroelectric perovskite
Perovskite
A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide , known as the perovskite structure, or XIIA2+VIB4+X2−3 with the oxygen in the face centers. Perovskites take their name from this compound, which was first discovered in the Ural mountains of...
materials can be forced to change geometry by the application of an electric field. The encoded regions become optically active due to the Pockels effect
Pockels effect
The Pockels effect , or Pockels electro-optic effect, produces birefringence in an optical medium induced by a constant or varying electric field. It is distinguished from the Kerr effect by the fact that the birefringence is proportional to the electric field, whereas in the Kerr effect it is...
.
Decoding process
The pattern of ferroelectric domain orientations can be read out optically. The refractive indexRefractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
of the ferroelectric material at wavelengths from near-infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
through to near-ultraviolet is affected by the electric field within the material. A changing pattern of electric field domains within a ferroelectric substrate results in different regions of the substrate having different refractive indices. Under these conditions, the substrate behaves as a diffraction grating
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
, allowing the pattern of domains to be inferred from the interference pattern present in the transmitted readout beam.
See also
- Electro-optic effectElectro-optic effectAn electro-optic effect is a change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light...
- BirefringenceBirefringenceBirefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
- Holographic memory
- Magneto-optic effectMagneto-optic effectA magneto-optic effect is any one of a number of phenomena in which an electromagnetic wave propagates through a medium that has been altered by the presence of a quasistatic magnetic field...
Other articles about ferroelectric data storage
Bo-Kuai Lai, Inna Ponomareva, Ivan Naumov, Igor Kornev, Huaxiang Fu, Laurent Bellaiche, and Greg Salamo, press release, University of Arkansas
University of Arkansas
The University of Arkansas is a public, co-educational, land-grant, space-grant, research university. It is classified by the Carnegie Foundation as a research university with very high research activity. It is the flagship campus of the University of Arkansas System and is located in...
, 16 Mar. 2006