Infrared and Terahertz radiations are advantageously exploited in different field of basic and applied science for providing information on vibrational, phononic, electronic and many other low-energy excitations of a wide variety of inorganic and organic materials. Due to their long-wavelength nature, however, the maximum spatial resolution achievable, when performing IR/THz microscopy, cannot exceed a fraction of l (i.e. a few microns in the IR and around 100 microns in the THz range) and this limitation is determined, ultimately, by diffraction. Moreover, the diffraction limit is hardly reachable with conventional radiation sources (like for instance black body radiators) due to their intrinsic low-brilliance characteristics.

In this framework, the use of synchrotron (IRSR) radiation since the nineties, has revolutionized the field of IR/THz microscopy providing the possibility to actually reach the diffraction limit and opening this technique to spatial resolved measurements at few microns of spatial resolution. However, the utilization of IRSR implies to perform experiments in synchrotron facilities with the need to apply for beamtime request.

Moreover, go beyond the diffraction limit is highly desirable in order to extend IR/THz microscopy to spatial scales comparable to those characterizing naturally and artificially nanostructured materials and heterogeneous systems. Beating the diffraction barrier and improving the spatial resolution to the nanometric scale can be obtained by using near-field sensitive techniques. The key idea is to coupling an AFM tip with a Michelson interferometer (Nano-FTIR). Properly illuminating the tip (for instance with a broad band source) and measuring the near-field scattered light from the interaction volume (the spatial region between the tip and the sample) one can acquire a spectrum with a spatial resolution comparable to the tip size (i.e. tens of nanometers). This geometry allows to efficiently get rid of the large thermal background at IR and THz frequencies, while enabling a full spectroscopic characterization of the sample, according to the bandwidth of the source. Thanks to these technological advancements Nano-FTIR, is becoming an increasingly used technique.