THz spectroscopy reaches sub-particle resolution

Conventional techniques of Terahertz spectroscopy (which use the range of electromagnetic radiation between infrared and microwave) reach a spatial resolution that, depending on the radiation used, cannot go beyond an intrinsic limit, the so-called diffraction limit, which is between 3 and 3000 microns. This limitation thus only allows the investigation of ensembles, in which the relevant physical parameters are estimated as the mean value of the size, orientation, shape, and density of nano-particles or nano-domains. Exceeding this limit is a goal that researchers have long attempted to reach.
A team of researchers of the Nest laboratory of the Nanoscience Institute of CNR (CnrNano) and Scuola Normale Superiore, in collaboration with the University of Regensburg, was now able to produce a three dimensional map of a photoexcited single nanowire, with a resolution of 10 nanometers, thanks to a series of sophisticated experiments based on a combination of spatially resolved ultrafast detection and near-field scanning optical microscopy techniques. These three-dimensional maps revealed the formation of depleted charge layers on ultrafast time scales. These results open new horizons for the THz spectroscopy, for the first time beyond the diffraction limit. The results were published in the journal Nature Photonics 8, 841-845 (2014).