Development of Passive Near-field Spectroscopy for Thermal Evanescent Wave

The local dynamics on materials generate thermal evanescent waves that are strongly localized on material surfaces. Sensing the thermal evanescent waves with scattering-type scanning near-field optical microscopy (s-SNOM) without any external light sources enables imaging of the local dynamics at the nanoscale. Here, we report passive THz scanning near-field optical spectroscopy (SNOS), in which a wavelength selective mechanism was constructed on s-SNOM. We have achieved detecting far-field spectrum at wavelengths of 8.0 - 15.5 mu m and broadband near-field signals of an Au/SiC sample at room temperature. The spectrum of the thermal evanescent wave enables a detailed analysis of the material surface.