Advanced Raman Techniques and Combinations
Does the excitation wavelength influence the measurement?
The wavelength has a strong effect on the measurement outcome and the obtainable information. It influences:
- The Raman signal: The Raman scattering intensity is proportional to ν 4, where ν is the frequency of the excitation laser radiation, i.e. lower excitation wavelength lead to higher Raman signals.
- The fluorescence signal: Many samples show strong fluorescence when excited in the UV or blue region and low fluorescence when excited in the red or NIR region of the spectrum. The fluorescence signal is comparatively strong and could obscure the weaker Raman signal.
- The spatial resolution: The shorter the excitation wavelength, the higher the spatial resolution. Caution: For the spatial resolution, the NA of the objective should also be considered.
- The sample damage: For short wavelengths the high photon energy may cause sample damage at a lower laser power than for longer wavelengths.