Simplified Calibration of Instrument Response Function for Raman Spectrometers Based on Luminescent Intensity Standards

Published Raman spectra are rarely corrected for variations in spectrometer sensitivity across the Raman spectrum, which leads to often severe distortion of relative peak intensities that impede calibration transfer and library searching. A method was developed that uses the known luminescence of standards which fluoresce in response to laser irradiation. Since the standards are observed with the same sampling geometry as the Raman sample of interest, their spectra are subject to the same instrumental response function. After one-time calibration of the standards' fluorescence output against a known tungsten source, the unknown Raman spectrum may be corrected for instrumental response by a simple formula. In practice, the user need only run the standard under the same conditions as the Raman sample, then apply a short GRAMS algorithm. The approach is demonstrated for coumarin 540a and Kopp 2412 glass standards, with 514.5- and 785-nm laser light, respectively. Once the corrected spectrum is in hand, the absolute Raman cross section of a given Raman feature may be determined by comparison to known scatterers such as benzene.