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

• Published in: IEEE photonics technology letters 2019-08, Vol.31 (15), p.1261-1264
• Main Authors: Sakuma, Ryoko, Lin, Kuan-Ting, Kim, Sunmi, Kimura, Fuminobu, Kajihara, Yusuke
• Format: Article
• Language: English
• Subjects: Chain dynamics; Chemical bonds; Diffraction; Diffraction efficiency; electrooptic devices; Gratings; Gratings (spectra); infrared imaging; Light sources; Microscopes; Microscopy; Molecular motion; Optical device fabrication; Optical imaging; Optical microscopy; Optical scattering; Optical sensors; Organic chemistry; phototransistors; Spatial resolution; Spectral resolution; spectroscopy; Surface waves; Wavelengths
• ISSN: 1041-1135; 1941-0174
• DOI: 10.1109/LPT.2019.2924728

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~\mu \text{m} ) 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 \mu \text{m} . 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.