Session L33: Focus Session: Dielectric, Ferroelectric, and Piezoelectric Oxides: Lattice Dynamics, Polarons, and Structure
2:30 PM–5:30 PM, Tuesday, March 22, 2011
Room: C143/149
Sponsoring Units:
DMP DCOMP
Chair: Matt Dawber, Stony Brook University
Abstract ID: BAPS.2011.MAR.L33.2
Abstract: L33.00002 : Amplitude and phase gratings based on spatially modulated densities of optically generated polarons in thermally reduced LiNbO$_3$
2:42 PM–2:54 PM
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Abstract 
Authors:
Hauke Bruening
(University of Osnabrueck, Germany)
Mirco Imlau
(University of Osnabrueck, Germany)
In thermally reduced, nominally pure LiNbO$_3$ a variety of small polarons can be observed, being responsible for the distinct photochromic properties of this material. In this contribution we use a spatially modulated excitation of polarons for the recording of holographic gratings. These gratings inherit some of the pronounced features of the polarons like a stretched-exponential relaxation behavior with a lifetime in the ms-range. Beside amplitude gratings we also find phase gratings leading to a high diffraction efficiency in some recording and readout geometries. The origin of these phase gratings can't be explained by the classic photorefractive effect due to Fe$_{\mathrm{Li}}$ or other photorefractive dopants. In contrast, our findings are discussed in the frame of a model taking into account a local change of the refractive index by the polaronic distortion of the crystal lattice. Measurements of activation energies also indicate that these gratings can be attributed to the small bound ($\mathrm{Nb}^{4+}_{\mathrm{Li}}$)-polaron.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.L33.2