Controlled reduction of Fe-doped KNbO3 by proton-irradiation
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文摘
We demonstrate the controlled and reproducible adjustment of the photorefractive properties such as gain and response time in Fe-doped KNbO3 by using MeV proton-irradiation. The reduction is caused by a change in the reduction ratio in the irradiated region due to the production of oxygen vacancies during proton-irradiation. We demonstrate that the reduction ratio R can be precisely adjusted over a very large range from up to , unmatched by former reduction methods, by simply choosing the appropriate irradiation dose. By applying this technique, we were able to alter the photorefractive gain Γ from 2.5 cm−1 up to 34 cm−1, the absorption constant α from 0.06 cm−1 up to 2.1 cm−1 and the grating buildup time τ from 1.6 ms down to 34 μs at an intensity W/cm2 (corresponding to a power of 2.5 mW in the interaction region) in a 1000 ppm Fe-doped KNbO3 crystal, for example. We also present a refined theoretical model for strongly reduced KNbO3, based on earlier work [J. Opt. Soc. Am. B 8 (1991) 2196], together with a set of the basic material parameters for these crystals, which completely explains all the measurements.