Terahertz applications in cultural heritage: case studies D. Giovannacci a* , D. Martos-Levif b , G. C. Walker d , M. Menu c , V. Detalle b a Cercle des Partenaires du Patrimoine, Champs sur Marne 77420, France. b Laboratoire de Recheche des Monuments Historiques UMR3224, Champs sur Marne, 77420 France. c Centre de Recherche et de Restoration des Musées de France, Paris, 75001, France. d School of Systems Engineering, University of Reading, Reading, UK. * david.giovannacci@culture.gouv.fr ABSTRACT Terahertz (THz) spectroscopy and imaging is a non-destructive, non-contact, non-invasive technology emerging as a tool for the analysis of cultural heritage 1 . THz Time Domain Spectroscopy (TDS) techniques have the ability to retrieve information from different layers within a stratified sample, that enable the identification of hidden sub-layers in the case of paints and mural paintings 2 . In this paper, we present the THz TDS 2 system developed in the European Commission's 7th Framework Program project CHARISMA [grant agreement no. 228330]. Bespoke single processing algorithms; including a deconvolution algorithm 3,4,5 can be deployed to increase the resolution and the global performance of the system. The potential and impact of this work is demonstrated through two case studies of mural paintings, where the capability to reveal the stratigraphy of the artworks is demonstrated. Keywords: Terahertz, reflection imaging, signal analysis, mural paintings, conservation, under-painting, Fourier analysis 1. INTRODUCTION There is a demand from conservation experts in the community of cultural heritage - encompassing artworks, museum artifacts or historical monuments – for less intrusive and non-destructive tools to gain information about the subject. Increasingly the demand is for information regarding internal structures and indications of life histories of an object; particularly when the artifact is composed of multi-layers and insulating components, as is often the case with mural paintings. Many dielectric materials which are opaque or highly scattering at optical wavelengths are transparent at THz frequencies which penetrate most non-polar, non-metallic media 1 . This technique combines a series of elements to provide a range of information about culturally significant objects under analysis: spectroscopy provides material characterization; time-of-flight analysis illustrates radiation penetration and stratiographic information in addition to the ability to parametrically image of optically opaque materials. THz radiation is able to provide depth information from tens of micrometers to approximately one centimeter into the wall surface. These properties providing mesoscopic details without necessitating sample extraction—either in the laboratory or in the field. The technique provides information at depth not accessible by other commonly used imaging techniques, giving improved spatial resolution compared to sub- surface radar, and penetrating further into the wall than UV and infrared techniques which are limited to surface information. THz radiation is also non-destructive because its low photon energy is non-ionizing and molecular heating—due to absorption—is low. The ability to retrieve information from different layers within a stratified sample using terahertz pulsed reflection imaging and spectroscopy is now well known in cultural heritage. In this paper, the authors will describe some examples of the contribution of THz TDS for the science of conservation. The two mural painting case studies are: ―Les trois homes armés de lance ―(Collection Campana, P44, Musée du Louvre), and the Doom Painting, a mural painting at St Thomas Church, Salisbury , UK. Fundamentals of Laser-Assisted Micro- and Nanotechnologies 2013, edited by Vadim P. Veiko, Tigran A. Vartanyan, Proc. of SPIE Vol. 9065, 906510 · © 2013 SPIE · CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2049818 Proc. of SPIE Vol. 9065 906510-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 12/23/2013 Terms of Use: http://spiedl.org/terms