应用太赫兹焦平面成像方法研究氧化镁晶体在太赫兹波段的双折射特性`  

Birefringence characteristics of magnesium oxide crystal in terahertz frequency region by using terahertz focal plane imaging

作　　者：姜伟 赵欢 汪国崔 王新柯[1] 韩鹏[1] 孙文峰[1] 叶佳声[1] 冯胜飞[1] 张岩[1] Jiang Wei;Zhao Huan;Wang Guo-Cui;Wang Xin-Ke;Han Peng;Sun Wen-Feng;Ye Jia-Sheng;Feng Sheng-Fei;Zhang Yan(Department of Physics,Capital Normal University,Beijing 100048,China)

机构地区：[1]首都师范大学物理系,北京100048

出　　处：《物理学报》2020年第20期330-337,共8页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11774243,11774246);首都师范大学青年创新团队(批准号:19530050146);首都师范大学科技创新能力建设项目(批准号:19530050170,19530050180)资助的课题.

摘　　要：高效可集成太赫兹波片和偏振片是重要的太赫兹光学元器件.由传统的石英晶体及液晶等材料制作的太赫兹波片和偏振片由于其对太赫兹光响应度低并难于集成而难以应用于太赫兹集成光学领域.为了寻找用以制备高效可集成太赫兹偏振元件的材料,本工作应用太赫兹焦平面成像方法研究了<100>晶向的氧化镁晶体对太赫兹波段圆偏振光偏振态的影响.通过实验观察到氧化镁晶体可以使入射的圆偏振光转化成为线偏振光.为了进一步验证氧化镁晶体对太赫兹光相位的影响,还应用透射式太赫兹时域光谱系统测量了氧化镁晶体在太赫兹波段的寻常光和非寻常光的折射率.通过对比氧化镁晶体中寻常光和非寻常光的位相差,证明氧化镁晶体在太赫兹焦平面成像实验中起到了1/4波片的作用.这一结果表明氧化镁晶体是一种制备太赫兹频段可集成波片及其相关偏振器件的重要材料.Fabricating integratable and high-efficiency optical polarization devices is one of the fundamentally important challenges in the field of terahertz optics.Compared with the traditional polarization materials such as quartz crystal and liquid crystal,MgO crystal is one of the most important potential candidates for fabricating terahertz optical devices due to its high transmittance in terahertz frequency region.To determine the birefringence characteristics of MgO crystal in the terahertz frequency region,the modulation of the polartization state of a terahtertz wave through a<100>crystalline MgO flake is studied using terahertz focal plane imaging method.Within this approach,the polarization of a terahertz wave can be intuitively identified from the imaging of the amplitude and the phase of the z-direction component of terahertz electronic field.By measuring the imaging of both the amplitude and the phase of terahertz field with and without passing through the<100>crystalline MgO flake,it is found that the left and right circularly polarized light are converted into perpendicular linearly-polarized light after passing through the MgO flake.The polarization direction of the linearly polarized light changes with the rotating of MgO flake along the direction perpendicular to the light propagation.The conversion between the linearly polarized light and the circularly polarized light is analyzed by using the Jones matrix approach.These properties indicate that the<100>crystalline MgO flake acts as a quarter wave plate for terahertz waves.To further identify the character of terahertz quarter wave plate,the refractive index of the ordinary and extrordinary light within terahertz frequency region of crystalline MgO crystal are measured by using transmission terahertz time-domain spectroscopy system.By comparing the phase difference between the ordinary and extraordinary light after passing through the MgO flake,it is shown that a quarter of wavelength difference between the ordinary and extraordinary light is obtained.

关 键 词：太赫兹 焦平面成像 双折射 

分 类 号：O734[理学—晶体学] O441.4