A system has been developed to investigate documents that are suspected of having been altered, forged, or erased. The system is based on the fact that each ink and paper has characteristic luminescence properties. Lasers are used to excite luminescence from the document, and the luminescence, along with its spectral distribution, is detected by a set of scanning mirrors that efficiently couple the light to a wavelength selector (monochromator) and photodiodes. Compared to previous systems, this system offers major improvements in sensitivity, versatility, and convenience of operation. These refine-ments are achieved by exploiting the capabilities of the lasers and of digital data processing/acquisition.