Terahertz imaging super-resolution for documental heritage

THz time-domain spectroscopy (THz-TDS) and pulsed imaging have been demonstrated to be able to provide a non-invasive examination of cultural heritage materials. However, the spatial resolution of THz pulsed imaging is of the order of 1 mm for THz waves, a value that is often not sufficient for the examination of small details on written heritage. This paper will focus on the development of a far-field super-resolution THz imaging system based on a free-standing knife edge and a reflective confocal configuration for the THz beamline. This system has been designed for the recognition of inks, pigments, and dyes used in graphic signs and forthe detection of texts b uried beneath graphical layers. To optimize the set-up preliminary experiments were realized by imaging the diffraction pattern of a slit, where the freestanding knife set-up showed an improved resolution. After, a reflective set-up was realized and tested on paper samples with graphite patterns. Results demonstrated the super-resolution of THz imaging by showing written features separated by less than the wavelength used. The future direction will be the application of the set-up to real ancient documents for their diagnostics.