Heritage 2023, 6, 1531–1540. https://doi.org/10.3390/heritage6020082 www.mdpi.com/journal/heritage Article Time-Gated Pulsed Raman Spectroscopy with NS Laser for Cultural Heritage Xueshi Bai 1 and Vincent Detalle 1,2, * 1 Centre de Recherche et de Restauration des Musées de France (C2RMF), 14 Quai François-Mitterrand, 75001 Paris, France 2 SATIE, Systèmes et Applications des Technologies de l’Information et de l’Energie, CY Cergy-Paris Université, Pôle SIAME, CNRS UMR 8029, 5 Mail Gay Lussac, 95031 Neuville sur Oise, France * Correspondence: vincent.detalle@cyu.fr Abstract: Raman spectroscopy, a non-destructive reference technique, is used in heritage science to directly identify materials like pigments, minerals, or binding media. However, depending on the material, the laser source can induce a strong fluorescence signal that may mask the Raman signal during spectral detection. This photo-induced effect can prevent the detection of a Raman peak. A pulsed Raman spectroscopy, using a time-gated detection and pulsed laser, is proven capable of rejecting the fluorescence background and working with the environmental light, which makes Raman spectroscopy more adapted for in situ applications. In this paper, we investigated how an ns pulsed laser can be an excitation source of Raman spectroscopy by focusing on different parameters of laser excitation and collection. With proper implementation, this pulsed Raman technique can be used for cultural heritage with an ns pulsed laser for the first time. Keywords: time-gated Raman spectroscopy; pulsed Raman spectroscopy ns laser; heritage science; fluorescence rejection 1. Introduction Raman spectroscopy is one of the most efficient nondestructive techniques for identifying materials and is applied in many different domains, especially for cultural heritage [1–10]. However, the laser source can generate a strong fluorescence when organic materials are present. Laser-induced fluorescence or, more generally, photoluminescence may mask the Raman signal during spectral detection, which means that no Raman peak can be determined by the spectra [11,12]. Therefore, in the 70s, the time-gated Raman spectroscopy technique was developed with a very short-pulsed laser to eliminate the impact of the fluorescence [13,14]. Harries et al. were the first team to compare the level of fluorescence background rejection in a time-gated experiment to that of continuous excitation on a fluorophore-doped benzene Raman band at 992 cm −1 [14]. The ambient light does not interfere with time-gated Raman spectral results and improves the signal-to-noise ratio of weak Raman signals in the presence of fluorescence [14–17]. Its applications have emerged in different domains, such as mineralogy, planetary sciences, biotechnology, biomedical, pharmaceutical identification, hot temperature, environmental sensing, and process industrial sensing [13]. However, the pulsed Raman approach for in situ cultural heritage conservation applications has never been demonstrated in the literature. Time-resolved Raman spectroscopy needs a photon detector with high sensitivity (single photon counting ability), a fast external trigger, and a temporal resolution in the sub-nanosecond range, such as intensified-charge-coupled device (ICCD) cameras, the most common detector for pulsed Raman. New, high-quality ICCD detectors can rapidly Citation: Bai, X.; Detalle, V. Time-gated Pulsed Raman Spectroscopy with NS Laser for Cultural Heritage. Heritage 2023, 6, 1531–1540. https://doi.org/10.3390/ heritage6020082 Academic Editor: Vittoria Guglielmi Received: 31 December 2022 Revised: 23 January 2023 Accepted: 30 January 2023 Published: 1 February 2023 Copyright: © 2023 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/license s/by/4.0/).