LASER FLUORESCENCE TECHNIQUE TO MEASURE MULTIPLE PARAMETERS IN HYPERSONIC FLOWS

A NEW PLANAR LASER INDUCED FLUORESCENCE TECHNIQUE WHICH WILL PROVIDE THE FLOW VELOCITY AND THE CONCENTRATION OF VARIOUS SPECIES AT MANY POINTS ON A PLANE OF A HYPERSONIC FLOW (WITH AND WITHOUT CHEMISTRY) IS PRESENTED. THE TECHNIQUE HAS THE POTENTIAL OF MEASURING TEMPERATURE AS WELL. UNLIKE OTHER TECHNIQUES, THE PROPOSED APPROACH WILL MAKE USE OF BREADBOARD PULSED LASERS. IN THE PROPOSED METHOD, THE ABSORPTION LINE OF A SELECTED SPECIES IS EXCITED WITH A VARIABLE BANDWIDTH TUNABLE EXCIMER LASER. THE FLUORESCENCE IS PROPORTIONAL TO THE STRENGTH OF THE ABSORPTION LINE AND ITS POSITION WITHIN THE LASER LINE. THE FLOW VELOCITY CAUSES THE ABSORPTION LINE TO BE DOPPLER SHIFTED WITH THE LASER LINE RESULTING IN A CHANGE IN THE FLUORESCENT SIGNAL. SPECIES CONCENTRATION CAN BE DIRECTLY MEASURED FROM THE INTENSITY OF THE SIGNAL. TEMPERATURE MEASUREMENTS WOULD REQUIRE A SECOND LASER SHEET WITH A SHIFTED FREQUENCY. THE PROPOSED METHOD RESOLVES THE NARROWBAND REQUIREMENT NORMALLY ASSOCIATED WITH FLUORESCENCE SPECTROSCOPY AND WILL MAKE USE OF BROADBAND LASERS WHICH ARE READILY AVAILABLE. THIS METHOD HAS THE POTENTIAL OF LEADING TO INSTRUMENTS THAT WILL EXPAND CURRENT SPECTROSCOPIC CAPABILITIES AND WILL HAVE A WIDER COMMERCIAL ACCEPTANCE.