Confocal Terahertz Imaging of Ancient Manuscripts
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Terahertz imaging has the potential to identify and decipher portions of ancient manuscripts, which may be unreadable at infrared and visible wavelengths. We use a scanning confocal terahertz microscope to scan a medieval parchment with music notes and pentagrams written with different inks. The microscope is based on a continuous-wave solid-state source at 0.3 THz, emitting in the free space with a horn antenna, and a high numerical-aperture ellipsoidal reflector. We present terahertz images with diffraction-limited lateral resolution of approximately 0.5 mm, where the different inks all give similar high contrast. Symbols written on the “verso” side of the parchment, barely glimpsed in the near-infrared photograph, leave a clear imprint in the terahertz images. Artifacts due to imperfect flatness of the parchment are also briefly discussed.
KeywordsConfocal microscopy Schottky diode detector Terahertz Paper Ink Diffraction limit
We acknowledge support from the Grant office of Sapienza University of Rome through project THESMA. We thank S. Nieddu, S. Cristelli, and G. Amico for their valuable help in the experiment.
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