Optical Coherence Tomography (OCT)
OCT provides 2D and 3D virtual cross-sectional images of an object in a non-invasive and non-contact way. It is suitable for the investigation of translucent and transparent materials (e.g. varnishes, glass, glazes). OCT is also used in a medical context, in Optician settings to create a detailed 3D image and assessment of eye health- thus proving the technique's safety and applicability to delicate and vulnerable structures!
ISAAC is equipped with a range of OCTs, the majority of which are developed in our Lab. These range in central wavelengths from the near- to the mid- infrared, offering a range of specifications from ultra-high resolution (~1 microns) to deep penetration into highly scattering materials. We also have a bespoke hybrid system which combines OCT and VIS/NIR Hyperspectral Imaging. Detailed specifications are given in the tables below.
Ultra High Resolution-OCT examining an easel painting from the National Gallery's collection
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Mounting of the probe head is flexible and various adaptations are possible. The speed of acquisition ranges from a few seconds to a few minutes for an image cube of a 1cm x 1cm area.
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A sampled section of the above National Gallery painting: Top: virtual OCT cross-section Bottom: paint cross section sample under Visible Light Microscopy
Applications OF OCT
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high resolution and high contrast imaging of underdrawings
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detection of delamination of internal layers, e.g. enamel
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monitoring of varnish removal
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monitoring of glass deterioration
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non-contact examination of subsurface microstructure of intact objects
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measuring the hydraulic conductivity of porous materials such as rock art panels
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study of the manufacturing techniques of ancient artefacts etc.
ISAAC instrumentation
OCT System
Ultra-High Resolution OCT @810 nm
Telesto 2
@1310 nm
SWIR (Long Wavelength) OCT
@1960 nm
MWIR (Long Wavelength) OCT @3600 nm
Developer
ISAAC Lab
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Thorlabs
ISAAC Lab
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ISAAC Lab
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Depth Penetration
Moderate
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Moderate Deep
Deep
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Deep
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Depth Resolution (Air/Polymer)
1.8 µm / 1.2 µm
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5.5 µm / 3.7 µm
9 µm / 6 µm
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9 µm / 6 µm
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Transverse Resolution
7 µm
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15 µm – 20 µm
17 µm
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27 µm
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Working
Distance
64 mm
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10 mm
40 mm
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70 mm
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Service
MOLAB/
FIXLAB
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MOLAB/
FIXLAB
MOLAB/
FIXLAB
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FIXLAB
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Our in-house developed Hybrid OCT system combines an optical coherence tomography (OCT) system and a reflectance spectral imaging system into one instrument. OCT provides 2D and 3D virtual cross-sectional images in a non-invasive and non-contact way. VIS-NIR Spectral Imaging can provide identification of materials. The simultaneous use of the two analysis methods allows for a 1:1 spatial alignment between the spectral images and OCT 3D volumetric data sets, providing additional context on the layer structure.
ISAAC Hybrid OCT System:
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Developer
OCT Depth Resolution (air/polymer)
OCT Transverse Resolution
Working Distance
Spectral Imaging Spectral Range
Spectral Imaging Spectral Resolution
Spectral Imaging Transverse Resolution
Hybrid OCT @ 1350 nm​ &
VIS/NIR Microscopic Spectral Imaging
ISAAC Lab
5 µm / 3.3 µm
10 µm
40 mm
415 nm – 845 nm
10 nm
5 µm
example Heritage science Projects
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selected Publications
​This is a selection of our OCT publications. Our full publication list can be found here.
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Faluweki, M.K., Cheung, C.S., & Liang, H. 2023. Simultaneous Measurement of Refractive Index and Dispersion using Optical Coherence Tomography for Restoration of Transparent Works of Art. The European Physics Journal Plus, 138, 825. https://doi.org/10.1140/epjp/s13360-023-04458-4
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Read, M., Cheung, C.S., Liang, H., Meek, A. and Korenberg, C. 2021. A Non-Invasive Investigation of Egyptian Faience Using Long Wavelength Optical Coherence Tomography (OCT) at 2µm. Studies in Conservation 67, 168-175. https://doi.org/10.1080/00393630.2020.1871208
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Leona, M., Fukunaga, K., Liang, H., Baglioni, P., Festa, G. And Levchenko, V. 2021. From Physics to Art and Back. Nature Revews Physics 3, 681–684. https://doi.org/10.1038/S42254-021-00362-X
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Read, M., Cheung, C.S., Ling, D., Korenberg, C., Meek, A., Kogou, S. and Liang, H., 2019. A Non-Invasive Investigation of Limoges Enamels using both Optical Coherence Tomography (OCT) and Spectral Imaging: A Pilot Study. In: H. Liang and R. Groves, eds., Optics for Arts, Architecture, and Archaeology Vii. SPIE Optical Metrology, Munich, Germany, 24-27 June 2019. SPIE Proceedings 11058, 1105803 https://doi.org/10.1117/12.2527092​​
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Thickett, D., Cheung, C.S., Liang, H., Twydle, J., Maev, R.G. and Gavrilov, D., 2017. Using Non-Invasive Non-Destructive Techniques to Monitor Cultural Heritage Objects. Insight - Non-Destructive Testing and Condition Monitoring, 59 (5), pp. 230-234. http://doi.org/10.1784/insi.2017.59.5.230
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Liang, H., Mari, M., Cheung, C.S., Kogou, S., Johnson, P. and Filippidis, G., 2017. Optical Coherence Tomography and Non-Linear Microscopy for Paintings – A Study of the Complementary Capabilities and Laser Degradation Effects. Optics Express, 25 (16), pp. 19640-19653. https://doi.org/10.1364/OE.25.019640
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Cheung, C.S., Spring, M. and Liang, H., 2015. Ultra-High Resolution Fourier Domain Optical Coherence Tomography for Old Master Paintings. Optics Express, 23 (8), pp. 10145-10157. https://doi.org/10.1364/OE.23.010145
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Cheung, C.S., Daniel, J.M.O., Tokurakawa, M., Clarkson, W.A. and Liang, H., 2015. High-Resolution Fourier Domain Optical Coherence Tomography in the 2 mm Wavelength Range using a Broadband Supercontinuum Source. Optics Express, 23 (3), pp. 1992-2001. https://doi.org/10.1364/OE.23.001992
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Cheung, C.S., Tokurakawa, M., Daniel, J., Clarkson, W.A. and Liang, H., 2013. Long Wavelength Optical Coherence Tomography for Painted Objects. Proceedings of SPIE, 8790, 87900j https://doi.org/10.1117/12.2021700
Bemand, E. and Liang, H., 2013. Optical Coherence Tomography for Vulnerability Assessment of Sandstone. Applied Optics, 52 (14), pp. 3387-3393. https://doi.org/10.1364/AO.52.003387
Liang, H., Lange, R., Peric, B. and Spring, M., 2013. Optimum Spectral Window for Imaging of Art with Optical Coherence Tomography. Applied Physics B: Lasers and Optics, 111 (4), pp. 589-602. https://doi.org/10.1007/s00340-013-5378-5
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Bemand, E., Bencsik, M. and Liang, H., 2011. OCT and NMR for Non-Invasive In-Situ Monitoring of the Vulnerability of Rock Art Monuments. Proceedings of SPIE, 8084, 80840h https://doi.org/10.1117/12.890084​​​