On the one hand, the oscillation of the permanent dipole moment can be detected by means of infrared radiation. A glowing bar (“Globar”), a quantum cascade laser, or a synchrotron may act as a light source in the infrared. On the other hand, the oscillatory change in the induced dipole moment, i.e. polarizability, is monitored by means of the Raman effect. Many variants of the Raman effect, such as stimulated Raman scattering (SRS), coherent anti-Stokes Raman scattering (CARS), or surface-enhanced Raman scattering (SERS) have been researched in order to enhance signal, lower detection limit, target specific changes, and shorten measurement times.