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Proceedings Paper

High-temperature recording of strong permanent diffraction gratings in copper-doped lithium niobate crystals based on a zero-electric-field photorefractive effect
Author(s): U. Hartwig; K. Peithmann; B. Sturman; K. Buse
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Paper Abstract

Diffraction gratings, which do not rely on the electro-optic effect, are recorded in copper-doped lithium niobate crystals: At elevated temperatures (approx. 180 °C), the crystals are illuminated by an interference pattern. The light pattern excites electrons from filled Cu+ traps into the conduction band. They are captured by empty Cu2+ traps elsewhere. The resulting electric fields are compensated by ions, such as H+, that are thermally mobilized. Therefore the redistribution of electrons can continue which finally results in a high modulation of Cu+ and Cu2+ traps. This process is called "thermal fixing" and is known since decades. However, here we report about a novel and relevant effect resulting from the electron concentration grating. The Cu+ traps absorb mainly in the near UV and visible spectral range, Cu2+ traps have their absorption peak in the near infrared. A modulation of Cu+ and Cu2+ trap concentrations therefore results in a pronounced absorption modulation. This immediately implies an absorption grating, but another consequence is even more dramatic: The Kramers-Kronig relations link changes of the absorption to changes of the refractive index. Thus the narrow absorption bands of copper in lithium niobate lead to refractive index changes over a vast wavelength range. Maximum index changes of the order of 10−4 are achieved. The resulting gratings can be recorded in any crystal orientation and are of interest for applications in non-linear optics.

Paper Details

Date Published: 7 October 2005
PDF: 8 pages
Proc. SPIE 5911, Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and Applications XI, 59111F (7 October 2005); doi: 10.1117/12.624645
Show Author Affiliations
U. Hartwig, Institute of Physics (Germany)
K. Peithmann, Helmholtz-Institute for Radiation and Nuclear Physics (Germany)
B. Sturman, Institute of Automation and Electrometry (Russia)
K. Buse, Institute of Physics (Germany)

Published in SPIE Proceedings Vol. 5911:
Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and Applications XI
Francis T. S. Yu; Ruyan Guo; Shizhuo Yin, Editor(s)

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