Development of near field laser induced ablation spectroscopy

该研究项目的目的是发展近场激光诱导烧蚀光谱，并分析其化学成分，以检测100nmNmφ区域内的原子发射。问题是要克服光的衍射极限，限制激光诱导的烧蚀区域。我们的想法是利用飞秒脉冲激光的尖端增强场，这种增强场在几十纳米范围内是有效的。我们期望被激发的原子和离子在烧蚀后发出特征光，并获得化学成分的信息。我们已经安装了近场光学扫描显微镜。激发光为800 nm、脉宽为150ps的脉冲飞秒光，照射在W尖端。结果表明，13mJ/cm2辐照可在玻璃表面形成宽50 nm、深10 nm的Au、Al薄膜烧蚀区。没有W尖端的照射，不会发生烧蚀。该烧蚀区域超过了衍射极限，飞秒脉冲激光与尖端增强场相结合可以有效地诱导纳米区域的烧蚀。另一方面，没有观察到光发射。它被认为是因为脉冲光也是如此。激发被烧蚀的原子和离子的简称。在本研究中，我们还研制了光热扫描近场光学显微镜(PT-SNOM)。横向分辨率提高到200 nm。PT-SNOM可用于检测对生物材料无活性的非荧光分子。此外，还可以发现针尖增强的光热效应，并可以安装无孔PT-SNOM。

The aim of the research project is to develop the near-field laser induced ablation spectroscopy and to analyze the chemical composition to detect the atomic emission within 100 nmφ area. The problem is to overcome the diffraction limit of light and confine the ablation area induced by laser beam. Our idea is to utilize the tip enhanced field with femtosecond pulse laser beam and such a enhanced field is effective within several tens nanometer. We expect that the excited atoms and ions emit characteristic light after ablation and information on chemical composition is obtained.Near-filed optical scanning microscope has been installed by ourselves. Pulsed femtosecond light with 800 nm and 150 fs pulse width is used as an excitation light, and irradiates the W. tip. It has been found that irradiation with 13 mJ/cm^2 induces the ablation area with 50 nm width and 10 nm depth for Au and Al thin films on a glass. Without W tip in irradiation, no ablation takes place. This ablation area is beyond the diffraction limit and a combination with femtosecond pulse laser and tip-enhanced field is effective to induce nano-area ablation. On the other hand, no light emission has been observed. It is considered for the reason that pulse light is too. short to excite the ablated atoms and ions. Further, optimization of optical geometry is needed.In this research, we have also developed the photothermal scanning near field optical microscope (PT-SNOM). The lateral resolution is enhanced to 200 nm. PT-SNOM can be applied to detect the non-fluorescent molecules, which are inactive to biomaterials. Further, tip enhanced photothermal effect can be found out and the apertureless PT-SNOM can be installed.