What is fluorescence and how does it affect Raman spectroscopy?

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. In the context of Raman spectroscopy, it occurs when the sample absorbs the laser light and then re-emits it as broad-spectrum visible light. Fluorescence is often much stronger than the weak Raman signal and can completely obscure Raman peaks, making the spectrum difficult or impossible to interpret. Fluorescence contributes to a high background in the spectrum, which reduces the signal-to-noise ratio and can mask small or weak Raman features.