Compact Raman spectrometers: Data handling methods

Measurements have been made on a compact dispersive Raman spectrometer of the type often proposed for on-line measurements. Quantitative use of the details of spectra that are produced by this system require different data treatments than those which have been described for longer-focal-length instruments. The data sets are sparsely sampled, and they cover a wide spectral window. Owing to sparse sampling, spectra as recorded have the appearance of piecewise linear approximations. It is necessary to interpolate additional data points in order to observe details of peaks, such as exact positions of maxima. With wider spectral windows, procedures for calibration of the wavenumber axis which have been previously described do not meet our performance criterion: an accuracy of 0.1 cm(-1) or better. A model that involves a fifth-order polynomial is needed. On the basis of the performance of this model, atomic lines which give satisfactory results when used as wavenumber references have been identified. Details of a self-modeling procedure for removal of broad-band spectral interferences are described, and its performance is demonstrated.