Terahertz spectroscopy and imaging for material analysis in conservation science

Terahertz (THz) waves can penetrate opaque materials and fingerprint spectra appear as those in infrared bands. The technique is expected to be used as a new non-invasive analysis method for various materials. Time domain reflection imaging, in particular, uses THz pulses that propagate in specimens, and in this technique, pulses reflected from the internal boundaries of the specimen indicate the internal structure. We have developed a spectral database of painting materials, and applied THz time domain imaging for analysis of artworks. Experimental results, including first ever non-invasive cross section image of a tempera masterpiece, proved that THz wave can observe layer structure of the artwork from the wood support, gesso preparation layers, and the painting layer. This technique should also be useful to detect internal defect of various types of opaque dielectric materials such as multi layer insulations.