| 摘要: | 鈮酸鋰晶體是一種被廣泛使用於全像光儲存的光折變材料。然而由於光折變非線性效應，因此鈮酸鋰晶體在照光時很容易產生光致散射現象，也就是所謂的光扇效 應。光扇現象對於大部分的全像儲存術來說，都是一種很嚴重的雜訊來源，也因此瞭解鈮酸鋰晶體中的光扇現象是一件非常有意義且重要的工作。本論文乃基於此動機，從全像術的概念以及光折變晶體光學出發，探討光折變鈮酸鋰晶體在各種實驗條件下的光扇效應特性以及其應用。 在現象研究方面，我們探討了不同晶體擺向以及將晶體浸入不同溶液時，扇射效應的不同。此外我們也探討了不同照光光束直徑、不同照光偏振態和不同光強對鈮酸 鋰晶體中光扇效應的影響。我們發現在同調光照射、晶體光軸垂直光路的情況下，在鈮酸鋰晶體中總是會產生光扇效應。此外，這一部份的工作也可以幫助我們瞭解光扇效應的特性，並對我們後續要抑制或應用光扇效應時有所助益。 在光扇效應的應用研究方面，我們提出利用光扇效應在光折變鈮酸鋰晶體中以同調光單光束記錄影像資料。據我所知這種記錄法在過去從未有人提出過。除此此外， 我們還提出利用同調光單光束記錄法在晶體中記錄灰階影像的方法，並證實了用同調光單光束記錄法也可以進行多功儲存。我們也把同調光單光束記錄法應用在動態擾動介質中的單向成像。我們提出的架構是所有動態擾動介質中的單向成像術中，最簡單的，也是唯一一種可以接受任何偏振態光的方法。最後，我們發現雖然非同調光（白光）在晶體中不會產生任何光扇效應，但仍然可以在光折變鈮酸鋰晶體中記錄邊緣強化的影像資料。據我們所知，在過去從未有人能單以極弱的白光在光折變晶體中產生折射率變化，甚至是記錄影像。我們也對這個現象提出了一個符合實驗的理論模型。 Lithium niobate is one of the widely used photorefractive materials in the field of holography and optical signal processing. However, there is always the effect of light-induced scattering, the “fanning effect”, in lithium niobate crystal under light illumination. The fanning effect is due to the nonlinear photorefractive effect, and it will reduce the signal-to-noise ratio of the storage system. Therefore it is an important issue to investigate the fanning effect in lithium niobate crystal. Based on this idea, in this thesis I discussed the phenomenological characteristics of fanning effect in lithium niobate crystal in different configurations. I also proposed some applications using fanning effect. In studying the characteristics of fanning effect, we investigated the fanning effect in different crystal orientations, liquids in which the crystal is immersed, light polarization states, light spot sizes, and light intensities. We found that when the crystal is x-cut, fanning effect always occurs regardless of the polarization state is ordinary or extraordinary. On the other hand, different immersing liquids or light spot sizes do not change the phenomenon of fanning effect. In applying fanning effect, we proposed a novel method to record images in lithium niobate using only object beam. The recording is due to fanning effect, and it can be analyzed using the model of fanning hologram. Using this recording method, we accomplished gray-level pattern multiplexing. We further demonstrated one-way imaging through dynamic turbid media using this recording method. Our method is, to our knowledge, the simplest one-way imaging method, and it is also the only one that can work on any polarization state of light. Finally, although incoherent light never induces fanning light, we found it can also induce variation of refractive index of lithium niobate crystal. We also investigated its mechanism, and suggested some applications using the incoherent one beam recording method. |
