By combining dedicated near-field generation and detection techniques with Raman spectroscopy, optically inactive phonon activity is predicted. Observation of these phonons opens a new era as a novel analytical technique beyond near-field microscopy/spectroscopy which has previously only been concentrated on obtaining higher spatial resolution. As a possible example of optically inactive phonon observation, measurement of a Raman spectrum of polydiacetylene was demonstrated.
Yoshihito Narita, Yoshihito Narita,
"Observation of optically inactive phonons for development of a unique near-field spectroscopy method," Journal of Nanophotonics 1(1), 011580 (1 September 2007). https://doi.org/10.1117/1.2753516