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Optical cleaning of congruent lithium niobate crystals


Lithium niobate (LiNbO3), also called the ‘silicon of photonics’, is indispensable in advanced photonics and nonlinear optics1,2,3,4,5,6,7,8,9,10. For many applications, however, the material is too polluted by transition metals, which are unavoidable at the parts per million level. These impurities serve as sources and traps for photoelectrons, causing optical damage and hampering the usability of LiNbO3. Efforts have therefore been made to get rid of the photoexcitable electrons11,12. Here we introduce a method termed ‘optical cleaning’. We show theoretically and experimentally that, if the material is heated to moderate temperatures, allowing ions to migrate and to maintain charge neutrality, an appropriately moving light beam pushes photoexcitable electrons out of the illuminated region like a brush, and provides exponential cleaning. This promises purification levels that are beyond the reach of current technologies.

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Figure 1: Principle of optical cleaning.
Figure 2: Optical cleaning with a static light beam.
Figure 3: Optical cleaning with a moving light beam.
Figure 4: Concentration profiles showing experimental and simulated results.
Figure 5: Evidence for optical damage suppression.


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The authors thank M. Falk for useful discussions, and the Deutsche Forschungsgemeinschaft (Research Unit 557) and the Deutsche Telekom AG for financial support.

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The project was planned by K.B., M.K. and D.H. The experiments were performed by M.K. and P.W. Data were analysed by B.S., M.K., P.W., D.H. and K.B.

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Correspondence to K. Buse.

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Kösters, M., Sturman, B., Werheit, P. et al. Optical cleaning of congruent lithium niobate crystals. Nature Photon 3, 510–513 (2009).

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