A Comparative Analysis of the Analytical Capabilities of Coherent Anti-Stokes Raman Spectroscopy (CARS) Relative to Raman Scattering and Absorption Spectroscopy

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Abstract
The performance capabilities of coherent anti-stokes Raman spectroscopy (CARS) relative to incoherent Raman scattering and absorption spectroscopy are considered for gases. Four gases are considered for model calculations: hydrogen, nitrogen, oxygen, and carbon monoxide. The signal/noise ratio is estimated for these molecules under a number of assumed experimental conditions. The signal/noise ratios for CARS and Raman scattering scale quite differently with partial pressure and temperature. CARS offers distinct advantages when detecting a major component of a gas mixture at total pressures of considerably less than 1 atm pressure. Raman scattering offers 1 to 2 orders of magnitude greater sensitivity for a signal/noise ratio of unity when detecting a minor component of a gaseous mixture at 1 atm total pressure. These model calculations should be of use when a specific experimental method is to be chosen for spectroscopic examination.