title: Thin layered drawing media probed by THz time-domain spectroscopy.
abstract: Dry and wet drawing materials were investigated by THz time-domain spectroscopy in transmission mode. Carbon-based and iron-gall inks have been studied, some prepared following ancient recipes and others using current synthetic materials; a commercial ink was studied as well. We measured the THz signals on the thin films of liquid inks deposited on polyethylene pellicles, comparing the results with the thick pellets of dried inks blended with polyethylene powder. This study required the implementation of an accurate experimental method and data analysis procedure able to provide a reliable extraction of the material transmission parameters from a structured sample composed of thin layers, down to a thickness of a few tens of micrometers. THz measurements on thin ink layers enabled the determination of both the absorption and the refractive index in an absolute scale in the 0.1-3 THz range, as well as the layer thickness. THz spectroscopic features of a paper sheet dyed by using one of the iron-gall inks were also investigated. Our results showed that THz time-domain spectroscopy enables the discrimination of various inks on different supports, including the application on paper, together with the proper determination of the absorption coefficients and indices of refraction.
authors.affiliation: European lab. for Non-Linear Spectroscopy (LENS), Univ. di Firenze, via N. Carrara 1, I-50019 Sesto Fiorentino, Firenze, Italy. torre@lens.unifi.it and Institute of Optical Materials and Technolgies Acad. J. Malinowski, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, blok 109, 1113 Sofia, Bulgaria.
authors.forename: J
authors.initials: J
authors.lastname: Tasseva
authors.affiliation: European lab. for Non-Linear Spectroscopy (LENS), Univ. di Firenze, via N. Carrara 1, I-50019 Sesto Fiorentino, Firenze, Italy. torre@lens.unifi.it.
authors.forename: A
authors.initials: A
authors.lastname: Taschin
authors.affiliation: European lab. for Non-Linear Spectroscopy (LENS), Univ. di Firenze, via N. Carrara 1, I-50019 Sesto Fiorentino, Firenze, Italy. torre@lens.unifi.it.
authors.forename: P
authors.initials: P
authors.lastname: Bartolini
authors.affiliation: Istituto Nazionale di Ottica, INO-CNR, Largo Fermi 6, I-50125 Firenze, Italy.
authors.forename: J
authors.initials: J
authors.lastname: Striova
authors.affiliation: Istituto Nazionale di Ottica, INO-CNR, Largo Fermi 6, I-50125 Firenze, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Fontana
authors.affiliation: European lab. for Non-Linear Spectroscopy (LENS), Univ. di Firenze, via N. Carrara 1, I-50019 Sesto Fiorentino, Firenze, Italy. torre@lens.unifi.it and Dip. di Fisica e Astronomia, Univ. di Firenze, via Sansone 1, I-50019 Sesto Fiorentino, Firenze, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Torre