Pulse Sequenced CARS: Background Suppression and Nonlinear Interferences
Coherent Anti-Stokes Raman Scattering (CARS) is a convenient spectroscopic tool for studies of solutions and mixtures in either solid, liquid or gas phase. Unfortunately, the CARS process generates a background signal even when the lasers are tuned off resonance due to the non-linear response of the electrons to the applied field (the electronic Kerr effect). The background interferes with the resonant signal, since they are both coherently generated, to produce a distorted line shape. In the case of a weak Raman mode or in dilute mixtures the non-resonant background signal can be easily comparable to or larger than the resonant contribution of interest, at best producing a distorted bandshape through interference and at worst completely covering the resonance. This severely limits the usefulness of CARS in these situations.
KeywordsDriving Frequency Resonant Signal Nonlinear Interference Rotational Reorientation Vibrational Raman Mode
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