Processing and analysis of THz time-domain spectroscopy imaging applied to cultural heritage

Integrated Imaging and Spectroscopic Analysis of Painted Fresco Surfaces Using Terahertz Time-Domain Technique

“…The instrument utilized in this research is a commercial THz-TD system (TOPTICA Photonics, Munich, Germany, TeraFlash Pro), equipped with a mode-locking Erbium-doped fiber laser (λ = 1560 ± 10 nm, pulse width 50-60 fs, repetition rate 100 MHz). A thorough description of the system is presented in our previously published papers [13,14,21]. For the purposes of this study, imaging data were acquired using a reflection configuration under a nitrogen atmosphere to suppress air moisture contribution and enhance the spectral identification of pigments.…”

“…Inherently, the presence of tilting or curvature on the sample surface makes it difficult to extract accurate values of the complex refractive index [13]. Finally, various additional secondary effects can complicate the analysis of the THz data, such as Fabry-Perot, multiple-scattering, and water vapor in the atmosphere, which pose significant challenges in data pre-processing, particularly when examining heritage artefacts with multiple material layers and uneven surfaces [4,14].…”

“…In the past 20 years, researchers have been investigating the potential of THz radiation for examining works of art, ranging from oil paintings on canvas to mummies and architectural specimens. One of the earliest applications of THz imaging dates to 2008, when Jackson et al showed the capability of this technique to uncover graphite underdrawings beneath a lime plaster layer on a mock-up wall painting sample [14]. In 2010, Fukunaga et al applied THz imaging to analyze historical mural paintings, comparing the intensity in reflection at far-infrared frequencies with the distribution of pigments determined via Raman and X-ray fluorescence [3].…”

“…The second problematic condition when dealing with heritage object, i.e., studying uneven surfaces, was tackled by A. Artesani and co-authors in 2023 [13]. They proposed a self-referenced method to computationally remove surface geometrical curvature and consequently correct the phase value, enabling the determination of more accurate material absorption coefficients [14,21].…”

Continuous wave THz imaging of multi-walled carbon nanotubes polymer composites

“…The progress of visualization technologies today makes it possible to apply them in the art [9], archeology [10], medicine [11], food [12] and electronic industries [13]. Over the last decades, material defectoscopy at terahertz (THz) frequency range became popular [14].…”