AN INFRARED OPTOACOUSTIC SPECTROMETER WITH WIDE APPLICABILITY FOR MEASUREMENT OF TRACE GAS CONCENTRATIONS

EXISTING INSTRUMENTATION FOR CHEMICAL ANALYSIS OF GAS MIXTURES DO NOT PROVIDE THE CAPABILITY FOR REAL-TIME MEASUREMENT OF A BROAD RANGE OF SPECIES AT TRACE (PPB) CONCENTRATION LEVELS. SUCH A CAPABILITY IS IMPORTANT IN MANY APPLICATIONS IN ATMOSPHERIC RESEARCH, POLLUTION CONTROL, TOXIC GAS SENSING, AND INDUSTRIAL PROCESS MONITORING. ALTHOUGH SPECIALIZED LASER METHODS HAVE BEEN DEMONSTRATED FOR MEASURING SELECTED SPECIES, NONE OF THE METHODS DEVELOPED TO DATE HAS THE DESIRED COMBINATION OF HIGH SENSITIVITY AND WIDE GENERALITY. THIS STUDY WILL INVESTIGATE THE OPTOACOUSTIC DETECTION OF GAS SPECIES USING NEW HIGHER POWER TUNABLE DIODE LASERS THAT ARE NOW COMMERCIALLY AVAILABLE. THIS APPROACH COMBINES THE HIGH SENSITIVITY OF OPTOACOUSTIC DETECTION WITH THE GENERALITY OFTUNABLE INFRARED DIODE LASER SPECTROSCOPY FOR MEASUREMENT OFMANY DIFFERENT SPECIES. A GOAL OF PHASE I IS TO DEMONSTRATEDETECTION SENSITIVITY EQUIVALENT TO SPECIES CONCENTRATIONS WELL BELOW 1 PPB FOR MOST INFRARED-ACTIVE MOLECULES. THE PHASE I STUDY WILL EMPHASIZE AN ASSESSMENT OF DESIGN FACTORSAND MEASUREMENT APPROACHES TO OPTIMIZE THE SENSITIVITY UNDERCONDITIONS IN WHICH A GAS MIXTURE IS BEING CONTINUOUSLY SAMPLED. THE RESULTS OF PHASE I WILL PROVIDE THE REQUIRED DATA TO PERMIT THE PHASE II DEVELOPMENT OF PROTOTYPE INSTRUMENTATION THAT CAN BE USED FOR ULTRASENSITIVE REAL-TIME CHEMICAL ANALYSIS OF GAS MIXTURES IN A WIDE RANGE OF RESEARCH AND INDUSTRIAL APPLICATIONS.