Remote Laser Spectroscopy
at standoff distances for Heritage applications
Raman spectroscopy is an analytical technique capable of identifying materials by measuring the spectrum of scattered laser light from the object. The shift of wavelength resulting from molecular vibrations allows highly specific identification of the material. It is non-destructive and non-contact. With the development of efficient laser sources and sensitive detectors in the last three decades, it has become one of the most widely used analysis methods in the field of heritage science research.
Benefiting from the advancement in laser optics and sensor technologies, laser-based analytical methods such as Raman spectroscopy, laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF), have allowed a wide range of applications in heritage science.
Remote Raman analysis of murals of St. Barnabas Cathedral (Nottingham, UK).
Addressing the Challenge
Heritage samples are often immovable and fragile, sometimes at lofty heights or otherwise inaccessible, which limits the possibilities of sampling or contact measurements, and therefore requires in situ, non-destructive and even remote measurements. Remote laser spectroscopy detects light signals from a standoff distance (>5m), using a telescope and optical fibre for light collection. It overcomes the above limitations and significantly broadens the range of possible application scenarios.
LIBS is a type of atomic emission spectroscopy in which highly energetic laser pulses strike the surface of the sample and ablate a small amount of material, then create a plasma in high temperature. In the plasma, the excited ions will give characteristic emission lines. LIBS can detect the characteristic lines for each element and therefore evaluate the chemical compositions of the sample. As only a tiny amount of material (<1mm in diameter) is consumed in the process, LIBS is considered micro-destructive.
Testing the LIBS instrumentation to reveal a hidden green paint layer. Image a: The laser is applied to a small area, close to an existing area of paint loss which confirms the presence of a green underlayer. Image b: The LIBS laser successfully ablates the top layers of paint during successive laser pulses, to reveal and analyse the green under-layer.
Yu Li gave an oral and poster presentation, along with a demonstration, about remote sensing analysis of architectural interiors: a study of St. Barnabas Cathedral at the 2nd Global Heritage Showcase and Exhibition 2019 held at Nottingham Trent University, Nottingham. (July 2019)
Yu Li gave an oral presentation about long-range remote spectroscopy for wall paintings and architectural interiors at Optics for Arts, Architecture, and Archaeology VII, SPIE Optical Metrology, in Munich, Germany. (June 2019)
Yu Li gave an oral presentation about long range remote Raman spectroscopy for wall paintings at “A closer look at Murals. Recent advances in the conservation and scientific investigation of Wall Paintings” Symposium held at the British Museum, London. (May 2019)
Yu Li gave an oral presentation about long range remote Raman spectroscopy for wall paintings at the School of Science and Technology Annual Research Conference 2019 at Nottingham Trent University, Nottingham. (May 2019)
Haida Liang gave an oral presentation about long range remote Raman spectroscopy for cultural heritage at the TECHNART 2019: the European conference on the use of Analytical methods for Characterization of Works of Art in Bruges, Belgium. (May 2019)
Yu Li gave an oral presentation about a study of St. Barnabas Cathedral for remote sensing analysis of architectural interiors at the Science and Heritage Interdisciplinary Research Workshop held at Nottingham Trent University, Nottingham. (March 2019)
Yu Li presented a poster and gave a special oral presentation about a remote Raman system at standoff distances for wall paintings at the 12th conference on Lasers in the Conservation of Artworks (LACONA 12) in Paris, France. (September 2018)
Yu Li presented a poster about a remote Raman system at standoff distances for wall paintings at the Global Heritage Research Theme Showcase Event held at Nottingham Trent University, Nottingham. (18 May 2018)
A preliminary investigation of a set of lace, pottery and alabaster samples at the Nottingham Castle Museum and Art Gallery was conducted in November 2017 identifying the dyes and pigments applied on these samples by our in-house developed mobile Raman spectroscopy system.
Yu Li, Chi Shing Cheung, Sotiria Kogou, Alex Hogg, Haida Liang, and Stig Evans. 2021. Standoff laser spectroscopy for wall paintings, monuments and architectural interiors. In Transcending Boundaries: Integrated Approaches to Conservation. ICOM-CC 19th Triennial Conference Preprints, Beijing, 17–21 May 2021, ed. J. Bridgland. Paris: International Council of Museums. (Accepted)
Haida Liang (2020). Chapter 11. A systematic multi-modal non-invasive investigation of wall paintings at the UNESCO site of Mogao caves in China. In Sambit Datta (Ed.). Architectural Heritage in Asia: Computational Perspectives. Abingdon, UK: Routledge. (to appear in)
Professor Haida Liang (Nottingham Trent University)
Dr Quentin Hanley (Nottingham Trent University)
Dr Golnaz Shahtahmassebi (Nottingham Trent University)
Yu Li (Nottingham Trent University)