Progress in Hologram Writing in Bi₂TeO₅ Crystals

Abstract

Choosing a proper volumetric memory material is a key question in holographic recording. Photorefractive bismuth tellurite crystals are a new candidate for this purpose. The crystal exhibits a long-living (more than 6 years) photorefractive signal component that develops in the four-wave mixing write process without any specific fixing.

In our contribution, we present the performance of Bi₂TeO₅ crystals that were grown by the Czochralski technique. Their photorefractive performance was tested by experiments investigating the four-wave mixing saturation diffraction efficiency. Moreover, two-dimensional images were written in Bi₂TeO₅ crystals in a typical holographic storage setup.

An improved crystal quality and the use of a stable Nd:YAG laser (532 nm) have led to an enhanced photorefractive response. The saturation diffraction efficiency of the written grating exceeded 40% in a given crystal orientation and light polarization (9 W/m² beams, 8 min saturation time, without external electric field). Holograms can be written with low intensity laser beams (data arm: 110 μW, reference arm: 680 μW) and with short exposure time (5 s). However, these conditions are not suitable for self-fixing of the image. Holograms written with longer exposures (1–8 min) are of good quality, with sharp contours and low background. Their modulation depth allowed observing the holograms by half an hour, thus approaching self-fixation processes. Supports: COST Action P2, German — Hungarian joint R&D found, Hungarian Research Found OTKA (T-029756), Deutsche Forschungsgemeinschaft, DE 486/4–2.