Photon induced electric field poling
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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.
The encoding process proceeds by application of ultraviolet 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 plasmons. 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.
The pattern of ferroelectric domain orientations can be read out optically. The refractive index 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.
References discussing techniques described in this article
- "Influence of ultraviolet illumination on the poling characteristics of lithium niobate crystals", Manfred Muller, elisabeth Soergel, and Karsten Buse, Applied Physics Letters, vol. 31, no. 9, Sept. 2003
- "Light-induced polaronic absorption at low temperature in pure and (Fe,Ce,Cr) doped SrxBa1-xNb2O6 or Ba1-xCaxTiO3 crystals and photodissociation of vis centers into small polarons", S. E. Kapphan, L. Kislova, M. Wierschem, T. Lindemann, M. Gao, R. Pankrath, V. S. Vikhnin, and A. B. Kutsenko, preprint, University of Osnabrück, Germany
- "Some properties of lithium niobate crystals", Karsten Buse, Physical Institute, University of Bonn, 2004
- "Electric polarization induced by optical orientation of dipolar centers in non-polar piezoelectrics", Alexander Grachev and Alexei Kamshilin, Optics Express, vol. 13, no. 21, Oct. 2005
- "Optical Parametric Amplification with Periodically Poled KTiOPO4", Anna Fragemann, doctoral thesis, Department of Physics, Royal Institute of Technology, Stockholm, Sweden, 2005
- "Photoinduced electronic transport in K1−xLixTaO3", P. Sangalli, E. Giulotto, L. Rollandi, P. Calvi, P. Camagni, and G. Sammomggia, Phys. Rev. B 57, pp. 6231–6234, no. 11, 15 Mar. 1998
- "Non-destructive polarisation readout by UV illumination of ferroelectric thin films", A. L. Kholkin, Ceramics Laboratory, École polytechnique fédérale de Lausanne, 1996–1997
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, 16 Mar. 2006