Broadband vibrational nano-spectroscopy with a synchrotron infrared source*

Scattering-scanning near-field optical microscopy (s-SNOM) is capable of providing chemical contrast with deep sub-wavelength spatial resolution of a few 10's of nanometers. Unfortunately, the wide applicability of the technique has been hindered by the lack of suitable broadly-tunable or broadband IR sources that can provide the necessary high spectral irradiance. Here, we demonstrate broadband, Fourier-transform infrared spectroscopic s-SNOM using infrared synchrotron radiation from the Advanced Light Source (ALS). We show near-field spectra spanning the full mid-infrared, including the fingerprint absorption region (700 cm$^{-1}$ --- 4000 cm$^{-1}$) and spectroscopic multi-modal imaging in combination with laser-based IR sources. We discuss the potential of the approach for a wide range of soft and hard matter nanoscale spectroscopic applications.