Research On Two-beam Coupling And Light-induced Absorption Of Near-stoichiometric LiNbO₃Crystals

The optical volume holographic storage technology has so many advantages, such as the highstorage density, the large storage capacity, parallel transmission, high addressing rate and so on.These advantages make optical volume holographic storage so great in competition with other storagetechnologies and more and more people pay attention to this technology. Two-color holographicstorage realizes the nonvolatile readout in optical volume storage. Storage material is the key factor tothe optical volume holographic storage, so it becomes a hot topic to find material suitable to opticalvolume storage. Since people found the nonlinear optical effect of LiNbO₃crystals, LiNbO₃crystalshave acquired rapid development in the holographic storage technology, and optimizing LiNbO₃crystals has became the most important task in holographic storage research.In this paper, we have firstly studied the two-beam coupling effect of Fe-dopednear-stoichiometric LiNbO₃crystals （SLN:Fe）, the wavelength of incident light is532nm. The resultsshow higher concentration of impurity, higher incident intensity and smaller rate of incident intensitycan make the response time shorter, and the response time of extraordinary light is shorter than that ofordinary light. Bigger rate of incident intensity can lead bigger effective gain coefficient, and theeffective gain coefficient of extraordinary light is larger than that of ordinary light, but theconcentration makes no difference to the effective gain coefficient nearly.We have also researched light-induced absorption using the pump （365nm）-probe （785nm）method with near-stoichiometric LiNbO₃:Fe and LiNbO₃:Tb crystals, measured absorption coefficientand response time of the crystals. The result shows the dark decay process of light-induced absorptionexhibits a stretched-exponential behavior. What’s more is both higher pump light intensity and higherconcentration of impurity will make the life time of small polarons smaller, oxidation and reductiontreatment will lead bigger and smaller life time of small polarons respectively. And higher pump lightintensity makes stretched factor smaller, oxidation and reduction treatment makes the stretched factorbigger and smaller respectively.In this paper, we have done so many researches on the two-beam coupling effect andlight-induced absorption of LiNbO₃crystals, and these researches can help us to understand theprocess of light-induced absorption and physical mechanism of two-color holographic storage.