I'm currently analyzing the Raman spectra of coloured plastic samples and have encountered a wavy, oscillating pattern in the spectra of some coloured samples. I was wondering what the possible reasons behind it. I'm curious to know if the fluorescence effect could be causing this pattern.
If your film has a well-defined thickness, you can get an interference pattern whose periodicity is determined by the refractive index and that thickness. This seems to be the case here.
Jürgen Weippert Thanks a lot for your response. I saw this pattern in other shapes of samples like fragments and fibres. The image I shared was of a cloth fibre made of polystyrene. As I noticed this pattern in coloured samples, but not in non-coloured ones. So I thought it might be related to the effect of the colourant used in our sample but I am not sure what is the reason behind it.
I haven't done this in a while, but I believe to recall the analysis procedure was as follows:
Plot the spectrum as a function of the absolute frequency instead of the relative Raman shift. Determine the frequency periodicity of what you have there. Recalculate this frequency to the associated wavelength and divide the result by the material's refractive index. That should yield a quantity equal to one of the material's spatial dimensions, so a film thickness or maybe a fiber diameter.
Hopefully I haven't messed up the order of steps here, but that's how I recall it.
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