Forensic Application of Raman Spectroscopy to the Analysis of Intersecting Lines in Questioned Documents

Forensic document examiners in the Department of Justice have identified specific needs in the analysis of intersecting lines with respect to sequence and dating of lines in questioned documents such as forgeries and alterations. Raman spectroscopy has great potential in forensics, in part because it is nondestructive to evidence. Raman has recently shown promise in successfully identifying and differentiating several different types of inks. There is, however, a shortfall in the ability to time-sequence marks, and to identify specific inks and pigments, especially in the case of intersecting lines. To date, this has received little attention. One major problem is the fluorescence of paper fibers and inks which masks valuable spectral information that identifies the inks. Diffusion of inks across different layers of paper and other inks is another problem that could make time-sequencing lines very difficult. The goal of this project is to overcome the problem of fluorescence and to determine a method that successfully sequences intersecting lines. Raman spectroscopy will be used in various modes such as changing wavelengths of the lasers, scanning at different depths in the sample, and employing surface-enhanced Raman scattering. The hypothesis is that Raman is capable of differentiating and identifying different inks under these circumstances, using a reference library of inks and a computational spectral subtraction technique