Developmsnt of scanning optical probe microscope using a metallic probe

我们应用近场扫描光学显微镜（NSOM）使用金属探针尖端的生物样品。在以小鼠胚胎心肌细胞为样本的测试中，我们可以观察到我们的NSOM图像的精细结构（折射率的变化）。这种结构不能用扫描电子隧道显微镜（STM）观察到.此外，我们还阐明了：（1）NSOM图像与样品的表面轮廓不同，（2）它们的浓度随照明的偏振态而变化，（3）倏逝波的干涉局限于周期性结构的样品表面。因此，我们可以将它应用于以前的透明模式系统所不能观察到的非透明样品，如半导体或金属样品。为了评价该系统的分辨性能，我们使用半导体材料作为样品，其表面具有周期为240 nm的周期性结构。在实验中，我们可以观察到空间分辨率为60 nm的电磁场局部化现象。计算结果证实，在金属针尖的顶端有很高的电场强度，约为入射光的40倍。这一结果表明，金属针尖NSOM系统可以提取针尖尖端附近的纳米光学信息，如果将其与双光子吸收或二次谐波等非线性光学技术相结合，将成为一种新的成像系统，从而有效地利用针尖的场增强效应。

We applied the near-field scanning optical microscope (NSOM) using a metallic probe tip to biological samples. In testing with murine embryonal myocardial cell as a sample, we can observe the fine structure (the variance of refractive index) in our NSOM images. This structure cannnot be observed by a scanning electrontunneling microscope (STM). In addition, we clarify that 1) NSOM images are different to the surface profile of samples, and that 2) their contasts vary with the polarizing state of illumination, and that 3) the interference of the evanescent wave is localized on the sample surface of periodical structure.We developed our metal-tip NSOM to a reflecting-mode system. Therefore, we can apply it to apply the nontransparent samples, such as semi-conductor or metallic samples, which cannot be observed by a former transparent mode system. To estimate resolving performance of this system, we use the semi-conducting materials as a sample, whose surface has periodical structure with a period of 240 nm. In experiments, we can observe the localization of the electromagnetic field with a spatial resolution of 60nm.Electromagnetic simulations of the metal-tip NSOM have carried out in 3D model using realistic size and materials. A results of calculation confirmes that there is high electric intensity at the apex of the metallic tip, which is about 40 times greater than the incident light. This result shows that the metal-tip NSOM system can extract the nanometric optical information at the vicinity of the tip apex, and that new imaging system will be available, if it is combined with nonlinear optics such as two photon absorption or SHG.This may make effective use of field enhancement of the tip.