Infrared photorefractive effect in doped KNbO_3 crystals

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Abstract
The photorefractive sensitivity of potassium niobate crystals doped with Ce, Co, Cu, Fe, Mn, Ni, and Rh and double-doped with Mn and Rh is investigated over an extended spectral range. We present experimental evidence on extrinsic properties important for the photorefractive effect, such as absorption and effective trap density. Photorefractive gratings are investigated with two-wave mixing experiments. Results on exponential gain, response time, and photorefractive sensitivity at near-infrared wavelengths are reported. The best photorefractive sensitivities at 860 and 1064 nm were obtained in crystals doped with Rh, Fe, Mn, and Mn–Rh. This makes them suitable for applications at laser-diode wavelengths; at 1064 nm, however, Rh:KNbO3 shows a better photorefractive sensitivity than the others.