Thermal hologram fixing in pure and doped KNbO_3 crystals

Abstract

We demonstrate holographic fixing by means of a thermal cycling procedure in pure and doped photorefractive KNbO3 crystals. At elevated temperatures (70–100°C) the photoinduced grating is compensated for by a secondary grating that is formed by charge carriers whose thermal activation energy is ~1.0 eV. The secondary carriers are stable at room temperature and form the fixed grating after cooling the crystal. They are believed to be represented by ions or ion vacancies. By using our fixing mechanisms the holographic storage time in KNbO3 can be increased by a factor of 106.