Tunable laser absorption measurements in high-temperature gases

A systematic investigation was conducted of line-of-sight absorption measurements of high temperature gases using tunable lasers. Techniques were developed for experimental data acquisition and reduction, for selection of absorption transitions, and for the determination of spectral parameters. The techniques were demonstrated for tunable diode laser measurements of CO;A mathematical model was derived for experimental data analysis. An algorithm was developed to calculate the model using the fast Fourier transform. Reliable programs were developed to fit the experimental data to the mathematical model. Overlapping lines could be handled by the fitting programs. Procedures were established to retrieve temperature and concentrations from the model parameters. The uncertainties in temperature and concentrations deduced from a given absorption measurement can be minimized by using the techniques developed in this work.;The error sources in line-of-sight measurements were investigated to help select optimum spectral lines for absorption measurements. An Energy-Temperature curve was proposed for each species to assist the selection. Selection criteria were developed, which may be integrated into an expert system for the choice of optimum lines for high temperature diagnostics.;The integrated intensities and line widths of spectral lines of the absorbing species must be known for absorption diagnostics. Techniques for determining integrated intensities and line widths from absorption measurements were reviewed and new methods were proposed to retrieve these data for overlapping lines and for unidentified lines.;The techniques developed in this work may be extended to absorption modulation detection methods and to three-dimensional absorption measurements. They may also be used in other spectroscopic diagnostic techniques.