Investigation Of Electric-field Effects Of Photorefractive Process In SBN: Cr Crystals

SBN:Cr is one of the most promising photorefractive materials for various nonlinear optical applications due to its high photorefractive sensitivity and rapid response in red spectral region. By examining the micro mechanism of photorefractive effect, we can find that an external dc electric-field can greatly alter (improve or worsen) the photorefractive properties of SBNrCr. So it is important to study electric-field effects in these materials. In this thesis, the characters of beam coupling and transmission in SBN:Cr crystals under external dc electric-fields are investigated theoretically and experimentally. The main contents are as follows.(1) Effects of externally applied electric fields on photorefractive two-beam coupling are analyzed. Theoretic dependence of the intensity gain factor on applied field E0 in SBN:60 is presented. And the experimental results obtained in two SBN:61:Cr crystal samples with different dopant concentration show clearly that for properly applied fields, a larger F can be achieved effectively than that obtained with no field applied. And the steady-state coupling response time rdecreases from 0.8s to 0.3s. But there are almost no changes in 2peak with fields applied. (2) Using the characters of two-beam coupling in SBN:61:Cr crystals under applied fields, applications in image edge-enhancement and photorefractive edge-enhancement joint transform correlator are investigated. It is found that when external electric fields are exploited to enhance the image edge, the edge can be made sharper. And the photorefractive edge-enhancement joint transform correlator can provide higher ± 1 correlation peak and narrower correlation width with the presence of electric-fields. (3) We explore photorefractive screening solitons and characters of beam transmission in SBN:61:Cr crystals. The dependence of beam diameter at the crystal output face on applied field is presented. And influences of the limiting space charge field of the crystals on the experimental results are analyzed. (4) Light-induced scattering in SBN:61:Cr crystals under applied fields and its suppression are studied. A new method is proposed that the scattering light can be suppressed through erasure of scattering gratings by higher power pump beam (coherent or incoherent).