Reconstruction of Obliterated Characters in Polycarbonate through Spectral Imaging

In forensic sciences, there is an increasing demand for nondestructive and reliable methods to retrieve obliterated information in polymers. This study demonstrates a case study for the potential of Raman spectroscopy to reconstruct abraded serial numbers. Residual strain and local variations in the structural arrangement are nondestructively imaged through peak shifts and variations of the full width at half-maximum of specific Raman lines, respectively. We qualitatively validate our approach by successfully recovering an obliterated letter stamped with a pressure of ∼170 MPa in a polycarbonate sample, with a subsequent quantitative statistical analysis. The detection threshold is estimated from the propagation depth of plastic deformations to a value of ∼750-800 μm, substantially larger than typical obliteration depths, 200 μm in our case for an initial profile depth of 120 μm.