IPERION HSIntegrating Platforms for the European Research Infrastructure ON Heritage Science
Technique: Optical Coherence Tomography (1960 nm)

OCT (1960 nm)

The 1960nm Fourier domain OCT consists of a supercontinuum laser source, a fibre based Michelson Interferometer and a spectrometer with a 2D sterling cooled InSb detector. The OCT probe has a typical working distance of 4cm from the surface of an object. The axial or depth resolution, that is the resolution in the direction normal to the object surface, is 6 microns (in paint) or 9 microns (in air). Depending on the objective lens, the typical resolution in the plane of the surface of an object is 17 microns and the field of view is 7 mm x 7mm. It can collect an image cube consisting of 500 x 500 depth profiles in ~2 minutes using rapid scanning XY galvo-mirrors. The typical laser intensity at the object surface is 1-2 mW. The small OCT probe can be mounted on a motorised XYZ translation stage to take adjacent image cubes to mosaic a larger area.

Potential Results

The major advantages of OCT are the ability to see the layers and microstructures below the object surface in a non-contact and non-invasive manner (intensity of light used for examination is in the order of a few milliwatts), rapid data collection with online display of images with no need for object preparation. Given the non-invasive nature of the technique, the number of measurements across the entire surface can be unlimited, making it possible to have a representative view of the whole object. The penetration depth in OCT imaging is often limited by the opacity of the material rather than the instrumental limits. The long wavelength Fourier domain OCT operating at central wavelength of 1960nm provides a larger penetration depth in materials than OCTs at shorter wavelength. Systematic studies on the spectral transparency of historic artists' paint found that the most transparent spectral window to image pigmented layers is around 2200nm.