Near-field infrared nanospectroscopy using IR ultra-short pulses

提出并研制了一种新型的红外吸收光谱显微测量系统。将红外显微系统与光参量现象产生的红外超短脉冲相结合，获得了比传统系统更高的空间分辨能力和信噪比。我们观察到分散在CaF_2衬底上的直径为10μm的聚苯乙烯小球体在3.4μm的红外脉冲下的吸收图像，对应于聚苯乙烯中的C-H拉伸振动模式。可以分辨出两个彼此相邻的小球体，这意味着达到了等于波长衍射极限的空间分辨率。在5.8μm的红外脉冲下获得了光刻胶的周期性结构图像，对应于酯键中的C=O拉伸振动模式。我们还研究了达到亚微米空间分辨率的近场红外微光谱的可能性。为了实现红外区域的超分辨能力，在开发原子力显微系统控制悬臂梁的基础上，利用硅微机械工艺设计并制作了尖端孔径小的悬臂梁。然后，我们搭建了一个由红外脉冲源、红外显微镜、300-500nm口径悬臂梁和AFM模块组成的近场红外显微镜。该系统实现了近场红外探头10^<-3>的高光吞吐量。吞吐量比传统的锐化光纤探针大10^2倍。这些新型显微光谱系统将与时间分辨光谱技术相结合，有助于观察单个分子的动力学。

We proposed and developed a novel microscopic system for measuring infrared absorption spectra. Higher spatial-resolving capability and signal-to-noise ratio were achieved than those of a conventional system by combining an infrared microscopic system with infrared ultra-short pulses generated by an optically parametric phenomenon. We observed an absorption image of small polystyrene spheres (diameter : 10μm) dispersed on a CaF_2 substrate with IR pulses of 3.4μm which corresponds to C-H stretching vibration mode in polystyrene. Two small spheres adjacent to each other could be discerned, which means that spatial resolution equal to the diffraction limit of the wavelength was achieved. A distinct image of periodic structure of photoresist was also obtained with the IR pulses of 5.8μm which corresponds to C=O stretching vibration mode in an ester bonding.We also studied a possibility of near field infrared microspectroscopy which attains submicron spatial resolution. To realize the super resolving capability in infrared region, we design and fabricated a cantilever having a small aperture at an apex using a silicon micromachine process besides developing an atomic force microscopic system for controlling the cantilever. Then, we built a near field infrared microscope consisting of the IR pulse source, the IR microscope, the cantilevers having a 300-500nm aperture and the AFM module. High optical throughput of 10^<-3> for the near field IR probe was achieved in the system. The throughput was greater than the conventional sharpened-fiber probe by a factor of 10^2. These novel microspectroscopic systems will contribute to observation of dynamics of a single molecule by combining with time-resolved spectroscopic technique.