We have developed novel methods of near-field microspectroscopy by combining near-field optical microscopy with linear and non-linear optical techniques. The developed near-field microscope achieves high spatial resolution and high time resolution, and is applied to studies of local excitations and wave functions of single noble metal nano-particles. We demonstrate that the plasmon wave functions and the optical fields in the vicinity of nanoparticles are visualized by the near-field methods. Based on these results, we clearly show that localized electromagnetic field enhancement in the vicinity of nanoparticles is one of the most important factors in surface-enhanced spectroscopies. We also extended the methods to ultrafast optical measurements, and show space-resolved ultrafast transient response of single gold nanorods. The characteristic spatio-temporal features observed in the nanorods are revealed to be arising from the changes of the plasmon-mode wave functions upon elevation of photo-induced electronic temperature of the nanorod.
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