Very High Sensitivity Spectrometer for Atmospheric Measurements

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The accurate measurement of concentrations or fluxes of trace gases in the atmosphere is crucial to many areas of atmospheric research. Instrumentation based on tunable diode laser absorption spectroscopy has wide generality for detection of many atmospheric species. To date, however, such systems have usually been bulky and awkward to operate and do not have adequate sensitivity for the measurement of a number of important species in the atmosphere at low concentrations. The goal of this program is to develop a rapid response, high sensitivity sensor using single-mode liquid nitrogen- cooled lead-salt diode lasers. In Phase I of this program, techniques that substantially reduce the problem of optical fringes in multiple pass absorption cells were developed. These fringes are often the limiting factor for achieving high sensitivity. The major objectives of the Phase II research are to improve further the sensitivity for infrared diode laser absorption and the study methods for simplifying instrument design using infrared fiber optics. A prototype spectrometer will be assembled for local field measurements of ambient hydrogen peroxide concentrations in order to demonstrate ultrasensitve, real-time detection of trace atmospheric species. Results of the Phase II study will provide the required design information for Phase III commercial development of instrumentation for atmospheric research.