Application and development of advanced laser diagnostics for flame measurements

The application of hydrogen coherent anti-Stokes Raman scattering (CARS) for temperature measurements in low-pressure diamond-forming flames and the development of new polarization spectroscopy (PS) diagnostic techniques are the subjects of this Ph.D. dissertation research. The objectives of the low-pressure diamond-forming flame experiments were to measure detailed temperature profiles for comparison with a numerical flame model and to investigate the presence and magnitude of the temperature jump at the deposition substrate surface. Temperature jumps of approximately 100 K were observed in these rich, premixed oxy-acetylene flames ranging from 30 Torr to 125 Torr. The presence of this discontinuity in diamond-forming flames may have a significant effect on surface chemical model development. In these low-pressure flames, the ability to resolve fully the near-substrate temperature profiles will be extremely useful for the validation and improvement of surface chemistry models.; The use of PS in the mid-infrared using a single-mode optical parametric generator (OPG) for the detection of CO₂ has been demonstrated. Numerical modeling of the CO₂ PS signal generation process has also been performed for comparison with the experimental PS signals. The experimental PS line shapes agree very well with the numerical calculations. These results are promising for using PS in detecting hydrocarbon molecules as hydrocarbon molecules have strong absorption resonances in the infrared region of the spectrum.; The objectives of the theoretical work on short-pulse PS were to obtain fundamental insight into the physics of the short-pulse PS signal generation process and to investigate the diagnostic potential of the short-pulse PS for species concentration measurements. Short-pulse laser significantly decreases the collision-rate dependence of the PS signal compared with the long-laser pulse-length regime. For a saturating pump beam, the short-pulse PS signal was found to be nearly independent of collision rate. This insensitivity of the short-pulse PS signal to the collision rate in the medium enhances greatly the potential for quantitative application of the technique for concentration measurements in reacting flows. The underlying physics of the short-pulse PS is explored in detail by studying the effects of collision rate, Doppler broadening and the pump laser intensity on the PS signal generation processes.