Study of holographic recording gratings in the Bi2TeO5 photorefractive crystal and their applications

Abstract

In the presence of a modulated pattern of light onto photorefractive crystal, charge carriers are excited from photoactive center somewhere inside the forbidden energy band gap to the conduction band (electron) or valence band (hole) where they accumulate and diffuse away under the action of diffusion gradient or drifted in the presence of an externally applied electric field. After moving along the conduction band or valence band they are retrapped somewhere else, excited again, and so on. The charge carriers accumulate in the darker regions of the material leaving behind an opposite electric charge so that a space charge field arises and, because of the electro-optic effect, an index-of-refraction modulation results. In this way, a spatial modulation of light is recorded in the volume of the photorefractive crystal. If uniform light is projected onto the sample the photosensitive electronic grating is erase. Permanent volume holograms or gratings are interesting for different applications and particularly useful as narrow band light filters. Bismith Tellurite Oxide Bi$_{2}$TeO$_{5}$ crystals have already been reported by other researchers, that called the attention about its interest for application and for academic challenger in the characterization process. Recently we show \cite{deOliveira:20} that the undoped photorefractive Bi$_{2}$TeO$_{5}$ crystal allow recording fixed grating in the volume without any thermic process. In this project we investigate the formation of fast, slow and fixed gratings in undoped photorefractive Bi$_{2}$TeO$_{5}$ crystal. This project is devoted to the analysis of the fixing process and of the resulting fixed grating for applications such as filters. This project is an extension of another (submitted) international cooperation project between Queen's University Belfast, Instituto Nacional de Pesquisa Espaciais (INPE) and the Laboratório de Óptica da Faculdade de Tecnologia/UNICAMP, that was submitted to UK Espace Agency (Registered with the Charity Commission for Northern Ireland (NIC101788). QUB also holds a VAT registration number (GB 254 7995 11), alongside EORI Numbers GB254799511000 and XI254799511000).All research developed in this project will be carried out in the Laboratório de Óptica Da Faculdade de Tecnologia/UNICAMP. (AU)