掺铁铌酸钾晶体中的光感生各向异性散射及其光学限制效应

Research on light-induced anisotropic scattering in KNbO3:Fe crystal and its optical limiting effect

光学限制器是光学系统的保护装置,其保护特性是由光限制材料与光强或功率有关的光学非线性效应所产生的,其中光折变晶体中的光感生散射便为该效应之一,多年来受到世界研究者的广泛研究和关注。对于这类光感生散射,有人提出它是由晶体的表面和体散射产生的,研究使用的晶体为LiNbO3:Fe、LiTaO3、BaTiO3,并使用固定的晶体样品和聚焦透镜间距。为了进一步探索该散射的产生机理,本文研究了掺铁铌酸钾晶体在激光照射下产生的光感生各向异性散射特性,利用Z扫描技术测量了该晶体中的光感生折射率变化,并对晶体中光散射形成的光学限制特性进行了研究。分析表明该各向异性散射主要是由掺铁铌酸钾晶体中光感生的柱面透镜效应所导致的。利用光折变晶体中光感生光散射效应的光学限制器,一方面可以通过改变晶体尺寸、透镜焦距、小孔光阑大小等来调整其性质,另一方面因其利用的是低功率连续波激光进行工作,所以能够承受更大的功率和更长的寿命。

Optical limiter is the protective device of optical system,the protective characteristic of it is caused by the optical nonlinear effects related with light intensity or power of the light-limiting material,and photo-induced scattering in photorefractive crystal is one of these effects,which has attracted worldwide attention for many years.For this kind of photo-induced scattering,some researchers proposed that it is caused by the surface and volume scattering of crystals,and the experiments were performed with LiNbO3:Fe,LiTaO3,and BaTiO3,crystals at fixed distances between focusing lenses and samples.In order to further explore the generation mechanism of the scattering,the characteristics of the light-induced anistropic scattering under laser irradiation in KNbO3:Fe crystal are experimentally investigated.The light-induced refractive index changes in KNbO3:Fe crystals have been measured by Z-scan technique.Meanwhile,the optical limiting properties of light scattering in crystals have been studied.The results show that the scattering from KNbO3:Fe crystal is mainly due to the light-induced lensing.The optical limiter using light scattering effect in photorefractive crystal,can be adjusted by changing the crystal size,lens focal length,small aperture size and so on.Meanwhile,because it work with low power continuous wave laser,it can withstand higher power and longer life.