Deformation monitoring on ancient terracotta warriors by microscopic TV-holography

In order to investigate deterioration processes on the famous 2000-yr-old Chinese Terracotta warriors, deformation measurements were performed with TV-holography. The aim of the investigations is to estimate the suitability of several conservation agents and procedures, which are developed to preserve the extremely endangered paint layers of the figures. Due to the occurrence of small-scale deformation areas the field of view had to be reduced. A microscopic system was constructed and typical object deformations due to shrinkage and swelling are presented. To investigate the individual layers of the multilayered objects a shortcoherent superluminescence diode instead of a laser diode is used in a further modification. By changing the path length of one of the interfering beams it is possible to select a region limited in depth where deformations are measured even if it is located below the surface. Results on an artificial test object and on original terracotta fragments demonstrate the capabilities of this new short-coherence TV-holography system.