ORCID Profile
0000-0003-1722-7626
Current Organisation
Nottingham Trent University
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Publisher: Elsevier BV
Date: 09-2020
Publisher: Springer Science and Business Media LLC
Date: 15-08-2015
Publisher: The Optical Society
Date: 14-10-2019
DOI: 10.1364/OE.27.031338
Publisher: Springer Science and Business Media LLC
Date: 10-2022
DOI: 10.1140/EPJP/S13360-022-03305-2
Abstract: A mobile remote standoff Raman spectroscopy system operational at typical distances of 10 m was developed specifically for research of historical sites and wall paintings recently. Here we present an upgrade to that system informed by a thorough experimental investigation of the relevant laser-induced degradation issues. Reflectance spectroscopy as a more sensitive technique than Raman spectroscopy was used for monitoring and a new phenomenon of reversible alterations was detected in many paint s les at very low laser intensities of less than 1 W/cm 2 when Raman measurements detected no changes. Contrary to conventional wisdom, the intensity threshold for safe operation was found to decrease significantly for larger incident irradiation area in the case of a vermilion oil paint s le. Damage threshold in intensity for each material needs to be determined for different spot sizes, which can be orders of magnitude lower for 1 mm spot size compared with micro-Raman. Results from this study is also relevant to portable Raman systems which use similarly large spot sizes. However, the larger spot size still generates more Raman photons overall under safe operation than micro-Raman systems. Continuous-wave (CW) lasers are found to be best suited to efficient, that is more Raman signal detected over a given measurement time, and safe Raman operation than ns-pulse lasers at the same wavelength. While the damage threshold in intensity for ns-pulse lasers is much higher than that of CW lasers, the pulse energy allowed in one pulse for safe operation is still too low to allow detection of Raman signal, and the need for multiple pulses makes pulse laser inefficient owing to the low repetition rate necessary to ensure adequate heat dissipation between pulses. The safety of the upgraded system was evaluated and found that no permanent laser-induced degradation was detected within 60 s of laser irradiation for any of the paint s les.
Publisher: Springer Science and Business Media LLC
Date: 02-09-2016
Publisher: Wiley
Date: 09-08-2021
DOI: 10.1002/XRS.3188
Abstract: Self‐organising map (SOM), an unsupervised machine learning algorithm based on neural networks, is applied to introduce a novel approach for the analysis of XRF spectral imaging data. This method automatically reduced hundreds of thousands of XRF spectra in a spectral image dataset to a handful of distinct clusters that share similar spectra. In this study, we show how clustering and the combination of spatial and spectral information can be used to aid materials identification and deduce the paint sequence. The efficiency and accuracy of the method is presented through the analysis of a Peruvian watercolour painting from the Getty Research Institute collection. Confirmation of the interpretation was provided by complementary non‐invasive techniques, such as optical microscopy, reflectance and Raman spectroscopies.
Publisher: Springer Science and Business Media LLC
Date: 16-03-2018
Publisher: The Optical Society
Date: 04-08-2017
DOI: 10.1364/OE.25.019640
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Sotiria Kogou.