Analysis of Darkly Colored Samples by FT-Raman Spectroscopy
Samples that are darkly colored or black have traditionally been very difficult to study by Raman spectroscopy because the sample can absorb the excitation laser beam, causing thermal emission or decomposition of the sample. This thermal emission appears as a broadband, featureless background superimposed over the range of the Raman spectrum, and usually precludes the observation of any useful vibrational information. Samples that are black in the visible region of the spectrum are often “black” in the near infrared (NIR) as well. Thus, these types of samples are also problematic for Fourier transform (FT)-Raman using NIR excitation (typically from a Nd: YAG laser at 1.064 μm).