Holographic Pattern Fixing in Electro-Optic Crystals

Abstract

This paper describes the results of an investigation into techniques for obtaining erasure resistant holograms in electro-optic crystals. The most successful approach made use of thermally activated ionic drift during or after recording. The samples are heated for about 30 min at 100°C to obtain optically nonerasable holograms with as much as 50% diffraction efficiency in LiNbO3 or in doped Ba2NaNb5O15.

Storage of 1000 holograms with use of a dual-wavelength method

“…Similar diagrams can be drawn readily for the reflection and 90°geometries also. A grating is recorded in the usual manner, with signal and reference beams at the first wavelength 1 . We reconstruct this grating at the second wavelength 2 by introducing the readout beam at an angle tilted with respect to the recording reference beam.…”

“…Several methods have been developed to address this problem. [1][2][3][4][5][6][7][8][9][10] We use the dual-wavelength method 8 -10 to demonstrate experimentally the longterm storage of 1000 holograms. The motivation for using different wavelengths of light for recording and readout is simple: If a crystal has an absorption spectrum with a substantial variation as a function of wavelength, by recording at a wavelength 1 at which the crystal is highly sensitive and reading out at a second wavelength 2 at which the crystal is relatively insensitive, we can reduce the decay of the gratings caused by the readout illumination.…”

Temperature dependence of absorption in photorefractive iron-doped lithium niobate crystals

“…This technique is called ''thermal fixing.'' 5 The electronic spacecharge pattern is copied to an ionic one that is persistent against illumination at room temperature. 6 Although thermal fixing is applied frequently, only little is known about how the electronic excitation and transport parameters are affected by heating.…”

Trapping of dielectric particles with light-induced space-charge fields

“…Therefore, a device can be prepared in the lab and then used for particle manipulation at any place needed. Thermally fixed gratings 6 together with a simple white-light lamp can also overcome the problem of slow grating decay in the crystals. Photorefractive crystals are furthermore known to have very high spatial resolution, i.e., with masks and ultraviolet light, structures with feature sizes well below 1 m are achievable.…”

“…1. Arbitrary field patterns can be recorded and fixed either thermally 6 or optically. 7 The goal of the present work is to trap particles of sizes between 100 nm and some tens of micrometers on the surface of a photorefractive crystal.…”