Nonresonant background suppression in CARS spectra of dispersive media using phase mismatching.
A nonresonant background suppression technique using coherent cancellation through phase mismatching is discussed and applied for a noncollinear beam configuration. A cuvette structure consisting of a glass, a sample, and a glass layer is regarded. Phase mismatching is shown to be a useful method to suppress nonresonant contributions from cuvette glass walls as well as those originating from the sample. A numerical calculation reveals a limit for the background suppression which can be achieved with this technique. Measurements using ethanol as a sample show the possibility to compensate the nonresonant background originating from the cuvette walls and to effectively suppress the nonresonant contribution in the spectrum of the sample by a factor of 10-50, yielding Lorentzian bands biased by a constant background. Direct measurement of depolarization ratios without interfering nonresonant background is demonstrated for ethanol and shows that this technique can readily be combined with the polarization sensitive CARS technique.
Scholten
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TA
Lucassen
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GW
De Mul
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FF
Greve
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J