LiNbO_(3):Fe晶体中圆偏振光散射引起的偏振态变化(特邀)

Polarization State Variation Induced by the Circularly Polarized Light Scattering in LiNbO_(3):Fe Crystal(Invited)

报道了LiNbO_(3):Fe晶体内光致散射过程中偏振态的变化。将圆偏振光聚焦成极细的光片,并将其照射在c轴沿竖直方向放置的晶体上,研究了不同入射角时的光散射现象。在散射光从产生到达到稳态的数十分钟内,散射光主要在平行于c轴的方向上产生,同时在平行于光片的方向上存在分量,散射光产生速度随入射角的增大而减小。进一步观察表明,圆偏振光通过晶体后变成普通椭圆偏振光,不同入射角下出射光椭圆度也不同。结合晶体内部形成的噪声光栅,建立了圆偏振光的散射模型,并计算分析了偏振态变化的原因和机理。这一发现提出了一种利用光折变晶体的光致散射特性产生椭圆偏振光的方法,在基于光折变材料的光存储、光子晶格等方面有应用价值。

Doped LiNbO;crystal is one kind of photorefractive mediums which are used for optical storage.When light passes through LiNbO_(3)crystal,it will cause local refractive index change and form noise grating. The noise grating diffracts the incident light,transferring part of the light energy to the scattered light,namely,light-induced scattering. In recent years,the modulation instability,generation process and energy transfer efficiency of light scattering in LiNbO;crystals have been widely studied. Since a single component of linearly polarized light is used for the incident,no variation of the polarization state of the outgoing light is observed. However,considering the difference of energy transmission efficiency between o-light and e-light,it is reasonable to guess that the polarization state of the outgoing light may change when another light is incident. According to our investigation,there is no research in this field. In this work,the variation of the polarization state of LiNbO_(3):Fe crystal during the light-induced scattering process is reported. The circularly polarized light is focused into a thin light sheet and irradiated on the crystal with the c-axis along the vertical direction. The light scattering phenomenon at different incident angles is studied. In the tens of minutes from the generation of the scattered light to the steady state,the scattered light mainly grows in the direction parallel to the c-axis,and there is also a component in the direction parallel to the light sheet. The growth rate of scattered light decreases with the increase of the incident angle. Further observation manifests that the circularly polarized light becomes ordinary elliptically polarized light after passing through the crystal,and the ellipticity varies with the incident angle. Combined with the noise grating formed in the crystal,the scattering model of circularly polarized light is established,and the reason and mechanism of polarization state change are analyzed through calculation. Qualitative analysis shows that the ellipticity of scattered light is related to the transmission coefficient τ and azimuth angle,and the left-handed or right-handed polarization state is also related to the phase difference δbetween o-light and e-light. This discovery proposes a method to generate elliptically polarized light using the light-induced light-scattering properties of photorefractive crystals,which can be applied to optical storage and photonic lattice based on photorefractive materials.