Short wave infrared OCT
spectral domain OCT
Fourier Domain OCT
Spectral radar OCT

OCT enables the fast, non-invasive volumetric measurements of the surface and sub-surface structure at a resolution of microns, for objects which are moderately absorbing in the IR. The technique relies on interferometry, with a singular depth profile (A-scan) being reconstructed from the measured spectrum. By scanning the illumination spot across the object, a 3D or 2D virtual cross section of the object's stratigraphy can be collected over a small region. In OCT virtual cross sections, contrast is provided by variations in the material refractive index with bright regions corresponding to boundaries (interfaces) between structures and layers or from scattering sites. 2D OCT virtual cross-sections (B-Scans) are usually presented as convenient cross-sectional views, similar to microscopic images of sample cross-sections extracted from the object. 3D information of an entire volume (a cube) may be also collected by combining a sequence of 100 to 1000 B-Scan cross-sections across the surface. ​ This OCT is optimised to provide a larger penetration depth in materials than OCTs at shorter wavelength making it more suitable to the investigation of more scattering materials like paints and enamels. Systematic studies on the spectral transparency of historic artists' paint found that the most transparent spectral window to image pigmented layers is around 2200nm.

Optical coherence tomography (oct)

Analysis Method

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