The fundamental principle of CARS involves the interaction of a pump and a Stokes beam with the sample. When these two beams, of different frequencies, coincide within a specimen, they excite molecular vibrations. A third beam, called the probe beam, then interacts with these vibrations, producing an anti-Stokes signal. This signal is detected and used to create an image. The coherence of the process results in a significantly stronger signal compared to spontaneous Raman scattering, making CARS particularly useful for imaging at the nanoscale.
