Precision of multiplex CARS temperature measurements

It is pointed out that coherent anti-Stokes Raman scattering (CARS) is gaining acceptance as the most promising tool for the diagnostics of reactive media. It is capable of performing instantaneous and spatially resolved temperature and concentration measurements in combusting flows as well as in low density plasmas. An important question which remains is related to the accuracy of the CARS measurement. In the present investigation, the accuracy of multiplex CARS temperature measurements is studied theoretically and experimentally. Various causes for uncertainty are analyzed and their contribution is evaluated. Some causes, such as the Poisson noise, are nearly irreducible, and, thus, constitute a fundamental limitation. However, the residual uncertainty attributable to Poisson noise is quite small (5-10 K) in practical situations. The major cause of uncertainty remains the dye laser spectral noise. Approaches for reducing this error are considered.