Knowledge Bank

Coherent anti-Stokes Raman Spectroscopy (CARS) has been shown to be a useful technique for obtaining Raman spectra with very high signal to noise ratios. The high conversion efficiency of the four photon CARS process combined with the production of a signal in the form of a collimated beam gives CARS a signal to noise advantage over spontaneous Raman experiments of the order of 10$\mathrm{<mrow\; data-mjx-texclass="ORD">8</mrow>}$. Discrimination against fluorescence is very efficient since both spatial filtering and frequency filtering can be used. The CARS experiment will be reviewed with emphasis on the verification of elementary efficiency formulae. The CARS theory will also be reviewed with emphasis on the new selection rules of this four photon process and the larger number of polarization ratio experiments. Recent experiments illustrating resonance enhancement will be discussed.