Development of near field laser induced ablation spectroscopy

点击翻译按钮获取中文摘要

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.