Theory of Thermal Hologram Fixing and Application to LiNbO3:Cu

Abstract

Volume phase holograms in a n electrooptic crystal like LiNbO, must be fixed so that they are not destroyed upon reading. By heating up the crystal mobilized ions may partially eompensetc the electronic space charge field, and a subsequent development procedure fixes the hologram. A general theory of this t'hermal fixing process is developed and applied to ZiNb0,:Cu. Charge transport by the photovoltaic effect, by drift in a space charge field and by diffusion is taken into account. It is unlikely that mobile protons alone are responsible for the fixing effect. Volumenphasenhologramme in einem elektrooptischen Kristall wie LiNbO, miissen fixiert werden, so daR sie nach dem Lesen nicht zerstort werden. Die durch Aufheizen der Kristalle mobilisierten lonen konnen partiell das elektronische Raumladungsfeld kompensieren und ein darauffolgendes Entwicklungsverfahren fixiert das Hologramm. Eine allgemeinc Theorie dieses thermischen Fixierungsprozesses wird aufgestellt und auf LiNbO,: Cu angewendet. Ladungstransport durch den pliotovoltaischen Effekt, durch Drift in einem Raumladungsfeld und durch Diffusion werden berucksichtigt. Es ist unwahrscheinlich, da13 bewegliche Protonen allein fur den Fixierungseffekt verantwortlich sind.

Holographic storage dynamics in lithium niobate: theory and experiment

“…4,9,[11][12][13][14][18][19][20][21][22] In general, it is agreed that above 70-80°C the ionic conductivity in this crystal largely prevails over the dark electronic conduction because of Fe 2ϩ -electron detrapping. At temperatures somewhat below 60°C, however, the dark conductivity is due predominantly to electrons and is characterized by a small activation energy (0.1-0.4 eV) that is due to the thermally assisted small polaron electronic conduction associated with the Nb Li 4ϩ defect center.…”

“…[8][9][10][11][12][13][14] What differentiates our study is the fact that, by taking advantage of the great disparity between the ionic and the electronic transport time constants that are involved in typical crystals, especially lithium niobate (LiNbO 3 ), we are able to obtain simple analytic expressions 9 for the time-dependent field in each of the phases defined above under realistic conditions.…”

Temperature dependence of light‐induced scattering in a Ce:Fe:LiNbO₃ photorefractive crystal

“…Most of the values chosen are based on previous publications concerning LiNbO 3 . 25,26 However, the activation energy of the electrons, ⑀ e ϭ0.11 eV, is a little lower than the reported data ͑0.18 eV͒ 27 but is still reasonable because our sample of LiNbO 3 crystal is heavily doped with Fe, which could result in a decreased activation energy of electrons, as pointed out by Barkan, Entin, and Marennikov. 28 The initial scattering noise to input beam ratio (m o ) is assumed to be 5ϫ10 Ϫ3 , which corresponds to a scattering light intensity of about 20 W. We also assume the average angle between the scattered light and the input beam is about ϭ4 deg.…”

Theoretical limits for the performance of two-center holographic recording

“…Among the photorefractive crystals, lithium niobate (LiNbO 3 ) has been most extensively investigated [1,[4][5][6]. Conventional holographic recording experiments were performed in singly-doped LiNbO 3 crystals, specially in LiNbO 3 :Fe [1][2]4,6] and LiNbO 3 :Cu [7][8]. In these cases, read-out process results in the erasure of the stored information.…”