利用扫描近场光学显微镜的偏振衬度对各向异性微晶的观察

利用扫描近场光学显微镜的偏振衬度对罗丹明6G的微晶进行观察,结果表明,用圆偏振入射光进行观察时,光学图像与表面形貌图有很好的对应关系。而用线偏振入射光进行观察时,随着入射偏振态的不同,成像差别较大:当偏振态方向沿着具有各向异性吸收的晶粒主吸收方向时,在垂直于主吸收方向上有很高的衬度,但图像分辨率较低;而入射偏振态垂直于主吸收方向时,衬度降低,分辨率提高;在与主吸收方向成45°角入射时,可以得到分辨率和衬度都比较好的图像。

Investigating Anisotropic Micro-crystal Using Polarization Contrast in Scanning Near-field Optical Microscope

A scanning near-field optical microscope(SNOM) was used to observe rodamine 6G micro-crystal by using polarization contrast. SNOMimage with a round polarized incident light correlated well with the shear-force topography image of crystals. However, with linearly polarized light, anisotropic absorption was found. When the polarization direction was parallel to strongly absorbing direction, the optical contrast came mainly from the sample absorption, therefore, well resolution was obtained in its perpendicular direction. However, when the polarization direction was perpendicular to the strongly absorbing direction, optical contrast came mainly from the complex interaction between the near-field light and the sample, which improved the resolution in the perpendicular direction. When the direction was 45° to the absorbing direction, optical contrast came from both of the near-field interaction mechanism and the absorbing mechanism, and a good resolution image was obtained. The present work demonstrates that the polarization contrast has a great application to the studies of anisotropic materials.