Implementation and Evaluation of a Spectroscopic System for Passive Near-Field Microscopy

Long wavelength infrared (LWIR) is highly attractive spectra to the correspondence of chemical bonding and molecular motion. In recent years, we have developed a passive LWIR scattering-type scanning near-field optical microscopy (s-SNOM) that detects surface waves introduced by such local phenomena (wavelength: 14.5 μm) with a spatial resolution of 20 nm without any external light sources. Here, we report a newly developed passive near-field spectroscopic system that allows a spectroscopic measurement of detectable wavelengths ranging from 8 to 16 μm. We designed and built a grating-based optical system and proved to have a diffraction efficiency of more than 60% over the detectable wavelengths ranges. This newly developed spectroscopic system would have the potential to distinguish the energy of different wavelengths with a spectral resolution of 100 nm.