Pockels effect of $LiNbO_3$ is investigated and its Pockels coefficient $r_{22}$ and ($n_o^3r_{13}-n_e^3r_{33}$) are measured by applying D.C. voltages from 0-6 kV. The measured values are $r_{22} = 5.89 × 10^{-12}n/V$ and $n_o^3r_{13}-n_e^3r_{33} = 160 × 10^{-12}m/V$. The frequency dependence of the Pockls effect is measured. By applying a 2.7 kV D.C. pulse (Δτ = 25 μsec) to the specimen and taking the Fourier transform of the electrical pulse and the light flux transmitted through the crystal, the frequency dependence of $r_{22}$ are obtained. The graph extrapolated toward $ω=0$ approaches to the above values or $r_{22}$ already obtained.
Undoped $LiNbO_3$ single crystal and $Bi_{12}GeO_{20}$(BGO) crystal are photorefractive electro-optic materials which are of use in real time holographic image storage. Photorefractive effects are commonly found in the materials, besides $LiNbO_3$ and BGO crystals, such as $BaTiO_3, KNbO_3, KH_2PO_4, LiTaO_3, (Pb, La) (Zr, Ti)O_3$ ceramics. The characteristics of diffraction efficiencies of the undopend $LiNbO_3$ single crystal and BGO crystal are measured by using argon ion laser (λ=5145Å writing source) and He-Ne laser (λ=6328Å reading source).
As the diffraction efficiency of undoped $LiNbO_3$ single crystal is very low ($10^{-4}$ order) and the writing and erasing time of holographic grating is very long (the order of $10^2$ minute), this crystal can not be used in a real time image processing. For 5 kV/cm field intensity, maximum diffraction efficiency of BGO crystal is found to be adequate for a real time image processing. For 5 kV/cm field intensity, maximum diffraction efficiency of BGO crystal is found to be $1.9×10^{-2}$. And by increasing the applied electric field intensity, diffraction efficiency is made to increase. The erasing time of the holographic grating record in BGO crystal is about 480 msec which is short enough for any real time application in optical storage and/or image processing.
