Ultra-high resolution Fourier domain optical coherence tomography for old master paintings

Area of Science:

• Art Conservation Science
• Optical Imaging
• Non-invasive Analysis

Background:

• Optical Coherence Tomography (OCT) is increasingly used in art conservation, history, and archaeology.
• Current commercial OCT systems have limitations in depth resolution ( > 4 μm) for analyzing paint and varnish layers.
• Conventional microscopic examination of sampled cross-sections offers higher resolution (~1 μm) but is micro-destructive.

Purpose of the Study:

• To develop an ultra-high resolution fiber-based Fourier domain optical coherence tomography system.
• To achieve a constant axial resolution of 1.2 μm in paint and varnish.
• To enhance non-invasive subsurface imaging capabilities for art conservation applications.

Main Methods:

• Development of a fiber-based Fourier domain optical coherence tomography system.
• Characterization of axial resolution (1.2 μm) and sensitivity roll-off (< 2 dB over 1.2 mm depth).
• Imaging of thin varnish and glaze layers on intact objects.

Main Results:

• The developed OCT system achieved a constant axial resolution of 1.2 μm in varnish/paint over a 1.5 mm depth range.
• The system demonstrated minimal sensitivity roll-off (< 2 dB over 1.2 mm) with low incident power (~1 mW).
• Non-invasive 'virtual' cross-section images showed thin varnish layers with high clarity, comparable to micro-destructive methods.

Conclusions:

• The ultra-high resolution OCT system provides unprecedented contrast and clarity for imaging thin layers in art conservation.
• This non-invasive technology offers a valuable alternative to micro-destructive techniques for subsurface analysis of cultural heritage objects.
• The system's high resolution and sensitivity enable detailed examination of varnish and glaze layers.