Abstract-Quantitative diagnostics of ancient paper using THz time-domain spectroscopy

M. Missori, 

D. Pawcenis, 

J. Bagniuk, 

A. Mosca Conte, 

C. Violante, 

M.S. Maggio, 

M. Peccianti,

O. Pulci,  

J. Łojewska, 

https://www.sciencedirect.com/science/article/pii/S0026265X17308391

In this work we have studied the terahertz spectra of modern artificially aged and ancient paper samples using terahertz time-domain spectroscopy. Hydrothermal artificial aging was performed in closed and open reactors. Ancient paper samples were produced during the 15th century in European countries. The main aim of the work is the quantitative assessment of spectral feature observed by terahertz spectroscopy as a function of degradation. To this goal, the state of degradation of paper samples was characterized by crystallinity measurements obtained by using X-ray diffraction and by the degree of polymerization of cellulose polymers obtained by size exclusion chromatography. The behavior of the terahertz spectra was formerly investigated as a function of the hydration of paper samples. This allowed discriminating between the spectral features induced by the presence of water and those induced by degradation of paper. Results indicate clear dependences of spectral parameters from the evolution of crystallinity and the degree of polymerization. They can be used as a nondestructive analytical method to assess the state of degradation of ancient paper by terahertz spectroscopy.

Abstract-Integral equation technique for scatterers with mesoscopic insertions: Application to a carbon nanotube

M. V. Shuba, A. V. Melnikov, P. P. Kuzhir, S. A. Maksimenko, G. Y. Slepyan, A. Boag, A. Mosca Conte, O. Pulci, and S. Bellucci

https://journals.aps.org/prb/accepted/6107dO76Q9410a3e03fb802612edf10544872aa61

We present the electromagnetic scattering theory for a finite-length nanowire with embedded mesoscopic object. The theory is based on a synthesis of the integral equation technique of classical electrodynamics and the quantum transport formalism. We formulate Hall\'en type integral equations, where the canonical integral operators from wire antenna theory are combined with special terms responsible for the mesoscopic structure. The theory is applied to calculate the polarizability of a finite-length single-walled carbon nanotube (CNT) with a short low-conductive section (LCS) in the microwave and sub-terahertz ranges. The LCS is modeled as a multichannel two-electrode mesoscopic system. The effective resistive sheet impedance boundary conditions for the scattered field are applied on the CNT surface. It is shown that the imaginary part of the polarizability spectrum has three peaks. Two of them are in the terahertz range, while the third one is in the gigahertz range. The polarizability spectrum of the CNT with many LCSs has only one gigahertz peak which shifts to low frequencies as the number of the LCS increases. The physical nature of these peaks is explained, and potential applications of nanoantennas are proposed

Abstract-Terahertz absorption by cellulose: Application to ancient paper artifacts

M. Peccianti, R. Fastampa, A. Mosca Conte, O. Pulci, C. Violante, J. Łojewska, M. Clerici, R. Morandotti, and M. Missori

https://journals.aps.org/prapplied/accepted/ce07fYc6Le011c53637216614e26e35315d5a921c

Artifacts made of cellulose, such as ancient documents, pose a significant experimental challenge in the THz transmission spectra interpretation due to their small optical thickness. In this Letter we describe a method to recover the complex refractive index of cellulose fibers from the THz transmission data obtained on single freely standing paper sheets in the 0.2\textendash 3.5~THz range. By using our technique, we were able to eliminate Fabry-Perot effects and recover the absorption coefficient of the cellulose fibers. The obtained THz absorption spectra are explained in terms of absorption peaks of the cellulose crystalline phase superimposed to a background contribution due to a disordered hydrogen bonds network. The comparison between the experimental spectra with THz vibrational properties simulated by density functional theory calculations confirms this interpretation. In addition, evident changes in the THz absorption spectra are produced by natural and artificial aging on paper samples, whose final stage is characterized by a spectral profile with only two peaks at about 2.1~THz and 3.1~THz. These results could be used to provide a quantitative assessment of the state of preservation of cellulose artifacts.