Recently we see an increasing number of applications in Raman spectroscopy.
Thermoelectrically cooled CCD array detectors and techniques like
surface enhanced resonance Raman spectroscopy (SERRS) enable an increase
in sensitivity sufficient for applications in forensics [1]. In Raman
spectroscopy the analyte is excited with monochromatic laser-light. The
scattered light (rayleigh scattering) contains the excitation wavelength,
which can be removed by holographic filters, and signals at longer (Stokes
shift) and shorter wavelength (anti stokes shift). Usually the Stokes signals
are more intensive and therefore monitored as the Raman spectrum.
Position and intensity of Raman signals depend on the maximum absorption
wavelength of the analyte. Therefore appropriate excitation wavelengths
are needed. Fluorescence of the analyte or the substrate may cover
the Raman signals, which can be avoided by blocking the fluorescence.
In document examination we are mainly interested in inks and dyes
therein. We are confronted with a great variety of dyes of different hues,
which means they have different absorption maxima. The dyes belong to different
chemical classes such as inorganic and organic pigments, acid and basic
dyes, substantive and reactive dyes, triphenylmethane dyes, azo dyes
etc.