Scattering type near-field optical microscopy (s-SNOM) combined with coherent ultrafast mid infrared light source can provide a time domain approach to vibrational spectroscopy at nanometer scale. The molecular free induction decay behavior is observed with tip scattering and phase sensitive heterodyne detection, asymmetric FT-IR measurements are carried out on surface polymer samples. This approach demonstrates vibrational spectroscopy with sub-diffraction limit spatial resolution and enables spectroscopic studies on heterogeneous samples that suffer from spatial inhomogeneous broadening. High sensitivity of about one thousand vibrational bonds is also demonstrated. A prospective time resolved pump/probe implementation with IR s-SNOM will be discussed.
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