DEVELOPMENT OF CONCENTRATION MODULATED ABSORPTION AS A COMBUSTION DIAGNOSTIC

USING CONCENTRATION MODULATED SPECTROSCOPY, THIS STUDY WILL EXTEND WORK IN LASER TECHNIQUES FOR POINT MEASUREMENTS IN COMPLEX COMBUSTION SYSTEMS TO HIGH SENSITIVITY MEASUREMENT OF CONCENTRATIONS OF A WIDE VARIETY OF MOLECULAR SPECIES. THIS TECHNIQUE, WHICH USES A SINGLE LASER TO BOTH PERTURB MOLECULAR LEVEL POPULATIONS AND DETECT THIS PERTURBATION, HAS SEVERAL FEATURES THAT MAKE IT ATTRACTIVE FOR THE QUANTITATIVE DETECTION OF TRANSIENT SPECIES IN COMBUSTION AND OTHER REACTIVE SYSTEMS. AMONG ITS MOST ATTRACTIVE FEATURES IS ITS ABILITY TO MEASURE AN ABSOLUTE SPECIES CONCENTRATION, WITHOUT A PRIOR KNOWLEDGE OF THE MOLECULAR ABSORPTION COEFFICIENT, UNDER THE CONDITION THAT AN INDEPENDENT MEASUREMENT OF DIRECT TRANSMISSION PROVIDES A SECOND EQUATION BY WHICH THE UNKNOWN ABSORPTION CROSS-SECTION MAY BE ELIMINATED, IN THE ONE APPLICATION TO A COMBUSTION SYSTEM SO FAR ATTEMPTED, THE TECHNIQUE'S SENSITIVITY HAS BEEN EQUAL TO SUCH METHODS AS LASER INDUCED FLUORESCENCE, WITHOUT ITS DIFFICULTIES IN QUANTIFICATION. SINCE THE EFFECT IS GENERATED ONLY IN THE SMALL VOLUME DEFINED BY THE FOCUSING OF PUMP AND PROBE LASER BEAMS, THE TECHNIQUE PROVIDES BOTH A POINT MEASUREMENT CAPABILITY AND THE ACCESSIBILITY ASSOCIATED WITH ALMOST COLLINEAR LASER BEAMS.